Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
Chem Soc Rev. 2013 Mar 7;42(5):2100-29. doi: 10.1039/c2cs35269a. Epub 2012 Dec 17.
In 1861 Thomas Graham gave birth to a new field of science, today known as colloid science. Nowadays, the notion "colloid" is often used referring to systems consisting of two immiscible phases, one of which is finely dispersed into the other. Research on colloids deals mostly with sols (solids dispersed in a liquid), emulsions (liquids dispersed in liquid), and foams (gas dispersed in a liquid). Because the dispersed particles are small, there is a lot of interface per unit mass. Not surprisingly, therefore, the properties of the interface have often a decisive effect on the behaviour of colloids. Water-air interfaces have a special relevance in this field: many water-insoluble molecules can be spread on water and, given the right spreading conditions and enough available surface area, their spreading proceeds until a monolayer (a one-molecule thick layer) eventually remains. Several 2D phases have been identified for such monolayers, like "gas", "liquid expanded", "liquid condensed", and "solid". The central question of this review is whether these 2D phases can also exist as colloidal systems, and what stabilizes the dispersed state in such systems. We shall present several systems capable of yielding 2D phase separation, from those based on either natural or fluorinated amphiphiles, to polymer-based ones. We shall seek for analogies in 3D and we shall try to clarify if the lines between these 2D objects play a similar role as the interfaces between 3D colloidal systems. In particular, we shall consider the special role of molecules that tend to accumulate at the phase boundaries, that is, at the contact lines, which will therefore be denoted "line-actants" (molecules that adsorb at a 1D interface, separating two 2D colloidal entities), by analogy to the term "surfactant" (which indicates a molecule that adsorbs at a 2D interface separating two 3D colloidal entities).
1861 年，托马斯·格雷厄姆（Thomas Graham）开创了一个新的科学领域，如今被称为胶体科学。如今，“胶体”一词通常用于指代由两个不混溶相组成的系统，其中一相被精细分散到另一相中。胶体研究主要涉及溶胶（固体分散在液体中）、乳状液（液体分散在液体中）和泡沫（气体分散在液体中）。由于分散粒子很小，单位质量的界面很多。因此，毫不奇怪，界面的性质通常对胶体的行为有决定性的影响。水-空气界面在这一领域具有特殊的相关性：许多不溶于水的分子可以在水面上展开，并且在适当的展开条件和足够的可用表面积下，它们的展开会一直进行，直到最终只剩下单层（一层分子厚的层）。已经确定了几种这样的单层的二维相，如“气体”、“液体膨胀”、“液体凝聚”和“固体”。这篇综述的核心问题是这些二维相是否也可以作为胶体系统存在，以及是什么稳定了这些系统中的分散状态。我们将介绍几种能够产生二维相分离的系统，从基于天然或氟化两亲物的系统到基于聚合物的系统。我们将寻找 3D 中的类似物，并尝试澄清这些二维物体之间的线是否与 3D 胶体系统之间的界面起着类似的作用。特别是，我们将考虑那些倾向于在相边界（即接触线）处聚集的分子的特殊作用，因此，这些分子将被称为“线活性剂”（吸附在一维界面上的分子，将两个二维胶体实体分隔开），这与术语“表面活性剂”（表示吸附在二维界面上的分子，将两个三维胶体实体分隔开）类似。
