pH-responsive water-in-oil emulsions with reversible phase inversion behavior stabilized by a novel dynamic covalent surfactant

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

“…Meanwhile, the intensity of CHO at δ = 9.8 ppm (Wang et al, 2012) in the case of PEG‐CHO was smaller than that in the case of the C6‐NH 2 and PEG‐CHO mixture. All these results indicate the formation of both DIB and C6‐DIB‐PEG (Li & Liu, 2022; Liu et al, 2022; Mu et al, 2022; Wang et al, 2022). Compared with PEG and PEG‐CHO, a characteristic peak at ~1644 cm −1 was found in the FTIR spectrum of C6‐DIB‐PEG (Figure S2).…”

“…In order to study the surface activity of C6‐DIB‐PEG, it is necessary to first demonstrate the DIB formation between the precursors C6‐NH 2 and PEG‐CHO (Scheme 1). According to dynamic imine chemistry, an alkaline condition favors DIB formation (Li & Liu, 2022; Liu et al, 2022; Minkenberg et al, 2011; Ren et al, 2021; Wang et al, 2022; Zentner et al, 2019). Thus, it is reasonable that C6‐DIB‐PEG should form under the condition of pH = 12.0.…”

“…Switchable (Liu et al, 2006) or stimuli‐responsive surfactants (Brown et al, 2013) may well address this issue because switchable surfactants will be reversibly interconverted between active and inactive forms under appropriate stimuli. A number of studies have demonstrated that emulsions can be demulsified on demand under appropriate stimuli such as pH (Wang et al, 2022), CO 2 /N 2 (Chen et al, 2020; Xu et al, 2018), redox (Zhang, Chen, et al, 2016), and light (Takahashi et al, 2016) to achieve oil–water two‐phase separation, which can then be used to realize oil retrieval (Ceschia et al, 2014; Xu et al, 2018).…”

“…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.…”