Hello all! This is just a quick note to say that I will be attending the Gordon Research Conference Colloidal, Macromolecular & Polyelectrolyte Solutions next week. I always enjoy the format of GRCs, and the speaker line-up looks really good. If you’re attending the conference, please come over and introduce yourself. I’m looking forward to meeting as many of the delegates as possible.
Serin
COMPLOIDS Summer School “Physics of Complex Colloids”, Varenna, July 3-13 2012
The Marie-Curie Initial Training Network COMPLOIDS (http://www.itn-comploids.eu), an academic consortium dedicated to research in colloidal science, is organizing the summer school “Physics of complex colloids”. The aim of the school is to cover the most exciting modern topics in the physics of colloids including colloidal interactions and phase diagrams, hydrodynamics in colloids, simulation techniques, colloidal arrested states of matter, structural investigations of colloids, synthesis, applications, non-equilibrium phenomena, and active Brownian motion. The minicourses discussing each of these topics will be complemented by specialized seminars focused on recent developments. Lecturers and speakers include P. Chaikin, M. Dijkstra, D. Frenkel, M. Fuchs, C. N. Likos, G. Naegele, R. Piazza, W. C. K. Poon, B. Vincent, C. Van den Broeck, E. Trizac, P. Vekilov, A. G. Yodh, and E. Zaccarelli,
The school will be held at the International School of Physics “Enrico Fermi” in Varenna, Italy, July 3-13 2012. To learn more about the school and to apply, visit http://www.itn-comploids.eu/summerschool or the website of the International School of Physics “Enrico Fermi” (http://www.sif.it/SIF/en/portal/activities/fermi_school/mmxii) or contact the organizers (Clemens Bechinger c.bechinger@physik.uni-stuttgart.de, F. Sciortino francesco.sciortino@uniroma1.it, P. Ziherl primoz.ziherl@ijs.si).
We would like to bring to your attention the Aspen Center for Physics 2012 Winter Conference in Biological Physics, January 2-7, 2012: “Growth and Form: Pattern Formation in Biology.” We have an exciting program planned, with a list of invited speakers that can be found at the conference web page.
We encourage all those who are interested to submit an application.
The deadline for applications is October 15, with notifications to start November 1. Post-deadline applications will be considered only as space permits.
Please see the on-line application form . Limited financial support is available for junior participants.
In a recent talk at the Physical Aspects of Polymer Science conference in the UK, Olli Ikkala discussed his work looking at the self-assembly of polymers and biopolymers.
The self-assembly of polymers is a powerful tool for creating or increasing the functionality of a material. Several different functionalities can often be combined in one material, which may also respond to external stimuli. The scale of the pattern required determines the material that should be used. For example surfactants and amphiphiles self-assemble with patterns on the 1-10nm scale, block copolymers on the 10-100nm scale and colloidal platelets or nanofibres form patterns >100nm. Examples of self-assembled functional materials include tuneable optically active materials, electrically conducting materials and porous materials for use as filters or catalysis templates.
But what if we want to do something more fancy and use biological materials to form structures? This is exactly what Ikkala has been doing, using nature as his inspiration. Examples in his talk included the self-assembly of diblock copolypeptides to form ‘woodpile’ like structures with well-defined lamellae spacing’s. Also discussed was the formation and assembly of cellulose nanofibres to form mechanically robust macrofibres. This was done via a wet extrusion process. The resulting materials have excellent mechanical properties. Using these nanocellulose fibres to form aerogels and coating with titania dioxide results in materials with excellent oil absorbency. This was demonstrated in a nice video. Since the materials float on water and only absorb oil (no water), the materials could potentially be used to clean up oil spills.
Ikkala is also interested in using nanoclays to produce artificial nacre. The replication of nacre in the lab often involves time consuming, complex, energy intensive processes. The use of nanoclays enables lightweight nacre-mimetic films to be created in a roll-to-roll process. These materials have good strength and are very good heat shields. In a video played by Ikkala it was seen that a few mm of the nanoclay nacre was sufficient to protect silk, held on the other side, from damage by a 3000°C (?) heat torch. According to Ikkala: nanoclays are a “good approach to mimicking nacre, but the [material design] is not yet complete”. They do however “know exactly what they need to do” to iron out the problems.
Other work by Olli Ikkala, which may be of interested to Soft Matter readers includes:
Controlled growth of silver nanoparticle arrays guided by a self-assembled polymer-peptide conjugate, Soft Matter (2010).
Long and entangled native cellulose I nanofibres allow flexible aerogels and hierarchically porous templates for functionalities, Soft Matter (2008).
Tailoring of the hierarchical structure within electrospun fibres due to supramolecular comb-coil block copolymers, Soft Matter (2007).
Group photo of delegates at the conference. Olli Ikkala is on the front row, second from the left.
This week saw the 25th biennial meeting of the UK’s Polymer Physics Group (PPG) take place at the University of Surrey. The PPG is part of the Institute of Physics and has strong ties with the Royal Society of Chemistry. This year celebrates the 25th meeting of the group and is also the 50th anniversary of the UK’s first ever meeting on the physics of polymers, which was held in Bristol in 1961. For those interested the proceedings of that first meeting were published in the British Journal of Applied Physics.
