Soft Matter Blog

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.