A pseudo-thermodynamic description of dispersion for nanocomposites

Publication date: 27 October 2017
Source:Polymer, Volume 129
Author(s): Yan Jin, Gregory Beaucage, Karsten Vogtt, Hanqiu Jiang, Vikram Kuppa, Jay Kim, Jan Ilavsky, Mindaugas Rackaitis, Andrew Mulderig, Kabir Rishi, Vishak Narayanan
Dispersion in polymer nanocomposites is determined by the kinetics of mixing and chemical affinity. Compounds like reinforcing filler/elastomer blends display some similarity to colloidal solutions in that the filler particles are close to randomly dispersed through processing. It is attractive to apply a pseudo-thermodynamic approach taking advantage of this analogy between the kinetics of mixing for polymer compounds and thermally driven dispersion for colloids. In order to demonstrate this pseudo-thermodynamic approach, two polybutadienes and one polyisoprene were milled with three carbon blacks and two silicas. These samples were examined using small-angle x-ray scattering as a function of filler concentration to determine a pseudo-second order virial coefficient, A2, which is used as an indicator for compatibility of the filler and polymer. It is found that A2 follows the expected behavior with lower values for smaller primary particles indicating that smaller particles are more difficult to mix. A2 is analogous to the excluded volume and long-range interaction potential for non-equilibrated nanocomposites. The measured values of A2 can be used to specify repulsive interaction potentials for coarse grain DPD simulations of filler/elastomer systems. In addition, new methods to quantify the filler percolation threshold and filler mesh size as a function of filler concentration are obtained. The results represent a new approach to understanding and predicting dispersion in polymer nanocomposites based on a thermodynamic analogy.

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