Analytical Science Laboratory, Kao Corporation.
Department of Innovation Systems Engineering, Graduate School of Engineering, Utsunomiya University.
J Oleo Sci. 2021;70(9):1253-1259. doi: 10.5650/jos.ess21129.
Compression-induced formation of condensed-phase domains in adsorbed monolayers of alkylgalactosides (AGs) at the air/water interface was observed. When an aqueous solution of AGs was poured into a Langmuir trough, the AG molecules were spontaneously adsorbed from the solution at the air/water interface to form the adsorbed or Gibbs monolayer in an expanded, liquid-like phase at equilibrium. The monolayer was subsequently laterally compressed by the barriers of the trough, while simultaneously observing the system using a Brewster angle microscope (BAM). The surface pressure-film area isotherm upon compression showed a kink at a surface pressure (π) comparable to or several mN・m higher than the surface pressure at the critical micelle concentration (π), followed by a plateau region. BAM observations revealed that condensed-phase domains were formed in the homogeneous expanded phase at the plateau. Hence, the plateau corresponds to a first-order phase transition from the expanded phase to the condensed phase. As expected, the compressed adsorbed monolayer was in a metastable state because the surface pressure decreased with time, and the condensed-phase domains disappeared when compression was discontinued. The transient formation of a quasi-stable condensed phase may originate from the combined effect of the lower solubility of AG molecules in water, moderately strong attractive intermolecular interactions between AG molecules at the air/water interface, and high-rate compression.
在空气/水界面处，观察到了压缩诱导的烷基半乳糖苷（AGs）吸附单层中凝聚相畴的形成。当将 AGs 的水溶液倒入 Langmuir 槽中时，AG 分子会自发地从溶液中吸附到空气/水界面，形成平衡时处于扩展、液态的吸附或 Gibbs 单层。随后，通过槽的障碍物对单层进行横向压缩，同时使用布鲁斯特角显微镜（BAM）对系统进行观察。在压缩过程中，表面压力-膜面积等温线在表面压力（π）处出现拐点，该表面压力与临界胶束浓度（π）相当或高出几个毫牛顿米（mN・m），随后出现一个平台区域。BAM 观察结果表明，在平台处的均匀扩展相中形成了凝聚相畴。因此，平台对应于从扩展相到凝聚相的一级相变。正如预期的那样，压缩吸附单层处于亚稳状态，因为表面压力随时间下降，并且当停止压缩时，凝聚相畴消失。准稳定凝聚相的瞬时形成可能源于 AG 分子在水中的溶解度较低、AG 分子在空气/水界面处的中等强度的分子间吸引力以及高压缩速率的综合影响。
