Powering smart materials by oscillatory chemical reactions

All plants and animals have the ability to adapt to the environment to some extent e.g. exhibit heliotropism (some flowers or leaves surfaces follow the direction of sunlight) or react to heat or pain. Following the same principle, instead of using materials designed to suit a range of conditions while not being optimal for any of them individually, we would prefer smart materials that have the ability to sense the conditions in their environment and adjust accordingly. The smart materials I am interested in are polymer gels that show a chemo-mechanical response, i.e. a change in the chemistry of the medium about the material results in a stepwise change in the volume that the material occupies by causing it to swell or collapse. This structural change may be used to force host molecules out of the gel structure (collapsing) or into the gel structure (swelling). One of the applications of the collapsing phenomenon is in drug delivery systems that would dispense drug molecules only under certain environmental conditions. On the other hand polymer gel swelling may be applied for the encapsulation of unwanted reaction inhibitors or pathogens in the media. Another application of smart polymer gels is as chemo-mechanical micro-valves where the valve (gel) is activated by a change in the medium. One example is a heat activated micro-valve. Upon heating the gel collapses and the valve opens while upon removing the heat the gel expands and the valve closes. This has direct application in the control of fluid flow and mixing in micro-size systems.An essential element in the application of smart materials is the stimulus that causes the occurrence of the change. The proposed research investigates the palladium-catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction in methanol envisioning many applications of its versatile nature and importantly application as a stimulus. This is an extraordinary chemical system that exhibits pronounced oscillations in pH and reaction heat output when operated in a stirred batch reactor. As a chemical oscillator it falls into the field of nonlinear chemical dynamics that studies phenomena related to the temporally periodic or nearly periodic variation of the concentrations of one or more species in a reaction. The best known reaction of this type is the Belousov-Zhabotinsky reaction. The PCPOC reaction is an oscillating system of higher complexity and an exceptional example of oscillatory behaviour in reactions catalysed by metal complexes. There are a number of reasons why the PCPOC reaction is of such great importance: it provides a novel and not well understood pH oscillator; it represents the first example of complex molecules synthesised from relatively simple reagents proceeding in a catalytic system in an oscillatory mode; when operating this system in an oscillatory regime high levels of product selectivity may be achieved compared to operating in a non-oscillatory mode; besides oscillations in pH, synchronised oscillatory heat output is present; it exhibits two relevant stimuli, pH and temperature; it may have application in propelling nano devices by generating an oscillating force when coupled with a block of gel.This study is aimed at the cooperative interplay between experimental and theoretical investigation into the application of this carbonylation reaction as a stimulus. Predictive physico-chemical models of the PCPOC reaction will be developed and this system will be researched with pH sensitive polymers, temperature responsive polymers and materials sensitive to both (i.e. temperature and pH responsive polymeric composite membranes) as: (1) an environment containing the smart material; (2) an enclosed environment communicating with the environment containing the smart material and (3) an enclosed environment containing the smart material communicating with the targeted environment.