Contact Angle Of Water Droplet Research Articles

Bioinspired flexible, breathable, waterproof and self-cleaning iontronic tactile sensors for special underwater sensing applications

Flexible tactile sensors are under high pursuit for wearable healthcare devices. However, challenges still exist in achieving both wearing comfortability through air permeability and hydrophobicity to resist water splash or even to be used in the special underwater circumstance. Inspired by the smart bio-structure of lotus leaf, we develop a flexible, breathable, waterproof and self-cleaning tactile sensor by sandwiching one ionogel electrolyte between two polydopamine (PDA)/MXene/stearic acid (STA) fabric electrodes. The micro-channels in the fabric and the through-holes in the gel endow the sensor with a high air breathability of 723.5 mm s−1 and the STA micro-sheets decorated on the outside surface of the sensor provide hydrophobicity with a large water droplet contact angle of 140.7° for the unique properties of self-cleaning and washability. By taking advantage of the supercapacitive sensing mechanism, the microstructures of MXene nanosheets on microfibers and the using of an interlayer with an internal aperture to initially separate electrodes and electrolyte, an extremely high sensitivity of up to 1677.79 kPa−1 is achieved. Practical sensing applications of the developed flexible sensors worn on different parts of human body for physiological signal monitoring, motion detection and silent information communication through Morse code in the special underwater circumstance are demonstrated.

Hydrophilic Surface Modification of Amorphous Hydrogenated Carbon Nanocomposite Films via Atmospheric Oxygen Plasma Treatment

Herein we investigated hydrophilic surface modification of SiOx containing amorphous hydrogenated carbon nanocomposite films (DLC:SiOx) via the use of atmospheric oxygen plasma treatment. The modified films exhibited effective hydrophilic properties with complete surface wetting. More detailed water droplet contact angle (CA) measurements revealed that oxygen plasma treated DLC:SiOx films maintained good wetting properties with CA of up to 28 ± 1° after 20 days of aging in ambient air at room temperature. This treatment process also increased surface root mean square roughness from 0.27 nm to 1.26 nm. Analysis of the surface chemical states suggested that the hydrophilic behavior of DLC:SiOx treated with oxygen plasma is attributed to surface enrichment with C-O-C, SiO2, and Si-Si chemical bonds as well as significant removal of hydrophobic Si-CHx functional groups. The latter functional groups are prone to restoration and are mainly responsible for the increase in CA with aging. Possible applications of the modified DLC:SiOx nanocomposite films could include biocompatible coatings for biomedical applications, antifogging coatings for optical components, and protective coatings to prevent against corrosion and wear.

Hybrid silicon-tellurium-dioxide DBR resonators coated in PMMA for biological sensing.

We report on silicon waveguide distributed Bragg reflector (DBR) cavities hybridized with a tellurium dioxide (TeO2) cladding and coated in plasma functionalized poly (methyl methacrylate) (PMMA) for label free biological sensors. We describe the device structure and fabrication steps, including reactive sputtering of TeO2 and spin coating and plasma functionalization of PMMA on foundry processed Si chips, as well as the characterization of two DBR designs via thermal, water, and bovine serum albumin (BSA) protein sensing. Plasma treatment on the PMMA films was shown to decrease the water droplet contact angle from ∼70 to ∼35°, increasing hydrophilicity for liquid sensing, while adding functional groups on the surface of the sensors intended to assist with immobilization of BSA molecules. Thermal, water and protein sensing were demonstrated on two DBR designs, including waveguide-connected sidewall (SW) and waveguide-adjacent multi-piece (MP) gratings. Limits of detection of 60 and 300 × 10-4 RIU were measured via water sensing, and thermal sensitivities of 0.11 and 0.13 nm/°C were measured from 25-50 °C for SW and MP DBR cavities, respectively. Plasma treatment was shown to enable protein immobilization and sensing of BSA molecules at a concentration of 2 µg/mL diluted in phosphate buffered saline, demonstrating a ∼1.6 nm resonance shift and subsequent full recovery to baseline after stripping the proteins with sodium dodecyl sulfate for a MP DBR device. These results are a promising step towards active and laser-based sensors using rare-earth-doped TeO2 in silicon photonic circuits, which can be subsequently coated in PMMA and functionalized via plasma treatment for label free biological sensing.

