Co-reporter:Nicholas Teo and Sadhan C. Jana
Langmuir November 7, 2017 Volume 33(Issue 44) pp:12729-12729
Publication Date(Web):October 19, 2017
DOI:10.1021/acs.langmuir.7b03139
The water-in-oil emulsion-templating method is used in this work for fabrication of open cell aerogel foams from syndiotactic polystyrene (sPS). A surfactant-stabilized emulsion is prepared at 60–100 °C by dispersing water in a solution of sPS in toluene. sPS gel, formed upon cooling of the emulsion to room temperature, locks the water droplets inside the gel. The gel is solvent exchanged in ethanol and then dried under supercritical condition of carbon dioxide to yield the aerogel foams. The aerogel foams show a significant fraction of macropores with a diameter of a few tens of micrometers, defined as macrovoids that originated from the emulsified water droplets. In conjunction, customary macropores of diameter 50–200 nm are derived from sPS gels. The macrovoids add additional openness to the aerogel structures. This paper evaluates the structural characteristics of the macrovoids, such as diameter distribution, macrovoid interconnect density, and skin layer density, in conjunction with the final aerogel foam properties.
Co-reporter:Sung Jun Kim, Sadhan C. Jana
Polymer 2017 Volume 126(Volume 126) pp:
Publication Date(Web):22 September 2017
DOI:10.1016/j.polymer.2017.03.039
•Skin layers are ubiquitous in aerogel monoliths.•Skin layers have higher density, thus lower air permeability.•Composite model yields skin layer thickness and skin layer permeability.•Skin layers are twice as much denser than the bulk.Skin layers are ubiquitous in synthesis of macro- and mesoporous polymer aerogel monoliths, are much denser than the bulk materials, and can potentially impact several properties of aerogels. This study evaluates the effects of skin layers on the values of air permeability in aerogel monoliths of syndiotactic polystyrene (sPS) prepared from thermo-reversible gelation of sPS solutions followed by supercritical drying in carbon dioxide. The sPS aerogel monoliths are primarily macroporous and conducive to provide air permeability of the order of 10−10 m2. However, the overall air permeability is substantially reduced due to the denser skin layers. A composite model is used to estimate the thickness, bulk density, and air permeability of skin layers from experimentally measured air permeability data. It is found that skin layers of the order of 0.5 mm in thickness form during synthesis of sPS monoliths from solution in tetrahydrofuran. The air permeability of the skin layer is about half that of the bulk material.Download high-res image (112KB)Download full-size image
Co-reporter:Stuti Rajgarhia, Sadhan C. Jana
Polymer 2017 Volume 123(Volume 123) pp:
Publication Date(Web):11 August 2017
DOI:10.1016/j.polymer.2017.07.032
•Secondary gas jet imparts higher stretching and results in substantial fiber diameter reduction.•Fiber diameter reduction is controllable.•Unique gradient morphology is promoted by faster solvent evaporation.This paper focuses on the effect of addition of a secondary gas jet on diameter and morphology of bi-component nanofibers produced using the gas jet fibers (GJF) process. In GJF process, a primary turbulent gas jet is used for liquid jet initiation, liquid jet stretching, and drying of the liquid jet into nanofibers. The secondary gas jet is added to provide additional stretching of the liquid jet so that fibers of even smaller diameter can be obtained. The location of the secondary jet in relation to the liquid delivery nozzle is varied to determine an area of influence of the secondary gas jet on fiber diameter and fiber morphology. The radius of the copper loop used to deliver the secondary gas jet is also varied to assess its effect on fiber diameter. The results show almost 100% reduction in nanofiber diameter of bi-lobal and interpenetrating network type nanofibers with appropriate placement of the secondary gas jet. The additional stretching also creates gradient morphology promoted by incomplete phase separation of the polymers as a consequence of much faster solvent loss.Download high-res image (132KB)Download full-size image
Co-reporter:Sung Jun Kim, Prasad Raut, Sadhan C. JanaGeorge Chase
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 7) pp:
Publication Date(Web):February 8, 2017
DOI:10.1021/acsami.6b14784
The role of electrostatic force on separation of airborne nanoparticles is evaluated in this work by considering a hybrid monolithic aerogel of syndiotactic polystyrene (sPS) and polyvinylidene fluoride (PVDF). The sPS part accounts for open pore structures in the monolith, while the PVDF chains contribute spontaneous polarity for particle capture by the electrostatic force. The hybrid aerogels are fabricated by thermoreversible gelation of sPS from a solution with PVDF in tetrahydrofuran followed by supercritical drying of the gel. sPS is present as the δ-form clathrate crystalline phase and PVDF as α- and γ-form crystalline phases in the hybrid. The presence of PVDF induces significant static charges on the surfaces of hybrid aerogels. The filtration efficiency is determined by passing airborne NaCl nanoparticles with diameter in the range 25–150 nm through the filter media. The experimental data reveal that air permeability of the hybrid system (∼10–10 m2) is close to that of sPS monoliths. The hybrid materials show filtration efficiency ≥99.999% in comparison to 98.889% observed for a sPS monolith with the same solid content.Keywords: aerogels; air permeability; airborne nanoparticles; electrostatic force; PVDF; sPS;
Co-reporter:Senlong Gu, Sadhan C. Jana
Polymer 2017 Volume 125(Volume 125) pp:
Publication Date(Web):8 September 2017
DOI:10.1016/j.polymer.2017.07.085
•Aerogel foams combine open cell polymer foams with mesoporous aerogels.•Macropores of ∼20 μm diameter have mesoporous cell walls.•Hierarchical pore structures with large macropores and mesopores.•High air permeability and high rate of hydrocarbon liquid absorption.A new class of macroscopic materials – the open cell aerogel foams (OCAFs) – are developed in this work that combine the attributes of open cell polymer foams and mesoporous polymer aerogels in single materials. The OCAFs have two functional elements – the large body of the materials is air-filled open cells with typical cell size greater than 1 μm and the walls between the open cells consisting of mesoporous aerogel formed by the polyurea strands of typical diameter 50 nm. The common foaming technologies cannot be easily adapted to obtain OCAF. This paper evaluates a strategy based on the use of templates of co-continuous immiscible polymer blends. The open cell macropores are created by selective dissolution of polystyrene from its co-continuous blend with polyethylene oxide. The gel networks of polyurea are then synthesized inside the macropores. Finally, the polyethylene oxide phase is removed by dissolution and the resultant material is dried under supercritical condition to obtain the OCAF. It is found that polyurea gel networks are initiated on the surfaces of polyethylene oxide template by nucleation and growth mechanism. The resultant polyurea OCAFs exhibit bulk density ∼0.06 g/cm3, BET surface area ∼130 m2/g, mesoporous solid networks, high air permeability, and close to 1500% weight gain in a few seconds when exposed to pump oil.Download high-res image (243KB)Download full-size image
Co-reporter:Stuti S. Rajgarhia, Sadhan C. Jana, and George G. Chase
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 33) pp:21683
Publication Date(Web):August 3, 2016
DOI:10.1021/acsami.6b07364
Polymer nanofibers with interpenetrating network (IPN) morphology are used in this work for the development of composite, hydrophobic filter media in conjunction with glass fibers for removal of water droplets from ultralow sulfur diesel (ULSD). The nanofibers are produced from hydrophobic polyvinyl acetate (PVAc) and hydrophilic polyvinylpyrrolidone (PVP) by spinning the polymer solutions using gas jet fiber (GJF) method. The nanofibers coat the individual glass fibers due to polar–polar interactions during the spinning process and render the filter media highly hydrophobic with a water contact angle approaching 150°. The efficiency of the resultant filter media is evaluated in terms of separation of water droplets of average size 20 μm from the suspensions in ULSD.Keywords: coalescing filtration; coating; hydrophobic and hydrophilic polymers; interpenetrating network morphology; nanofibers
Co-reporter:Sung Jun Kim, George Chase, Sadhan C. Jana
Separation and Purification Technology 2016 Volume 166() pp:48-54
Publication Date(Web):22 June 2016
DOI:10.1016/j.seppur.2016.04.017
•Mesopores make strong contributions to the capture of airborne nanoparticles.•Particle capture efficiency is greater than 99.95% with 1–3% by volume mesopores.•Air permeability insensitive to mesopores as macropore fraction remains high.•Depth filtration in conjunction with cake formation of nanoparticles is observed.•The hybrid aerogels become fragile at high silica content and give low efficiency.This study evaluates the role of small mesopore volume fraction in aerogel monoliths in achieving high efficiency airborne nanoparticle filtration. The diffusional flow in mesopores (diameter 2–50 nm) is more effective in nanoparticle capture than the viscous flow regime encountered in macropores (diameter > 50 nm). Substantial macropore fraction, however, is essential for achieving high air permeability. This idea is tested by evaluating the filtration efficiency of 25–150 nm diameter airborne sodium chloride nanoparticles and the permeability of air through hybrid aerogel monoliths with about 2–4% by volume mesopore content. The hybrid aerogels are prepared by growing discontinuous silica aerogel particles in the macropores of δ-form syndiotactic polystyrene (sPS). The results show that air permeability is not much affected by the silica content although the particle capture efficiency is increased to >99.95% due to the contribution of diffusional deposition aided by the mesopores. The aerogels develop cracks and reduce filtration efficiency at high silica content due to brittle nature of silica particle networks.Mesopores and macropores in hybrid monoliths govern respectively high efficiency and high air permeability.
