Katherine Thomas, Web Writer – Page 3

Author Archive

How do thin polymer films behave?

11 May 2011

Rupture of thin polymer films

Molecular dynamics at nanometric length scales – Friedrich Kremer

Glassy dynamics and the glass transition temperature, in thin polymer films, has been a hotly debated area of polymer research over the last few decades. In particular, how and whether the glass transition temperature (T_g) changes from bulk values as the film thickness decreases or the molecular weight of the polymer is varied. A survey of the literature does little to clear this up with evidence being easily found for a lowering, a rise or no change in T_g as the film thickness is decreased. In his talk at the APS March meeting in Dallas, Friedrich Kremer discussed some of his recent work on polymer dynamics, with the aim of resolving some of the seemingly conflicting results found in the literature.

Kremer and his group used broadband dielectric spectroscopy (BDS), spectroscopic ellipsometry, x-ray reflectometry and differential scanning calorimetry to study thin polymer films (5-250 nm) with varying molecular weights. He noted that for the BDS measurements two different sample geometries were used. In the first evaporated aluminum electrodes (~80 nm) below and above the film were used as the counter electrodes. This is the common method used for BDS measurements. In the second geometry silicon wafers were used at the electrodes, with insulating silica nanostructures serving as spacers. This technique avoids evaporation of metal onto the films, allowing thinner films to be probed. Information on this technique can be found in Rev. Sci. Instrum.

In Kremer’s opinion sample preparation is the key to the conflicting results found in the literature. As such he was keen to stress that for all measurements his group performed, the samples were prepared in the same manner: Films were spin coated and then annealed at T = T_g + 50°C for 24hrs under vacuum in an oil-free environment. His results show that for films down to 5 nm in thickness and molecular weights varying from 300 – 8000 kg/mol, no change in the glassy dynamics is observed. No discrepancy between the different experimental techniques is seen, which all indicate that there is no shift in the glass transition temperature for thin films.

Kremer then went on to try to answer the questions of why he did not observe any change in the glassy dynamics while others do. The answer, he claims, can be found by carefully reading the experimental section of each paper. It all lies in how the films are prepared. Residual solvent can act as a plasticiser, while non-equilibrated films may have metastable states. Both of these result in altered dynamics. In the seminal paper on the polymer glass transition temperature by Keddie, Jones and Cory, they observe a decrease in of ~ 30°C in T_g as films thickness is reduced from 100 nm to 10nm. All films were annealed at 160°C for 48 hrs in vacuum – a temperature and time sufficient to remove residual solvent and relax stresses. However, experiments were conducted in air. According to Kremer, for PS at 150°C in air, chemical degradation occurs changing the molecular dynamics.

In other works, such as that of Dalnoki-Veress et al. and Ellison et al., annealing of the films after spin coating was insufficient to remove residual solvent, which would explain the molecular weight dependent behaviour and the altered dynamics observed. It should be mentioned that Kremer was keen to emphasise that he was not attacking any of these publications or their authors. He merely wanted to explain the reason for the divergence in results and show that films can be formed with no T_g shift. The results of Kremer and has group have been published in Macromolecules, EPJ Special topics and Macromolecules.

Kremer is not the only one to have recently shown that sample preparation is key when considering the properties of thin polymer films. The papers by Raegen et al. and Thomas et al. agree with his conclusions and show that if films are annealed for long enough above T_g, then any anomalous behaviour disappears and bulk dynamics are restored.

The glassy dynamics of thin polymer films is still a hot area of debate, but perhaps recent papers show that there is in fact no contradiction in the literature. It just comes down to sample preparation!

Locomotion in fluids

19 Apr 2011

Various low Reynolds number swimmers. (a) E coili bacterium. (b) Swimming spermatozoon of Ciona intestinalis. (c) Paramecium cell.

This month’s fluid dynamics symposium, run by the Max-Planck Institute for Dynamics and Self-Organisation was on the topic of locomotion in fluids. Talks were given by Anders Andersen from the Technical University of Denmark, on Copepod dynamics, Albert Bae from UC San Diego, on swimming amoebae and Eric Stellamanns from the Max-Planck Institute for Dynamics and Self-Organisation, on Trypanosome motility.

