Preparation and Characterization of Composites with the Fillers Comprised of Low-Dimensional van der Waals Materials
- Sudhindra, Sriharsha
- Advisor(s): Balandin, Alexander A
Abstract
In this dissertation, the methods for preparation and experimental testing of polymer-based composites with fillers comprised of quasi-one-dimensional charge-density-wave (CDW) material – Niobium Trisulfide (NbS3) are presented. Owing to the crystal growth conditions, the NbS3 crystals appear as a mixture of various polymorphs. Among these polymorphs, only the NbS3-II polymorph reveals the charge density wave (CDW) characteristics. Prior to composite preparation, the synthesized crystals were characterized with the metrology techniques of transmission electron microscopy (TEM) to determine their crystal structure and studied with Raman spectroscopy as a function of temperature to observe the CDW property. The use of CDW van der Waals materials, as fillers, is expected to provide novel functionalities to the composites if one develops preparation techniques that preserve the intrinsic properties of the fillers. This task is challenging because composite preparation involves mechanical mixing, centrifugation, and other processing steps that typically result in damage and high concentrations of defects and impurities. The process of the composite preparation starts with liquid phase exfoliation to acquire fillers. The tested polymer materials included epoxy resin, UV-cured epoxy resin, and Polyvinylidene fluoride (PVDF). The composites have been characterized using differential scanning calorimetry, Raman spectroscopy, ellipsometry, optical microscopy, and parallel-plate capacitance measurements. The electrical capacitance measurements of PVDF thin films with NbS3 fillers demonstrated a significant change in the dielectric constant at the temperature near the CDW transition. The results of this dissertation research prove that temperature-dependent Raman spectroscopy can be used as an efficient characterization technique to distinguish NbS3-II polymorph with CDW properties from other NbS3 phases and add to the development of methods for the preparation of composites with the quasi-1D van der Waals materials.