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特性对于设计和优化新型药物输送系统、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体系非常重要。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，但很难用单一的实验甚至单一的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，特别是当显微镜直接解决散射的主要限制时。然而，高分辨率成像有其自身的实验局限性：必须用固体、导电、低蒸汽压版本的原始材料取代流体样本，才能与电子或扫描隧道显微镜的要求兼容。经验表明，制作扫描隧道显微镜电子显微镜样品的最佳方法是快速冷冻，然后进行冷冻-断裂复制。在冷冻-破裂复制中，快速冷冻的样品在低温和高真空下破裂，以暴露流体的内部结构。然后，通过蒸发金属阴影膜来复制断口表面，以在透射电子显微镜图像中提供对比度或为扫描隧道显微镜提供导电性，随后是碳背衬膜，以为后续处理和成像提供足够的强度。该技术的分辨率为横向约2 nm，垂直约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、片状、六角和立方形表面活性剂液晶、囊泡、脂质体、热致液晶等，并可以同时将纳米颗粒及其顺序、取向和缺陷分解到100微米长的尺度。该奖项支持一种新的冷冻-断裂系统，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大约8小时减少到大约1小时。在新设备中，样品通过真空气闸装载，电子束蒸发源也可以通过气闸进行外部调节。因此，主真空室永远不会被排气。在我们目前的仪器上，必须打破真空以引入样品，更换蒸发源，并在处理后取出样品。每次取样运行都需要至少对主室进行3次排气，其间有必要的停泵时间。更快的周转时间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污染伪影。新设备上的蒸发器是由外部控制的，以更少的停机时间提供更高分辨率的复制胶片。冷冻断裂设备将供该系和大学的其他研究人员使用。加州大学圣巴巴拉分校的这种仪器被一个研究复杂流体和生物材料的合作科学家小组广泛使用，加州大学(Depotech，Alliance PharmPharmticals)和其他地方(U特拉华大学)的工业和学术合作者也大量使用这种仪器。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).%%%***