Redox and Doubly pH-Switchable Pickering Emulsion

Abstract

In this work, a novel Pickering emulsion is stabilized by silica nanoparticles functioned with a redox and pH-responsive surfactant FA-DMDA-Ox that is prepared simply by direct neutralization of ferrocenecarboxylic acid (FA) and N,N-dimethyldodecylamine (DMDA) and exhibits redox and doubly pH-switchable behavior. Here, the Pickering emulsion can be stabilized easily by combining hydrophilic silica nanoparticles with less than 0.1 wt % FA-DMDA-Ox. After adding Na 2 SO 3 and H 2 O 2 alternately, the demulsification and emulsification of this Pickering emulsion are controlled reversibly. Moreover, the emulsion is switched "off" upon the addition of HCl and switched "on" upon the addition of NaOH and is also switched off upon the addition of NaOH and switched on upon the addition of HCl, which demonstrate the doubly pHswitchable behavior. Based on the analysis of ζ-potential, contact angle, and adsorbed amount of silica nanoparticles, the pH and redox-switchable mechanism of the Pickering emulsion are analyzed. Here, the redox-switchable behavior is induced by the reversible adsorption and desorption of FA-DMDA-Ox on the surface of silica nanoparticles. The pH-switchable behavior is driven by the controllable dispersion systems of silica nanoparticles and FA-DMDA-Ox because of the doubly pH switchability of FA-DMDA-Ox. More importantly, upon adding fresh oil after removing the original oil, the Pickering emulsion is recycled three times. Hence, the multiswitchable Pickering emulsion can be expected to be treated as a multifunctional material in practical applications, such as oil or wax removal in the petroleum industry.

Salt-Resistant Switchable Pickering Emulsions Stabilized by Mesoporous Nanosilica Hydrophobized In Situ by pH-Insensitive Surfactants

“…In recent years, stimuli-responsive PEs that can be transformed between stable and unstable states under an external stimulus have been developed to overcome this challenge. Various triggers including light, , CO 2 /N 2 , − pH, − redox, − temperature, , and magnetic fields − have been used to regulate the surface activity of the NPs and hence change the emulsion stability. On the other hand, such “switchable” PEs can also be prepared, comparatively conveniently, using inorganic NPs that can be made hydrophobic in situ by the action of stimuli-responsive surfactants. − …”

Gelator-Enhanced Organohydrogels with Switchable Mechanics and High-Strain Shape-Memory Capacity

“…The hydrophilic PDMA and hydrophobic PLMA polymer chain segments are chemically connected at the oil–water interface during emulsion polymerization, producing an integrated amphiphilic network on the molecular dimension. The nanoclay plays an important role in this work. , On the one hand, it acts as a Pickering emulsifier that adsorbs on the oil/water interface to prevent the aggregation of oil droplets. − Owing to the high adsorption energy of these solid emulsifiers, Pickering emulsions generally show high stability compared to normal emulsions, even at high temperature . In this work, stable emulsions at high temperature are an indispensable condition due to the need for oil-phase fluidity and successful polymerization above T gel .…”

“…30−35 Owing to the high adsorption energy of these solid emulsifiers, Pickering emulsions generally show high stability compared to normal emulsions, even at high temperature. 36 In this work, stable emulsions at high temperature are an indispensable condition due to the need for oil-phase fluidity and successful polymerization above T gel . On the other hand, it acts as a multifunctional cross-linker in the aqueous phase.…”

Redox- and pH-responsive emulsions based on TiO2 nanoparticles and ferrocene derivates

“…It can be observed that the zeta potential increased from initial À49.05 mV to 0 mV upon increasing the Fc + A concentration from 0 mmol L À1 to 2 mmol L À1 , confirming the adsorption of Fc + A on the surface of TiO 2 nanoparticles, and a further increase in Fc + A concentration would cause charge inversion. 25,36 Moreover, it should be noted that both zeta potential and specific surface area of unmodified TiO 2 nanoparticles were much higher than those of Fe 3 O 4 and SiO 2 nanoparticles, as shown in Table 1. 32,33,37 Therefore, there might be a stronger electrostatic interaction between TiO 2 nanoparticles and Fc + A, which enabled real-time modification of nanoparticles by Fc + A.…”

“…21,22 As we all know, triggers such as pH, CO 2 , redox, ion, magnetic field and light have been widely used for constructing responsive Pickering emulsions. [23][24][25][26][27][28] Yu et al 29 described a pH-responsive behaviour of Pickering emulsions stabilized with alumina nanoparticles and a selenium-containing surfactant, in which the sodium carboxyl group could be reversibly transformed between its anionic and non-ionic states, resulting in the emulsification and demulsification of Pickering emulsions. Besides, Pickering emulsions with multi-responsiveness such as pH-temperature, CO 2 -temperature, light-magnetic field have been also widely studied.…”