Synthesis of Ni doped-TiO2 Thin Film Photocatalysts on Glass Surfaces

Thin film of TiO2 modified Ni2+ cationic (Ni doped-TiO2) thin films were synthesized from titanium tetraisopropoxide (TTIP) and Ni(NO3)2.6H2O using the combined sol-gel and dip coating method followed by calcination at 500oC for an hour. This study aims to determine the concentration of Ni2+ and the optimum number of layers for application as self-cleaning. Frontier transform infrared (FTIR) spectrophotometric analysis observed a shift in the vibration absorption peak of Ti-O towards a smaller wave number as an indication that the Ni2+ cationic have incorporated in the TiO2matrix in forming Ni-TiO2. Based on the of x-ray diffraction (XRD) it is known that Ni-TiO2 has anatase crystalline phase with a crystallite size of 149.20 nm. Diffuse reflectance ultraviolet-visible (DRSUV-Vis) spectrophotometry showed a decrease in the bandgap energy (3.2 eV to 2.22 eV). Surface morphological by scanning electron microscopy (SEM) method showed that the addition of polyethylene glycol (PEG) resulted in a more homogeneous distribution of particles than thin films without PEG. The self-cleaning activity of Ni-TiO2 was tested for surface hydrophilic properties by measuring the contact angle of water and oil droplets under visible light illumination.

Overcoming the Hydrophobic Nature of Zinc Phenylacetate Through Co-Crystallization with Isonicotinamide

Zinc phenylacetate (Zn-PA), a substitute for sodium phenylacetate as an ammonia-scavenging drug is hydrophobic, which poses problems for drug dissolution and solubility. We were able to co-crystallize the zinc phenylacetate with isonicotinamide (INAM) and produce a novel crystalline compound (Zn-PA-INAM). The single crystal of this new crystal was obtained, and its structure is reported here for the first time. Zn-PA-INAM was characterized computationally by ab initio, Hirshfeld calculations, CLP-PIXEL lattice energy calculation, and BFDH morphology analysis, and experimentally by PXRD, Sc-XRD, FTIR, DSC, and TGA analyses. Structural and vibrational analyses showed a major modification in intermolecular interaction of Zn-PA-INAM compared to Zn-PA. The dispersion-based pi-stacking in Zn-PA is replaced by coulomb-polarization effect of hydrogen bonds. As a result, Zn-PA-INAM is hydrophilic, improving the wettability and powder dissolution of the target compound in an aqueous solution. Morphology analysis revealed, unlike Zn-PA, Zn-PA-INAM has polar groups exposed on its prominent crystalline faces, reducing the hydrophobicity of the crystal. The shift in average water droplet contact angle from 128.1° (Zn-PA) to 27.1° (Zn-PA-INAM) is strong evidence of a marked decrease in hydrophobicity of the target compound. Finally, HPLC was used to obtain the dissolution profile and solubility of Zn-PA-INAM compared to Zn-PA.

