RELATIONSHIP BETWEEN OPTICAL TRANSPARENCY AND NANOSTRUCTURAL FEATURES OF SILICA AEROGELS
RELATIONSHIP BETWEEN OPTICAL TRANSPARENCY AND NANOSTRUCTURAL FEATURES OF SILICA AEROGELS
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DOI：
10.1016/0022-3093(95)00021-6
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发表时间：
1995-06-01
影响因子：
3.5
通讯作者：
FRICKE, J
中科院分区：
文献类型：
--
作者：
EMMERLING, A;PETRICEVIC, R;FRICKE, J
二氧化硅气凝胶被认为在太阳能建筑的透明隔热系统中具有很大的应用前景。这些高度多孔材料的光学透明度受制备时的反应参数和所用前体的影响。以前，它表明，由于体散射的特定消光降低与宏观密度增加和溶胶-凝胶起始溶液的pH值增加。最近，还发现在测量精度内，如果相对于绝对尺度进行两种类型的测量，则气凝胶块体的光散射强度等于朝向散射角零的外推小角X射线散射强度。与此同时，已经进行了超小角X射线散射测量，以关闭光和常规小角X射线散射之间的动量空间中的差距。因此，可以说，近各向同性（瑞利）散射是由相同的纳米结构的不均匀性的气凝胶网络，导致特征的小角度散射图案。因此，各向同性散射光的量以及因此光学消光可以直接与称为相关体积的量相关。对于各种二氧化硅气凝胶，它示出了后者如何取决于凝胶网络的纳米结构特征，如平均粒径，颗粒间排列，孔径和排序参数，这占浓度效应。
Silica aerogels are considered to be of great promise for use in transparent thermal insulation systems in solar architecture. The optical transparency of these highly porous materials is influenced by the reaction parameters upon preparation and the precursor used. Previously it was shown that the specific extinction due to bulk scattering decreases both with increasing macroscopic density and increasing pH-value of the sol-gel starting solution. Recently, it was also found that within the measurement accuracy the light scattering intensity of the aerogel bulk equals the extrapolated small-angle X-ray scattering intensity towards scattering angle zero if both types of measurement are performed with respect to an absolute scale. In the meantime, ultra small-angle X-ray scattering measurements have been performed in order to close the gap in momentum space between light and conventional small-angle X-ray scattering. As a result it can be stated that the nearly isotropic (Rayleigh) scattering is caused by the same nanostructural inhomogeneities of the aerogel network which lead to the characteristic small-angle scattering pattern. As a consequence, the amount of isotropically scattered light and thus the optical extinction can be directly related to a quantity called the correlation volume. For a variety of silica aerogels, it is shown how the latter depends on the nanostructural features of the gel network, such as average particle size, interparticle arrangement, pore diameter and an ordering parameter, which accounts for concentration effects.