Surfactant Self-Assembly in Cylindrical Pores: Insights from Mesoscale Simulations

Motivated by the inconclusive results of three small-angle neutron scattering experiments on nonionic surfactants adsorbed in nanoporous silica, we determine the structure of the surfactant aggregates by computer simulations and provide a deeper understanding of the self-assembly mechanism. The experiments showed that surfactants adsorbed into the nanometer-sized cylindrical pores of SBA-15 self-assemble into aggregates that are far smaller than bulk aggregates. Their morphology has been assumed to depend on the hydrophilicity of the pores. Because of the limited resolution of the scattering experiments, a detailed analysis of the morphological changes was not feasible. Here we show that our mesoscale simulations reproduce the experimental findings and also allow us to study the subtle interplay between aggregation and adsorption. We find that increased adsorption in more hydrophilic pores leads to an increase in the effective area required by the surfactant head groups and consequently to a decrease in aggregate size.