The influence of PDMS-polyisoprene diblock copolymers on the dynamic rheological properties of silica-filled uncured polyisoprene was investigated. Unlike binary silica-polyisoprene systems, the ternary systems in our study showed a decrease in low-amplitude dynamic storage modulus (G') with room-temperature storage time. This aging behaviour is accompanied by an increase in the concentration PDMS segments at the filler-polymer interface, as measured by solid-state 1H NMR. The decrease in G' is thus attributed to a progressive disruption of a filler-filler network by selective block copolymer adsorption onto the filler surface.

A new method to prepare novel nanocomposites has been studied in which a polyhedral oligomeric silsesquioxane (POSS) monomer is grafted to a polyisoprene-block-polystyrene copolymer to yield an inorganic-organic hybrid copolymer (POSS-g-PI-block-PS). PS-block-PI copolymers (SI) were synthesized via anionic polymerization in tetrahydrofuran (THF) as solvent. The polyisoprene block of the SI diblock copolymers in this study featured a very high vinyl group fraction (65 mole % of 3,4- addition and 35 mole % of 1,2-addition) available to react with hydride-substituted POSS (isobutyldimethyl silane-POSS) to form a grafted block copolymer. Due to the immiscibility between POSS-grafted PI block and PS block, the grafted block copolymer developed a microdomain structure. The volume fraction of PS block in the grafted block copolymer was varied in the range of 0.45 to 0.37 in order to yield cylindrical PS microdomains in the matrix of POSS-grafted PI. After exposure to an oxygen plasma, it is expected that preferential erosion of the grafted block copolymer will occur for the organic potion (PS microdomains) thus leaving a well-defined nanoporous surface structure for nonlithographic functionalization of coated substrates.

Gold nanoparticles with thiol stabilizing layers were prepared with various fractions of end-functional thiols. Alcohol end-groups were further elaborated to norbornyl moieties so that a ruthenium alkylidene initiator could be tethered to the nanoparticle surfaces. In two different nanoparticle formulations the functional thiols possessed hydrocarbon chains that held the metal centers either near to or far from the surface of the thiol stabilizing layer. The tethered organometallic complexes were used to initiate polymerization from the nanoparticle surfaces. Liquid crystalline polymer was grown from nanoparticles where the metal center was tethered far from the surface but polymerization could not be initiated when the metal centers were held close to the surface. We hypothesize that steric hindrance is controlled by the length of the tethering thiol. Polarized optical microscopy showed that the polymer coated gold nanoparticles could still form a nematic mesophase at elevated temperature although the orientation of mesogens is restricted by crowding at the nanoparticle surface. Samples of unbound polymer were also prepared and exhibited similar transition behavior.

We present a mesoscale model that describes the tensile stress of silica-filled polydimethylsiloxane (PDMS) under elongation. Atomistic simulations of a single chain of PDMS, interacting with itself and/or a hydroxylated silica surface provide estimates of the microscopic forces required to stretch or uncoil a chain of PDMS, or detach it from a silica surface Using these results, we develop a mesoscale, inter-particle strength model for uncrosslinked, silica-filled PDMS. The strength model includes these atomistic forces, as determined from the simulations, a small entropic component, and a Gaussian probability distribution to describe the distribution of chain lengths of PDMS strands connecting two silica particles and the chain lengths in the free ends. We obtain an analytic stress/strain expression whose predictions agree with experiment.

The overall goal of this research is to explore techniques for the development of novel binary magnetic oxide nanoclusters uniformly distributed within a polymer matrix. These CoFe2O4 nanoclusters were synthesized at room temperature, and are confined within the self-assembled nanoscale structure exhibited by block copolymers templates. The diblock copolymers were synthesized by ring opening metathesis polymerization of norbornene and norbornene trimethylsilane and the binary magnetic oxide was introduced through a nanoreaction scheme using wet chemical methods. Transmission electron micrographs of microtomed thin sections of these nanocomposites show that the metal oxide nanoclusters are ellipsoidal in shape and are uniformly distributed within the polymer matrix. A SQUID magnetometer was used to study the magnetic properties of the polymeric nanocomposites at applied fields up to 5 Tesla and at a temperature range between 300 °K and 5 °K. Mössbauer spectroscopy was used to study the structure of the nanoconfined metal oxide, and confirmed the synthesis of CoFe2O4 nanoclusters exhibiting an inverse spinel structure. This study provided a better understanding of the nucleation, growth and distribution of metal oxide nanoclusters within block copolymers and indicated ways to control the magnetic properties of polymeric based nanocomposite materials. The development of such binary metal oxide - block copolymer nanocomposites is targeting the functionalization of such nanostructures into magnetic device technologies.

