Tamim Saiful I, Bostwick Joshua B
Department of Mechanical Engineering, Clemson University, Clemson, SC, 29634, USA.
NPJ Microgravity. 2021 Nov 2;7(1):42. doi: 10.1038/s41526-021-00169-1.
A soft viscoelastic drop has dynamics governed by the balance between surface tension, viscosity, and elasticity, with the material rheology often being frequency dependent, which are utilized in bioprinting technologies for tissue engineering and drop-deposition processes for splash suppression. We study the free and forced oscillations of a soft viscoelastic drop deriving (1) the dispersion relationship for free oscillations, and (2) the frequency response for forced oscillations, of a soft material with arbitrary rheology. We then restrict our analysis to the classical cases of a Kelvin-Voigt and Maxwell model, which are relevant to soft gels and polymer fluids, respectively. We compute the complex frequencies, which are characterized by an oscillation frequency and decay rate, as they depend upon the dimensionless elastocapillary and Deborah numbers and map the boundary between regions of underdamped and overdamped motions. We conclude by illustrating how our theoretical predictions for the frequency-response diagram could be used in conjunction with drop-oscillation experiments as a "drop vibration rheometer", suggesting future experiments using either ultrasonic levitation or a microgravity environment.
一个柔软的粘弹性液滴的动力学由表面张力、粘度和弹性之间的平衡所支配，其材料流变学通常与频率有关，这些特性被用于组织工程的生物打印技术以及抑制飞溅的液滴沉积过程中。我们研究了柔软粘弹性液滴的自由振荡和受迫振荡，推导了（1）具有任意流变学特性的柔软材料自由振荡的色散关系，以及（2）受迫振荡的频率响应。然后我们将分析限制在开尔文 - 沃伊特模型和麦克斯韦模型的经典情况，它们分别与软凝胶和聚合物流体相关。我们计算了复频率，其由振荡频率和衰减率表征，因为它们取决于无量纲弹性毛细管数和德博拉数，并绘制了欠阻尼和过阻尼运动区域之间的边界。我们通过说明如何将我们对频率响应图的理论预测与液滴振荡实验结合起来用作“液滴振动流变仪”来得出结论，并提出了未来使用超声悬浮或微重力环境的实验建议。
