REG: Imaging of Transition-State Microstructures in Surfactant Aggregates by Time-resolved Cryogenic Transmission Electron Microscopy

摘要cts-9809286 a。玻色/ U。罗德岛大学化学工程系将购买一台自动化的、气动驱动的混合和微升液体输送设备，并修改我们目前的受控环境玻璃化系统（CEVS），以便对基于表面活性剂的胶体中的非平衡微结构进行成像。这些实验代表了正在进行的对这些系统中聚合体形成和破碎动力学研究的一部分。在快速混合饲料溶液后，混合物将被输送到一个多孔的碳网格上，然后在控制的时间延迟后，通过吸盘进入冷冻机。这将允许标本在混合后的预定时间玻璃化，同时捕获聚集在其原生状态。这些样品具有明确的年龄，然后将使用低温透射电子显微镜进行检查，以便直接识别中间状态结构。对CEVS提出的改进将提供关键和独特的能力，以数十毫秒（对应于许多基于表面活性剂的系统的重要弛豫时间之一）甚至更高的分辨率对微结构进行成像。这些实验将使鉴定新的、潜在有用的、热力学亚稳态或动力学稳定的过渡态成为可能。还将进行一系列其他技术的补充实验，包括时间分辨小角中子散射和时间分辨静态和动态光散射。结合低温透射电镜，迄今为止，表面活性剂胶体体系相变动力学的最完整图像将能够开发，测量将进行一组精心挑选的单一和混合表面活性剂体系，在一定温度范围内，盐和两亲体浓度，和初始状态。将确定表面活性剂的化学性质、结构和溶液条件对自组装动力学的具体作用。将建立可用于调节聚合体形成和破裂的动力学以及过渡状态结构的关键变量。这些实验将导致对控制表面活性剂聚集体的自组装和分解的因素的全面和一般的理解，并将为理解更复杂的分子系统中的聚集奠定基础。他们将有助于设计平衡、亚稳或动力学稳定的表面活性剂基聚集体的策略，这些聚集体的寿命和形态可针对特定应用进行调整，如封装、药物输送、污染物去除和胶束超滤。它们还将为将来的结构转变和动力学模拟提供重要的比较数据。

ABSTRACT CTS-9809286 A. Bose/U. of Rhode Island The Department of Chemical Engineering at the University of Rhode Island will purchase an automated, pneumatically-driven mixing and microliter liquid delivery device, as well as modify our current Controlled Environment Vitrification System (CEVS) in order to image non-equilibrium microstructures in surfactant-based colloids. The experiments represent part of an ongoing investigation of the dynamics of aggregate formation and breakup in these systems. Following rapid mixing of feed solutions, the mixture will be delivered onto a holey carbon grid, then plunged past blotters into a cryogen after a controlled time delay. This will permit specimen vitrification at predetermined times after mixing, while trapping aggregates in their native states. These samples, with well-defined ages, will then be examined using cryogenic transmission electron microscopy, so that intermediate state structures can be identified directly. The proposed modification on the CEVS will give a critical and unique ability to image microstructures with a resolution of tens of milliseconds (corresponding to one of the important relaxation times in many surfactant-based systems) and higher. The experiments will enable identification of new, potentially useful, thermodynamically metastable or kinetically stable transition states. Complementary experiments using a range of other techniques, including time-resolved small angle neutron scattering and time-resolved static and dynamic light scattering will also be conducted. In conjunction with the cryo-TEM, the most complete picture of phase transition dynamics in surfactant colloidal systems to date will be able to be developed measurements will be made for a carefully selected set of single- and mixed-surfactant systems, over a range of temperatures, salt and amphiphile concentrations, and initial states. The specific roles played by surfactant chemistry, architecture and solution conditions on the kinetics of sel f-assembly will be determined. Key variables that can be used to modulate the dynamics of formation and breakup of aggregates, as well as transition-state structures, will be established. These experiments will result in a comprehensive and generic understanding of the factors that control self-assembly and breakup of surfactant aggregates, and will lay the ground work for understanding aggregation in more complex molecular systems. They will aid in the development of strategies for designing equilibrium, metastable or kinetically stable surfactant-base aggregates with lifetimes and morphologies tuned for specific applications such as encapsulation, drug delivery, contaminant removal and micellar ultrafiltration. They will also provide important data for comparison with future simulations of structural transitions and dynamics.