Copepod hydrodynamics

Copepods are a group of small crustaceans and zooplankton found in both salt and fresh water environments. In terms of other plankton Copepods are fairly large, ranging in size from a few hundred microns to a few millimetres. In order to catch prey and escape from predators, the Copepods have small sensory hairs along their antenna and tails. These hairs or setae, detect small disturbances in the surrounding environment. If the disturbance is small (only picked up by few hairs) then the Copepod knows prey is nearby and can attack. If the disturbance is large (picked up by many hairs) then the Copepod knows to get ready to flee a potential predator.

In order to capture prey, the Copepods use ambush feeding. Most of the time the Copepod is motionless in the water waiting for prey to swim by. When one does, the Copepod springs into motion capturing the prey. The whole process of detection to capture takes only a few milliseconds, with the Copepod attacking at speeds of ~100 mm/s. On Anderson’s website a series of images can be found showing the attack process.

Apart from the speed and motion during attack, the main point of interest is that the prey remains stationary during the whole process, despite the Copepod moving substantially. This is of course necessary for a successful ambush; if the prey notices the Copepod moving it will potentially be able to escape. Simulations show that only a very thin viscous boundary layer develops around the attacking Copepod due to its high Reynolds number ~100, minimising the flow around the prey and preventing detection. The results were published in PNAS.

Also discussed in the talk were the kinematics of escape jumps in the Copepods. Copepods of all sizes use a cycle of power strokes and passive coasting to move from one place to another. Each cycle lasts 10-20 ms with the ratio of the stroke time to coasting time varying with the size of the Copepod. This mechanism results in a highly fluctuating escape velocity, with speeds of 120-450 mm/s being reached. The results can be found in the Journal of the Royal Society Interface, where a simple swimming model in used to accurately capture the kinematics of the motion.

APS March Meeting – Prize Winners

07 Apr 2011

AFM image of protein fibres

In addition to the conference, the APS prizes and awards are conferred at the APS March meeting. Of the 18 awarded this year, 8 went to researchers in the soft matter field. Below I have highlighted some of the winners along with some information about their work.

John Dillon Medal – Raffaele Mezzenga, University of Fribourg

This prize was awarded to Mezzenga for exceptional contributions to the understanding of self-assembly principles and their use to design and control materials with targeted functionalities. Menzzenga’s work involves the study of protein fibrils. While important in neuro-degenerative diseases, protein fibrils are also found as building blocks in food. Menzzenga’s talk focused on his work on the formation of long linear multi-stranded protein fibre structures and their self-assembly. A discussion on how these fibres are formed was recently published in Soft Matter (doi:10.1039/c0sm00502a). Initially single filaments are formed. Short-ranged interactions between the filaments then lead to aggregation and almost perfect alignment of the filaments to form multi-stranded fibrils. Twisting of the fibrils then results from repulsive electrostatic interactions between the fibrils. Other recent papers look at the disassembly of protein fibrils (Soft Matter doi: 10.1039/C0SM01253J) and whether and how lyotropic liquid crystal phases can be used to host, encapsulate and direct the assembly of amyloid fibrils (Soft Matter doi:10.1039/c0sm01339k).

Polymer prize – Gary Crest, Sandia National Laboratory and Kurt Kremer, Max-Planck Institute for polymer research

This prize was awarded jointly to Crest and Kremer for establishing numerical simulation as a tool, on an equal footing with experiment and theory, in the field of polymer science, as exemplified by the seminal simulations of entangled polymer melt dynamics.

