Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session P3: Simple Views on Bulk Polymers: Symposium Honoring P G de Gennes |
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Sponsoring Units: DPOLY Chair: Tom Witten, University of Chicago Room: Morial Convention Center RO2 - RO3 |
Wednesday, March 12, 2008 8:00AM - 8:36AM |
P3.00001: How Polymer Physics Was Born Invited Speaker: We review the physics of some of de Gennes' principal contributions to fundamental aspects of polymer solution science. These include critical phenomena views on interacting polymers, reptation, polyelectrolytes, and gels. [Preview Abstract] |
Wednesday, March 12, 2008 8:36AM - 9:12AM |
P3.00002: Polyelectrolyte Solutions Invited Speaker: Pierre-Gilles de Gennes once described polyelectrolytes as the ``least understood form of condensed matter''. In this talk, I will describe the state of the polyelectrolyte field before and after de Gennes' seminal contributions published 1976-1980. De Gennes clearly explained why electrostatic interactions only stretch the polyelectrolyte chains on intermediate scales in semidilute solution (between the electrostatic blob size and the correlation length) and why the scattering function has a peak corresponding to the correlation length (the distance to the next chain). Despite many other ideas being suggested since then, the simple de Gennes scaling picture of polyelectrolyte conformation in solution has stood the test of time. How that model is used today, including consequences for dynamics in polyelectrolyte solutions, and what questions remain, will clarify the importance of de Gennes' ideas. [Preview Abstract] |
Wednesday, March 12, 2008 9:12AM - 9:48AM |
P3.00003: Block Copolymers Invited Speaker: In 1969 (Rep. Prog. Phys. 32, 187(1969)) de Gennes proposed a simple way to understand and describe mesophase organization of block copolymers in what we now call the strong segregation limit. The following year he showed how self-consistent methods due to Edwards can be applied to understand subtle correlation effects in polymer melts (J. Physique 31, 235(1970)) and established theoretical framework for quantitative interpretation of scattering experiments and of what we call now weak segregation regime of block copolymers. This was the basis of the theory of order-disorder transition in multiblock copolymers that he published in 1980 (Faraday Transactions). In this pioneering work he also discussed the role of blocks' polydispersity. Eventually, as early as in 1977 de Gennes realized that block copolymers ``are most promising systems for deeper understanding of lyophilic phase diagrams'' (in Suppl. Solid State Phys Ed. Ehrenreich 1977) and this vision led not only to some very interesting theories of block copolymer solutions, but also to some very quantitative model of membranes and interfaces elasticity and to a very influential theory of microemulsions (J. Phys. Chem. 86, 2294(1982)). Since 1980 tens of thousands of papers dealing with block copolymers were published, but it should be stressed that in seventies it has been a very unknown area. Clearly de Gennes' visionary interest in block copolymers had, and has, a tremendous impact in the field. I will illustrate using several examples from very different areas how de Gennes' deep understanding of block copolymers and the theoretical methods he introduced influenced both theory and experiments and I will also show how they are relevant for many present and future industrial applications. [Preview Abstract] |
Wednesday, March 12, 2008 9:48AM - 10:24AM |
P3.00004: Percolation and Gelation Invited Speaker: The sol-Gel transition, as well as the vulcanization of Polymers chains, was described long ago by Flory, Stockmayer, Zimm within mean field approximation. This however had strong limitations because both excluded volume interactions and loops were neglected. An important progress was made when an analogy between percolation and gelation was made by de Gennes and Stauffer. We will discuss some recent experiments showing the relevance of percolation in the description of the sol-gel transition, as well as another important concept also introduced by de Gennes concerning the possibility of observation of classical exponents in the case of vulcanization. We will also consider briefly the influence of diffusion on aggregation properties. Our understanding of dynamical properties close to the sol-gel transition is lower than that of the static ones. Some analogies were given by de Gennes to describe various hydrodynamic limits, but the experimental results still lead to some discussions. Finally, we will mention some generalizations and open questions. [Preview Abstract] |
Wednesday, March 12, 2008 10:24AM - 11:00AM |
P3.00005: Liquid Crystalline Polymers and Networks -- orientation, molecular shape change, mechanics Invited Speaker: In a prescient paper of 1969, Pierre-Gilles de Gennes envisaged both liquid crystal polymers and elastomers. 10 years later, these systems were realised. After 25 years, monodomain elastomers were prepared and displayed phenomena he had predicted: rods incorporated into polymers induce liquid crystallinity in polymer melts and elastomers; orientational order causes shape changes in the back bones of such polymers; mechanical ramifications follow in networks, e.g. spontaneous elongations and contractions on changing order. The latter are proposed as the basis of micro-actuation and artificial muscles, both heat and light-driven. In 1969, de Gennes already described ideal networks heated through the nematic-isotropic transition losing all their order by mechanical relaxation. It is not obvious, but is true in theory and largely in experiment, even in highly non-ideal networks. He also envisaged that a cholesteric network, where there is a topological memory of chirality imprinted by crosslinking chains in a twisted state. Chirality cannot relax away on entering the isotropic phase, even in systems without molecular chirality (for instance those crosslinked in the presence of chiral solvent that is subsequently exchanged away). His chiral elastomers have found application as mechanically-tuneable, rubber lasers. De Gennes also constructed the first continuum elastic theories of nematic elastomers (1982), though distortions are generally very large. His elasticity has informed non-linear elasticity that works even at large amplitudes. I shall describe de Gennes' many contributions, and the current state of a field that has since yielded still more remarkable phenomena. [Preview Abstract] |
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