Nanoporous Surface Morphology Research Articles

Development of highly sensitive relative humidity sensor based on nanoporous PCPDTBT thin film

A novel type of capacitive humidity sensor with surface-type electrode geometry is presented in the present study. The high sensitivity and significantly high bandwidth associated with this planar-type humidity sensor (Al/PCPDTBT/Al) allow the facile and reliable estimation of ambient humidity. The use of a polymer sensing material Poly[2,6-(4,4-bis-(2-ethylhexyl)− 4 H-cyclopenta[2,1-b;3,4-b՛]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) with hierarchical nanoporous surface morphology and large surface/volume ratio ensures the sensor’s stable performance coupled with swift response to ambient humidity changes. Specifically, at a relatively lower frequency bias signal (i.e., 1 kHz), a fairly higher order of humidity sensitivity has been observed, i.e., 415.07 pF/%RH. While, sensitivities at significantly higher AC signal frequencies (i.e., 10 and 100 kHz) have been experimentally determined to be 345.18 pF/%RH and 154.72 pF/%RH, respectively. Likewise, the resistive sensitivity of the humidity sensor has been estimated to be − 3624.88 kΩ/%RH, − 2381.11 kΩ/%RH and − 1338.14 kΩ/%RH, at 1, 10 and 100 kHz test frequencies, respectively. The operating mechanism of the capacitive humidity sensor relies on an increase in the dielectric constant of the PCPDTBT active sensing layer accompanied by the rise in the ambient humidity levels. In addition to enhanced bandwidth and improved capacitive and resistive sensitivity, the mean response & recovery time of the fabricated device have been recorded to be ∼ 4 min, 17 s and ∼8 min, 43 s, respectively.

Fabrication and cellular interactions of nanoporous tantalum oxide.

Tantalum possesses remarkable chemical and mechanical properties, and thus it is considered to be one of the next generation implant materials. However, the biological properties of tantalum remain to be improved for its use in tissue engineering applications. To enhance its cellular interactions, implants made of tantalum could be modified to obtain nanofeatured surfaces via the electrochemical anodization process. In this study, anodization parameters were adjusted to obtain a nanoporous surface morphology on tantalum surfaces and systematically altered to control the pore sizes from 25 to 65 nm using an aqueous HF:H2 SO4 electrolyte. Results indicated the formation of Ta2 O5 -based nanoporous surface layers, which had up to 28% more surface area and increased nanophase roughness (more than twofolds) compared to nonporous tantalum upon the anodization. It was observed that the nanoporous tantalum oxide surfaces promoted nearly 25% more fibroblast proliferation at 5 days in vitro and 15.5% more cellular spreading. Thus, nanoporous tantalum oxide surfaces can be used to increase biological interactions of the cells and provide a means of improving bioactivity of tantalum for biomaterial applications.

Aqueous asymmetric supercapacitor based on RuO2-WO3 electrodes

Designing high-energy asymmetric supercapacitors(SC) with appropriate positive and negative electrodes is urgently required to expand their practical applicability. The redox-active materials are beneficial for high-energy SC applications because of their multiple oxidation states and higher energy storage capacity than the traditional carbon-based materials. In this work, for the first time, we have designed and developed high-energy aqueous asymmetric SC by combining hexagonal WO3 and hydrous RuO2 in a single cell. Initially, the hexagonal (h) WO3 and hydrous RuO2 is directly prepared on three-dimensional conducting carbon cloth. Because of their higher electrical conductivity, nanoporous surface morphology, and redox activity, the prepared hydrous RuO2 and WO3 exhibit excellent electrochemical features in the positive and negative potential window, respectively, with aqueous H2SO4 electrolyte. The assembled RuO2//h-WO3 asymmetric SC device exhibits outstanding electrochemical performance in an operating voltage window of 1.6 V, excellent cycling stability of ∼171.75% (after 6500 cycles), and energy density of 1.25 Wh/cm3 (16.92 W h/kg) at a power density of 40 W/cm3 (540 W/kg). These results show that redox-active materials can prominently enhance the energy storage capacity of SC than the traditional carbon-based asymmetric SCs.

