Fundamental experiments on the response of solutions, polymers, and modified polymeric materials to electromagnetic radiation

• Main Author: Dallas, George
• Other Authors: Materials Engineering Science
• Format: Others
• Language: en
• Published: Virginia Tech 2014
• Subjects: LD5655.V856 1991.D344; Polymers > Effect of radiation on; Solution (Chemistry)
• Online Access: http://hdl.handle.net/10919/38885; http://scholar.lib.vt.edu/theses/available/etd-07282008-134534/

This dissertation is divided into two sections. In the first section dielectric and magnetic properties were analyzed for a series of materials: bisphenol A solutions, a poly(amideimide), and polymers filled with either carbon black, iron particles, or aluminum flake. The second section deals with the influence of volatiles and low temperature aging on the dynamic mechanical and dielectric properties of a poly(amide-imide). In the first investigation, solutions of bisphenol A in tetrahydrofuran (THF) or diglycidylether of bisphenol A (DGEBA) in either toluene or tetrahydrofuran were used to identify the influence of chemistry, solvent, and concentration (0 - 2.6M) on dielectric loss (ɛ") and storage (ɛ') at (2.45 GHz). A number of solutions were examined as a function of frequency and temperature to obtain a mechanistic explanation for the single frequency data. The results showed the relaxation time shifting to higher frequencies with increased temperature and shifting to lower frequencies after a critical concentration. A polymer derived from bisphenol A and the diglycidylether of bisphenol A was sandwiched between two microwave inactive quartz plates to show selective heating of a 0.002" film. The poly(amide-imide's) dielectric storage and loss values (ɛ', ɛ") were examined as a function of temperature. The metal filled systems showed nonlinear behavior for dielectric loss (ɛ"), magnetic loss (µ"), and normalized magnetization (Gauss), which were explained by a percolation model. A critical volume fraction (Φ_C) was identified in the 0.15 - 0.25 volume fraction range. Scaling of dielectric and magnetic properties above Φ_C was 1.2 for aluminum flake, 1.5 for iron, and 5 for carbon black. The development of structure that occurred with increased filler content was monitored by scanning electron microscopy (SEM) and showed qualitative agreement with percolation behavior. At low volume fractions, there were individual particles, then clusters, then veins of material that extended many particle lengths. The second part of this dissertation dealt with the influence of volatiles on the dynamic mechanical and dielectric values of a poly({amide-imide). Experiments were conducted in both the temperature and time domains. These data were complemented by thermogravimetry (TG), thermogravimetry-mass spectrometry (TG-MS), and thermomechanical analysis (TMA). The isothermal desorption of volatiles (150 - 165°C) could be monitored by either mechanical, dielectric, or gravimetric techniques. The mechanical experiments revealed two peaks for water: one a low temperature peak (-90 - -50°C) and the other at (100 - 190°C). The dielectric analysis revealed two peaks for as received poly(amide-imide). The first was between -50 to 0°C, the other was between 0 to 50°C. The low power dielectric analysis and volatile desorption behavior were combined to explain the structure that developed after poly(amideimide) spheres were subjected to similar thermal or microwave processing conditions. Thermal processing produced a closed cell structure and a rough surface, while microwave processing produced an open cell structure at a smooth air-surface interface. === Ph. D.