Biological physics doctoral thesis award “Evolution and emergence of structure” – Erez Lieberman-Aiden, Havard University

Lieberman-Aiden received this years award for outstanding doctoral thesis in biological physics. This is not the only award that Lieberman-Aiden has recently received. He was also the winner of the Lemelson-MIT student prize in 2010 for his inventive work on mapping out the 3-D structure of the genome. As a graduate student Lieberman-Aiden developed Hi-C, a new technology which allowed for the 3-D structure of the genome to be probed, providing insight into how the double helix DNA folds and fits in to the nucleus of a human cell. The results were published in Science. Further information on his work and publications can be found on his website.

Leroy Apker Award – Chai Wei Hsu, Wesleyan University.

The Leroy-Apker prize recognises achievements in physics by undergraduate students. The prize was awarded jointly to Christopher Chudzicki for his work on parallel entanglement distribution on hypercube networks and to Chai Wei Hsu for his work on the self-assembly of DNA-linked nanoparticles. Chai Wei Hsu looked at the phase behaviour of nanoparticles tethered with DNA strands and developed a theoretical description for the behaviour observed. These nanoparticles are able to self assemble into well ordered structures due to the complimentary bonding of base pairs. Chai’s thesis is available online here.

A paper on the self-assembly of DNA structures has also recently appeared in Soft Matter. In their article ‘Self-assembling DNA templates for programmed artificial biomineralization’, Samano et al. discuss the use of DNA-directed patterning of inorganic materials for various technological applications including electronics and photonics.

Max Delbruck Biological Physics Prize – Xiaowei Zhuang, Havard University.

This prize, for outstanding achievement in biological physics, was awarded to Zhuang for her contributions to the field of single molecule biophysics and super-high resolution imaging. A Professor at Havard, Zhuang’s research involves developing tools to visualise biomolecular processes on scales smaller than the resolution limit of conventional light microscopy. In her talk she discussed a new method of imaging – Stochastic Optical Reconstruction Microscopy (STORM). This technique utilises photo-switchable fluorescent probes. The final image is reconstructed from a series of images. Only a fraction of the probes are switched on for each image in the cycle, allowing the positions of the probes to be determined with nanometer accuracy. The imaging method was described in Nature Methods.

A full of prize winners for 2011 can be found on the APS website.

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APS March meeting 2011 – bacterial competition

29 Mar 2011

The annual APS March meeting was held last week at the convention centre in Dallas. The conference consisted of over 660 session and 7350 contributed talks (according to my rough calculation) on subjects ranging from quantum computing to the physics of evolution to polymer dynamics. Due to the shear number of talks, I will split the conference into a series of blogs rather than one long one, which no-one would want to read!

Deadly competition between sibling bacteria colonies – Avraham Be’er, University of Texas, Austin.

In this invited talk, Avraham Be’er discussed the growth of competing bacterial sibling colonies. A single colony of bacteria grows with radial symmetry at a constant speed. However, for two colonies of P. dendritiformis, equidistant from the centre and inoculated simultaneously, the dynamics differ. Initially the growth of each colony is radially outwards and independent of the other colony. However, while the distance is still large, growth in the centre, between the two colonies, decelerates and a gap forms between the two colonies. The colonies become asymmetric in shape and growth. (See Be’er’s website for pictures of the growing colonies.)

Be’er and co-workers have shown that the reason for this inhibition of growth is a toxic material secreted by the bacteria (doi:10.1073/pnas.0811816106). The toxin is lethal once it exceeds a well-defined threshold. Extracting the toxin and depositing it outside a growing single colony results in growth inhibition and cell death, which would otherwise not be seen. This toxin, termed ‘sibling lethal factor’ (Slf), lyses cells, rupturing them and is not limited to this bacteria (although the toxicity varies for different bacteria). The bacteria seem to have evolved to produce Slf and kill their own siblings, but only when there are two competing colonies. Slf is not secreted when there is only one colony.

