Abstract:
We demonstrate a novel yet straightforward methodology of stabilizing aqueous two-phase systems (ATPS) using
oppositely charged nanoparticles (OCNPs). We employ commercialgrade, Ludox, OCNPs to induce self-assembly. This self-assembly
route promotes the stronger adsorption of nanoparticles at the water−
water interface by triggering the formation of 2D and 3D aggregates of
varying sizes and shapes. The interplay of this size and shape promotes
stability due to increased Gibbs detachment energy and modulates the
resulting cluster adsorption at the interface, thereby the structural state
of emulsions. We demonstrate the influence of polymers’ and particles’
composition on the structural transformation from droplet−bijel−
droplet using a phase diagram. For the first time, such a structural
transition and the single pathway are reported within the domain of
ATPS to produce stable bijels or colloidal capsules. It is asserted that the essential condition of three-phase contact angle (θ) = 90°
to favor the formation of bijels can be established by selecting a suitable experimental condition using a phase diagram without
employing any complicated surface modification procedures reported in the literature. Further, the mechanistic route favoring the
formation of bijels and emulsion droplets at different experimental regimes is presented based on the empirical study using turbidity
and zeta potential measurements. These studies reveal that the formation of bijels will be most favored when the parameter M (ratio
of weight fraction of positively charged nanoparticles to negatively charged nanoparticles) is chosen between 0.7 and 4. It is
intriguing to note the fact that, while the droplets stabilized by OCNPs have shown good resilience under high centrifugal action, the
bijels produced in this way continued to remain stable for a long time, offering a facile route to prepare the bijels with a hierarchical
bicontinuous network structure
