微乳液是熱力學穩定的體系，在化粧品領域逐漸受到重視。傳統的微乳液配方中乳化劑含量約5~40%。當配方中含有高濃度之界面活性劑時，可能使皮膚細胞膜失去保護、屏障之功能，而引起皮膚之刺激性反應。
本研究以如何減少界面活性劑在微乳液配方中之使用量為主要方向，探討機械力及界面活性劑與助界面活性劑對製備微乳液的影響和形成之微乳液的穩定性。並藉由繪製三相圖觀察在不同之油、水及界面活性劑比例下乳化系統的相形態。在此研究中選擇C12-15烷基苯甲酸酯與聚氧乙烯山梨糖醇苷脂肪酸酯系列之乳化系統，此系統之乳化液黏度較高，在利用動態光散射法進行粒徑分析時，計算出之粒徑大小較不可信，因此本實驗仍是以外觀觀察乳化液是否清澈透明為判斷形成微乳液與否之依據。
實驗結果顯示於乳化C12-15烷基苯甲酸酯時，界面活性劑使用Tween 20會比使用Tween 80易形成微乳液。而在使用Tween 20作為微乳化之界面活性劑時，添加已六醇作為助界面活性劑可以在形成微乳液時，明顯降低界面活性劑的使用量。至於不同的機械力對微乳液的形成則没有顯著的影響。而形成之微乳液在安定性測試時，經3個月之觀察大部份都能維持於穩定的狀態。 Preparation of microemulsion has attracted much attention in cosmetic field due to its thermodynamically stability. The content of emulsifier in microemulsion formulation is typically around 5 to 40%. Skin may lose its protection and barrier function because of the high concentration of surfactant in the formulation and that might induce irritation.
In this study, it is attempted to reduce the amount of surfactant used in micro emulsion formulation. The influence of mechanical force, the amount of surfactant and co-surfactant on the formation of microemulsion and the stability of formed microemulsion were studied.
The experimental results show that using Tween 20 as surfactant is easier to form microemulsion with C12-15 Alkyl benzoate than using Tween 80. The addition of sorbitol as co-surfactant can reduce the amount of surfactant used for the formation of microemulsion. Different mechanical force has no significant effect on the formation of microemulsion.
Due to the high viscosity of the emulsion it is hard to measure the particle size of the emulsion by Dynamic Light Scattering Method. The stability test results shows that a clear solution may become phase separated after three months observation.The results were expressed by ternary-phase diagram.
It is concluded that Tween 20 is a better surfactant than Tween 80 for making microemulsion of C12-15 Alkyl benzoate. The addition of sorbitol can significant reduce the amount of Tween 20 used for preparing microemulsion. Clear appearance or particle size alone cannot be the criteria for determining whether the emulsion is microemulisified or not. With the help of ternary-phase diagram it is more clear to see the status of emulsion with varions ratio of oil, water and surfactant phase.
