SURFACE FORCES BETWEEN GLASS SURFACES IN CETYLTRIMETHYLAMMONIUM BROMIDE SOLUTIONS

A new surface apparatus has been used to study the interactions between glass surfaces immersed in CTAB (cetyltrimethylammonium bromide) solutions. At low surfactant concentrations CTAB adsorbs to form a monolayer, and the surfaces become adhesive in contact. At a concentration of 5 x 10(-5) M the charge on glass is neutralized, and the surfaces experience an attractive force in excess of that expected from van der Waals interactions. At concentrations just below the critical micelle concentration, CTAB adsorbs to the hydrophobic interface to form loosely packed bilayers, but the surfaces always come to an adhesive minimum. These observations are quite different from those made when mica is used as the substrate. A comparison between the results obtained for the two substrates is made, and the reasons for the differences are discussed. Glass has a lower area per charge compared with mica, and this results in less tightly packed monolayers and in turn bilayers on glass when compared with mica.