양쪽성 계면활성제는 등전점 이하의 pH 조건에서 양이온 계면활성제로 작용함으로써 유연력을 나타낼 수 있으며, 등전점 이상의 pH 조건에서는 음이온 혹은 비이온 계면활성제로 작용하여 세정력을 나타낼 수 있다. 따라서 pH에 따른 양쪽성 계면활성제의 특성을 활용하면 한 종류의 계면활성제 분자로 세정력과 유연력을 동시에 발휘할 수 있다. 본 연구에서는 betaine 양쪽성 계면활성제에 대하여 계면활성제의 기본적인 물성(CMC, 표면장력, 계면장력, 접촉각, 점도, 계면활성제 시스템의 상거동 등)을 측정하였으며, 또한 계면활성제 수용액에 대하여 QCM(quartz crystal microbalance) 실험과 zeta potential 측정을 통하여 양쪽성 계면활성제가 양이온 계면활성제에서 음이온 계면활성제로 작용이 전환되는 등전점을 결정하였다. Betaine 계면활성제의 CMC는 약 10-4 mol/L이며, CMC에서의 표면장력은 약 32 mN/m이었다. Spinning drop tensiometer를 사용하여 1 wt% 계면활성제 수용액과 n-decane 오일 사이의 계면장력을 pH 2~10의 조건에서 측정한 결과, 계면장력은 pH 5까지 증가하다가 그 이후 감소하는 경향을 보였으며, 평형에 도달하는 시간도 유사한 경향을 나타내었다. 본 연구에서 사용한 betaine 양쪽성 계면활성제의 등전점을 QCM 실험을 통하여 측정한 결과, 등전점은 pH 3.0~3.3에 존재하였으며, 이 결과는 zeta potential 측정 결과와 동일함을 확인하였다.

A zwitterionic surfactant shows not only detergency but also mildness effect since it shows characteristics of a nonionic or an anionic surfactant above an isoelectric point, while showing characteristics of a cationic surfactant below an isoelectric point. Therefore, a zwitterionic surfactant can serve as a dual function surfactant by a single molecule through the interconversion of cleaning and softening effects depending on pH variations of the aqueous solution. In this study, physical properties of betaine surfactant such as CMC, surface tension, interfacial tension, contact angle and viscosity were measured and phase behavior study was performed. Also dual function characteristics of betaine zwitterionic surfactant were investigated by measuring an isoelectric point using QCM(quartz crystal microbalance) and zeta potential measurement. The CMC of betaine surfactant was near 10-4 mol/L and the surface tension at CMC was about 32 mN/m. The interfacial tension between 1 wt% aqueous solution and n-decane measured by spinning drop tensiometer at pH 2~10 resulted in an increase in interfacial tension until pH 5 and a decrease with pH after 5 and equilibration time showed the similar trend with an increase in pH. The isoelectric point of betaine surfactant measured by QCM experiment_x000D_ was found to exist between 3.0 and 3.3, which is the same as the result determined by zeta potential measurement.

Zwitterionic Surfactant Betaine Isoelectric Point Mildness Cleaning

McBain MEL, Hutchinson E, Solubilization and Related Phenomena, Academic Press, New York(1955)
OH SG, KIM JG, KIM JD, Korean J. Chem. Eng., 4(1), 53 (1987)
Park SJ, Yoon HH, Song SK, Korean J. Chem. Eng., 14(4), 233 (1997)
Su YL, Liu HZ, Korean J. Chem. Eng., 20(2), 343 (2003)
Baek K, Lee HH, Cho HJ, Yang JW, Korean J. Chem. Eng., 20(4), 698 (2003)
Cutler WG, Kissa E, Detergency: Theory and Technology, Marcel Dekker, New York(1987)
Ro YC, Nam KD, J. Korean Ind. Eng. Chem., 5(5), 749 (1994)
Ro YC, Kim TY, Jeong JK, Nam KD, J. Korean Ind. Eng. Chem., 7(2), 215 (1996)
Ro YC, Lee SJ, Nam KD, J. Korean Ind. Eng. Chem., 6(4), 548 (1995)
Rendall K, Tiddy GJT, Trevethan MA, J. Colloid Interface Sci., 98, 565 (1984)
Rosen MJ, Gao T, Nakasuji Y, Masuyama A, Colloid Surf. A: Physicochem. Eng. Aspects, 88, 1 (1994)
Rang MJ, Lim JC, Miller CA, Thunig C, Hoffmann HH, J. Colloid Interface Sci., 175(2), 440 (1995)
Harwigsson I, Tiberg F, Chevalier Y, J. Colloid Interface Sci., 183(2), 380 (1996)
Maria PD, Fontana A, Gasbarri C, Siani G, Tetrahedron, 61, 7176 (2005)
Yaseen M, Lu JR, Webster JRP, Penfold J, Biophysical chemistry, 117, 263 (2005)
Yaseen A, Wang Y, Su TJ, Lu JR, J. Colloid Interface Sci., 288(2), 361 (2005)
Park J, Lim J, Appl. Chem., 10(2), 605 (2006)
Han DS, Yoo KM, Park JS, Chi GY, Lee KM, Cho IS, Lim JC, Appl. Chem., 11(1), 229 (2007)
Hoffmann H, Thunig C, Miller CA, Colloid Surf., 67, 223 (1992)
Nilsson PG, Pacynko WF, Tiddy GJT, Current Opinion Colloid Interface Sci., 9, 117 (2004)
Limin Z, Ganzuo L, Zhiwei S, Colloid Surf. A: Physicochem. Eng. Aspects, 190, 275 (2001)
Jeong MW, Oh SG, Kim YC, Colloid Surf. A: Physicochem. Eng. Aspects, 181, 247 (2001)
Chiu TY, James AE, Colloid Surf. A: Physicochem, Eng. Aspects, 280, 58 (2006)