Predictive formulation of high-solid-content complex dispersions

尺寸为约1-50微米的固体颗粒在液相中的高固含量分散体（HSCD）普遍存在于工业应用中，从水泥和陶瓷浆料到催化剂修补基面涂料、油漆、食品和钻井液。这些不同产品的可靠和有效的加工和制造对配方技术提出了“巨大的挑战”，因为在高固体体积分数下，工艺流程和产品行为变得越来越不稳定和不可预测。但是在许多应用中，实现高体积分数通常是期望的：在一般的工艺流程中，以保持生产量并降低能量/材料成本;在陶瓷制造中，较高体积分数的绿色体烧结成机械强度更强的产品;增加用于喷雾干燥的浆料的体积分数减少干燥时间;较高体积分数的钻井液减少钻孔中的流体和气体流入和坍塌的问题。相反，大粘度下的不稳定流动有时实际上是期望的，只要它是可预测的，例如，在破碎聚集体以在混合器中分散催化转化器修补基面涂层或颜料方面。 在所有这些应用和许多其他应用中，控制和预测给定配方的流变学的能力-“拨号”所需的行为-将改变配方科学和HSCD的实践。然而，经验反复表明，随着体积分数的增加，流动和应力变得越来越不稳定，表征、测量、控制和预测变得越来越具有挑战性和不可靠。HSCD的常规流变学表征通常再现性差，并且在应用中遇到的复杂的非流变几何形状中也不能预测正确的流动行为。众所周知，超出制造商控制的微小变化，例如由于加工条件的不可预见变化或供应商的变化，可能会产生灾难性影响（例如，正常流动的制剂可能突然破裂而不是流动）。除此之外，工业应用跨越许多长度尺度，从< 100颗粒直径的挤出成型和印刷薄膜到超深的钻孔，因此预测和表征HSCD流面临着规模扩大和规模缩小的同时要求。面对这些普遍存在的挑战，由于高体积分数下的流动基础科学尚未被理解，预测性工程工具尚未建立，配方设计师经常诉诸于积累的经验和非正式程序，如“手指流变学”（手指之间摩擦样品！）指导他们的工作。因此，现有的配方往往是次优的，由这些配方产生的问题主要通过试错来解决，而与配方创新相关的风险严重限制了新产品和新工艺的开发。我们的愿景受到项目团队成员最近重大科学进展的启发，通过研究人员和主要多部门行业合作伙伴的紧密合作，改变HSCD制定的实践。我们新的科学认识将提供新的表征、测量、预测和控制方法，从而实现基于HSCD的产品的可靠工艺和制造。该项目将使制造商能够根据合理的设计原则，使用从特征良好的可重复流量测量中推导出的参数来制定产品。这种方法将在多个长度尺度和多个应用部门的控制和可预测性方面产生阶跃变化。

High-solid-content dispersions of solid particles of size about 1-50 microns in a liquid phase (HSCDs) occur ubiquitously in industrial applications, from cement and ceramic pastes to catalyst washcoats, paints, foods and drilling fluids. The reliable and efficient processing and manufacture of these diverse products presents 'grand challenges' to formulation technology because at high solids volume fraction process flow and product behaviour become increasingly unstable and unpredictable. But achieving high volume fraction is often desirable in many applications: in generic process flow, to maintain throughput and cut energy/materials costs; in ceramics manufacture, higher volume fraction green bodies sinter to mechanically stronger products; increasing volume fraction of a slurry for spray drying reduces drying time; higher volume fraction drilling fluids reduce problems of fluid and gas influx and collapse in bore holes. Conversely, unstable flow at large viscosity is sometimes actually desirable, as long as it is predictable, e.g., in breaking aggregates to disperse catalytic converter washcoats or pigments in a mixer. In all these applications and many others the ability to control and predict rheology for a given formulation--to 'dial up' required behaviour--would transform formulation science and practice with HSCDs. However, experience repeatedly shows that as volume fraction increases, the flow and stress become increasingly unstable, and characterization, measurement, control and prediction increasingly challenging and unreliable. Conventional rheological characterization of HSCDs is often poorly reproducible and also fails to predict correct flow behaviour in the complex, non-rheometric geometries encountered in applications. Notoriously, small changes beyond the manufacturer's control, e.g. due to unforeseen variations in processing conditions or a change in supplier, can have catastrophic effects (e.g. a normally flowable formulation can suddenly fracture rather than flow). On top of this, industrial applications span many length scales, from < 100-particle-diameter extrusion mouldings and printed films to kilometre-deep bore holes so that predicting and characterizing HSCD flow faces the simultaneous requirements of scale up and scale down. Faced with these ubiquitous challenges, and because the basic science of flow at high volume fraction is not understood and predictive engineering tools are not established, formulators often resort to accumulated experience and informal procedures such as 'finger rheology' (rubbing samples between fingers!) to guide their work. Thus, existing formulations are often sub-optimal, and problems arising from these formulations are solved mostly by trial and error, while the risk associated with formulation innovation severely limits development of new products and processes. Our vision, inspired by recent major scientific advances by members of the project team, is to transform practice in the formulation of HSCDs through a tight collaboration of researchers and major multi-sector industry partners. Our new scientific understanding will provide new methodology of characterization, measurement, prediction and control, leading to reliable process and manufacture of HSCD-based products. The project will enable manufacturers to formulate their products according to rational design principles, using parameters deduced from well-characterised reproducible flow measurements. This approach will yield step changes in control and predictability over multiple length scales and multiple application sectors.