Browsing by Subject "Polystyrene"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Characterization of surfactant dispersed single wall nanotube - polystyrene matrix nanocomposite(2009-05-15) Ayewah, Daniel Osagie, OyinkuroCarbon nanotubes (CNT) are a new form of carbon with exceptional electrical and mechanical properties. This makes them attractive as inclusions in nanocomposite materials with the potential to provide improvements in electrical and mechanical properties and allows for the creation of a new range of multifunctional materials. In this study single wall carbon nanotubes (SWCNT) were dispersed in polystyrene using a solution mixing method, with the aid of a surfactant. A good dispersion was achieved and the resulting nanocomposites were characterized for electrical conductivity and mechanical properties by 3 point flexural and fracture toughness tests. Results show a significant improvement in electrical properties with electrical percolation occurring between 0.1 and 0.2 wt%. A minor improvement was observed in the flexural modulus but the strength and fracture toughness values in the nanocomposites decreased relative to the neat material. Scanning electron microscopy (SEM) was performed to characterize the morphology and fracture surface of the specimens. The results of testing and microscopy show that the presence of the nanotubes has an adverse effect on the crazing mechanism in Polystyrene (PS) resulting in a deterioration of the mechanical properties that depend on this mechanism.Item The dynamic mechanical response of polymer-based nanocomposites and network glasses(2004) Putz, Karl William; Green, Peter F. (Peter Fitzroy)The structural entities, atomic or molecular, that constitute a material and their spatial organization within the material largely determine the properties of the material. Different classes of materials respond to external forces often in ways that are fundamentally connected to their structure. Polymer melts exhibit time-dependent viscoelastic behavior in response to external stresses. If the deformation is rapid then the response of the polymer is largely elastic, whereas for sufficiently slow deformations the response is time-dependent and dissipative. In the solid state, an amorphous polymer responds to sufficiently small forces through local relaxations of segments of the molecules. Inorganic network glass melts typically exhibit viscoelastic behavior in the vicinity of the glass transition temperature, Tg, whereas below Tg ionic entities that compose the structure undergo hopping processes in response the external perturbations. This dissertation is largely devoted to understanding the response, or relaxations, of two different classes of materials: polymer based nanocomposites and inorganic network glasses, to external periodic mechanical perturbations. Polymer nanocomposites, materials in which a polymer serves as the host for nanomaterials, may possess properties that differ substantially from those of the pure polymer. Interactions between polymer segments and the foreign particles and the geometry, size, and dispersion of the foreign particles profoundly influence the properties of the composite. Small concentrations (~ few percent) of particles of nano-scale dimensions have been shown to be particularly effective at modifying the properties of the polymer because of the large interfacial area. In this dissertation the influence of C60 fullerenes and of single walled carbon nanotubes on the dynamical mechanical and rheological properties of PS and PMMA is examined. The second problem examined was the mechanical response of inorganic network glasses based on tellurium oxide to mechanical perturbations. Often alkali oxides are included in the glass composition because they improve processability of the glass melt by decreasing Tg. Through a series of dynamic mechanical and rheological experiments, it is shown that the relaxations which characterize the response of the glass increase by up to an order of magnitude when two distinct types of alkali ions are present compared to one.Item Glass transition kinetics of amorphous polymers(Texas Tech University, 2007-12) Badrinarayanan, Prashanth; Simon, Sindee L.; McKenna, Gregory B.; Dai, Lenore L.; Quitevis, Edward L.The glass transition temperature (Tg), an important characterizing parameter for amorphous materials, is correctly measured only on cooling, whereas the limiting fictive temperature (Tf') is measured on heating. Both parameters depend on the rate of cooling. In this work a comparison of the values of Tg measured on cooling and Tf' measured on heating is performed for a polystyrene sample using both capillary dilatometry and DSC. The results indicate that Tg is systematically lower than Tf', presumably due to the breadth of relaxation on cooling. The Tool-Narayanaswamy-Moynihan (TNM) model is used to fit the experimental data in order to ascertain the origins of higher value of Tg compared to Tf'. The values of Tg and Tf' are used to examine the relationship between the timescales of volume and enthalpy relaxation. The analysis in this study suggests that both properties exhibit similar timescales at temperatures above and below the nominal Tg. The divergence of times required to reach equilibrium noted in the literature at temperatures several degrees below than nominal Tg is attributed to the effect of nonlinearity. Experimental results are presented that corroborate this hypothesis. The data from dilatometry and DSC measurements is also used to apply an isoconversion analysis to determine the variation of activation energy throughout the glass transition. Although isoconversion methods have been used in the literature to determine the variation of activation energy with conversion through the glass transition using DSC heating curves, the results in this work demonstrate that the method should be applied on cooling rather than heating. In addition, it is shown that the conversion dependence is simply due to the non-Arrhenius temperature dependence known to be exhibited by glass-forming materials near Tg. Finally, the ability of the TNM model to describe the enthalpy relaxation data obtained at low heating rates for polycarbonate blends is examined in order to test the sensitivity of the model parameters to changes in chemical composition.Item Phase Selectively Soluble Polystyrene-Supported Organocatalysts(2014-08-10) Khamatnurova, TatyanaAlkane phase selectively soluble poly(4-alkylstyrene) supports have been developed. 