We present simulation results of the effect of nanoscopic and micron-sized fillers on the structure, dynamics and mechanical properties of polymer melts and blends. At the smallest length scales, we use molecular dynamics simulations to study the effect of a single nano-filler on the structure and dynamics of the surrounding melt. We find a tendency for polymer chains to be elongated and flattened near the filler surface. Additionally, the simulations show that the dynamics of the polymers can be dramatically altered by the choice of polymer-filler interactions. We use time-dependent Ginzburg-Landau simulations to model the mesoscale phase-separation of an ultra-thin blend film in the presence of an immobilized filler particle. These simulations show the influence of filler particles on the mesoscale blend structure when one component of the blend preferentially wets the filler. Finally, we present some preliminary finite element calculations used to predict the effect of mesoscale structure on macroscopic ultrathin film mechanical properties.

Layered nanocomposites of molybdenum disul.de (MoS2) andp oly (ethylene oxide) (PEO) were studied using x-ray di.raction of powder and oriented thin.lm samples. Thermal gravimetric analysis provided information on the composition of the material. The e.ects of the molecular weight of PEO andthe atmospheric relative humidity on the structure were also investigated. A basal plane spacing of 14.3 °, corresponding to an expansion of 8.1 ° between MoS2 layers, was foundfor dry samples, in agreement with the literature. At about 30% humidity, the expansion increases to 10.6°. This increase corresponds approximately to the thickness of one monolayer of water. The spacing is constant until around80% humidity, when the expansion begins to increase again, reaching up to 25 ° near 100% humidity. X-ray coherence lengths in the direction perpendicular to the planes averaged13, 7 and 2 MoS2 layers for the dry, 58% humid and nearly 100% humid samples, respectively.

Carbon coated silica made by flame synthesis was investigated for reinforcement of styrene-butadiene (SBR) rubber. These composite silica/carbon fillers were examined through small angle x-ray scattering (SAXS), TEM, and AFM showing that these fillers have a rough fractal surface and have fractal aggregate structures. The carbon coated silica fillers were compounded with elastomers and their effect on reinforcement was measured using dynamic mechanical analysis and tensile testing. These fillers were also compared to commercial fumed silica, carbon black, and carbon black/silica composite fillers.

Carbon black in a polymer melt was used to model self-organized processes. A gradual growth of ionic concentration in the polymer melt induced a complex behavior, including a rapid increase in AC conductivity after a time delay. Colloid theory can provide an effective interpretation. The metamorphoses of the carbon black assembly include soft axial order generation, soft lateral order generation, axial condensation, and lateral condensation of carbon black particles, respectively. Similar processes are expected to be effective in generating complex carbonaceous organic structures in natural water.

Commercial silicone rubbers typically contain submicron particles dispersed within them, the particles being responsible for the mechanical properties required for commercial success. Fumed silica has long been used for the reinforcement of higher-perfomance silicone rubber compositions, but high-porosity aerogels can function as well. The object of the work here was to compare the state of dispersion of some high-porosity aerogels with that of a fumed silica.

Model silicone HCR (“heat-cured rubber”) compositions were prepared, and their mechanical properties characterized. Thin sections of the rubbers were then examined by TEM.

Much of the fumed silica had been dispersed to give sub-micron sized features, although a number of larger features were present. The hydrophobic aerogel, in contrast, had been dispersed to give even finer features in the rubber, with very few super-micron fragments. The state of dispersion of the hydrophilic aerogel was quite different, showing many poorly-broken down large fragments up to 5 µm or more in diameter. The visual appearance of the compound reflected this poorer state of dispersion.

Molecular orientation of octadecyl alkyl side chains at the poly (vinyl octadecyl carbamates-co-vinyl acetate) polymer-air interface has been studied using surface sensitive sum frequency generation (SFG) spectroscopy. At 280C, below the side chain crystalline transition temperature, the SFG spectra show strong methyl vibrations indicating ordered alkyl side chains at the polymer-air interface. In the liquid state (980C), the SFG spectra show higher contributions from the methylene vibrations indicating higher gauche defects at the interface. This surface order to disorder transition is gradual and spans over a broad temperature range (50-900C), where the bulk is in the smectic liquid crystalline state.

Only a limited number of structural studies have been performed on polyurethanes using scanning probe techniques to determine both the microstructure and the corresponding distribution of hard and soft segments within samples. This type of information is needed to better understand the mechanical properties of these materials and to facilitate modeling. In order to address these issues, we have fabricated a series of compression molded segmented poly(ester urethane) samples with hard (HS) to soft segment ratios from 19 to 100%. Samples were examined using scanning probe phase imaging techniques to obtain the topography and corresponding distribution of hard domains before and after heating at 100°C.

