论文标题
探测软材料中局部非线性粘弹性特性
Probing local nonlinear viscoelastic properties in soft materials
论文作者
论文摘要
可以衡量局部速率依赖机械性能的最小侵入性实验方法对于理解在广泛应用中软材料的行为至关重要。基于针头的测量技术，例如空化流变和体积控制的腔体扩展（VCCE），可以进行最小的侵入性局部机械测试，但仅限于测量弹性材料的性能。在这里，我们提出了VCCE技术的几种增强功能，以使其适应低至中延长速率（$ 10^{ - 2} $ - $ 1 $ S $ s $ {}^{ - 1} $）的粘弹性响应的表征。该提出的技术在腔扩张设置中以受控的拉伸速率进行了几个膨胀 - 浮肿的循环，然后采用较大的变形粘弹性模型来捕获测得的材料响应。该技术在软PDMS橡胶上的应用揭示了具有高精度和可重复性的显着依赖性材料响应，同时隔离了用于直接推断出准矛盾的弹性模量的平衡状态。通过证明其捕获可调PDMS系统速率依赖材料响应变化的能力，进一步确定了该技术。测得的粘弹性特性用于解释基于针的方法不敏感的材料响应的早期报道：证明常规使用恒定体积速率腔扩张可以引起高伸展速率，从而导致粘弹性加强和幻觉速率不敏感的材料响应。因此，我们在先前的研究中以高估了准息弹性模量可能高估的警告说明，并表明这项工作中提出的延长速率控制的扩展方案对于准确估算了准和动态材料参数至关重要。
Minimally invasive experimental methods that can measure local rate dependent mechanical properties are essential in understanding the behaviour of soft and biological materials in a wide range of applications. Needle based measurement techniques such as Cavitation Rheology and Volume Controlled Cavity Expansion (VCCE), allow for minimally invasive local mechanical testing, but have been limited to measuring the elastic material properties. Here, we propose several enhancements to the VCCE technique to adapt it for characterization of viscoelastic response at low to medium stretch rates ($10^{-2}$ - $1$ s${}^{-1}$). The proposed technique performs several cycles of expansion-relaxation at controlled stretch rates in a cavity expansion setting and then employs a large deformation viscoelastic model to capture the measured material response. Application of the technique to soft PDMS rubber reveals significant rate dependent material response with high precision and repeatability, while isolating equilibrated states that are used to directly infer the quasistatic elastic modulus. The technique is further established by demonstrating its ability to capture changes in the rate dependent material response of a tuneable PDMS system. The measured viscoelastic properties are used to explain earlier reports of rate insensitive material response by needle based methods: it is demonstrated that the conventional use of constant volumetric rate cavity expansion can induce high stretch rates that lead to viscoelastic stiffening and an illusion of rate insensitive material response. We thus conclude with a cautionary note on possible overestimation of the quasistatic elastic modulus in previous studies and suggest that the stretch rate controlled expansion protocol, proposed in this work, is essential for accurate estimation of both quasistatic and dynamic material parameters.
