Supramolecular Crystals and Crystallization with Nanosized Motifs of Giant Molecules

Abstract

Supramolecular crystals and crystallization are general concepts used to describe broader aspects of ordered structures and their formation in the three-dimensional (3D) bulk and solution and in 2D thin film states at length scales ranging from sub-nanometers to sub-micrometers. Although the fundamental crystallographic principles are still held in these structures, starting from their basic repeating units (motifs), it is not necessary that each atomic position within their motifs possesses translational symmetry in long range order, but could have quasi-long range or short range order. As a result, the motif becomes the smallest unit for constructing 3D or 2D ordered structures that maintain the long range translational order. The formation of these supramolecular ordered structures essentially follows the physical principle of phase transformations, involving either nucleation and growth or spinodal decomposition mechanisms. However, larger ordered structures require stronger and more cooperative interactions to sustain their structures in equilibrium or stable states. We propose utilization of collective secondary interactions, similar to those found in biological and living systems, to generate sufficient interactions and stabilize these structures. Furthermore, when the basic unit of the structure becomes increasingly larger and heavier, thermal (density) fluctuations during the phase transitions may not be sufficiently large to overcome transition barriers of the basic unit. In these cases, external fields might be required to stimulate the magnitude of thermal (density) fluctuation and/or redistribute (thus, decrease) a single transition barrier into several stepwise transition sequences with lower barriers for each transition, and thus increase the speed of phase transformations.