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One of the primary objects of this research was to determine, if possible, the nature of the radiation damage prior to thermal decomposition. The X-ray study has not wholly achieved this although more information has been derived from it than from similar work on AgMnO₄ However, the diffuse reflections obtained do indicate, quite strongly, the creation of point defects during irradiation. This is of value since such assumptions have been made in the explanation of the kinetics of decomposition of a number of irradiated solids (BaN₆,CaN₆). In addition the X-ray work has suggested future research which should produce useful information; namely, a precise study of the diffuse reflections. Another object of the research was to attempt to determine what characteristics, if any, of the kinetics of the decomposition of an unirradiated solid would predetermine a marked irradiation effect. It is obvious that the type of nuclear growth which occurs e.g. branching chain, or power law, does not characterise a substance with regard to a possible irradiation effect . The photosensitivity, or otherwise, also does not determine whether there will be an irradiation effect. However, the one property that the substances which have been studied, have in common, is a polyatomic anion, but here again ammonium dichromate does not show an acceleration of the decomposition after irradiation. Consequently it is considered that it is not possible to say, a priori, whether a solid will undergo an accelerated decomposition after irradiation. Each new solid, unless it belongs to a particular class e.g. the alkaline earth azides , must be considered afresh. Nevertheless it does appear that the irradiation effect can take two forms: - (i) the production of an unstable compound e.g. nickel oxalate, the decomposition of which affects the normal pyrolysis; and (ii) the production of point defects which determine the nature of the subsequent thermal decomposition e.g . CaN₆ . It is possible that the effect requires an interaction of the created point defects with the existing line defects.

Excess molar volumes have been determined for four ternary chlorobenzene + dibutyl ether + alkane mixtures at 25°C. Results of these measurements are used to test the applications and limitations of BAB, Redlich-Kister, Kohler and Hwang et al. cubic models. For the systems studied, Redlich- Kister, Kohler and Cubic models were found to provide reasonable predictions. Differences between experimental and predicted ΔV^ex_123 values were about ±0.020 cm^3mol^-1 or less at most ternary compositions. Solubilities are reported for anthracene in binary mixtures containing propanol and butanol with alkanes at 25°C. Results of these measurements are used to test the NIBS/Redlich-Kister expression. The three-parameter form of this expression is found to provide reasonable mathematical representation with deviations between experimental and back-calculated values being less than ±1%.

[From Introduction] The first step in the study of the thermal decompositions of solids is an examination of the kinetics, since this casts much light on the mechanism of the reaction. It must be borne in mind, however, that a theoretical expression, derived on the basis of a particular mechanism, even if it fits the observed experimental results, is not conclusive proof of the validity of the mechanism when applied to the decomposition under examination.

The complexity of the fiber-matrix interphase in a composite is largely due to the myriad of variables (material, processing, and design) that affect its formation. The interphase, thus formed, has to be characterized at several levels (micro-structural, chemical, and mechanical) in order for one to fully understand the nature of the bond between the fiber and matrix and in order to perform a stress analysis of the fiber-interphase-matrix assemblage. A thorough thermo-mechanical characterization of the interphase is difficult, at present, due to the necessity of studying the interphase in situ, its small dimension (usually on the order of a micrometer), and its general complexity. However, a cursory glance at the literature shows that great progress has been made in all of the three levels of characterization mentioned above for various composite systems. Several recent attempts have focused on the physical characterization (evaluation of volume fraction, thickness, Young's modulus, shear modulus and coefficient of thermal expansion) of the interphase. Models of physical properties (thickness, Young's modulus, Poisson's ratio and coefficient of thermal expansion) of the interphase have been considered by several researchers in an effort to study the influence of the interphase on overall composite properties and behavior. Hypotheses on interphase formation and properties have been proposed and tested by some researchers. Both experimental characterization as well as modeling studies are necessary to achieve a more profound understanding of the interphase and its behavior. The interphase, in a composite, is usually modeled as a homogeneous region, despite the fact that it may have spatial property variations.However, it is important to the understanding of composite behavior to incorporate a realistic interphasial region into the analysis and testing of composite material systems. A new thermo-elastic model for the interphase properties in fiber-reinforced thermosets is proposed. The Young’s modulus and coefficient of thermal expansion of the interphase are assumed to be functions of distance from the fiber in this model. The Poisson’s ratio of the interphase is assumed to be the same as that of the matrix. The new model is used in a concentric cylinder assemblage analysis for the determination of the residual thermal stresses in unidirectional fiber-reinforced epoxies. The governing field equations in terms of displacements are solved in “closed form”. It is found that, although the solution is dilute, the property variations in the interphase have a distinct effect on the residual thermal stresses. This is significant, considering the fact that residual thermal stresses play an important role in controlling the structural performance of a composite. The new model is used in Mori-Tanaka analyses for the determination of non-dilute local stress fields in unidirectional fiber-reinforced epoxies under thermo-mechanical loading situations. The governing field equations in terms of displacements are solved in “closed form”. It is found that property variations in the interphase have a distinct effect on the local stresses. This is also significant, considering the fact that local stresses play an important role in controlling the structural performance of a composite. A model composite system consisting of a coated glass rod embedded in Epon 828 is considered; coatings are applied to the glass rod in succession to simulate two different interphase types. The model composite specimens are loaded in transverse compression and transverse shear, and the resulting in-plane displacements are measured by the use of the Moire interferometry technique. Differences in displacement fields between the various specimens, due to the presence of interphasial regions, are found to be minimal. More sensitive measurements are needed to measure pointwise displacements in the interphasial (coatings) region. / Ph. D.

