Improved Electrical Signal of Non-Poled 3D Printed Zinc Oxide-Polyvinylidene Fluoride Nanocomposites.

Polyvinylidene fluoride (PVDF) presents highly useful piezo and pyro electric properties but they are predicated upon the processing methods and the ensuing volume fraction of the ß-phase. Production of PVDF with higher ß-phase content for additive manufacturing (AM) is particularly desirable because it can enable the creation of custom parts with enhanced properties. Necessary steps from compounding to the testing of a 3D printed piezo sensitive sensor are presented in this paper. AM process variables and the influence of zinc oxide (ZnO) nanofiller on crystallinity, viscosity, and electromechanical properties of PVDF, have been explored. Fourier-transform infrared spectroscopy (FTIR) measurements confirm that a high cooling rate (HCR) of 30 °C min-1 promotes the conversion of the α-into the ß-phase, reaching a maximum of 80% conversion with 7.5-12.5% ZnO content. These processing conditions increase the elastic modulus up to 40%, while maintaining the ultimate strength, ≈46 MPa. Furthermore, HCR 10% ZnO-PVDF produces four times higher volts per Newton when compared to low cooling rate, 5 °C min-1, pristine PVDF. A piezoelectric biomedical sensor application has been presented using HCR and ZnO nanofiller. This technique also reduces the need for post-poling which can reduce manufacturing time and cost.

Microstructural Characterization and Property of Carbon Fiber Reinforced High-Density Polyethylene Composites Fabricated by Fused Deposition Modeling.

As a promising industrial thermoplastic polymer material, high-density polyethylene (HDPE) possesses distinct properties of ease to process, good biocompatibility, high recyclability, etc. and has been widely used to make packaging, prostheses and implants, and liquid-permeable membranes. Traditional manufacturing processes for HDPE, including injection molding, thermoforming, and rotational molding, require molds or post processing. In addition, part shapes are highly restricted., Thus, fused deposition modeling (FDM) is introduced to process HDPE materials to take advantage of FDM's free of design, no mold requirement, ease and low cost of processing. To improve the mechanical properties (such as stiffness and strength) and thermal resistance of HDPE, carbon fiber (CF) was incorporated into HDPE, and CF-reinforced HDPE composites were successfully fabricated using FDM process. In addition, the effects of CF content on surface quality, microstructure characterizations, tensile properties, dynamic mechanical properties, and thermal properties have been investigated. Experimental results show that an appropriate CF content addition is beneficial for improving surface quality, and mechanical and thermal properties.

Water Condensation and Droplet Shedding Behavior on Silica-Nanospring-Coated Tubes.

In this work, the water condensation performance of methylated silica-nanospring (SN)-coated horizontal aluminum tubes is assessed. Coated samples with varying nanospring mat thicknesses, from 784 to 2902 nm, were studied, which exhibited static contact angles and CA hysteresis values of 155° and 16°, respectively. Dropwise condensation and increased droplet shedding were observed on these coated tubes. Video analysis determined that tubes with 15 and 20 min SN growth times experienced an 84% increase in the condensate removal rate over the baseline. Moreover, with a hybrid wettability consisting of alternating regions of SN and bare aluminum, a 96% increase in condensate removal was experienced. Additionally, the average droplet departure size was reduced on these SN-coated tubes. SEM imaging and XEDS analysis were also performed on the tubes and revealed that the coating was reasonably durable having withstood the condensation environment. Moreover, the coated tubes were shown to exhibit the same XEDS spectra both before and after testing.

Characterization of Methyl-Functionalized Silica Nanosprings for Superhydrophobic and Defrosting Coatings.

Thin non-perfluoroalkoxy superhydrophobic coatings are desirable for heat exchangers because of their lower thermal resistance and reduced environmental concerns. Coatings requirements must also include robustness and longevity and facilitate high defrosting rates in refrigeration applications to warrant their adoption and use. Methyl-functionalized silica nanosprings (SN) possess water droplet static contact angles above 160° with contact angle hysteresis values as low as 6.9° for a sub-micrometer-thick coating. The methyl functional groups render the silica surface hydrophobic, whereas the geometrical and topographical characteristics of the nanosprings make it super-hydrophobic. Results show that SN are capable of removing 95% of the frost from the surface at a lower temperature than the base aluminum substrate. The sub-micrometer SN coating also decreases the time to defrost by ≈1.5 times and can withstand more than 20 frosting-defrosting cycles in a high humidity environment akin to real working conditions for heat exchangers.

