Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F4: Polymer Architecture Effects on Structure DynamicsInvited
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Sponsoring Units: DPOLY Chair: Michael Rubinstein, Univ of NC - Chapel Hill Room: Ballroom IV |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F4.00001: Topology Matters: Structure and dynamics of ring polymers Invited Speaker: Dieter Richter In this talk I present recent experimental advances addressing the structure and dynamics of rings. I focus mainly on neutron scattering results that reveal experimental insight on a molecular scale. Structural investigations characterizing rings as compact objects in the melts are put into theoretical context. In contrast to the plateau regime common for all other high molecular weight polymer systems, the dynamic modulus of pure ring systems is characterized by a power law decay, while the viscosity displays a much weaker molecular weight dependence as a corresponding linear melt. The dynamics of ring melts is uniquely addressed by neutron spin-echo spectroscopy. The sub-diffusive center of mass motion at short times agrees well with simulation as well as theoretical concepts. In the internal dynamics the basic length scale of the ring molecule, the loop size, manifests itself clearly. The experiments reveal strong evidence for loop motions and call for further theoretical work describing them. Finally, small fractions of ring molecules in linear melts turn out to be very sensitive probes in order to scrutinize the dynamics of the host with the potential to reveal fundamental aspects of the dynamics of branched polymer systems. $\backslash $pardReview Letters 131, 168302 (2014)Review Letters 115, 148302 (2015)Matter 11, DOI: 10.1039/C5SM01994J (2015) [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:27PM |
F4.00002: From chromosome crumpling to the interacting randomly branched polymers Invited Speaker: Ralf Everaers The conformational statistics of ring polymers in melts or dense solutions is strongly affected by their quenched microscopic topological state. The effect is particularly strong for non-concatenated unknotted rings, which are known to crumple and segregate and which have been implicated as models for the generic behavior of interphase chromosomes. In [1] we have used a computationally efficient multi-scale approach to identify the subtle physics underlying their behavior, where we combine massive Molecular Dynamics simulations on the fiber level with Monte Carlo simulations of a wide range of lattice models for the large scale structure. This allowed us to show that ring melts can be \textit{quantitatively} mapped to coarse-grained melts of \textit{interacting} randomly branched primitive paths. To elucidate the behavior of interacting branched polymers, we use a combination of scaling arguments and computer simulations[2]. The simulations are carried out for different statistical ensembles: ideal randomly branching polymers, melts of interacting randomly branching polymers, and self-avoiding trees with annealed and quenched connectivities. In all cases, we perform a detailed analysis of the tree connectivities and conformations. We find that the scaling behaviour of average properties is very well described by the Flory theory of Gutin et al. [Macromolecules 26, 1293 (1993)]. A detailed study of the corresponding distribution functions allows us to propose a coherent framework of the behavior of interacting trees, including generalised Fisher-Pincus relationships and the detailed analysis of contacts statistics. [1] Ring Polymers in the Melt State: The Physics of Crumpling, Angelo Rosa and Ralf Everaers, Phys. Rev. Lett. 112, 118302 (2014) \newline [2] Conformations of randomly branching polymers with volume interactions, Angelo Rosa, A.Y. Grosberg, M. Rubinstein and Ralf Everaers, in preparation. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 1:03PM |
F4.00003: Self-Similar Conformations and Dynamics of Non-Concatenated Entangled Ring Polymers Invited Speaker: Ting Ge A scaling model of self-similar conformations and dynamics of non-concatenated entangled ring polymers is developed. Topological constraints force these ring polymers into compact conformations with fractal dimension D$=$3 that we call fractal loopy globules (FLGs). This result is based on the conjecture that the overlap parameter of loops on all length scales is equal to the Kavassalis-Noolandi number 10-20. The dynamics of entangled rings is self-similar, and proceeds as loops of increasing sizes are rearranged progressively at their respective diffusion times. The topological constraints associated with smaller rearranged loops affect the dynamics of larger loops by increasing the effective friction coefficient, but have no influence on the tubes confining larger loops. Therefore, the tube diameter defined as the average spacing between relevant topological constraints increases with time, leading to ``tube dilation''. Analysis of the primitive paths in molecular dynamics (MD) simulations suggests complete tube dilation with the tube diameter on the order of the time-dependent characteristic loop size. A characteristic loop at time t is defined as a ring section that has diffused a distance of its