Co-reporter:Yannan Duan, Sadhan C. Jana, Bimala Lama, Matthew P. Espe
Journal of Non-Crystalline Solids 2016 Volume 437() pp:26-33
Publication Date(Web):1 April 2016
DOI:10.1016/j.jnoncrysol.2016.01.016
•A unique silylation process rendered the aerogels strongly hydrophobic.•Post-gelation silylation produced the best results — compressive modulus doubled.•Bulk density and fractal dimensions weakly dependent on the degree of silylation•A monolayer coating significantly increased the surface energy.•Some aerogels were superhydrophobic.In this work, silica gel networks were modified with a silylating agent dimethoxy-methyl (3,3,3-trifluoropropyl) silane (SiF3) to obtain hydrophobic aerogels of various surface energy values. The baseline aerogels were synthesized from tetraethoxy silane (TEOS) using a two-step sol–gel process followed by supercritical drying in liquid carbon dioxide. The resultant aerogels were characterized using scanning electron microscopy, Instron tensile tester, contact angle goniometry, and nitrogen adsorption–desorption isotherms. Three modification methods were studied. In method 1, TEOS and SiF3 were combined before gelation; in method 2, SiF3 was added after TEOS was hydrolyzed and before its condensation, and in method 3, SiF3 was added after the gels were produced from TEOS. It was found that method 3 produced the best results in terms of achieving high values of hydrophobicity and compressive properties. The data on solid state 13C and 29Si NMR spectra revealed chemical reactions between the silylating agents and the silanol groups on silica surface. The bulk density and the fractal dimensions of silica networks gleaned from small angle X-ray scattering (SAXS) data showed weak dependence on the degree of silylation. The silylation process rendered the aerogels strongly hydrophobic and also doubled its compressive modulus.
Co-reporter:Monoj Ghosh;Dr. Mehdi Lohrasbi;Dr. Steven S. C. Chuang;Dr. Sadhan C. Jana
ChemCatChem 2016 Volume 8( Issue 15) pp:2525-2535
Publication Date(Web):
DOI:10.1002/cctc.201600387
Abstract
Mesoporous TiO2 nanofibers with controlled diameter, crystal size, and anatase versus rutile crystal structures are produced by calcination at 500–700 °C of precursor nanofibers of polyvinylpyrrolidone and titanium isopropoxide, obtained from a scalable gas jet fiber spinning process. These TiO2 nanofibers are used in the photocatalytic oxidation of gas-phase ethanol at room temperature on exposure to UV irradiation. The experimental trends are analyzed using electron–hole (e-h) charge recombination inferred from high-intensity photoluminescence emission spectra, specific surface area, crystallinity, and the proportions of anatase and rutile phases. The nanofibers show a photocatalytic activity that is up to an order of magnitude higher than that of commercial-grade P25 TiO2 nanoparticles because of slower e-h recombination phenomena in the former. The results show that ethanol undergoes complete oxidation into CO2 and H2O on the nanofibers without the accumulation of the intermediate products acetaldehyde and formic acid.
Co-reporter:Senlong Gu, Chunhao Zhai, and Sadhan C. Jana
Langmuir 2016 Volume 32(Issue 22) pp:5637-5645
Publication Date(Web):May 16, 2016
DOI:10.1021/acs.langmuir.6b01043
This paper reports preparation of polymer aerogel microparticles via sol–gel reactions inside micrometer size droplets created in an oil-in-oil emulsion system. The oil-in-oil emulsion system is obtained by dispersing in cyclohexane the droplets of the sols of polybenzoxazine (PBZ) or polyimide (PI) prepared in dimethylformamide. The sol droplets transform into harder gel microparticles due to sol–gel reactions. Finally, the aerogel microparticles are recovered using supercritical drying of the gel microparticles. The PBZ and PI aerogel microparticles prepared in this manner show mean diameter 32.7 and 40.0 μm, respectively, mesoporous internal structures, and surface area 55.4 and 512.0 m2/g, respectively. Carbonization of PBZ aerogel microparticles maintains the mesoporous internal structures but yields narrower pore size distribution.
Co-reporter:Stuti S. Rajgarhia, Rafael E. Benavides, Sadhan C. Jana
Polymer 2016 Volume 93() pp:142-151
Publication Date(Web):14 June 2016
DOI:10.1016/j.polymer.2016.04.018
•The same two immiscible polymers are organized in IPN, core-shell, or bi-lobal morphological forms in single nanofibers.•Only the hydrodynamic forces via the Gas Jet Fiber (GJF) process is used to obtain nanofibers.•Phase separation of polymers are triggered by solvent evaporation promoted by rapid stretching of the liquid jet.This study investigates morphology control of polymer nanofibers produced from solutions of two immiscible polymers in mutually miscible solvents by gas jet fiber (GJF) method. The morphology is controlled by selecting the solvents with a range of vapor pressure and solubility parameter to govern respectively the evaporation rates and the polymer-solvent affinity. Bi-component nanofibers with core–shell, bi-lobal, and interpenetrating network (IPN) morphology are produced by evaporation-induced phase separation of the polymers during spinning of homogeneous solutions of hydrophobic polyvinyl acetate (PVAc) and hydrophilic polyvinyl pyrrolidone (PVP) in two mutually miscible solvents. The tendency of phase-separation is inferred from the values of polymer-solvent mixture affinity. The results indicate that solvent pairs with closely matched vapor pressure yield IPN morphology, while solvents with large differences in vapor pressure produce core–shell morphology. Bi-lobal morphology is produced for solvent pairs with moderate differences in vapor pressure. In each case, nanofibers of smaller diameter are obtained when solvent pairs of lower vapor pressure are used.
