Incorporation of nano-clay saponite layers in the organo-clay hybrid films using anionic amphiphile stearic acid by Langmuir–Blodgett technique

Abstract

In general cationic amphiphiles are used to prepare organo-clay hybrid film in Langmuir–Blodgett (LB) technique. In this present communication we demonstrated a unique technique to prepare the organo–clay hybrid films using an anionic amphiphile. The T–O–T type clay saponite was incorporated onto a floating stearic acid monolayer via a divalent cation Mg2+. Salt MgCl2 was mixed along with the clay dispersion in the LB trough and amphiphile solution was spread onto the subphase in order to make the organo-clay hybrid films. It was observed that salt (MgCl2) concentration on the subphase affects the organization of nano-dimensional clay platelet (saponite) in organo-clay hybrid films at air–water interface as well as in LB films. Noticeable changes in area per molecule and shape of the isotherms were observed and measured at subphases with different salt concentrations. Infrared reflection absorption spectroscopy studies reveal that only an in-plane (996cm−1) vibration of ν (SiO) band occurred when the salt concentration was 10mM. However, both in-plane (996cm−1) and out-of-plane (1063cm−1) vibrations of the ν (SiO) band of saponite occurred when the subphase salt concentration was 100mM. Also the out-of-plane vibration of ν (OH) of saponite was prominent at higher salt concentration. This is because at lower salt concentration clay sheets remain flat on the surface whereas; at higher MgCl2 concentration they aggregated and form stacks of saponite layers. Also they may be slightly tilted with a very small tilt angle at higher salt concentration making a favorable condition for both in-plane and out-of-plane vibrations of ν (SiO) in the hybrid films. Observed decrease in starting area per molecule in the pressure area isotherm measured at higher salt concentration also supports the tilting of clay layers at air–clay dispersion interface. Attentuated total reflectance Fourier transform infrared spectroscopy and Atomic Force Microscopy investigations of the hybrid films prepared with subphase using different salt concentrations also support this thesis.