Hydrophilic Hydrophobic Surfaces Research Articles

A strategy for accelerating condensation by radiative cooling with hydrophilic-hydrophobic surface

Using radiative cooling technology for dew collection is a promising solution to the freshwater resource crisis. Environmental factors such as solar radiation intensity, ambient temperature, and humidity can influence both the radiative cooling process and the condensation process. In this study, the influence mechanisms of environmental factors on the radiation condensation effect are studied through simulation. Then, TiO2 nanoparticles are sprayed on the surface of the PDMS film to form a hydrophobic-hydrophilic surface. The experimental research is conducted at an ambient temperature of 25 ℃ and a relative humidity of 70%−90% to analyze the change in condensation water. The experimental results indicate that after TiO2 nanoparticles are added to PDMS film, the emissivity in the atmospheric transparency window and the surface hydrophilicity of the film are increased, which effectively improves the condensation effect. The condensation rate has reached 916.6 g∙m−2∙h−1. At 70% relative humidity, the condensation water of PDMS film with TiO2 nanoparticles increased by 58%, and the improvement effect is most significant at lower relative humidity. It has great application prospects in arid and water-scarce areas.

Self-Assembly Nanochaperone with Tunable Hydrophilic-Hydrophobic Surface for Controlled Protein Refolding.

Nanochaperones (nChaps) have significant potential to inhibit protein aggregation and assist in protein refolding. The interaction between nChaps and proteins plays an important role in nChaps performing chaperone-like functions, but the interaction mechanism remains elusive. In this work, a series of nChaps with tunable hydrophilic-hydrophobic surfaces are prepared, and the process of nChaps-assisted denatured protein refolding is systematically explored. It is found that an appropriate hydrophilic-hydrophobic balance on the nChap surface is critical for enhancing protein renaturation. This is because only the optimal interaction between nChap and protein can simultaneously guarantee the suitable capture and sufficient release of client proteins. The findings in this work will provide an effective reference for the design of nChaps and contribute to the development of the potential of nChaps in the future.

Design of hydroxyl-functionalized nanoporous organic polymer with tunable hydrophilic-hydrophobic surface for solid phase extraction of neonicotinoid insecticides.

As being widely used insecticides, neonicotinoid residues are toxic and harmful to human health and aquatic ecosystems. Thus, the sensitive monitoring of neonicotinoids in water and food samples is highly desirable to reduce their risks to humans. Herein, four novel hydroxyl-functionalized nanoporous organic frameworks (OH-NOP1, OH-NOP2, OH-NOP3 and OH-NOP4) with tunable hydrophilic-hydrophobic surface have been designed and fabricated for the first time by employing luteolin as monomer and 4,4'-bis(chloromethyl)-1,1'-biphenyl as crosslinker at the molar ratio of 3:1, 1:1, 1:3 and 1:6, respectively. When the molar ratio of luteolin to crosslinker was 1:3, OH-NOP3 was obtained and it presented the highest affinity with excellent adsorption performance towards the studied neonicotinoids. The adsorption mechanism was proposed to be the strong hydrogen bond, polar interaction, Lewis acid-base interaction and pore adsorption between OH-NOP3 and neonicotinoids. Then, utilizing OH-NOP3 as sorbent for solid phase extraction cartridges, an effective method for extraction and preconcentration of neonicotinoids followed by high performance liquid chromatography analysis has been developed for quantitative detection of neonicotinoids from water and edible fungi. The method provided good linearity over the range of 0.06-100.0ngmL-1 for lake water, 1.5-100.0ngg-1 for pleurotus eryngii and sea-shroom. Low detection limit (at the signal to noise ratio of 3) was achieved in the range of 0.02-0.08ngmL-1 for water, 0.50-0.60ngg-1 for pleurotus eryngii and 0.50-0.80ngg-1 for sea-shroom, while the limit of quantification was 0.06-0.25ngmL-1, 1.50-1.80ngg-1 and 1.50-2.50ngg-1, respectively. Satisfactory method recoveries (85.1-112%) were obtained, with relative standard deviations below 8.2%. This study offered a new strategy for designing efficient sorbents to adsorb or remove organic pollutants based on the structure and properties of substrates.

