Interfacial science in material design

Dr Dominika Zabiegaj

Department of Mechanical and Construction Engineering at Northumbria University

https://www.northumbria.ac.uk/about-us/our-staff/z/dominika-katarzyna-zabiegaj/

DOMINIKA.ZABIEGAJ@NORTHUMBRIA.AC.UK

https://www.linkedin.com/in/dominika-zabiegaj-3660a381/?locale=en_US

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Dr Dominika Zabiegaj is a Vice Chancellor Fellow in Future Engineering. She is involved in research as well as teaching and learning activities.

Dr Zabiegaj joined the Multidisciplinary Research Team (MDRT) at MCE in March 2017. More recently she worked for the National Research Council (CNR) in Genova, at the Department of Condensed Matter Chemistry and Technologies for Energy.

She graduated from AGH University of Science and Technology in Krakow, Poland (2010). She completed her Master’s Engineer degree in Glass Technology, at the Department of Materials Science and Ceramics. During her Masters, Dr Zaniegaj was also a student of the University of Genova, at the Department of Chemistry and Chemistry in Industry. She was an active member of the Multicultural Archeometallurgy Lab research team. In 2015 she gained her PhD in Material Science and Technology at the University of Genova, Italy.

Her research interests include the multidisciplinary study of Material Processing Technology, materials corrosion, nanopowders and particle dispersions, absorption and novel materials with unique absorptive, photocatalytic or structural properties.

She believes that: The main motivation for the design of novel materials is based not only on the fact that properties of different components can be combined in one material but also on the multidisciplinary studies coming from various fields researchers. Where the different scientific approaches, perspectives and experiences come into one benefit.

The role of interfacial science is to design materials with unique properties by manipulating their physicochemical properties. In this talk Dr  Zabiegaj introduced a few of these materials with a focus on foams and emulsions as templates to achieve porous media with many applications, from water purification to bone replacement and bio-infiltration.

The following are notes from the on-line lecture. Even though I could stop the video and go back over things there are likely to be mistakes because I haven’t heard things correctly or not understood them. I hope Dr Zabiegaj, and my readers will forgive any mistakes and let me know what I got wrong.

Dr Zabiegaj began her talk by asking the audience how they would define the word “success”.

The replies included: having a happy life, being satisfied with achievements, reaching the highest goals, persevering, success in overcoming obstacles, being financially stable, having time to spend with the family etc.

The reason why she asked this question was because she wanted to get across the fact that success in research is often thought of something that is straightforward, but in reality, it isn’t.

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The main audience for the talk was sixth formers (16-19-year-old students doing post 16 courses) to make them realise that they will encounter setbacks in their lives

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Very important advice for students studying for exams.

Dr Zabiegaj did her first degree at the AGH University of Science and Technology

https://www.agh.edu.pl/en

https://en.wikipedia.org/wiki/AGH_University_of_Science_and_Technology

AGH University of Science and Technology is a technical university in Poland, located in Kraków. The university was established in 1919, and was formerly known as the University of Mining and Metallurgy. It has 15 faculties and one school, which will become a faculty in the near future.

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She did not find her course straightforward but didn’t consider the obstacles as obstacles, but regarded them as lessons to be learnt.

She followed her first degree with a master’s degree in Glass Technology, at Department of Materials Science and Ceramics. This involved doing research into some 10th and 11th century items of jewellery for the Muzeum Narodowe.

https://www.mnw.art.pl/

https://en.wikipedia.org/wiki/National_Museum,_Warsaw

The National Museum in Warsaw (Polish: Muzeum Narodowe w Warszawie), popularly abbreviated as MNW, is a national museum in Warsaw, one of the largest museums in Poland and the largest in the capital.

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Above shows images of the old pieces of jewellery

As a material engineer, she was very happy to be working on them. Questions she was attempting to answer were “what stage of corrosion have they reached?” “How can further corrosion be prevented?” “Where can they be placed?”

She found a couple of the items very interesting.

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A “gold” ring that was actually made of glass. It was a ring for a 14-year-old boy. He would have worn it on his little finger. It was a way of giving information about his social status and the financial status of his family.

The archaeologists who found the item were surprised at the necessary technology involved in producing a glass ring that appeared gold-like. There was also a red line on the top of the ring.

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Goldish ring actually made of glass with red lines on surface

Not terribly visible but there also red glass “fibres” around the ring’s surface. This showed polish mediaeval craftsmen to have knowledge of advanced techniques and productions.

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Enamelled glass. Seven hundred years ago Polish craftsmen knew how to enamel, to prevent corrosion, to make the object interesting and to get the item sold.

Dr Zabiegaj’s job during her master’s degree was to characterise the objects. Trying to find ways of characterising the corrosion products that were happening on the surface.

She used several techniques but had to be careful as the items were very valuable. Samples could not be taken. It couldn’t be scratched as the museum expected to get the items back completely intact.

There were plenty of corrosion products involving iron, copper, oxygen and carbon (from organic materials). The carbon was identified by use of a microscope.

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https://en.wikipedia.org/wiki/Scanning_electron_microscope

https://science.howstuffworks.com/scanning-electron-microscope2.htm

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A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector (Everhart-Thornley detector). The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometre.

Specimens are observed in high vacuum in a conventional SEM, or in low vacuum or wet conditions in a variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments

Twelfth century copper ring with glass beads

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Blue wasn’t the original colour of the “crown” in the ring. It was much more intense and it was green, but over time it turned light blue due to continuous ion exchange between the glass surface and the environment.

https://en.wikipedia.org/wiki/Ion_exchange

The term encompasses a large variety of processes where ions are exchanged between two electrolytes.

https://en.wikipedia.org/wiki/Electrolyte

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water.

