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Title: Colloid-microgel mixtures : phase behaviour and temperature response
Author: Bayliss, Katie
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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Recently, interest has been shown in stimuli responsive microgel particles as depletants, capable of inducing entropy driven phase transitions in colloidal systems. Due to their temperature induced deswelling transition , which occurs above ~32 'c, poly(N-isopropylacrylamide) (pNIPAM) microgels present opportunities for the easy modulation of depletion interactions between colloids. The aim of the current project was to gain an understanding of the phase behaviour of colloidal particles mediated by pNIPAM microgels both below and above the volume phase transition temperature (VPTT) , for potential applications in formulation science. For this purpose, a simple model system comprising an aqueous suspension of polystyrene (PS) latex particles, stabilised with Synperonic PE/ Pl05 PEOPPO- PEO (Pl05) copolymer, and pNIPAM microgels was developed . The majority of experiments were conducted at a microgel/ colloid size ratio, q, close to 0.1 at room temperature. A phase diagram for the colloid-microgel mixture at room temperature was determined experimentally using differential interference contrast (DIC) microscopy. At sufficient microgel volume fraction, mixtures were found to separate into colloidal fluid and solid phases. At higher particle concentrations, gelation was observed. The phase diagram was compared to that for a colloid-linear polymer mixture at similar q. Similarities in the two systems were found in the position of the fluid- solid phase boundary; however , differences in the kinetics of phase separation were apparent in the earlier onset of gelation in the colloid-microgel phase diagram. This result may be due to the greater rigidity of the microgels. Interestingly, the colloidmicrogel gel line was found to coincide with the theoretical metastable fluid-fluid phase boundary calculated for binary hard sphere systems at q = O.l.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available