Co-reporter:Senlong Gu, Zhen Li, Toshikazu Miyoshi and Sadhan C. Jana
RSC Advances 2015 vol. 5(Issue 34) pp:26801-26805
Publication Date(Web):10 Mar 2015
DOI:10.1039/C5RA02635K
Time-efficient gelation of benzoxazine using p-toluenesulfonic acid (TSA) as the catalyst in several solvents and controllable pore structure formation in the resultant polybenzoxazine (PBZ) aerogels are reported. The aerogel building blocks (spheres vs. strands) and the pore surface area show strong dependence on the solvent and the gelation temperature.
Co-reporter:Monoj Ghosh and Sadhan C. Jana
RSC Advances 2015 vol. 5(Issue 127) pp:105313-105318
Publication Date(Web):14 Dec 2015
DOI:10.1039/C5RA20963C
Nanometer size bi-component semiconducting metal oxide (SMO) fibers with tailored morphology are fabricated via a Gas Jet Fiber (GJF) spinning process using a polymer template in conjunction with conventional precursor sol–gel chemistry. The GJF process is capable of producing SMO fibers with morphological forms such as mesoporous or solid cylindrical core–shell and side-by-side.
Co-reporter:Andrew Shinko, Sadhan C. Jana and Mary Ann Meador
RSC Advances 2015 vol. 5(Issue 127) pp:105329-105338
Publication Date(Web):07 Dec 2015
DOI:10.1039/C5RA20788F
Mechanically robust polyurea aerogels with controlled porosity are synthesized from aromatic isocyanates, aromatic diamines, and a triamine crosslinker. Linear, isocyanate end-capped polyurea oligomers are first synthesized from the reactions between the diamine and 4,4′-diphenylmethane diisocyanate in anhydrous N-methyl-2-pyrrolidone (NMP). The oligomers are then cross-linked with 1,3,5-triaminophenoxylbenzene to produce the gels. The gels are dried under supercritical conditions of carbon dioxide after exchanging NMP with acetone and acetone with liquid carbon dioxide. The aerogels are mesoporous with mean pore diameter in the range of 9–16 nm, have a bulk density of 0.19–0.26 g cm−3, porosity of 79–86%, and surface areas between 106 and 309 m2 g−1. Pore size distributions broaden and shift to larger diameter as the crosslink density is reduced. The spectroscopic evidence suggests that hydrogen bonding is effective in reducing the shrinkage of aerogels, especially when linear oligomers of higher molecular weight are used. These materials show onset of thermal decomposition at 250 °C and offer high compressive moduli in the range of 12–69 MPa.
Co-reporter:Yannan Duan, Sadhan C. Jana, Bimala Lama and Matthew P. Espe
RSC Advances 2015 vol. 5(Issue 88) pp:71551-71558
Publication Date(Web):21 Aug 2015
DOI:10.1039/C5RA11769K
Mechanically reinforced organic–inorganic hybrid silica aerogels are produced from simultaneous hydrolysis and condensation reactions of silane precursors – tetraethoxy silane (TEOS) and aminopropyltriethoxysilane (APTES) – and silane-modified polyurethane urea molecules each carrying multiple (≥3) reactive silane groups. In this manner, the post-gelation crosslinking reactions are avoided, the amount of polymer introduced into the aerogel structures is controlled, and the chain length between two crosslink points is tailored. The long chain polymer molecules introduce a certain degree of flexibility to the hybrid aerogel structures. The morphology, compressive properties, and surface area are obtained respectively using scanning electron microscopy, Instron tensile testers, and Brunauer–Emmett–Teller (BET) surface area analysis. The data on solid state 13C and 29Si NMR spectra reveal chemical reactions of the silane-modified polymers with the silica particle networks. Small angle X-ray scattering (SAXS) data are used to determine the fractal dimension of the silica networks. It is found that the self-crosslinkable multifunctional polyurethane urea chains form coatings on the silica networks and produce large enhancements in compressive modulus although with increases in shrinkage and bulk density.
Co-reporter:Kushal Bahl
Journal of Applied Polymer Science 2014 Volume 131( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/app.40123
ABSTRACT
In this study, surface modification of lignosulfonates (LSs) was investigated for potential reinforcement of styrene–butadiene rubber compounds. Lignins are naturally occurring amorphous, highly branched polymers consisting of aromatic and aliphatic segments with polar functional groups such as hydroxyl, methoxy, carbonyl, and carboxyl. The polarity and hydrophilic nature render lignin incompatible with nonpolar rubber materials. In this study, cyclohexylamine (CA) modification of LS was evaluated for enhancement of compatibility with rubber via proton transfer and hydrogen bonding interactions. X-ray photoelectron spectroscopy data confirm attachment of CA onto the surface of LS. The cure and scorch times of rubber compounds were shortened, and the crosslink density enhanced with an increase of the amount of CA in modified LS. The tensile strength at break increased by almost 45%; the 100% modulus and elongation at break also showed significant improvements. The values of storage modulus and loss tangent increased by 13% and 18%, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40123.
Co-reporter:Kushal Bahl, Toshikazu Miyoshi, Sadhan C. Jana
Polymer 2014 Volume 55(Issue 16) pp:3825-3835
Publication Date(Web):5 August 2014
DOI:10.1016/j.polymer.2014.06.061
•In hybrid fillers, lignin molecules form coating layers on carbon black particles.•Coating layer formation is promoted by π-π interactions between lignin and carbon black.•Lignin in hybrid fillers assumes the shape and size of carbon black aggregates.•Hybrid fillers are found responsible for reduction of filler networking of CB in rubber compounds.•A reduction in filler networking leads to reduction of viscoelastic loss in rubber compounds.This study investigates novel hybrid fillers for lowering of viscoelastic dissipation in rubber compounds by exploiting non-covalent interactions between lignin and carbon black (CB). Lignin is naturally occurring three-dimensional amorphous polymer consisting of phenyl propane units with hydroxyl, methoxy, and carbonyl substitutions and is capable of producing non-covalent interactions via π–π stacking with CB particles. The hybrid fillers are obtained by precipitating lignin from solutions onto carbon black particles. The fractal nature similar to CB particles and the presence of lignin coating layers on CB particles are confirmed by electron microscopy images. The coating layers are promoted by strong π–π interactions as revealed from Raman spectroscopy and 1H spin-lattice relaxation data and supported by a drop in zeta potential values. The hybrid fillers show much less networking than CB and reduce the viscoelastic dissipation in model rubber compounds by as much as 10% in comparison to the compounds of only CB.
Co-reporter:Kushal Bahl, Nicole Swanson, Coleen Pugh, Sadhan C. Jana
Polymer 2014 Volume 55(Issue 26) pp:6754-6763
Publication Date(Web):15 December 2014
DOI:10.1016/j.polymer.2014.11.008
•Lignin interacts with PB-g-PPFS via arene–perflouroarene interactions.•PB-g-PPFS improves the tensile strength of lignin filled SBR compounds by 20%.•PB-g-PPFS improves dispersion of lignin–carbon black hybrid filler in SBR.•PB-g-PPFS reduces the viscoelastic loss of lignin filled SBR compounds.This study investigated the role of polybutadiene-g-polypentafluorostyrene (PB-g-PPFS) as a coupling agent between lignin and styrene butadiene rubber (SBR) in preparation of compounds with higher mechanical strength and lower viscoelastic loss. Lignins are three-dimensional amorphous polymers consisting of benzene rings carrying alkyl, alkoxy, and hydroxyl groups as substituents. These substituents render lignin electron-rich. The PPFS domains in PB-g-PPFS provide an electron-deficient π-ring system that can couple lignin with rubber via arene–perfluoroarene interactions. PB-g-PPFS molecules were synthesized with 2:1 molar ratio of pentafluorostyrene and polybutadiene, respectively. The arene–perfluoroarene interactions were confirmed by UV–vis spectroscopy and the morphology was examined by scanning electron microscopy. The tensile strength improved by 20% and 10% for compounds of lignin and lignin–carbon black hybrid fillers, respectively. The loss tangent value reduced due to improved filler–rubber interactions promoted by PB-g-PPFS compounds.