Manipulating the release of growth factors from biodegradable microspheres for potentially different therapeutic effects by using two different electrospray techniques for microsphere fabrication

Appropriate administration of growth factors is of great importance for directing cell behavior in regenerative medicine, which usually needs suitable carriers to protect the growth factors and to control their releases in specific spatiotemporal manners. Electrospray techniques, particularly emulsion electrospray and coaxial electrospray, have been proven effective to generate capsular/core-shell structured microspheres for growth factor delivery with superior convenience and high bioactivity retention. However, the difference in the release behavior of growth factors from emulsion electrosprayed microspheres and coaxial electrosprayed microspheres remains ambiguous, which causes the difficulty in selecting appropriate approach for certain growth factor-based therapy. In our investigation, vascular endothelial growth factor (VEGF) was used as a model molecule to be encapsulated in the microspheres prepared respectively by emulsion electrospray and coaxial electrospray using the same biodegradable poly(lactic-co-glycolic acid) (PLGA) polymer, for which size distribution, structure, morphology and in vitro degradation properties were studied and found to be tunable by different electrospray techniques. PLGA microspheres fabricated by emulsion electrospray presented nanoporous surface morphology and interior multi-compartment cores, resulting in sustained VEGF release. In comparison, the microspherical vehicles made by coaxial electrospray showing golf-ball-like textured surface morphology and interior monolithic cores led to initial fast release of VEGF. Vascular endothelial cells responded differently under the stimuli of locally released VEGF from different types of electrosprayed PLGA microspheres. The underlying mechanisms for different release behaviors of the encapsulated growth factors that were affected by microspherical vehicles formed by different electrospray techniques were presented, which would offer the design rationale for growth factor delivery vehicles with specific release kinetics, suiting for different therapeutic purposes.

Tuning Superhydrophilic Nanostructured Surfaces to Maximize Water Droplet Evaporation Heat Transfer Performance

Spraying water droplets on air fin surfaces is often used to augment the performance of air-cooled Rankine power plant condensers and wet cooling tower heat exchangers for building air-conditioning systems. To get the best performance in such processes, the water droplets delivered to the surface should spread rapidly into an extensive, thin film and evaporate with no liquid leaving the surface due to recoil or splashing. This paper presents predictions of theoretical/computational modeling and results of experimental studies of droplet spreading on thin-layer, nanostructured, superhydrophilic surfaces that exhibit very high wicking rates (wickability) in the porous layer. Analysis of the experimental data in the model framework illuminates the key aspects of the physics of the droplet-spreading process and evaporation heat transfer. This analysis also predicts the dependence of droplet-spreading characteristics on the nanoporous surface morphology and other system parameters. The combined results of this investigation indicate specific key strategies for design and fabrication of surface coatings that will maximize the heat transfer performance for droplet evaporation on heat exchanger surfaces. The implications regarding wickability effects on pool boiling processes are also discussed.

Synthesis and Photoelectrochemical Properties of Anodic Oxide Films on Titanium Formed by Pulse Anodization

Nanostructured titanium oxide represents one of the most important semiconductors suitable for a variety of technological applications. TiO2 nanopore arrays were fabricated by pulse anodization of titanium foil under specific alternating-voltage conditions. The anodic titanium oxide layer (ATO) with a structural modulation of pores was formed by a two-step electrochemical anodization at 20°C. The titanium foil was pre-textured at the cell potential of 60 V in an ethylene glycol solution containing NH4F (0.38 wt%) and H2O (1.79 wt%). After the first anodization, the oxide layer was removed, and the sample was re-anodized using different sequences of potential pulses. The morphology, structure and photoelectrochemical properties of the fabricated nanoporous TiO2 were characterized in detail. It was established that too high or too long potential pulses result in separation of individual stacked layers. Moreover, the nanoporous surface morphology of oxide can be destroyed by a lengthy pulse anodization process. These results indicated that strict control of pulse anodization conditions and a number of anodizing cycles are essential to fabricate ATO layers with a modulated nanopore shape. The bamboo-like ATO layers formed by pulse voltage anodizing exhibited enhanced photoelectrochemical properties when compared to the oxide layer formed at the constant voltage conditions.

VOPcPhO:P3HT composite micro-structures with nano-porous surface morphology

In this paper, composite micro-structures of Vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine) (VOPcPhO) and Poly (3-hexylthiophene-2,5-diyl) (P3HT) complex with nano-porous surface morphology have been developed by electro-spraying technique. The structural and morphological characteristics of the VOPcPhO:P3HT composite films have been studied by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The multidimensional VOPcPhO:P3HT micro-structures formed by electro-spraying with nano-porous surface morphology are very promising for the humidity sensors due to the pore sizes in the range of micro to nano-meters scale. The performance of the VOPcPhO:P3HT electro-sprayed sensor is superior in term of sensitivity, hysteresis and response/recovery times as compared to the spin-coated one. The electro-sprayed humidity sensor exhibits ∼3 times and 0.19 times lower hysteresis in capacitive and resistive mode, respectively, as compared to the spin-coated humidity sensor.

