Application of electrospray spreading to a modified Langmuir–Blodgett technique for organo-clay hybrid film preparation

Abstract

A clay mineral, montmorillonite, is exfoliated into discrete clay nanosheets bearing negative charges in aqueous dispersions. When amphiphilic cations are spread on a surface of a clay mineral dispersion, clay nanosheets adsorb onto a floating film of the amphiphilic cations, forming a hybrid film. In conventional procedures, a solution of an amphiphilic cation is spread on a dispersion by manual operation. In this work, we instead applied an electrospray (ES) spreading method. A chloroform solution of octadecylammonium chloride (ODAH+Cl−) was spread on clay mineral dispersions by ES method at different infusion rates. The surface pressure-molecular area isotherm curves of the films exhibited the unusual dependence on the infusion rates; the curves shifted to a larger molecular area with the increase of infusion rate, while they shifted back to a smaller area with the further increase of infusion rate. The following formation mechanism was proposed. In case of the low infusion rate, the solution drops were so fine that some evaporated before they arrived at the interface. Under these conditions, the hybrid film contained ODAH+Cl− salt particles. In case of the high infusion rate, the large solution drops hit violently the dispersion surface, affording a hybrid film with multi-layered domains.