Suman Khushboo, Shanbhag Sachin, Joshi Yogesh M
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India.
Department of Scientific Computing, Florida State University, Tallahassee, Florida 32306, USA.
J Chem Phys. 2023 Feb 7;158(5):054907. doi: 10.1063/5.0129416.
A system undergoing sol-gel transition passes through a unique point, known as the critical gel state, where it forms the weakest space spanning percolated network. We investigate the nonlinear viscoelastic behavior of a colloidal dispersion at the critical gel state using large amplitude oscillatory shear rheology. The colloidal gel at the critical point is subjected to oscillatory shear flow with increasing strain amplitude at different frequencies. We observe that the first harmonic of the elastic and viscous moduli exhibits a monotonic decrease as the material undergoes a linear to nonlinear transition. We analyze the stress waveform across this transition and obtain the nonlinear moduli and viscosity as a function of frequency and strain amplitude. The analysis of the nonlinear moduli and viscosities suggests intracycle strain stiffening and intracycle shear thinning in the colloidal dispersion. Based on the insights obtained from the nonlinear analysis, we propose a potential scenario of the microstructural changes occurring in the nonlinear region. We also develop an integral model using the time-strain separable Kaye-Bernstein-Kearsley-Zapas constitutive equation with a power-law relaxation modulus and damping function obtained from experiments. The proposed model with a slight adjustment of the damping function inferred using a spectral method, compares well with experimental data at all frequencies.
经历溶胶-凝胶转变的系统会经过一个独特的点，即临界凝胶态，在该状态下它会形成最弱的跨越空间的渗流网络。我们使用大振幅振荡剪切流变学研究了处于临界凝胶态的胶体分散体的非线性粘弹性行为。使临界点处的胶体凝胶在不同频率下承受应变幅度不断增加的振荡剪切流。我们观察到，随着材料从线性转变为非线性，弹性模量和粘性模量的一次谐波呈现单调下降。我们分析了整个转变过程中的应力波形，并获得了作为频率和应变幅度函数的非线性模量和粘度。对非线性模量和粘度的分析表明，胶体分散体中存在周期内应变强化和周期内剪切变稀现象。基于从非线性分析中获得的见解，我们提出了非线性区域中发生微观结构变化的一种可能情况。我们还使用时间-应变可分离的凯伊-伯恩斯坦-基尔斯利-扎帕斯本构方程以及从实验中获得的幂律松弛模量和阻尼函数，开发了一个积分模型。通过频谱方法对阻尼函数进行微调后的所提出模型，在所有频率下都与实验数据吻合良好。
