Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m−1 K−1 near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.
Magnetic nanoparticles that can be transported in subsurface reservoirs at high salinities and temperatures are expected to have a major impact on enhanced oil recovery, carbon dioxide sequestration, and electromagnetic imaging. Herein we report a rare example of steric stabilization of iron oxide (10) nanoparticles (NPs) grafted with poly(2-acrylamido-2-methylpropanesulfonate-co-acrylic acid) (poly-(AMPS-co-AM) that not only display colloidal stability in standard American Petroleum Institute (API) brine (8% NaCI + 2% CaCl2 by weight) at 90 C for 1 month but also resist undesirable adsorption on silica surfaces (0.4% monolayer NPs). Because the AMPS groups interacted weakly with Ca2+, they were sufficiently well solvated to provide steric stabilization. The PAA groups, in contrast, enabled covalent grafting of the poly(AMPS-co-AA) chains to amine-functionalized 10 NPs via formation of amide bonds and prevented polymer desorption even after a 40000-fold dilution. The aforementioned methodology may be readily adapted to stabilize a variety of other functional inorganic and organic NPs at high salinities and temperatures.
Metal oxides have gained significant interest aspseudocapacitor electrodes due to reversible faradaicsurface reactions that allow for high power density andgreater energy storage than carbon based electric doublelayer capacitors. However, classically investigatedmaterials like RuO2, MnO2, and Ni(OH)2 suffer from highcost, low life cycles, or limited potential windows,respectively.1-3 As such, there is growing demand for newmaterials with improved energy storage and stability.Herein, we demonstrate the capacitive characteristics ofthree lanthanum based perovskite type oxides, LaMnO3,LaNiO3, and LaCoO3. Based on the inherent nature ofperovskites to contain oxygen vacancies, we demonstratethrough cyclic voltammetry that perovskites store chargethrough anions in alkaline electrolytes, likely in the formof hydroxides. This hypothesis was tested by inducingextrinsic oxygen vacancies in LaMnO3 through a lowtemperature reduction in H2/Ar. It was found thatsubstoichiometric LaMnO3-δ exhibits ~20% greatercapacitance, highlighting the significance of oxygenvacancies as charge-storage sites in these perovskite typeoxides. Importantly, due to the well-known oxide andproton ionic conduction characteristics of perovskites, wedemonstrate that charge storage is not limited to thesurface of these materials. Rather, it may extend into thebulk of the structure, leading to higher energy storagethan traditional psuedocapacitors which are inherentlylimited by surface confined reactions. As the first study ofthese materials for pseudocapacitor applications, onlymoderate structural and electrochemical optimizationshave been carried out. As such, the high specificcapacitances of >500F/g and high cycling stability for thematerials of this study imply a promising future forperovskite structured pseudocapacitors.
Size, surface charge, and material compositions are known to influence cell uptake of nanoparticles. However, the effect of particle geometry, i.e., the interplay between nanoscale shape and size, is less understood. Here we show that when shape is decoupled from volume, charge, and material composition, under typical in vitro conditions, mammalian epithelial and immune cells preferentially internalize disc-shaped, negatively charged hydrophilic nanoparticles of high aspect ratios compared with nanorods and lower aspect-ratio nanodiscs. Endothelial cells also prefer nanodiscs, however those of intermediate aspect ratio. Interestingly, unlike nanospheres, larger-sized hydrogel nanodiscs and nanorods are internalized more efficiently than their smallest counterparts. Kinetics, efficiency, and mechanisms of uptake are all shape-dependent and cell type-specific. Although macropinocytosis is used by both epithelial and endothelial cells, epithelial cells uniquely internalize these nanoparticles using the caveolae-mediated pathway. Human umbilical vein endothelial cells, on the other hand, use clathrin-mediated uptake for all shapes and show significantly higher uptake efficiency compared with epithelial cells. Using results from both upright and inverted cultures, we propose that nanoparticle internalization is a complex manifestation of three shape- and size-dependent parameters: particle surface-to-cell membrane contact area, i.e., particle–cell adhesion, strain energy for membrane deformation, and sedimentation or local particle concentration at the cell membrane. These studies provide a fundamental understanding on how nanoparticle uptake in different mammalian cells is influenced by the nanoscale geometry and is critical for designing improved nanocarriers and predicting nanomaterial toxicity.
This paper demonstrates the capabilities and benefits of using dynamic traffic assignment (DTA) to analyze traffic impacts caused by transit services. The City of Austin’s proposed urban rail system is used as a case study. The urban rail connects the CBD, the University of Texas at Austin campus, and other large traffic generators. The majority of the rail system shares right-of-way with traffic. However, several segments have completely dedicated guideway. Previous analyses have focused either on microsimulation (which is limited in spatial area and does not consider route choice changes) or regional planning (which typically lacks detailed inputs and does not directly model transit impedances in the traffic assignment process). DTA provides a connection between these two methods: it can model route choice behavior using realistic inputs at a fine time scale across a large spatial area. Five scenarios with varying mode split percentages were modeled. At low ridership levels, corridors with major geometric modifications experienced more congestion. This caused travel pattern changes, increasing the volume on nearby parallel corridors.