Exploiting poly(ε-caprolactone) grafted from hydrohydroxymethylated sunflower oil as biodegradable coating material of water-soluble fertilizers

In the present study, hyperbranched poly(ε-caprolactones) were prepared and used as coating materials to prepare slow release diammonium phosphate (DAP) fertilizer. Firstly, the sunflower oil was hydrohydroxymethylated by one-pot two-step process using Rh(acac)(CO)2 as catalyst, and triethylamine as ligand. Next, the bio-based hyperbranched poly(ɛ-caprolactone) (PCL) were prepared in open air by in-situ ring-opening polymerization of ε-caprolactone using hydrohydroxymethylated sunflower oil as macro-initiator and tetra(phenylethynyl)tin (Sn(C ≡ CPh)4) as catalyst. The structures of the prepared polymers (SFO-O-g-PCL) were confirmed by nuclear magnetic resonance (1H NMR) and the infrared spectroscopy (FTIR). Furthermore, molecular weight values around 20.000 g.mol−1 of PCL grafted in SFO-O-g-PCL were obtained, the thermal stability and morphology of the coated film were also evaluated using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) respectively. The hydrophobic character of the films prepared from SFO-O-g-PCL was confirmed by measuring the contact angle of water droplets. In the second part, the DAP granular fertilizers were uniformly coated by the prepared material (SFO-O-g-PCL) using a laboratory rotary drum. Then the slow release performance in water of the coated and uncoated DAP fertilizer granules was evaluated by tracking the cumulative concentration of P2O5 released. Thus, it was found that only 10 % of P2O5 was released after 2 h of essay from the coated DAP compared to a total release of P2O5 from uncoated DAP (conventional fertilizer) during the same period. This finding opens a wide perspective to combine the advantages of hydrophobic polyesters and bio-based oils to produce biodegradable coating agents.

Temperature- and pH-Responsive Schizophrenic Copolymer Brush Coatings with Enhanced Temperature Response in Pure Water

Novel brush coatings were fabricated with glass surface-grafted chains copolymerized using surface-initiated atom transfer radical polymerization (SI-ATRP) from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA188) and acrylamide (AAm), taken in different proportions. P(OEGMA188-co-AAm) brushes with AAm mole fraction >44% (determined with XPS and TOF-SIMS spectroscopy) and nearly constant with the depth copolymer composition (TOF-SIMS profiling) exhibit unusual temperature-induced transformations: The contact angle of water droplets on P(OEGMA188-co-AAm) coatings increases by ∼45° with temperature, compared to 17-18° for POEGMA188 and PAAm. The thickness of coatings immersed in water and the morphology of coatings imaged in air show a temperature response for POEGMA188 (using reflectance spectroscopy and AFM, respectively), but this response is weak for P(OEGMA188-co-AAm) and absent for PAAm. This suggests mechanisms more complex than a simple transition between hydrated loose coils and hydrophobic collapsed chains. For POEGMA188, the hydrogen bonds between the ether oxygens of poly(ethylene glycol) and water hydrogens are formed below the transition temperature Tc and disrupted above Tc when polymer-polymer interactions are favored. Different hydrogen bond structures of PAAm include free amide groups, cis-trans-multimers, and trans-multimers of amide groups. Here, hydrogen bonds between free amide groups and water dominate at T < Tc but structures favored at T > Tc, such as cis-trans-multimers and trans-multimers of amide groups, can still be hydrated. The enhanced temperature-dependent response of wettability for P(OEGMA188-co-AAm) with a high mole fraction of AAm suggests the formation at Tc of more hydrophobic structures, realized by hydrogen bonding between the ether oxygens of OEGMA188 and the amide fragments of AAm, where water molecules are caged. Furthermore, P(OEGMA188-co-AAm) coatings immersed in pH buffer solutions exhibit a 'schizophrenic' behavior in wettability, with transitions that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and any transition blocked for pH = 9.

Structural, thermal, and surface wetting properties of epoxy resin/multiwalled carbon nanotubes composites

The structural, thermal and surface-wetting properties of epoxy resin/multiwalled carbon nanotubes (EP/MWCNTs) composites were studied by preparing nanocomposites by the physical mixing assisted by ultrasonication. The materials were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The contact angles of water droplets formed on the sample surfaces were measured to study their surface-wetting properties. FTIR showed the successful cross-linking of the EP matrix and good interaction between MWCNT and epoxy matrix in the nanocomposites. XRD attested that the incorporation of MWCNT in the EP did not influence the nature of the physical and chemical structures of the matrix polymer. Based on TGA results, the composites with chemically modified nanotubes were found to possess slightly higher thermostability than the analogous materials fabricated with the neat MWCNTs. Further, the EP/pristine MWCNT composites exhibited hydrophobic behavior while the EP/chemically modified MWCNT composites were comparatively hydrophilic which is attributed to the introduction of carboxyl groups during the chemical treatment of the nanotubes with strong acid.