Threefold growth efficiency improvement of silica nanosprings by using silica nanosprings as a substrate.

The growth efficiency of one-dimension (1D) nanostructures via the vapor-liquid-solid process is commonly attributed to parameters such as precursor vapor pressure, substrate temperature, and the choice of the catalyst. The work presented herein is an investigation of the use of silica nanosprings (SNs) as a 3D substrate for improving the growth efficiency of SN themselves. SNs are a 1D nanomaterial that form a nonwoven structure with optimal geometric characteristics and surface properties that mitigate collisions between growing nanosprings and ripening of the gold catalyst, which should improve SN yield. Nanospring growth, for an eight hour period, on an SN coated surface relative to an equivalent flat substrate increased from ≈25 mgh-1 to ≈80 mgh-1, respectively. All things being equal, by splitting the typical amount of catalyst, in this case gold, between the first and second growth, the double growth procedure produced more than three times more nanosprings than the equivalent single growth of a SN. In addition, using an SN as a substrate increased the sustained growth condition from four to eight hours, and thus increased by a factor of ten the gravimetric yield of SNs relative to the mass of gold used.

Self-assembled monolayers of thiols adsorbed on Au/ZnO-functionalized silica nanosprings: photoelectron spectroscopy-analysis and detection of vaporized explosives.

Self-assembled monolayers (SAMs) of thiols of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol, which have been selected for their propensity to interact with vaporized explosives, have been attached from solution onto gold decorated ZnO-coated nanosprings. X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) have been used to investigate the surface electronic structure of the SAMs coated nanosprings. On the basis of XPS analysis, it has been determined that the packing densities of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol on gold (zinc oxide) are 5.42 × 10(14) (2.83 × 10(14)), 3.26 × 10(14) (2.54 × 10(14)), 9.50 × 10(13), 2.55 × 10(14) (1.12 × 10(14)), and 5.23 × 10(13) molecules/cm(2), respectively. A single S 2p core level doublet is observed for 4-mercaptobenzoic acid and 11-(1-pyrenyl)-1-undecathiol, which is assigned to the S-Au bond. The S 2p core level for L-cysteine, 6-mercaptohexanol, and DL-thioctic acid consist of two doublets, where one is S-Au bond and the other is the S-Zn bond. Analysis of the C/S ratios agrees well with the stoichiometry of the respective thiols. UPS analysis shows that the hybridization of S 3p states and Au d-bands produces antibonding and bonding states, above and below the Au d-bands, which is characteristic of molecular chemisorption on Au nanoparticles. Gas sensors were constructed with thiolated nanosprings and their responsiveness to ammonium nitrate at 100-150 °C was tested. Nanosprings sensors functionalized with 4-mercaptobenzoic acid and 6-mercaptohexanol showed the strongest responses by a factor of 4 to 5 relative to the less responsive thiols. The response to ammonium nitrate can be correlated to the packing density and ordering of the SAMs.

Thermal and optical activation mechanisms of nanospring-based chemiresistors.

Chemiresistors (conductometric sensor) were fabricated on the basis of novel nanomaterials--silica nanosprings ALD coated with ZnO. The effects of high temperature and UV illumination on the electronic and gas sensing properties of chemiresistors are reported. For the thermally activated chemiresistors, a discrimination mechanism was developed and an integrated sensor-array for simultaneous real-time resistance scans was built. The integrated sensor response was tested using linear discriminant analysis (LDA). The distinguished electronic signatures of various chemical vapors were obtained at ppm level. It was found that the recovery rate at high temperature drastically increases upon UV illumination. The feasibility study of the activation method by UV illumination at room temperature was conducted.

A novel enzymatic microreactor with Aspergillus oryzae ß-galactosidase immobilized on silicon dioxide nanosprings.

