Acquisition of a High Vacuum Freeze-Fracture System for Microstructural Characterization of Complex Fluids and Biomaterials

从微米到纳米尺度的复杂流体和生物材料的表征对于新型药物递送系统、新型介孔材料、聚合物-表面活性剂相以及其他自组装和软材料系统的设计和优化至关重要。虽然更常用的技术，如x射线、中子和光散射，揭示了这些长度尺度上的平均结构特征，但很难用单个实验甚至单个散射技术来检查从纳米到数百微米的范围。用电子显微镜成像复杂的流体和生物材料是散射研究的必要补充，特别是因为显微镜直接解决了散射的主要局限性。然而，高分辨率成像有其自身的实验局限性：流体样品必须被原始材料的固体、导电、低蒸汽压版本所取代，以满足电子或扫描隧道显微镜的要求。经验表明，制备STM透射电镜样品的最佳方法是快速冷冻，然后进行冻裂复制。在冻裂复制中，快速冻结的试样在低温和高真空条件下断裂，以暴露流体的内部结构。然后通过蒸发金属遮蔽膜来复制断口表面，以提供TEM图像的对比度或STM的导电性，然后使用碳背衬膜为后续处理和成像提供足够的强度。该技术的横向分辨率约为2nm，纵向分辨率约为0.5 nm。该技术已被证明是一系列复杂流体和生物材料的理想选择，包括聚合物和表面活性剂凝胶、表面活性剂胶束和微乳液、生物膜、层状、六边形和立方表面活性剂液晶、囊泡、脂质体、热致液晶等，并能同时解析纳米级颗粒及其顺序、取向和缺陷到100微米的长度尺度。该合同为一种新的冷冻破裂系统提供了支持，该系统将显著提高样品的吞吐量，将每次样品运行的周转时间从约8小时减少到约1小时。在新设备中，样品通过真空气闸加载，电子束蒸发源也可以通过气闸进行外部调节。因此，主真空室从不通风。在我们目前的仪器上，必须打破真空来引入试样，更换蒸发源，并在处理后取出试样。每次样品运行要求主腔至少排气3次，其间有必要的泵停机时间。更快的周转将使我们能够更有效地检查更多的样品，更好的真空将提供更高的分辨率和更少的由于污染造成的伪影。新设备上的蒸发器由外部控制，以提供更高分辨率的复制膜，减少停机时间。冻裂设备将提供给系里和学校的其他研究人员。加州大学圣巴巴拉分校的仪器被一个研究复杂流体和生物材料的科学家合作小组大量使用，也被加州（Depotech, Alliance Pharmaceuticals）和其他地方（U. Delaware）的工业和学术合作者大量使用。陶氏化学)。% % % * * *

9802591ZasadzinskiCharacterization of complex fluids and biomaterials from the micron to nanometer scale is extremely important for the design and optimization of novel drug delivery systems, new mesoporous materials, polymer-surfactant phases and other self-assembling and soft material systems. While more commonly used techniques such as x-ray, neutron, and light scattering reveal much about the averaged structural features over these length scales, it is difficult to examine the range from nanometers to hundreds of microns with a single experiment or even a single scattering technique. Imaging complex fluids and biomaterials with electron microscopy is a necessary complement to scattering studies, especially as microscopy directly addresses the main limitations of scattering. However, high resolution imaging has its own experimental limitations: the fluid sample must be replaced by a solid, conductive, low vapor pressure version of the original material to be compatible with the requirements of electron or scanning tunneling microscopy. Experience has shown that the best method of making samples for TEM of STM is by rapid freezing, followed by freeze-fracture replication. In freeze-fracture replication, the rapidly frozen specimen is fractured at low temperature and high vacuum to expose the interior structure of the fluid. The fracture surface is then replicated by evaporation of a metal shadowing film to provide contrast in the TEM image or conductivity for STM, followed by a carbon backing film to provide sufficient strength for subsequent processing and imaging. The resolution in the technique is about 2 nm lateral and 0.5 nm vertical. The technique has proven to be ideal for a range of complex fluids and biomaterials including polymer and surfactant gels, surfactant micelles and microemulsions, biomembranes, lamellar, hexagonal and cubic surfactant liquid crystals, vesicles, liposomes, themotropic liquid crystals, etc. and can simultaneously resolve nanometer sized particles and their order, orientation and defects to 100 micron length scales.This award provides support for a new Freeze-fracture System which will significantly improve the throughput of samples, decreasing the turnaround times from about 8 hours to about 1 hour per sample run. In the new equipment, the samples are loaded through a vacuum airlock, and the electron beam evaporation sources can also be externally adjusted via airlocks. Hence, the main vacuum chamber is never vented. On our current instrument, vacuum must be broken to introduce the specimen, replace the evaporation sources, and to remove the specimen after processing. Each sample run requires that the main chamber be vented at least 3 times, with the necessary pump down time in between. The faster turnaround will allow us to examine more samples more efficiently and the better vacuum will give higher resolution and less artifacts due to contamination. The evaporators on the new equipment are externally controlled to provide higher resolution replicating films with less down time.The freeze-fracture equipment will be available to other researchers in the department and the University. The instrumentation at the University of California at Santa Barbara is heavily used by a collaborative group of scientists studying complex fluids and biomaterials, and by industrial and academic collaborators in California (Depotech, Alliance Pharmaceuticals) and elsewhere (U. Delaware. Dow Chemical).%%%***