Novel poly(imide siloxane) copolymers were prepared and developed as high performance fiber coatings. These copolymers were synthesized and characterized extensively as a function of chemical composition. The polyimides were then utilized to coat prototype fibers which were subsequently evaluated regarding thermal stability, thermal behavior, and hydrophobicity. The polymer series included poly(imide siloxane)s which were prepared in two steps, the first involving the generation of soluble poly(amic acid} intermediates which were then cyclodehydrated by heating in a coamide solution, at temperatures ranging from 140 to 170°C, resulting in soluble polymer which exhibited excellent thermal and mechanical properties. Because of the different nature of the imide and siloxane, a two phase microstructure developed at relatively low block molecular weight. X-ray photoelectron spectroscopy (XPS) and contact angle measurements indicated that the surface of the copolymer films was dominated by siloxane. A series of coating solutions was prepared, controlling the solution concentration, solvent, and viscosity. Polybenzimidazole and Kevlar aramid multifilament yarns were immersion coated, dried, and evaluated. Due to the surface segregation of siloxane, these coated fibers advantageously displayed lower moisture sorption as measured in three environments of different humidities. Thus, the coating acted as a hydrophobic barrier. These coated fibers were also evaluated by thermogravimetric analysis (TGA) which displayed that the dynamic thermo-oxidative stability was improved. Finally, thermal expansion coefficients were measured in order to determine coating integrity or matrix/resin integrity under thermal stress. / M.S.

This study aimed to quantify resistant starch (RS) beta-glucans (BG) and fructo-oligosaccharides (FOS) in Indian and Canadian wheat varieties and in chapaties made from these; and to assess the effects of soy flour on the levels of these components and its effects on the sensory and functional properties of the wheat-soy chapaties. Seven wheat varieties (Indian / Canadian) were milled into flour; supplemented with 0 % (control), 10 %, 20 % or 30 % defatted soy flour and made into chapaties. Flours and chapaties (freeze-dried, pulverized) were assayed for BG, FOS, RS and simple sugars (glucose / sucrose). Sensory evaluation was carried out by (9 point) hedonic rating of chapaties by 20 untrained Indian panelists. Flour water-holding capacity and water absorption indices (WAI) were determined. RS content of flours ranged from 7.1 g/100 g to 12.6 g/100g, but decreased when made into chapaties, (< 1 g/100 g), and decreased further with soy flour addition. BG content in flours ranged from 0.8 g/100 g to 1.4 g/100 g, while FOS content ranged from 1.3 g/100 g to 2.3 g/100 g. Minimal changes were observed in BG and FOS content when made into chapaties. Simple sugars were minimal in flours and chapaties. WAI of wheat flour was increased with addition of soy bean flour. Addition of up to 30 % soybean flour elevated the sensory acceptability of chapaties. While there is a decrease in RS with chapati making, the levels of BG and FOS are largely unchanged with processing. / Master of Science

A system to measure chromatic dispersion in single-mode optical fibers with near point wavelength resolution is described. Differential propagation constant data for the test fiber is collected by using an acousto-optic modulator to frequency-shift laser light passed to an optical heterodyne. Theoretical developments include a frequency-domain calculation technique for interpreting empirical results. The system is proven infeasible, however, due to inherent noise sensitivity / M.S.

Modern engineering structures often incorporate new materials and complex designs for which existing techniques for nondestructive evaluation prove inadequate, especially for dynamic and in-service measurements. At the same time, optical fiber sensors have been identified as an ideal candidate for embedded and attached measurements of material parameters such as strain, temperature, or state of damage. In particular, sensors based on optical fiber modal interference phenomena have been shown to be capable of highly sensitive detection of static and dynamic strain. This work reviews known applications of modal domain sensing to measurement science to date, and discusses the principles behind the method. A general expression for the intensity distribution emerging from a multimode fiber is formulated, covering both few mode and highly multimode fibers, and new expressions for their sensitivity to both radial and axial strain are derived. Optimized multimode fibers are seen to show an intrinsic phase sensitivity which rivals or even surpasses that of the single mode interferometer, especially in the case of applied radial strain. The use of modal domain sensors for real-time ultrasonic wave transduction is described as a particular application to NDE, with experimental results being presented with regard to acoustic emission monitoring as well as the detection and analysis of shock waves due to impact. Finally, optimization schemes and alternatives for such sensors are addressed, and recommendations for future work are raised. / Ph. D.

