An insight into the thermo-thickening behavior of wormlike micellar solutions based on ultra-long-chain surfactants

Quan Yin; Qiang Tian; James Doutch; Asante O Frimpong; Xiao Xu; Hongyao Yin; Peixun Li; Yujun Feng

doi:10.1039/d2cp00687a

An insight into the thermo-thickening behavior of wormlike micellar solutions based on ultra-long-chain surfactants

Phys Chem Chem Phys. 2022 May 11;24(18):11112-11123. doi: 10.1039/d2cp00687a.

Authors

Quan Yin¹, Qiang Tian², James Doutch³, Asante O Frimpong⁴, Xiao Xu⁴, Hongyao Yin¹, Peixun Li³, Yujun Feng¹

Affiliations

¹ Polymer Research Institute, State Key Laboratory Polymer Materials Engineering, Sichuan University, Chengdu 610065, China. yjfeng@scu.edu.cn.
² State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China.
³ ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OXON OX11 0QX, UK. peixun.li@stfc.ac.uk.
⁴ School of Chemistry and Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.

PMID: 35475436
DOI: 10.1039/d2cp00687a

Abstract

Generally, the solution viscosity of wormlike micelles (WLMs) assembled from common surfactants decreases upon an increase in the temperature, following the Arrhenius law. However, abnormal thermo-thickening behavior has been repeatedly observed for WLMs formed by ultra-long-chain (≥C18) surfactants. It would be useful to unravel the mechanism behind this phenomenon. Here, three C₂₂-tailed surfactants with an erucyl tail, two of them containing carboxylate or sulfonate head groups (UC₂₂DAB and UC₂₂DAS) and a cationic one with an iodide counterion (UC₂₂DAI), and two C₁₈-tailed betaines with olemido- and stearamidopropyl hydrophobic chains (UC₁₈DAS and C₁₈DAS) were characterised in terms of their viscosity and viscoelastic behavior with increasing temperature to examine the roles of head groups, tail length and tail nature. Their micellar structures were elucidated at various temperatures using small angle neutron scattering (SANS), small angle neutron X-ray scattering (SAXS) and molecular dynamics simulation. It is found that the thermo-thickening behavior of ultra-long-chain surfactants is ascribed to the prolonged persistence length and increased entanglement points. When the temperature is increased, an increase in viscosity is always accompanied by a longer persistent length, thus a larger hydrodynamic volume. The iceberg structure around the hydrophobic tail of surfactants can be destroyed at high temperatures leading to the self-assembly of these surfactants. In this self-assembly process, compared to cationic surfactants, zwitterionic surfactants can form WLMs more readily due to weak electrostatic repulsions between their head groups; the longer tails give the surfactants enhanced hydrophobicity to form WLMs with a long breaking time; the cis-unsaturation and the resulting kink in the hydrophobic tails give the surfactants good solubility, which is not conducive to the formation of micelles. In brief, the zwitterionic, longer tail and saturated tail surfactants can form WLMs with a prolonged persistence length at elevated temperatures.