Publications

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    ABSTRACT: In this work, we developed an interatomic potential for saturated hydrocarbons using the modified embedded-atom method (MEAM), a reactive semi-empirical many-body potential based on density functional theory and pair potentials. We parameterized the potential by fitting to a large experimental and first-principles (FP) database consisting of 1) bond distances, bond angles, and atomization energies at 0 K of a homologous series of alkanes and their select isomers from methane to n-octane, 2) the potential energy curves of H2, CH, and C2 diatomics, 3) the potential energy curves of hydrogen, methane, ethane, and propane dimers, i.e., (H2)2, (CH4)2, (C2H6)2, and (C3H8)2, respectively, and 5) pressure-volume-temperature (PVT) data of a dense high-pressure methane system with the density of 0.5534 g/cc. We compared the atomization energies and geometries of a range of linear alkanes, cycloalkanes, and free radicals calculated from the MEAM potential to those calculated by other commonly used reactive potentials for hydrocarbons, i.e., second-generation reactive empirical bond order (REBO) and reactive force field (ReaxFF). MEAM reproduced the experimental and/or FP data with accuracy comparable to or better than REBO or ReaxFF. The experimental PVT data for a relatively large series of methane, ethane, propane, and butane systems with different densities were predicted reasonably well by MEAM. Although the MEAM formalism has been applied to atomic systems with predominantly metallic bonding in the past, the current work demonstrates the promising extension of the MEAM potential to covalently bonded molecular systems, specifically saturated hydrocarbons and saturated hydrocarbon-based polymers.
    Physical Chemistry Chemical Physics 01/2014; · 4.20 Impact Factor
  • Sasan Nouranian
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    ABSTRACT: Molecular dynamics (MD) simulation is a powerful tool for exploring various materials phenomena at the nanoscale. However, successful prediction of these phenomena and associated material properties relies on the availability and use of an interatomic potential that correctly captures the energetics of the atomic interactions. Recently, a great deal of research interest has been expressed towards the MD simulation of damage initiation and evolution in various materials, specifically polymers and polymer/metal systems. Most interatomic potentials do not allow dynamic bond making and bond breaking during simulation, which is a prerequisite for studying the damage phenomena associated with the polymer failure at the molecular scale. Moreover, a great number of potentials have not been parameterized for multicomponent material systems. The objective of this work is to develop an interatomic potential for hydrocarbon-based polymers based on the modified embedded-atom method (MEAM), a reactive semi-empirical N-body potential based on density functional theory and pair potentials. To achieve the objective, an initial parameterization of the MEAM potential was performed for saturated hydrocarbons. The potential was parameterized by fitting to a large experimental and first-principles (FP) database consisting of bond distances, bond angles, and atomization energies of a homologous series of alkanes and their select isomers from methane to n-octane, and various potential energy curves of H2, CH, and C2 diatomics, hydrogen, methane, ethane, and propane dimers, and select pressure-volume-temperature (PVT) data of alkanes. The atomization energies and geometries of a range of linear alkanes, cycloalkanes, and free radicals calculated from the MEAM potential were compared to those calculated by other commonly used potentials for hydrocarbons, i.e., second-generation reactive empirical bond order (REBO) and reactive force field (ReaxFF). MEAM reproduced the experimental and/or FP data with great accuracy, comparable to or better than REBO or ReaxFF. The experimental PVT data for a relatively large series of methane, ethane, propane, and butane systems with different densities were predicted reasonably well by MEAM. This work is the first attempt to expand the parameter database of the MEAM potential beyond atomistic systems, i.e., metals and metallic alloys, to covalently bound molecular systems. The details of potential parameterization and results of various atomistic calculations are presented.
