Charge Density Overcomes Steric Hindrance of Ferrocene Surfactant in Switchable Oil‐in‐Dispersion Emulsions

Abstract

A ferrocene surfactant can be switched between single and double head form (FcN + C 12 /Fc + N + C 12 ) triggered by redox reaction. FcN + C 12 can neither stabilize an O/W emulsion alone nor an oil-in-dispersion emulsion in combination with alumina nanoparticles due to the steric hindrance of the ferrocene group. However, such steric hindrance can be overcome by increasing the charge density in Fc + N + C 12 , so that oil-in-dispersion emulsions can be co-stabilized by Fc + N + C 12 and alumina nanoparticles at very low concentrations (1 × 10 À 7 M ( � 50 ppb) and 0.001 wt %, respectively). Not only can reversible formation/destabilization of oil-in-dispersion emulsions be achieved by redox reaction, but also reversible transformation between oil-in-dispersion emulsions and Pickering emulsions can be obtained through reversing the charge of alumina particles by adjusting the pH. The results provide a new protocol for the design of surfactants for stabilization of smart oil-indispersion emulsions.

Surface Wettability-Switchable Janus Fiber Fragments Stabilize Pickering Emulsions for Effective Oil/Water Separation

“…The extra particles would disperse in the continuous phase to prevent droplet coalescence when the particle level was greater than the critical concentration . With the solid particle concentration increased, the thickness and package rate on the droplet surfaces enhanced the steric hindrance and emulsion stability, and the stability mechanism changed from bridge to steric hindrance and then to space network control with increasing the particle concentrations. , In addition, compared with microspheres, the use of nonspherical particles for Pickering emulsions may reduce surface tensions on the droplet surface. There were three adsorption stages for the self-assembly of particles at the oil/water interface.…”

pH‐ and Redox‐Responsive Pickering Emulsions Based on Cellulose Nanocrystal Surfactants

“…The water dispersible CNC‐OSO 3 − used in this work was prepared by sulfuric acid hydrolysis method. Ferrocene terminated polystyrene (PS‐Fc, M n =3.2 K, PDI=1.1, Scheme S1 and Figures S1–S3) was dissolved in toluene and oxidized by sodium hypochlorite (NaClO, 40 mg mL −1 ) via an electron transfer reaction [15, 16, 18] . The resultant PS‐Fc + ‐containing toluene solution was used as the oil phase.…”

“…Ferrocene terminated polystyrene (PS-Fc, M n = 3.2 K, PDI = 1.1, Scheme S1 and Figures S1-S3) was dissolved in toluene and oxidized by sodium hypochlorite (NaClO, 40 mg mL À 1 ) via an electron transfer reaction. [15,16,18] The resultant PS-Fc + -containing toluene solution was used as the oil phase. The interfacial activity of CNC-OSO 3 À and PS-Fc + at different pH was investigated firstly, using HCl (1.0 mM) and NaOH (1.0 mM) solutions to vary the pH of aqueous phase.…”

CO2-switchable emulsions with controllable size and viscosity

“…Although interconversions between the OID emulsions and Pickering emulsions were obtained with the pH and redox reaction triggers, 39,40 the accumulated salts during the switching cycles affected the stabilities and droplet sizes of the emulsions, which limited the number of cycles. For example, the OID emulsions became unstable aer 5 cycles with the redox reaction triggers.…”

“…36 However, OID emulsions are always only temporarily stable (for less than one month), which limits their applicability when long-term stability is required, such as in foods and cosmetics. 37,38 Recently, transformations between OID emulsions and Pickering emulsions have been achieved with pH and redox triggers; 39,40 however, the accumulation of salts during pH changes or redox reactions always affected the stability of the emulsion.…”