Along with a full oral and poster programme and invited talks from Olli Ikkala, Cait MacPhee, William Koros and Dieter Richter, a number of prizes were awarded at the conference. Prof. Tom McLeish from the University of Durham was awarded the Founders Prize. He is the sixth recipient of this award, which is given to a scientist who has made an outstanding contribution to Polymer Physics in the UK or Ireland.
Katherine Thomas (me!) was awarded the Students Prize for her paper on the non-equilibrium behaviour observed in thin polymer films published in Phys. Rev. E. This work looks at the interplay of the polymer film deposition procedure, the resulting non-equilibrium behaviour and the relaxation towards thermal equilibrium. A follow up paper to this work on the direct measurement of stresses in spin-cast films was recently published in Soft Matter. A previous post on this topic can be found here.
The exchange lecture with the American Physical Society Division of Polymer (DPoly) was given by Bradley Olsen. Proteins and enzymes are interesting materials for photovoltaics, catalysts and CO2 reduction and sequestration. Olsen is interested in incorporating proteins into materials so that they can be used in the above applications. He does this by forming protein-polymer diblock copolymers. These block copolymers can then be self-assembled enabling their structure to be easily controlled. His recent papers in Soft Matter can be found here and here.
The first place poster prize was awarded to Mike Smith at the University of Nottingham. Smith had three posters at the conference on ‘Optical properties of large amyloid spherulites’, ‘ Stretching dense colloidal suspensions: from flow to fracture’ and ‘Cracking in thin films of colloidal particles on elastomeric substrates’.
Congratulations to all the prize winners. The conference was very successful and highly enjoyable. It was one of the best conferences I have been to (and not just because they gave me a prize). I would highly recommend that those interested attend their next meeting in two years time.
Images of two nematodes (Panagrellus redivivus) merging.
Last week (8-12th August) saw the 5th European postgraduate fluid dynamics conference (EPFDC-2011) take place in Goettingen, Germany. The conference was jointly hosted by the Institute of Aerodynamics and Flow technology and the Max Planck Institute for Dynamics and Self-Organization. Organised by postgraduate students, the conference is an open-forum for PhD students allowing them to present their results in talks and posters to an audience of their peers.
The sessions were wide ranging in their themes, which included turbulent flows, applied aerodynamics, hydrodynamic stability and geophysical flows. The conference also featured talks on the swimming of micro-organisms, biofluid dynamics and the patterning of polymer melt films.
The hydrodynamics of swimming micro-organisms
Douglas Brumley is a PhD student at DAMTP, University of Cambridge. His talk focused on his work on the low Reynolds number swimmer Volvox carteri. Volvox forms spherical colonies of up to 50,000 biflagelated cells. The cells on the surface of the colony beat their flagella in a coordinated fashion, resulting in a net fluid motion around the colony. Various pictures and videos of the flagella and fluid motion can be found on the DAMTP website. Brumley’s work focuses on modelling the flow fields around the Volvox colonies and characterising the metachronal wave propagating on its surface.
Recent publications in Soft Matter on similar low Reynolds number swimmers include: Hydrodynamic synchronization at low Reynolds number doi: 10.1039/C0SM01121E, The collective motion of nematodes in a thin liquid layer doi: 10.1039/C0SM01236J and Swimmer-tracer scattering at low Reynolds number doi: 10.1039/C0SM00164C.
Flow through shunts at low Reynolds number
Adriana Setchi is currently a PhD student at Imperial College London. In her talk Setchi discussed her work on the modelling of flow in shunts in the small intestine. Shunts are used by doctors in the small intestine to by-pass diseased areas, or to shorten the intestine for weight loss. While medical doctors are able to carry out the implantation of shunts effectively, the dynamics of flow in these by-passes are not well understood. To model the flow, Setchi finds solutions to the Papkovich-Fadle-eigenfunction and applies them to various flow scenarios.
Recent publications in Soft Matter on dynamics in the small intestine include: The adsorption and competitive adsorption of bile salts and whey protein at the oil-water interface doi: 10.1039/C1SM05840A, Transitions in the internal structure of lipid droplets during fat digestion doi:10.1039/C0SM00491J.
Registration now open for the 7th International Symposium on Stimuli-Responsive Materials (October 24-26th, 2011 in Hattiesburg, MS, USA). Leading scientists from a variety of disciplines will discuss recent advances in adaptive materials at the interfaces of chemistry, physics, biology, and engineering. This symposium will build on a successful six year history of assembling experts in the area of stimuli-responsive/smart materials to discuss issues related to fundamental science and real-world applicability. For more information, visit the website here.
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 (Tg) 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 Tg 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 = Tg + 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 Tg 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 Tg 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 Tg, 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!
Related articles in Soft Matter
Rotella et al., Probing interfacial mobility profiles via the impact of nanoscopic confinement on the strength of the dynamic glass transition.
Boucher et al., Physical aging of polystyrene/gold nanocomposites and its relation to the calorimetric Tg depression.
Bäumchen et al., Can liquids slide? Linking stability and dynamics of thin liquid films to microscopic material properties.
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.
Related papers in Soft Matter
Two recent interesting papers, published in Soft Matter, on the locomotion in fluids include: Life around the scallop theorem, Eric Lauga. This paper reviews methods of locomotion for swimmers at low Reynolds numbers. Hydrodynamic synchronisation at low Reynolds number, Ramin Golestanian et al. This paper reviews recent experimental and theoretical work on hydrodynamic synchronisation, such as that seen between bacterial flagella.
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.
