微小槽道内向列型液晶非对称流动特性及机理研究

Microfluidic chips are widely applied in biology, medicine, chemical engineering and numerous other fields. Microvalve is the core component of microfluidic chips to control flow. Existing temperature-control microvalves have various features, but they have such weaknesses in common as complex structure, difficulties in processing and integration and so on, which hinders the rapid development of microfluidic chips. This project proposes a new way to realize an intelligent mass transport and control by means of the asymmetric flow of nematic liquid crystals in microchannels with non-uniform temperature field. We focus on the key question, the formation mechanism of the asymmetric flow of nematic liquid crystals, by studying the flow of nematic liquid crystals confined in microchannels and subjected to a horizontal temperature gradient. Experiments and simulations are combined to analyze the influence of temperature on physical parameters of nematic liquid crystals. New correlations of physical parameters of nematic liquid crystals are fitted. The fundamental characteristics of the flow and temperature distribution of nematic liquid crystals in microchannels are obtained. The effect of the temperature distribution on the asymmetric flow of nematic liquid crystals is explored. Then, it is to reveal the coupling mechanism of the flow and temperature fields of nematic liquid crystals. Moreover, the evolution of the asymmetrical distribution of the flow profile is discussed with various aspects of microchannels. Finally, the formation mechanism of the asymmetric flow of nematic liquid crystals is clarified. Some innovative achievements in terms of the flow, mass transport and control of nematic liquid crystals in microchannels are expected to be made in this project, which will build a theoretical foundation for the new temperature-control microvalve based on nematic liquid crystals, as well as stimulating the development of microfluidic chips.

微流控芯片广泛应用于生物、医药和化工等众多领域，微阀是其控制流体的核心元件。现有温控微阀各具特色，但普遍存在结构复杂、加工和集成化难度大等问题，阻碍了微流控芯片的快速发展。本项目提出利用非均匀温度场下微小槽道内向列型液晶非对称流动特性来实现智能化质量输运与控制的设想，以水平温度梯度下微小槽道内向列型液晶流动过程为研究对象，紧紧抓住“向列型液晶非对称流动形成机理”关键科学问题，采用实验测量和数值模拟相结合的方法，分析温度对向列型液晶物性参数的影响规律，拟合物性参数新关联式，认知向列型液晶温度分布和流动的基本特性，揭示向列型液晶温度场与流场耦合机制，探讨微小槽道深宽比对向列型液晶非对称流动的影响规律，最终阐明向列型液晶非对称流动的形成机理。本项目有望在微小槽道内向列型液晶流动及质量输运与控制方面取得创新性成果，从而为基于向列型液晶新型温控微阀的发展奠定理论基础，为微流控芯片提供新的动力。

微流控芯片广泛应用于生物、医药和化工等众多领域，微阀是其控制流体的核心元件。现有温控微阀各具特色，但普遍存在结构复杂、加工和集成化难度大等问题，阻碍了微流控芯片的快速发展。本项目提出了利用非均匀温度场下微小槽道内向列相液晶非对称流动特性来实现智能化质量输运与控制的设想。采用实验测量和数值模拟相结合的方法，研究了水平温度梯度下微小槽道内向列相液晶流动过程。结果表明：（1）向列相液晶旋转粘度和弹性系数等物性参数均会受温度、浓度、掺杂盐和碱及其浓度的影响。平行于向列相液晶指向矢方向的导热系数和热扩散系数均大于垂直于指向矢方向。建立了与温度和浓度等相关的物性参数新关联式，其中，旋转粘度新关联式的最大相对误差为22.60%。（2）提出了基于流变仪间接获得向列相液晶剪切能的新方法，与X射线衍射仪测量结果相比，最大相对误差仅为3%，但研究成本降低约60%。此外，提出了基于向列相溶致液晶自组装能力随温度变化规律的“一步法”，用于研究分子长径比对物性参数等影响。（3）验证了向列相热致液晶的粘弹耦合理论在溶致液晶中的适用性，实验与理论分析结果最大误差为22.61%。（4）水平温度梯度作用下，微小槽道内高温区向列相液晶流速明显高于低温区，高低温区速度差和分流比会随水平温差增大而增大。而在一般流体中，并未发现非对称流动现象。（5）随着微小槽道深宽比的增大，向列相液晶浮力效应几乎可以忽略，但壁面锚定作用强度逐渐减小，微小槽道内流动的非对称性减弱，高低温区分流比呈减小趋势。向列相液晶粘弹耦合关系是产生非对称流动的主要因素。本项目研究结果对发展复杂流体流动传热理论、拓展向列相液晶应用领域和推动微流控芯片的快速发展有重要的意义。