Syntheses and properties of new photo-responsive gemini surfactants containing azobenzene group

Abstract

A new asymmetric gemini type of photo-responsive cationic surfactants, N,N,N-(azobenzene-4-oxy-2-hydroxypropyl)dimethyl-N,N',N'-(alkyloxy-2-hydroxypropyl) dimethylethylene diammonium methylsulphate (GnAZ0DA, n = 4, 8, and 12), were synthesized. The surfactants had ammoniums in both head groups, two carbons as a spacer, azobenzene in one tail group, and alkyl groups in the other tail group. A simple process was designed to conduct the synthesis under mild conditions that included atmospheric pressure, a temperature at or below 100 degrees C, and the use of easy-to-remove solvents. The synthesized GnAZ0DA series showed good solubility in water solution and returned high yields ranging from 87.0% to nearly 100% throughout the experiment. 92.5% of trans-GnAZ0DA was converted to the cis form when exposed to UV light, and 73% was reversibly converted to the trans form when exposed to visible light. The critical micelle concentration (CMC) of the trans-G4AZ0DA was 1.89 x 10(-3) mol/L, while the value for the 92.5% of the cis-G4AZ0DA was 4.45 x 10(-3) mol/L. Light irradiation may be used to control the CMC values. Additionally, this study examined the wettability, foaming power, and emulsion stability of the surfactants and compared them to the commercialized surfactants, sodium lauryl ether sulfate (SLES) and dodecyl benzene sulfonate (DBS).