Study of the molecular behaviour of ionic liquid colloidal suspension using rheometry and NMR

Smith, Catherine Franklin (2017). Study of the molecular behaviour of ionic liquid colloidal suspension using rheometry and NMR. University of Birmingham. Ph.D.

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In this thesis, a systematic investigation has been carried out to study the effect of cations and anions on the interactions and aggregation of silica nanoparticles in ionic liquid colloidal suspensions. Suspensions of hydrophobic and hydrophilic silica nanoparticles in four ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate, [C\(_2\)mim][BF\(_4\)], 1-butyl-3-methylimidazolium tetrafluoroborate, [C\(_4\)mim][BF\(_4\)], 1-ethyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide, [C\(_2\)mim][NTf\(_2\)], and 1-butyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide, [C\(_4\)mim][NTf\(_2\)], have been studied.
Shear thinning rheology was observed in all systems. Suspensions of [C\(_2\)mim][BF\(_4\)] and [C\(_4\)mim][BF\(_4\)] showed shear thickening behaviour at high hydrophilic silica nanoparticle concentrations. Magnetic resonance velocity imaging experiments were performed to study the local rheology of the suspensions, which compared well with the bulk rheology, but indicated shear banding in suspensions of [C\(_4\)mim][NTf\(_2\)] with hydrophilic nanoparticles. No hydrogen bonding, between either cation or anion with silica nanoparticles, was observed by IR spectroscopy. With increasing silica concentration, a decrease in the NMR \(T\)\(1\) relaxation time of protons on the imidazolium ring, of the cation, was observed for all ionic liquids indicating it is the cation that interacts with the nanoparticles. For all ionic liquid suspensions investigated, clusters of nanoparticles were observed by dynamic light scattering. However, for suspensions of hydrophilic silica in [C\(_4\)mim][NTf\(_2\)] and hydrophobic silica in [C4mim][BF4], high proportions of single nanoparticles were also present. These data have been interpreted in terms of the formation of colloidal gels and glasses.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Chemistry
Funders: None/not applicable
Subjects: T Technology > TP Chemical technology


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