Thermoelectric materials offer the tantalizing potential of energy ‘for free’ from waste heat. To be efficient thermoelectrics, materials need high electrical conductivity and low thermal conductivity to maintain a temperature gradient – property requirements that meant that, until recently, inorganic conductors and semiconductors like bismuth tellurides dominated. Of course, such inorganic materials bring some inherent disadvantages despite their good performance: toxicity, scarcity of constituents, and complex – and therefore costly – processing.
Polymers and polymer composites have been investigated as thermoelectric materials too, but May 2011 saw one of the most impressive breakthroughs in the field: Xavier Crispin, Magnus Berggren, and their colleagues showed that polymers could compete with inorganic materials in thermoelectric performance whilst bringing all their inherent advantages to the mix.1 With appropriate tuning of oxidation levels they demonstrated that the electrical conductivity of the well-known poly(3,4-ethylenedioxythiophene) (PEDOT) could be optimized against the thermal conductivity to give thermoelectric performance that is second only to polyacetylene in polymers. In addition, PEDOT has the advantages over polyacetylene of air-stability and simple processability.
The field of thermoelectrics is an example of a common phenomenon: polymers making their mark in an area where it was once thought that they could not compete. Yet compete they do in many fields – and often excel because of their processing advantages. 2011 was another bumper year for breakthroughs in many aspects of polymer science, and one where it proved to be more useful than ever.
Thermoelectrics were not the only energy applications high on many agendas, as the topic benefits from outstanding funding while the world seeks alternatives to oil. In one of the highest profile areas of energy research, polymer solar cells benefitted from extensive research – from new polymers to morphology control and device optimization – and reports of 9.3% efficiency devices from Mitsubishi Japan emerged.2 The once-elusive-sounding 10% efficiency looks excitingly within reach.
In more classic polymer physics, Daniel Read, Tom McLeish and colleagues showed in a highlight reported in September that they could connect the viscoelastic properties to the topological structure of highly branched entangled polymers.3 The problem with low density polyethylene used in many industrial applications is that the branching structures can vary wildly between molecules, making predicting properties almost impossible. The researchers reduced the problem to concentrate on its most vital constituents, focusing on the segments of the molecules at maximum stretch, which would most actively affect the melt's rheology. Making this structure—property connection will enable the optimization of the rheology of this industrially essential polymer, and could even help with in silico design of new materials.
“Polymer scientists can make an impact on multiple fronts”
A recent advance in the field of measurement techniques will make the study of biopolymer networks' properties possible at an unprecedented level of sensitivity and detail; a deeper understanding of biopolymer behavior has the potential to help us better understand disease mechanisms in the body, enabling us to push towards new treatments. The approach of Daniel Blair, Andreas Bausch and their colleagues combined a rheometer and confocal microscope system.4 They have so far applied it to a network made from the muscle filament protein actin to study its mechanical response under shear, and expect a major application to be the study of silk fibers under stress.
As these examples show, the versatility and variety of polymers mean that polymer scientists have the opportunity to make an impact on multiple fronts that can make a difference to our lives. It's this vibrancy in the field that we've been pleased to echo within our pages at the Journal of Polymer Science: Polymer Physics over the last year. Even in our Reviews series alone, we've taken a look at energy applications like thermoelectrics and solar cells, more biologically focused topics such as DNA translocation, neural implant materials, and biodegradable biomaterials, and more fundamental studies such as superhydrophobic surfaces and imaging techniques. This is just a small cross-section of the full collection, and we've made them all free to access so everyone can download them and see the full breadth of the recent physics of polymers.5
We're also proud to present our cover gallery, a stunning set of images that show the beauty of polymer physics;6 we continue to promote our best papers on MaterialViews.com, to ensure their exposure to the whole materials science community; and of course we still publish papers online just 15 days after acceptance. To submit your work, go to www.polymerphysics.org.
We look forward to seeing what 2012 holds in store for polymer science, and are excited to be able to bring you the most up-to-date news in the field at the Journal of Polymer Science: Polymer Physics. Enjoy this issue, and sign up for ToC alerts at www.polymerphysics.org to make sure you don't miss a thing next year.