Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N4: Polymer Entanglement and Elasticity |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: William Graessley, Princeton University Room: LACC 515A |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N4.00001: Predicting The Tube Diameter For Polymer Melts and Solutions Invited Speaker: A simple conjecture, relating the tube diameter to a characteristic length called the packing length, works well for all flexible entangled polymer melts. This is a remarkable result, because the tube diameter represents the confining effect of uncrossability of the chains, whereas the packing length is determined only by a chain's bulkiness and flexibility. I extend this conjecture to solutions: first for theta solvents, where it is shown to be equivalent to the Colby-Rubinstein scaling picture, and then for good solvents. In the latter case, it turns out that the number of blobs per entanglement strand is not a constant as had been previously assumed, but depends on the ratio of the packing length to the thermal blob size. Finally, I suggest that the packing length can be related to the Gauss winding number density, thus providing a topological basis for the conjecture. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N4.00002: A primitive path analysis of entangled polymer melts and networks Invited Speaker: Ralf Everaers Computer simulations provide unprecedented access to the microscopic structure and dynamics of polymeric systems. In particular, they are an ideal tool to study and analyze topological constraints on the dynamics of entangled polymer chains which can slide past but not through each other. We (i) show how the microscopic foundation of the tube model can be established by analyzing the topological state of polymeric liquids in terms of primitive paths, (ii) provide a unified view on loosely and tightly entangled systems, (iii) present an extension of the tube model to polymer networks which is (iv) shown to describe the microscopic and macroscopic response to strain of randomly end-linked and randomly cross-linked networks and (v) discuss the interpretation of scattering experiments addressing these issues. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:48AM |
N4.00003: Convective constraint release, chain stretch and hopping tubes: details matter. Invited Speaker: This talk will discuss constitutive equations, for entangled polymer melts and solutions, which incorporate the effects of convective constraint release (CCR) and chain stretch. The model for CCR is based on the conjecture that constraint release events produce local hops of the tube, giving rise to a dynamical equation similar to the Rouse model. Two recent articles [R.S. Graham et al, J. Rheol. 47, 1171-1200 (2003) and D.J. Read, J. Rheol. 48, 349-377 (2004)] have used this idea to derive, and solve, a PDE for the tube motion. The first article presents the more detailed model, including all known relaxation processes; it has been used to predict neutron scattering from melts in non-linear flow as well as melt and solution rheology. The second article uses an ``infinite tube" limit of the equations to examine in detail the CCR process and the coupling to chain stretch. It shows that ``details matter" – the equations appear to be highly sensitive to the nature of the tube on deformation, and in particular to the lower lengthscale cutoff to the CCR process. This talk will highlight these issues, and present a computer simulation scheme that can be used to further investigate the problem. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:24AM |
N4.00004: Yield-like flow transition in entangled polymers: what do we understand about non-Newtonian polymer flow behavior? Invited Speaker: In this talk, we discuss the latest results from our experimental studies of flow behavior of entangled polymers, in the context of the prevailing physical picture [1] prior to this work [2]. The model entangled polymers under study were 1,4-polybutadiene melts and their solutions. Flow behavior of these PBD samples was examined under various experimental conditions where shear flow was imposed by applying either a constant torque or a constant velocity on one of the two surfaces in a cone-plate shear cell (commonly known as controlled-stress or controlled-rate measurements respectively), and small or large step-strain was applied by a sudden displacement of one of the two surfaces in the same cell. The flow responses were found to be drastically different under these different conditions. When the applied shear stress was of a comparable magnitude to the elastic plateau modulus of the entangled solutions, a sharp yield-like constitutive transition was observed, revealing a discontinuous relationship between the shear rate and the shear stress, which was not anticipated according to the understanding prior to these experimental results. Such a discontinuity does not manifest itself in controlled-rate experiment and therefore has not been seen outside our lab. The implications of these results will be discussed to project our future efforts and activities. [1] Bent, J. et al, Science, 301, 1691 (2003); Graham, R. S et al, J. Rheol, 47, 1171 (2003). [2] Tapadia, P.; Wang, S. Q., Phys Rev. Lett., 91, 198301 (2003); Tapadia, P.; Wang, S. Q., Macromolecules, 37, 9083 (2004). [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 11:00AM |
N4.00005: Entanglements and Elasticity in Polymer Networks Invited Speaker: We develop and solve a molecular model for nonlinear elasticity of entangled polymer networks, called non-affine slip-tube model. This model combines and generalizes several successful ideas introduced over the years in the field of rubber elasticity. Each chain passes through a sequence of slip-links. The topological constraints imposed by neighboring network chains on a given one are represented by the confining potential acting on the slip-links. This topological potential restricts fluctuations of the network chains to the non-affinely deformed confining tube and changes upon network deformation. Network chains are allowed to fluctuate and redistribute their length along the contour of their confining tubes. The dependence of the stress \textit{$\sigma $} on the elongation \textit{$\lambda $} is usually represented in the form of the Mooney stress $f^{\ast }$\textit{(1/$\lambda )=\sigma $/($\lambda -$1/$\lambda $}$^{2})$. We find a simple expression for the Mooney stress $f^{\ast }$\textit{(1/$\lambda )$=G}$_{c}+G_{e}$\textit{/(0.74$\lambda $+0.61$\lambda $}$^{-1/2}-0.35)$ where $G_{c}$ and $G_{e}$ are phantom and entangled network moduli. This allows analyzing the experimental data in the form of the universal plot and to obtain the two moduli $G_{c}$ and $G_{e}$ related to the densities of the cross-links and entanglements of the individual networks. The predictions of our new model are in good agreement with experimental data for uniaxially deformed polybutadiene, polydimethylsiloxane, and natural rubber networks. We generalize our non-affine slip-tube model to describe swelling of entangled networks in both good and theta solvents and find that non-affine effects due to entanglements decrease upon swelling. We also calculate the dependence of stress on strain in uniaxially deformed swollen networks. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700