화학공학소재연구정보센터
Langmuir, Vol.19, No.8, 3114-3120, 2003
Stubby surfactants for stabilization of water and CO2 emulsions: Trisiloxanes
Amphiphiles of anew class, with very short and bulky CO2-philic headgroups, the trisiloxane surfactants of the form ((CH3)(3)SiO)(2)Si(CH3)(CH2)(3)EOnR, where EO stands for ethylene oxide, are shown to be very interfacially active at the CO2-water interface, as indicated by their effectiveness in forming and stabilizing both concentrated and dilute emulsions of water and CO2. A transition in morphology from water-in-CO2 (W/C) to CO2-in-water (C/W) emulsions is induced by manipulating the surfactant hydrophilic-to-CO2-philic balance (HCB) through variation of the number of EO groups. This inversion in morphology is in agreement with a minimum in interfacial tension at the water-CO2 interface. Microscopy and turbidimetry are used to follow the time evolution of the particle size and stability of dilute W/C emulsions. Dilute W/C emulsions formed with a trisiloxane surfactant containing seven EO groups show unparalleled stability against flocculation, indicating effective solvation of the trisiloxane group by CO2. Such enhanced stability suggests that the prevalence of CH3 groups on the surfactant tails favors solvation by CO2, and that the stubby nature of these CO2-philic groups minimizes tail overlap, leading to weaker intermolecular tail-tail interactions and thus minimal flocculation. Consequently, the stability of dilute W/C emulsions with stubby nonfluorous trisiloxane tails is enhanced compared to the stability of those with longer, more overlapping tails.