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首页> 外文期刊>Current Forestry Reports >Scrolling of Supramolecular Lamellae in the Hierarchical Self-Assembly of Fibrous Gels
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Scrolling of Supramolecular Lamellae in the Hierarchical Self-Assembly of Fibrous Gels

机译：纤维凝胶等分层自组装中超分子薄片的滚动

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SummaryLamellar supramolecular assemblies are a common feature of fibrous gels formed by molecules such as peptides and ureas. Competition between gelation and crystallization is highly solvent dependent and can be governed by the dynamics of nascent lamellae in solution. We hypothesize that gel fibrils are formed when the scrolling of lamellae outpaces multilayer stacking. Crystallographic data on model picolyl bis(urea)s were correlated with their gelation properties. Most structures are lamellar, and gels involving fibrous aggregates form concomitantly alongside crystalline solvates. A distinguishing feature of?these solvate crystals is that the lamellae have unequal numbers of picolyl groups on opposite faces. Atomistic molecular dynamics simulations show that this asymmetry causes isolated lamellae to scroll spontaneously into fibrils, whereas symmetrical lamellae adopt flat, crumpled, or saddle-like morphologies. Scrolling represents a general mechanism for gel formation, affording networks of unbranched fibers with monodisperse diameters dictated by the equilibrium curvature of the folding lamellae.Graphical Display OmittedHighlights?We propose a general mechanism for gelation by hydrogen-bonding supramolecular gelators?Gels arise when multilayer aggregation is outpaced by scrolling of isolated monolayers?Stabilization of the surface by scrolling defines the maximum fibril diameterThe Bigger PictureGels are extremely important soft materials with everyday applications in areas such as soaps, lubricants, catalysis, and the oilfield chemistry. Although gels are commonly based on polymers, there is a great deal of interest in small-molecule gelators that aggregate through non-covalent interactions such as hydrogen bonding and π-stacking to give 3D sample-spanning fibrous assemblies. It is very difficult to predict the emergent complexity of gel structure, and gelators are commonly discovered by trial and error. The properties of a gel depend on the structural evolution of its fiber network, but the mechanisms governing fiber growth are not currently understood. In this work, we show that homogeneous gel fibers arise from the scrolling of sheet-like rafts of hydrogen-bonded gelators whenever opposite sides of the sheet possess different surface energies. On the basis of this observation, we propose a general predictive mechanism for gel self-assembly.Gelation by small molecules is enormously topical in catalysis, nanomaterials, drug delivery, and pharmaceutical crystallization. The way in which gelators self-organize to give a 3D gel network is poorly understood. How does a system progress from a continuous pattern of supramolecular motifs to a network of fibers with well-defined morphologies? Why are gel fibers so homogeneous, and why do they form instead of crystals? This work shows, predictively, that gels arise by the scrolling of sheets with asymmetric surface structures.
机译：SummaryLamellar超分子组装是通过分子如肽和脲形成的纤维的凝胶的一个共同特点。凝胶化和结晶之间的竞争是依赖高度溶剂，并且可以通过在溶液中新生薄片的动力学的管辖。我们假设薄片赶不上多层堆叠时滚动形成的凝胶纤维。上模型吡啶甲基双晶体学数据（脲），用它们的凝胶化性能相关。大多数结构是片状，且涉及纤维状集合体凝胶随之一起形成结晶溶剂化物。的？这些溶剂化物晶体一个显着特点是，薄片具有不相等的数量上相对面上吡啶甲基的基团。原子论分子动力学模拟结果表明，这种不对称导致分离的薄片自发滚动成纤丝，而对称的薄片采用平坦的，弄皱，或鞍状形态。滚动表示用于凝胶形成的通用机制，得到与由的折叠lamellae.Graphical显示OmittedHighlights？我们提出通过氢键超分子胶凝剂凝胶化的一般机制的平衡所决定的曲率直径的单分散无支链的纤维的网络？凝胶出现时多层聚合通过分离单层的滚动速度超过？通过滚动定义最大原纤维diameterThe更大PictureGels表面的稳定化与在诸如肥皂，润滑剂，催化，和油田化学日常应用极其重要的软质材料。尽管凝胶剂通常是基于聚合物，有在通过非共价相互作用聚集小分子胶凝剂如氢键和π堆叠，得到三维样品跨过的纤维集合体的极大兴趣。这是很难预测的凝胶结构的新兴的复杂性，胶凝剂是通过试验和错误通常发现的。凝胶的性质取决于其光纤网络的结构演变，但治纤维生长的机制目前尚未了解。在这项工作中，我们表明，均匀的凝胶纤维从片​​状氢键合胶凝剂的排上的滚动出现每当片材的相对侧上具有不同的表面能。在此观察的基础上，我们提出了凝胶自assembly.Gelation一般预测机构通过小分子是在催化，纳米材料，药物递送，以及药物结晶极大局部。其中胶凝剂自组织以得到三维的凝胶网络的方式是知之甚少。如何做一个系统的超分子图案，以纤维具有良好定义的形态网络的连续图案进步？为什么凝胶纤维那么均匀，为什么它们形成的，而不是晶体？这项工作表明，预测其凝胶通过用非对称表面结构的片材的滚动引起的。

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