Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan; Laboratory of Fluid Mechanics and Rheology, Department of Chemical Engineering, University of Patras, Patras 26500, Greece.
J Colloid Interface Sci. 2021 Nov;601:454-466. doi: 10.1016/j.jcis.2021.05.103. Epub 2021 May 21.
Under specific conditions, rod-like cellulose nanocrystals (CNC) can assemble into structurally ordered soft glasses (SGs) with anisotropy that can be controlled by applying shear. However, to achieve full structural control of SGs in real industrial processes, their response to mixed shear and extensional kinematics needs to be determined. We hypothesise that by knowing the shear rheology of the CNC-based soft glass and adopting a suitable constitutive model, it is possible to predict the structure-property relationship of the SG under mixed flows.
We use an aqueous suspension with 2 wt% CNC at 25 mM NaCl to form a structurally ordered SG composed of a CNC network containing nematic domains. We combine rheometry and microfluidic experiments with numerical simulations to study the flow properties of the SG in shear, extension, and mixed flow conditions. Extensional flow is investigated in the Optimised Shape Cross-slot Extensional Rheometer (OSCER), where the SG is exposed to shear-free planar elongation. Mixed flow kinematics are investigated in a benchmark microfluidic cylinder device (MCD) where the SG flows past a confined cylinder in a microchannel.
The SG in the MCD displays a velocity overshoot (negative wake) and a pronounced CNC alignment downstream of the cylinder. Simulations using the thixotropic elasto-visco-plastic (TEVP) model yield near quantitative agreement of the velocity profiles in simple and mixed flows and capture the structural fingerprint of the material. Our results provide a comprehensive link between the structural behaviour of a CNC-based SG and its mechanistic properties, laying foundations for the development of functional, built-to-order soft materials.
在特定条件下，棒状纤维素纳米晶体（CNC）可以组装成具有各向异性的结构有序软玻璃（SG），这种各向异性可以通过施加剪切来控制。然而，要在实际的工业过程中实现对 SG 的完全结构控制，需要确定它们对混合剪切和拉伸运动学的响应。我们假设，通过了解基于 CNC 的软玻璃的剪切流变特性，并采用合适的本构模型，有可能预测混合流下 SG 的结构-性能关系。
我们使用浓度为 2wt%的 CNC 在 25mM NaCl 水溶液中形成一个由含有向列畴的 CNC 网络组成的结构有序的 SG。我们将流变学和微流控实验与数值模拟相结合，研究 SG 在剪切、拉伸和混合流动条件下的流动特性。在优化形状十字缝拉伸流变仪（OSCER）中研究拉伸流动，其中 SG 暴露于无剪切的平面拉伸中。在基准微流控圆柱装置（MCD）中研究混合流动动力学，其中 SG 在微通道中流过受限圆柱。
MCD 中的 SG 显示出速度超调（负尾流）和圆柱下游 CNC 的明显取向。使用触变弹性粘塑性（TEVP）模型进行的模拟产生了简单和混合流动中速度分布的近乎定量的一致性，并捕捉到了材料的结构特征。我们的结果在基于 CNC 的 SG 的结构行为与其力学性能之间建立了全面的联系，为功能化、定制软材料的发展奠定了基础。
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