Browsing by Author "Whitby CP"
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- ItemInterfacial colloidal assembly guided by optical tweezers and tuned via surface charge(Elsevier Inc, 2022-09) Pradhan S; Whitby CP; Williams MAK; Chen JLY; Avci EHYPOTHESIS: The size, shape and dynamics of assemblies of colloidal particles optically-trapped at an air-water interface can be tuned by controlling the optical potential, particle concentration, surface charge density and wettability of the particles and the surface tension of the solution. EXPERIMENTS: The assembly dynamics of different colloidal particle types (silica, polystyrene and carboxyl coated polystyrene particles) at an air-water interface in an optical potential were systematically explored allowing the effect of surface charge on assembly dynamics to be investigated. Additionally, the pH of the solutions were varied in order to modulate surface charge in a controllable fashion. The effect of surface tension on these assemblies was also explored by reducing the surface tension of the supporting solution by mixing ethanol with water. FINDINGS: Silica, polystyrene and carboxyl coated polystyrene particles showed distinct assembly behaviours at the air-water interface that could be rationalised taking into account changes in surface charge (which in addition to being different between the particles could be modified systematically by changing the solution pH). Additionally, this is the first report showing that wettability of the colloidal particles and the surface tension of the solution are critical in determining the resulting assembly at the solution surface.
- ItemNanoprecipitation to produce hydrophobic cellulose nanospheres for water-in-oil Pickering emulsions(Springer Nature B V, 2024-07) Tiban Anrango BA; Naiya MM; Van Dongen J; Matich O; Whitby CP; Chen JL-YIn recent years, there has been growing interest in replacing petroleum-based water-in-oil (W/O) emulsifiers with sustainable and less toxic natural materials. Pickering emulsifiers are considered well-suited candidates due to their high interfacial activity and the ability to form emulsions with long-term stability. However, only sporadic examples of natural materials have been considered as inverse Pickering emulsifiers. This study describes the synthesis of a series of hydrophobic cellulose nanospheres by bulk modification with acyl groups of different chain lengths followed by nanoprecipitation, and their application as inverse emulsifiers. Modification with acyl groups of longer chain length (C16, C18) afforded lower degrees of substitution, but resulted in greater thermal stability than groups with shorter acyl chains (C12, C14). Formation of nanospheres with low aspect ratios and narrow size distributions required low initial cellulose concentrations (< 1% w/v), high volumetric ratios of antisolvent to solvent (> 10:1), and slow addition rates (< 20 mL/h). The modified cellulose nanospheres were able to reduce the interfacial tension between water and hexane from 45.8 mN/m to 31.1 mN/m, with an effect that increased with the number of carbons in the added acyl chains. The stearate-modified nanospheres exhibited superhydrophobic behavior, showing a contact angle of 156° ± 4° with water, and demonstrated emulsification performance comparable to the commonly used molecular surfactant sorbitan stearate. Our findings suggest that hydrophobically modified cellulose nanospheres have the potential to be a bio-derived alternative to traditional molecular W/O emulsifiers.