Subtilisin was also found in the bacterial secretions. This protein is non-toxic. However, when Slf is exposed to subtilisin it is cleaved from a non-toxic protein of ~20 kDa to the toxic Slf ~12 kDa. The results suggest that subtilisin acts to regulate growth of the colony. Below a threshold value the subtilisin promotes growth and expansion of the colony. Above this threshold value Slf is secreted, reducing the density of cells (doi:10.1073/pnas.1001062107). The results also indicate that when the levels of Slf are small, rather than cell death occurring, the cells can instead enter a vegetative state. These vegetative cells ‘cocci’ are immobile, have a slow expansion and are spherical rather than rod-like in shape. These cocci cells are observed to switch back simultaneously and spontaneously to the healty rod-shaped cells, with growth continuing as before.

Is food the way forward?

07 Mar 2011

A water/oil/water duplex emulsion

When someone asks you about food, the first things that come to mind are taste, smell, texture and appearance, but not perhaps science. However, over recent years a number of popular science and cookery books have started to appear, highlighting how physics and chemistry are important when we cook. Indeed a number of chefs have even started to exploit science, conducting unusual culinary experiments, to create gastronomical delights.

For the academic year 2010/2011, Harvard University introduced a new course for their first year undergraduates “Science and cooking – from haute cuisine to the science of soft matter”. Lectures, conducted by internationally renowned Chefs and faculty, used food and cooking to introduce undergraduates to fundamental principles in applied physics and engineering. Titles of the lectures included “Heat, temperature and chocolate”, “Emulsions: Concepts and stabilising oil and water” and “Olive oil and viscosity”. In an interview with Physicsworld, David Weitz discussed one lecture where Joan Roca (El Celler de Can Roca) made a ‘super cool’ dessert. Joan distilled water with eucalyptus to make a very pure water. This was placed into a refrigerator and cooled it to -5C. On removal from the fridge, the water was still liquid. The liquid was then poured onto a dessert Joan was making. As soon as it hit the dessert, it froze. The dessert was supercooled as well as being ‘super cool’. This led naturally to a discussion on supercooling.

For those in the Soft Matter community, science and food is not a new concept. Understanding soft matter from colloids, to gels, to foams and emulsions and how it behaves are important in the structure, stability, taste, flavour and nutrition of food. A quick search of ‘food’ brings up over two hundred articles in Soft Matter alone, including a food science web theme issue. A few recent articles are highlighted below.

Understandably, the course at Harvard was particularly popular with the students, as well as the chefs – who also learnt a lot about what goes on when they cook. What is perhaps particularly interesting, from David Weitz’s comments on the course, is that not only did students give a round of applause when a new culinary dish was created, but also when a new equation was introduced. While inviting international chefs to give lectures is not possible for every scientific institution, taking an everyday topic like food might perhaps be the pathway to inspire and promote science in those both young and old.

Designer colloids – towards healthy everyday foods?

In this review paper (doi:10.1039/c001018a), Norton and Norton discuss the design and construction of colloids to encapsulate and release micronutrients. The aim is to create foods with reduced calorific content that look, taste and smell good. To reduced calorific content, pure fat can be replaced by an emulsion with the water phase containing very few calories. If this is designed in the correct way, such that the water is not released until the food reaches the stomach, then the consumer will not detect the water at all. A number of examples are given as to how this may be achieved using colloids, gels, Pickering emulsions and duplex emulsions. By careful design of the system, it is possible to add water to levels regarded as impossible e.g. 50% or more in chocolate. However, it is important that the whole process from eating to digestion is considered in the design of the emulsions and colloids. For example, when stabilised by emulsifiers that are not broken down by the stomach, emulsions stay intact. This means that the body is unaware of the content of fat in the food and can result in the consumer over eating. A recent study (highlighted in Chemistry World) has shown that the size of the fat droplet produced by the emulsion in the stomach is also important. Larger droplets take longer to digest and leave us feeling fuller for longer (doi:10.1039/C0SM01227K).

Nanoemulsions can also be utilised to encapsulate and deliver lipophilic components such as vitamins and drugs (doi:10.1039/c0sm00549e). In this tutorial review, McClements provides an overview of the current status in nanoemulsion research, from fabrication and properties to their applications and suitability for food products. Nanoemulsions are an exciting development over conventional emulsions, as they can be incorporated into transparent foods and beverages without changing the appearance of the product and have improved stability. However, wide spread use will not happen until suitable food-grade materials are identified and safety concerns overcome.

