Browsing by Subject "Polymer nanocomposites"
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Item Characterization of Nanoscale Reinforced Polymer Composites as Active Materials(2012-02-14) Deshmukh, SujaySingle walled carbon nanotube (SWNT)-based polymer nanocomposites have generated a lot of interest as potential multifunctional materials due to the exceptional physical properties of SWNTs. To date, investigations into the electromechanical response of these materials are limited. Previous studies have shown marginal improvements in the electromechanical response of already electroactive polymers (EAPs) with addition of SWNTs. However, in general, disadvantages of EAPs such as high actuation electric field, low blocked stress and low work capacity remain unaddressed. This dissertation targets a comprehensive investigation of the electromechanical response of SWNT-based polymer nanocomposites. Specifically, the study focuses on incorporating SWNTs in three polymeric matrices: a non-polar amorphous polyimide (CP2), a polar amorphous polyimide ((-CN) APB-ODPA), and a highly polar semicrystalline polymer (PVDF). In the first step, emergence of an electrostrictive response is discovered in the non-polar polyimide CP2 in the presence of SWNTs. Transverse and longitudinal electrostrictive coefficients are measured to be six orders of magnitude higher than those of known electrostrictive polymers like polyurethane and P(VDF-TrFE) at less than 1/100th of the actuation electric fields. Next, the effect of the polymer matrix on the electrostrictive response is studied by focusing on the polar (-CN) APB-ODPA. A transverse electrostriction coefficient of 1.5 m2/MV2 is measured for 1 vol percent SWNT- (-CN) APB-ODPA, about twice the value found for 1 vol percent SWNT-CP2. The high value is attributed to higher dipole moment of the (-CN) APB-ODPA molecule and strong non-covalent interaction between the SWNTs and (-CN) APB-ODPA matrix. Finally, polyvinylidene fluoride (PVDF) matrix is selected as a means to optimize the electrostrictive response, since PVDF demonstrates both a high dipole moment and a strong non-covalent interaction with the SWNTs. SWNT-PVDF nanocomposites fared better than SWNT-CP2 nanocomposites but had comparable response to SWNT-(-CN) APB-ODPA nanocomposites. This was attributed to comparable polarization in both the polar nanocomposite systems. To maximize the SWNT-PVDF response, SWNT-PVDF samples were stretched leading to increase in the total polarization of the nanocomposite samples and decrease in the conductive losses. However, the dielectric constant also decreased after stretching due to disruption of the SWNT network, resulting in a decrease of the electrostrictive response.Item Coarse-grained simulations to predict structure and properties of polymer nanocomposites(2010-12) Khounlavong, Youthachack Landry; Ganesan, Venkat; Sanchez, Isaac C.; Freeman, Benny D.; Truskett, Thomas M.; Ren, PengyuPolymer Nanocomposites (PNC) are a new class of materials characterized by their large interfacial areas between the host polymer and nanofiller. This unique feature, due to the size of the nanofiller, is understood to be the cause of enhanced mechanical, electrical, optical, and barrier properties observed of PNCs, relative to the properties of the unfilled polymer. This interface can determine the miscibility of the nanofiller in the polymer, which, in turn, influences the PNC's properties. In addition, this interface alters the polymer's structure near the surface of the nanofiller resulting in heterogeneity of local properties that can be expressed at the macroscopic level. Considering the polymer-nanoparticle interface significantly influences PNC properties, it is apparent that some atomistic level of detail is required to accurately predict the behavior of PNCs. Though an all-atom simulation of a PNC would be able to accomplish the latter, it is an impractical approach to pursue even with the most advanced computational resources currently available. In this contribution, we develop (1) an equilibrium coarse-graining method to predict nanoparticle dispersion in a polymer melt, (2) a dynamic coarse-graining method to predict rheological properties of polymer-nanoparticle melt mixtures, and (3) a numerical approach that includes interfacial layer effects and polymer rigidity when predicting barrier properties of PNCs. In addition to the above, we study how particle and polymer characteristics affect the interfacial layer thickness as well as how the polymer-nanoparticle interface may influence the entanglement network in a polymer melt. More specifically, we use a mean-field theory approach to discern how the concentration of a semiflexible polymer, its rigidity and the particle's size determine the interfacial layer thickness, and the scaling laws to describe this dependency. We also utilize molecular dynamics and simulation