    13 AIChE Annual Meeting; 11/2013
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    ABSTRACT: A design of experiments and response surface modeling were performed to investigate the effects of formulation and processing factors on the flexural moduli and strengths of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. VGCNF type (pristine, surface-oxidized), use of a dispersing agent (no, yes), mixing method (ultrasonication, high-shear mixing, and a combination of both), and VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)) were selected as independent factors. Response surface models were developed to predict flexural moduli and strengths as a continuous function of VGCNF weight fraction. The use of surface-oxidized nanofibers, a dispersing agent, and high-shear mixing at 0.48 phr of VGCNF led to an average increase of 19% in the predicted flexural modulus over that of the neat VE. High-shear mixing with 0.60 phr of VGCNF resulted in a remarkable 49% increase in nanocomposite flexural strength relative to that of the neat VE. This article underscores the advantages of statistical design of experiments and response surface modeling in characterizing and optimizing polymer nanocomposites for automotive structural applications. Moreover, response surface models may be used to tailor the mechanical properties of nanocomposites over a range of anticipated operating environments.
    Journal of Applied Polymer Science 10/2013; 130(3):2087-2099. · 1.40 Impact Factor
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    ABSTRACT: Modern computational methods have proved invaluable for the design and analysis of structural components using lightweight materials. The challenge of optimizing light-weight materials in the design of industrial components relates to incorporating structure-property relationships within the computational strategy to incur robust de-signs. One effective methodology of incorporating structure-property relationships within a simulation-based design framework is to employ a hierarchical multiscale modeling strategy. This paper reviews techniques of multiscale modeling to predict the mechanical behavior of amorphous polymers. Hierarchical multiscale methods bridge nanoscale mechanisms to the macroscale/continuum by introducing a set of structure-property re-lationships. This review discusses the current state of the art and challenges for three distinct scales: quantum, atomistic/coarse graining, and continuum mechanics. For each scale, we review the modeling techniques and tools, as well as discuss important recent contributions. To help focus the review, we have mainly considered research devoted to amorphous polymers.
    Journal of Engineering Materials and Technology 07/2013; 131(4):041206. · 0.72 Impact Factor
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    ABSTRACT: The effects of vapor-grown carbon nanofiber (VGCNF) weight fraction, high-shear mixing time, and ultrasonication time on the Izod impact strengths of VGCNF/vinyl ester (VE) nanocomposites were studied using a central composite design. A response surface model (RSM) for predicting impact strengths was developed using regression analysis. RSM predictions suggested that an 18% increase in impact strength was possible for nanocomposites containing only 0.170 parts per hundred parts resin (phr) of VGCNFs (∼0.1 v%) that were high-shear mixed for 100 min when compared to that of neat VE. In general, the predicted impact strengths increased for high-shear mixing times above 55 min and VGCNF weight fractions below 0.400 phr. The predicted strengths decreased as the VGCNF weight fraction was further increased. Scanning electron micrographs of the nanocomposite fracture surfaces showed that increased impact strength could be directly correlated to better nanofiber dispersion in the matrix.
    Journal of Applied Polymer Science 04/2013; 128(2):1070-1080. · 1.40 Impact Factor
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    54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; 04/2013
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    ABSTRACT: The effects of moulding condition and curing atmosphere on the flexural properties of a neat 33 wt.%-styrene epoxy vinyl ester (VE) were investigated. Specimens were prepared using either open or closed moulds, and thermally cured under either air or nitrogen atmosphere. Four-point bending tests were performed with both the top ("air-side") and the bottom ("mould-side") surfaces of the cured specimens in tension. The mean flexural moduli for nitrogen-cured and closed-mould specimens were 3% and 9% higher than for air-cured specimens, respectively. However, the mean flexural strength for open-mould air-cured specimens with their air-sides loaded in tension were 65% lower than the mean flexural strengths of open-mould nitrogen-cured or closed-mould specimens. This likely resulted from partial VE resin curing inhibition due to oxygen diffusion into the free surface region of the open-mould air-cured specimens. This creates gradients in the local stiffness and strength in the near-surface region due to lower crosslink density. This effect may be particularly important for thin specimens. These results underscore the significance of exposure to air during open-mould curing on the cured VE flexural properties. Such assessments are crucial for composite part manufacturing utilizing VEs.
