CO₂-responsive anionic wormlike micelles based on natural erucic acid

Abstract

Research interests highlighted in recent years a remarkable growing focus on stimuli-responsive surfactant wormlike micelles, particularly those using carbon dioxide as the trigger. In this article, we report a novel carbon dioxideresponsive wormlike micellar system based on natural erucic fatty acid and examined its solution properties through rheology, Fourier transform infrared spectroscopy and cryo-tranmission electron microscopy. When carbon dioxide is introduced into the erucic acid solution, high-viscelastic wormlike micelles shift to low-viscosity solutions in short-time scale, accompanied by decrease in pH from 11·34 to 8·90, which is accounted for the effect of pH on the existence form of erucic acid in aqueous solutions. Bubbling nitrogen under heating cannot make a converse process since the viscoelastic worms can only be obtained at a high pH. Compared with other carbon dioxide-responsive wormlike micelles, the current one is more readily obtained and more environment-friendly because it can be formed by simply changing pH value of the natural erucic acid solutions without needing complex organic synthesis or addition of hydrotropes. IntroductionStimuli-responsive materials whose properties respond remarkably on minor environmental change have attracted much attention in the last decade.1-3 Among all such materials, colloids and micelles represent important soft matters and play crucial roles in various industrial applications.2 Different micellar morphologies can be obtained by self-assembly of amphiphilic compounds such as surfactants or block copolymers. 4 One of such fascinating morphological aggregates is the wormlike or threadlike micelles. Above a critical overlapping concentration (C*), the wormlike micelles entangle into a dynamic 3D transient network reminiscent of polymer solutions to display remarkable macroscopic viscoelastic properties. However, unlike the polymer entanglements, they break and recombine in a dynamic process, and are thus called 'living' or 'equilibrium' polymers. 5,6 Because of their unique micellar structures and rheological response, 7,8 viscoelastic fluids based on wormlike micelles have been a key focus of research in soft matter from both theoreticians and experimentalists for fundamental studies as well as industry applications, including rheology control, 8

Responsive self-assemblies based on fatty acids

“…By increasing the pH to intermediate values, as NaOH or HCl [36]. Many examples of such control have been published for various types of surfactants [2].…”

“…Many examples of such control have been published for various types of surfactants [2]. Up to date, only one example is described in the literature on the use of CO 2 to tune fatty acid properties as surfactant [36]. The WLMs obtained from erucate solution at high pH described in the previous section have been used to study the effect of CO 2 as a trigger [36].…”

“…Up to date, only one example is described in the literature on the use of CO 2 to tune fatty acid properties as surfactant [36]. The WLMs obtained from erucate solution at high pH described in the previous section have been used to study the effect of CO 2 as a trigger [36]. When CO 2 is injected by bubbling into the WLMs solution, carbonic acid is produced within a few seconds and the pH decreases ( Fig.…”

“…Indeed, it is well known that solutions of spherical micelles yield low viscosities, whereas the formation of WLMs or vesicles can have strong effects on the rheological properties providing in some cases highly viscous solutions [35,36,50,51]. In literature, most of the reported studies deal with single structural modification induced by an external stimulus leading to only one major change in the rheological properties.…”

Photoresponsive self-assemblies based on fatty acids

“…7 This method has been applied successfully to tune fatty acid self-assemblies based on erucic acid molecules in aqueous medium from wormlike micelles to spherical micelles. 8 However, to the best of our knowledge, there is no example in the literature dealing with the light as a trigger to tune self-assemblies based on fatty acid molecules. Our approach to achieve photoresponsive self-assemblies based on fatty acid molecules as surfactants was to combine fatty acid self-assemblies with a photoacid generator (PAG) in solution.…”