Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium
Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium
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DOI：
10.3390/s20113120
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发表时间：
2020-06-01
期刊：
影响因子：
3.9
通讯作者：
Markl, Daniel
中科院分区：
文献类型：
--
作者：
Naftaly, Mira;Tikhomirov, Iliya;Markl, Daniel
多孔材料的孔隙率是从催化和分离技术到多孔纸和药片等许多产品的关键质量属性。特别是反映从表面可进入的孔隙空间的开孔孔隙率，对于流体需要进入孔隙以实现产品功能的应用至关重要。本研究提出了一种方法，使用太赫兹时域光谱（THz-TDS）加上折射率匹配介质来测量开孔率和分析粉末压块的散射损失。可以在不知道完全致密材料的折射率的情况下评估开孔孔隙率。该方法用于制药级乳糖粉末的压片。在四种不同的压力下压缩粉末，并在将粉末浸泡在折射率匹配介质中之前和之后通过THz-TDS进行测量，即，石蜡确定干燥和浸泡样品的折射率变化使得能够计算开孔孔隙率。结果表明，孔隙度始终低于总孔隙度，并随着压缩压力的增加而减小。浸泡样品的散射损耗显著降低，并且散射中心（颗粒和/或孔径）为太赫兹波长的量级或略小于太赫兹波长。这种新方法有助于更好地理解材料特性（粒度）、颗粒特性（开孔率）和性能相关特性之间的联系，例如，片剂的崩解和溶出性能。
The porosity of porous materials is a critical quality attribute of many products ranging from catalysis and separation technologies to porous paper and pharmaceutical tablets. The open porosity in particular, which reflects the pore space accessible from the surface, is crucial for applications where a fluid needs to access the pores in order to fulfil the functionality of the product. This study presents a methodology that uses terahertz time-domain spectroscopy (THz-TDS) coupled with an index-matching medium to measure the open porosity and analyze scattering losses of powder compacts. The open porosity can be evaluated without the knowledge of the refractive index of the fully dense material. This method is demonstrated for pellets compressed of pharmaceutical-grade lactose powder. Powder was compressed at four different pressures and measured by THz-TDS before and after they were soaked in an index-matching medium, i.e., paraffin. Determining the change in refractive index of the dry and soaked samples enabled the calculation of the open porosity. The results reveal that the open porosity is consistently lower than the total porosity and it decreases with increasing compression pressure. The scattering losses reduce significantly for the soaked samples and the scattering centers (particle and/or pore sizes) are of the order of or somewhat smaller than the terahertz wavelength. This new method facilitates the development of a better understanding of the links between material properties (particles size), pellet properties (open porosity) and performance-related properties, e.g., disintegration and dissolution performance of pharmaceutical tablets.