Co-reporter:Jason P. Randall, Mary Ann B. Meador and Sadhan C. Jana
Journal of Materials Chemistry A 2013 vol. 1(Issue 22) pp:6642-6652
Publication Date(Web):19 Apr 2013
DOI:10.1039/C3TA11019B
This study evaluated the effectiveness of dimethyldiethoxysilane (DMDES) precursor in improving the elastic recovery behavior of silica aerogels reinforced with epoxy through amine sites on the silica surface. In the study, two aminosilanes – 3-aminopropyltriethoxysilane (APTES) and bis(trimethoxysilylpropyl)amine (BTMSPA) – were considered as reactive sites for cross-linking with epoxy. Because of the way the samples were formulated, BTMSPA offered half the number of amine sites compared to APTES at the same level of substitution. Replacing tetraethoxysilane (TEOS) with at least 15 mol% DMDES reduced the number of silicon–oxygen bonds in the aerogel networks and resulted in improved elastic recovery, but up to an order of magnitude lower compressive modulus. BTMSPA aerogels demonstrated strong elastic response without DMDES, with some samples showing near complete recovery. However, these aerogels offered lower modulus than APTES aerogels.
Co-reporter:Xiao Wang, Huan Zhang and Sadhan C. Jana
Journal of Materials Chemistry A 2013 vol. 1(Issue 44) pp:13989-13999
Publication Date(Web):2013/10/11
DOI:10.1039/C3TA13099A
This paper evaluates the properties of aerogels obtained from sulfonated syndiotactic polystyrene (ssPS) and polyaniline-coated ssPS and elaborates two applications of such aerogel materials. The syndiotactic polystyrene (sPS) chains were sulfonated in chloroform solutions and ssPS gels at several levels of sulfonation were synthesized. The ssPS gels with high surface area were used as templates to adsorb, protonate, and polymerize aniline. The aerogels recovered after supercritical drying were characterized by scanning electron microscopy, wide angle X-ray diffraction (WAXD), nitrogen adsorption–desorption isotherms, and differential scanning calorimetry. The data revealed that enough crystalline domains remained in ssPS to offer mechanical integrity to the gel network, although the pore surface area reduced significantly at high sulfonation levels. The sulfonic acid groups in ssPS aerogel promoted fast moisture absorption. A large fraction of mesopores appeared in polyaniline-coated ssPS aerogels. The polyaniline-coated ssPS aerogel layer rendered an insulating macroporous membrane electrically conductive.
Co-reporter:Xiao Wang and Sadhan C. Jana
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 13) pp:6423
Publication Date(Web):June 17, 2013
DOI:10.1021/am401717s
A class of inorganic–organic hybrid mesoporous aerogel structure was synthesized by growing gel in a gel. In Type 1, silica gels were grown inside the macropores of thermoreversible syndiotactic polystyrene (sPS) gel, while Type 2 hybrid aerogels were obtained by thermoreversible gelation of sPS chains in the mesopores of preformed silica gel. The hybrid gels were converted into aerogels by exchanging the solvent with liquid carbon dioxide followed by supercritical drying. The hybrid aerogels presented cocontinuous networks of pearl-necklace silica particles and crystalline strands of sPS and exhibited the “petal effect” due to the presence of superhydrophobic sPS and hygroscopic silica. The compressive modulus and compressive strain show large enhancements over sPS and silica aerogels indicating synergy, although Type 1 hybrid aerogels were found to be more robust. The hybrid aerogels showed fast absorption and high absorption capacity for a representative hydrocarbon liquid.Keywords: hybrid; silica aerogel; surface property; syndiotactic polystyrene aerogel; synergy;
Co-reporter:Numan Erden
Macromolecular Chemistry and Physics 2013 Volume 214( Issue 11) pp:1225-1237
Publication Date(Web):
DOI:10.1002/macp.201200315
Co-reporter:Xiao Wang, Sadhan C. Jana
Polymer 2013 Volume 54(Issue 2) pp:750-759
Publication Date(Web):24 January 2013
DOI:10.1016/j.polymer.2012.12.025
This work investigated the effects of multi-walled carbon nanotubes (MWCNTs) on density, surface area, compressive strength, and electrical conductivity of syndiotactic polystyrene (sPS) aerogels. The non-covalently modified MWCNTs were dispersed in sPS solution before thermo-reversible gelation of the polymer. The aerogels were obtained by exchanging the solvent with liquid carbon dioxide and by removing carbon dioxide under supercritical condition. The materials were characterized by electron microscopy, wide angle X-ray diffraction, differential scanning calorimetry, and nitrogen adsorption and desorption isotherms. It was found that sPS phase formed strands of approximately 50 nm in diameter and that MWCNTs formed an interpenetrating network within the sPS aerogel. The presence of MWCNTs caused little changes in morphology, crystalline structure of sPS, and surface areas of the aerogels, but significantly increased the compressive modulus and electrical conductivity. The electrical conductivity also showed sensitivity to compressive strain.
Co-reporter:Xiao Wang and Sadhan C. Jana
Langmuir 2013 Volume 29(Issue 18) pp:5589-5598
Publication Date(Web):April 10, 2013
DOI:10.1021/la400492m
This study evaluates a method for rendering syndiotactic polystyrene (sPS) aerogels hydrophilic using polyethylene oxide (PEO) of different molecular weights. The highly porous sPS aerogels are inherently hydrophobic although applications involving absorption of moisture and removal of particulate solids may benefit from the high surface area of sPS aerogels provided some degree of hydrophilicity is induced in these materials. In this work, sPS gels are prepared by thermo-reversible gelation in tetrahydrofuran in the presence of PEO. The gels are dried under supercritical conditions to obtain aerogels. The aerogels are characterized by scanning electron microscopy, nitrogen-adsorption porosimetry, helium pycnometry, and contact angle measurements. The data reveal that the pore structures and surface energy can be controlled by varying the concentration and molecular weight of PEO and using different cooling rates during thermo-reversible gelation. In the first case, sPS aerogels, aerogels containing PEO of a low molecular weight or low concentration show superhydrophobic surface presenting the “lotus effect”. In the second case, PEO at a higher concentration or with higher molecular weight forms phase-separated domains yielding new hydrophilic macropores (>10 μm) in the aerogel structures. These macropores contribute to the superhydrophobic surface with the “petal effect”. The cooling rate during gelation shows a strong influence on these two cases.
Co-reporter:Rafael E. Benavides, Sadhan C. Jana, and Darrell H. Reneker
Macromolecules 2013 Volume 46(Issue 15) pp:6081-6090
Publication Date(Web):July 30, 2013
DOI:10.1021/ma400900s
In this work, the mechanism of fiber formation from polymer solutions under the action of gas jets in a process named gas jet fibers (GJF) method is studied. The GJF method relies on high velocity gas jet converting polymer solutions streaming from a nozzle into a liquid jet and then into fibers. Polymer nanofibers with diameter as low as 100 nm are continuously produced from polymer solutions. A series of interrelated phenomena including polymer jet initiation and stretching, flapping motion, bending instabilities, and concurrent solvent evaporation were found to influence fiber formation. Specifically, the behavior of the liquid jets, stretching rates, and the onset of the bending instabilities are revealed using high speed video photography. The results indicate that both the initial stretching from flapping and the extension from bending instabilities play important roles in fiber attenuation.