    Polymers and Polymer Composites 03/2013; 21(2):61-64. · 0.31 Impact Factor
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    ABSTRACT: A full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high-shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120°C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single-factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (∼20% increase over neat VE) by using high-shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at ∼0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at ∼0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF-enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments.
    Journal of Applied Polymer Science 01/2013; 130(1):234-247. · 1.40 Impact Factor
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    ABSTRACT: In this study, data mining and knowledge discovery techniques were employed to validate their efficacy in acquiring information about the viscoelastic properties of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites solely from data derived from a designed experimental study. Formulation and processing factors (VGCNF type, use of a dispersing agent, mixing method, and VGCNF weight fraction) and testing temperature were utilized as inputs and the storage modulus, loss modulus, and tan delta were selected as outputs. The data mining and knowledge discovery algorithms and techniques included self-organizing maps (SOMs) and clustering techniques. SOMs demonstrated that temperature had the most significant effect on the output responses followed by VGCNF weight fraction. SOMs also showed how to prepare different VGCNF/VE nanocomposites with the same storage and loss modulus responses. A clustering technique, i.e., fuzzy C-means algorithm, was also applied to discover certain patterns in nanocomposite behavior after using principal component analysis as a dimensionality reduction technique. Particularly, these techniques were able to separate the nanocomposite specimens into different clusters based on temperature and tan delta features as well as to place the neat VE specimens (i.e., specimens containing no VGCNFs) in separate clusters. Most importantly, the results from data mining are consistent with previous response surface characterizations of this nanocomposite system. This work highlights the significance and utility of data mining and knowledge discovery techniques in the context of materials informatics.
    Advanced Engineering Informatics 01/2013; 27(4):615–624. · 1.59 Impact Factor
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    ABSTRACT: This paper characterizes the failure of a polymeric clamp hanger component using finite element analysis coupled with experimental methods such as scanning electron microscopy, X-ray computed tomography, and mechanical testing. Using Fourier transform infrared spectroscopy, the material was identified as a polypropylene. Internal porosity that arose from the manufacturing procedure was determined using three dimensional X-ray computed tomography. From static mechanical experiments, the forces applied on the component were determined and used in a finite element simulation, which clearly showed the process of fracture arising from the pre-existing processing pores. The fracture surfaces were observed under a scanning electron microscope confirming the finite element simulation results illustrating that low-cycle fatigue fracture occurred in which the fatigue cracks nucleated from the manufacturing porosity.
    Engineering Failure Analysis 12/2012; 26:230–239. · 1.13 Impact Factor
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    ABSTRACT: The effects of four critical formulation and processing factors on the flexural moduli and strengths of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites were investigated using a mixed-level full factorial experimental design. The factors included vapor-grown carbon nanofiber (VGCNF) type (pristine, surface-oxidized), use of a dispersing agent (no, yes), mixing method (ultrasonication, high-shear mixing, and a combination of both), and VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)). Response surface models were developed to predict flexural moduli and strengths as a function of VGCNF weight fraction. The use of surface-oxidized carbon nanofibers, a dispersing agent, and high-shear mixing at 0.48 phr of VGCNF gave an average increase of 19% in the flexural modulus over that of the neat VE. High-shear mixing with 0.60 phr of VGCNF resulted in a remarkable 49% increase of nanocomposite flexural strength. This study highlights the use of design of experiments and response surface modeling to both predict and optimize nanocomposite mechanical properties.