Effect of Surface-Modified Nanosilicas on the Electrical Breakdown Strength in Epoxy Nanocomposites

Hydrophilic surface of fumed nanosilica was treated with a trimethylsilane coupling agent to achieve its hydrophobic surface, and the surface modification was confirmed by thermogravimetric weight loss and increasing contact angle of water droplet. The effects of the surface-modified nanosilica content on the electrical and mechanical properties of epoxy nanocomposites were studied to apply to the insulators for heavy electrical equipment. Epoxy nanocomposites were prepared by mixing epoxy base resin/curing agent/accelerator/trimethylsilane-modified nanosilica in the weight ratio of 100:80:1:0–7 g. High-voltage direct current breakdown strength increased with increasing modified nanosilica content. High-voltage alternating current breakdown strength was maximum when the nanosilica content was 1 phr (part per one hundred of epoxy resin), and thereafter, the value gradually decreased as the nanosilica content increased. Tensile strength of epoxy nanocomposite with trimethylsilane-modified nanosilica (7 phr) is 78.76 MPa, which is 20% higher than that of neat epoxy resin. The dielectric permittivity increases with increasing amount of the trimethylsilane-modified nanosilica.

The effect of atmospheric plasma jet treatment on honeydew melon seed

Non-thermal atmospheric gas plasma is popular for its flexibility and inexpensive cost. NTP is used in food preservation, medical therapy, biotechnology, and agriculture. This study examines how atmospheric plasma jets affect honeydew seed germination, water intake, and growth. In this research, high voltage (1.0–1.4 kV) was varied at a certain frequency with Argon gas. Honeydew melon seeds were a plasma treat sample. Untreated and treated seeds were separated at first. The seeds were examined for a few days after plasma treatment with varying voltage and exposure times. Wider pores reduce contact angle and promote wettability. Optical Contact Angle (OCA) measured the water droplet contact angle. Finally, plasma- treated seeds were compared to untreated seeds to determine plasma’s impact on seed quality.

Electrospinning of ultrafine non‐hydrolyzed silk sericin/PEO fibers on PLA: A bilayer scaffold fabrication

AbstractWe report the feasibility of electrospinning of protein‐polymer multilayered scaffolds with selected materials such as non‐hydrolyzed silk sericin (SS), polyethylene oxide (PEO), and polylactic acid (PLA), with tuned fiber size and properties for each layer. We present a new innovative way for the electrospinning (ES) of non‐hydrolyzed SS mixed with PEO yielding fibers with an average diameter ranging between 120 and 150 nm. Different SS:PEO ratios have been electrospun to study the effect of the concentration of SS protein on the fibers size and shape, as well and their electrospinnability. Electrospun SS:PEO fibers display weak to no mechanical resistance (non‐measurable) and their deposition onto a sturdier scaffold is necessary to allow their use in biomedical and/or pharmaceutical fields. Therefore, bilayer scaffolds have been fabricated consisting of a PLA support and SS:PEO fibers obtained from the optimized SS:PEO ratio (1.2:4). They are composed of a sturdy hydrophobic layer of PLA fibers and a layer of sticky hydrophilic SS:PEO fibers. The scaffolds have been characterized extensively by Fourier transforms infra‐red (FTIR) spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and their resistance to mechanical stress. Finally, hydrophobicity of both layers has been determined by measuring the contact angle of water droplets on the scaffolds, further proving the bilayer nature of the scaffolds.