Co-reporter:Yannan Duan, Sadhan C. Jana, Bimala Lama, and Matthew P. Espe
Langmuir 2013 Volume 29(Issue 20) pp:6156-6165
Publication Date(Web):April 23, 2013
DOI:10.1021/la4007394
Proper selection of silane precursors and polymer reinforcements yields more durable and stronger silica aerogels. This paper focuses on the use of silane-end-capped urethane prepolymer and chain-extended polyurethane for reinforcement of silica aerogels. The silane end groups were expected to participate in silica network formation and uniquely determine the amounts of urethanes incorporated into the aerogel network as reinforcement. The aerogels were prepared by one-step sol–gel process from mixed silane precursors tetraethoxysilane, aminopropyltriethoxysilane (APTES), and APTES-end-capped polyurethanes. The morphology and mechanical and surface properties of the resultant aerogels were investigated in addition to elucidation of chemical structures by solid-state 13C and 29Si nuclear magnetic resonance. Modification by 10 wt % APTES-end-capped chain-extended polyurethane yielded a 5-fold increase in compressive modulus and 60% increase in density. APTES-end-capped chain-extended polyurethane was found to be more effective in enhancement of mechanical properties and reduction of polarity.
Co-reporter:Rafael E. Benavides, Sadhan C. Jana, and Darrell H. Reneker
ACS Macro Letters 2012 Volume 1(Issue 8) pp:1032
Publication Date(Web):July 30, 2012
DOI:10.1021/mz300297g
A new, simple, and effective method is reported for production of polymer fibers ranging from a few tens of nanometers to a few micrometers from polymer solutions. The method capitalizes on a high velocity expanding gas jet to turn polymer solutions streaming from nozzles into fibers with smooth or wrinkled fiber surface morphology and with core–shell and side-by-side arrangements. The polymer solution is brought in contact with the gas jet on a flat surface, at the tip of a circular needle, and at the surface a pendant drop. The fiber diameter bears relationship with capillary number of the liquid jet and polymer concentration in the solution. Several levels of fiber conglutination are observed as function of collection distance from the nozzle set up.
Co-reporter:Ángela A. Beltrán-Osuna, Bin Cao, Gang Cheng, Sadhan C. Jana, Matthew P. Espe, and Bimala Lama
Langmuir 2012 Volume 28(Issue 25) pp:9700-9706
Publication Date(Web):May 18, 2012
DOI:10.1021/la301561j
In this work, a new antifouling silica hydrogel was developed for potential biomedical applications. A zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), was produced via atom-transfer radical polymerization and was appended to the hydrogel network in a two-step acid–base-catalyzed sol–gel process. The pCBMA silica aerogels were obtained by drying the hydrogels under supercritical conditions using CO2. To understand the effect of pCBMA on the gel structure, pCBMA silica aerogels with different pCBMA contents were characterized using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and the surface area from Brauner–Emmet–Teller (BET) measurements. The antifouling property of pCBMA silica hydrogel to resist protein (fibrinogen) adsorption was measured using enzyme-linked immunosorbent assay (ELISA). SEM images revealed that the particle size and porosity of the silica network decreased at low pCBMA content and increased at above 33 wt % of the polymer. The presence of pCBMA increased the surface area of the material by 91% at a polymer content of 25 wt %. NMR results confirmed that pCBMA was incorporated completely into the silica structure at a polymer content below 20 wt %. A protein adsorption test revealed a reduction in fibrinogen adsorption by 83% at 25 wt % pCBMA content in the hydrogel compared to the fibrinogen adsorption in the unmodified silica hydrogel.
Co-reporter:Sayantan Roy, Jie Feng, Vincenzo Scionti, Sadhan C. Jana, Chrys Wesdemiotis
Polymer 2012 Volume 53(Issue 8) pp:1711-1724
Publication Date(Web):3 April 2012
DOI:10.1016/j.polymer.2012.02.034
This study investigated the factors responsible for molecular interactions leading to self-assembly between the molecules of sorbitol and polyhedral oligomeric silsesquioxane (POSS) carrying organic and inorganic side groups. The study also assessed the utility of such molecular adducts as processing aids which will aid preparation of polymer compounds, films, and spun fibers. Several POSS molecules containing silanol functionalities and alkyl and phenyl substituents were used to separately evaluate the effects of hydrogen bonding and π−π interactions on formation of molecular adducts. The molecular adducts were studied using differential scanning calorimetry, wide angle X-ray diffraction, scanning electron microscopy, mass spectrometry, oscillatory shear rheology, and molecular dynamics simulation. The study revealed that POSS-sorbitol self-assembled structures were formed only when hydrogen bonding and π−π interactions worked cooperatively. In addition, self-assembled molecules were of amorphous nature although POSS and sorbitol were crystalline.
Co-reporter:Yannan Duan, Sadhan C. Jana, Anna M. Reinsel, Bimala Lama, and Matthew P. Espe
Langmuir 2012 Volume 28(Issue 43) pp:15362-15371
Publication Date(Web):October 9, 2012
DOI:10.1021/la302945b
This study evaluated polyhedral oligomeric silsesquioxane (POSS) molecules as useful, multifunctional reinforcing agents of silica aerogels. Silica aerogels have low-density and high surface area, although their durability is often compromised by the inherent fragility and strong moisture absorption behavior of the silica networks. POSS molecules carrying phenyl, iso-butyl, and cyclohexyl organic side groups, and several Si–OH functionalities were incorporated into silica networks via reactions between Si–OH functionalities in POSS molecules and silanes. Solid state 13C and 29Si NMR spectra established that greater than 90% of POSS molecules grafted onto silica networks and led to an increase in fractal dimensions. An almost 6-fold increase in compressive modulus was achieved with less than 5 wt % trisilanol phenyl POSS, and a 50-fold decrease in polarity with negligible changes in density were seen in aerogels modified with less than 5 wt % trisilanol isobutyl POSS.
Co-reporter:Sayantan Roy, Byoung J. Lee, Zahi M. Kakish, and Sadhan C. Jana
Macromolecules 2012 Volume 45(Issue 5) pp:2420-2433
Publication Date(Web):February 23, 2012
DOI:10.1021/ma202783p
This study investigates the issues involving reinforcement of isotactic polypropylene (iPP) spun fibers by molecular adducts originating from the synergistic interactions of polyhedral oligomeric silsesquioxane (POSS) containing silanol functionalities (silanol–POSS) and di(benzylidene)sorbitol (DBS). The molecular adducts of silanol–POSS and DBS were low viscosity liquids at fiber spinning temperature, turned into cylindrical domains during fiber spinning, and remained as nanoparticles in the fibers. The fibers were analyzed by differential scanning calorimetry, wide-angle X-ray diffraction , scanning electron microscopy, and transmission electron microscopy. It was observed that iPP compounds with 2–5 wt % silanol–POSS and 1 wt % DBS could be spun into fibers with close to 40% reduction in diameter compared to unfilled iPP. These fibers offered 60–80% increase in tensile modulus, 50–60% increase in tensile strength, and 100% increase in yield strength compared to unfilled iPP. The silanol–POSS particles were found to be of cylindrical shape with approximately 100 nm in diameter and 200–300 nm in length. The improvements in mechanical properties were correlated with iPP crystallinity and orientation factor.
