Comparison of Mobility Modes in Polymer Solutions Undergoing Thermal-Induced Phase Separation
- PDF / 90,742 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 79 Downloads / 212 Views
Comparison of Mobility Modes in Polymer Solutions undergoing Thermal-induced Phase Separation
Philip K. Chan Department of Chemistry, Biology and Chemical Engineering Ryerson University 350 Victoria Street, Toronto, Ontario, Canada, M5B 2K3
ABSTRACT The thermal-induced phase separation method is used to fabricate polymer membranes and polymer-dispersed liquid crystal films from polymer solutions. The resultant morphology consists of solvent droplets dispersed uniformly in a solid polymer matrix. Up till now, the modeling and computer simulation of the thermal-induced phase separation phenomenon in polymer solutions have considered the mobility to be a constant. The objective of this presentation is to compare the following three mobility modes: (1) mobility as a constant, (2) mobility following fast mode theory, and (3) mobility following slow mode theory. We present computer simulation results from models composed of the Cahn-Hilliard theory for phase separation, Flory-Huggins free energy density for polymer solutions, and the three aforementioned mobility modes. The numerical results indicate that there is no significant difference in the morphology formed; the only difference occurs in the phase separation time. Furthermore, the numerical results show that the only difference between the slow and fast mode theories is a factor of two; the mobility of the fast mode theory is twice that of the slow mode theory.
INTRODUCTION The thermal-induced phase separation method is used on polymer solutions to fabricate microporous materials such as polymer membranes for separation purposes and polymerdispersed liquid crystal films for electro-optic devices [1,2]. The polymer solution undergoes spinodal decomposition after it is instantaneously quenched into the unstable region [3]. A droplet-type morphology forms for noncritical concentrations while an interconnected structure forms for critical concentrations. Modeling and computer simulation of the thermal-induced phase separation phenomenon in polymer solutions have been performed in the past [4] using the Cahn-Hilliard equation [5] for spinodal decomposition. The mobility, however, was kept constant in ref. [4]. Other possible forms for the mobility include the slow mode and fast mode theories [6]. The objective of this paper is to compare preliminary numerical results from the modeling and computer simulation of the thermal-induced phased separation phenomenon (spinodal decomposition) in a polymer solution for the following three types of mobility: (a) constant, (b) slow mode theory, and (c) fast mode theory.
DD4.6.1
THEORY The nonlinear Cahn-Hilliard (C-H) theory is based on the following expression for the total free energy of an inhomogeneous binary solution: F=
∫ ( f (c) + κ ∇c )dV 2
(1)
where κ is a positive constant related to the interfacial constant and c is the concentration. In this paper, c is defined as the low molecular weight solvent volume fraction. The first term in equation (1) represents the homogeneous free energy, while the second term takes
Data Loading...
