Understanding Thermodynamics and Structural Dynamics in Polymer Systems

This talk will cover work done on understanding the thermodynamics and structural dynamics of two important types of polymer systems respectively, solutions and blends. Polymer solutions are very often encountered in polymer processing and knowledge of their phase behavior therefore becomes essential. Experimentally, phase separation can be measured by the convenient and rapid method of thermo-optical analysis. A turbidimeter built for this purpose was used to measure, as a function of temperature and composition, changes in transmitted light intensity through solutions of PMMA and PS in a common cyclohexanol solvent. Theoretically, phase behavior can be modeled using a number of thermodynamic models. However, determining which model best describes a given system is not trivial. In view of this, the applicability of two powerful models, the Sanchez-Lacombe equation of state and the UNIFAC-FV activity coefficient model were tested against the collected data. Results are presented.

Although macroscopic miscibility exists, a pair of polymers with highly dissimilar glass transition temperatures, like PEO and PMMA, can exhibit different dynamical processes at a microscopic scale. Of particular interest are the processes associated with the glass transition temperature and how this transition is affected by blending. Four different neutron scattering techniques in combination with selective deuterium labeling have been used to study this polymer blend. Experiments probed spatial scales between 2 and 40Å, time scales between 0.01 ps and 10 ns, and temperatures below and above the glass transition temperature. Two techniques probing different time scales, neutron backscattering (BS) and time-of-flight (TOF), were used to follow the self-motion of each component in turn. Triple-axis spectrometry allowed us to link the identity of scattering centers with the spatial region of their scattered intensity in the static structure factor. Neutron spin-echo (NSE) was then used to assess relative motion between the identified pairs of scattering centers.

Back to Archives - 2003

Back to Seminar Home Page

Last modified 24-December-2003 by website owner: NCNR (attn: )