Title

Computer Simulation Study of Waterborne Two-Component Polyurethane Film Formation

Author

Shihai Yang

Date of Award

2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Ras B. Pandey

Advisor Department

Physics and Astronomy

Abstract

In this thesis, a coarse-grained computer simulation model is presented to study the film growth and macroscopic morphological feature (film thickness, surface roughness and longitudinal constituent density profile) in a multi-component polymer system. The mixture consists of reactive hydrophobic ( H ) and polar groups (P ) in a reactive aqueous solvent ( A ) which is also allowed to evaporate. Characteristics of each component such as hydrophobic and polar interactions, molecular weights, and specific functionality for the covalent bonding are used to describe the waterborne two-component polyurethane (WB 2K-PUR) film growth as an example. Systematic approach is employed to study the film growth step by step starting from the mixture of its basic ingradients. Attempts are made to capture such realistic features as perceived reaction kinetics and polymerization mechanism in the model. Constituents move stochastically via the Metropolis algorithm to explore thermo-dynamic equilibration while the kinetic reactions are incorporated through flexible covalent bonding (Bond Fluctuation Model) which may arrest the growth before reaching equilibrium. Film thickness grows and its interface evolves and equilibrates as the simulation continues. Power-law dependence is found for the initial growth of film thickness ( h ) and surface roughness (W ) with time (t ), i.e., h ∝ tγ , W ∝ tβ , with all simulations. In addition to the study of film evolution and surface morphlogy, constituent density profiles along the longitudinal direction are also investigated to develop a deep understanding of film infra-structure as well as to track the post-reaction product distribution. Effects of parameters such as temperature, relative humidity (initial water concentration), stoichiometry (NCO:OH ratio) and reaction rate are examined specifically in these simulations. Qualitative agreements with laboratory observations are found with our simulation results.