Sengupta Rajarshi, Tirumkudulu Mahesh S
Department of Chemical Engineering, Indian Institute of Technology Powai, Mumbai, India.
Soft Matter. 2016 Apr 7;12(13):3149-55. doi: 10.1039/c5sm03008k. Epub 2016 Feb 29.
Colloidal dispersions are known to display a fascinating network of cracks on drying. We probe the fracture mechanics of free-standing films of aqueous polymer-particle dispersions. Thin films of the dispersion are cast between a pair of plain steel wires and allowed to dry under ambient conditions. The strain induced on the particle network during drying is relieved by cracking. The stress which causes the films to crack has been calculated by measuring the deflection of the wires. The critical cracking stress varied inversely to the two-thirds' power of the film thickness. We also measure the velocity of the tip of a moving crack. The motion of a crack has been modeled as a competition between the release of the elastic energy stored in the particle network, the increase in surface energy as a result of the growth of a crack, the rate of viscous dissipation of the interstitial fluid and the kinetic energy associated with a moving crack. There is fair agreement between the measured crack velocities and predictions.
众所周知，胶体分散体在干燥时会呈现出迷人的裂缝网络。我们探究了水性聚合物颗粒分散体自支撑薄膜的断裂力学。将分散体的薄膜浇铸在一对普通钢丝之间，并在环境条件下干燥。干燥过程中颗粒网络上产生的应变通过开裂得以释放。通过测量钢丝的挠度计算出导致薄膜开裂的应力。临界开裂应力与薄膜厚度的三分之二次方成反比。我们还测量了移动裂纹尖端的速度。裂纹的运动被模拟为颗粒网络中储存的弹性能的释放、裂纹扩展导致的表面能增加、间隙流体的粘性耗散速率以及与移动裂纹相关的动能之间的竞争。测量得到的裂纹速度与预测结果相当吻合。
