Experimental Study of Criticality & Crossover Phenomena in Complex Fluid Mixtures

临界性的实验研究

• 批准号: 9805260
• 负责人: Jan Sengers
• 金额: $ 41.3万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-08-01 至 2002-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9805260&HistoricalAwards=false
• 关键词: Experimental; Study; Criticality; & Crossover

Jan Sengers is supported by a grant from the Theoretical and Computational Chemistry program to perform experimental studies of criticality and crossover phenomena in complex fluid mixtures. This research will elucidate how the properties of complex fluids are affected by the interplay of the properties of the fluid very near the critical point, where the long range interactions are the cause of the universal behavior, and the classical mean field (van der Waals-like) region where the local microscopic structure plays the dominant role. The cross-over static and dynamic phenomena will be studied using optical techniques. A test of crossover from universal scaling behavior asymptotically close to the critical point to mean-field behavior upon increase of the distance from the critical point is proposed for solutions of polymers in low-molecular weight solvents. The hypothesis to be tested is that the extent of the crossover is affected by a competition between the correlation length of the critical fluctuations, and the size of the polymer molecule. The investigation will try to probe experimentally this point by performing highly accurate light scattering measurements of polymers and blends (ethane+ n-heptane, and ethane+ n- dodecane, as well as others such as methylcyclohexane and polystyrene) of varying chain lengths. The influence of the chain length on the correlation length of the critical fluctuations will be studied.A reliable understanding of phase-transition and critical behavior of complex fluids and fluid mixtures is needed for many innovative applications such as supercritical extraction, enhanced oil recovery, and supercritical pollution oxidation. Critical phenomena in fluids have been the subject of many experimental and theoretical studies, and the surprising result of these studies has been the discovery of phenomenon known as critical point universality: the observation that microscopic structure of fluids becomes unimportant in the vicinity of a critical point. The current study is directed at a detailed understanding of this phenomenon. This knowledge could have a substantial impact on a number of areas that rely on supercritical fluids for chemical processing.

简·斯泰尔斯得到了理论和计算化学计划的资助，以进行复杂流体混合物中临界性和交叉现象的实验研究。 这项研究将阐明复杂流体的性质是如何影响的流体性质的相互作用非常接近的临界点，长程相互作用的普遍行为的原因，和经典的平均场（货车范德华）区域的局部微观结构起主导作用。交叉静态和动态现象将使用光学技术进行研究。 本文提出了一个检验方法，检验了聚合物在低分子量溶剂中的溶液随离临界点距离的增加从渐近接近临界点的普适标度行为到平均场行为的交叉。 要测试的假设是，交叉的程度是受关键波动的相关长度之间的竞争，和聚合物分子的大小。 该研究将尝试通过对不同链长的聚合物和共混物（乙烷+正庚烷，乙烷+正十二烷，以及其他如甲基环己烷和聚苯乙烯）进行高度精确的光散射测量来实验性地探索这一点。研究了分子链长度对临界涨落关联长度的影响，为超临界萃取、提高原油采收率、超临界污染氧化等创新应用提供了可靠的理论依据。 流体中的临界现象一直是许多实验和理论研究的主题，这些研究的令人惊讶的结果是发现了被称为临界点普遍性的现象：观察到流体的微观结构在临界点附近变得不重要。 目前的研究旨在详细了解这一现象。 这一知识可能会对一些依赖超临界流体进行化学加工的领域产生重大影响。