RGO-Modified paper supported Globe Thistles-Like NiCo2S4 flexible electrodes enhancing H2O2 sensing

The Globe Thistles-Like (GTL) NiCo2S4 nanostructures were supported on reduced graphene oxide modified filter paper (FP). The prepared GTL NiCo2S4/rGO/FP is investigated as a disposable and flexible electrode for the electrochemical detection of H2O2 in alkaline media. Owing to the rich redox active sites, the synergistic effect between Co3+ and Ni2+, and the rapid electron transportation of substituting sulfur (S) for oxygen (O) in NiCo2O4, the GTL NiCo2S4/rGO/FP exhibits considerable enzyme-free H2O2 sensing performance with wide linear H2O2 ranging from 38.8 to 37306.8 μM, high sensitivity of 2.4326 mA mM−1 cm−2, and low detection limit of 0.08 μM. The GTL NiCo2S4/rGO/FP electrode has stable sensing performance and is highly selective toward analyte for physiological interfering species. The excellent electrochemical performance of GTL NiCo2S4/rGO/FP composite is attributed to the GTL structure of NiCo2S4. By studying the hydrothermal reaction time, electrochemical active surface area, and hydrophilic-hydrophobic surfaces of GTL NiCo2S4/rGO/FP composite, the relationship between the microstructure and sensing performance of the composite was elucidated. Surely this study opens up new possibilities for the application of low-cost, biodegradable flexible electrode materials in wearable sensors in the near future.

Experimental study on the boiling/condensation heat transfer performance of a finned tube with a hydrophilic/hydrophobic surface

Currently, a increasing number of exchange tubes are requied for both boiling heat transfer and condensation heat transfer. Thus, it is necessary to enhance, both the boiling heat transfer performance and condensation heat transfer performance of the tube is necessary. However, few studies have been conducted in this field. A stepped lattice finned tube is suggested to enhance both boiling heat transfer and condensation heat transfer. There is room for the heat transfer enhancment of efficiency considering that wettability can also influence the heat transfer. Hence, in this study, the heat transfer performances of tubes with hybrid Hydrophilic-hydrophobic surfaces and functional fins are experimentally investigated. The condensation heat transfer coeffient and boiling heat transfer coefficient of the tube with an inner hydrophobic cavity wall and outer hydrophilic fin are nearly 3 times and 1.8 times those of the smooth tube, respectively. In boiling heat transfer, the inner hydrophobic surface can lower the bubble nucleation barrier and the outer hydrophilic surface can prevent the heat transfer surface from being covered by a vapour film. In condensation heat transfer, the outer hydrophilic surface can lower the droplet nucleation barrier and the inner hydrophobic surface contributes to dropwise condensation.

The Self-Actuating Droplet That Can Turn: A Molecular Dynamics Simulation

Water collection remains a fundamental challenge to stable and efficient operation of the solar desalination system. Functional surfaces that can realize self-actuation of droplets have shown great potential in improving droplet dynamics without external energy. Therefore, a surface that can make a droplet move spontaneously along a curve was designed for smart droplet manipulation, and the mechanism of the droplet motion was revealed through molecular dynamics simulations. Influences of the wettability difference between the curved track and the background, the width of curved track, and the temperature were evaluated via simulations. The results show that the surface on which the curved track and the background are both hydrophobic enables a faster actuating velocity of the droplet than the hydrophilic-hydrophobic surface and the hydrophilic-hydrophilic surface. The width of the curved track also affects the actuating velocity of the droplet and increasing the TRACK width can increase the actuating velocity of the droplet. However, actuation of the droplet slows down if the width of the curved track is too large. Overall, the mechanism driving the motion of the droplet along the curve was investigated, which opens new opportunities for the application and manufacturing of water collection in solar desalination.

Hydrophobic, partially hydrophobic, and hydrophilic ZnO@SiO2 nanoparticles as fluorescent partitioning tracers for oil sensing applications

(a) Schematic representation of various functionalities on the surface of ZnO@SiO 2 nanoparticles. The partially hydrophobic (PH-NPs, S2), hydrophobic (HP-NPs, S3), and hydrophilic (H-NPs, S4) functionalities were developed on the surface of ZnO@SiO 2 NPs using various silanes having methyl, octyl, and amino groups, respectively. (b,c) The fluorescent NPs (S4) stayed entirely in the water phase due to the presence of –NH 2 group (hydrophilic nature), while the fluorescent NPs (S3) moved completely toward the oil phase due to the presence of octyl-group (hydrophobic nature) on their surface. However, the luminescent NPs (S2) were shifted toward the interface between two phases due to partially hydrophobic character ( CH 3 ) on their surface. • ZnO@SiO 2 NPs were synthesized via a modified sol–gel Stober protocol. • Surface functionalities were attained by co-condensation of various silanes. • Surface chemistry and partitioning behavior of ZnO@SiO 2 NPs were investigated. • ZnO@SiO 2 NPs have excellent fluorescence stability in aqueous environments. • Stability of ZnO@SiO 2 NPs was examined under harsh reservoir conditions. Fluorescent nano-tracers are being utilized for oil sensing applications in the reservoir. In this work, we developed various hydrophobic, partially hydrophobic, and hydrophilic zinc oxide encapsulated silica nanoparticles (ZnO@SiO 2 NPs) as smart nano-agents for oil sensing applications. The surface of ZnO@SiO 2 NPs was functionalized by co-condensation using various silanes in combination with tetraethyl orthosilicate (TEOS). Cryogenic TEM images display the average size of ZnO QDs (S0) and ZnO@SiO 2 nanoparticles (S1) around ∼5.3 nm and ∼50 nm, respectively. The surface chemistry and partitioning behavior of photoluminescent ZnO@SiO 2 NPs were investigated before and after mixing with the model oil under normal and UV light. The chemical and photoluminescence (PL) stability of ZnO@SiO 2 NPs was monitored in harsh reservoir conditions, such as variable temperature (30–100 °C) and high salinity (0–80 g L −1 ) environment. The results demonstrated that the surface modification and functionalization of these nano-agents with different functional groups (methyl, octyl) improved the nano-agents’ selectivity and stability after changing their hydrophilic-hydrophobic surface characters. This work is opening new research in the field of oil sensing, which promotes their potential utilization as cost-effective and efficient fluorescent tracer materials for the oil exploration industries.

