ETH Zurich, Department of Health Sciences and Technology, Laboratory of Food & Soft Materials, Schmelzbergstrasse 9, 8092 Zurich, Switzerland.
Nat Commun. 2013;4:1917. doi: 10.1038/ncomms2911.
Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S(2D)(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena.
二维形状各向异性胶体的排列在自然界中无处不在，从界面病毒组装到淀粉样斑块形成均有涉及。因此，二维自组装的原理一直受到理论和实验的研究，然而，对于二维各向同性-向列相转变的本质存在分歧的基本解释。在这里，我们采用单分子原子力显微镜、低温扫描电子显微镜和被动探针粒子跟踪技术研究了半柔性β-乳球蛋白纤维在液相界面的吸附和液晶有序化。纤维的刚性随界面密度的增加而变化，最大刚性是由纤维的取向引起的，随后的减小是由于拥挤和域弯曲引起的。通过依赖于长度尺度的序参量 S(2D)(d)，解析和量化了各向同性和向列性区域的共存。向列性表面分数随界面纤维密度的增加而增加，但对于固定的界面密度，取决于初始体相浓度，这归因于观察到的二维各向同性-向列共存是由于非平衡现象。
