본 연구에서는 비이온 계면활성제 C12E5 수용액과 비극성 탄화수소 오일 시스템에 대한 상평형 및 동적 거동 실험을 수행하였다. 온도를 증가시킴에 따라 oil-in-water(O/W) microemulsion(μE)이 excess 오일상과 평형을 이루는 2상영역으로부터 middle-phase μE이 excess water, excess 오일상과 각각 평형을 이루는 3상 영역을 거쳐서 water-in-oil(W/O) μE이 excess 물상과 평형을 이루는 2상으로 전이되었다. 또한 탄화수소 오일의 사슬 길이가 증가할수록 상전이 온도가 증가하였다. O/W μE이 존재하는 낮은 온도 조건에서는 비극성 오일의 종류와 상관없이 오일이 계면활성제 마이셀에 의하여 가용화되어 시간에 따라 크기가 선형적으로 감소하였다. 한편 middle-phase μE을 포함한 3상이 형성되는 조건에서는 매우 낮은 계면장력으로 인하여 오일이 수용액 상에 빠른 속도로 가용화되었고 작은 drop 형태로 유화되었다. 반면에 W/O μE의 2상을 형성하는 온도에서는 과포화로 인하여 일어나는 자발적 유화 현상과 물과 계면활성제의 오일상으로의 확산으로 인한 오일의 크기가 증가하였다. 비극성 탄화수소 오일과 계면활성제 수용액 사이의 시간에 따른 계면장력을 25 ℃에서 측정한 결과, 탄화수소 오일의 사슬 길이가 증가함에 따라 평형에서의 계면장력 값과 평형에 도달하는데 소요되는 시간이 모두 증가하였다.

Phase equilibrium and dynamic behavior studies were performed in systems containing C12E5 nonionic surfactant solution and nonpolar hydrocarbon oil. The phase behavior result showed an oil-in-water(O/W) microemulsion(μE) in equilibrium with excess oil phase at low temperatures and a water-in-oil(W/O) μE in equilibrium with excess water phase at high temperatures. For intermediate temperatures a 3 phase region containing excess water, excess oil, and a middle-phase microemulsion was observed and the transition temperature was found to increase with an_x000D_ increase in the chain length of a hydrocarbon oil. Dynamic behavior at low temperatures showed that an oil drop size decreased linearly with time due to solubilization into micelles and the solubilization rate decreased with an increase in the chain length of a hydrocarbon oil. On the other hand, both spontaneous emulsification of water into oil phase and expansion of oil drop with time were observed because of diffusion of surfactant and water into oil phase. Under conditions of a 3 phase region including a middle-phase μE, both rapid solubilization and emulsification of oil into aqueous surfactant solution were found mainly due to the existence of ultra-low interfacial tension. Interfacial tensions were measured as a function of time for n-decane oil drops brought into contact with 1 wt% surfactant solution at 25 ℃. Both equilibrium interfacial tension and equilibration time were found to increase with an increase in the chain length of a hydrocarbon oil.

Dynamic Behavior C12E5 Nonionic Surfactant Nonpolar Oil Solubilization Spontaneous Emulsification

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