Acta Physico-Chimica Sinica ›› 2020, Vol. 36 ›› Issue (10): 1909049.doi: 10.3866/PKU.WHXB201909049

Special Issue: Frontiers in Colloid and Interface Chemistry

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Wormlike Micelle to Gel Transition Induced by Brij 30 in Ionic Liquid-Type Surfactant Aqueous Solution

Yimin Hu, Jie Han(), Rong Guo()   

  • Received:2019-09-26 Published:2020-06-11
  • Contact: Jie Han,Rong Guo E-mail:hanjie@yzu.edu.cn;guorong@yzu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21673202);the National Natural Science Foundation of China(21922202);the Priority Academic Program Development of Jiangsu Higher Education Institutions, China

Abstract:

Wormlike micelles and low-molecular-weight hydrogels are composed of three-dimensional networks that endow them with viscoelasticity, but their viscoelastic properties are markedly different. The viscosity of wormlike micelles is attributed to a transient network, while that of gels is due to a stable network. Under certain conditions, wormlike micelles can undergo transition to gels with an increase in the density of the network. In our previous study, we found that the wormlike micelle formed by the ionic liquid-type surfactant 1-hexadecyl-3-octyl imidazolium bromide ([C16imC8]Br) without any additive has high viscoelasticity. The inclusion of a nonionic surfactant polyoxyethylene lauryl ether (Brij 30) is expected to enhance the viscoelasticity of [C16imC8]Br wormlike micelles via electrostatic shielding and strong hydrophobic interactions, which may be the driving factor for the wormlike micelle-to-gel structural transition. The morphology and viscoelasticity of [C16imC8]Br wormlike micelles with Brij 30 were studied as a function of concentration by rheological measurements and freeze-fracture transmission electron microscopy. The thermal stability and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels were studied using rheology. The interaction between Brij 30 and [C16imC8]Br was studied by zeta potential measurements and nuclear magnetic resonance (NMR) spectroscopy. Upon the inclusion of Brij 30 into the [C16imC8]Br wormlike micelles, the viscoelasticity of the Brij 30/[C16imC8]Br samples first increased and then decreased with an increase in the Brij 30 concentration, at different initial concentrations of [C16imC8]Br. At a certain Brij 30 concentration, the Brij 30/[C16imC8]Br samples rheologically behaved as a gel. The maximum viscoelasticity of the [C16imC8]Br (4.06% (w))/Brij 30 gel was observed at a Brij 30/[C16imC8]Br molar ratio of 4.55. The viscoelasticity of the Brij 30/[C16imC8]Br gels was positively correlated with the activation energy of the gels. The gel-sol transition temperature of the Brij 30/[C16imC8]Br gels also increased first and then decreased with an increase in the Brij 30 concentration. The highest gel-sol transition temperature of the Brij 30/[C16imC8]Br (4.06% (w)) gel was observed at a Brij 30/[C16imC8]Br molar ratio of 2.93. The Brij 30 concentration had a notable impact on the viscoelasticity, thermal stability, and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels. The zeta potential and 1H NMR measurements revealed that the neutral Brij 30 molecules are inserted into the palisade layer of the [C16imC8]Br wormlike micelles via hydrophobic interactions. This decreased the electrostatic repulsion between the [C16imC8]Br headgroups, which in turn induced the rapid growth of wormlike micelles and the formation of a stiffer network structure. Finally, the wormlike micelles underwent a structural transition to gels. The obtained results would aid in better understanding the relationship between wormlike micelles and gels, and may be of potential value for industrial and technological applications.

Key words: Wormlike micelle, Gel, Ionic liquid-typed surfactant, Brij 30, Activation energy, Transition

MSC2000: 

  • O648