size during time t. We derive dynamic scaling exponents in terms of fractal dimensions of an entangled ring and the underlying primitive path and a parameter characterizing the extent of tube dilation. The results reproduce the predictions of different dynamic models of a single non-concatenated entangled ring. We demonstrate that traditional generalization of single-ring models to multi-ring dynamics is not self-consistent and develop a FLG model with self-consistent multi-ring dynamics and complete tube dilation. Various dynamic scaling exponents predicted by the self-consistent FLG model are consistent with recent computer simulations and experiments. We also perform MD simulations of nanoparticle (NP) diffusion in melts of non-concatenated entangled ring polymers. NPs larger than the undilated tube diameter undergo power-law sub-diffusion in entangled rings in contrast to strong suppression in entangled linear chains. This result demonstrates that there is no long-lived confining tube in entangled ring polymers, which agrees with complete tube dilation in the self-consistent FLG model. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:39PM |
F4.00004: Polymer Crystallization under Confinement Invited Speaker: George Floudas Recent efforts indicated that polymer crystallization under confinement can be substantially different from the bulk. This can have important technological applications for the design of polymeric nanofibers with tunable mechanical strength, processability and optical clarity. However, the question of \textit{how}, \textit{why} and \textit{when} polymers crystallize under confinement is not fully answered. Important studies of polymer crystallization confined to droplets$^{\mathrm{\thinspace }}$and within the spherical nanodomains of block copolymers emphasized the interplay between heterogeneous and homogeneous nucleation. Herein we report on recent studies$^{\mathrm{1-5}}$ of polymer crystallization under hard confinement provided by model self-ordered AAO nanopores. Important open questions here are on the type of nucleation (homogeneous vs. heterogeneous), the size of critical nucleus, the crystal orientation and the possibility to control the overall crystallinity. Providing answers to these questions is of technological relevance for the understanding of nanocomposites containing semicrystalline polymers. [1] H. Duran, M. Steinhart, H.-J. Butt, G. Floudas, \textit{Nano Letters} \textbf{2011}, \textit{11},\textit{1671}. [2] Y. Suzuki, H. Duran, M. Steinhart, H.-J. Butt,$^{\mathrm{\thinspace }}$G. Floudas, \textit{Soft Matter }\textbf{2013}, \textit{9}, 2769. [3] Y. Suzuki, H. Duran, W. Akram, \quad M. Steinhart, G. Floudas, \quad H.-J. Butt, \textit{Soft Matter}, \textbf{2013}, \textit{9}, 9189. [4] Y. Suzuki, H. Duran, M. Steinhart, H.-J. Butt, G. Floudas, \textit{Macromolecules }\textbf{2014}\textit{, 47, }1793$.$ [5] Y. Suzuki, H. Duran, M. Steinhart, M. Kappl, H.-J. Butt,$^{\mathrm{\thinspace }}$G. Floudas\textit{, Nano Letters} \textbf{2015}, \textit{15}, 1987-1992. *In collaboration with Y. Suzuki, H. Duran, M. Steinhart, H.-J. Butt [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 2:15PM |
F4.00005: Rheology of Rings: Current Status and Future Challenges Invited Speaker: Gregory McKenna Understanding the dynamics of circular or ring-like polymers has been a subject of investigation since the 1980s and is one which remains an area that is not fully understood [1-5]. Part of the reason for this is the difficulty of making synthetic rings of sufficient size to establish the nature of the entanglement dynamics, if entanglements even exist in these materials. Furthermore, there is now strong evidence that small amounts of linear impurities can impact the dynamics. Hence, one of the major challenges to our understanding of ring dynamics is to make large molecular weight rings of sufficient purity that the dynamics of the rings themselves can be determined. In the present work the current state of understanding of the dynamics of rings is outlined and current work from our group of collaborators [6] to make extremely large circular polymers using Echeverria Coli as a route to make pure rings (circular DNA) in sufficient quantity and size to determine the dynamics of these materials will be shown. First results of ring dynamics in dilute solution are presented and new results on concentrated and entangled solutions will be discussed. Remaining challenges will be elucidated. [1] J. Klein, Macromolecules, 19, 105-118 (1986). [2] J. Roovers, Macromolecules, 18, 1359-1361 (1985). [3] G.B. McKenna, G. Hadziioannou, P. Lutz, G. Hild, C. Strazielle, C. Straupe, P. Rempp and A.J. Kovacs, Macromolecules, 20, 498-512 (1987). [4] M. Kapnistos, M. Lang, D. Vlassopoulos, W. Pyckhout-Hintzen, D. Richter, D. Cho, T. Chang and M. Rubinstein, Nat. Matls., Nat. Mater., 7, 997-1002 (2008). [5] Y. Doi, K. Matsubara,Y. Ohta, T. Nakano, D. Kawaguchi, Y.Takahashi, A. Takano and Y. Matsushita, Macromolecules, 48, 3140$-$3147 (2015). [6] Y. Li, K.-W. Hsiao, C. A. Brockman, D. Y. Yates, R. M. Robertson-Anderson, J.A. Kornfield, M. J. San Francisco, C. M. Schroeder and G. B. McKenna, Macromolecules, 48, 5997-6001 (2015). [Preview Abstract] |
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