Deciphering the role of antisolvent on the structural and optical properties of CH3NH3PbI3 film and its impacts on the performance and stability of n-i-p perovskite solar cells

This study presents an in-depth morphological, structural, and optical study of CH3NH3PbI3 (MAPbI3) film during the antisolvent dripping time, and their relevance to the stability and performance of perovskite solar cells (PSCs) is revealed. The detrimental role of the antisolvent is best demonstrated by using chlorobenzene (CB) as an antisolvent and comparing PSC devices fabricated from CB-free versus PSCs containing CB at different dripping times (5, 10, 15, 20, and 25 s) before the end of deposition of CH3NH3PbI3 film (deposition time was 30 s). Scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis absorption spectroscopy, Urbach energy analysis, steady-state photoluminescence (PL) spectra, current-voltage (I–V), external quantum efficiency (EQE), and water droplet contact angle measurement techniques were utilized to evaluate the characteristics of obtained MAPbI3 films, photovoltaic parameters, and the stability of constructed n-i-p PSCs. It was observed that changing the antisolvent dripping time changes the optical and structural properties of the MAPbI3 layer, including the direct and indirect optical band gap, refractive index, extinction coefficient, dielectric constant, optical conductivity, Urbach energy, dislocation density, lattice strain, crystallite size, and lattice parameters. The above-mentioned parameters were investigated in detail. Accordingly, by dripping the CB at 20 s before the end of the deposition process (labeled as a sample of 20 s), the created MAPbI3 layer had a smoother and pinhole-free surface, resulting in higher crystallinity than the other samples. The values of the direct band gap of the created MAPbI3 films varied from 1.51 to 1.61 eV, corresponding to samples CB-free and 20 s, respectively. For all samples, the indirect band gap was 60 meV lower than the direct band gap. Also, the sample at 20 s had a lower Urbach energy, indicating that this sample's interband defects are less than other models. In addition, the PSCs with CB-dripping at 20 s exhibited higher power conversion efficiency (13.95%) and outstanding stability of power output (<16% decay) as compared to the device without CB-dripping (>82% decay) after keeping in ambient air for about 1450 h at 40 ± 10% RH and 25 ± 5 °C. This systematic comparative study of the structural and optical properties of the perovskite layer can provide a promising platform for achieving high-quality perovskite films to overcome the shortcomings of instability and degradation.

A strategy for fabricating multi-level micro-nano superamphiphobic surfaces by laser-electrochemistry subtractive-additive hybrid manufacturing method

To achieve superamphiphobic properties on the surface of copper, a novel strategy for fabricating multi-level micro-nano superamphiphobic membranes by laser-electrochemistry subtractive-additive manufacturing method is explored. To test the properties of the metal surface prepared by this method, a variety of testing experiments are carried out. The experiment results shows that the contact angle (CA) of water and oil droplets are 161° ± 4° and 151° ± 4°, while those rolling CAs are 2° and 10°, which shows that the prepared surface had excellent superamphiphobic properties. Through the wettability test at different temperatures, the surface hydrophobicity of the prepared samples at low temperature 5 °C is worse than that at a room temperature 25 °C. According to droplet bounce test, the water drops experiences two complete bouncing processes on the surface of the prepared samples when the laser scanning interval is equal to the laser spot diameter, which indicates that the stable Cassie state is related to the multi-level micro-nano structures. In addition, the superamphiphobic surfaces fabricated in this paper have perfect functionality and stability, which provides a novel method for the potential application in the automotive, aerospace, and shipbuilding industries.

Proportional scaling molecular dynamics simulations of the wetting experiments of water droplets on ink-patterned printing paper.

In experiments, printing paper is imprinted with three different ink micropatterns (square, grid, and stripe). The wetting contact angle of water droplets on a heterogeneous surface is then investigated using a proportionate scaling molecular dynamics (MD) simulation, where the water droplets and the ink-patterned printing paper are both shrunk by a factor of 200 000 collectively. The errors from the theoretical values are always less than 1°, which is much less than the bias of experimental measurement data, according to the modeling contact angles. It has been demonstrated that this proportionate scaling approach works well to appropriately explain the interaction between micro-/nanostructures and liquids.