The middle ages were very different to the 21st century. There was plenty of water and organic materials in the streets. There was no infrastructure for taking water out of the cities and people just emptied their urine and faeces into the streets

The glass bead in the ring was losing its colour because of ion exchange. The ions responsible for the colour.

Ions were leaving the glass structure turning it light blue.

Dr Zabiegaj became aware of a research group in Italy that studied old metallurgical objects – archaeometallurgy.

https://en.wikipedia.org/wiki/Archaeometallurgy

Archaeometallurgy is the study of the history and prehistoric use and production of metals by humans. It is a sub-discipline of archaeology and archaeological science.

Dr Zabiegaj joined the research group and continued her master’s qualification, partly, at the University of Genova, at Department of Chemistry and Chemistry in Industry

https://unige.it/en/

https://en.wikipedia.org/wiki/University_of_Genoa

The University of Genoa, known also with the acronym UniGe (Italian: Università di Genova), is one of the largest universities in Italy. It is located in the city of Genoa and regional Metropolitan City of Genoa, on the Italian Riviera in the Liguria region of northwestern Italy. The original university was founded in 1481.

The research group were working with very old objects including rings and they help Dr Zabiegaj to identify the corrosion products on the glass and the glass ring construction, including the metal parts.

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She enjoyed working with the group and came to some very interesting conclusions.

Analysis of ring from University of Genoa

Metal hoop in metallurgic microscope

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The ring was set into a piece of resin and investigated in monochromatic and polychromatic light.

https://en.wikipedia.org/wiki/Metallography

In monochromatic light the golden colour was showing up the pure alloy of the ring. The research group were able to figure out the original composition of the alloy and what amount of the surface that had been converted into corrosion products. The black bits around the gold were the corrosion products

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The group also looked at the ring with polychromatic light which allowed them to see how much space on the ring was taken up by the corrosion products, and what those products were. The various colours indicated there were different corrosion products.

There was plenty of iron in the alloy and that is where most of the corrosion products were coming from. I have to admit that it isn’t obvious in the images that there are different colours

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Red areas, indicated by Dr Zabiegaj’s pointer, are regions of iron oxide

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Slight yellow areas are areas of iron dioxide

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Greenish grey areas are corrosion products coming from the environment.

The colours are very good indications of the materials present.

https://en.wikipedia.org/wiki/Iron_oxide

Iron oxides are chemical compounds composed of iron and oxygen. There are sixteen known iron oxides and oxyhydroxides, the best known of which is rust, a form of iron(III) oxide

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Rust

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Green and reddish-brown stains on a limestone core sample, respectively corresponding to oxides/hydroxides of Fe2+ and Fe3+.

Questions and answers 1

Were the images shown so far taken using a regular microscope or scanning electron microscope?

The images were taken with a regular optical microscope as you can’t use anything that would be destructive because the items were old, valuable and of historic interest.

All the techniques used were non-destructive

Back to talk

Dr Zabiegaj’s really enjoyed this early part of her career because she got to know scientists from all over the world and she learnt many new techniques from her time in Italy.

Engineers share ideas, perspectives and experiences. They help each other resolve problems and learn from each other.

It was during her time in Italy that made her want to continue with science and do a PhD in Genoa at the institute of condensed matter, chemistry and technologies for energy (funded and overseen by the national research council in Italy)

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Genoa

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https://www.icmate.cnr.it/en/

https://www.cnr.it/en/institute/031/institute-of-condensed-matter-chemistry-and-energy-technologies-icmate

The National Research Council (Cnr) is the largest public research institution in Italy, the only one under the Research Ministry performing multidisciplinary activities.

https://en.wikipedia.org/wiki/National_Research_Council_(Italy)

The institution was founded in 1923. The first president was Vito Volterra, succeeded by Guglielmo Marconi. The process of improvement of the national scientific research, through the use of specific laws, (see Law 59/1997), affects many research organizations, and amongst them is CNR, whose “primary function is to carry on, through its own organs, advanced basic and applied research, both to develop and maintain its own scientific competitiveness, and to be ready to take part effectively in a timely manner in the strategic fields defined by the national planning system”.

After finishing her PhD she was able to work for ESA.

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https://www.esa.int/

https://en.wikipedia.org/wiki/European_Space_Agency

The European Space Agency is an intergovernmental organisation of 22 member states dedicated to the exploration of space.

Initially she thought that ESA was just for a certain type of scientist but she realised that it encompasses may fields. Not just “them” but “us”.

Introducing foams

https://en.wikipedia.org/wiki/Foam

Foam is an object formed by trapping pockets of gas in a liquid or solid

Foams are found in every aspect of our lives. We shampoo with them, wash dishes with them and eat them (e.g. mayonnaise).

As a materials engineer Dr Zabiegaj has worked with a lot of materials that are metastable. A metastable material is not stable, having a higher energy state than normal, but is able to maintain that state until it experiences some sort of disturbance.

Foams are metastable because as soon as they are created, they are destroyed if there have been any disruptions/disturbances to them. They can have very short lives.

https://en.wikipedia.org/wiki/Metastability

Dr Zabiegaj is now in charge of a research group that develops materials based on foams with the goal of stabilising them using particles and nanoparticles. She is looking for the driving force for all the processes that are4 occurring, what was driving all the particles involved.

