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Title: Microgel particles in non-aqueous colloid - polymer mixtures
Author: Bonham, Jessica Anne
ISNI:       0000 0004 6059 703X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Abstract:
Microgel particles are cross-linked polymer latex particles that can form stable colloidal dispersions and swell in response to their environment. This project focuses on microgels, in particular poly(styrene) particles cross-linked with either divinyl or diisopropenylbenzene, that can be swollen in non-aqueous solvents. The synthesis and characterisation of the particles is discussed as well as their extent of swelling as a function of solvency, cross-linker type and density, initiator and temperature. Finally, the behaviour of micro gel particles in binary and ternary mixtures with non-adsorbing polymer and / or hard spheres is also studied. Microgel particles are synthesised using a number of different mechanisms, crosslink densities and initiators. Dynamic and static light scattering studies are used to calculate the swelling ratios of these particles and it is found that the solvency has a: key role in determining the swelling of these particles, as does the cross-link density. With the exception of solvency, micro gel particles swollen in non-aqueous solvents are not known to swell or deswell in response to other external stimuli. The temperature response of the particles made in this project is measured using dynamic and static light scattering, rheology and small angle neutron scattering. A fairly limited response is found in decalin and cyclohexane, in agreement with predictions of the classic Flory-Rehner theory for (macroscopic) polymer gels. The initiator used during particle synthesis has a significant impact on whether the particles can be redispersed in various solvents. A neutral, oil soluble initiator produces particles that can be redispersed in a number of solvents, whereas using an anionic, water soluble initiator produces particles that can only be redispersed . in polar solvents. The initiators, therefore, effect the functionalisation and surface charge of the particles which affects their ability to be redispersed in solvents. Zeta potential and conductivity measurements point at the existence of such charged groups however these are notoriously difficult to measure and not yet fully ' understood. The effect of micro gel particle softness on the phase behaviour of colloid - polymer mixtures is studied using differential interference contrast microscopy and rheology. Diisopropyl adipate is used as the solvent as this combines good swelling conditions for the particles with a low volatility that enables rheology studies to be carried out. The phase behaviour of microgel - polymer mixtures is significantly different to hard sphere - polymer mixtures with the same size ratio, where highly crosslinked, fiuorescently labelled poly(styrene) particles are used as the hard spheres. The soft particles require a higher polymer concentration to phase separate due to penetration of the non-adsorbing polymer into the soft particles which weakens the depletion interaction. Furthermore, the microgel particles form a stable cluster phase which is thought to be because they are near density matched. Hence, small aggregates of the particles do not settle under gravity and remain in solution. The phase behaviour of the hard sphere - polymer mixtures was as expected, based on current literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.702920  DOI: Not available
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