DISCUSSION OF THE MALLOUK AND FOX LECTURES

摘要

A general theme of the Session II talks by Professors Mallouk and Fox was the formation, structure and properties of layered systems. In the context of modular chemistry, an extended layer may be thought of as a two-dimensional network of modules composed of atoms, molecules, ions, polymers, or, as illustrated in Prof. Mallouk's talk, the exfoliated leaflets of a layered solid. Though novel bulk solids can in principle be built up by sequential formation of such layers, this may be a very time-consuming process, as Prof. Mallouk points out below in response to a question. On the other hand, as single layers or the components of a heterostructure of several layers, extended layers have a large and potentially significant role to play in the separation and interconnection of functional modules and phases. Prof. Chidsey began the discussion by commenting on some of the possibly important structural features of extended layers and some of the implications for a modular chemistry in two dimensions. He argued that various degrees of lateral "order" are possible and valuable in a two-dimensional network of modules. The most obvious, 2-dimensional crystalline order, is possible and is achieved in some self-assembled monolayers and in many inorganic layers on crystalline substrates. Such crystalline layers will usually be composed of multiple domains separated by domain boundaries, and it is important to consider what role may be played by the defects at these domain boundaries. Prof. Chidsey argued that multiple domains are a very common and hard-to-avoid consequence of forming extended, crystalline 2-dimensional arrays of modules starting from many different places independently. Less ordered 2-dimensional networks of modules including glassy and liquid-like arrangements may be adequate or even preferable for some uses. In fact in some cases, the modules may usefully be arranged in a dilute way in two dimensions in what could be called a 2-dimensional gas.