She had to start learning about completely new things. That matter is not just built up of things we can see, but built up of things we can’t see. Things that we didn’t know existed, but are, in fact, all around us. So, she started working with nanoparticles and that involved finding out about surfactants.

https://en.wikipedia.org/wiki/Surfactant

Surfactants are molecules that spontaneously bond with each other to form sealed bubbles. Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, or dispersants.

The word “surfactant” is a blend of surface-active agent, coined c.  1950.

https://en.wikipedia.org/wiki/Surface_tension

Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension allows insects (e.g. water striders), usually denser than water, to float and slide on a water surface.

At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion).

There are two primary mechanisms in play. One is an inward force on the surface molecules causing the liquid to contract. Second is a tangential force parallel to the surface of the liquid. The net effect is the liquid behaves as if its surface were covered with a stretched elastic membrane.

Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons (mN) per meter at 20 °C) than most other liquids. Surface tension is an important factor in the phenomenon of capillarity.

Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.

In materials science, surface tension is used for either surface stress or surface energy.

Effect of amphiphile chain length on wet foam stability of porous ceramics Naboneeta Sarkar, Jung Gyu Park, Sangram Mazumder, Ashish Pokhrel, Christos G.Aneziris and Ik Jin Kim

https://www.sciencedirect.com/science/article/pii/S0272884214018495

Particles at liquid interfaces: foam stabilisation

Abstract to the above paper

Inorganic oxide particles such as Al2O3 are partially hydrophobized using carboxylic acids of different chain length to produce wet foams exhibiting high air contents and remarkable stability. Stabilization of wet foam is achieved by in-situ hydrophilization which is very important to avoid the instability that occurs due to large interfacial area of the gas liquid interface. The concentration of amphiphilic molecules in the initial suspension and the chain length of their hydrophobic tail are modified to tailor the degree of surface hydrophobicity of the Al2O3 particles. Hydrophilization ofAl2O3 surface is achieved through the adsorption of carboxylic acid exhibiting a functional hydroxyl group that efficiently anchors on the particle surface and a short hydrophobic tail remains in contact with the aqueous phase. The wet foam features adsorption free energy of 2.05 x 10–13 J to 8.22 x 10–13 J and Laplace pressure of 0.60 to 1.64 mPa which indicate good wet foam stability of about 80–90%. Ó& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: Porous ceramics; Direct foaming; Wet foam stability; Amphiphilec hain length; Laplace pressure

https://en.wikipedia.org/wiki/Laplace_pressure

The Laplace pressure is the pressure difference between the inside and the outside of a curved surface that forms the boundary between a gas region and a liquid region. The pressure difference is caused by the surface tension of the interface between liquid and gas.

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Possible approaches to attach colloidal particles at gas–liquid interfaces by tuning their surface-wetting properties. Centre left: Schematic illustration of the stabilisation of gas bubbles with colloidal particles (the particle size is exaggerated for clarity). Centre right: The absorption of partially lyophobic particles at the gas–liquid interface, illustrating the balance in tension responsible for the attachment of particles. Above right: The approaches used to tune the wetting properties of originally hydrophilic particles to illustrate the universality of the foaming method developed. The same principles can be easily extended to other types of particles, by using different surface modifiers as well as liquid and gaseous phases.

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The red circles with tails are the surfactants. The heads are hydrophilic and the tails are hydrophobic. They are interacting with the particles

https://en.wikipedia.org/wiki/Hydrophile

A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.

In contrast, hydrophobes are not attracted to water and may seem to be repelled by it.

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The surfactants are sent to the frontier (also known as the interface) particles between the bubbles and the continuous phase (coloured blue in the above diagrams) liquid if we are talking about foams.

The molecules of the surfactants are interacting with the particles from the bulk and sending them to the interfacial layer. The driving force for this is the partial wettability of the particles.

https://en.wikipedia.org/wiki/Wetting

Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. Wetting deals with three phases of matter: gas, liquid, and solid. It is now a centre of attention in nanotechnology and nanoscience studies due to the advent of many nanomaterials in the past two decades (e.g. graphene, carbon nanotube, boron nitride nanomesh).

Wetting is important in the bonding or adherence of two materials. Wetting and the surface forces that control wetting are also responsible for other related effects, including capillary effects.

There are two types of wetting: non-reactive wetting and active wetting.

The surfactants are modifying the interfacial properties

The energy of attachment or free energy gained (E) by the absorption of a particle of radius (R) at the interface can be calculated using following equation:

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where ϒ is the surface tension of the suspension and θ is the contact angle.

The particle hydrophobicity can be modified by the interaction with surfactants.

In theory everything looks perfect. So, what comes next?

Methodology

Dr Zabiegaj has worked with microscopes and many other devices but one of the most interesting ones was a surface tension measurement device called a profile analysis interferometer.

https://en.wikipedia.org/wiki/Tensiometer_(surface_tension)

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Surface scientists use a goniometer/tensiometer to measure contact angle, surface tension, and interfacial tension.

She wanted to design a stable solid material foam so she started working with foams and investigated the bubbles in the foams.

The foam with bubbles of air spread out in the liquid, e.g. water or oil and she worked out the surface tension of these bubbles. The profile analysis interferometer was a crucial device not only for the design of the particles and many other things.

