触变/非触变水凝胶的傅里叶变换流变学研究

FOURIER-TRANSFORM RHEOLOGY OF THIXOTROPIC/NON-THIXOTROPIC HYDROGELS

通过傅里叶变换流变学(FTR)方法,考察了2种屈服应力流体(触变性凝胶和非触变性凝胶)在不同频率大振幅振荡剪切流场(LAOS)下的非线性流变行为.研究发现2种凝胶不同的内部结构对LAOS下的非线性行为和屈服转变行为有显著的影响.对于非触变性凝胶,其非线性强度随应力的增大呈连续变化的趋势,并且转变过程体现了微结构单元形变、松弛以及相对滑移与振荡频率的耦合关系;而对于触变性凝胶,其非线性强度随应力增加呈现非单调变化,表明了固液转变过程是通过多次的局部结构破坏发生的。

The nonlinear viscoelasticity of a thixotropic yield stress fluid（3.0 wt% Laponite hydrogel） and a non-thixotropic one（0.25 wt% Carbopol hydrogel） under large amplitude oscillatory shear（LAOS） was investigated by Fourier-transform rheology（FTR）.The relative intensities of the 3rd harmonic（I3/I1） and the relative phase angle of the 3rd harmonic（Φ3） of these two hydrogels under different stress amplitudes were compared.It is found that both the nonlinear viscoelasticity and the solid-liquid transition behavior of these two hydrogels differ greatly because of their different microscopic structures.For the Carbopol hydrogel,the nonlinear intensities change gradually with the increase of applied stress,and the transition behavior shows the correlations between the deformation,relaxation as well as relative slip of the microgel particles and the oscillatory frequency.While for the Laponite hydrogel,the nonlinear viscoelasticity exhibits a non-monotonic change,which indicates several times of shear rupture of local house-of-card structure before the full solid-liquid transition.