Temperature dependence of the conductivity of filled diblock copolymers

Effect of the Interplay between Polymer-Filler and Filler-Filler Interactions on the Conductivity of a Filled Diblock Copolymer System

We investigate the relative roles of the involved interactions and micro-phase morphology in the formation of the conductive filler network in an insulating diblock copolymer (DBC) system. By incorporating the filler immersion energy obtained by means of the phase-field model of the DBC into the Monte Carlo simulation of the filler system, we determined the equilibrium distribution of fillers in the DBC that assumes the lamellar or cylindrical (hexagonal) morphology. Furthermore, we used the resistor network model to calculate the conductivity of the simulated filler system. The obtained results essentially depend on the complicated interplay of the following three factors: (i) Geometry of the DBC micro-phase, in which fillers are preferentially localized; (ii) difference between the affinities of fillers for dissimilar copolymer blocks; (iii) interaction between fillers. The localization of fillers in the cylindrical DBC micro-phase has been found to most effectively promote the conductivity of the composite. The effect of the repulsive and attractive interactions between fillers on the conductivity of the filled DBC has been studied in detail. It is quantitatively demonstrated that this effect has different significance in the cases when the fillers are preferentially localized in the majority and minority micro-phases of the cylindrical DBC morphology.

Spinodal Decomposition of Filled Polymer Blends: The Role of the Osmotic Effect of Fillers

The reported work addresses the effect of fillers on the thermodynamic stability and miscibility of compressible polymer blends. We calculate the spinodal transition temperature of a filled polymer blend as a function of the interaction energies between the blend species, as well as the blend composition, filler size, and filler volume fraction. The calculation method relies on the developed thermodynamic theory of filled compressible polymer blends. This theory makes it possible to obtain the excess pressure and chemical potential caused by the presence of fillers. As a main result of the reported work, we demonstrate that the presence of neutral (non-adsorbing) fillers can be used to enhance the stability of a polymer blend that shows low critical solution temperature (LCST) behavior. The obtained results highlight the importance of the osmotic effect of fillers on the miscibility of polymer blends. The demonstrated good agreement with the experiment proves that this effect alone can explain the observed filler-induced change in the LCST.