Journal Articles
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Item Rouse mode analysis of chain relaxation in polymer nanocomposites(Royal Society of Chemistry, 2015) Kalathi, J.T.; Kumar, S.K.; Rubinstein, M.; Grest, G.S.Large-scale molecular dynamics simulations are used to study the internal relaxations of chains in nanoparticle (NP)/polymer composites. We examine the Rouse modes of the chains, a quantity that is closest in spirit to the self-intermediate scattering function, typically determined in an (incoherent) inelastic neutron scattering experiment. Our simulations show that for weakly interacting mixtures of NPs and polymers, the effective monomeric relaxation rates are faster than in a neat melt when the NPs are smaller than the entanglement mesh size. In this case, the NPs serve to reduce both the monomeric friction and the entanglements in the polymer melt, as in the case of a polymer-solvent system. However, for NPs larger than half the entanglement mesh size, the effective monomer relaxation is essentially unaffected for low NP concentrations. Even in this case, we observe a strong reduction in chain entanglements for larger NP loadings. Thus, the role of NPs is to always reduce the number of entanglements, with this effect only becoming pronounced for small NPs or for high concentrations of large NPs. Our studies of the relaxation of single chains resonate with recent neutron spin echo (NSE) experiments, which deduce a similar entanglement dilution effect. © 2015 The Royal Society of Chemistry.Item Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers(American Chemical Society service@acs.org, 2017) Ge, T.; Kalathi, J.T.; Halverson, J.D.; Grest, G.S.; Rubinstein, M.The motion of nanoparticles (NPs) in entangled melts of linear polymers and nonconcatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a and is related to the hopping diffusion of NPs in the entanglement network. In contrast to the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled nonconcatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers. © 2017 American Chemical Society.Item A facile synthesis of halloysite nanotubes based polymer nanocomposites for glass coating application(Elsevier Ltd, 2018) Buruga, K.; Kalathi, J.T.Halloysite-based polymethyl methacrylate (HNT-PMMA) and polystyrene (HNT-PS) nanocomposite coatings for glasses were synthesized by ultrasound-assisted solution blending method. The coatings were then dip-coated on four different types of soda-lime glass and the spectral, mechanical properties of the coated glasses were analyzed. The coated glass samples displayed a better scratch resistance and surface hydrophobicity, compared to uncoated samples, without any significant changes in their inherent spectral properties. The thermal and mechanical properties (Tg and tensile strength) of the nanocomposites were also enhanced compared to neat polymers. The improvement in thermal and scratch resistance of the coatings is ascribed to the inclusion of halloysite nanotubes (HNTs) in the polymer matrix. Hence, HNT-based PMMA/PS nanocomposite coatings can be effectively used for glasses in automotive and architectural applications. © 2017 Elsevier B.V.Item Polystyrene-halloysite nano tube membranes for water purification(Korean Society of Industrial Engineering Chemistry A-803 Twin Bldg 275-3 Yangjae-Dong Seocho-Kul Seoul 137-130, 2018) Buruga, K.; Kalathi, J.T.; Kim, K.-H.; Ok, Y.S.; Boukhvalov, B.Membrane technologies are a sustainable solution for treatment of water and wastewater. Here, the technical feasibility of polystyrene-halloysite nanotube (PS-HNT) membranes, fabricated by an ultrasound-assisted solution casting method, was explored for water purification. To this end, the effects of various solvents on the structure, morphology, thermal, and mechanical properties of PS-HNT membranes were investigated. Introduction of HNTs (5 wt%) into the polystyrene matrix demonstrated excellent thermal and mechanical properties along with good water flux, rejection of unwanted components, recovery, and regeneration cycles. These membranes were overall useful enough to purify real wastewater collected from pulp and paper mill. © 2017 The Korean Society of Industrial and Engineering ChemistryItem Low-temperature sonochemical synthesis of high dielectric Lanthanum doped Cerium oxide nanopowder(Elsevier Ltd, 2018) Kishor Kumar, M.J.; Kalathi, J.T.Lanthanum (La) doped Cerium Oxide (CeO2) nanopowder was