The role of entropy in interfacial interactions between polymer-grafted reduced graphene oxide and acrylate copolymers

Abstract

This research examines the role of entropy in interfacial interactions between poly (butyl acrylate) (PBA) chains grafted onto chemically reduced graphene oxide (rGO) and the surrounding acrylate copolymer matrix. Grafted particles were prepared via atom transfer radical polymerization (ATRP) and subsequently dispersed in butyl acrylate-methyl methacrylate copolymer matrices. Based on theoretical predictions, the number-average molecular weight of the copolymer matrices (P) and grafted chains (N), as well as the grafting density of PBA, were controlled to achieve a P/N ratio of about one and grafting density of 0.023 chains/nm², as evaluated by gel permeation chromatography and thermal gravimetry, respectively. To evaluate the role of entropic interaction between PBA-grafted particles and the copolymer matrix at equal interfacial adhesion energy, the content of butyl acrylate in the copolymer was varied in the radical polymerization, so that the molar ratio of butyl acrylate to methyl methacrylate in the copolymer was 50:50, 60:40, and 70:30, respectively. Polymer dynamics measured by dynamic-mechanical-thermal analysis and dielectric analysis revealed that increasing the butyl acrylate content in the copolymer matrix significantly improves the interfacial interaction between rGO and the polymer matrix. This was explained by the similarity in flexibility and entropy matching between the matrix and grafted chains, which resulted in enhanced chain interlocking and entanglement at the interface. The nanocomposite containing the copolymer matrix with a 70:30 molar ratio exhibited the highest positive shift in glass transition temperature (T_g) upon incorporating polymer-grafted rGO. Additionally, the dielectric loss analyses using the HN model confirmed that the most significant increase in relaxation time relative to the pure matrix belongs to the same nanocomposite.