techniques on a model PNC to determine if the polymer-nanoparticle interaction can influence the entanglement network of a polymer melt.Item Conductive nickel nanostrand-reinforced polymer nanocomposites(2013-05) Lu, Chunhong; Krifa, MouradConductive and flexible nanocomposites can have wide applications in textiles, including wearable sensors, antenna, electrodes, etc. The objective of this research is to develop electrically conductive fibers and films that are flexible and deformable for use in textile structures able to accommodate the drape and movement of the human body. To achieve this objective, we evaluate the electrical properties of PEDOT:PSS/nickel nanostrand as well as nylon 6/nickel nanostrand nanocomposites. Nickel nanostrands (NiNS) were first used to reinforce an intrinsically conductive polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT:PSS), in order to fabricate nanocomposite films with high electrical conductivity. The electrical properties of the films were evaluated by the Van der Pauw method. The addition of 10 wt% nanostrands in PDOT:PSS provided a two order of magnitude improvement in electrical conductivity. In addition to PDOT:PSS, nylon 6/NiNS nanocomposite fibers were produced using electrospinning and exhibited diameters in the sub-micron range. The NiNS-reinforced fibers had electrical conductivity that exceeded the ESD range, which offers the potential for use in protective textile applications.Item Effects of electrical fields in aligning SWNTs during production of polymer/SWNTs nanocomposites(2008-08) Hernandez, Rocio; Rivero, Iris V.; Kobza, John E.; Wang, ShirenSingle Wall carbon nanotubes (SWNTs) are distinguished by their exceptional mechanical strength and electrical properties. However, these properties can only be inherited by nanocomposites if SWNTs are strongly bonded, uniformly distributed, and aligned within the composite matrix during their manufacturing processing. Conversely, the limited availability and economical constraints presented by bulk manufacturing process of nanocomposite materials have been hindering factors in devising their utilization for structural applications and thus their commercialization. This study is focused on the application of an electrical field to align SWNTs during the casting process of polymer nanocomposites where the experimental methodology is comprised of preparing samples exhibiting various percent weights of SWNTs in the polymer matrix while applying distinct electrostatic field strengths. Specifically, SWNTs are dispersed into a semi-crystalline polymer, poly (ethylene-co-vinyl alcohol) (EVOH) matrix. The resulting nanocomposites were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and tensile testing to evaluate their physical, thermal, and mechanical properties. The highest electrostatic field strength used in this study (204V/mm, 60Hz) aligned low concentrations of SWNTs through the polymer matrix. Unfortunately, it also formed large agglomerations when using higher concentrations of SWNTs, and affected the tensile strength of the nanocomposite properties. The electrical field did not affect thermal characteristics, but the addition of SWNTs to the polymer matrix accelerated the melting of small crystals.Item Engineering nanocomposite polymer membranes for olefin/paraffin separation(2011-12) Gleason, Kristofer L.; Becker, Michael F.; Kovar, Desiderio; Hallock, Gary A.; Keto, John W.; Goodenough, John B.In this dissertation, I have investigated applying the laser ablation of microparticle aerosol (LAMA) process to the production of nanocomposite polymer membranes for olefin/paraffin separation. Experimental results for three major thrusts are presented: 1) an investigation into the scalability of the LAMA process, 2) a new laser ablation technique for nanoparticle production from aqueous feedstocks, and 3) characterization of olefin-selective polymer nanocomposite membranes produced using LAMA. The propensity for Ag nanoparticles to form agglomerates in LAMA is investigated. Nanoparticle samples were collected on TEM grids at several feedstock aerosol densities. As the density increased, the particle morphology shifted from single nanoparticles 5 nm in diameter to chained agglomerates of 20 nm diameter primary particles. The results are in agreement with a numerical model of Brownian agglomeration and diffusion. Factors influencing nanoparticle morphology, such as temperature, initial nanoparticle charge, and feedstock aerosol density are discussed. It is shown that agglomeration occurs on a much longer timescale than the other processes, and can be treated independently. A new nanoparticle synthesis technique is presented: laser ablation of aqueous aerosols. A Collison nebulizer is used to generate a mist of ~10 [mu]m diameter water droplets containing dissolved transition metal salts. Water from the droplets quickly evaporates, leaving solid