    12 AIChE Annual Meeting; 10/2012
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    ABSTRACT: Surface oxidation effects on the liquid vinyl ester (VE) monomer distributions near two oxidized vapor-grown carbon nanofiber (VGCNF) surfaces were studied using molecular dynamics simulations. Two overlapping graphene sheets containing oxygenated functional groups represented the oxidized VGCNF surfaces. Two liquid VE bisphenol-A dimethacrylates (designated VE1 and VE2, respectively) and styrene constituted the resin. Temporally and spatially averaged relative monomer concentrations, calculated in a direction away from the oxidized graphene surfaces, showed increased styrene and VE1 concentrations. Monomer molar ratios found within a 10Å thick region adjacent to the oxidized graphene sheets were substantially different from those in the bulk resin. Curing should result in the formation of a very thin interphase region of different composition. The crosslink structure of such an interphase will be distinct from that of an unoxidized VGCNF surface. The enhanced VE1 concentration near this oxidized surface should give a higher crosslink density, leading to a stiffer interphase than that adjacent to unoxidized VGCNF surfaces. VGCNF–matrix adhesion may also be modified by the different interphase monomer molar ratios. These studies may facilitate multiscale material design by providing insight into carbon nanofiber–matrix interactions leading to improved macroscale composite properties.
    Carbon. 03/2012; 50(3):748-760.
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    ABSTRACT: Molecular dynamics simulations were used to study the effect of vapor-grown carbon nanofiber (VGCNF) surface oxidation on VGCNF-vinyl ester (VE) resin monomer interactions. It was anticipated that the interfacial interactions between resin monomers and the oxidized carbon nanofiber surface would result in different local molar ratios of the resin monomers compared to the bulk resin. The resin was comprised of styrene and two VE monomers with either one or two bisphenol A groups in their backbones (designated as VE1 and VE2, respectively). Differences in local molar ratios of these resin monomers may result in the formation of an interphase region in the final cured nanocomposite. The time-averaged relative concentration profiles were used to monitor the temporal and spatial distributions of the resin monomers in a simulation cell of size 60×50×60 Å3. Initially the cell was filled with monomers in a ratio consistent with a 33 wt% commercial epoxy vinyl ester resin (Derakane 441-400, Ashland Co.). The idealized VGCNF surface was represented by two overlapped (shingled) graphene sheets, which were in contact with the resin. Oxidation of the graphene sheets was represented by the introduction of functional groups on the edges and the surfaces of the graphene sheets. The edges were more highly oxidized than the surfaces, containing of hydroxyl, phenolic, lactone, quinone, hydroquinone, and anhydride functional groups. Hydroxyl, epoxide, aromatic, ketone and carboxylic acid groups were attached to the surfaces (e.g. basal planes). These functional groups have been previously identified in our laboratory [1]. The NVT (constant number of atoms, N; constant volume, V; constant temperature, T) ensemble was used for simulations. All simulations were conducted with a simulation time of 10 ns at 1000 K for monomer distribution equilibration followed by another 5 ns simulation at 300 K. The relative concentration profiles were generated for the direction roughly perpendicular to the graphene sheet surfaces. The VE1 monomer concentration was higher near the oxidized graphene surface, compared to a simulation performed using a pristine graphene [2], where VE1 was depleted near the graphene surface. Styrene accumulated in the interfacial region in both cases, but more so for the pristine surface. Overall, a ~5 Å thick interfacial region was observed near each surface of the graphene sheet. In these regions, the monomer molar ratios differed from those in the bulk resin. The increased concentration of VE1 near the oxidized carbon nanofiber surface may lead to a stiffer interphase compared to the bulk matrix. In addition, favorable VGCNF-matrix polar interfacial interactions may lead to increased interfacial adhesion and subsequently, increase the interfacial shear strength in the final cured nanocomposite. The results of this study can be extended to other resins and surfaces. [1] Lakshminarayanan, PV, Toghiani, H, Pittman, CU. Nitric acid oxidation of vapor grown carbon nanofibers. Carbon 2004; 42: 2422-2433. [2] Nouranian, S, Jang, C, Lacy, TE, Gwaltney, SR, Toghiani, H, Pittman Jr, CU. Molecular dynamics simulations of vinyl ester resin monomer interactions with a pristine vapor-grown carbon nanofiber and their implications for composite interphase formation. Carbon (In Press).