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Professor Marshall Stoneham

21 Feb 2011

On Friday (18th February 2011), I received an email from the Institute of Physics (IOP). It informed me that the President of the IOP, Professor Marshall Stoneham FRS CPhys FInstP, had sadly passed away. Prof. Stoneham had a very successful career in academia, publishing and in industry. Most recently he worked at the London centre for Nanotechnology and University College London, where he was the Emeritus Massey Professor of Physics

In December I attended a talk by Prof. Stoneham at the CMMP10 conference in Warwick. His talk was well attended and his style engaging. The talk titled ‘Where physics meets biology’, discussed (amongst other things) how quantum mechanics could be used to explain how humans smell. His proposal was that receptors in the nose are actuated by electron tunnelling from a donor to an acceptor mediated by the odorant molecule.

Each odorant has its own vibrational frequency. When the vibrations of the odorant cause electrons in the nasal receptors to tunnel between energy states, a nerve signal is sent to the brain and the smell detected. Different vibrational frequencies are detected by different receptors. Since different smells have different frequencies, each odorant smells different. This model termed the ‘swipe card’ model allows receptors to ‘read’ an odorant molecule by detecting its vibrational spectrum along with matching its size and shape. “The shape must be good enough, but it is something else that carries the decisive information”. The results were published in Phys. Rev. Lett. doi=10.1103/PhysRevLett.98.038101.

Prof. Stoneham was the author of over 500 papers and a number of books on a wide range of subjects from biology to quantum computing and from nuclear safety to self-organisation. He was the recipient of the Gutrine gold medal of the IOP in 2006 for his wide-ranging theoretical work on defects in solids and the Royal Society’s Zeneca prize in 1995. Marshall Stoneham will be greatly missed by the physics community.

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The potential of microfluidics

14 Feb 2011

From top to bottom: Cholesteric particles formed via microfluidics. Flow-focusing microfluidic device. Gel emulsion in a channel. Fluorescence image of a dye-containing gel emulsion.

This week I attended a talk at the MPI for Dynamics and Self-Organisation in Goettingen, Germany by Nicolas Bremond from the EPSCI, Paris. The talk was titled “Microfluidic investigations of the destabilisation of emulsions via coalescence”. Nicolas discussed the use of microfluidic devices to study coalescence of emulsion droplets in the absence and presence of an ac electric field. The results have been published in Physical Review Letters and in the Journal of Fluid Mechanics.

In the absence of an electric field, a series of moving pairs of droplets in a microfluidic device were created. A widening of the channel, and therefore slowing of the fluid, was used to force the droplets together. Monitoring of the separation of the droplets showed that coalescence occurred just after closest proximity i.e. when they were separating. Nicolas believes that the separation of the droplets momentarily reduces the fluid pressure between the droplets, causing the high-pressure water in the droplets to burst through the barrier.

Amongst many of the movies shown in the talk was this one, which I have found on the web. It shows that this coalescence mechanism can also trigger coalescence in neighbouring droplets. This mechanism could perhaps be responsible for the clumping of industrial emulsion droplets.

My favourite video of the talk was one showing the behaviour of the emulsion droplets under an applied ac electric field. When the ratio of the radius of the droplet to the channel width is equal to 0.8 the droplets can be made to kiss each other; they come into contact with each other before separating again. On separation deformation of the droplets is observed. Unfortunately I haven’t found a video of this online, but a sequence of images can be seen in the Physical Review Letters paper.

Although not mentioned in the talk, Nicolas has also recently had his paper Formation of liquid-core capsules having a thin hydrogel membrane: liquid pearls published in Soft Matter.

Microfluidics offers an interesting method for studying the coalescence of emulsions under flow. However, this is not its only application as seen in the latest issue and advance articles of Soft Matter. Shashi Thutupalli et al. (doi:10.1039/c0sm00312c) demonstrate the use of microfluidics to self-assemble surfactant bilayer networks in water-oil emulsions. These bilayer membranes display a range of different electrical behaviours, which could be exploited to create wet circuitry. Formation of emulsions in this way, offers a feasible approach to construct complex devices out of molecular-sized components via controlled self-assembly.