Co-reporter:Jason P. Randall, Mary Ann B. Meador, and Sadhan C. Jana
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 3) pp:613
Publication Date(Web):March 1, 2011
DOI:10.1021/am200007n
Silica aerogels are highly porous solid materials consisting of three-dimensional networks of silica particles and are typically obtained by removing the liquid in silica gels under supercritical conditions. Several unique attributes such as extremely low thermal conductivity and low density make silica aerogels excellent candidates in the quest for thermal insulation materials used in space missions. However, native silica aerogels are fragile at relatively low stresses. More durable aerogels with higher strength and stiffness are obtained by proper selection of silane precursors and by reinforcement with polymers. This paper first presents a brief review of the literature on methods of silica aerogel reinforcement and then discusses our recent activities in improving not only the strength but also the elastic response of polymer-reinforced silica aerogels. Several alkyl-linked bis-silanes were used in promoting flexibility of the silica networks in conjunction with polymer reinforcement by epoxy.Keywords: conformal coatings; flexible aerogels; nanoporous materials; polymer cross-linking; silica aerogel; skeletal density; sol−gel
Co-reporter:Sayantan Roy, Vincenzo Scionti, Sadhan C. Jana, Chrys Wesdemiotis, Anna M. Pischera, and Mathew P. Espe
Macromolecules 2011 Volume 44(Issue 20) pp:8064-8079
Publication Date(Web):September 22, 2011
DOI:10.1021/ma201595j
This study investigates the nature of interactions between the molecules of polyhedral oligomeric silsesquioxane (POSS) containing silanol functionalities (silanol–POSS) and di(benzylidene)sorbitol (DBS) encountered in the development of nanocomposite fibers from the compounds of POSS, DBS, and isotactic polypropylene (iPP). The interactions were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and oscillatory shear rheology. Mass and NMR spectrometry revealed that the molecules of silanol–POSS and DBS formed several amorphous noncovalent molecular complexes promoted by hydrogen bonding. More abundant complex formation was observed with silanol–POSS molecules carrying four silanol groups and phenyl substitutions. Such complex formation deterred fibrillation of DBS when the compounds of iPP, DBS, and silanol–POSS were cooled from homogeneous melt states. It was also revealed that POSS–DBS complexes were of much lower viscosity than iPP.
Co-reporter:I. Sedat Gunes, César Pérez-Bolívar, Guillermo A. Jimenez, Omur Celikbicak, Fengyu Li, Pavel Anzenbacher Jr., Chrys Wesdemiotis, Sadhan C. Jana
Polymer 2011 Volume 52(Issue 23) pp:5355-5361
Publication Date(Web):27 October 2011
DOI:10.1016/j.polymer.2011.09.011
Ternary non-covalent interactions between carbon nanofibers (CNFs), oxidized carbon nanofibers (ox-CNFs), poly(methyl methacrylate) (PMMA) chains, and benzotriazole-containing UV stabilizers were analyzed using Fourier-transform infra red spectroscopy (FTIR), time-resolved fluorescence emission spectroscopy, and fluorescence lifetime imaging microscopy. The results indicated that PMMA chains form hydrogen bonds both with ox-CNF fibers and the UV stabilizer molecules. It was also determined that UV stabilizers strongly interact with CNF particles via π-π interactions. The extent of π-π and hydrogen bonding interactions was determined to be lower between ox-CNF particles and UV stabilizers due to less perfect graphitic structure of the former. The morphology of the composites indicated that the hydrogen bonds between PMMA chains and ox-CNF particles resulted in highly improved state of filler dispersion in ox-CNF/PMMA composites.Fluorescence lifetime imaging microscopy (FLIM) and scanning electron microscopy (SEM) images showing distinctive features of interactions between PMMA, UV stabilizers, and (a) CNF and (b) ox-CNF particles.
Co-reporter:I. Sedat Gunes, César Pérez-Bolivar, Feina Cao, Guillermo A. Jimenez, Pavel Anzenbacher and Sadhan C. Jana
Journal of Materials Chemistry A 2010 vol. 20(Issue 17) pp:3467-3474
Publication Date(Web):14 Jan 2010
DOI:10.1039/B922027E
Non-covalent interactions between filler particles and polyurethanes were investigated using fluorescence emission spectroscopy. The results were used in the analysis of shape memory (SM) performance of polyurethanes. Composites of shape memory polyurethane (SMPU) and carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), organoclay, silicon carbide, and carbon black were prepared from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol. It was revealed by fluorescence emission spectroscopy that primarily the urethane groups located in the hard segments of SMPU interacted with the polar functional groups on filler particles. A close correlation between the extent of non-covalent filler–matrix interactions, soft segment crystallinity, and SM properties of polyurethane composites was discussed. It was observed that weak non-covalent interactions of polymer chains with CNF and SiC particles caused significant reductions in soft segment crystallinity of SMPU and hence the shape memory properties of the composites.
Co-reporter:I. Sedat Gunes, Guillermo A. Jimenez, Sadhan C. Jana
Carbon 2009 Volume 47(Issue 4) pp:981-997
Publication Date(Web):April 2009
DOI:10.1016/j.carbon.2008.11.053
The effectiveness of carbonaceous, electrically conductive fillers in shape memory actuation of polyurethane composites by resistive heating was evaluated. Specifically, the dependence of electrical resistivity on specimen temperature and imposed tensile strains encountered in shape memory test cycles was determined for shape memory polyurethane (SMPU) composites of carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), and carbon black (CB). The SMPU composites with crystalline soft segments were synthesized from diphenylmethane di-isocyanate, 1,4-butanediol, and poly(caprolactone)diol in a low-shear chaotic mixer and in an internal mixer. The materials synthesized in the chaotic mixer showed higher soft segment crystallinity and lower electrical percolation threshold. A reduction in soft segment crystallinity was observed in the presence of CNF and ox-CNF; the reduction was smaller in the case of ox-CNF. Only the composites of CB showed pronounced positive temperature coefficient (PTC) effects. The observed PTC effects bore a close relationship with non-linear thermal expansion during heating. The composites of CNF and ox-CNF did not show PTC effects due to low levels of soft segment crystallinity. The resistivity of composites of CB increased by several orders of magnitude with imposed tensile strain while composites of CNF and ox-CNF showed weak dependence on strain.
Co-reporter:Guillermo A. Jimenez
Polymer Engineering & Science 2009 Volume 49( Issue 10) pp:2020-2030
Publication Date(Web):
DOI:10.1002/pen.21442
Abstract
Composites of carbon nanofibers (CNFs), oxidized carbon nanofibers (ox-CNFs), and shape-memory thermoplastic polyurethane (TPU) were prepared in a chaotic mixer and their shape-memory properties evaluated. The polymer was synthesized from 4,4′-diphenylmethane diisocyanate, 1,4-butanediol chain extender, and semicrystalline poly(ε-caprolactone) diol soft segments. The shape-memory action was triggered by both conductive and resistive heating. It was found that soft segment crystallinity and mechanical reinforcement by nanofibers produced competing effects on shape-memory properties. A large reduction in soft segment crystallinity in the presence of CNF and stronger mechanical reinforcement by well-dispersed ox-CNF determined the shape-memory properties of the respective composites. It was found that the maximum shape recovery force, respectively, 3 and 4 MPa, was obtained in the cases of 5 and 1 wt% CNF and ox-CNF, respectively, compared with ∼1.8 MPa for unfilled TPU. The degree of soft segment and hard segment phase separation and thermal stability of the composites were analyzed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.
