http://hdl.handle.net/1813/14126 2013-06-18T22:25:44Z 2013-06-18T22:25:44Z Jesperson, M.L. Mirau, P.A. Meerwal, R.A. Vaia, R.A. Rodriguez, R. Giannelis, E.P. http://hdl.handle.net/1813/30470 2012-10-16T05:01:05Z 2010-06-10T00:00:00Z

Title: Canopy Dynamics in Nanoscale Ionic Materials Authors: Jesperson, M.L.; Mirau, P.A.; Meerwal, R.A.; Vaia, R.A.; Rodriguez, R.; Giannelis, E.P. Abstract: Nanoscale ionic materials (NIMS) are organic inorganic hybrids in which a core nanostructure is functionalized with a covalently attached corona and an ionically tethered organic canopy. NIMS are engineered to be liquids under ambient conditions in the absence of solvent and are of interest for a variety of applications. We have used nuclear magnetic resonance (NMR) relaxation and pulse-field gradient (PFG) diffusion experiments to measure the canopy dynamics of NIMS prepared from 18-nm silica cores modified by an alkylsilane monolayer possessing terminal sulfonic acid functionality, paired with an amine-terminated ethylene oxide/propylene oxide block copolymer canopy. Carbon NMR studies show that the block copolymer canopy is mobile both in the bulk and in the NIMS and that the fast (ns) dynamics are insensitive to the presence of the silica nanoparticles. Canopy diffusion in the NIMS is slowed relative to the neat canopy, but not to the degree predicted from the diffusion of hard-sphere particles. Canopy diffusion is not restricted to the surface of the nanoparticles and shows unexpected behavior upon addition of excess canopy. Taken together, these data indicate that the liquid-like behavior in NIMS is due to rapid exchange of the block copolymer canopy between the ionically modified nanoparticles.

2010-06-10T00:00:00Z Qi, G. Fu, L. Duan, X. Choi, B-H. Abraham, M. Giannelis, E.P. http://hdl.handle.net/1813/30468 2012-10-12T05:02:04Z 2011-08-04T00:00:00Z

Title: Mesoporous amine-bridged polysilsesquioxane for CO2 capture Authors: Qi, G.; Fu, L.; Duan, X.; Choi, B-H.; Abraham, M.; Giannelis, E.P. Abstract: A novel class of amine-supported sorbents based on amine-bridged mesoporous polysilsesquioxane was developed via a simple one-pot sol-gel process. The new sorbent allows the incorporation of a large amount of active groups without sacrificing surface area or pore volume available for CO2 capture, leading to a CO2 capture capacity of 3.2 mmol g−1 under simulated flue gas conditions. The sorbent is readily regenerated at 100°C and exhibits good stability over repetitive adsorption-desorption cycling. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

2011-08-04T00:00:00Z Cheng, X. McCoy, J.H. Israelachvili, J.N. Cohen, I. http://hdl.handle.net/1813/30467 2012-10-12T05:01:47Z 2011-09-02T00:00:00Z

Title: Imaging the microscopic structure of shear thinning and thickening colloidal suspension Authors: Cheng, X.; McCoy, J.H.; Israelachvili, J.N.; Cohen, I. Abstract: The viscosity of colloidal suspensions varies with shear rate, an important effect encountered in many natural and industrial processes. Although this non-Newtonian behavior is believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics are difficult to measure. By combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension's structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by hydrodynamic lubrication forces. This combination of techniques illustrates an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids.

2011-09-02T00:00:00Z Yang, Z. Shen, J. Archer, L.A. http://hdl.handle.net/1813/30466 2012-10-12T05:01:25Z 2011-06-13T00:00:00Z

Title: An In Situ Method of Creating Metal Oxide-Carbon Composites and Their Application as Anode Material for Lithium-Ion Batteries Authors: Yang, Z.; Shen, J.; Archer, L.A. Abstract: Transition metal oxides are actively investigated as anode materials for lithium-ion batteries (LIBs), and their nanocomposites with carbon frequently show better performance in galvanostatic cycling studies, compared to the pristine metal oxide. An in situ, scalable method for creating a variety of transition metal oxide-carbon nanocomposites has been developed based on free-radical polymerization and cross-linking of poly(acrylonitrile) in the presence of the metal oxide precursor containing vinyl groups. The approach yields a cross-linked polymer network, which uniformly incorporates nanometre-sized transition metal oxide particles. Thermal treatment of the organic-inorganic hybrid material produces nearly monodisperse metal oxide nanoparticles uniformly embedded in a porous carbon matrix. Cyclic voltammetry and galvanostatic cycling electrochemical measurements in a lithium half-cell are used to evaluate the electrochemical properties of a Fe(3)O(4)-carbon composite created using this approach. These measurements reveal that when used as the anode in a lithium battery, the material exhibits stable cycling performance at both low and high current densities. We further show that the polymer/nanoparticle copolymerization approach can be readily adapted to synthesize metal oxide/carbon nanocomposites based on different particle chemistries for applications in both the anode and cathode of LIBs.