Sara Abalde-Cela et al. demonstrate the use of a flow-focusing microfluidic device to form highly mono-disperse plasmonic agarose beads containing silver nanoparticles in their paper doi:10.1039/c0sm00601g, while Daniel Wenzlik et al. used microfluidics to prepare cholesteric liquid crystal particles from cellulose derivatives doi:10.1039/c0sm01368d.

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International Year of Chemistry

30 Jan 2011

Nanoparticles for cancer drug delivery and detection

Last week saw the launch of the International Year of Chemistry (IYC) 2011 in Paris. The theme of the year is to emphasis the importance of chemistry for sustainable development in all aspects of human life. Chemistry has an important role in solving some of the major challenges facing the world, such as human health, food security, providing clean water, energy and sustainable development. This is highlighted in the most recent issues of Soft Matter with articles on the development of nanoparticles for cancer applications, devices for the controlled release of pheromones with potential applications in the agricultural industry and highly functional renewable nanomaterials.

A further goal of the IYC is to promote Women in chemistry. 2011 is the 100th anniversary of Marie Curie’s receipt of the Nobel Prize in chemistry.

Many events are planned throughout 2011 to celebrate chemistry. Many of the activities are aimed at catching the attention and imagination of the younger generation. In Canada a video contest has been launched for school students. The aim is to produce a short chemistry related You-Tube video. The prize is a $2500 scholarship for further education.

In the UK, the Royal Society of Chemistry (RSC) announced the biggest global experiment which will take place on the 22nd June. Children across the world are encouraged to take part in an experiment into the properties and quality of water. More information can be found on the RSC website.

Further information of the events can be found on the RSC website and the IYC website (I have had some trouble accessing their website). Events are being organised worldwide in countries including India, Singapore, Thailand, Brazil, Australia, America, Canada and across Europe.

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Superhydrophobic surfaces

10 Jan 2011

Droplets on a superhydrophobic surface.

Superhydrophobic surfaces capture the imagination of scientists and non-scientists alike and have been studied for over a century. Recently there has been renewed interest in this field due to the potential technological applications of self-cleaning water repellent surfaces. A quick search of Soft Matter, shows that Progress in superhydrophobic surface development, published in 2008, is one of the most read articles of 2010 and has been cited over 160 times.

Current research in this field is focussed on two main areas; the development of rough surfaces with low surface energy and understanding the stability of superhydrophobic surfaces. Below I have highlighted a couple of recent interesting papers in these areas.

Metastable underwater superhydrophobicity

Superhydrophobic teflon surface.

Superhydrophobicity is often considered to be a thermodynamically stable wetting state. In this paper researchers at the University of Cambridge studied the stability of the air film separating the substrate and the water in an underwater experiment. They found that the air film is in fact unstable and decays rapidly. The onset time for decay is dependent on the immersion depth of the superhydrophobic teflon substrate. In nature superhydrophobic surfaces are found, almost exclusively, on surfaces only intermittently exposed to water. The results of this paper help to explain why underwater superhydrophobicity is so rare in nature and raises interesting questions on their viability for some commercial applications.

The paper was published in Physical Review Letters doi:10.1103/PhysRevLett.105.166104. Details on the superhydrophobic surface used for the experiments can be found in Soft Matter doi: 10.1039/B613947G. This paper also has two nice movies attached as supplementary information. Another recent paper on this topic is the Hot Article Cassie-Wenzel and Wenzel-Cassie transitions on immersed superhydrophobic surfaces under hydrostatic pressure.

