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Powering Smart Materials by Oscillatory Chemical Reactions

Powering Smart Materials by Oscillatory Chemical Reactions

Project leader

Dr Katarina Novakovic

Dates

October 2009 to December 2014

Sponsors

EPSRC

Description

All plants and animals have the ability to adapt to the environment to some extent. For example, plants may exhibit heliotropism - they follow the direction of sunlight. Animals react to heat or pain. We usually design materials to suit a range of conditions while not being optimal for any of them. Following the same principles, smart materials would be able to sense and adjust to the conditions in their environment.

Polymer gels show a chemo-mechanical response. A change in the chemistry of the medium about the material results in a change in the volume that the material occupies. The material swells or collapses. We can use this structural change to force molecules out of the gel structure (collapsing) or into the gel structure (swelling).

Drug delivery systems can make use of the collapsing phenomenon. They would dispense drug molecules only under certain environmental conditions. We can use swelling to encapsulate unwanted reaction inhibitors or pathogens in the media.

We can also use smart polymer gels in chemo-mechanical micro-valves. In this case, a change in the medium activates the valve (gel). One example is a heat-activated micro-valve. When heated, the gel collapses and the valve opens. When the heat is removed, the gel expands and the valve closes. We can use such valves to control fluid flow and mixing in micro-size systems.

Investigating the properties of PCPOC

An essential element in the application of smart materials is the stimulus that causes the occurrence of the change. We are investigating the palladium-catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction in methanol. There are many applications of its versatile nature and application as a stimulus. It is an extraordinary chemical system. It 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. This field considers phenomena related to the periodic variation of the concentrations of species in a reaction. The Belousov-Zhabotinsky reaction is the best known reaction of this type.

The PCPOC reaction is an oscillating system of higher complexity. It is an exceptional example of oscillatory behaviour in reactions catalysed by metal complexes. It provides a novel and not well understood pH oscillator. It is the first example of complex molecules synthesised from simple reagents in a catalytic system in an oscillatory mode. It is of great importance because:

  • we can achieve high levels of product selectivity when operating this system in an oscillatory regime
  • besides oscillations in pH, synchronised oscillatory heat output is present
  • it exhibits two relevant stimuli, pH and temperature
  • it may propel nanodevices by generating an oscillating force when coupled with a block of gel

We are studying the cooperative interplay between experimental and theoretical investigation into the application of carbonylation reaction as a stimulus.

We will develop predictive physico-chemical models of the PCPOC reaction. We will research this system with:

  • pH sensitive polymers
  • temperature responsive polymers
  • materials sensitive to both (temperature and pH responsive polymeric composite membranes)

as:

  • an environment containing the smart material
  • an enclosed environment communicating with the environment containing the smart material
  • an enclosed environment containing the smart material communicating with the targeted environment