Using profile analysis tensiometry for monitoring auto-oscillations caused by the hydrolysis of 3-(trimethoxysilyl)propyl methacrylate when contacting water

Abstract

3-(trimethoxysilyl)propyl methacrylate (TPM) hydrolyzes via the alkoxy groups attached to silicon when it comes into contact with an aqueous phase and forms surface active 3-(trihydroxysilyl)propyl methacylate (THPM) molecules. Their formation and adsorption at the water/air interface, i.e. decrease in the surface tension, can be used as a sensor to follow the hydrolysis process and can help to explain the role of these molecules in the emulsion formation and stabilization process. The target of this contribution is to demonstrate the experimental details of a surface tension sensor using a bubble profile analysis tensiometer for monitoring the chemical reaction of TPM with water and to explain the peculiarities observed in the measured signal, i.e. irregularities in the dynamic surface tension. Auto-oscillations of the surface tension were observed during the measurements, which are connected to a complex of different types of flows in the volume of the aqueous phase. The kinetics of the reaction and hence of the surface tension can be controlled by changing the pH of the aqueous phase. It is also possible to prevent auto-oscillations by means of a continuous gentle stirring of the aqueous phase, which then allows a quantitative monitoring of the rate of the TPM/water reaction.