Photorheological Response of Aqueous Wormlike Micelles with Photocleavable Surfactant

Abstract

Recently, we have reported a new cinnamic acid-type photocleavable surfactant, C4-C-N-PEG9 that experiences a photocleavage through UV-induced cyclization in aqueous solution, yielding a coumarin derivative (7-butoxy-2H-chromen-2-one) and an aminated polyoxyethylene compound. Here, we have studied the effects of C4-C-N-PEG9 on the photorheological behavior of viscoelastic wormlike micelles formed by aqueous mixture of nonionic surfactants, polyoxyethylene phytosterol ether (PhyEO20) and tetraoxyethylene dodecyl ether (C12EO4). The 4.9 wt % PhyEO20/H2O + 2.4 wt % C12EO4 solution forms wormlike micelles, and its viscosity is ~10 Pa·s. We have found that the addition of C4-C-N-PEG9 into this viscous, non-Newtonian fluid system decreases the viscosity. Viscosity decreased in parallel to the C4-C-N-PEG9 concentration reaching ~0.003 Pa·s at 2.5 wt % of C4-C-N-PEG9. However, viscosity of the C4-C-N-PEG9 incorporated system increased significantly (~200 times at 1.5 wt % of C4-C-N-PEG9 system) upon UV irradiation. Small-Angle X-ray scattering studies have shown that addition of C4-C-N-PEG9 favors wormlike-to-sphere type transition in the micellar structure. However, UV irradiation in the C4-C-N-PEG9 incorporated system causes one-dimensional micellar growth. Since C4-C-N-PEG9 has relatively bigger headgroup size compared to the C12EO4, addition of C4-C-N-PEG9 into wormlike micelles reduces the critical packing parameter resulting in the formation of spherical aggregates. UV irradiation induced one-dimensional micellar growth is caused due to photocleavage of the C4-C-N-PEG9 into a less surface-active coumarin derivative and an aminated polyoxyethylene compound, as confirmed by UV-vis spectrometry and HPLC measurements. The hydrophobic coumarin derivative formed after cleavage of C4-C-N-PEG9 goes to the micellar core and is responsible for decreasing the viscosity. However, the hydrophilic aminated polyoxyethylene prefers to reside at the vicinity of headgroup of PhyEO20 reducing the interhead repulsion, increasing the critical packing parameter and the viscosity as well.

Wormlike micelles formed using Gemini surfactants with quaternary hydroxyethyl methylammonium headgroups

“…6b, the shape of the pair-distance distribution function p(r) indicates the presence of a core-shell structure, due to the differing electron density distributions in the core and shell regions. 45 The hydrophobic radius of the core-shell structure is 1.7 nm, determined using the r value at which the p(r) function rst reaches zero. This value is a bit smaller than that (1.9 nm) calculated using Tanford's formula based on a 14-carbon chain length, perhaps due to the close packing of the hydrophobic chains of Gemini surfactants.…”

Light-Triggered Rheological Changes in a System of Cationic Wormlike Micelles Formulated with a Photoacid Generator

“…There are several studies describing smart WLMs that are responsive to pH. The various strategies in these studies include the use of a pH-responsive surfactant, 21,28,29 the combination of a conventional surfactant and a pH-responsive organic compound such as oxalic acid, 28 hydroxycinnamic acid, 22 or benzenedioic acid, 31 CO 2 . 21,32−34 It is possible to formulate pH-responsive WLMs that can be triggered over any pH rangeacidic, 30,39 neutral, 23 or basic.…”

Multicompartment-like aggregates formed by a redox-responsive surfactant encapsulated polyoxometalate in DMF/butanol mixed solvent

“…[1][2][3] Their self-assemblies formed in solution have exhibited attractive application potentials for photorheological uids, novel materials and drug delivery. [4][5][6] By a supra-molecular strategy, through various noncovalent interactions like electrostatic or charge-transfer interactions, hydrogen bonding, van der Waals forces, p-p stacking, etc., the assemblies could be imparted with characteristics of versatility, exibility, and reversibility. [7][8][9] Among them, surfactants containing a ferrocene group have been frequently used due to their excellent redox-responsive character and perfect processability, which allow them to be widely employed in electrochemistry, liquid-crystalline materials, and sensing.…”