Controlling Rheology by Tuning Colloidal Interactions

通过调节胶体相互作用来控制流变

• 批准号: 1033851
• 负责人: Ralph Colby
• 金额: $ 29万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-15 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1033851&HistoricalAwards=false
• 关键词: Controlling; Rheology; Tuning; Colloidal; Interactions

Chain-like structures of colloidal particles, held together by van der Waals inter-particle forces, are being constructed. The interaction energy between the charged particles in these chains can be controlled and tuned by added salt, allowing chain-like structures with particle-particle interaction energies of 2-50 kT to be easily constructed. This is done by annealing two flat surfaces onto otherwise spherical polystyrene colloids. By adding the proper salt concentration, these charged colloids can be aggregated so that the two flats each associate with flats on other particles, in the secondary energy minimum between the particles, giving flexible polymer-like structures assembled from colloids with two flats. This allows study of the rheology of suspensions of these chains. The volume fraction of particles and the ionic strength will be adjusted in order to tune colloidal interactions. If the conditions that make colloidal polymers show rheopexy (aggregation under flow that we have observed in solutions of globular proteins and synovial fluids) can be identified, then their lubrication properties will be studied under conditions with and without rheopexy. This will be done in order to determine the connection between rheopexy and the superior lubrication in weakly structured fluids, thereby identifying the optimal interaction energy for lubrication.Spherical charged colloids with two flats are a model system with both the net charge repulsion and chain-like aggregation character of globular proteins, but the colloids allow interactions to be tuned simply by changing ionic strength and are large enough to be seen in an optical microscope. Identifying the connections between interaction energy, rheology and lubrication will have far-reaching consequences on fundamental understanding in biology and pedantic design of synthetic lubricants. Do globular proteins in synovial fluid just happen to have the interactions necessary to make synovial fluid have time-dependent rheology (rheopexy) and allow synovial fluid to be a superior lubricant to anything we know how to synthesize? Can superior lubricants then be designed based on this new understanding?By studying model systems of small particles, it is hoped to understand why the joint fluids of mammals are so much better lubricants than synthetic ones. There are practical implications for both understanding how joint fluids function and how better synthetic lubricants might be constructed. These research activities will be coupled with efforts to recruit Puerto Rican high school students into college and careers in science and engineering. Laura Mely Ramírez, the Chemical Engineering Ph.D. student on this project, plans annual returns to her alma mater, Academia María Reina (AMR) High School for girls in San Juan, Puerto Rico, to talk with students there about the opportunities that science and engineering offer. The current high school dropout rate in Puerto Rico is 51%, and that can be improved upon by providing students with a good role model, in Miss. Ramírez. AMR High School has yearly Career Days, and Miss. Ramírez plans to visit the school and spend a day discussing with students and showing demonstrations of nanotechnology.

通过货车范德华力将胶体颗粒连接在一起的链状结构正在被构建。这些链中带电粒子之间的相互作用能可以通过添加盐来控制和调节，从而可以容易地构建具有2-50 kT的粒子-粒子相互作用能的链状结构。 这是通过将两个平坦表面退火到另外的球形聚苯乙烯胶体上来完成的。通过添加适当的盐浓度，这些带电胶体可以聚集，使得两个平面各自与其他颗粒上的平面相关联，在颗粒之间的二次能量最小值中，给出由具有两个平面的胶体组装的柔性聚合物状结构。 这允许研究这些链的悬浮液的流变学。将调节颗粒的体积分数和离子强度以调节胶体相互作用。如果可以确定使胶体聚合物表现出粘流性（我们在球状蛋白溶液和滑液中观察到的流动下的聚集）的条件，那么将在有和没有粘流性的条件下研究它们的润滑性能。这样做是为了确定弱结构流体中的流变固定性和上级润滑之间的联系，从而确定润滑的最佳相互作用能。具有两个平面的球形带电胶体是一种模型系统，既具有球形蛋白质的净电荷排斥作用，又具有链状聚集特征，但是胶体允许通过改变离子强度来简单地调整相互作用，并且胶体大到足以在光学显微镜中看到。确定相互作用能、流变学和润滑之间的联系将对生物学的基本理解和合成润滑剂的迂腐设计产生深远的影响。滑液中的球状蛋白是否恰好具有必要的相互作用，使滑液具有时间依赖性流变性（流变固定性），并使滑液成为比我们已知的任何合成物更上级的润滑剂？那么，基于这种新的理解，能否设计出上级润滑剂？通过研究小颗粒的模型系统，人们希望了解为什么哺乳动物的关节液比合成的润滑剂好得多。 这对于理解关节液的功能以及如何构造更好的合成润滑剂都有实际意义。 在开展这些研究活动的同时，还将努力招收波多黎各高中生进入大学，从事科学和工程方面的职业。 Laura Mely Ramírez，化学工程博士这个项目的学生，计划每年回到她的阿尔马母校，波多黎各圣胡安的玛丽亚雷纳（AMR）女子高中，与那里的学生谈论科学和工程提供的机会。目前波多黎各的高中辍学率是51%，这可以通过为学生提供一个良好的榜样来改善，在密西西比州。拉米雷斯AMR高中每年都有职业日，小姐。Ramírez计划参观学校，花一天时间与学生讨论并展示纳米技术。