    2011 AIChE Annual Meeting; 10/2011
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    ABSTRACT: A molecular dynamics simulation study was performed to investigate the role of liquid vinyl ester (VE) resin monomer interactions with the surface of pristine vapor-grown carbon nanofibers (VGCNFs). These interactions may influence the formation of an interphase region during resin curing. A liquid resin having a mole ratio of styrene to bisphenol-A-diglycidyl dimethacrylate VE monomers consistent with a commercially available 33 wt.% styrene VE resin was placed in contact with both sides of two pristine graphene sheets overlapped like shingles to represent the outer surface of a pristine VGCNF. The relative monomer concentrations were calculated in a direction away from the graphene sheets. At equilibrium, the styrene/VE monomer ratio was higher in a 5 Å thick region adjacent to the nanofiber surface than in the remaining liquid volume. The elevated concentration of styrene near the nanofiber surface suggests that a styrene-rich interphase region, with a lower crosslink density than the bulk matrix, could be formed upon curing. Furthermore, styrene accumulation in the immediate vicinity of the nanofiber surface might, after curing, improve the nanofiber–matrix interfacial adhesion compared to the case where the monomers were uniformly distributed throughout the matrix.
    Carbon 08/2011; 49(10):3219-3232. · 6.16 Impact Factor
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    Sasan Nouranian
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    ABSTRACT: The use of nanoreinforcements in automotive structural composites has provided promising improvements in their mechanical properties. For the first time, a robust statistical design of experiments approach was undertaken to demonstrate how key formulation and processing factors (nanofiber type, use of dispersing agent, mixing method, nanofiber weight fraction, and temperature) affected the dynamic mechanical properties of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Statistical response surface models were developed to predict nanocomposite storage and loss moduli as functions of significant factors. Only ∼0.50 parts of nanofiber per hundred parts resin produced a roughly 20% increase in the storage modulus versus that of the neat VE at room temperature. Optimized nanocomposite properties were predicted as a function of design factors employing this methodology. For example, the use of high-shear mixing (one of the mixing methods in the design) with the oxidized VGCNFs in the absence of dispersing agent or arbitrarily with pristine VGCNFs in the presence of dispersing agent was found to maximize the predicted storage modulus over the entire temperature range (30-120 °C). To study the key concept of interphase in thermoset nanocomposites, molecular dynamics simulations were performed to investigate liquid VE resin monomer interactions with the surface of a pristine VGCNF. A liquid resin having a mole ratio of styrene to bisphenol A-diglycidyl dimethacrylate monomers consistent with a 33 wt% styrene VE resin was placed in contact with both sides of pristine graphene sheets, overlapped like shingles, to represent the outer surface of a pristine VGCNF. The relative monomer concentrations were calculated in a direction progressively away from the surface of the graphene sheets. At equilibrium, the styrene/VE monomer ratio was higher in a 5 A thick region adjacent to the nanofiber surface than in the remaining liquid volume. The elevated styrene concentration near the nanofiber surface suggests that a styrene-rich interphase region, with a lower crosslink density than the bulk matrix, could be formed upon curing. Furthermore, styrene accumulation in the immediate vicinity of the nanofiber surface might, after curing, improve the nanofiber-matrix interfacial adhesion compared to the case where the monomers were uniformly distributed throughout the matrix.