The effect of surface pretreatment on the adhesive bonding and bond durability of carbon fiber/epoxy and carbon fiber/bismaleimide matrix composites was studied. Methyl ethyl ketone (MEK) wipe, peel ply, grit blast and gas plasma treatments were the pretreatments of interest. Chemical and physical changes which occurred in the cured composite surfaces following pretreatment were characterized with x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), contact angle analysis, diffuse reflection infrared spectroscopy (DRIFT), profilometry and scanning electron microscopy (SEM). Double lap shear and Boeing wedge configurations were used to evaluate the strength as well as the durability of the composites bonded with an epoxy film adhesive. Fluoropolymer residues which were found on the composite surfaces were fully removed by grit blasting and oxygen plasma treatments, but not by an MEK wipe. The use of a peel ply prevented fabrication contamination from depositing on the bonding surfaces. In addition to its cleaning effect, oxygen plasma was also capable of incorporating additional polar functionality into the composite surface. The presence of the fluoropolymer contamination on the MEK-wiped surface resulted in low surface energy and wettability, whereas peel ply, grit blast and oxygen plasma improved both the surface energy and the wettability of the composite surfaces. The grit blasted and peel ply surfaces were observed to have a significant degree of roughness, as measured by profilometry and seen by SEM. A rubber-toughened epoxy film adhesive was used for the bonding studies. Lap shear strengths were evaluated under ambient conditions as well as at 82°C, both dry and following a 30 day/71°C water exposure. Wedge durability testing was carried out in a dry 75°C oven, 75°C water, 100°C water and aircraft de-icing fluid. Relative to the MEK-wiped controls, lap shear strength as well as hot/wet durability was improved by the peel ply and oxygen plasma treatments for both epoxy and bismaleimide composites. Grit blasting was seen to have some utility for the epoxy composites at room temperature, but was generally observed to be detrimental to strength and durability, particularly in the case of the bismaleimide composites. In order to separate the effect of surface chemistry from the effect of surface roughness on composite bond strength, a study was carried out in which surface functionality was varied while the topography remained constant. For this purpose, peel ply surfaces, which have a consistent and reproducible degree of roughness, were treated with fluoropolymer compounds and gas plasmas, as well as left untreated. It was found that the removal of fluoropolymer contamination was the main contributor to the observed bond strength improvement following plasma treatment; however, highly functionalized oxygen plasma-treated surfaces showed evidence of improved durability in a hot aqueous environment. The effect of elapsed time following oxygen plasma treatment of epoxy composites was also studied. XPS atomic concentration, wettability by water and a liquid epoxy resin, and lap shear strengths were plotted as a function of time following removal from the plasma reactor. Changes which occurred in the chemistry and wettability of an oxygen plasma-treated surface had a subsequent negative effect on the lap shear strengths of the bonded specimens. A study was carried out using model epoxy and bismaleimide compounds in thin film form, for the purpose of studying surface chemistry and interfacial reactions following an oxygen plasma treatment. XFS and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe the reactions which occurred. Close correspondence was found between the XPS and IR-RAS analysis of functional groups incorporated into the surface of the films by the plasma treatment. IR-RAS analysis of the model surfaces following exposure to a neat, liquid epoxy resin revealed that, while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin. / Ph. D.