Cyclodextrin as a green anti-agglomerant agent in oil–water emulsion containing asphalt

Hydrate form spontaneously in submarine oil/gas pipelines. The large-scale aggregation of hydrate cause pipeline blockage and threatens safe oil/gas production. The use of anti-agglomerant agents (AAs) is a cost-effective method to prevent hydrates from clogging pipeline. However, conventional AAs such as Span 80 are not applicable in oil/gas pipelines rich in asphalt, because asphalt is easy to occupy the binding sites on the water droplet surface. Through molecular simulation, it is found that cyclodextrin (CD) shows excellent anti-agglomerant characteristics in oil–water system containing asphalt by forming stable hydrogen bonds with water molecules. CD and asphalt interact through electrostatic and dispersive interaction to form stable W/O supramolecular surfactant. Compared with Span 80, the initial contact time between water droplets and hydrate is delayed by 5 times (from 22.1 ns to 113.9 ns) after adding CD molecules. The contact angle of water droplets on the hydrate surface also increased from 48.4 ± 2.4° to 64.4 ± 2.2°. CD-asphalt interaction prevents water droplets from spreading on the hydrate surface by maintaining the stability of emulsion. The unique properties of CD provide a molecular basis for the development of more green and efficient AAs. Subsequent research will be carried out around the compounding of CD and other AAs, and it is expected to play a better anti-aggregation effect.

Natural Superhydrophobic Surfaces and Application

Superhydrophobicity refers to the phenomenon that the contact angle of various low surface tension water droplets on the solid surface is greater than 150°. Over the past few years, people have paid more attentions in the superhydrophobic surfaces’ design and application. The superhydrophobic surfaces are meaningful for basic research and various practical applications, such as self-cleaning, drag reduction, lubrication, and more. This paper summarizes the recent advances and developments in superhydrophobic surfaces systematically. Furthermore, in this work, the authors focus on the basic concepts of superhydrophobic surfaces and commonly used synthetic methods. Electrodeposition and electrospinning methods are mainly introduced. Finally, we also discuss the limitations and challenges encountered in the study of superhydrophobicity, mainly with regard to the fact that drag should be reduced to improve energy harvesting efficiency.

An experimental evaluation of polyamide membrane-silica nanoparticles for the concentration of pomegranate juice

Membrane processes are used in the food and nutrient industry in terms of their proper performance and selective separation. Using the membranes in fruit juice concentrating operations improves its quality via shelf-life increases. The advantage of reverse osmosis (RO) and membrane technology over other methods is its non-chemical reaction to fruit juice which increases the concentration of fruit juice. The membranes were made of three layers of non-woven polyester layer for the mechanical strength of the membrane, polyester sulfone polymer with polyamide consisting of polymerization of M-Phenylenediamine (MPD) and benzene tricarbonyl chloride. Trimethyl chloride (TMC) was used to modify the properties of the membrane in the second layer using silica nanoparticles. The feed was sugar-free pomegranate juice added by SUNICH Company with an initial Brix value of 14.9% and an input feed of 6.6% to the RO system. The DESIGN-EXPERT method for the design of experiments (DOE) by considering three parameters of weight percentage of polyester sulfone polymer (12, 16, and 20%), silica nanoparticles (0, 0.1, and 0.2 wt%), and operating pressure were used (20, 25, and 30 times). Under optimal conditions, 46.15% of the concentrated pomegranate juice were obtained by experiment and the amount of brix increased from 33.24% to 47.21%. Scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and contact angle tests for membranes were used. In the analysis of contact angle by examining the degree of hydrophilicity and contact angle of water droplets, it was found that the presence of silica nanoparticles and polyamide layer caused more hydrophilicity of membranes. It can be concluded that the pressure parameter, together with the presence of nanoparticles and polymer percentages, contribute to the most successful procedure of concentrating pomegranate juice.

