Microfluidics of Complex Fluids: Extensional Rheology from Optimisation to Experiment

微流体技术在能源、医学、生物技术、化学和工程等领域都有广泛的应用。目前，微流控设备的市场规模约为每年15亿美元，并将在未来几十年内不断增长。例子包括用于生产乳剂的芯片实验室设备、化学反应器、医疗诊断、药物和化学品的输送、生物材料的分离和标记以及分析化学。许多此类应用需要处理复杂流体（例如聚合物溶液或生物流体），这些流体具有非牛顿流变行为，如剪切变薄和粘弹性，其效果在微观尺度上得到增强。对于粘弹性复杂流体而言，由于流体具有较强的拉伸增稠特性，拉伸对流体行为的影响往往导致比牛顿流体大得多的流动阻力。这使得粘弹性流体拉伸特性的全面实验表征在工业环境中至关重要：-准确描述其行为，-有效控制其流动，-设计高效安全的设备/组件，-检测其成分中的细微差异（例如，用于产品质量控制），-用于最终产品的质量保证（例如，在聚合物或食品加工行业）。此外，粘弹性生理流体的性质(例如：滑液（唾液和血液）与其功能密切相关，拉伸粘度的变化提供了液体降解和无法实现所需体内功能的迹象。关于健康和患病生物液体的流变学信息必然会对疾病（例如糖尿病和关节炎患者）的发生和进展提供新的认识，从而导致改进治疗方法和模拟物或假体液体的配方。本课题的目标是开发一种基于微流体的拉伸流变仪设计；这需要在形状优化计算工具的指导下进行复杂的实验。弱粘弹性流体的拉伸特性的微流体表征将为使用传统仪器实际上难以解决的重要流体力学提供新的见解。该项目的技术成果将是一个概念验证的最佳拉伸流变仪设计；工程科学成果将是在微观尺度上对粘弹性流动的新见解。长期影响将是对使用粘弹性流体的过程（例如喷墨印刷和涂层过程）的更高程度的控制，这可能会为这些材料的新应用打开大门，目前还无法预见。

Microfluidics finds application in technologies ranging across energy, medicine, biotechnology, chemistry and engineering. The current market for microfluidic devices is some US$1.5Bn per year, and is set to rise over coming decades. Examples include lab-on-a-chip devices for the production of emulsions, chemical reactors, medical diagnostics, the delivery of drugs and chemicals, isolation and tagging of biomaterials, and analytical chemistry. Many of these applications require handling complex fluids (e.g. polymeric solutions or biofluids) that have non-Newtonian rheological behaviour, such as shear thinning and viscoelasticity, the effects of which are enhanced at the microscale. For viscoelastic complex fluids the effect of extension on the fluid behaviour often leads to much larger flow resistances than with Newtonian Fluids due to strong extensionally-thickening behaviour. This makes thorough experimental characterisation of the extensional properties of viscoelastic fluids crucial in an industrial context:- to accurately describe their behaviour,- to effectively control their flow,- for designing efficient and safe devices/components,- to detect subtle dissimilarities in their composition (e.g. for product quality control),- for quality-assurance of the final product (e.g. in polymer or food processing industries).Moreover, properties of viscoelastic physiological fluids (eg. synovial fluid, saliva and blood) are closely linked to their functionality, and changes to the extensional viscosity provide indications of fluid degradation and an inability to achieve the desired in vivo functionality. Rheological information about healthy and diseased biofluids is bound to shed new light upon the onset and progression of diseases (e.g., diabetes and arthritis sufferers), leading in turn to improved therapeutics and formulation of analogue or prosthetic fluids.The project aim is to develop a microfluidic-based extensional rheometer design; this requires sophisticated experiments guided by shape-optimisation computational tools. Microfluidic characterisation of the extensional properties of weakly viscoelastic fluids will provide new insight into important fluid mechanics that is practically intractable using conventional instruments. The project's technological outcome will be a proof-of-concept optimal extensional rheometer design; the engineering science outcome will be new insight into viscoelastic flows at the microscale. The long-term impact will be a much higher degree of control over processes using viscoelastic fluids (e.g. inkjet printing and coating processes), and this is likely to open the door to new, currently unforeseen, applications of these materials.