particles which are ablated by an excimer laser. Ablation results in plasma breakdown and photothermal decomposition of the feedstock material. For AgNO₃ ablated in He gas, metallic Ag nanoparticles were produced. For Cu(NO₃)₂ ablated in He gas, crystalline Cu₂O nanoparticles were produced. For Ni(NO₃)₂ ablated in He gas, crystalline NiO nanoparticles were produced. A combination of AgNO₃ and Cu(NO₃)₂ ablated in a reducing atmosphere of 10%H₂/He yielded nonequilibrium Ag-Cu alloy nanoparticles. Membranes composed of poly(ethylene glycol diacrylate) (PEGDA) and Ag nanoparticles were produced by the LAMA process. Permeation and sorption measurements for the light olefins and paraffins were conducted for these membranes. The membranes showed very little improvement in olefin/paraffin selectivity compared with neat PEGDA membranes. Using the LAMA implementation described here, it was impossible to produce membranes with high Ag loading. Whether membranes containing more Ag would exhibit improved selectivity remains an open question.Item Multifunctional cyanate ester/MWNT nanocomposites : processing and characterization(2013-12) Lao, Si Chon; Moon, T. J. (Tess J.); Koo, Joseph H.Tomorrow’s lightweight, high-performance composite systems will be made of structures built with materials that have unprecedented intrinsic properties for performing a wide range of functions, such as EMI shielding, thermal management, flame resistance, lightning strike protection, acoustic damping, and health-monitoring. Current structures require parasitic components, e.g., metal strips, copper wire meshes, strain gauges, and heat sinks to provide these functions. By eliminating parasitic components, future high-performance multifunctional systems can achieve the intended objectives, while maintaining optimum weight, reliability, cost, and fuel efficiency. With the continuing growth of polymer composites in industries, such as aerospace, automotive, and wind energy, research and development on lightweight, high-performance composites that possess extraordinary properties for future multifunctional systems has generated considerable interest and excitement. Recent advances in nanomaterial synthesis and functionalization have shown that tailored property combinations are possible with reduced parasitic content to achieve multifunctionality. Cyanate ester (CE), a class of high-performance thermosetting resins (high T [subscript g], >250°C), has received considerable attention due to its good mechanical properties, thermal stability, flammability properties, ease of process, and volatile-free curing process. Multiwall carbon nanotubes were selected due to their unique combination of excellent mechanical, electrical, and thermal properties. The principal objective of this work is to determine the extent to which several different processing techniques will affect the MWNT dispersion and corresponding nanocomposite properties, such as thermal, flammability, mechanical, and electrical properties. A processing-structure-property relationship, as well as performance of this class of carbon-based CE nanocomposite, will be established. Therefore, a major scientific contribution of this study will be the development and characterization of a novel, multifunctional CE nanocomposite. Different mixing instruments, such as high shear mixer, ultrasonicator, planetary centrifugal mixer, etc. were used to disperse the nanotubes in the cyanate ester resin matrix. Microstructural morphology characterizations by SEM, STEM, and TEM show that various degrees of dispersions of MWNTs were obtained by the different mixing techniques. An attempt to quantify the MWNT dispersion was made. Electrical resistivity of samples processed by both stand mixer and three-roll mill passes the ESD requirement; however, the MWNT percolation thresholds by the two techniques are different. Thermal analysis shows that the addition of the Fe³+ catalyst or the coupling agent lowers the glass transition temperature and degrades the mechanical properties (e.g., storage modulus, tangent of phase angle delta) of the CE resin. On the other hand, processing techniques only affect the mechanical properties of the resin. Thermal stability of CE is only slightly affected by different processing techniques, as well as the addition of MWNTs. Much more significantly, flammability characterization shows that the incorporation of either the Fe³+ catalyst or the coupling agent substantially increases the peak heat release rate (PHRR) relative to the neat CE resin value.Item Optimization of Polymer-based Nanocomposites for High Energy Density Applications(2012-07-16) Barhoumi Ep Meddeb, AmiraMonolithic materials are not meeting the increasing demand for flexible, lightweight and compact high energy density dielectrics. This limitation in performance is due to the trade-off between dielectric constant and dielectric breakdown. Insulating