SILAR deposited Bi2S3 thin film towards electrochemical supercapacitor

Bi2S3 thin film electrode has been synthesized by simple and low cost successive ionic layer adsorption and reaction (SILAR) method on stainless steel (SS) substrate at room temperature. The formation of interconnected nanoparticles with nanoporous surface morphology has been achieved and which is favourable to the supercapacitor applications. Electrochemical supercapacitive performance of Bi2S3 thin film electrode has been performed through cyclic voltammetry, charge-discharge and stability studies in aqueous Na2SO4 electrolyte. The Bi2S3 thin film electrode exhibits the specific capacitance of 289Fg−1 at 5mVs−1 scan rate in 1M Na2SO4 electrolyte.

Effect of processing parameters for electrocatalytic properties of SnO2 thin film matrix for uric acid biosensor

RF sputtered tin oxide (SnO2) thin film matrix has been efficiently exploited for the detection of uric acid. The deposition parameters for SnO2 thin film have been optimized to yield better electrocatalytic properties. A correlation between its electrocatalytic properties with the structural and electrical properties has been made. SnO2 thin film prepared under optimized growth parameter (70% argon in reactive gas ambient of Ar and O2) exhibits higher mobility of charge carrier and high carrier concentration thereby resulting in enhanced charge transfer characteristics. High surface coverage of uricase onto SnO2 thin films (4.28 × 10(-4) mole cm(-2)), low value of Michaelis-Menten constant (km) 0.18 mM, good linearity in detection of uric acid in the range 0.05-1.00 mM and a fast response of 5 s are attractive features of prepared SnO2 thin film based bioelectrodes for efficient detection of uric acid. The nanoporous and rough surface morphology of SnO2 thin film besides its high carrier mobility in comparison to that of ITO is responsible for the obtained enhanced sensitivity (∼700 μA mM(-1)) and improved sensing response characteristics towards uric acid.

Effects of Anodic Oxidation in Ethylene Glycol Based Electrolyte on the Corrosion Resistance and Biocompatibility of NiTi Shape Memory Alloy

Nickel titanium (NiTi) is the most attractive shape memory alloy in industrial and in medical application but suffer from corrosion attack by body fluids. Nowadays, Electrochemical anodization has become a popular surface modification method for biomaterials. In this study we prepared TiO2 coating with nanoporous surface morphology on NiTi shape memory alloy by using electrochemical anodization in ethylene glycol based electrolyte followed by annealing in 600 °C and explored its appropriateness for biomedical applications. Morphology and crystal structure of the film was characterized by Field emission scanning electron microscopiy (FE-SEM) and X-ray diffraction (XRD) tests. The corrosion resistance of the treated NiTi alloy was investigated by potentiodynamic polarization test and The findings showed that the anodization in ethylene glycol solution extremely increased the corrosion resistance and hence biocompatibility.

Micro- and nano-morphological modification of aluminum surface for adhesive bonding to polymeric composites

The aim of the present study is to demonstrate the effect of micro and nanomorphological modifications of aluminum surface on adhesion strength. While former studies have investigated surface morphological changes after employing various surface treatment methods, this study proposes a micropatterning method to provide designed surface topography for adhesion strength enhancement. An oxalic acid-based anodizing process was also applied after micro-scale patterning on aluminum surface to incorporate nanopores into the micropatterned surface topography. The adhesion strength of an aluminum/composite bond was assessed in terms of interfacial fracture toughness under various mixed-mode loading conditions using a single-leg bending test. Microscale periodic grooves incorporated with nanoporous surface morphology significantly improved the adhesion strength. Although bond strength enhancement can be attained in any mixed mode loading condition, the surface topography modification technique is more effective in sliding mode dominant loadings than in opening-mode dominant loadings. The bond strength improvement is explained by the increased implementation of mechanical interlock mechanism which increases the resistance for crack growth by altering the trajectory of crack propagation from the bi-material interface toward the polymeric composite.

Pt nanoparticle-supported multiwall carbon nanotube electrodes for amperometric hydrogen detection

