Accelerated versus decelerated settling velocity of a drop

液滴的加速与减速沉降速度

• 批准号: 1262718
• 负责人: Thomas Ward
• 金额: $ 25.1万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1262718&HistoricalAwards=false
• 关键词: Accelerated; versus; decelerated; settling; velocity

1236316WardEmulsions are liquid-liquid mixtures that are subject to sedimentation driven by gravitational forces. Examples of dilute-dispersed phase emulsions that are relevant for biological applications, or derived from bio-materials, include pharmaceutical drugs (e.g. propofol), topical creams (e.g. facial creams) and vegetable oil fuel emulsions. These emulsions are all derived from some form of lipid (fatty acid, triglyceride) that may be converted directly in a surfactant via a hydrolysis or saponification chemical reaction. Converting a percentage of the fatty acids directly into a surfactant would provide an easy one step process for stabilizing certain biologically relevant emulsion. It is well known that surfactants, when adsorbing to an interface from the bulk-dispersed phase, will lead to decelerated motion of a droplet. The decelerated motion is caused by a Marangoni stress generated by concentration gradients due to the accumulation of surfactant at the rear of the droplet that oppose droplet sedimentation. The researchers will study a process to generate desorption dominated motion which would cause a reversal in the Marangoni stresses and therefore produce accelerated droplet motion when compared with sedimentation of a droplet with a clean interface. To generate stresses that cause droplet acceleration one must produce more surfactant at the interface than the long elapsed time, equilibrium surface coverage value. The researchers will demonstrate that this stress reversal may be produced by generating surfactant at the interface through a fast chemical reaction. A key objective of this proposal is a study of both accelerated and decelerated steady low Reynolds number droplet sedimentation in a viscous liquid. The unique feature in this project is droplet sedimentation in the presence of dilute surfactant species generated by an interfacial chemical reaction. The study includes a combination of experiments and mathematical/computational analyses. The goal is to experimentally measure the translational velocity of a single droplet as a function of the input parameters which are the reactant types (vegetable oils and dispersed-aqueous sodium hydroxide), concentration of reactants, and droplet volume. Parallel to the experiments, a mathematical analysis is performed using a power series expansion of Legendre and Gegenbauer polynomials to satisfy the steady interfacial species conservation laws containing thermodynamic relationships for adsorption/desorption and chemical reaction kinetics combined with momentum transport equations in the Stokes flow limit.This project will explore novel physical phenomenon associated with the sedimentation speed of a single droplet. The research should provide additional insight for current and future processes that utilize the long term storage of dilute emulsions since these processes depend on the velocity of a single sedimenting droplet. Further understanding of long term storage processes will be vital for emulsions produced from biological material since decomposition limits their shelf life. An undergraduate student from an HBCU will work in the PI's lab during the summer to participate in the project. The research results also will be disseminated though departmental websites and at conference meetings.

1236316Ward 乳液是液液混合物，会在重力驱动下发生沉淀。与生物应用相关或衍生自生物材料的稀分散相乳液的例子包括药物（例如异丙酚）、外用霜剂（例如面霜）和植物油燃料乳液。这些乳液均源自某种形式的脂质（脂肪酸、甘油三酯），可以通过水解或皂化化学反应直接在表面活性剂中转化。将一定百分比的脂肪酸直接转化为表面活性剂将为稳定某些生物相关乳液提供简单的一步过程。 众所周知，当表面活性剂从本体分散相吸附到界面时，会导致液滴运动减速。减速运动是由浓度梯度产生的马兰戈尼应力引起的，该应力是由于表面活性剂在液滴后部的积累而阻碍液滴沉降而产生的。研究人员将研究一种产生解吸主导运动的过程，该过程会导致马兰戈尼应力逆转，因此与具有干净界面的液滴沉降相比，会产生加速的液滴运动。为了产生导致液滴加速的应力，必须在界面处产生比经过较长时间的平衡表面覆盖值更多的表面活性剂。研究人员将证明，这种应力逆转可能是通过快速化学反应在界面处产生表面活性剂来产生的。该提案的一个关键目标是研究粘性液体中加速和减速稳定的低雷诺数液滴沉降。该项目的独特之处在于，在界面化学反应产生的稀释表面活性剂物质存在的情况下，液滴沉积。该研究包括实验和数学/计算分析的结合。目标是通过实验测量单个液滴的平移速度，作为输入参数的函数，这些输入参数是反应物类型（植物油和分散的氢氧化钠水溶液）、反应物浓度和液滴体积。与实验并行，使用勒让德和格根鲍尔多项式的幂级数展开进行数学分析，以满足稳定界面物质守恒定律，其中包含吸附/解吸热力学关系和化学反应动力学，并结合斯托克斯流量极限中的动量传递方程。该项目将探索与单个液滴沉降速度相关的新颖物理现象。 这项研究应该为当前和未来利用稀释乳液长期储存的过程提供更多的见解，因为这些过程取决于单个沉降液滴的速度。进一步了解长期储存过程对于由生物材料生产的乳液至关重要，因为分解限制了其保质期。 HBCU 的一名本科生将在暑假期间在 PI 的实验室工作，参与该项目。研究结果还将通过部门网站和会议传播。