Materials World Network : Heterogeneous Nucleation on Nanoporous Substrates

这是美国约翰霍普金斯大学和英国帝国理工学院的Naomi Chayen的联合研究和教育项目，目的是研究直径在1-10纳米范围内的大分子物种晶体的非均质成核。具有这种中尺度的典型物种包括蛋白质和大分子，并通过很大程度的内部构型熵与胶体球（在较大尺度上）和分子（在较小尺度上）区别开来；由于这个原因，它们很难结晶。这里的工作建立在Chayen的实验观察上，即大分子在纳米孔基质上的成核速率大大提高。工作假设是，当使用与大分子宽度顺序相同的高度随机孔隙时，大分子的结晶熵在多孔基质上被最小化，这与成核速率的增强特别相关。这一观点与一种已发表的观点相矛盾，即基底曲率会增强结晶性，而我们并不这样认为。我认为这与多孔基质上的大分子有关。使用一种新的基底材料，详细研究了大分子在多孔基底上的成核速率随过饱和、温度、表面化学和孔径的变化。用银/金合金合金化制备纳米孔金。纳米孔金是一种随机、均匀的介孔材料，其平均孔径可以在3-50纳米之间变化，仅使用简单的化学方法。它的表面也很容易被化学修饰，所有这些特征加在一起使它成为这种研究的完美选择。纳米孔金在这里也很有用，因为可以制造出具有等效曲率的金纳米颗粒，我们可以比较和对比含金胶体溶液中的结晶和多孔基板上的结晶。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改性。通过结合这些专门化，将有效地进行纳米孔基质上非均相晶体成核的基础研究。合作的结构是大量交换学生和初级人员。本研究结果将对非均相成核的基本原理产生新的认识，对蛋白质和胶体结晶具有普遍的适用性。此外，国际合作将有助于建立成核理论和实验网络，连接薄膜冶金和固相结晶学科，并涉及本科生和研究生的各个阶段。

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.