Rosu Cornelia, Balamurugan Sreelatha, Cueto Rafael, Roy Amitava, Russo Paul S
School of Materials Science and Engineering and Georgia Tech Polymer Network, GTPN and ‡School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
Department of Chemistry and Macromolecular Studies Group and ∥Center for Advanced Microstructures and Devices, CAMD, Louisiana State University , Baton Rouge, Louisiana 70803, United States.
J Phys Chem B. 2016 Jul 28;120(29):7275-88. doi: 10.1021/acs.jpcb.6b03863. Epub 2016 Jul 19.
When a particle is introduced into a liquid crystal (LC), it distorts the LC director field, leading to new arrangements of the particles. This phenomenon is ordinarily studied using >100 nm particles and ∼2 nm mesogens. Usually the particle surface and mesogens are chemically distinct, which adds an enthalpic effect, even though the more interesting interactions are entropic. To raise the structures to the visible regime, while minimizing chemical differences between the particle surface and mesogen, silica particles coated with an α-helical polypeptide have been prepared and dispersed in lyotropic polypeptide LCs. The polypeptide is poly(γ-stearyl-α,l-glutamate) or PSLG. To make the particles easy to manipulate and easy to find, the silica core included superparamagnetic magnetite (Fe3O4) and covalently attached dye. Two methods were used to place polypeptides on these magnetic, fluorescent particles: a multistep grafting-to approach in which whole polypeptides were attached and a one-pot grafting-from approach in which the polymerization of the monomers was initiated from the particle surface. These approaches resulted in sparse and dense surface coverages, respectively. The influence of surface curvature and polypeptide molecular weight on the design of sparsely covered particles was investigated using the grafting-to approach. The aggregated grafting-from particles when freshly dispersed in a PSLG/solvent matrix disrupted the orientation of the characteristic cholesteric LC (ChLC) phase directors. In time, the hybrid particles were expelled from some domains, enabling the return of the familiar helical twist of the cholesteric mesophase. The sparsely coated grafting-to hybrid particles when inserted in the PSLG/solvent matrix assembled into stable islet-like formations that could not be disrupted even by an external magnetic field. The bulk particles aligned in chains that were easily manipulated by a magnetic field. These results indicate that polypeptide ChLCs can control and facilitate colloidal assembly of particles with matching surfaces.
当一个粒子被引入到液晶（LC）中时，它会使液晶指向矢场发生畸变，从而导致粒子的新排列。通常使用大于100 nm的粒子和大约2 nm的液晶元来研究这种现象。通常粒子表面和液晶元在化学性质上是不同的，这会增加焓效应，尽管更有趣的相互作用是熵效应。为了将结构提升到可见范围，同时最小化粒子表面和液晶元之间的化学差异，制备了涂有α-螺旋多肽的二氧化硅粒子，并将其分散在溶致多肽液晶中。该多肽是聚（γ-硬脂酰-α，l-谷氨酸）或PSLG。为了使粒子易于操作和易于发现，二氧化硅核心包含超顺磁性磁铁矿（Fe3O4）和共价连接的染料。使用两种方法将多肽放置在这些磁性、荧光粒子上：一种是多步接枝法，将整个多肽连接上去；另一种是一锅法接枝法，单体从粒子表面引发聚合。这些方法分别导致了稀疏和密集的表面覆盖。使用接枝法研究了表面曲率和多肽分子量对稀疏覆盖粒子设计的影响。当新分散在PSLG/溶剂基质中时，聚集的接枝法粒子破坏了特征胆甾相液晶（ChLC）相指向矢的取向。随着时间的推移，杂化粒子从一些区域被排出，使得胆甾中间相熟悉的螺旋扭曲得以恢复。当插入到PSLG/溶剂基质中时，稀疏包覆的接枝法杂化粒子组装成稳定的胰岛状结构，即使受到外部磁场也不会被破坏。大量粒子排列成链，很容易被磁场操纵。这些结果表明，多肽胆甾相液晶可以控制并促进具有匹配表面的粒子的胶体组装。