Self-cleaning solar cells

The accumulation of dust on solar cell panels is a big problem, as it can greatly reduced the efficiency of the panel. In this paper the team in Korea, led by Young-Bum Park, applied a self-cleaning superhydrophobic PDMS surface to a solar cell and studied its properties. The self-cleaning PDMS coating consists of arrays of hollow cylinders formed through micromolding. Dust removal was tested by spraying carbon power on to the surface and washing with water droplets. The carbon coated surfaces had a strongly reduced efficiency of 6.10%. After cleaning the efficiency recovered to 9.76%. The initial efficiency was 11.20%. This work demonstrates that superhydrophobic surfaces can prevent the degradation of solar cell efficiency through a self-cleaning effect. The transparency and flexibility of the PDMS surfaces make it feasible for a while host of applications where self-cleaning is desired. The paper was published in the Journal of Materials Chemistry doi:10.1039/C0JM02463E.

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Soft matter theme at CMMP10

21 Dec 2010

The annual condensed matter and materials physics conference CMMP10 was held last week at the University of Warwick. This year the conference included a number of symposia relevant to the soft matter community including biological physics, polymer physics and soft matter in action. Soft matter plenary lectures were given by Prof. Marshall Stoneham “Where quantum physics meets biology”, Prof. Dame Athene Donald “Self-assembly of proteins”, Prof. Christopher Ober “Will polymers be used to make the next generation nanoworld” and Prof. Mike Cates “Understanding liquid crystals using mesoscopic computer simulation”.

Below I have highlighted a couple of interesting talks. The conference proceedings will be published in the Journal of Physics: Conference Series (JPCS).

Magnetic alignment of anisotropic structures in solution.

Alex Holmes (University of Bristol) introduced the new Birmingham 17T cryomagnet designed for use in small angle neutron scattering (SANS) measurements. The magnet operates in the temperature range of 1.6K to 300K and magnetic field up to 17T with 0.1% uniformity over 10 nm.

Here Alex discussed initial experiments carried out at the Institut of Laue-Langevin, showing the viability of this technique for studying soft matter. The results show that the magnetic field can be used to align rod-like viruses, which behave as cholesteric liquid crystals at high concentrations. A transition from a multi-domain cholesteric structure at zero field, to a nematic phase at high field was observed.

The cryomagent offers an interesting technique to the soft matter community to study the behaviour of soft materials in the presence of high magnetic field and the group are open to collaborations. More information is available on their website.

AFM nanotools to investigate skin cells

In his talk, James Beard (University of Bath) discussed a novel approach to modifying AFM tips using electron beam induced deposition using a scanning electron microscopy (SEM). The secondary electrons interact with contaminants in the SEM leaving behind a deposit of amorphous carbon on surfaces exposed to the electron beam. A variety of highly durable ‘nanotools’ can be formed in this manner such as ‘nanoscapels’, ‘nanoneedles’ with lengths of 500nm and thicknesses of 10-50 nm and ‘nanotomes’.

James demonstrated the use of the nanoscapel probes for cutting biological samples with high precision and nanoneedles to investigate the mechanical properties of corneocyte cells using a nanoindentation technique. The results of the experiments were published in Nanotechnology doi: 10.1088/0957-4484/20/44/445302.

Micro-wrinkled bilayer structures with gradient wetting properties

Kevin Langley (University of Nottingham) demonstrated, in his talk, the use of Aluminium-elastomer bilayers to form micro-wrinkled structures. The Aluminium capping layer was thermally evaporated onto a thick pre-strained elastomer substrate. The strain was then released causing the bilayer to wrinkle with a well defined wavelength and amplitude, dependent on the capping layer thickness and the applied pre-strain.

Kevin was able to create gradient wavelength wrinkled surfaces. Such a surface provides anisotropic wetting properties and could be used as a gradient energy surface to, amongst other things, move water droplets. Similar surfaces have been fabricated through UV-ozone etching of elastomers (Soft Matter doi:10.1039/B705112C) .

A short movie was played, demonstrating that the droplets did indeed move when placed onto these surfaces and vibrated close to their resonant frequency. These surfaces are an interesting candidate for low cost gradient energy surfaces. The results have been published in Langmuir doi: 10.1021/la1036212.

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