非离子表面活性剂Brij 30诱导离子液体型表面活性剂C16imC8Br蠕虫状胶束向凝胶的转变

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

蠕虫状胶束和小分子水凝胶是由具有粘弹性的三维网络构成。但它们具有不同的粘弹性。蠕虫状胶束以黏性为主,这主要是由暂时平衡的网络决定。凝胶以弹性为主,三维网状结构稳定。在某些情况下,蠕虫状的胶束通过网络结构的增强可以转化为凝胶。在我们之前的研究中发现由离子液体型表面活性剂1-十六烷基-3-辛基咪唑溴化铵([C16imC8]Br)形成的蠕虫状胶束在不含添加剂时,具有较高的粘弹性。非离子表面活性剂十二烷基聚氧四乙烯醚(Brij 30)的加入有望通过静电作用和疏水相互作用增强([C16imC8]Br)蠕虫状胶束的粘弹性,促进蠕虫状胶束向凝胶的转变。利用流变学和冷冻刻蚀透射电镜研究了具有Brij 30的蠕虫状胶束的微观形貌和粘弹性随浓度的变化。采用流变学方法研究了Brij 30/[C16imC8]Br凝胶的热稳定性和凝胶-溶胶转变温度。通过zeta电位测量和核磁共振研究了Brij 30和[C16imC8]Br之间的相互作用。在[C16imC8]Br的不同初始浓度下,Brij 30/[C16imC8]Br样品的粘弹性随Brij 30浓度的增大先增大后减小。在一定的Brij 30浓度下,Brij 30/[C16imC8]Br样品具有凝胶的流变特性。[C16imC8]Br(4.06%(w,质量分数))/Brij 30凝胶的黏弹性最大值出现在Brij 30/[C16imC8]Br的摩尔比(Mr)为4.55时。Brij 30/[C16imC8]Br凝胶的粘弹性与凝胶的活化能呈正相关。Brij 30/[C16imC8]Br凝胶的凝胶-溶胶转变温度也随着Brij30浓度的增加先升高后降低。Brij 30/[C16imC8]Br(4.06%(w))凝胶的最大值出现在Brij 30/[C16imC8]Br的摩尔比为2.93时。Brij 30浓度对Brij 30/[C16imC8]Br凝胶的粘弹性、热稳定性和凝胶-溶胶转变温度有很大影响。zeta电位和核磁氢谱测量结果表明,电中性Brij 30分子在疏水作用下插入到[C16imC8]Br虫状胶束的栅栏层。它减少了[C16imC8]Br头基之间的静电斥力,这种斥力导致了蠕虫状胶束的快速生长和更强的网状结构的形成。最后,蠕虫状胶束转变成凝胶。所得结果将有助于更好地理解蠕虫状胶束与凝胶之间的关系,具有潜在的工业和技术应用价值。

Wormlike micelles and low-molecularweight hydrogels are composed of threedimensional 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.