Cellulose Nanocrystal Laden Oil-Water Interfaces: Interfacial Viscoelasticity, Emulsion Stability, and the Dynamics of Three-Phase Contact-Lines

We study the influence of cellulose nanocrystals on the oil-water interfacial viscoelasticity and consequently on the emulsification and the three-phase (oil-water-solid) contact-line movement. Cellulose nanocrystals (CNCs) are used in combination with hexadecyl trimethyl ammonium bromide (CTAB) as the source of nanoparticle- surfactant dispersion. We use two samples of oils (i) heptane (representing a low viscosity system) and (ii) mineral oil (representing a high viscosity system). The emulsification stability map is developed for the heptane-water systems at various CNC-CTAB concentrations. The map displays stable emulsion formations when dilatational interfacial viscoelasticity is above similar to 40 mN/m. The coupled interfacial rheology and microscale characterization analysis show that CNCs become surface active by the adsorption of surfactants, migrate to the oil-water interface, and create a viscoelastic interface. The CNC-CTAB interfacial layer prevents the drop coalescence, creating highly stable medium internal phase emulsions. The emulsification experiments are further performed with a high viscosity mineral oil sample, where similar stability trends as heptane emulsions are obtained. Furthermore, it is shown that the CNC-CTAB-laden drops wet a hydrophilic solid surface, submerged in the mineral oil, with a wetting radius growing according to r similar to t(alpha). Similar to the spreading of the surfactant (CTAB-laden) drops, three regimes are identified, an initial retardation regime (alpha <= 0.5), a second early-time viscous-dominated regime (alpha similar to 1), and the late-time Tanner regime (alpha = 0.1). However, the CNC-CTAB viscoelastic interfacial layer increases the duration of the early-time spreading regime by one order of magnitude.

Automated summary

The study investigates the influence of cellulose nanocrystals on oil-water interfacial viscoelasticity, demonstrating that the nanocrystals can enhance emulsification stability and create stable emulsions. Additionally, the nanocrystals aid in preventing drop coalescence and prolonging the duration of the early-time spreading regime in emulsification experiments.