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

1133279 PI：提出了对接近玻璃化转变和堵塞转变的热敏胶体分散体的老化、动力学和流变学的基本研究。这项调查将PI在玻璃物理、老化和流变学方面的专业知识和经验运用到理解胶体玻璃的新颖且变革性的方法中。虽然相关的行为已被广泛研究的实验中，悬浮液已受到剪切变形在一个固定的浓度，有很少的作品，其中的响应后，快速，恒定的体积浓度变化。热敏颗粒的出现，如聚（N-异丙基丙烯酰胺）（PNIPAAM）系统的溶胀和解溶胀在水中随温度变化改变了这种情况，并提供了一个实验路线的承诺，以调查玻璃样行为，特别是，结构恢复为基础的行为的胶体分散体附近的玻璃或堵塞转变。除了这些颗粒的热敏性之外，它们也是气压敏感的，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，因为它有望验证或无效胶体物理学中的一个常见的基本假设，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堵塞行为相关的浓度范围内的行为有关。特别提出使用响应性PNIPAAM和PS/PNIPAAM核/壳颗粒沿沿着两条不同路径（T和P）穿过浓度相边界（液体到玻璃）进行温度和压力跳跃实验，使用漫射波光散射探测非平衡胶体的老化动力学。这些实验将提供第一个广泛的分类的结构恢复行为的胶体玻璃在科瓦奇编目签名的结构恢复，即，本征等温线、接近不对称性和记忆效应。结果将提供洞察粒子的“硬度”或“柔软度？和胶体玻璃脆性对老化的动力学影响。经典的物理老化实验，使用扭转流变仪也将进行热敏响应制度的Struik最初提出的分子玻璃的方法。虽然在文献中有很多工作，解决了集中的胶体系统的动力学的背景下的平衡动力学和他们的分歧与浓度，目前的工作是变革性的，因为它适用于有关的概念的非平衡行为的分子玻璃明确的浓度跳跃引起的热和压力响应性能的PNIPAAM为基础的胶体。因此，胶体系统的动力学的新的理解将被创建。该项目将为各级学生提供胶体表征和合成方法以及玻璃状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中学女生的外展活动。

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.