polymers are of interest owing to their high inherent electrical resistance, low dielectric loss, flexibility, light weight, and low cost; however, capacitors produced with dielectric polymers are limited to an energy density of ~1-2 J/cc. Polymer nanocomposites, i.e., high dielectric particles embedded into a high dielectric breakdown polymer, are promising candidates to overcome the limitations of monolithic materials for energy storage applications. The main objective of this dissertation is to simultaneously increase the dielectric permittivity and dielectric breakdown without increasing the loss, resulting in a significant enhancement in the energy density over the unmodified polymer. The key is maintaining a low volume content to ensure a high inter-particle distance, effectively minimizing the effect of local field on the composite's dielectric breakdown. The first step is studying the particle size and aspect ratio effects on the dielectric properties to ensure a judicious choice in order to obtain the highest enhancement. The best results, as a combination of dielectric constant, loss and dielectric breakdown, were with the particles with the highest aspect ratio. Further improvement in the dielectric behavior is observed when the nanoparticles surface is chemically tailored to tune transport properties. The particles treatment leads to better dispersion, planar distribution and stronger interaction with the polymer matrix. The planar distribution of the high aspect ratio particles is essential to limit the enhancement of local fields, where minimum local fields result in higher dielectric breakdown in the composite. The most significant improvement in the dielectric properties is achieved with chemically-treated nano TiO2 with an aspect ratio of 14 at a low 4.6 vol% loading, where the energy density increased by 500% compared to pure PVDF. At this loading, simultaneous enhancement in the dielectric constant and dielectric breakdown occurs while the dielectric loss remains in the same range as that of the pristine polymer.Item Preparation, properties, and structure-property relationships of graphene-polymer nanocomposites(2012-12) Potts, Jeffrey Robert; Ruoff, Rodney S.; Paul, Donald R; Bielawski, Christopher W; Ellison, Christopher J; Liechti, Kenneth MThe overall objective of this work was to develop processing, structure, and property relationships in graphene/polymer nanocomposites. To this end, different types of graphene platelets were produced from graphite oxide, dispersed into various thermoplastics and elastomers, and the morphology and properties of the resulting nanocomposites were evaluated. A range of tests were carried out on the nanocomposites to assess property improvements, including stress-strain testing, dynamic mechanical analysis, and thermal and electrical conductivity testing. Extensive morphological characterization, primarily through transmission electron microscopy (TEM) analysis, was performed to gain insight into the mechanisms behind the observed property improvements. The processing method used to disperse graphene platelets into a given polymer was found to exert significant influence over the nanocomposite morphology and properties. In both thermoplastics and elastomers, liquid-based dispersion methods were typically found to yield a better dispersion of graphene platelets compared with melt processing; the effectiveness of melt processing appeared to depend in part upon the method used to produce the graphene platelets. Latex compounding of graphene platelets and natural rubber generated nanocomposites with a network morphology with properties that were sensitive to further processing. The effect of graphene platelet intrinsic structure on nanocomposite properties was studied and property improvements with other nanofillers were compared to graphene platelets. The impact of platelet oxidation on nanocomposite properties was explored in two different systems and produced varying results depending on the polarity of the polymer matrix. An increased average aspect ratio of graphene platelets was not found to improve mechanical properties or a lower percolation threshold when dispersed in natural rubber. Graphene platelets produced superior reinforcement to multi-walled carbon nanotubes and exfoliated montmorillonite when dispersed in natural rubber; however, the carbon nanotubes produced the largest thermal and electrical conductivity enhancements. Qualitative observation of platelet dispersion by TEM was found to provide excellent correlation with nanocomposite properties when comparing different processing methods or filler materials. The average platelet aspect ratio of three different nanocomposite systems was determined by quantitative TEM analysis and used as a parameter in composite models to generate modulus predictions. Good agreement was found between model predictions and the experimental data.