The detected effects of driptips and leaf wettability on the kinetic energy of throughfall in rubber‐based agroforestry in Xishuangbanna

AbstractDriptips play important roles in controlling soil erosion and in the water cycle. The driptips size distribution and the morphology of water droplets on the leaves among rubber (Hevea brasiliensis) and intercropping species (Camellia sinensis, Citrus reticulata, Flemingia macrophylla and Theobroma cacao) were measured. Driptip‐producing experiments were conducted indoors on stabilized leaves of five species with artificially mist spray. In all five foliage species, the diameter of the driptips from rubber leaves was the lowest. Furthermore, the relationship between driptips size and the mean leaf width at 3 mm from the rubber leaf tip was significantly positively correlated. Leaf wettability as measured by water droplets height linearly increase with the total volume of water which dropped on the leaves of all five species. The contact angle of the water droplets and the total volume of the droplet were significantly negatively correlated. Based on physical theory, the kinetic energy of the driptips was calculated by estimating the diameters of the driptip from all five species. The results indicated that it was important to consider the kinetic energy of driptips in selection of intercropping species when constructing rubber‐based agroforestry plantations. Understanding the relationship between driptips size and the development of leaf tips (leaf width at 3 mm from the leaf tip) will require more experiments with different leaf inclinations, and the results also confirmed that using the contact angle of water droplets to assess leaf wettability. This study can help to predict canopy water processes, such as canopy water storage and drainage.

Micropatterned cellulosic films to modulate paper wettability

A new class of micropatterned cellulose nanocrystal (CNC) free-standing films which modulate the surface hydrophobicity by controlling the dimensions of the channels are fabricated. Micropattern silicon molds are fabricated with photolithography and etching techniques. CNC and carboxymethyl cellulose (CMC) suspensions are vacuum dried on the molds, with a layer of nanocellulose fibers spray coated on top to create the free-standing film. Sharp 5 µm × 6 µm channels are obtained with a 2.2 wt% suspension with a 10:1 ratio of CNC:CMC. This is the smallest patterned channel size that has been achieved and is more than an order of magnitude lower than those achievable with techniques such as laser cutting. The water droplet contact angle can be tuned to resist or promote wetting, varying from 106° for 5 µm × 6 µm channels to 41° for 500 µm × 18 µm channels, without changing the surface chemistry. Dynamic advancing contact angle measurements show a slip and stick pattern, increasing linearly as the droplet volume increased and then sharply dropping, as the pinning on the channel edge is overcome by the increasing droplet volume. We demonstrate a new class of cellulose materials with finely tunable morphology to control liquid interaction and a scalable process to fabricate those at large scale.

ZnO nanostructure fabricated by electrochemical deposition

Electrochemical deposition method was employed to fabricate ZnO nanorods on zinc foil substrate in this paper. The structural observations of ZnO nanorods with different aspect ratios were carried out by field- emission scanning electron microscopy. The microstructures of ZnO nanorods were also characterized by X-ray diffraction and the changes in surface hydroxyls with electrochemical deposition time were analyzed by X-ray photoelectron spectroscopy. The study results show the aspect ratios of ZnO nanorods and the density of their surface hydroxyls are responsible for their superhydrophobicity. The fluorinated polymer coated ZnO nanorods showed an excellent superhydrophobic behavior with 167◦ contact angle of water droplet, which is larger than that of fluorinated polymer flat surface. The more the surface hydroxyls are, the more hydrophilic the surfaces are. Meanwhile, the larger the aspect ratio of ZnO nanorod arrays is, the larger its drophobicity is. The results of this study might have a simple and feasibility pathway to the fabrication of superhydrophobic cleaning materials used in engineering fields.