A Study of Latex Film Formation by Atomic Force Microscopy. 2. Film Formation vs Rheological Properties:  Theory and Experiment

Abstract

In this second paper of a series dealing with the film-forming behavior of latex systems, we show the relationship between the kinetics of film formation and rheological properties. The kinetics of film formation were followed using atomic force microscopy (AFM), with results that showed the kinetics obeyed time/temperature superposition principles, with the same time/temperature shifts used to superimpose rheological data. This demonstrates a direct relationship between film formation kinetics and rheological properties. A new theory based upon these observations is presented, in which the Boltzmann superposition principle and a time-dependent compliance function J ( t ) are used to relate the time-dependent biaxial strain ψ( t ) to the time-dependent driving stress σ( t ). The compliance function J ( t ) of the latex polymer was obtained by transformation of the master stress relaxation function G ( t ), which in turn was obtained from time/temperature superposition of experimental stress relaxation data. A comparison of theoretical predictions and experimental data for the kinetics of film formation shows good agreement over the 4 decades of time followed experimentally. The agreement is believed to be within the accuracy of the transformation of G ( t ) to J ( t ).