    04/2011; ProQuest, UMI Dissertation Publishing., ISBN: 1249037719
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    ABSTRACT: A design of experiments approach demonstrated how four formulation and processing factors (i.e., nanofiber type, use of dispersing agent, mixing method, and nanofiber weight fraction) affected the dynamic mechanical properties of carbon nanofiber/vinyl ester nanocomposites. Only
    Journal of Composite Materials 01/2011; 45(16):1647-1657. · 0.94 Impact Factor
  • Models, Databases, and Simulation Tools Needed for the Realization of Integrated Computational Materials Engineering: Proceedings of the Symposium Held at Materials Science & Technology 2010, October 18-20, 2010 Houston, Texas, USA, Edited by Steven M. Arnold, Terry T. Wong, 01/2011: chapter Some Key Issues in Multi-Scale Modeling of Thermoset Nanocomposites/Composites: pages 128-140; ASM International., ISBN: 1615038434
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    ABSTRACT: The role of interphase, the matrix region immediately surrounding the nanoreinforcement, in polymeric nanocomposites is believed to be pivotal in determining the ultimate mechanical properties of these materials. Though this has been confirmed for thermoplastic matrix nanocomposites, no clear understanding now exists for thermoset matrix nanocomposites. Here, a molecular dynamics (MD) simulation was performed on vinyl ester (VE)/vapor-grown carbon nanofiber (VGCNF) nanocomposites, where the interactions of resin constituents (VE monomers and styrene) with the surface of two overlapping (shingled) graphene sheets representing the surface of a pristine carbon nanofiber were investigated. This could have implications during the formation of an interphase region in the resin curing step. Using the Accelrys Materials Studio v5.0 MD simulation software, a periodic boundary system containing VE monomers and styrene in contact with both sides of the graphene sheets were constructed. The resin system was based on Derakane 441-400 epoxy VE resin (Ashland Co.) with 33 wt% styrene. This resin is a mixture of VE monomers with an average molecular weight of 690 g/mol and n = 1.62 bisphenol-A groups in the backbone. In the simulation, 38 VE monomers with n = 1, 62 VE monomers with n = 2, and 320 styrene molecules were used to represent the true monomer mole ratios. The total number of atoms was 17180. Using the COMPASS force filed, the simulation cell of liquid resin and graphene sheets was relaxed for 50000 steps (time step of 1 fs) at 300 K before the dynamics simulation using the Conjugate Gradient method. The density was adjusted to 1.18 g/cm3, which is in accordance with the experimentally measured density. Then, dynamics simulation was started using the NVT ensemble at 10 K with a time step of 1 fs. The simulation ran for 1 ps at this temperature. Next, the temperature was ramped up to 50 K and further up to 600 K in increments of 50 K. At each intermediate temperature the dynamics simulation ran for 1 ps except for 300 K where it ran for 100 ps. At 600 K, the simulation ran for a total time of 10 ns. The trajectory files were saved every 100 ps. The system was then cooled down to 300 K in the same manner and the simulation ran for another 5 ns. Time-averaged concentration profiles were obtained for styrene and VE monomers. Based on the results, styrene accumulates on the nanofiber surface yielding a higher styrene to VE oligomer ratio in the interphase region. This suggests that, in contrast to most thermoplastic matrices, a softer interphase may result in VE/VGCNF nanocomposites when the curing is completed since the crosslink density will be lower in this region due to higher styrene concentration. This assumes that the polymerization kinetics are fast enough that a growing chain end remains in this interface region long enough that the polymerization composition will reflect this local equilibrium concentration of monomers.
    2010 AIChE Annual Meeting; 11/2010
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    ABSTRACT: Recent advances in the field of polymer nanocomposites and nanophased hybrid composites have provided new opportunities in the design and fabrication of novel light-weight structural materials for use in automotive parts. Though preliminary studies show promising improvements in the mechanical, thermal, and other properties of traditional composites reinforced with small amounts of nanoreinforcing agents including nanotubes, nanofibers, nanoclays, etc., a more systematic study is needed encompassing formulation, mixing, and processing of nanocomposites. This is specifically true because of issues with the dispersion of nanoreinforcements in the polymer matrix and a lack of knowledge with respect to the factors affecting the ultimate properties of interest. In this study, which builds on our previous studies [1,2], a designed experimental approach has been employed to study the effect of three formulation factors on the viscoelastic properties of vapor-grown carbon nanofiber/vinyl ester nanocomposites. These factors are: nanofiber weight fraction, nanofiber type (pristine/oxidized), and use of a dispersing agent. The mixing procedure used in these studies was a coupled high-shear mixing/ultrasonication technique. Using analysis of variance and regression techniques, a response surface model was developed for the current design and optimal conditions were determined. The nanofiber weight fraction was the major factor with significant effect on the storage and loss moduli, while the other factors had minor effects. The results were further compared to the cases studied previously [1,2] where the mixing method involved only ultrasonication or high-shear mixing.
    11/2009;
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    50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; 05/2009

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