聚合物载体中水杨酸晶体的太赫兹极化率测定

极化率作为材料的重要微观属性,与其呈现出的多种宏观属性等紧密相关,在新型药物及功能材料的设计中扮演着关键角色.对于微观结构存在复杂分子间作用的物质体系,获取其太赫兹波段的动态极化率具有重要意义.极化率的实验测定建立在其本征介电常数的准确测定之上,太赫兹时域光谱系统凭借其相干探测属性,可直接提供太赫兹波在穿透样品后的相位...

Polarizability Measurements for Salicylic Acid Embedded in Polymer Matrix Using Terahertz Time-Domain Spectroscopy

Polarizability acts as an essential property in the design of novel materials. It is of great significance to obtain the dynamic polarizability over terahertz frequencies for substance containing complex intermolecular interactions. The experimental access of the polarizability is based on the accurate determination of its intrinsic dielectric constant. Meanwhile, thecoherent detection scheme of terahertz time-domain spectroscopy (THz-TDS) makes it an ideal alternative for dielectric constants measurements. However, most organic crystalline materials occupy strong absorption features over terahertz frequencies, and samples for THz characterization are commonly prepared by homogeneously dispersing the analyte within the THz transparent polymer matrix. The application of the dilution matrix makes the dielectric constants of mixture samples measured by the THz-TDS cannot be directly utilized to calculate the polarizability. We proposed in this work a ternary model based on the Landau, Lifshitz and Looyenga (LLL) theory to extract the intrinsic dielectric constants of analyte by removing the dielectric contribution of trapped air and polymer background. The extracted intrinsic dielectric constants can be further used to calculate polarizability combining with the Clausius-Mossotti equation. The proposed methodology is exemplified in detail with the polarizability determination of crystalline salicylic acid (SA) embedded in twopolymer matrixpolyethylene (PE) and polytetrafluoroethylene (PTFE), respectively. Mixture pellets at three concentrations are designed for THz-TDS measurement for each polymer matrix. The application of the proposed method on the original dielectric spectra of mixture pellets provides intrinsic dielectric constants and polarizability values of salicylic acid with promising consistency. The results reported in this work also represent the first experimentally measured polarizability values for crystalline salicylic acid, which is (17.2±0.2) and (17.6±1.0) Å3 for analyte embedded in PE and PTFE respectively.