Microscopic mechanisms of graphene dispersion by amphiphilic polymeric surfactants in paraffin-based phase change materials

Graphene, as a thermally conductive nanofiller, holds significant promise for enhancing the heat transfer capabilities of paraffin-based phase change materials (PCMs). However, its intrinsic tendency to aggregate and sediment in nonpolar media severely limits practical applications. In this study, we investigated the dispersion mechanism of an amphiphilic polymeric dispersant—polyisobutylene succinimide (PIBSI)—which has demonstrated excellent performance in stabilizing graphene in eicosane-based PCMs. Using all-atom molecular dynamics simulations, molecular models of PIBSI, eicosane, and graphene were constructed to elucidate the self-assembled interfacial configuration, absorption dynamics and interlayer interaction energetics. Simulations show that PIBSI adsorbs onto the graphene surface via its polar succinimide head group, while the hydrophobic polyisobutylene tail extends into the solvent phase, forming a steric barrier that inhibits re-aggregation. Moderate surface oxidation of graphene (5 %) enhances interfacial binding via electrostatic contributions, while excessive oxidation (10 %) begins to weaken the dispersant–graphene affinity. Potential of mean force (PMF) calculations reveal that increasing PIBSI concentration from 3 % to 6 % raises the interlayer energy barrier by 13.7 % and shifts it to greater separation distances, indicating strengthened steric and electrostatic repulsion. These results offer molecular-level insights into the dispersion mechanisms, guiding future efforts to optimize dispersant structure and loading in the design of high-performance graphene-enhanced PCM systems.