Co-reporter:Ling Du, Sadhan C. Jana
Journal of Power Sources 2008 Volume 182(Issue 1) pp:223-229
Publication Date(Web):15 July 2008
DOI:10.1016/j.jpowsour.2008.03.071
The hygrothermal effects on mechanical, thermal, and electrical properties of highly conductive graphite-based epoxy composites were investigated. The highly conductive graphite-based epoxy composites were found to be suitable for applications as bipolar plates in proton exchange membrane (PEM) fuel cells. The hygrothermal aging experiments were designed to simulate the service conditions in PEM fuel cells. Specifically, the composite specimens were immersed in boiling water, aqueous sulphuric acid solution, and aqueous solution of hydrogen peroxide. The water uptake, changes in surface appearance and dimensions, glass transition behavior and thermal stability, and electrical and mechanical properties were evaluated. The water uptake at short time increased linearly with the square root of time as in linear Fickian diffusion. The presence of graphite significantly reduced both the rate and extent of water uptake. No discernible changes in specimen dimensions, surface appearance, and morphology of the composites were observed. The electrical conductivity and mechanical properties remained almost unchanged. The wet specimens showed slight reduction of glass transition temperature (Tg) due to plasticization of epoxy networks by absorbed water, while the re-dried specimens showed small increase of Tg. The composites maintained high electrical conductivity of about 300–500 S cm−1 and good mechanical properties and showed thermal stability up to 350 °C.
Co-reporter:I. Sedat Gunes;Feina Cao
Journal of Polymer Science Part B: Polymer Physics 2008 Volume 46( Issue 14) pp:1437-1449
Publication Date(Web):
DOI:10.1002/polb.21480
Abstract
The effects of thermal expansion on shape memory performance of shape memory polyurethanes and their nanocomposites with organoclay, carbon nanofiber (CNF), silicon carbide (SiC), and carbon black (CB) were evaluated. The shape memory test cycle involved tensile deformation at above the trigger temperature to initiate shape memory function, cooling to room temperature to fix the shape, and shape recovery induced by heating to above the trigger temperature. Phenomenological models were used to interpret the experimental data on coefficient of thermal expansion (CTE). It was found that Kerner model showed good fit for composites of SiC and CB, and Halpin model gave better fit for composites of organoclay and CNF. It was observed that thermal expansion exerts negative effect on recovered strain, the extent of which depends on the magnitude of temperature gradient, CTE, and the level of tensile strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1437–1449, 2008
Co-reporter:Ling Du, Sadhan C. Jana
Journal of Power Sources 2007 Volume 172(Issue 2) pp:734-741
Publication Date(Web):25 October 2007
DOI:10.1016/j.jpowsour.2007.05.088
Carbon-filled epoxy composites are developed for potential application as bipolar plates in proton exchange membrane (PEM) fuel cells. These composites are prepared by solution intercalation mixing, followed by compression molding and curing. Electrical conductivity, thermal and mechanical properties, and hygrothermal characteristics are determined as function of carbon-filler content. Expanded graphite and carbon black are used as synergistic combination to obtain desired in-plane and through-plane conductivities. These composites show high glass transition temperatures (Tg ∼ 180 °C), high thermal degradation temperatures (T2 ∼ 415 °C), in-plane conductivity of 200–500 S cm−1 with 50 wt% carbon fillers, in addition to offering high values of flexural modulus, flexural strength, and impact strength, respectively 2 × 104 MPa, 72 MPa, and 173 J m−1. The presence of carbon fillers helps reduce water uptake from 4 to 5 wt% for unfilled epoxy resins to 1–2 wt%. In addition, morphology, electrical, mechanical, and thermal properties remain unchanged on exposure to boiling water and acid reflux. This data indicate that the composites developed in this work meet many attributes of bipolar plates for use in PEM fuel cells.
Co-reporter:Sadhan C. Jana;Dhawal P. Dharaiya;Sergei F. Lyuksyutov
Polymer Engineering & Science 2006 Volume 46(Issue 1) pp:19-28
Publication Date(Web):15 NOV 2005
DOI:10.1002/pen.20445
A minor polymer was deformed into lamellar and fibrillar morphological forms in a chaotic mixer, which rendered the resultant immiscible blend electrically conductive along the flow direction. This was demonstrated using a blend consisting of 10 wt% polypropylene (PP), polyamide 6 (PA6), and 1 wt% conductive carbon black (CB) particles. It was found that PP-phase containing CB particles deformed into lamellar and fibrillar morphological forms produced continuous networks in the flow direction, and provided conductivity by double percolation. Breakup of PP fibrils into droplets destroyed the continuous conductive networks, although conductivity was sustained purportedly due to migration of CB particles from the bulk to the surface of closely spaced PP droplets. This was augmented by the formation of much smaller PP droplets in the presence of CB particles. On continued mixing, the blend eventually turned into insulator as CB particles migrated from the polymer–polymer interfaces to PA6 phase. POLYM. ENG. SCI., 46:19–28, 2006. © 2005 Society of Plastics Engineers
Co-reporter:Asim Pattanayak
Polymer Engineering & Science 2005 Volume 45(Issue 11) pp:1532-1539
Publication Date(Web):4 OCT 2005
DOI:10.1002/pen.20373
In this study, bulk polymerized clay-tethered thermoplastic polyurethane (TPU) composites were synthesized that offered much improved tensile strength with negligible changes in tensile modulus. These composites contained intercalated, tethered layered silicate particles and were synthesized by mixing low molecular weight prepolymer chains containing unreacted –NCO groups with reactive layered silicate clay followed by catalyzed chain extension reaction with butanediol. The molar ratio of –NCO and –OH functional groups in the composite was varied between 1.0 and 1.2. It was found that an appreciable amount of –NCO groups was consumed in reaction with moisture present in the clay and some in quaternary ammonium ion-catalyzed dimerization and trimerization. Composites with –NCO to –OH molar ratio 1.1 provided the best improvement in mechanical properties—the composite with 5 wt% clay provided a 60% increase in tensile strength and 50% increase in strain at break, while the tensile modulus increased only by 15% over TPU. POLYM. ENG. SCI., 45:1532–1539, 2005. © 2005 Society of Plastics Engineers
Co-reporter:Dhawal P. Dharaiya
Journal of Polymer Science Part B: Polymer Physics 2005 Volume 43(Issue 24) pp:3638-3651
Publication Date(Web):2 NOV 2005
DOI:10.1002/polb.20657
This study investigated the role of layered silicate clay on morphology development in chaotic mixing of two immiscible polymers, polypropylene (PP) and polyamide 6 (PA6). The study showed that clay particles helped to produce droplets of much smaller size and with narrower size distribution due to their direct influence on the breakup of PP domains. In the experiments, a small quantity of organically modified layered silicate clay was initially mixed in PP and the mixture was blended with PA6 in a chaotic mixer. All morphological forms, such as lamellas, fibrils, and droplets were seen as in the case with no clay. The clay particles reduced interfacial tension between PP and PA6 phases. As a consequence, the PP domains sustained lamellar and fibrillar forms, and thin fibrils were formed. These thin fibrils in turn broke rapidly into smaller droplets. It was also found that a large fraction of clay particles migrated into PA6 phase and contained intercalated PA6 chains in their galleries. These results indicate that clay particles did not participate in compatibilization in this system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3638–3651, 2005
Co-reporter:Chang-Min Hong;Jongdae Kim
Polymer Engineering & Science 2004 Volume 44(Issue 11) pp:2101-2109
Publication Date(Web):29 OCT 2004
DOI:10.1002/pen.20215
The effect of shear-induced conductive filler migration on surface and volume conductivity of injection molded articles of polystyrene and polypropylene with carbon black was investigated. It was found that the loss of conductivity was most significant when the mean particle concentration was at or slightly above the percolation threshold. The compounds with mean particle concentration well above the percolation threshold showed no loss at all. The conductivity decreased with the increase of shear rate used in molding. The removal of surface layers by excimer laser led to restoration of the conductivity to the value of well-mixed, compression-molded specimens. The thickness of surface layer removed before conductivity was restored was found to be a strong function of the shear rate and the nature of polymer used. Polym. Eng. Sci. 44:2101–2109, 2004. © 2004 Society of Plastics Engineers.