2011-06-13T00:00:00Z Kaushik, A.P. Clancy, P. http://hdl.handle.net/1813/30464 2012-10-12T05:01:03Z 2011-04-03T00:00:00Z

Title: Trapping dynamics of diindenoperylene (DIP) in self-assembled monolayers using molecular simulation Authors: Kaushik, A.P.; Clancy, P. Abstract: All-atom Molecular Dynamics simulation methods employing a well-tested intermolecular potential model, MM3 (Molecular Mechanics 3), demonstrate the propensity for diindenoperylene (DIP) molecules to insert between molecules of a self-assembled monolayer (SAM) during a deposition process intended to grow a thin film of this organic semiconductor molecule onto the surface of self-assembled monolayers. The tendency to insert between SAM molecules is fairly prevalent at normal growth temperatures and conditions, but is most strongly dependent on the density and the nature of the SAM. We posit the existence of an optimal density to favor surface adsorption over insertion for this system. DIP is less likely to insert in fluorinated SAMs, like FOTS (fluorooctatrichlorosilane), than its unfluorinated analog, OTS (octatrichlorosilane). It is also less likely to insert between shorter SAMs (e.g., less insertion in OTS than ODTS (octadecyltrichlorosilane)). Very short length, surface-coating molecules, like HDMS (hexamethyldisilazane), are more likely to scatter energetic incoming DIP molecules with little insertion on first impact (depending on the incident energy of the DIP molecule). Grazing angles of incidence of the depositing molecules generally favor surface adsorption, at least in the limit of low coverage, but are shown to be dependent on the nature of the SAM. The validity of these predictions is confirmed by comparison of the predicted sticking coefficients of DIP at a variety of incident energies on OTS, ODTS, and FOTS SAMs with results obtained experimentally by Desai et al. (2010)[23]. The simulation predictions of the tendency of DIP to insert can be explained, in large part, in terms of binding energies between SAM and DIP molecules. However, we note that entropic and stochastic events play a role in the deposition outcomes. Preliminary studies of multiple deposition events, emulating growth, show an unexpected diffusion of DIP molecules inserted within the SAM matrix in a clear attempt of the DIP molecules to aggregate together. (C) 2011 Elsevier B.V. All rights reserved.

2011-04-03T00:00:00Z Ha, D-H. Moreau, L.M. Bealing, C.R. Zhang, H. Hennig, R.G. Robinson, R.D. http://hdl.handle.net/1813/30463 2012-10-12T05:00:37Z 2011-04-15T00:00:00Z

Title: The structural evolution and diffusion during the chemical transformation from cobalt to cobalt phosphide nanoparticles Authors: Ha, D-H.; Moreau, L.M.; Bealing, C.R.; Zhang, H.; Hennig, R.G.; Robinson, R.D. Abstract: We report the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticles (NPs), epsilon-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP). Extended X-ray absorption fine structure (EXAFS) investigations were used to elucidate the changes in the local structure of cobalt atoms which occur as the chemical transformation progresses. The lack of long-range order, spread in interatomic distances, and overall increase in mean-square disorder compared with bulk structure reveal the decrease in the NP's structural order compared with bulk structure, which contributes to their deviation from bulk-like behavior. Results from EXAFS show both the Co2P and CoP phases contain excess Co. Results from EXAFS, transmission electron microscopy, X-ray diffraction, and density functional theory calculations reveal that the inward diffusion of phosphorus is more favorable at the beginning of the transformation from epsilon-Co to Co2P by forming an amorphous Co-P shell, while retaining a crystalline cobalt core. When the major phase of the sample turns to Co2P, the diffusion processes reverse and cobalt atom out-diffusion is favored, leaving a hollow void, characteristic of the nanoscale Kirkendall effect. For the transformation from Co2P to CoP theory predicts an outward diffusion of cobalt while the anion lattice remains intact. In real samples, however, the Co-rich nanoparticles continue Kirkendall hollowing. Knowledge about the transformation method and structural properties provides a means to tailor the synthesis and composition of the NPs to facilitate their use in applications.

