Molecular Layers under Control

The goal of the proposed research is to investigate a new concept for preparing multi-component organic thin films with engineered molecular-scale organization and composition using liquid crystal (LC)-based inks combined with patterned anchoring alignment stamps. The central idea is to couple molecular order and composition in a multicomponent self-assembled monolayer (SAM) deposited from a nematic ink to a pattern on a stamp through an elastic strain field produced by competitive LC anchoring at the stamp- and SAM surfaces. The concept resembles strained heteroepitaxial growth at a solid-solid interface, except that the strain field is provided by a nematic LC, rather than the substrate, and results from anchoring and elastic forces, rather than an epitaxial mismatch. Despite the fact that LC elastic constants are much weaker than those of most solids, by selecting systems with an appropriate balance of energies we show how the LC can nevertheless have a significant influence, while affording considerable flexibility in structural and compositional control.The research is motivated by both fundamental interests and the practical importance of developing alternative approaches for creating chemically functionalized surfaces with designer architectures at nanometre to micron length scales. In addition to furthering our basic understanding of LC-surface interactions, phase behaviour, and pattern formation in organic thin films, the techniques to be developed in this work represent a step toward preparing materials with tailored physical and chemical properties, potentially useful for applications ranging from controlled wetting and adhesion, to chemical sensing and LC display technology.The concepts we propose to investigate represent a fundamentally new approach for using macroscopic influences to harness and control self-assembly at the molecular-scale, drawing upon ideas from LC science and multiphase systems. To carry out the work, an interdisciplinary collaboration is proposed between Prof. David Patrick, the Visiting Fellow and expert in LCs and LC-surface interactions, and Dr. Stuart Clarke, an expert in multiphase systems and the physical chemistry of organic thin films. Dr. Patrick, who is a Professor of Chemistry and Director of the Advanced Materials Science and Engineering Centre at Western Washington University, is a pioneer in unconventional uses of thermotropic LC solvents to prepare organized materials, while Clarke's group at Cambridge specialises in the molecular-scale properties of multi-component and multi-phase systems. The collaboration will combine these two areas of study.While at Cambridge, the Visiting Fellow will interact with other groups in the Chemistry Department and BP Institute, as well as those at several other universities across the UK, who will benefit from the expertise he brings in these novel approaches. Longer term, the proposed research will lay the foundations for a sustained collaboration that can continue after Patrick returns to his home institution.The proposed experimental programme would produce a comprehensive picture of the relationships between film composition and structural properties, LC forces, and the thermodynamics of monolayer formation in self-assembled monolayers deposited using LC inks. Although great deal of attention has been given to understanding the influence surfaces exert on LCs, including surfaces decorated with SAMs, the reverse situation-that is, LCs influencing surfaces-has hardly been considered at all. Taken together, the results of these experiments should provide a definitive assessment of the feasibility of LC-based inks, while deepening our understanding of the scientifically interesting and technologically important underlying phenomena.

There is presently a great deal of interest in understanding how principles of self-assembly can be applied to produce materials with tailored physical, chemical, and biochemical properties. Likewise, the interfacial properties of liquid crystals (LCs) and their interactions with solid surfaces is a topic of importance within the scientific community and beyond. The proposed programme, linking LC forces to self-assembling systems is therefore very timely. The academic beneficiaries of this research will include other workers in the fields of self-assembly, surface chemistry, materials science, and LCs. The wider scientific and technology development communities will also benefit from the advancements we expect to make. For example, success in demonstrating the principles as described herein would open the door for numerous related approaches, including the use of lower symmetry LC ink phases such as smectics, cholesterics, and ferroelectrics, perhaps allowing the imprinting of more complex structural features, and the use of other building blocks besides thiols, such as organosilanes, polymers, nanoparticles, etc. Combining the pattering features of LC-based inks with spatial patterning by microcontact printing or related methods could permit new dimensions of thin film design, enabling the preparation of materials in which composition, nanometre-scale structure, and mesoscopic patterning are controlled simultaneously in a single deposition step. Although the stamp constructions used here will employ macroscopic patterns, the concepts should be extendable to micron- or even submicron-scale control. While our focus is on understanding fundamental principles and concepts, the development of LC-based inks and patterned anchoring stamps could also be very important in further applications to a number of technologies, including: -Organic electronics - the performance of molecular materials for electronic and optoelectronic applications such as organic thin film transistors, organic light-emitting diodes, organic photovoltaics, etc. is often very sensitive to the nanometre-scale organisation of the constituent building blocks. The ability to use LC forces to direct self-assembly or crystallisation in these systems into predefined arrangements would therefore represent a significant advance potentially useful in a wide variety of applications. - LC displays - recent research into alternative display architectures based on micropatterned anchoring films has led to the discovery of novel multi-stable switching modes, improvements in viewing angles, and other performance advantages. To realize the potential of these approaches, new technologies are needed for the preparation of large area, low cost patterned anchoring films. The method to be investigated in this research could be particularly well suited for such applications. - Designer surfaces - engineered surfaces capable of displaying specific chemical, biochemical, and physical properties underpin a broad range of applications, from control over adhesion, wetting, and friction, to biomineralization and heterogeneous catalysis. The principles and concepts resulting from this research provide a fundamentally new approach to controlling surface properties, thereby creating opportunities to produce new surface structures and compositions more precisely tailored to the needs of specific applications. The consequential development in the future of new technology based on the system we are exploring will be of general benefit to society. More immediately, the Cambridge group will benefit from the expertise Prof. Patrick will bring in LC materials. His presence at Cambridge, and more broadly, in the United Kingdom will benefit other researchers working on ordered systems, thin films, and nanomaterials through opportunities for direct interaction.