Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F68: Polymer Physics Prize SymposiumInvited Prize/Award
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Sponsoring Units: DPOLY Chair: Kurt Kremer, Max Planck Inst Room: Four Seasons 4 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F68.00001: Statistical Mechaincs and Phase Transitions of Semiflexible Polymers Invited Speaker: Kurt Binder By large scale computer simulations theoretical concepts on semiflexible polymers are tested. When the chain stiffness varies, crossover scaling of the polymer radius occurs in bulk dilute solutions. For contour lengths L exceeding the persistence length l, gaussian coils occur only in d=3 dimensions : in d=2 coil swelling due to excluded volume begins for L > l. The initial decay length of orientational correlations in d=2 is twice as large as in d= 3; but adsorbed chains do not behave strictly two-dimensional, perpendicular excursions occur on a lateral scale of the deflection length, and a gradual crossover of the decay length of orientational correations is found. The adsorption threshold scales with the minus 1/3 power of l. In concentrated lyotropic solutions, nematic order occurs; the transition depends on both ratios L/l and D/l (D = chain thickness). The effect of deflection length fluctuations on nematic order is elucidated, and the transition to smectic order is studied. |
Tuesday, March 3, 2020 8:36AM - 9:12AM |
F68.00002: Cartilage-inspired superlubricious hydrogels Invited Speaker: Jacob Klein The uniquely-efficient lubrication of articular cartilage up to high physiological pressures in the major joints (hips and knees) has been attributed to surface boundary layers of macromolecules complexed with phosphatidylcholine (PC) lipids, where the exposed highly hydrated phosphocholine groups massively reduce friction via the hydration lubrication mechanism. We have emulated nature by constructing hydrogels exposing similar PC-based boundary layers at their surfaces, and by incorporating such PC lipids in the hydrogel bulk we achieve self-maintaining lubricant layers which permanently reduce the friction and wear of the hydrogels by up to a 100-fold or more, down to the superlubrication level (coefficient of friction < 0.01) at contact stresses up to many MPa. Such hydrogels hold promise in a wide range of biomedical applications. |
Tuesday, March 3, 2020 9:12AM - 9:48AM |
F68.00003: Some Thoughts On Polyelectrolyte Persistence Length Invited Speaker: Philip Pincus Electrically charged, intrinsically flexible polymers in low ionic strength aqueous solutions are known to be stretched in order to reduce the Coulomb self-energy. As the solution ionic strength increases with added salt, Debye screening weakens the repulsion between distant parts of the chain and the polymer is envisioned as a semi-flexible chain with a persistence length that is governed by the Debye screening length. However for nearly fifty years, the dependence of this electrostatic persistence length on ionic strength has been controversial. This presentation will discuss recent experiments and theoretical thoughts that might contribute to unraveling this dilemma. |
Tuesday, March 3, 2020 9:48AM - 10:24AM |
F68.00004: Conformational properties and phase behavior of polymers in ionic liquids Invited Speaker: Arun Yethiraj Ionic liquids have generated considerable excitement for their varied potential applications and their interesting physical properties. The viability of ionic liquids (ILs) in materials applications is limited by their lack of mechanical integrity, which may be provided by mixing them with a polymeric material. Recent experiments on polymers in ILs have unearthed a wealth of interesting phenomena that raise fundamental questions. This talk focuses on computational studies of PEO in imidazolium ILs. We develop a physically motivated first principles force field for PEO and [BMIM] [BF4]; this force field is in quantitative agreement with experiment with no adjustable parameters. Based on the same quantum calculations we develop a hierarchy of united atom models with decreasing resolution and increasing computational efficiency. Microsecond simulations are required to obtain converged properties of the polymer, which displays a combination of ring-like and extended conformations. The simulations show the existence of a lower critical solution temperature which arises from conformational restrictions on the polymer molecules at low temperatures. |
Tuesday, March 3, 2020 10:24AM - 11:00AM |
F68.00005: Phase transitions in single grafted molecules Invited Speaker: Friederike Schmid We use Brownian dynamics simulations and analytical theory to study and compare |
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