A series of RF plasmas was chosen to modify the surface chemical composition of Hercules IM7 carbon fibers. A two-liquid tensiometric method was used to determine the surface energy parameters y(ds) and I(psf) of the fibers. An XPS analysis of air and argon plasma treated fibers indicated a significant surface oxidation of the fibers which translated into low y(ds) values and high I(psf)values. An ammonia plasma was shown to remove an outer layer from the surface of the fibers. It also increased y(ds) compared to as-received fibers without affecting the non-dispersion (IPsf) XPS results indicated that methane and ethylene plasmas deposited a layer of low surface energy hydrocarbon on the fiber surface. A trifluoromethane plasma and a tetrafluoromethane plasma introduced a significant amount of fluorine containing groups in the fiber surface in the form of a fluorinated plasma polymer in the first case and through direct attack of the fiber surface by fluorine atoms in the second case. The surface chemical composition and the surface energy parameters of two series of commercially treated carbon fibers were also determined and compared to the results on IM7 carbon fibers. The adhesion of carbon fibers to polyethersulfone (PES) was measured by using the microbond pull-out test, and compared to the adhesion of the same fibers to an epoxy resin. The load required to debond the microdroplet was used as a measure of the bond strength. The data were also analyzed in terms of interfacial fracture energy accordIng to the model developed by Jiang and Penn (1992). The microbond pull-out test results showed no significant relation between the fiber surface chemical composition or the fiber surface energy, and the adhesion to PES. However, plasmas which have a strong ablative character such as the ammonia and the tetrafluoromethane plasmas did improve the fiber-PES adhesion, when compared to as-received fibers. The study of the fiber-epoxy systems revealed that a chemical effect contributed to the adhesion improvement but to a lesser extent than the "cleaning" effect of the surface treatment. The results support the two part mechanism proposed by Drzal and extend its application to carbon fiber-thermoplastic systems, but in this case the chemical effect is minimal. / Ph. D.

Solutions of cellulose esters with different concentrations in dimethylacetamide (DMAc) and with different types of substituents were studied in relation to their liquid crystalline (LC) solution behavior. Classical LC behavior was revealed for all solutions. Critical polymer concentration (V_p^c) is highest for cellulose acetate (CA) and lowest for cellulose acetate butyrate (CAB) with highest degree of butyration. This is opposite to the classical model by Flory which predicts an increase in V_p^c with decreasing aspect ratio (L/d). Fibers were spun from isotropic and anisotropic DMAc solutions of cellulose esters by dry jet/wet spinning process. The mechanical properties, orientation, and crystallinity of the fibers increased as spinning progressed from the isotropic to the anisotropic solution state. High butyryl content enhances both overall solubility and the formation of LC solutions at lower concentration, but it results in lower fiber properties. Unmodified cellulose (C) and cellulose hexanoate (CH) also exhibited LC behavior. The V_p^c value for CH was lower than that obtained for CAB with maximum degree of butyration. This indicates that bulky substituents may lower V_p^c values. The formation of high modulus (152 g/d) cellulose fibers from LC solutions is attributed to the air-gap that exists in the dry jet/wet spinning process. Presence of lithium chloride (LiCl) in the LC solutions of CAB exhibited ionic interactions. Mechano-sorptive creep behavior of the fibers spun from these solutions decreases in the presence of residual LiCl salt. Fibers from blends of CAB and of C with lignin (L) were spun from Lc solution. Morphological investigations demonstrate that CAB and L formed intimately mixed blends whereas C and L were partially mixed. The mechanical properties of the fibers with L increased due to good phase mixing of CAB and L molecules in the fiber matrix. / Ph. D.

