pH-Responsive Nanoemulsions Based on a Dynamic Covalent Surfactant

Abstract

Developing solid-free nanoemulsions with pH responsiveness is desirable in enhanced oil recovery (EOR) applications. Here, we report the synthesis of an interfacial activity controllable surfactant (T−DBA) through dynamic imine bonding between taurine (T) and p-decyloxybenzaldehyde (DBA). Instead of macroemulsions, nanoemulsions can be prepared by using T−DBA as an emulsifier. The dynamic imine bond of T−DBA enables switching between the active and inactive states in response to pH. This switching of interfacial activity was used to gate the stability of nanoemulsions, thus enabling us to turn the nanoemulsions off and on. Using such dynamic imine bonds to govern nanoemulsion stability could enable intelligent control of many processes such as heavy oil recovery and interfacial reactions.

Investigation of Factors Influencing Formation of Nanoemulsion by Spontaneous Emulsification: Impact on Droplet Size, Polydispersity Index, and Stability

“…It was observed that the mean droplet size (152.1 nm) and PDI (0.154) of OA-based NE system was significantly increased in the buffer of acidic pH 1.2 compared to NE system at pH 6.8 ( p < 0.05) ( Figure 4 a). OA-based NE formulation contains a carboxyl group as a pH-responsive group, which upon pH changes resulted in the protonation or deprotonation of the responsive group in the formulation system [ 37 ]. A pKa value of 4.89 of OA indicates that it will exist almost entirely in the anion form at pH values of 5–9 [ 38 ] and get protonated upon a change in pH to acidic pH 1.2.…”

“…A pKa value of 4.89 of OA indicates that it will exist almost entirely in the anion form at pH values of 5–9 [ 38 ] and get protonated upon a change in pH to acidic pH 1.2. This switching of the responsive group between deprotonated to protonated state due to the change in pH of the aqueous phase is responsible for contributing to the pH-responsive nature of the NE [ 37 ] and results in an increase in mean droplet size of OA-based NE formulation at pH 1.2. On the contrary, it was observed that the mean droplet size (210.1 nm) of C90-based NE system was significantly larger in a buffer of pH 6.8 compared to the mean droplet size (153.5 nm) of C90-based NE system at pH 1.2 ( p < 0.05) ( Figure 4 b).…”

Nanoemulsion and Solid Nanoemulsion for Improving Oral Delivery of a Breast Cancer Drug: Formulation, Evaluation, and a Comparison Study

“…A calibrated pH meter (WTW- INO LAB, Switzerland) was used to measure the pH of all prepared formulations by immersing the instrument bulb into 30 mL of each formulation ( Mahtab et al, 2016 , Ren et al, 2021 ).…”

Recyclable dynamic imine‐based nonionic surfactants and potential use in postprocessing of eluted emulsions

“…Thanking the dynamic covalent chemistry (Belowich & Stoddart, 2012), dynamic imine‐based surfactants (DIBS) are pH‐switchable and have attracted extensive attention (Li & Liu, 2022; Liu et al, 2022; Minkenberg et al, 2011; Ren et al, 2021; Wang et al, 2022; Zentner et al, 2019). Unlike traditional pH‐switchable surfactants, DIBS can be “cleaved” reversibly between a surfactant and two precursors (Li & Liu, 2022; Liu et al, 2022; Minkenberg et al, 2011; Ren et al, 2021; Wang et al, 2022; Zentner et al, 2019). The pH‐stimulus is simple to operate and the DIBS is fast to respond.…”

“…The pH‐stimulus is simple to operate and the DIBS is fast to respond. The reversible formation of DIBS‐based micelles (Ren et al, 2021), vesicles (Minkenberg et al, 2011), and emulsions (Li & Liu, 2022; Liu et al, 2022; Wang et al, 2022) have been observed under reversible pH tuning. However, most of the DIBS reported so far are ionic in nature; the nonionic DIBS (Zentner et al, 2019) is rarely reported.…”