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We are looking forward to welcoming you to Bristol. The team of people you will be working with on this project are all members of the Colloid and Interface Science Research Group in the School of Chemistry. While you are here you will share in the experience of a real research team!
Colloids may seem unfamiliar, but they are very common and very important and consist of very tiny particles of one kind of substance (phase) in another phase. They include things like emulsions, foams, aerosols, gels and so on. Our team consists of myself, Professor Brian Vincent... I am Head of the Research Group and also Leverhulme Professor of Physical Chemistry in the University... and my colleagues Dr Patricia Marr and Mr Robin Mogford.
Do not be worried if some of the terms in this sheet are not ones you have come across before... all will be explained to you.
The controlled release of active pharmaceuticals (drugs), agrochemicals, flavours, perfumes and so on is today a major technological challenge for a wide variety of modern chemical industries. In for example medicine and agriculture, it is crucially important to be able to control the release dosage and release rate of active substances. In some cases we need to have a decreasing (exponentially decaying) rate of release (technically known as first-order release kinetics) and in others a constant rate of release (zero-order release kinetics). In another case, we might need a sudden release after a certain delay time. To achieve these goals, a number of encapsulated systems based on a "liquid-core/solid shell particle morphology" have been devised.
In our project we are going to make and investigate one particular particle system which gives rise to a decreasing rate of release of material (first-order release kinetics). This will use core/shell particles, dispersed in water, where the liquid core of the particle is a hydrocarbon containing the dissolved "active material", which might in real life be the drug, and the shell is a polymer, in this case poly(methylmethacrylate) [PMMA]. As our model "active material", we shall use the substance p-nitroanisole, which has a low solubility in water.
First you will make the core/shell particles. This is reasonably straight forward. It involves the emulsification (using a Silverson emulsifier unit) of an oil phase into an aqueous (water) phase to form, initially, oil/water droplets. The oil:water ratio is ~ 1 by volume.
Our oil phase will consist of a solution of the polymer (PMMA) and the model active ingredient dissolved in a mixture of a high boiling-point organic solvent (hexadecane) and a low boiling point organic solvent (dichloromethane). Our aqueous phase will contain a water-soluble polymer (polyvinylalcohol, PVA), which adsorbs at the oil/water interface and stabilises the oil droplets in the emulsion and stops them coalescing.
The emulsion is allowed to stand in a fumehood for several hours, during which time the low boiling organic solvent (dichloromethane) evaporates from inside the oil droplets. As a result, the PMMA polymer separates from the hydrocarbon solution, and collects at the droplet surface, forming the shell, and leaving the liquid core of hexadecane containing the model active substance. This is because although PMMA dissolves in the hexadecane-dichoromethane mixture, it dissolves hardly at all in hexadecane on its own.
You will then be able to examine the particles you have made by optical and/or electron microscopy, and obtain your own micrographs of the particles.
You will also be able to measure how fast the active compound is released from inside the particles you have made. By now, the model active compound will, of course, have slowly diffused out of each particle core, across the polymer shell, and into the water phase to form a saturated water solution. You will be able to investigate the rate of release of the remaining active molecules from the particles you have made, by diluting this aqueous phase by a given amount, and then measuring the change in the concentration of the active compound in the water, as a function of time. You can do this using a UV/Visible spectrophotometer.
You will be working in three teams (one UK + one Japanese student in each team), and each team will prepare core/shell particles with different polymer shell thicknesses. You will do this by adding different quantities of the PMMA polymer to the initial oil phase. If time permits, you will break open some particles from each team, and see if we can observer the differences in shell thickness.
The three groups will correlate the release rates that they obtain with the thickness of the polymer shells for their particles. We will then be able to present your findings at the Friday presentations, using Powerpoint.
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