利用大幅振荡剪切研究Laponite凝胶的流变性质

Large Amplitude Oscillatory Shear Rheology of Laponite Gels

通过大幅振荡剪切(LAOS)流变学方法,研究了NaCl浓度对Laponite悬浮体系的结构及非线性黏弹性的影响.在线性黏弹性区,Laponite体系的储能模量G'随着NaCl浓度的增加而逐渐增大.体系的非线性黏弹性用响应应力的Fourier变换三次谐波的相对振幅I3/1与Lissajous曲线的定量参数GM,GL,ηM和ηL描述.当NaCl浓度较低时,I3/1随应变振幅γ0的增加而缓慢增加;当NaCl浓度较高时,I3/1随γ0的增加迅速增大,达到平台值.不同NaCl浓度试样的GM和GL随γ0变化的曲线区别不大,但ηM和ηL随γ0变化曲线在非线性区域出现峰值且区别较大.NaCl浓度越高,ηM和ηL出现峰值的γ0越小,峰值越大.结果表明,Laponite凝胶的非线性黏弹性与凝胶网络结构有关,随着NaCl浓度的增加,粒子间的静电相互作用距离缩短,粒子间距减小,形成了更紧密的网络结构.但这种网络在较大的应变下很容易被破坏,出现非线性黏弹性.

Effect of salt concentration on the rheology behavior of Laponite suspension was investigated with large amplitude oscillatory shear（LAOS） rheology.Nonlinear viscoelasticity of Laponite suspensions was demonstrated by the related amplitude I3/1,the minimum-strain modulus（GM）,large-strain modulus（GL）,minimum-strain rate viscosity（ηM）,and large-strain rate viscosity（ηL）.I3/1 increased gradually with γ0 for the samples with low NaCl concentration.As the concentration of NaCl increased,I3/1 increased abruptly with γ0 and reached a plateau value.The relationship of GM and GL parameters with γ0 showed no difference among samples with different NaCl concentrations.The ηM and ηL parameters exhibited a large peak in the relationship with γ0,which differed significantly among samples with different NaCl concentrations.The higher the NaCl concentration was,the higher the peak value was.These results suggested that the nonlinear viscoelasticity of Laponite gels depended on their network structure.By increasing NaCl concentration,the electrostatic interaction between Laponite particles was screened and the distance between Laponite particles was reduced,leading to a more condensed gel network.This network was easily broken under LAOS,showing obvious nonlinear viscoelasticity.