Phase behavior for systems containing polyoxyethylene nonylphenyl ether (NP) nonionic surfactant, water, and D-limonene was studied as a function of surfactant concentration and temperature. The result showed an oil-in-water microemulsion in equilibrium with excess oil phase was formed at low temperatures, whereas a water-in-oil microemulsion in equilibrium with excess water phase was formed at high temperatures. For intermediate temperatures a three phase region containing water, oil, and a middle-phase microemulsion was observed. Phase Inversion Temperatures (PIT), at which a middle-phase microemulsion containing equal volumes of oil and water coexisted with excess oil and water phases, were found to be 45 ℃ and 55 ℃ for NP-9 systems, respectively. Addition of butyl diglycol (BDG) and butyl triglycol (BTG) as cosurfactants lowered the temperature necessary for the formation of a three phase region and produced a middle-phase microemulsion over a wide range of temperatures. the solubilization of abietic acid, triolein, and lubricant using three different types of microemulsions showed that the maximum soil removal was obtained with the water-in-oil microemulsion in all cases. Addition of cosurfactants promoted the solubilization mainly due to a decrease in interfacial tension.

본 연구에서는 polyoxyethylene nonylphenyl ether (NP) 계의 비이온 계면활성제, 물, D-limonene 오일의 3성분 계에 대하여 계면활성제 농도와 온도에 따른 상평형 실험을 수행하였다. 비교적 낮은 온도 조건에서는 O/W microemulsion (μE)과 excess oil의 2상이 형성되었고 높은 온도 조건에서는 excess water+W/O μE의 2상이 형성되었으며, 중간 온도 영역에서는 middle-phase μE이 excess water, excess oil과 평형을 이루는 3상이 형성됨을 알 수 있었다. Middle-phase μE이 동일한 부피의 물과 오일을 포함하는 Phase Inversion Temperature (PIT)는 NP-9의 경우 45 ℃, NP-10의 경우 55 ℃이었다. 3성분계 시스템에 cosurfactant로서 butyl diglycol (BDG), butyl triglycol (BTG)을 각각 첨가한 결과 알코올/계면활성제 비율(A/S)을 증가시킴에 따라 middle-phase μE을 형성하는 온도는 감소하였으며, 3상이 존재하는 온도범위는 증가하였다. 피가용화제로서 abietic acid, triolein, 산업용 윤활유을 사용하여 서로 다른 조성 조건에서 형성된 3가지 형태의 μE에 가용화 시킨 결과 W/O μE의 가용화력이 가장 크게 나타났으며, cosurfactant를 첨가할 경우 계면장력이 낮아짐에 따라 가용화는 증가하였다.