Ft-Ir Study of the Dynamics of Entangled Polymer Melts

The dynamics of entangled polymer melts have been examined using polarized Fourier-Transform infrared (FT-IR) spectroscopy. Based on the reptation model, the motion of a chain in the presence of topological entanglements is that of a one dimensional random walk along the chain contour. This motion allows the end portions of the chain to escape the initial oriented tube and form a new tube. The new tube is assumed to have a random orientation. Therefore, we utilized the infrared dichroism technique to quantitatively measure the orientation relaxation of the uniaxially strained polymer melts, which gives a direct measure of the fraction of the chain which remains in its initial tube. Three types of experiments were done to study the dynamics of linear entangled polymer melts. (1) Homo-polymer Melts. In this case, different monodisperse molecular weight atactic polystyrenes were used, and the FTIR measured the normalized Hermans orientation function, F(t), as a function of relaxation time, t, and molecular weight, M. We observed that F(t) = 1 $-$ αt$\sp{1/2}$M$\sp{-3/2}$, for t $$ P, and became independent of P when M $$ P, the matrix chain can move faster than the labelled chain. Thus, some segments of the labelled chain are relaxed due to the constraint release of the surrounding matrix chains. (3) Relaxation Mechanism. A centrally deuterated triblock polystyrene was used. The FTIR results showed that the deuterated center block loses little orientation initially and then decays in a predictable exponential manner after some time. These observations strongly support the reptation model for melt dynamics. In this thesis, we have showed that infrared dichroism is an excellent method to study the polymer melt dynamics, and the reptation model provides a good description for the motion of entangled polymer chains.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Metallurgical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Lee, Andre Yan-Jyh

• Engineering, Materials Science

Identifier

(UMI)AAI8721689

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71842