Chromonic phase behaviour based on planar discs functionalized with EO (ethylenoxy) groups

Lead Research Organisation: Durham University
Department Name: Chemistry

Abstract

Chromonics are a fascinating class of lyotropic liquid crystals. They are usually formed in water from plate-like molecules, which self-assemble into aggregate stacks (rods or layers), which in turn self-organise to form liquid crystals.

Chromonics are very poorly understood. Researchers are just beginning to understand how self-assembly is influenced by the interactions between molecules and how the process can be controlled by use of additives (such as small molecules or salt). Moreover, many known chromonic materials are based on industrial dyes, which are very difficult to purify; and this hampered some of the early investigations into phases and phase behaviour.

Despite these difficulties it is beginning to be recognised that chromonic systems are far more common than once thought. Formation of stacked aggregates in dilute solution and/or chromonic mesophases at higher concentrations, have been widely reported in aqueous dispersions of many formulated products such as pharmaceuticals and dyes used in inkjet printing. Recently, there has been greatly enhanced interest in chromonics materials as functional materials for fabricating highly ordered thin films, as biosensors, and chromonic stacks have also been used to aid in the controllable self-assembly of gold nanorods.

This proposal seeks to develop a novel class of chromonic molecules: nonionic chromonics based on ethylenoxy groups. Here, we will design new chromonic phases demonstrating novel structures (such as hollow water-filled columns and layered brick-like phases), which can be used for future applications. We will also investigate and control the self-assembly process, in a class of materials that can be purified, that are not influenced as strongly by salt (compared to most industrial dyes), where structural changes can be easily engineered by minor changes to a synthetic scheme, and where addition of other solvents can lead to major changes in both self assembly and phase behaviour. We will also use state-of-the-art modelling and theory, which has recently been shown to provide new insights into self-assembly in chromonics, to help design new materials. Here, the use of quantitative and semi-quantitative molecular modelling provides for the possibility of "molecular engineering" new phases.

To accomplish our goals for this project we will bring together synthetic organic chemistry to design and make new materials; state-of-the-art physical organic measurements to characterise both the nature of self-assembly and the novel chromonic phases formed; and state-of-the-art modelling/theory to predict, explain and help control the chromonic aggregation.

Planned Impact

Direct impact of results: The key transferable from our work is "a greater control of self-assembly" in chromonics. We expect to be able to directly transfer to beneficiaries what we learn in terms of controlling both the strength of interactions between chromonic molecules in aqueous (and other) solutions, and also in controlling the structures we can form by self-assembly. Most immediately (in terms of products), we identify formulated chemicals (such as dyes for ink-jet printing, fabric dyes and photographic dyes) as an area where controlling chromonic assembly is essential. We have included Fujifilm scientist Dr. Owen Lozman as part of our management group for the project, in order to aid in both dissemination of science to industry and also to help in directing the science as it develops. In the area of pharmaceutical actives (drugs) we note that most (if not all) pharmaceutical companies have problems with the formulation of drugs that form mesophases. Usually this stops the use of the material (though potentially controlled self-assembly may be used in the future in terms of alternative formulations of drug products). What we learn in terms of controlling self-assembly (particularly removing it) will be very useful here. (We have included a letter of support from collaborators at Bristol-Myers Squibb (a leading BioPharma).) In terms of new materials, there is both industrial and academic interest in using novel self-assembled structures to template new inorganic structures for applications in catalysis and other areas. Here, we have put in place a collaboration with Dr Rodriguez Abreu based at the International Iberian Nanotechnology Laboratory (INL, Portugal), who will work with promising new candidate structures resulting from this proposal.


Impact of techniques: The synthetic and experimental physical organic chemistry methods used in this work will be useful to many industrialists. In terms of UK competitiveness, the area represented by this proposal addresses the fundamental science that underpins several key industries contributing to UK economy: consumer chemicals, dye chemistry and medicinal formulation. Major companies such as P&G, Unilever, Syngenta, Dow Chemicals, BASF and many more will benefit from our techniques and methodology. Moreover, the techniques we use for developing coarse-grained models for atomistic models and the modelling codes for the coarse-grained simulations, will be of general use in areas as diverse as micelles, phase separation in soft matter, other areas of self-assembly and bio-modelling. We intend to enhance the impact of our work by making our codes for coarse-graining and coarse-grained modelling freely available from this grant.


People: we will be training 4 two-year PDRAs. There is strong demand in industry for experimentalists trained in this area of physical organic chemistry (highlighted by EPSRCs recent initiative in this area). Also, in the light of the International Review of Chemistry, there is a huge need for skilled researchers in the area of modelling to tackle societal challenges.
 
Description Have shown via atomistic simulation that planar disk molecules with EO (ethylenoxy) groups can self-assemble in solution to produce single molecule columns. These can be used to produce a chromonic liquid crystal phase. Have produced coarse-grained models that can simulate chromonics at the mesophase level, for the first time. Have discovered that subtle changes in molecular structure can be used to change the structure of the self-assembled columns leading to ways of making new nanostructures by "simulation designed" self-assembly. Have shown that careful design of molecular interactions can lead to unexpected features, such as chiral columns made from achiral molecules. A new type of "layered" chromonic mesophase has been discovered.
Exploitation Route It should be possible to use the simulation approach that we have introduced for chromonic systems to study aggregation in solution for a range of organic molecules, with applications to future solution processes for producing organic semiconductor systems.

We are in discussions with drug companies who are interested in planar drug molecules in solution, where it is vital to understand aggregation in solution for control of dosage.

There are potential exploitation routes in relation to future organic semiconductor systems, and solution processing of these type of molecules.

As we have shown that it is possible to predict chromonic phase diagrams, this opens up the possibility of understanding and predicting the release of drugs from chromonics or reversed lyotropic systems, for future use of such systems as drug delivery systems.
Sectors Chemicals,Energy,Healthcare,Pharmaceuticals and Medical Biotechnology

URL http://community.dur.ac.uk/mark.wilson/