synthesized at a relatively lower temperature (70°C), without calcination in a simple, faster, and efficient way through sonochemical method. X-ray diffraction (XRD) results confirmed the formation of a cubic fluorite structure of nanocrystalline CeO2 and lattice deformation due to La-doping in CeO2. TEM analysis revealed that the size of La-doped CeO2 particles is in the range of 20?50 nm. In addition, selective area electron diffraction (SAED) and high-resolution TEM (HRTEM) analyses portrayed the nano-crystallinity, lattice fringe pattern, and d-spacing details of La-doped CeO2 powder. Lanthanum doping in CeO2 was further confirmed by a shift in Raman band towards the lower frequency (from 464 cm?1 to 457cm?1) along with peak intensity increase. Photoluminescence (PL) emission spectra showed that emission intensity of the La-doped CeO2 at 510 nm is increased due to oxygen vacancy mediated charge transfer. All these results confirm the successful doping of La in CeO2. The La-doped CeO2 powder possesses a high dielectric constant (?r) of 106 and a low dielectric loss (tan ?) of < 0.4 % at 1 kHz. The La-doped CeO2 finds potential applications on developing devices in the field of a thin film capacitor, transistors, and solid oxide fuel cells. © 2018 Elsevier B.V.Item Fabrication of ?-MPS-Modified HNT–PMMA Nanocomposites by Ultrasound-Assisted Miniemulsion Polymerization(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Buruga, K.; Kalathi, J.T.Halloysite nanotubes (HNTs) were modified with ?-methacryloxypropyltrimethoxysilane (?-MPS) to improve their interaction with the polymer, and the modified HNTs (MHNTs) were subsequently used for the synthesis of MHNT–polymethylmethacrylate (PMMA) nanocomposites by miniemulsion polymerization assisted by ultrasound. Reduced agglomeration of HNTs due to modification with ?-MPS was evident from scanning electron microscopy analysis. Modification of HNTs and exfoliation of MHNTs in the polymer nanocomposite were confirmed by the presence of their respective characteristic peaks in Fourier-transform infrared spectra and x-ray diffraction patterns. Transmission electron microscopic analysis showed that the surface of the MHNTs differed significantly from that of unmodified HNTs. MHNT–PMMA nanocomposite exhibited significantly higher glass-transition temperature (Tg) compared with neat PMMA or unmodified HNT–PMMA nanocomposite. Hence, such modification of HNTs along with miniemulsion polymerization assisted by ultrasound is a promising approach to achieve better dispersion of HNTs in the polymer and to obtain nanocomposites with enhanced properties. © 2018, The Minerals, Metals & Materials Society.Item Performance of halloysite nanotube/poly(styrene-co-methylmethacrylate) nanocomposite coatings for the protection of soda-lime glass(Elsevier Ltd, 2019) Buruga, K.; Kalathi, J.T.Polymer-based coatings for the protection of glass surfaces are used considerably in the construction and automotive industries. This research article focuses on the potential use of halloysite nanotubes (HNT)/Poly(Styrene-co-Methylmethacrylate) (PS-co-PMMA) nanocomposites as coatings for the protection of soda-lime glass. The effect of HNT content and coating thickness on the spectral properties of the glass, morphology, surface-wettability, and thermo-mechanical properties of the nanocomposite coatings were investigated and reported. The inherent spectral behavior of glass was not altered significantly by the coatings when the content of HNTs in coatings was ? 5 wt %. The coated glasses also exhibited a slight increase in the solar skin protection factor (SSPF), but notable improvement in the solar material protection factor (SMPF) when the HNT content was high in coatings. Thermogravimetric analysis (TGA) revealed that the HNT/PS-co-PMMA nanocomposite coatings possess excellent thermal stability compared to the neat copolymer. The surface wettability of coated glasses by water droplets decreased substantially due to coatings as evident from contact angle measurements. The HNT/PS-co-PMMA nanocomposites also displayed enhanced tensile strength and scratch resistance with increasing HNT content of coatings up to 5 wt%. Overall, the performance of the coated glass was enhanced by the coatings. © 2018 Elsevier B.V.Item Synthesis of poly(styrene-co-methyl methacrylate) nanospheres by ultrasound-mediated Pickering nanoemulsion polymerization(Springer Netherlands rbk@louisiana.edu, 2019) Buruga, K.; Kalathi, J.T.Poly (styrene-co-methyl methacrylate) (PS-co-PMMA) nanospheres were synthesized by ultrasound-mediated Pickering nanoemulsion polymerization using halloysite nanotubes (HNTs) as a stabilizer. A relatively high conversion (? 