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Synthesis and Structure-Conductivity Relationship of Polystyrene-block-Poly(vinyl benzyl trimethylammonium) for Alkaline Anion Exchange Membrane Fuel Cells
No full textBlock copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS-b-PVBTMABF4) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-PVBTMABF4 materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium hydroxide) (PS-b-PVBTMAOH) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS-b-PVBTMABF4 with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity relative humidity (RH)-dependent conductivity at 80 degrees C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90\% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. (c) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1751-1760, 201
Characterization of surface ligands on functionalized magnetic nanoparticles using laser desorption/ionization mass spectrometry (LDI-MS)
No full textFunctionalized magnetic nanoparticles (MNPs) have been characterized by laser desorption/ionization mass spectrometry (LDI-MS). Quantitative information about surface ligand composition and structure for monolayer and mixed monolayer protected Fe3O4 and FePt NPs can be obtained rapidly with very little sample consumption
Topological defects, surface geometry and cohesive energy of twisted filament bundles
No full textCohesive assemblies of filaments are a common structural motif found in diverse contexts, ranging from biological materials such as fibrous proteins, to artificial materials such as carbon nanotube ropes and micropatterned filament arrays. In this paper, we analyze the complex dependence of cohesive energy on twist, a key structural parameter of both self-assembled and fabricated filament bundles. Based on the analysis of simulated ground states of cohesive bundles, we show that the non-linear influence of twist derives from two distinct geometric features of twisted bundles: (i) the geometrical frustration of inter-filament packing in the bundle cross-section; and (ii) the evolution of the surface geometry of bundles with twist, which dictates the cohesive cost of non-contacting filaments at the surface. Packing frustration in the bundle core gives rise to the appearance of a universal sequence of topological defects, excess 5-fold disclinations, with increasing twist, while the evolution of filament contact at the surface of the bundle generically favors twisted geometries for sufficiently long filaments. Our analysis of both continuum and discrete models of filament bundles shows that, even in the absence of external torque or intrinsic chirality, cohesive energy universally favors twisted ground states above a critical (length/radius) aspect ratio and below a critical filament stiffness threshold
Development of a Capillary Flow Microfluidic E. coli Biosensor with On-chip Reagent Delivery using Water-soluble Nanofibers
No full textNanoimprinting Ultra Small and High Aspect Ratio Structures by using Rubber-toughened UV Cure Epoxy Resist
No full textPhotoinduced Disorder in Strongly Segregated Block Copolymer Composite Films for Hierarchical Pattern Formation
No full textSubmicrometer patterns of adjacent, well-ordered and disordered domains were obtained using optical lithography by area-selective, photoinduced disordering transitions within block copolymer composite films. Enantiopure tartaric acid was blended with poly(ethylene oxide-block-tert-butyl acrylate), PEO-b-PtBA, copolymers to yield well-ordered films. In the presence of triphenylsulfonium triflate, a photoacid generator, photoinduced disorder was achieved upon UV-exposure by deprotection of the PtBA block to yield poly(acylic acid). Poly(acrylic acid) is compatible with both PEO and tartaric acid and deprotection yields a phase mixed material and disorder within seconds. Tartaric acid performs two additional functions in this system. First, it increases segregation strength in PEO-b-PtBA, enabling well-ordered systems at low BCP molecular weights, small domain sizes, and rapid disordering kinetics. Second, the presence of tartaric acid suppresses PEO crystallization, resulting in smooth films and eliminating the influence of PEO crystallization on film morphology
Addition of perfluorocarbons to alginate hydrogels significantly impacts molecular transport and fracture stress
No full textPerfluorocarbons (PFCs) are used in biomaterial formulations to increase oxygen (O2) tension and create a homogeneous O2 environment in three-dimensional tissue constructs. It is unclear how PFCs affect mechanical and transport properties of the scaffold, which are critical for robustness, intracellular signaling, protein transport, and overall device efficacy. In this study, we investigate composite alginate hydrogels containing a perfluorooctyl bromide (PFOB) emulsion stabilized with Pluronic (R) F68 (F68). We demonstrate that PFC addition significantly affects biomaterial properties and performance. Solution and hydrogel mechanical properties and transport of representative hydrophilic (riboflavin), hydrophobic (methyl and ethyl paraben), and protein (bovine serum albumin, BSA) solutes were compared in alginate/F68 composite hydrogels with or without PFOB. Our results indicate that mechanical properties of the alginate/F68/PFOB hydrogels are not significantly affected under small strains, but a significant decrease fracture stress is observed. The effective diffusivity Deff of hydrophobic small molecules decreases with PFOB emulsion addition, yet the Deff of hydrophilic small molecules remained unaffected. For BSA, the Deff increased and the loading capacity decreased with PFOB emulsion addition. Thus, a trade-off between the desired increased O2 supply provided by PFCs and the mechanical weakening and change in transport of cellular signals must be carefully considered in the design of biomaterials containing PFCs. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013
Enhanced electrostatic discrimination of proteins on nanoparticle-coated surfaces
No full textTwo beta-lactoglobulin (BLG) isoforms, BLGA and BLGB, were used as a test bed for the differentiation of proteins using electrostatics. In these studies, the BLGA and BLGB binding to a highly charged, cationic gold nanoparticle (GNP) modified surface was investigated by atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy. The binding affinity, and more importantly, the selectivity of this surface towards these two almost identical protein isoforms were both significantly increased on the cationic GNP surface array relative to the values measured with the same free cationic GNP in solution. While protein recognition is traditionally achieved almost exclusively via orientation dependent short-range interactions such as hydrogen bonds and hydrophobic interactions, our results show the potential of protein recognition platforms based on enhanced electrostatic interactions
Assembled graphene oxide and single-walled carbon nanotube ink for stable supercapacitors
No full textWe describe the synthesis and fabrication of a graphene oxide (GO) and single-walled carbon nanotube (SWCNT) composite ink (GO-SWCNT ink) for electrochemically stable supercapacitors. Atomic force microscopy and scanning electron microscopy studies demonstrate that the obtained GO flakes are single layer with size distribution from 100 nm to 20 mu m. SWCNTs are dispersed using a GO aqueous solution (2 mg/mL) with sonication support to achieve a SWCNT concentration of 12 mg/mL, the highest reported value so far without surfactant assistance. Raman spectroscopy studies indicate that the full-width at half-maximum of the G band increases with the mixing of SWCNT and GO indicating that electronic structure changes via pi-pi interactions of GO sheets and SWCNTs. Paper-based electrodes of supercapacitor were conveniently fabricated with GO-SWCNT composite ink via a dip casting method. By using different concentrations of SWCNT in the ink, the paper electrodes provide different capacitance values. The highest value of specific capacitance reaches 295 F/g at a current density of 0.5 A/g with a GO/SWCNT weight ratio of 1:5. The cycling stability for the GO-SWCNT paper electrode supercapacitors indicates capacitance retention of 85% over 60,000 cycles