A number of significant differences were observed between the pre- and post-heat treated samples. Variations in structure and heat-induced morphological changes were directly related to HS content. Fine strand- or fibril-like structures were most prominent in the 23 and 19% HS sample but first appeared at 30% HS. Harder, thicker elongated structures dominated the surface of the100% HS sample and were seen to a limited extent on all samples, especially after annealing and quenching. The 23% HS sample surface structure depended on quenching rate and time after treatment.

In this paper, shape-stabilized phase change materials (PCMs) based on paraffin and thermoplastic elastomer poly(styrene-butadiene-styrene) are prepared. The shape-stabilized PCMs can keep the same shape in a solid state even when their temperature is above the melting point of the paraffin. They exhibit same phase transition characteristics as paraffin and up to 80% of the latent heat of paraffin. Thermal conductivity of the shape-stabilized PCMs is increased significantly by the introduction of expanded graphite (EG). The time for complete solidification and complete melting of the composite P(80)/S(20)/EG(3) is two ninths and two fifths of paraffin, respectively.

X-ray diffraction, Raman spectroscopy, and neutron scattering were used to characterize structure of carbon blacks. Different grades, N990, N774, N299, N134, and N110, untreated, after heat treatment and compressed at 2.5 GPa have been investigated. The average sizes of the crystallites obtained by X-ray diffraction agree with those estimated from Raman spectra. The distribution functions of crystallite sizes were evaluated from X-ray diffraction using the recently developed method. Heat treatment results in increased vertical and lateral sizes of graphitic crystallites. Postproduction pressure treatment has little effect on the average sizes of the crystallites, however, it affects the crystallite size distribution function. The magnitude of strain within the crystallites is affected by applied pressure. The relative concentration of amorphous carbon blacks estimated from Raman spectra decreases with increasing temperature but not with increased pressure. It is suggested that the initial growth is associated with alignment of the existing graphitic planes and later by incorporating aromatic carbon into the crystallites.

The effect of nanoparticles on the phase stability of an immiscible PS/PMMA blend was studied in thin film samples. Using AFM and selective dissolution we find that nanoparticles affect the domain evolution of the polymer blend. Annealing of the pure PS/PMMA blend at 190 °C leads to PS drops that protrude from the PMMA surface. Films containing the nanoparticles show similar surface features but these features become less regular and tend to get shallower and larger as the amount of nanoparticles increases. The characteristic length of the PS drops in the pure blend film is ∼ 7 microns and they cover 22 % of the surface. The corresponding numbers for the film containing 10% nanoparticles are 15 microns and 65%, respectively.

Motivated by recent experiments on filled polymer thin films, we study the effect of the presence of filler particles on phase separating mixtures. Using a generalized Cahn-Hillard-cook model, we show that the preferential wetting of one phase on the filler surface generates transient composition waves in the phase separating blends. The interference of the composition waves from different particles can stabilize the transient patterns, leading to desirable control of the morphology.

We have demonstrated that films of single clay platelets can be produced by the Langmuir technique where a solution of organoclay particles dissolved in xylene was spread at the air water interface. The total thickness of the layer was found to be 21 ± 3Å which is in good agreement with previous X-ray diffraction data. Scanning probe microscopy showed the individual platelets to be rectangular in shape with an aspect ratio in excess of 100 to 1 and of uniform organic surfactant coverage.

In an effort to determine the optimal balance of electrical and mechanical performance for electrically conductive polymer composites, three figures of merit were evaluated. All three figures of merit displayed peaks and/or discontinuities at a particular filler loading. These loadings appear to correspond to the critical pigment volume concentration for a given system. Composite systems based upon latex as the matrix starting material showed peaks in the figures of merit at very low carbon black concentrations (10 vol%), while composites prepared with polymer solutions or melts had peaks above 20 vol% carbon black. These differences in behavior are attributed to differences in microstructural evolution that occur with filler loading.

Particles of tread rubber debris produced by laboratory wear tests are imaged by light microscopy. The fractal dimension, DF, of the image perimeter is estimated. The sensitivity of DF with respect to the image acquisition and processing parameters is determined. Particles belonging to two types of undifferentiated debris, low severity (LS) and rasping (R), respectively, are analyzed. The values of DF have distributions, which, if suitably interpreted, allow the identification of either debris type with the following conditional probabilities: pLS|LS = 0.71 and pR|R = 0.81. The procedure can be eventually applied to environmental impact studies.

We have mapped the physics of a system of random copolymers onto a time-dependent density functional-type field theory using techniques of functional integration. Time in the theory is merely a label for the location of a given monomer along the extent of a flexible chain. We derive heuristically within this approach a non-local constraint which prevents segments on chains in the system from straying too far from each other, and leads to self-assembly. The structure factor is then computed in a straightforward fashion. The dependence of various calculated quantities on the average chain length are compared with experiments. The profile and size of spherulitic mesoscale domains is also computed.