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The foam with bubbles

Surface tension measurement at a constant area:

The profile of the drop under mechanical equilibrium is determined by the Laplace equation which holds valid at each point of the drop surface

https://en.wikipedia.org/wiki/Laplace’s_equation

In mathematics and physics, Laplace’s equation is a second-order partial differential equation named after Pierre-Simon Laplace who first studied its properties.

https://en.wikipedia.org/wiki/Pierre-Simon_Laplace

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Pierre-Simon, marquis de Laplace (23 March 1749 – 5 March 1827) was a French scholar and polymath whose work was important to the development of engineering, mathematics, statistics, physics, astronomy, and philosophy.

https://en.wikipedia.org/wiki/Young%E2%80%93Laplace_equation

In physics, the Young–Laplace equation is a nonlinear partial differential equation that describes the capillary pressure difference sustained across the interface between two static fluids, such as water and air, due to the phenomenon of surface tension or wall tension, although use of the latter is only applicable if assuming that the wall is very thin. The Young–Laplace equation relates the pressure difference to the shape of the surface or wall and it is fundamentally important in the study of static capillary surfaces. It is a statement of normal stress balance for static fluids meeting at an interface, where the interface is treated as a surface (zero thickness):

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Where ΔP is the Laplace pressure, the pressure difference across the fluid interface (the exterior pressure minus the interior pressure),  γ is the surface tension (or wall tension) and R and r are the principal radii of curvature.

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Optical tensiometers use the Young-Laplace equation to determine liquid surface tension automatically based on pendant droplet shape.

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The surface tension around the drop is measured by considering 11 to 33 points all over the profile of the drop being created and then the drop was made to move.

Dilational viscoelasticity vs. frequency by the oscillating drop method

https://www.youtube.com/watch?v=X–l6JJsSr0

https://www.youtube.com/watch?v=SZILt9VGfLs

https://www.youtube.com/watch?v=7P_c1_peG4o

The dynamic behaviour of a drop of water subject to a vertical oscillating force is studied experimentally. A hydrophobic surface was used to maintain the form of the drop. The deformation of the drop as a response to several frequencies was analysed by visualizing the oscillating patterns and measuring the maximum height of the drop as a function of time. The dynamic behaviour has been classified in three phases: harmonic, geometric and chaotic.

Applying perturbations to the area squeezes the drop in and out. As the drop is moving its profile changes and the disruptions are nearly sinusoidal

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https://www.dataphysics-instruments.com/knowledge/understanding-interfaces/interfacial-rheology/

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https://www.dataphysics-instruments.com/Images/Knowledge/UnderstandingInterfaces/Schematic-oscillating-drop-animated.svg

Sinusoidal oscillation of a pendant drop with interfacial area A and interfacial tension σ plotted against time. The phase shift is indicative to the interfacial elasticity and interfacial viscosity.

The surface tension variation due to area change

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ΔA is the peak-to-peak amplitude of the interfacial area, A0 is the mean interfacial area of the drop, γ is the surface tension

ε is a dilational viscoelasticity, defined as the response of the surface tension to sinusoidal perturbation (expansions /compressions) of the surface area, is a frequency dependent quantity related to the dynamic characteristics of the adsorption layers and to the kinetic processes involved.

The above formula can also be written as

E

E can be directly evaluated by acquiring for each frequency the response of the interfacial tension γ to a given harmonic surface area A.

Such measurements from one side provide information about the viscoelastic properties of the fluid interfaces, which are expected to play an important role in the stability of films, foams, and emulsions. In fact, in the case of surfactant-stabilized systems, the dilational viscoelasticity expresses the capability of the system to dampen external disturbances.

https://warwick.ac.uk/fac/cross_fac/sciencecity/programmes/internal/themes/am2/booking/particlesize/intro_to_dls.pdf

https://en.wikipedia.org/wiki/Dynamic_light_scattering

Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in suspension or polymers in solution.

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Hypothetical dynamic light scattering of two samples: Larger particles on the top and smaller particles on the bottom

https://en.wikipedia.org/wiki/Backscatter

In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface.

The scattering intensity is enhanced in the backward direction in this scenario.

https://en.wikipedia.org/wiki/Coherent_backscattering

In physics, coherent backscattering is observed when coherent radiation (such as a laser beam) propagates through a medium which has a large number of scattering centres (such as milk or a thick cloud) of size comparable to the wavelength of the radiation.

https://www.emerald.com/insight/content/doi/10.1108/prt.2002.12931ead.009/full/html

Back scatter optics allow particle size measurement at high concentration

https://upload.wikimedia.org/wikipedia/commons/1/1c/MLS_scan.gif

Measurement principle of multiple light scattering coupled with vertical scanning

https://en.wikipedia.org/wiki/Zeta_potential

Zeta potential is the electrical potential at the slipping plane. This plane is the interface which separates mobile fluid from fluid that remains attached to the surface.

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Diagram showing the ionic concentration and potential difference as a function of distance from the charged surface of a particle suspended in a dispersion medium

The zeta potential is a key indicator of the stability of colloidal dispersions. The magnitude of the zeta potential indicates the degree of electrostatic repulsion between adjacent, similarly charged particles in a dispersion. For molecules and particles that are small enough, a high zeta potential will confer stability, i.e., the solution or dispersion will resist aggregation. When the potential is small, attractive forces may exceed this repulsion and the dispersion may break and flocculate. So, colloids with high zeta potential (negative or positive) are electrically stabilized while colloids with low zeta potentials tend to coagulate or flocculate.

Zeta potential is not measurable directly but it can be calculated using theoretical models, and an experimentally-determined electrophoretic mobility or dynamic electrophoretic mobility.

https://en.wikipedia.org/wiki/Electrophoresis

Electrophoresis is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field.

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Electrophoresis is used in laboratories to separate macromolecules based on size.

https://www.tandfonline.com/doi/abs/10.1081/SPM-100100006?journalCode=lspr19

If something goes wrong and there is some deviation to the expected sinusoidal movement, it means that there is something interesting happening in the system.