2011-04-15T00:00:00Z Tiraferri, A. Yip, N.Y. Phillip, W.A. Schiffman, J.D. Elimelech, M. http://hdl.handle.net/1813/30462 2012-10-11T05:02:06Z 2010-11-10T00:00:00Z

Title: Relating performance of thin-film composite forward osmosis membranes to support layer formation and structure Authors: Tiraferri, A.; Yip, N.Y.; Phillip, W.A.; Schiffman, J.D.; Elimelech, M. Abstract: Osmotically driven membrane processes have the potential to treat impaired water sources, desalinate sea/brackish waters, and sustainably produce energy. The development of a membrane tailored for these processes is essential to advance the technology to the point that it is commercially viable. Here, a systematic investigation of the influence of thin-film composite membrane support layer structure on forward osmosis performance is conducted. The membranes consist of a selective polyamide active layer formed by interfacial polymerization on top of a polysulfone support layer fabricated by phase separation. By systematically varying the conditions used during the casting of the polysulfone layer, an array of support layers with differing structures was produced. The role that solvent quality, dope polymer concentration, fabric layer wetting, and casting blade gate height play in the support layer structure formation was investigated. Using a 1 M NaCl draw solution and a deionized water feed, water fluxes ranging from 4 to 25 L m(-2) h(-1) with consistently high salt rejection (>95.5%) were produced. The relationship between membrane structure and performance was analyzed. This study confirms the hypothesis that the optimal forward osmosis membrane consists of a mixed-structure support layer, where a thin sponge-like layer sits on top of highly porous macrovoids. Both the active layer transport properties and the support layer structural characteristics need to be optimized in order to fabricate a high performance forward osmosis membrane. (C) 2010 Elsevier B.V. All rights reserved

2010-11-10T00:00:00Z Schaefer, J.L. Moganty, S.S. Yanga, D.A. Archer, L.A. http://hdl.handle.net/1813/30460 2012-10-11T05:02:05Z 2011-02-15T00:00:00Z

Title: Nanoporous hybrid electrolytes Authors: Schaefer, J.L.; Moganty, S.S.; Yanga, D.A.; Archer, L.A. Abstract: Oligomer-suspended SiO(2)-polyethylene glycol nanoparticles are studied as porous media electrolytes. At SiO(2) volume fractions, phi, bracketing a critical value phi(y) approximate to 0.29, the suspensions jam and their mechanical modulus increase by more than seven orders. For phi > phi(y), the mean pore diameter is close to the anion size, yet the ionic conductivity remains surprisingly high and can be understood, at all phi, using a simple effective medium model proposed by Maxwell. SiO(2)-polyethylene glycol hybrid electrolytes are also reported to manifest attractive electrochemical stability windows (0.3-6.3 V) and to reach a steady-state interfacial impedance when in contact with metallic lithium.

2011-02-15T00:00:00Z Hur, K. Hennig, R.G. Escobedo, F.A. Wiesner, U.B. http://hdl.handle.net/1813/30457 2012-10-11T05:01:36Z 2010-11-19T00:00:00Z

Title: Mesoscopic structure prediction of nanoparticle assembly and coassembly: Theoretical foundation Authors: Hur, K.; Hennig, R.G.; Escobedo, F.A.; Wiesner, U.B. Abstract: In this work, we present a theoretical framework that unifies polymer field theory and density functional theory in order to efficiently predict ordered nanostructure formation of systems having considerable complexity in terms of molecular structures and interactions. We validate our approach by comparing its predictions with previous simulation results for model systems. We illustrate the flexibility of our approach by applying it to hybrid systems composed of block copolymers and ligand coated nanoparticles. We expect that our approach will enable the treatment of multicomponent self-assembly with a level of molecular complexity that approaches experimental systems.

2010-11-19T00:00:00Z Pendergast, M.T.M. Nygaard, J.M. Ghosh, A.K. Hoek, E.M.V. http://hdl.handle.net/1813/30456 2012-10-11T05:01:33Z 2010-07-02T00:00:00Z

Title: Using nanocomposite materials technology to understand and control reverse osmosis membrane compaction Authors: Pendergast, M.T.M.; Nygaard, J.M.; Ghosh, A.K.; Hoek, E.M.V. Abstract: Composite reverse osmosis (RO) membranes were formed by interfacial polymerization of polyamide thin films over pure polysulfone and nanocomposite-polysulfone support membranes. Nanocomposite support membranes were formed from amorphous non-porous silica and crystalline microporous zeolite nanoparticles. For each hand-cast membrane, water flux and NaCl rejection were monitored over time at two different applied pressures. Nanocomposite-polysulfone supported RO membranes generally had higher initial permeability and experienced less flux decline due to compaction than pure polysulfone supported membranes. In addition, observed salt rejection tended to increase as flux declined from compaction. Cross-sectional SEM images verified significant reduction in thickness of pure polysulfone supports, whereas nanocomposites better resisted compaction due to enhanced mechanical stability imparted by the nanoparticles. A conceptual model was proposed to explain the mechanistic relationship between support membrane compaction and observed changes in water flux and salt rejection. As the support membrane compacts, skin layer pore constriction increased the effective path length for diffusion through the composite membranes, which reduced both water and salt permeability identically. However, experimental salt permeability tended to decline to a greater extent than water permeability; hence, the observed changes in flux and rejection might also be related to structural changes in the polyamide thin film. (c) 2010 Elsevier B.V. All rights reserved.

2010-07-02T00:00:00Z