The adsorption of cationic surfactants on BN surface: Its effects on the thermal conductivity and mechanical properties of BN-epoxy composite

The adsorption of four cationic surfactants, dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), hexadecyltrimethylammonium bromide (HTAB), and octadecyltrimethyl ammonium bromide (OTAB), on boron nitride (BN) surface over the pH range of 5.5–8 was studied. The isoelectric point of BN was found at pH 4.3. The amount of surfactant adsorption was found to increase with the zeta potential of the surface and the surfactant chain length. The area occupied by the surfactant molecules also increased with increase in surfactant chain length. The results support the proposition that the surfactant molecule attached to the surface by having its headgroup attaching to the charged site on the surface and its tail projecting at an angle from the surface. The tail swung around in a right circular cone-shape space with the height of the cone varying with the surfactant chain length. The adsorption of the surfactant has changed the property of the BN surface from partial ionic to a hydrophobic surface with better wetting by the epoxy resin. This change has led to an increase in the thermal conductivity and mechanical properties of the surfactant-treated BN-epoxy composites.