99%) was obtained in a short span of time (60 min) relative to (?97%) for that obtained by conventional emulsion polymerization performed without ultrasound. The initial rate of polymerization and the conversion were found to be increasing with the acoustic intensity in the range of 12.5–25 W/cm2). The synthesized copolymer nanosphere particles exhibited a perfect spherical shape (from TEM analysis), good stability (from zeta-potential analysis), high molecular weight (Mw? 311 kDa from Gel permeation chromatography), and excellent thermal properties (Tg? 120°C from DSC and TGA) as a result of the combined physicochemical effects of acoustic cavitation. The formation of nanosized emulsion droplets stabilized by HNTs ultimately yielded nanospheres of PS-co-PMMA with an average size of ? 82.8 nm. The PS-co-PMMA nanospheres can have potential applications in medicine, dentistry, paper, paint, and automotive industries. © 2019, The Polymer Society, Taipei.Item Interface Dominated Dielectric Response of PS-Fe3O4 Patchy Microspheres(American Chemical Society service@acs.org, 2019) Kishor Kumar, M.J.; Kalathi, J.T.Polymeric-inorganic interface plays a vital role in enhancing dielectric properties of patchy microspheres, Janus particles, and nanocomposites. We performed the computational modeling and simulations along with experiments to understand the phenomena behind the improved dielectric permittivity of polystyrene-iron oxide (PS-Fe3O4) patchy microspheres. We addressed the fundamental insights into the role of the interfacial region on the dielectric properties. Based on the experimental outcomes and computational simulations on dielectric behavior including polarization and electric field formation, we propose a new mechanism of charge buildup at the interface. Computational results reveal that the creation of interface bound-charges at the inorganic-polymeric interface is responsible for the improved dielectric properties. We also fabricated PS-Fe3O4 patchy microspheres by Pickering emulsion polymerization using Fe3O4 particles as a solid stabilizer. The microstructure, composition, morphology, dielectric, and thermal properties of the synthesized patchy PS-Fe3O4 particles were investigated. The dielectric permittivity (k) of the neat PS increased from ?2.9 to ?14.8 after decorating with Fe3O4 particles. Impedance response of the patchy microspheres shows that the interface of PS-Fe3O4 stores more charges than bulk PS-Fe3O4. The dielectric behavior of patchy microspheres can be engineered by tuning the shape and position of the patches. The present studies on polymer-inorganic interface provide some insights into the mechanisms that control dielectric permittivity and nonlinear conduction in an applied electric field. © © 2019 American Chemical Society.Item A review on functional polymer-clay based nanocomposite membranes for treatment of water(Elsevier B.V., 2019) Buruga, K.; Song, H.; Shang, J.; Bolan, N.; Kalathi, J.T.; Kim, K.-H.Water is essential for every living being. Increasing population, mismanagement of water sources, urbanization, industrialization, globalization, and global warming have all contributed to the scarcity of fresh water sources and the growing demand of such resources. Securing and allocating sufficient water resources has thus become one of the current major global challenges. Membrane technology has dominated the field of water purification due to its ease of usage and fabrication with high efficiency. The development of novel membrane materials can hence play a central role in advancing the field of membrane technology. It is noted that polymer-clay nanocomposites have been used widely for treatment of waste water. Nonetheless, not much efforts have been put to functionalize their membranes to be selective for specific targets. This review was organized to offer better insights into various types of functional polymer and clays composite membranes developed for efficient treatment and purification of water/wastewater. Our discussion was extended further to evaluate the efficacy of membrane techniques employed in the water industry against major chemical (e.g., heavy metal, dye, and phenol) and biological contaminants (e.g., biofouling). © 2019 Elsevier B.V.