4-Methyl-, 4-tert-butyl, 4-dodecyl-, and 4-octadecylstyrene were copolymerized with 5-10 mol % of 4-chloromethylstyrene to afford co- and terpolymers containing chloromethyl pendant groups so that a fluorescent dye can be attached. By varying the structure and the length of the alkyl groups, derivatives of these polymers with covalently coupled fluorescent dansyl groups as catalyst surrogates show a significant increase in phase selective solubility in thermomorphic and latent biphasic systems. The advantage of alkyl-substituted polystyrenes is that they are phase-selectively soluble which means that a polymer-bound catalyst can be separated from products in a biphasic separation that avoids a solvent-intensive precipitation process. Coupling of a 4-dimethylaminopyridine (DMAP) analog, Cinchona alkaloid derivative or phosphine-ligated metal catalyst to the poly(4-alkylstyrene) supports was used to prepare alkylated-polystyrene-bound catalysts. The recycling of these polymer-supported catalysts was affected using a biphasic liquid/liquid separation step after a monophasic reaction. Alkyl-substituted soluble polystyrene supports are found to be highly phase selectively soluble in heptane phase so that organo- and transition metal catalysts can be separated from products by thermomorphic or latent biphasic separations with minimum loss of the catalyst in the polar phase, which was monitored by fluorescence spectroscopy or by inductively coupled plasma mass spectrometry (ICP-MS).Item Physical aging of glassy polymers in confined environments(2012-12) Murphy, Thomas Matthew; Paul, Donald R.; Freeman, B. D. (Benny D.); Ellison, Christopher J; Vanden Bout, David A; Sanchez, Isaac CThis research project investigated the physical aging of glassy polymers in confined environments. Many recent studies of aging in glassy polymers have observed that aging behavior is often strongly affected by confinement. Understanding aging in confined environments (e.g., thin polymer films and nanocomposites) is vital for predicting long-term performance in applications that use confined glassy polymers, such as gas separation membranes and advanced nanocomposite materials. Aging in bulk and layered films produced via layer-multiplying co-extrusion was studied using gas permeability measurement and differential scanning calorimetry (DSC). The layered films consisted of polysulfone (PSF) and a rubbery co-layering material, with PSF layers ranging in thickness from ~185 nm to ~400 nm. Gas permeation aging studies at 35 °C revealed that the PSF layers in layered films aged in a manner that was similar to bulk PSF and independent of layer thickness. This finding differs from what was observed previously in freestanding PSF films, in which aging depended strongly on thickness and was accelerated relative to bulk. Isothermal aging studies at 170 °C and cooling rate studies were performed on both bulk and layered samples using DSC. The aging of the PSF layers was similar to aging in bulk PSF for films having PSF layer thicknesses of ~640 nm and ~260 nm, while the film with 185 nm PSF layers showed a slightly higher aging rate than that of bulk PSF. The results of the DSC studies generally support the conclusions of our gas permeation aging studies. The absence of strong thickness dependence in aging studies of layered films tends to support the idea that the effect of film thickness on physical aging stems from interfacial characteristics and not merely thickness per se. The physical aging of thin polystyrene (PS) films at 35 °C was also investigated using gas permeation techniques. PS films of 400 nm and 800 nm did not exhibit aging behavior that was highly accelerated relative to bulk or strongly dependent on film thickness. At the thicknesses and aging temperature considered, the aging of PS shows much weaker thickness dependence than that seen in polymers like PSF and Matrimid.Item Study of dynamic effects in microparticle adhesion using Atomic force microscopy(Texas A&M University, 2005-02-17) Kaushik, AnshulThe adhesion and removal of particles from surfaces is a contemporary problem in many industrial applications like Semiconductor manufacturing, Bioaerosol removal, Pharmaceuticals, Adhesives and Petroleum industry. The complexity of the problem is due to the variety of factors like roughness, temperature, humidity, fluid medium etc. that affect pull-off of particles from surfaces. In particle removal from surfaces using fluid motion, the dynamic effects of particle separation will play an important role. Thus it is essential to study the dynamic effects of particle removal. Velocity of pull-off and force duration effects are two important dynamic factors that might affect pull-off. Particle adhesion studies can be made using the Atomic Force Microscope (AFM). The velocity of pull-off and force duration can be varied while making the AFM measurements. The objective of the current work is to obtain the dependence of pull-off force on pull-off velocity. Experiments were conducted using AFM and the data obtained from the experiments is processed to obtain