Co-reporter:Dhawal Dharaiya;Asjad Shafi
Polymer Engineering & Science 2003 Volume 43(Issue 3) pp:580-595
Publication Date(Web):7 APR 2004
DOI:10.1002/pen.10047
In this study we investigated the potential of phenoxy resins as compatibilizers in the blending of two high-volume engineering thermoplastics—polyamide 6 (PA6) and polybutylene terephthalate (PBT), in an effort to establish the usefulness of blending as a method of recycling of mixed plastic wastes. It was found that phenoxy resins formed miscible blends with PBT, formed grafted copolymers with PBT through ester exchange reactions, and—though formed immiscible blends with PA6—produced energetic interactions in the form of hydrogen bonding with PA6. The ternary blend systems of 70 parts PA6, 30 parts PBT, and respectively 5, 10, and 30 parts phenoxy resins, all by weight, revealed at two-phase nature—PA6 as the continuous phase and miscible blends of PBT and phenoxy resins as the dispersed phase—and were found to be stable to phase coarsening by annealing with mechanical properties at least as good as those of the component polymers.
Co-reporter:Sadhan C. Jana;Alberto Prieto
Journal of Applied Polymer Science 2002 Volume 86(Issue 9) pp:2159-2167
Publication Date(Web):17 SEP 2002
DOI:10.1002/app.11073
A new method is presented for the development of natural fiber composites of high-performance thermoplastic polymers considering poly(phenylene ether) (PPE) and wood flour as an example system. The large gap between the high processing temperature of PPE, typically between 280 and 320°C, and the low decomposition temperature of wood flour, about 200°C, was reduced by using a reactive solvent, a low molecular weight epoxy. The epoxy formed miscible blends with PPE, which offered much lower viscosity compared to PPE and processing temperatures well below the decomposition temperature of wood flour. In addition, the epoxy component accumulated around the polar wood flour particles upon polymerization during the fabrication step. The composite materials consisted of a thermoplastic continuous phase and two dispersed phases, one of polymerized epoxy and the other of wood flour particles coated with polymerized epoxy. These composites offered a significant reduction in density and better mechanical and physical properties when compared to commercially available grades of engineering polymer blends filled with short glass fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2159–2167, 2002
Co-reporter:Sadhan C. Jana;Alberto Prieto
Journal of Applied Polymer Science 2002 Volume 86(Issue 9) pp:2168-2173
Publication Date(Web):17 SEP 2002
DOI:10.1002/app.11072
Our earlier paper (Jana, S.C.; Prieto, A. J Appl Polym Sci 2002, 86, 2159) on the development of natural fiber composites of high-performance thermoplastic polymers described a new methodology for the manufacturing of composite materials of a high-temperature thermoplastic polymer, poly(phenylene ether) (PPE) and wood flour, a cellulosic natural filler. A thermosetting epoxy, used as a reactive solvent, reduced the processing temperature of PPE/epoxy blends to well below the decomposition temperature of natural fillers. In addition, the epoxy component, upon polymerization, formed coating layers around the filler particles to provide resistance against moisture diffusion and attacks by acids and alkali. This article describes the results of an investigation on two outstanding issues: (1) the influence of cellulosic wood particles and coupling agents on the speed of epoxy curing and reaction-induced phase separation and (2) the effects of coupling agents on the morphology of crosslinked epoxy at the surfaces of natural fillers and mechanical properties of the composites. It was found that wood particles expedited epoxy curing in the composites; the extent of epoxy curing, however, was reduced in the presence of coupling agents. Also, the coupling agents promoted complete coverage of wood flour particles by polymerized epoxy, although the mechanical properties deteriorated over systems without coupling agents. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2168–2173, 2002
Co-reporter:I. Sedat Gunes, César Pérez-Bolivar, Feina Cao, Guillermo A. Jimenez, Pavel Anzenbacher and Sadhan C. Jana
Journal of Materials Chemistry A 2010 - vol. 20(Issue 17) pp:NaN3474-3474
Publication Date(Web):2010/01/14
DOI:10.1039/B922027E
Non-covalent interactions between filler particles and polyurethanes were investigated using fluorescence emission spectroscopy. The results were used in the analysis of shape memory (SM) performance of polyurethanes. Composites of shape memory polyurethane (SMPU) and carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), organoclay, silicon carbide, and carbon black were prepared from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol. It was revealed by fluorescence emission spectroscopy that primarily the urethane groups located in the hard segments of SMPU interacted with the polar functional groups on filler particles. A close correlation between the extent of non-covalent filler–matrix interactions, soft segment crystallinity, and SM properties of polyurethane composites was discussed. It was observed that weak non-covalent interactions of polymer chains with CNF and SiC particles caused significant reductions in soft segment crystallinity of SMPU and hence the shape memory properties of the composites.
Co-reporter:Jason P. Randall, Mary Ann B. Meador and Sadhan C. Jana
Journal of Materials Chemistry A 2013 - vol. 1(Issue 22) pp:NaN6652-6652
Publication Date(Web):2013/04/19
DOI:10.1039/C3TA11019B
This study evaluated the effectiveness of dimethyldiethoxysilane (DMDES) precursor in improving the elastic recovery behavior of silica aerogels reinforced with epoxy through amine sites on the silica surface. In the study, two aminosilanes – 3-aminopropyltriethoxysilane (APTES) and bis(trimethoxysilylpropyl)amine (BTMSPA) – were considered as reactive sites for cross-linking with epoxy. Because of the way the samples were formulated, BTMSPA offered half the number of amine sites compared to APTES at the same level of substitution. Replacing tetraethoxysilane (TEOS) with at least 15 mol% DMDES reduced the number of silicon–oxygen bonds in the aerogel networks and resulted in improved elastic recovery, but up to an order of magnitude lower compressive modulus. BTMSPA aerogels demonstrated strong elastic response without DMDES, with some samples showing near complete recovery. However, these aerogels offered lower modulus than APTES aerogels.
Co-reporter:Xiao Wang, Huan Zhang and Sadhan C. Jana
Journal of Materials Chemistry A 2013 - vol. 1(Issue 44) pp:NaN13999-13999
Publication Date(Web):2013/10/11
DOI:10.1039/C3TA13099A
This paper evaluates the properties of aerogels obtained from sulfonated syndiotactic polystyrene (ssPS) and polyaniline-coated ssPS and elaborates two applications of such aerogel materials. The syndiotactic polystyrene (sPS) chains were sulfonated in chloroform solutions and ssPS gels at several levels of sulfonation were synthesized. The ssPS gels with high surface area were used as templates to adsorb, protonate, and polymerize aniline. The aerogels recovered after supercritical drying were characterized by scanning electron microscopy, wide angle X-ray diffraction (WAXD), nitrogen adsorption–desorption isotherms, and differential scanning calorimetry. The data revealed that enough crystalline domains remained in ssPS to offer mechanical integrity to the gel network, although the pore surface area reduced significantly at high sulfonation levels. The sulfonic acid groups in ssPS aerogel promoted fast moisture absorption. A large fraction of mesopores appeared in polyaniline-coated ssPS aerogels. The polyaniline-coated ssPS aerogel layer rendered an insulating macroporous membrane electrically conductive.
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