The single fiber pull-out test was employed to experimentally model the failure of an embedded optical fiber in neat resin. The objective was to evaluate load transfer between resin and fiber through the evaluation of the sensitivity of the single fiber pull-out test to the physical parameters of the polymer matrix. This was accomplished first by appropriately interpreting the load versus extension trace, second by determining the effect of fiber coating and embedding resin on the load carrying ability of the single fiber composite, third by characterizing the fiber/coating/resin system with respect to the physical parameters of the polymer and the failure mechanism of the composite as the cure temperature was varied, and fourth, by correlating the independent parameters of the polymer and fracture data. For the first time, the load versus extension trace generated by such experiments was thoroughly interpreted and mathematically modeled. To this end, the embedding resin was physically characterized through the determination of the glass transition temperature, T_g, the relative change in volume with sample preparation and thus the resulting normal pressure exerted on the embedded fiber by the resin material. The experimental fracture data was quantified by determining the strain energy release rate, SERR, for initiation of crack propagation and, with the consideration of friction, its continuation, as well as the interfacial shear stress, τ, of the bond, and τ associated with debonding and sliding. Based on a series of experiments of varying material parameters, a model material system was chosen: a polyimide coated fiber embedded in uncatalyzed tetraglycidyl-4-4'-diaminodiphenylmethane with 4,4’-diaminodiphenylsulfone. Cure temperatures, T_cure, of 150, 177, 230 and 250°C were employed. The average critical strain energy release rates increased from the 150 to 177 to 230°C sample sets, then decreased for the 250°C sample set. Since the T_g of the fully cured resin is 260°C, these results support the hypothesis of increasing residual stress as a function of T_cure for cure in the vitreous state. In regards to the 250°C cure data set, since T_cure was within T_g - 30°C the internal pressures due to crosslinking were minimized due to cure in a rubber-like state. The residual pressure, independently determined from both the resin characterization and fracture data, increased by a factor of 2.4 with a temperature increase from 150 to 230°C for the two hour cure period. The strain energy release rate and sliding interfacial shear stress of pull-out increased by a factor of 2.54 and 2.1, respectively. The coefficient of friction remained statistically constant at 0.6. Based on this work, it is concluded that the single fiber pull-out test is sensitive to fiber/matrix interactions via the physical parameters of the material system. Also, the failure response of the single fiber composite can be predicted for well characterized matrices. / Ph. D.

Mites are endemic and allergy to mite excreta and parts is one of the most common allergies. Health care practitioners have recommended the removal of carpets from homes of people with mite allergies. Little, if any, consideration is given to the fact that some persons may benefit directly from the presence of carpet in their homes. In the allergen and mite research literature, carpets are rarely described as having unique characteristics and are generally referred to as a generic entity. Carpets, however, do have unique characteristics that define their construction, appearance, wearability, and cleanability. Seventy-two pieces of commercially available, residential flooring materials were inoculated with identical numbers of mites, Dermatophagiodes farinae, and placed in the Textiles Conditioning Lab at Virginia Tech. The mites and carpet pieces were maintained in the lab, under identical, environmentally controlled conditions for 6 weeks, then the mites were extracted and counted. On the basis of the results of statistical tests run on the study data, the null hypothesis, that there is no difference between the numbers of mites grown on the different flooring conditions, was rejected. Statistically significant differences exist between the hard floor and the nylon carpet, between hard floor and olefin carpets, but no difference between hard floor and wool carpet. Nylon was the carpet fiber that was most supportive of the growth of house dust mites, olefin was the second most supportive, and wool carpet and hard floor were similar in being the least supportive. / Master of Science

High-resolution optical time-domain methods applied to measuring strain in an optical fiber are discussed. The use of this optical time-domain fiber sensor for measuring quasi-distributed strain along a cantilevered beam is experimentally demonstrated. This is accomplished by segmenting the sensor with air-gap sites, allowing reflections to be monitored. Physically looping these fiber segments many times over their interaction regions is shown to improve the sensitivity of the sensor. Also discussed are techniques to improve sensitivity by using a special tap-off coupler to recirculate optical pulses many times through the sensing region. Important in modeling these sensors is determining the photoelastic coefficient, which accounts for the photoelastic and Poisson effects on a strained fiber. The photoelastic coefficient is theoretically modeled using two methods involving waveguide and ray-optics theory. The results of these analyses are compared to experimentally determined values. / Master of Science