plots for pull-off force vs. particle size and pull-off force vs. pull-off velocity. The pull-off force is compared with the predictions of previous contact adhesion theories. A velocity effect on pull-off force is observed from the experiments conducted.Item The behavior and separation of polystyrene in mixed solvent systems(2009-05-15) Hamilton, Patrick NealNon-polar phase selective solubility of modified poly(4-n-alkylstyrene) supports can be measured using fluorescent dyes as catalyst surrogates with thermomorphic and latent biphasic systems. By modifying the solvent compositions in heptane/ethanol and heptane/N, N-dimethylacetamide, increased non-polar phase selective solubility of modified polystyrene supports can be attained. Likewise, by varying the structure and length of the pendant alkyl chain, an increase in non-polar phase selective solubility is measured. These heptane soluble polymer supports can be useful for applications involving heptane soluble polymer-bound reagents and catalysts. Various polar and non-polar polymer supports were synthesized with an attached solvatochromic catalyst surrogates to determine the solvent accessibility of the supported species in pure and mixed solvents. The results of these studies indicate that in pure solvents, the influence of both polar and non-polar polymer supports on the solvent microenvironment of these polymer-supported probes is minimal. In mixed solvent systems, a polymer-like solvent microenvironment is measured in solvent mixtures comprised of solvents the polymer has unfavorable interactions. Poly(4-n-alkylstyrene) and internally functionalized polyisobutylene supports are two such polymer supports that exhibit this behavior. For terminally functionalized polymers in mixed solvents, the solvatochromic behavior does not indicate a collapsed structure. In mixed solvents, there is minimal influence of the polymer support on the solvent microenvironment of these terminally functionalized polymers. The application of soluble polyisobutylene supported copper complexes in the ATRP polymerization of styrene was investigated. Using the difference in solubility of the product polystyrene and the polyisobutylene copper complex in heptane, a solid/liquid separation of the soluble copper complex from the solid product was achieved. The results of these polymerizations indicate that the polyisobutylene copper complex behaves exactly like a low molecular weight copper complex in terms of control over molecular weight and molecular weight distribution. After the polymerizations, the polyisobutylene complexes could be separated as a heptane solution and recycled in multiple polymerizations of styrene.Item Theoretical model of the pre-expansion of polystyrene foam(Texas Tech University, 1985-12) Wu, Tung-hoIn the production of expandable polystyrene (EPS) foam, it is desirable to be able to predict the density of the final product by some means other than empirical estimates. Therefore, a theoretical model was developed to predict the bulk density of EPS during a prepuffing expansion. This model was based on the assumption of an isothermal system with mass and momentum transfer processes governing the growth of a cell. Henry's law and the Flory-Huggin’ equation were used in a comparative way to describe the pneuaatogen-polymer melt equilibrium. The polymer melt was assumed to follow power law behavior. The resulting system of nonlinear ordinary differential and partial differential equations was reduced to a system of nonlinear ordinary differential equations by adopting a moment (integral) method- These equations were then solved by the Gear method of IMSL computer library. Considering the shape of cells, a lattice of face-centered cubic packing was chosen, and the cells were assumed to be of equal size. Finally, the bulk density of the complex multicelled EPS beads was estimated from the density of a single cell and was compared with the experimental data from air and helium pre-expansion processes. The influence of some variables (melt viscosity, interfacial tension, diffusion coefficient, gas solubility, concentration of pneumatogen, different expanding atmospheres, and nucleation density) on the bubble growth and the bead den* sity was also discussed.Item Transport properties of polystyrene above and below the glass transition temperature(Texas Tech University, 1983-12) Fike, Lawrence RobertIn the production of expandable polystyrene (EPS) foam, it is desirable to be able to predict the density of the final product by some means other than empirical estimates. Therefore, a mathematical model was developed to predict the density of EPS during a prepuffing expansion process. Use of the mathematical model requires some knowledge of the fundamental properties of viscosity, shear modulus, and mass diffusion coefficients for water and n-pentane through polystyrene. Since expansion is induced by thermal stimulus, these properties must be known as a function of temperature. The theoretical and experimental development in measuring these parameters constitute the bulk of the text in this thesis. A very simplistic Maxwell model for viscoelastic behavior was used as the basis for the theoretical development in the determination of the viscosity and shear modulus of polystyrene. Mass diffusion coefficients for water and n-pentane in polystyrene were determined by a solution to Fick's second law with appropriate initial and boundary conditions. Once the parameters had been determined, they were fit to an Arrhenius type model in order to determine temperature dependence. The transport properties were observed to be strongly affected by the polymer's glass transition. Finally, a computer program was developed and used to predict the density of EPS as a function of time during the expansion process.