Zhao Jianguo, Bolisetty Sreenath, Adamcik Jozef, Han Jun, Fernández-Ronco María P, Mezzenga Raffaele
Quanzhou Institute of Equipment Manufacturing, Haixi Institutes, Chinese Academy of Sciences , CN-362200 Quanzhou, China.
Laboratory for Advanced Fibers, EMPA , CH-9014 St. Gallen, Switzerland.
Langmuir. 2016 Mar 15;32(10):2492-9. doi: 10.1021/acs.langmuir.6b00276. Epub 2016 Mar 3.
Amyloid fibrils are charged semiflexible assemblies with very large aspect ratio (length to diameter, L/D). Because of this large aspect ratio, the isotropic (I) and nematic (N) phase coexistence expected from the first-order thermodynamic nature of the I-N phase transition, as predicted from the Onsager's theory, is vanishingly small and, in practice, challenging to experimentally observe. In this study we present a remarkable widening of the I + N biphasic region in β-lactoglobulin fibrils suspension via freeze-thaw (F-T) cycling. The demixing behavior can be induced and controlled by a slow growth of propagation front of the ice crystals, which grow by excluding the amyloid fibrils from the crystal phase and thus concentrating them in the liquid phase. The growth of the ice crystals is accompanied by the formation of concentrated and elongated tactoid-like structure in the liquid phase. During the subsequent thawing cycling, at large tactoid domains, the mismatch in density caused by the presence of amyloid fibrils is sufficient to generate a sedimentation of the N phase at the bottom of the vial, coexisting with an I phase on the top. We reason why, despite the remarkable stability of the coexisting I and N phases observed over several weeks after F-T cycling, the biphasic region is understood to be a nonequilibrium, metastable state. Yet, the results in this study suggest that the F-T treatment is an effective approach to stabilize multiphase coexistence of liquid crystalline phases in colloidal suspensions of anisotropic particles without the need of additives, such as depleting agents, needed to modify interaction potentials.
淀粉样纤维是具有非常大的纵横比（长度与直径之比，L/D）的带电半柔性聚集体。由于这种大的纵横比，根据昂萨格理论预测，从各向同性（I）向向列相（N）转变的一级热力学性质所预期的I相和N相共存极其微小，在实际中很难通过实验观察到。在本研究中，我们通过冻融（F-T）循环显著拓宽了β-乳球蛋白纤维悬浮液中的I + N双相区域。这种相分离行为可以由冰晶生长前沿的缓慢生长诱导和控制，冰晶通过将淀粉样纤维从晶相中排除从而使其在液相中富集来生长。冰晶的生长伴随着液相中形成浓缩且细长的类触体结构。在随后的解冻循环中，在大的触体区域，由淀粉样纤维的存在导致的密度不匹配足以使N相在小瓶底部沉降，与顶部的I相共存。我们推断，尽管在F-T循环后数周观察到共存的I相和N相具有显著的稳定性，但双相区域被认为是一种非平衡的亚稳态。然而，本研究结果表明，F-T处理是一种有效的方法，可在无需添加剂（如用于改变相互作用势的耗尽剂）的情况下，稳定各向异性颗粒胶体悬浮液中液晶相的多相共存。