Dr Zabiegaj was following the movements for many different systems, polymeric systems with ceramic particles, for carbon particles and ceramic particles together. She found this very interesting and it gave her ideas for what to do next.

Having worked out how a single drop was behaving she was able to predict how the entire system was behaving.

Eventually she was able to add particles to a liquid and create beautiful foams (see B in the image below) and manipulate the final structure of the materials

From the drop to the solid foam

Dispersing –> Foaming –> Gelling –> High temperature treatment

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Questions she wanted to answer:

How is the transition going to be secured from the wet foam that has been created from particles dispersed into the liquid?

How is the final solid going to be achieved? For example, a replacement for bones (see below)

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Bone replacement

Is the material going to be used as a filter?

Is it going to be used as a filter?

Is it going to used as a phase change material?

Is it going to be used for energy storage?

However she had a good idea of what to do.

Carbon based porous materials from particle stabilized wet foams

https://www.sciencedirect.com/science/article/abs/pii/S0927775715001612

D.Zabiegaj, E.Santini, M .Ferrari, L.Liggiei, F.Ravera

Highlights:

Methods combining direct foaming with gel-casting are effective to produce carbon solid foams;

Foams stabilized by carbon particles associated to ionic surfactant as precursor to porous materials:

High temperature treatments provide materials with hierarchical multi-porous structure:

The morphology and the specific area of the porous materials can be tailored changing the composition of the precursor.

In this work, a method was proposed for the production of carbon porous materials based on the foaming of a carbon colloidal dispersion in the presence of a short chain ionic surfactant (CTAB) and Poly(vinyl alcohol) followed by the in situ polymerization by cross-linking with 2,5-dimethoxy-2,5-dihydrofuran (DHF). The particle stabilized wet foams were used as templates for the gel-casting providing porous materials with carbon particles mainly distributed at the surface of the cells. This sample so obtained was then submitted to a high temperature treatment to remove all organic components from the matrix and get a compact carbon solid foam. The morphology of the samples obtained according to this procedure have been analysed via Scanning Electron Microscopy (SEM) and different aspects regarding both the procedure and the composition of the initial dispersion have been investigated such as the role of the surfactant, the dependence on the particle concentration and the temperature adopted during the thermal treatment.

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Dr Zabiegaj developed a set of procedures and was able to solve problems as they occurred. She discovered there was a very easy way of creating, fabricating and solidifying the materials (like making certain types of puddings) with the structure of foam. These were extremely porous, having plenty of spaces, as in the artificial bone. The absorption areas, specific surface area, were incredibly big. This made them suitable for carbon dioxide capture, for example, which would be extremely useful for the planet.

The various stages in included:

Bulk characterisation using the dynamic light scattering (DLS) and investigating the Z-potential;

Surface tension characterization using the drop profile tensiometer (PAT);

Measurement of the foam stability hrel = h/h0; h and h0 correspond to the actual height (at various times) and initial height of foam at the onset of the experiment, respectively

h is a height of the (changing) foam measured over time periods such as every 2 mins or every 5 minutes. As destabilisation processes are running the foam height will be decreasing and, at the bottom of the foam column the liquid fraction will be appearing, thus the liquid phase to foam phase  ratio will be changing as shown in the picture below.

h

h0 is the total height of the foam just after formation (at the start of the experiment) 

Morphology characterisation using SEM, BET, Mercury porosimetry and TGA

https://en.wikipedia.org/wiki/Scanning_electron_microscope

A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector (Everhart-Thornley detector). The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometre.

Specimens are observed in high vacuum in a conventional SEM, or in low vacuum or wet conditions in a variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments

https://en.wikipedia.org/wiki/BET_theory

Brunauer–Emmett–Teller (BET) theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of materials. The observations are very often referred to as physical adsorption or physisorption.

https://en.wikipedia.org/wiki/Porosimetry

Porosimetry is an analytical technique used to determine various quantifiable aspects of a material’s porous structure, such as pore diameter, total pore volume, surface area, and bulk and absolute densities.

The technique involves the intrusion of a non-wetting liquid (often mercury) at high pressure into a material through the use of a porosimeter. The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid’s surface tension.

https://en.wikipedia.org/wiki/Thermogravimetric_analysis

Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such as phase transitions, absorption, adsorption and desorption; as well as chemical phenomena including chemisorptions, thermal decomposition, and solid-gas reactions (e.g., oxidation or reduction).

Carbon particles

Size, shape and surface charge

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The carbon soot particles and the activated carbon 1 are nanoparticles. These are not very nice if they find their way into the human body so working with them requires precision, focus and adherence to health and safety procedures.

To make life more complicated Dr Zabiegaj decided to swap to activated carbon 2. This had much larger particles (on the micron scale and about 100 times bigger than activated carbon 1 particles).

She had to study the bubbles carefully, trying many variations and many different surfactants. Seeing if there was any tendency or deviation that the particles might be showing up on the interface. To see if they were stabilising the bubbles within the foam.

