Buried interfacial structures in cellulose-reinforced styrene–butadiene rubber composites probed by sum-frequency generation spectroscopy

Abstract

The mechanical properties of polymer composites are closely linked to the aggregation states of polymer chains at filler interfaces. Here, we employed sum-frequency generation (SFG) vibrational spectroscopy to investigate the interfacial organization in styrene-butadiene rubber (SBR) composites reinforced with cellulose nanofibers (CNF). Phenyl groups from the styrene (St) units in SBR were found to adopt an oriented conformation at the buried SBR/CNF interfaces. Moreover, increasing the St content enhanced interfacial interactions, leading to improved dispersion of CNF within the SBR matrix. Molecular dynamics simulations were conducted to support the experimental observations and revealed that the local orientation of phenyl groups remained similar across compositions, while differences in CNF dispersion were attributable to interfacial energy matching. These findings provide molecular-level insights into structure–property relationships in polymer composites and offer guiding principles for the rational design of high-performance composite materials.