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Structure and Properties of Core-Shell Gel Particles

Nilia Romero

Nilia Romero (previous student, left the group in 2002)

A microgel is a colloidal sized, spherical, covalently cross-linked polymer network. The size of a microgel is either sensitive to pH or temperature, although there are some microgels which respond to both stimuli.

Microgels have been investigated for use in a wide range of applications. The have been used in the paint industry because of their ability to impart shock resistance to films, because of their sponge like nature. Other potential applications include water purification, heat sensors and crude oil extraction. The diversity stems from the fact that microgels can be made from various types of monomer units, and have varied cross-linker concentrations, both factors imparting different properties upon the microgels.

The temperature-sensitive uptake or release of chemicals has been one of the most intensively investigated potential applications for microgels, because they exhibit very rapid swelling or shrinking in response to temperature change. Thus, temperature-triggered drug or chemical release is possible.

Most of these systems are based on poly-N-isopropylacrylamide (poly-NIPAM) or related copolymers.

In 1978, Philip Chibante and Pelton, prepared the first reported temperature-sensitive aqueous microgel. The microgel was a monodisperse, colloidal dispersion based on cross linked poly-NIPAM, a polymer which has a Lower Critical Solution Temperature (LCST) in water of 32°C. At room temperature, the particles are swollen, but being thermosensitive. They collapse as the temperature is increased above 32°C. This has been explained by a decrease in the hydrogen bonding between the amide groups of the polymer and the water molecules.

The above applications have been the motivation for this project, which aims are as follows:

Several techniques will be used in order to characterise the core shell particles and measure the deswelling of the layer (poly-NIPAM) with changes in temperature:

This project is funded by the University of Bristol and PDVSA-Intevep.