The use of silicon dioxide (SiO(2) ) nanosprings as supports for immobilized enzymes in a continuous microreactor is described. A nanospring mat (2.2 cm(2) × 60 µm thick) was functionalized with γ-aminopropyltriethoxysilane, then treated with N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP) and dithiothreitol (DTT) to produce surface thiol (--SH) groups. SPDP-modified ß-galactosidase from Aspergillus oryzae was immobilized on the thiolated nanosprings by reversible disulfide linkages. The enzyme-coated nanospring mat was placed into a 175-µm high microchannel, with the mat partially occluding the channel. The kinetics and steady-state conversion of hydrolysis of o-nitrophenyl ß-D-galactosylpyranoside at various substrate flow rates and concentrations were measured. Substantial flow was observed through the nanosprings, for which the Darcy permeability κ ≈ 3 × 10(-6) cm(2) . A simple, one-parameter numerical model coupling Navier-Stokes and Darcy flow with a pseudo-first-order reaction was used to fit the experimental data. Simulated reactor performance was sensitive to changes in κ and the height of the nanospring mat. Permeabilities lower than 10(-8) cm(2) practically eliminated convective flow through the nanosprings, and substantially decreased conversion. Increasing the height of the mat increased conversion in simulations, but requires more enzymes and could cause sealing issues if grown above channel walls. Preliminary results indicate that in situ regeneration by reduction with DTT and incubation with SPDP-modified ß-galactosidase is possible. Nanosprings provide high solvent-accessible surface area with good permeability and mechanical stability, can be patterned into existing microdevices, and are amenable to immobilization of biomolecules. Nanosprings offer a novel and useful support for enzymatic microreactors, biosensors, and lab-on-chip devices.

Pathogenesis of early atherosclerotic lesions in infants.

High serologic lipid levels, infections, and genetic susceptibility have been proposed as possible etiologic factors of initial atherosclerotic lesions of the coronary arteries in infancy. At a recent WHO annual meeting, it was stated that breast milk substitutes cause irreparable damage in infants. This prompted us to verify whether formula feeding and parental cigarette smoking might play a role in the pathogenesis of early atherosclerotic alterations in infancy. The major epicardial coronary arteries from 36 infants dying suddenly and unexpectedly (sudden infant death syndrome) were embedded in paraffin and serially cut for histologic examination. In 67% of the cases, multifocal coronary early atherosclerotic lesions of varying entities were detected. The alterations ranged from focal plaques with mild myointimal thickening to juvenile soft plaques reducing the arterial lumen. A significant correlation was observed between the early atherosclerotic lesions and the risk factors considered. In particular, we noted different morphologic patterns related to formula feeding and cigarette smoking. Baby formula feeding and parental cigarette smoking might have an atherogenic effect on the coronary walls as from the first months of life. The lesions appear to be larger and more diffuse when both these atherogenic factors are present.

Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial life.

BACKGROUND: Detecting microbial life in extraterrestrial locations is a goal of space exploration because of ecological and health concerns about possible contamination of other planets with earthly organisms, and vice versa. Previously we suggested a method for life detection based on the fact that living entities require a continual input of energy accessed through coupled oxidations and reductions (an electron transport chain). We demonstrated using earthly soils that the identification of extracted components of electron transport chains is useful for remote detection of a chemical signature of life. The instrument package developed used supercritical carbon dioxide for soil extraction, followed by chromatography or electrophoresis to separate extracted compounds, with final detection by voltammetry and tandem mass-spectrometry. RESULTS: Here we used Earth-derived soils to develop a related life detection system based on direct observation of a biological redox signature. We measured the ability of soil microbial communities to reduce artificial electron acceptors. Living organisms in pure culture and those naturally found in soil were shown to reduce 2,3-dichlorophenol indophenol (DCIP) and the tetrazolium dye 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). Uninoculated or sterilized controls did not reduce the dyes. A soil from Antarctica that was determined by chemical signature and DNA analysis to be sterile also did not reduce the dyes. CONCLUSION: Observation of dye reduction, supplemented with extraction and identification of only a few specific signature redox-active biochemicals such as porphyrins or quinones, provides a simplified means to detect a signature of life in the soils of other planets or their moons.

Supercritical fluid extraction and high-performance liquid chromatography-diode array-electrochemical detection of signature redox compounds from sand and soil samples.

A supercritical fluid extraction procedure and a chromatographic separation/detection method were developed for the detection of Earth-based microorganisms. After microbes in a sand or a soil sample were hydrolyzed in a diluted NH(4)OH/acetone solution, several redox compounds from bacteria could be effectively extracted with trimethylamine-modified supercritical CO(2) at 35 degrees C and 300 atm. These signature redox-active compounds were separated by a reversed-phase HPLC column in an ion-pair mode and then monitored with a diode array detector and an electrochemical detector. The analytical results demonstrated the feasibility of using the reported techniques to detect the chemical signature of life in barren desert sand samples.