Jamming and Glass-like Behavior of Thermosensitve and Barosensitive Particulate Dispersions

热敏和气压敏感颗粒分散体的干扰和类玻璃行为

• 批准号: 1133279
• 负责人: Gregory McKenna
• 金额: $ 23.71万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1133279&HistoricalAwards=false
• 关键词: Jamming; Glass; like; Behavior; Thermosensitve

1133279PI: McKennaA fundamental investigation of the aging, dynamics and rheology of thermo-sensitive colloidal dispersions near to the glass and jamming transitions is proposed. The investigation brings the PI's expertise and experience in glassy physics, aging and rheology to bear in a novel and transformative approach to the understanding of colloidal glasses. While the relevant behaviors have been extensively studied in experiments in which the suspension has been subjected to shearing deformations at a fixed concentration, there are very few works in which the response is followed after rapid, constant volume concentration changes. The advent of thermosensitive particles, such as the poly(n isopropyl acrylamide) (PNIPAAM) systems that swell and deswell in water with temperature variation have changed this situation and offer the promise of an experimental route to investigate the glass-like behavior, and specifically, the structural recovery based behavior of colloidal dispersions near to the glass or jamming transition. In addition to the thermo-sensitivity of these particles they are also barosensitive, i.e., application of pressure can change the particle swelling, hence isotropic stresses (pressure changes) impose concentration changes. The proposed research offers a transformational outcome as it promises to validate or invalidate a frequent underlying hypothesis in colloid physics that the colloidal glass is a model system for molecular glasses. Furthermore, independent of the specific outcome of the hypothesis validation, highly novel experimental results will be obtained that are relevant to the behavior of colloidal systems in the range of concentrations that are related to glass-like or jamming behaviors. It is specifically proposed to perform the temperature- and pressure-jump experiments using responsive PNIPAAM and PS/PNIPAAM core/shell particles to cross the concentration phase boundary (liquid-to- glass) along a two different paths (T and P) using diffusing wave light scattering to probe the aging dynamics of the non-equilibrium colloids. These experiments will provide the first extensive cataloguing of the structural recovery behavior of colloidal glasses in the Kovacs catalogued signatures of structural recovery, viz., intrinsic isotherm, asymmetry of approach, and memory effect. The results will provide insights to effects of particle "hardness" or "softness?"and colloidal glass fragility on the aging dynamics. Classical physical aging experiments using torsional rheometry will also be performed in the thermosensitive response regime following the methods originally proposed by Struik for molecular glasses. While there is much work in the literature that addresses the dynamics of concentrated colloidal systems in the context of the equilibrium dynamics and their divergence with concentration, the present work is transformative in that it applies concepts related to the non equilibrium behavior of molecular glasses explicitly in concentration-jumps induced by the thermo- and baro response properties of the PNIPAAM-based colloids. Thus, new understanding of the dynamics of colloidal systems will be created. The project will provide research training and experience to students at all levels in the methods of characterizing and synthesis of colloids and the physics of glassy colloids. The PI and his graduate students will also be involved in outreach activities of middle-school girls.

1133279PI：McKenna 提出了对接近玻璃和干扰转变的热敏胶体分散体的老化、动力学和流变学的基础研究。这项研究利用了 PI 在玻璃物理学、老化和流变学方面的专业知识和经验，以一种新颖且变革性的方法来理解胶体玻璃。虽然相关行为在悬浮液在固定浓度下受到剪切变形的实验中得到了广泛的研究，但很少有研究在快速、恒定的体积浓度变化后跟踪响应。热敏颗粒的出现，例如在水中随温度变化膨胀和消膨胀的聚（正异丙基丙烯酰胺）（PNIPAAM）系统，改变了这种情况，并为研究玻璃状行为提供了实验途径，特别是，接近玻璃或干扰转变的胶体分散体基于结构恢复的行为。除了这些颗粒的热敏感性外，它们还具有压力敏感性，即施加压力可以改变颗粒的膨胀，因此各向同性应力（压力变化）会引起浓度变化。拟议的研究提供了一个变革性的结果，因为它有望验证或否定胶体物理学中常见的基本假设，即胶体玻璃是分子玻璃的模型系统。此外，独立于假设验证的具体结果，将获得高度新颖的实验结果，这些结果与胶体系统在与玻璃状或干扰行为相关的浓度范围内的行为相关。特别建议使用响应式 PNIPAAM 和 PS/PNIPAAM 核/壳颗粒进行温度和压力跳跃实验，以使用扩散沿着两个不同的路径（T 和 P）穿过浓度相边界（液体到玻璃）波光散射探测非平衡胶体的老化动力学。这些实验将首次对胶体玻璃的结构恢复行为进行广泛的分类，在 Kovacs 编目的结构恢复特征中，即固有等温线、方法不对称性和记忆效应。研究结果将为了解颗粒“硬度”或“柔软度”以及胶体玻璃脆性对老化动力学的影响提供见解。使用扭转流变仪的经典物理老化实验也将按照 Struik 最初提出的分子玻璃方法在热敏响应范围内进行。虽然文献中有很多工作在平衡动力学及其与浓度的发散的背景下解决了浓胶体系统的动力学问题，但目前的工作具有变革性，因为它明确地应用了与分子玻璃的非平衡行为相关的概念。由基于 PNIPAAM 的胶体的热和气压响应特性引起的浓度跳跃。因此，将对胶体系统动力学产生新的理解。该项目将为各级学生提供胶体表征和合成方法以及玻璃胶体物理学方面的研究培训和经验。 PI 和他的研究生也将参与针对中学生的外展活动。