The purpose of this investigation was to examine the effects of thermal history during cooling from the melt on the degree of crystallinity, morphology, and mechanical properties of (polyphenylenesulfide) PPS/carbon fiber composites. Three thermal treatments were employed in this study: isothermal crystallization from the melt at 140,160,180,200, and 220°C, quenching from 315° C and then annealing at 160 and 200° C, and nonisothennal crystallization from the melt at rates varying from 0040 C/minute to 68° C/second. The effect of varying the thermal history of the sample on the degree of crystallinity developed in the matrix polymer was determined using differential scanning calorimetry. The effect of thermal history on and the resulting matrix morphology was examined by scanning electron microscopy. The subsequent effects of the degree of crystallinity and the morphology on the mechanical behavior of the samples were monitored by transverse tensile tests and flexural tests. In all cases, the transverse tensile and flexural moduli increased as the amount of crystallinity in the samples increased. However, samples with greater amounts of crystallinity did not always yield higher transverse tensile or flexural strengths. Upon examination of the composite samples by electron microscopy, it was observed that trends in the values of the transverse tensile and flexural strengths could be correlated with structural changes in the matrix. This paper is concerned with the simulation of the development of crystallinity and morphology (both amount of crystallinity and the size of spherulites) which arise during the cooling of a slab of a semicrystalline polymer reinforced with long continuous carbon fibers. This situation is commonly found during the processing of semicrystalline thermoplastic composites. Whereas published attempts at simulating this process have treated the composite material as a continuum and thereby used mass averaged physical properties (such as thermal conductivity, density, and specific heat), we use a quasi-continuum approach in which locally we consider the properties of the matrix and fiber separately. Once a temperature distribution is calculated using the continuum approach, the fmite element method is applied locally at various points in the slab to calculate the amount of crystallinity and the size of the developing spherulites. This is done by using the Avrami equation and the Hoffman and Lauritzen radial growth equation. The amount of crystallinity and the spherulite size are predicted as a function of fiber spacing and packing geometry, and the predictions are found to be in good agreement with experimental results obtained on polyphenylenesulfide/carbon fiber composites. The advantages of our approach over the continuum approach is that a relatively accurate prediction of the spherulite size is possible due to constraints imposed by the fiber on the spherulitic growth. / Ph. D.

This work describes the synthesis pathways to the development of optically and thermally responsive nanovalves with fast response times in nanoporous membranes. As an approach, we developed synthesis pathways to couple a thermally responsive polymer with metallic nanoparticles and build a nanocomposite that synergizes the capability of metallic nanoparticles to convert light into heat, and the fast thermal response exhibited by the polymeric material. In addition, we developed a technique to immobilize the synthesized nanocomposite to the surface of nanoporous membranes, which allowed building valves with light and heat triggering responses. This dissertation describes two syntheses pathways developed to produce optically and thermally responsive nanocomposites by coupling metallic nanoparticles, gold and silver, with a thermally responsive polymer, p-N-isopropyl acrylamide (PNIPAM). The coupling is achieved by using PNIPAM as a capping and nucleating agent in the in situ redox reaction of a silver salt with sodium borohydride, and using PNIPAM as a capping and stabilizing agent in the redox reaction of a gold salt with ascorbic acid. The size and shape of the nanoparticles were controlled and the synthesized nanocomposites exhibit “cocoon-like” structures due to the PNIPAM surrounding the metal nanoparticles, giving the capability to aggregate and resolubilize, through many thermal (shown for gold and silver nanocomposites) and optical (shown by exposing to 532 nm wavelength low-power lasers) cycles. The steady state and dynamic heat conduction of the heat generated from the particles was modeled and the results agreed with the observed optical switching at our experimental conditions. Finally, a method to incorporate nanocomposites into nanoporous membranes (NPM) was developed. It involved prior immobilization of PNIPAM through plasma-induced grafting, followed by a reduction in situ of a metallic salt. The composite NPMs showed thermal responses and through simulation of heat conduction within the pores using the model developed in this work we were able to conclude that the synthesized composite membranes will exhibit optical switching when exposed to focused low power lasers. The nanovalves developed in this work have potential applications as optothermally responsive valves for the spatio-temporal delivery of bioactive agents, cell array, and advanced cell culture systems. / text

The calculation of the thermal conductivity of condensed matter has posed a significant challenge to engineers and scientists for almost a century. Thermal conductivity models have been successfully applied to many materials however many challenges still remain. One serious challenge is the inability of current thermal conductivity models to calculate the thermal conductivity of highly complex materials. Another challenge is managing error introduced by using an effective interatomic potential, for many materials this problem is exacerbated because their effective potentials have not been extensively used or characterized. Recent interest in nanostructures has initiated a new set of challenges and unanswered questions. This work addresses different aspects of the aforementioned challenges by using zeolite MFI and gallium nitride as case studies.

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