Kunieda H, Umizu G, Yamaguchi Y
Graduate School of Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama, 240-8501, Japan
J Colloid Interface Sci. 1999 Oct 1;218(1):88-96. doi: 10.1006/jcis.1999.6400.
An effective cross-sectional area per surfactant molecule at hydrophobic interfaces of aggregates, a(S), in hexagonal (H(1)) and lamellar (L(alpha)) liquid crystals was calculated in homogeneous and mixed polyoxyethylene dodecyl ether systems as a function of polyoxyethylene (EO) chain length by means of small-angle X-ray scattering. The a(S) increases with increasing the EO chain length. The a(S) in the mixed surfactant system is considerably smaller than that in the single surfactant system, even if the average EO chain length is the same. The reduction of a(S) is larger than that predicted by ideal mixing of the surfactants. Moreover, if the EO chain lengths of the surfactants are more separated, the a(S) is smaller. The shapes of surfactant self-organizing structures may be governed by the balance of the attractive and the repulsive forces acting at the hydrophobic interfaces of the aggregates. According to this consideration, the mixing effect of surfactants with the different EO chain lengths on the a(S) in the L(alpha) phase was discussed. It is considered that the surfactant molecules are tightly packed in the aggregates since the reduction in repulsion force takes place in the excess EO chain part of the hydrophilic surfactant longer than the short EO chain of the lipophilic one. The lower surface tensions and the better stability of macroemulsions and the large solubilizing capacity of microemulsions result from the mixing effect. Copyright 1999 Academic Press.
借助小角X射线散射，在均相和混合聚氧乙烯十二烷基醚体系中，计算了六方相（H(1)）和层状相（L(α)）液晶中聚集体疏水界面处每个表面活性剂分子的有效横截面积a(S)，该面积是聚氧乙烯（EO）链长的函数。a(S)随EO链长的增加而增大。即使平均EO链长相同，混合表面活性剂体系中的a(S)也明显小于单一表面活性剂体系中的a(S)。a(S)的减小幅度大于表面活性剂理想混合所预测的幅度。此外，如果表面活性剂的EO链长差异更大，a(S)会更小。表面活性剂自组装结构的形状可能由聚集体疏水界面处吸引力和排斥力的平衡所决定。基于此考虑，讨论了不同EO链长的表面活性剂在L(α)相中的混合对a(S)的影响。据认为，由于亲水性表面活性剂中比亲脂性表面活性剂短EO链更长的过量EO链部分排斥力减小，表面活性剂分子在聚集体中紧密堆积。宏观乳液较低的表面张力和更好的稳定性以及微乳液较大的增溶能力都源于这种混合效应。版权所有1999年学术出版社。
