Syntheses and Characterization of a New Gemini Type of Photo-responsive Surfactants Containing an 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, 12, 14 and 18), were synthesized. The surfactants had ammoniums in both head groups, two carbons as a spacer, an azobenzene in one tail group, and alkyl groups in other tail group. A simple process was designed to conduct the syntheses with high yields ranging from 87.0% to nearly 100% throughout the experiment under mild conditions, including atmospheric pressure, temperature at or below 100, and use of easy-to-remove solvents. The synthesized GnAZ0DA series showed good solubility in water solution. The trans-GnAZ0DA series were converted to 92.5% of cis isomer when exposed to UV light, and were reversibly converted to 73.0% of trans isomer 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 of the 92.5% of cis-G4AZ0DA was 4.45 x 10-3 mol/L. Light irradiation could be used to control the CMC values. Additionally, this study examined the wettability, foaming power, and emulsion stability of the synthesized surfactants and compared them to commercialized surfactants, sodium lauryl ether sulfate (SLES) and dodecyl benzene sulfonate (DBS).

| 새로운 비대칭성 gemini type의 광감응성 양이온 계면활성제인 N,N,N-(azobenzene -4-oxy-2-hydroxypropyl)dimethyl-N',N',N'-(alkyloxy-2-hydroxypropyl) dimethylethylene diammonium methylsulphate (GnAZ0DA, n=4, 8, 12, 14, 그리고 18)가 합성되었다. 합성된 GnAZ0DA series는 양쪽 head group에 ammonium기를 가지며, 두개의 탄소를 spacer로 갖고, 한쪽 tail group에는 azobenzene group을, 그리고 다른 한쪽 tail group에는 alkyl기(R=4, 8, 12, 14, 그리고 18)를 갖는다. 전체적인 합성 과정을 상압, 100 이하, 그리고 제거하기 쉬운 solvent를 사용하는 등의 mild condition에서 반응이 잘 이루어지는 간단한 공정으로 설계하였다. 합성된 GnAZ0DA series는 물에서 뛰어난 용해도를 보였고, 전체적인 실험과정에서 87.0%부터 ~100%의 높은 수율로 얻을 수 있었다. trans-GnAZ0DA series는 350 ㎚의 UV 조사 시 92.5%의 cis form으로 전환됐으며, 다시 450 ㎚의 visible light 조사 시 초기 농도의 73.0%의 trans isomer로 재변환되었다. 대표적인 예로, trans-G4AZ0DA의 critical micelle concentration (CMC) value는 1.89 x 10-3 mol/L이며, 92.5%의 cis-G4AZ0DA의 CMC value는 4.45 x 10-3 mol/L이다. 이러한 CMC value는 빛의 조사를 통해서 제어될 수 있다. 또한 친수성 기판에서 접촉각 측정을 통해 합성한 계면활성제의 wettability에 대해 조사하였으며, 이들의 유화력 및 기포력을 측정하여 상용화된 계면활성제인 sodium lauryl ether sulfate (SLES)와 dodecyl benzene sulfonate (DBS)와 비교하였다.