- Title
- On the rheology of dispersions of temperature-responsive polymer-particle hybrids
- Creator
- Webber, Grant B.; Humphreys, Ben A.; Gascoigne, Levana; Clark, Gabrielle; Wanless, Erica J.
- Relation
- Chemeca 2019: Chemical Engineering Megatrends and the Elements. Proceedings of Chemeca 2019: Chemical Engineering Megatrends and the Elements (Sydney, Australia 29 September - 02 October, 2019) p. 291-304
- Publisher
- Engineers Australia
- Resource Type
- conference paper
- Date
- 2019
- Description
- The effect of temperature on the rheology of aqueous dispersions of poly(Nisopropylacrylamide) homopolymer or poly(oligoethylene glycol methacrylate) (POEGMA) statistical copolymer brush modified colloidal silica particles has been investigated using a controlled stress rheometer with cone and plane geometry. Both polymer brushes are temperature responsive, adopting a solvent swollen conformation at low temperatures and collapsing to a poorly-solvated film as temperature increases. The temperature at which the transition occurs is termed the lower critical solution temperature (LCST) and is dependent on the polymer. The collapse of the polymer brush reduces the effective volume of the polymerparticle hybrid and thus the dispersion volume fraction. For example, PNIPAM brush-modified particles, with a 250 nm diameter silica core, had a dynamic light scattering measured hydrodynamic radius of 625 nm at 10 degreesC which reduced to 350 nm at 45 degreesC; an effective reduction in volume of over 80% per particle. The viscosity measured as a function of temperature for a 10 wt% dispersion of the PNIPAM modified particles showed shear-history dependent behaviour, where the viscosity measured at low temperatures was significantly higher in the first shear cycle. This is in spite of the expected high degree of steric repulsion between the swollen brushes. As expected the viscosity of the dispersions decreased at higher temperatures, with the viscosity at a given shear rate at 40 degreesC more than half that measured at 10 degreesC. Interestingly, while dispersions of both brush-modified silica particles displayed gelling behaviour in oscillatory measurements, the frequency required was dependent on the temperature of the system. For both polymers the frequency required to induce gel-like behaviour, as measured by the cross-over of the storage and loss moduli, reduced as the temperature increased. This was attributed to the increasingly cohesive nature of the polymer brushes resulting in inelastic collisions during the applied oscillatory flow. Such hybrid polymer-particle dispersions have potential application as rheology modifiers in situations where temperature gradients exist, such as medical, mining and personal care applications.
- Subject
- temperature; aqueous dispersions; hybrids; polymers
- Identifier
- http://hdl.handle.net/1959.13/1452409
- Identifier
- uon:44431
- Identifier
- ISBN:9781925627336
- Language
- eng
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