There was plenty of work. Every single point on the graphs had to be repeated at least 3 times. Quick calculations were made around the points and the values multiplied by 3

Dispersion characteristics

Interaction with surfactant

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From DLS measurements:

The size does not depend on the surfactant concentration;

Surfactant does not induce aggregation

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Conditions: CSoot at 0.1 wt% at T = 25oC

https://www.researchgate.net/publication/263010354_Carbon_Soot-Ionic_Surfactant_Mixed_Layers_at_WaterAir_Interfaces

An experimental study is presented on the properties of aqueous dispersions containing carbon nanoparticles and different ionic surfactants which can modify the degree of hydrophobicity/philicity of particles favouring their transfer from the dispersion bulk to the interfacial layer. Aim of this work was to understand the particle-surfactant and particle-fluid interface interactions and their effect on those macroscopic surface properties of the mixed systems which are expected related to the stability and structure of the respective particle stabilized foams. To this purpose a systematic characterization of dispersions has been carried out, based on surface tension measurement against the surfactant concentration, using a drop Profile Analysis Tensiometer (PAT). These results have been crossed with the characterization of the bulk dispersion by Dynamic Light Scattering (DLS) and Z-potential measurements to check the effects of surfactant on the particle aggregation and on the particle surface charge, respectively. The stability of the foams obtained with the same compositions have been also investigated and correlated to the other surface and bulk properties.

Zabiegaj et al, JNN 15 (2015) 3618-3625

A lot of experimental work was required but Dr Zabiegaj finally found that CTAB average, which was the cationic surfactant, particles were behaving in a slightly different way.

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For CTAB concentration of 5e−4 M and 1e−3M the foams were more stable in presence of particles with respect to those stabilized by surfactant alone. For these concentrations, in fact, the particles were expected to be incorporated at the water-air interface. On the contrary, at the larger CTAB concentrations the CS-CTAB complexes were again strongly hydrophilic, due to the formation of the bilayer on their surface. Thus, the complexes did not adsorb at the liquid interface and the foam behaved like the corresponding one, stabilised by the bare surfactant.

The particle stabilized foams could be obtained from mixed particle-surfactant dispersions where appropriate compositions were adopted which ensured that adequate number of particles, with adequate degree of hydrophobicity, were adsorbed at the surface of the air bubbles in foams. Concluding these results provided new insight into the role of the composition of the initial dispersion in the production of particle-stabilized foams. Moreover, they could contribute to a better understanding of the relation between the interfacial properties of nanoparticles mixed systems and the stability and 3D structure of the respective disperse systems such as foams and solid foams

In theory detergents (washing powders) have the same tendency as the results outlined above. The particles are interacting with the surfactants to give a completely different behaviour.

In order to check she was working in the right direction Dr Zabiegaj needed to design a new experiment to check that her results were reliable, stable and that she wasn’t creating conglomerates. In other words, she needed to check that what CTAB was showing was definite and not erroneous

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Were the CTAB results stable?

In real life we all are all guilty of being sure of something which turns out to be wrong. In science, like life, it is important to check things out because it is likely that some things will be wrong and you need to find out what they are.

Dr Zabiegaj needed to check and test the particle. Were there conglomerates present or not?

Eventually she got to the point that she could produce the foams. What were the proportions of materials required? What quantity of particles needed to be used? What quantity of surfactant needed to be provided?

Everything needed to be checked out many times and she finally came up with an idea. She needed to increase the number of particles on the interface and carry out some tests to check the stability of the results.

Stability

Wet foam studies:

Foaming conditions require a production speed of 8000 rpm over a time period of 2 to 5 minutes;

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Surfactant covering particles concentration;

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Measuring the stability of the foam hrel = h/h

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The correct number of particles that covered the little tiny bubbles were able to stabilise the material giving her the final interconnected-structure of her porous material

It finally happened

Porous monoliths, the solid foams

The materials were obtained through direct foaming with gel-casting of the liquid foam.

Stable temple treated carbon monoliths were produced with high specific surface area, close to the original BET of the original powder

The materials produced had an open cell structure and hierarchical porosity (pore size ranging from 40mm to less than 0.7nm)

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Dr Zabiegaj managed to obtain many different types of materials from many different sources using many different particles. These included alumina particles, 3 different types of carbon and titanium dioxide.

The work took a long time, but it was ultimately successful. It was a quite intense process with long hours in the lab. However, it allowed her to talk to people from all over the world and she enjoyed reading scientific papers and journals in order to improve procedures. More importantly she was able to come up with interesting materials.

Questions and answers 2

1) Why were you studying mediaeval objects? Was it to help date them or was it simply to identify what caused the oxidation?

She was helping with archaeological excavations and helping the museum staff to put the objects in the right place in the museum. You don’t want items from different epochs to be mixed up together.

When objects are placed too close to each other they might be toxic to each other.

If one object has unfortunately absorbed water from the air you don’t want to place it next to a dry object, because it could absorb some of the water.

Back to the talk

How do you see coconuts?

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Coconut pirates who attack Moana

https://en.wikipedia.org/wiki/Moana_(2016_film)

Moana is a 2016 American 3D computer-animated musical adventure film produced by Walt Disney Animation Studios and distributed by Walt Disney Pictures.

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Caribbean holidays with beautiful beaches. Palm trees. Oil drum music

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Above left: Pina Coladas. Above right: Coconut chocolate bars

Dr Zabiegaj views on coconuts

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Food and cosmetics are the biggest users of coconuts. An incredible number of empty shells are left behind and the various coconut growing countries are struggling to cope with them.

Mexico is one of these countries. The citizens didn’t know what to do with the shells and ended up just burning them. This, of course, produced increased carbon dioxide emissions.

Dr Zabiegaj took on the job of coming up with a solution.

She turned the coconut shells into particles and from these particles she was able to create a wonderful absorbent material, having a nice open structure with lots of different uses.

