Suspension Rheology at Constant Pressure

恒压悬浮液流变学

• 批准号: 1337097
• 负责人: John Brady
• 金额: $ 30万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1337097&HistoricalAwards=false
• 关键词: Suspension; Rheology; Constant; Pressure

1337097PI: BradyColloidal suspensions are widely used in industry, medicine and in natural environments, and encompass systems as diverse as toothpaste, paints, the interior of a cell and sprayable solar panels. Understanding the rheological properties of suspensions is critical to their processing, dispensing, durability and performance. Most studies of suspension rheology have been at fixed volume (or fixed volume fraction). While this may be adequate for many applications, often suspension flows are not at fixed volume but rather at fixed stress (or fixed pressure or pressure drop). Is the flow behavior the same at fixed volume and fixed pressure? If the volume fraction of suspended particles is low enough it should be possible to covert one measurement into the other. But as the maximum flowing fraction is approached, it is no longer clear that the two conditions will lead to the same flow behavior. A simulation study of colloidal suspensions at fixed pressure, allowing the system to dilate or contract and the volume fraction fluctuate as necessary, is proposed. The Accelerated Stokesian dynamics simulation methodology will be adapted to permit the simulation volume to change and used to study the flow behavior of Brownian hard-sphere suspensions as the strength of the shearing forces compared to thermal Brownian forces is varied over a wide range. Complete microscale detail is available from simulation, including particle distribution functions, order parameters, short- and long-time particle displacements, etc., and will connect the observed macroscopic behavior to the underlying particle dynamics. Particular attention will be focused on the flow behavior as the maximum flowing fraction is approached and the scaling of the flow properties near this point.Understanding suspension rheology is an important subject in its own right, but examining the flow behavior as the maximum flowing fraction is approached may have important implications for glassy and jammed systems. Colloidal dispersions at rest are known to form a glass at volume fractions near 0.58, well below random close packing (0.64 for monodisperse spheres). Experiment on both rapid granular flows and viscous non-Brownian suspensions at fixed pressure and shear stress have shown very similar behaviors: the ratio of shear to normal stress - the friction coefficient - is the same in the two systems, as is the maximum flowing volume fraction, despite the very different microscale physics - inertial dynamics versus viscous forces. It is quite possible that Brownian colloidal dispersions will display a similar behavior, which would then make an important link between jammed granular media and colloidal glasses. If demonstrated, such a connection would transform our understanding of glasses and jammed systems, and possibly provide a universal understanding of jamming.This research will enable the design, at the particle scale, of colloidal dispersions to meet the flow requirements of specific applications in, for example, the paints and coatings industry, thus reducing energy consumption and product waste. Contributing to the understanding of glasses and glass-forming systems, and particular their dynamic properties, would have broad impact across disciplines from fundamental physics and chemistry to biology - the motion of proteins and protein complexes in the crowded interior of a cell has strong similarities with the hindered and heterogeneous motion in colloidal glasses. Finally, the graduate student supported by this research will be well-trained in continuum and statistical mechanics, colloidal physics and computational science, and will join the scientific workforce of the nation.

1337097PI：胸骨悬浮液被广泛用于工业，医学和自然环境中，并包含像牙膏一样多样化的系统，油漆，细胞的内部和可喷涂的太阳能电池板。了解悬浮液的流变特性对于它们的处理，分配，耐用性和性能至关重要。大多数悬浮流变学研究的固定体积（或固定体积分数）。尽管这可能适合许多应用，但悬架流通常不是固定体积，而是在固定压力下（或固定压力或压力下降）。在固定体积和固定压力下，流动行为是否相同？如果悬浮颗粒的体积分数足够低，则应该可以将一个测量掩盖到另一个测量中。但是，随着最大流动分数接近，不再清楚这两个条件将导致相同的流动行为。提出了对固定压力下胶体悬浮液的模拟研究，使系统得以扩张或收缩，并且提出了必要的体积分数波动。加速的Stokesian动力学仿真方法将被调整，以允许模拟体积变化，并用于研究布朗硬球悬浮液的流动行为，因为与热棕色力量相比，剪切力的强度在广泛的范围内变化。完整的微观细节可从仿真中获得，包括粒子分布函数，顺序参数，短时和长时间的粒子位移等，并将将观察到的宏观行为连接到基础粒子动力学。当接近最大流动分数并在此点附近的流量范围时，将特别关注流动行为。理解悬架流变性本身就是一个重要的主题，但是检查流动行为随着最大流动分数而接近最大的流动行为可能对玻璃系统和干扰系统具有重要意义。已知静止的胶体分散体在0.58附近的体积分数形成一个玻璃，远低于随机关闭堆积（单分散球体为0.64）。在固定压力和剪切应力下的快速颗粒流和粘性的非棕色悬浮液的实验表现出非常相似的行为：在两个系统中，剪切与正常应力的比率是摩擦系数 - 摩擦系数 - 尽管具有非常不同的显微镜物理学 - 惯性动力学 - 惯性动力学非常不同，但在两个系统中都是相同的。棕色胶体分散剂很可能会显示出类似的行为，然后在堵塞的颗粒培养基和胶体玻璃杯之间建立重要的联系。如果证明了这种联系，这种联系将改变我们对眼镜和障碍系统的理解，并可能对障碍物有普遍的理解。这项研究将使胶体分散剂的设计能够满足特定应用程序的流动要求，例如，涂料和涂料行业，从而减少能源消耗和产品废物。从基本的物理学和化学到生物学的跨学科，蛋白质和蛋白质复合物在细胞拥挤的内部的蛋白质和蛋白质复合物的运动中，对玻璃和玻璃形成系统的理解及其动态特性的贡献将产生广泛的影响。最后，这项研究支持的研究生将在连续和统计力学，胶体物理学和计算科学方面受过良好的培训，并将加入国家的科学劳动力。