Materials World Network : Heterogeneous Nucleation on Nanoporous Substrates

这是美国约翰·霍普金斯大学的研究人员和英国帝国理工学院的Naomi Chayen共同开展的研究和教育项目，目的是研究直径在1-10纳米范围内的大分子物种晶体的异相成核。具有这种中尺度的典型物种包括蛋白质和大分子，它们与胶体球(在较大的尺度上)和分子(在较小的尺度上)的区别在于很大程度的内部构型熵；因此，它们很难结晶。这里的工作建立在Chayen所做的实验观察的基础上，即大分子在纳米孔基质上的成核速度大大提高。工作假设是，成核速率的增强具体地与这样的想法相关联，即当使用具有大小为大小为大分子宽度量级的高度随机孔洞时，多孔衬底上的大分子结晶的熵最小。这一观点与一种已发表的观点形成了竞争，即基质的曲率增强了结晶，而我们认为这与多孔基质上的大分子无关。正在使用一种新的基质材料，详细研究大分子在多孔基质上的成核率随过饱和度、温度、表面化学和孔径大小的变化？由银/金合金脱合金制得的纳米多孔金。纳米多孔金是一种随机的、均匀的介孔材料，其平均孔径可以通过简单的化学方法在3-50 nm之间变化。它的表面也很容易进行化学修饰，所有这些特征结合在一起，使其成为这类研究的独特完美之处。纳米多孔金在这里也很有用，因为可以制造出具有相同曲率的金纳米颗粒，我们可以比较和对比在含有金胶体的溶液中的结晶和在多孔基质上的结晶。这项研究支持了伦敦帝国理工学院的Chayen小组和巴尔的摩约翰霍普金斯大学的Erlebacher小组之间的国际合作，前者专门研究蛋白质结晶，后者专门研究纳米多孔金属的合成和表面修饰。通过结合这些专业，将有效地开展纳米多孔衬底上异质晶体成核的基础研究。合作的结构是通过大量的学生和初级人员的交流来实现的。这项研究的结果将使人们对非均相成核的基本原理有新的理解，对蛋白质和胶体结晶具有普遍的适用性。此外，国际合作将有助于在形核理论和实验方面建立网络，连接薄膜冶金和溶液相结晶学科，并涉及本科生和研究生的所有阶段。

This a joint research and education project between investigators at Johns Hopkins University in the US and Naomi Chayen at Imperial College in the United Kingdom, with a goal to study the heterogeneous nucleation of crystals of macromolecular species with diameters in the 1-10 nm range. Typical species with this mesoscale include proteins and macromolecules, and are distinguished from colloidal spheres (at larger scales) and molecules (at smaller scales) by a large degree of internal configurational entropy; for this reason, they are difficult to crystallize. The work here builds on an experimental observation made by Chayen that the nucleation rate of macromolecules on nanoporous substrates is greatly enhanced. The working hypothesis is that the nucleation rate enhancement is specifically linked to the idea that the entropy of crystallization of macromolecules is minimized on porous substrates when a highly random porosity with void size of order the macromolecule width is used. This idea competes with a published notion that the substrate curvature enhances crystallization, which we don?t think is relevant for macromolecules on porous substrates. A detailed study of the nucleation rate of macromolecules over porous substrates as it varies with supersaturation, temperature, surface chemistry, and pore size, is being performed using a new substrate material ? nanoporous gold made by dealloying of silver/gold alloys. Nanoporous gold is a random, uniform, mesoporous material whose mean pore size can be varied from 3-50 nm using only simple chemistry. Its surface is also easily chemically modified, and all these features together make it uniquely perfect for this kind of study. Nanoporous gold is also useful here because gold nanoparticles with equivalent curvatures can be made, and we can compare and contrast crystallization in solutions containing gold colloid to crystallization on porous substrates. The research effort supports an international collaboration between the Chayen group at Imperial College, London, specializing in protein crystallization and the Erlebacher group at Johns Hopkins University, Baltimore, which specializes in the synthesis and surface modification of nanoporous metals. By marrying these specializations, a fundamental study of heterogeneous crystal nucleation on nanoporous substrates will be efficiently pursued. The collaboration is structured with significant exchange of students and junior personnel. The results of this research will yield new understanding of the fundamentals of heterogeneous nucleation, with general applicability to protein and colloidal crystallization. Furthermore, the international collaboration will help to build networks in nucleation theory and experiment, bridging the disciplines of thin film metallurgy and solution phase crystallization, and involving undergraduates and graduate students all stages.