Synthesis of activated carbon particles

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Chemical versus physical activation of coconut shell: A comparative study

Marcos J.Prauchner et. al.

https://www.sciencedirect.com/science/article/abs/pii/S138718111100566X

Granular activated carbons with high porosity were produced from dried endocarp of coconut shell using both physical activation with CO2 and chemical activation with H3PO4 or ZnCl2.

Dr Zabiegaj had been told that Mexico had very advanced equipment for the job. Unfortunately for her, Mexico has a different of what constitutes advanced equipment.

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Morphological particle evolution

http://rua.ua.es/dspace/handle/10045/75293?locale=en

D. Zabiegaj et al, Synthesis of carbon monoliths with a tailored hierarchical pore structure for selective CO2 capture, Journal of CO2 utilisation 26 (2018) 36-44

Carbon monolithic adsorbents exhibiting a hierarchical pore structure are produced via a synthesis route based on the stabilization of liquid foams followed by a carbonization step. The macro-microporous structure was achieved by the incorporation of microporous, biomass-derived activated carbon particles in the liquid foam enclosed by a cationic surfactant as stabilizer. This method yielded crack-free monoliths (solid foams) with a compressive strength of the order of 20 kPa. The microstructure and the textural properties of the final solid foams have been investigated by means of Scanning Electron Microscopy (SEM) and gas adsorption. The behaviour as selective CO2 adsorbents at 25 °C have been evaluated using breakthrough experiments under simulated post-combustion conditions (16% V/V CO2/N2), resulting in a selectivity factor of 13 over N2. The hierarchical pore structure of the monoliths allowed a rapid transport of the gas mixture through the macropores with no appreciable pressure drop, retaining more than 90 % of the adsorption capacity (∼ 0.868 mmol/g) after several adsorption/desorption cycles. Moreover, the monolith had shown a CO2 uptake capacity of 2.62 mmol/g under static condition at 1 bar and 25 °C. This study provided guidelines for the design of carbon-based foams decorated with carbon particles, which have morphological and textural properties that can be carefully selected for any gas-selective capture application.

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From the coconut shells Dr Zabiegaj was able to produce useable particles. Particles were divided into coarse and smooth particles and then further characterised.

Part of the work included checking the surface tension and checking if the particles were stable in the solution.

Following her previously designed procedure she found out that those particles that were going to be carbon again were having specific and a very interesting behaviour when they were made into a solution and when they made up the interface in foams.

Her findings were a good indication that stable foams would be produced. Solid foams from the particles as well as carbon green body foams were produced from the coconut shells.

So, a waste product has a second life.

The structure of the materials was interconnected with either big voids or small voids. Also, medium voids with a difference in the thickness. She was simply playing with the concentrations of the same particles. Doing this she was able to produce different monoliths that were followed by many different structures.

Coconut derived activated carbon

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Adsorption of gases at 77K

Carbon particles on the interface

Dispersion characteristics

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Processing carbon monoliths and carbon green body foams

Foaming at a speed of 8000 rpm over a time of 2 to 5 minutes

Gelling at a temperature of 80oC over a time of 3 hours

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Carbon Soot–Ionic Surfactant Mixed Layers at Water/Air Interfaces

https://www.researchgate.net/publication/263010354_Carbon_Soot-Ionic_Surfactant_Mixed_Layers_at_WaterAir_Interfaces

D. Zabiegaj et al, JNN 15 (2015) 3618-3625

An experimental study is presented on the properties of aqueous dispersions containing carbon nanoparticles and different ionic surfactants which can modify the degree of hydrophobicity/philicity of particles favouring their transfer from the dispersion bulk to the interfacial layer. Aim of this work was to understand the particle-surfactant and particle-fluid interface interactions and their effect on those macroscopic surface properties of the mixed systems which are expected related to the stability and structure of the respective particle stabilized foams. To this purpose a systematic characterization of dispersions has been carried out, based on surface tension measurement against the surfactant concentration, using a drop Profile Analysis Tensiometer (PAT). The results have been crossed with the characterization of the bulk dispersion by Dynamic Light Scattering (DLS) and Z-potential measurements to check the effects of surfactant on the particle aggregation and on the particle surface charge, respectively. The stability of the foams obtained with the same compositions has been also investigated and correlated to the other surface and bulk properties.

Concentration of surfactant-decorated particles

Impact on green foam morphology

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Solid foams

Dr Zabiegaj took her foams and started seeing what thermal treatment did to them. She was able to obtain many different structures.

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High temperatures used were 500oC, 900oC and 1500oC

1-hour heating time with a heating rate of 1oC/min

Inert atmosphere of argon using 100cm3/min

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Solid foams microstructure

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Heating them to high temperatures (e.g. 1500oC) produced something incredibly interesting and mechanically stable, but for the required purposes the nano-porosity for CO2 wasn’t quite good enough.

At 500oC with green bodies it was noticed that there was no nanoporosity.

A temperature of 900oC had the porosity just appearing and seemed to be the most successful nano-porosity for CO2.

After many hours in the lab which included mistakes as well as some good ideas, she finally came up with a temperature suitable for her purposes (900oC). She and her research group were able to obtain an absorbance suitable for CO2 capture.

Solid foams breakthrough

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Carrying out some more experiments just to be sure the materials were able to select between nitrogen and carbon dioxide. The red curve indicates that the material had a good affinity for carbon dioxide.

The research group is in a good position for selling the foams and producing real filters.