Platinum nanoparticles (Pt NPs) were grown directly on multiwall carbon nanotubes (MWNTs) using a wet chemical reduction process. Gas permeable Pt NP-supported MWNT (Pt/MWNT) electrodes were then formed on microporous PTFE membranes through the vacuum-filtration of a Pt/MWNT solution. The potential use of these electrodes in amperometric hydrogen sensor applications was assessed. Various material analysis methods such as SEM, TEM and XRD were employed in order to characterize the morphologies and microstructures of the Pt/MWNT nanocomposites. The electrodes exhibited a nanoporous interwoven surface morphology as a result of Pt agglomerates attached to the MWNTs. From the XRD and TEM measurements, individual polygonal Pt NPs were confirmed to have polycrystalline face-centered cubic (fcc) structures and very small particle sizes of 2–7 nm. The electrode fabrication process was sequentially optimized by adjusting the MWNT content, H 2PtCl 6 concentration, NaBH 4 concentration, and the drying temperature. At optimized conditions, the Pt/MWNT electrode displayed a high sensitivity greater than 200 μA/ppm, a fairly good selectivity to interfering CO species, and an excellent linear response over the wide concentration range of 5–1000 ppm. Furthermore, the performances of the electrodes were found to be better than those of binary NP-supported MWNT systems (Pt–Pd/MWNT, Pt–Zn/MWNT, Pt–Ni/MWNT and Pt–ZnO/MWNT).

Intra-surface plasmon coupling between smooth and nanoporous blocks in a goldnanorod

We report an intraparticle surface plasmon coupling in Au nanorod structures consisting of half smooth and half nanoporous surface morphology; the relative ratio and the diameter difference between each block were important in determining the overall optical properties of such nanostructures.

Nanoporous cerium oxide thin film for glucose biosensor

Nanoporous cerium oxide (CeO2) thin film deposited onto platinum (Pt) coated glass plate using pulsed laser deposition (PLD) has been utilized for immobilization of glucose oxidase (GOx). Atomic force microscopy studies reveal the formation of nanoporous surface morphology of CeO2 thin film. Response studies carried out using differential pulsed voltammetry (DPV) and optical measurements show that the GOx/CeO2/Pt bio-electrode shows linearity in the range of 25–300mg/dl of glucose concentration. The low value of Michaelis-Menten constant (1.01mM) indicates enhanced enzyme affinity of GOx to glucose. The observed results show promising application of the nanoporous CeO2 thin film for glucose sensing application without any surface functionalization or mediator.

CeO2 thin film for mediator-less glucose biosensors

AbstractPulsed laser deposited cerium oxide (CeO2) nanoporous thin film on platinum (Pt) coated glass has been used for immobilization of glucose oxidase (GOx) by electrostatic interaction. Atomic force microscopy studies reveal the formation of nanoporous surface morphology of CeO2 thin film. Differential pulse voltammetric and optical measurements show that the GOx/CeO2/Pt bioelectrode is sensitive to the detection of glucose over the concentration upto 300 mg/dl. A low value of enzyme's kinetic parameter (Michaelis-Menten constant∼1.01 mM) indicates enhanced enzyme affinity of GOx to glucose.

Effect of humidity on structure and electrochromic properties of sol–gel-derived tungsten oxide films

The influence of varying relative humidity (RH∼55 and 75%) during thin film deposition from an oxalato-acetylated peroxotungstic acid sol by dip coating, on the microstructure and electrochromic properties of pristine tungsten oxide (WO3) films obtained upon annealing is presented. The films fabricated under a relative humidity of 55% are amorphous whereas the ones cast under a substantially humid atmosphere (RH∼75%) are characterized by interconnected nanocrystallites with a triclinic phase and a nanoporous surface morphology as well. Upon lithium insertion, larger integrated values of transmission modulation and coloration efficiency are observed over the photopic and solar regions, for the films prepared under a RH∼75% as compared to that observed for the films deposited under a RH of 55%. Functional improvements are due to the larger surface area of nanocrystallites and a porous microstructure, a consequence of a higher degree of hydration and hydroxylation in the former films in contrast to the non-porous and a rather featureless structure of the latter films. Faster switching kinetics between the clear and blue states, a greater current density for lithium intercalation, a higher diffusion coefficient for lithium and a superior cycling stability, again shown by the film fabricated under a 75% RH confirm that the WO3 film microstructure is most conducive for a more facile ion insertion–extraction process, which hints at its potential for electrochromic window applications.

The Use of Spark Ablation to Produce Calcium Phosphate Films on Silicon

A method for fabrication of calcium phosphate films on crystalline silicon substrates which employs a high energy dc spark on silicon surfaces in the presence of Ca 1 0 (PO 4 ) 6 (OH) 2 is described. Such a process kinetically traps the desired calcium phosphate on the substrate with concomitant formation of a porous layer. Scanning electron micrographs of the silicon substrate show a nanoporous surface morphology for those areas exposed to spark processing. Energy dispersive X-ray analysis and infrared vibrational spectroscopy of the spark-processed regions of the Si substrate are clearly consistent with the presence of the desired biologically relevant material. In conjunction with an automated stage, facile formation of deliberate micrometer-size patterns is demonstrated.