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http://rua.ua.es/dspace/handle/10045/75293?locale=en

Synthesis of carbon monoliths with a tailored hierarchical pore structure for selective CO2 capture, journal of CO2 Utilisation 26 (2018) 36-44 D. Zabiegaj, et al

Carbon monolithic adsorbents exhibiting a hierarchical pore structure were produced via a synthesis route based on the stabilization of liquid foams followed by a carbonization step. The macro-microporous structure was achieved by the incorporation of microporous, biomass-derived activated carbon particles in the liquid foam enclosed by a cationic surfactant as stabilizer. This method yielded crack-free monoliths (solid foams) with a compressive strength of the order of 20 kPa. The microstructure and the textural properties of the final solid foams have been investigated by means of Scanning Electron Microscopy (SEM) and gas adsorption. The behaviour as selective CO2 adsorbents at 25 °C have been evaluated using breakthrough experiments under simulated post-combustion conditions (16% V/V CO2/N2), resulting in a selectivity factor of 13 over N2. The hierarchical pore structure of the monoliths allowed a rapid transport of the gas mixture through the macropores with no appreciable pressure drop, retaining more than 90 % of the adsorption capacity (∼ 0.868 mmol/g) after several adsorption/desorption cycles. Moreover, the monolith has shown a CO2 uptake capacity of 2.62 mmol/g under static condition at 1 bar and 25 °C. This study provides guidelines for the design of carbon-based foams decorated with carbon particles, which have morphological and textural properties that can be carefully selected for any gas-selective capture application.

The affinity for carbon dioxide remained after six cycles of absorption keeping the materials at 90% absorption capacity meaning that the materials could be used long term as filters without the need to exchange them for a good few cycles.

Questions and answers 3

1) How do you determine the affinity with a specific gas? Is that to do with the nanostructure of the foam?

Yes. There are plenty of voids in the 900oC treated material. A lot of highways for the gas molecules to pass through.

With the green bodies there was no terminal treatment or the treatment used wasn’t enough or high enough.

The walls didn’t have specific porosity so the gas molecules couldn’t hide within the material.

When the temperature was increased too much the porosity was becoming glassy and there was no place for carbon dioxide to be passing through, being hidden or being stuck.

With the right temperature various gases could pass through the structure but affinity was only happening for carbon dioxide, which was trapped in those tiny, narrow pores.

2) What can these foams be use for?

Carbon dioxide absorbers. Ironic that carbon coconut foam captures carbon.

Back to the talk

Particles at liquid interfaces: foam stabilisation

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About 40000 people die prematurely a year due to poor air quality and environmental pollution.

Our lungs are like foams. They are made up of very little sacs called alveoli. These are like tiny foam air bags which “float” inside the chest cavity. They are covered in surfactant. The surfactant is DPPC.

https://en.wikipedia.org/wiki/Dipalmitoylphosphatidylcholine

Dipalmitoylphosphatidylcholine (DPPC) is a phospholipid (and a lecithin) consisting of two C16 palmitic acid groups attached to a phosphatidylcholine head-group.

It is the main constituent of pulmonary surfactants, which reduces the work of breathing and prevents alveolar collapse during breathing. It also plays an important role in the study of liposomes and human bilayers.

DPPC works in a similar way to the man-made materials with one difference. We don’t want any particles to be attached to the interface. For example, imagine we are breathing in asbestos.

https://en.wikipedia.org/wiki/Asbestos

Asbestos is a term used to refer to six naturally occurring silicate minerals. All are composed of long and thin fibrous crystals; each fibre being composed of many microscopic ‘fibrils’ that can be released into the atmosphere by abrasion and other processes. Asbestos is an excellent electrical insulator and is highly heat-resistant, so for many years it was used as a building material. However, it is now a well-known health and safety hazard and the use of asbestos as a building material is illegal in many countries. Inhalation of asbestos fibres can lead to various serious lung conditions, including asbestosis and cancer.

https://en.wikipedia.org/wiki/Asbestosis

Asbestosis is long term inflammation and scarring of the lungs due to asbestos fibres. Symptoms may include shortness of breath, cough, wheezing, and chest tightness. Complications may include lung cancer, mesothelioma, and pulmonary heart disease.

People who worked with asbestos in the past inhaled the nanotubes, which passed through the respiratory system. The nano tubes interacted directly with DPPC surfactant and were moved to the interfaces. Eventually every alveolus was affected, making them rigid and decreasing the exchange of carbon dioxide and oxygen, decreasing the gas exchange between inside and outside. The lungs would work more slowly and eventually collapse.

Industries all over the world are producing soaps, detergents, shampoos, porous materials and concrete-bases Portland cement.

But there is a lot of ignorance in the behaviour of the lungs, probably due to the processes being invisible.

It is incredibly interesting, but very sad how many people are dying because of poor air quality.

Some of the pollutants affect the interface of the lungs, getting past the cell layer of the alveoli into the blood stream due to the cell membrane exchange. The bloodstream passes the pollutants to organs, and perhaps killing us.

We can use foams to save lives and save the planet by capturing carbon dioxide but on the other hand shorten our lives by inhaling poor quality air, this includes smoking too. The poorer air we are inhaling the faster we are degrading our lungs.

Questions and answers 4

1) Any other treatments besides temperature that can change the foam’s structure?

Particle concentration, composition, size of particles and shape of particles. The nature and concentration of surfactants.

2) Do you think you will be able to re-use the carbon trapped in the foam.

There are plenty of new technologies that are allowing the carbon dioxide to be added to a new form of concrete. If the carbon dioxide can be trapped in the gas state and liquified it can be added to concrete mixture. This decreases the time for the concrete to set. Normally concrete can take 24 days to fully settle down and form a rigid structure but adding liquid carbon dioxide can shorten the process to about 24 hours.

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