Magnetic quantum dots-stabilized foam fluid for enhanced oil recovery

Nanoparticle-stabilized foam fluid provided excellent efficiency in tertiary oil recovery, and a more appealing technique is to exploit reusable low-dimensional nanomaterials, which can achieve better oil-displacement efficiency during the period of global decarbonization. Herein, the magnetic quantum dots (MQDs) were synthesized and then modified by a silane-coupling ionic liquid (SIL) to produce unique quantum dots MQDs@SIL. A series of characterizations and foaming measurements reveal that MQDs@SIL with an average surface grafting density of 1.01 functional chains nm−2 at an ultra-low concentration (0.005 wt%) demonstrated distinct foam stability and salt resistance capability, as well as a unique defoaming performance in a constant magnetic field for regulated foam performance at high temperature. The stretched-straight functional chains and adequate hydrophilic-hydrophobic surface of MQDs@SIL substantially favor the nonreversible adsorption of MQDs@SIL on the gas–liquid interface, leading to an increased surface elasticity, and thus an enhanced foam stability. MQDs@SIL-stabilized foam liquid demonstrated exceptional plugging performance and achieved an enhanced oil recovery of 18.2 % in the stage of foam fluid flooding, exceeding most nanoparticle-stabilized foam fluids ever reported. Furthermore, MQDs@SIL with the unique magnetic property provided unique recycling and reusing benefits, emphasizing their potential applications for enhanced oil recovery.

Regioselective deposition of hydrophilic sites to enhance the fog collection performance of hydrophilic-hydrophobic surface

Due to the increasingly serious shortage of water resources, fog collection has attracted extensive attention of researchers. Through a simple electrodeposition method and subsequent immersion modification, a top-added hydrophilic sites method was proposed to fabricate hydrophobic-hydrophilic surface on a tape-covered stainless steel substrate. The intrinsic hydrophobicity of CeO2 coating helps build surface energy gradients to strengthen the drop shedding process and the hydrophility of regioselectively-deposited dopamine sites helps strengthen the droplet capture process. Therefore, the fog collection rate of the superhydrophobic-hydrophilic surface was 5 times higher than that of pristine substrate. This method provides a new idea for enhancing the fog collection performance of hydrophilic-hydrophobic surfaces.

Experimental investigation on the heat transfer enhancement of steam condensation on tube with hydrophilic-hydrophobic hybrid surface

The heat transfer enhancement of steam condensation on tube with hydrophilic-hydrophobic hybrid surface have been investigated comprehensively through experiment. It has been found that the steam condensation heat transfer performance on the tube with hydrophilic-hydrophobic hybrid surface has been enhanced significantly compared to that with hydrophilic surface. The results show that the steam pressure, cooling water velocity (flow rate) and non-condensable gas have influences on the steam condensation heat transfer performance on both tubes. The steam condensation heat transfer enhancement on the tube with hydrophilic-hydrophobic surfaces is due to the droplet drainage from hydrophobic stripes to hydrophilic stripes accelerating the discharge and formation of condensate from the tube. This work can be a guide for the design of enhanced condensing heat exchanger.

Dispersion of unfractionated CO2-derived protein-rich microalgae (Chlorella sp. HS2) for ecofriendly polymer composite fabrication

This study investigates unfractionated protein-rich microalgae (Chlorella sp. HS2) (HS2) as a new CO2-derived biomass filler resource with which to develop an ecofriendly microalgae-based polymer composite. Unfractionated HS2 is mixed with poly(ethylene-vinyl acetate) (EVA) over wide range of concentrations ranging from 10 to 70 wt%. The dispersion of HS2 is analyzed based on morphological, rheological and mechanical measurements. Protein-rich HS2 has hydrophilic-hydrophobic surface due to the existence of chemical functional groups (CO, N-H) caused by high protein content (51% protein), predicting compatibility with EVA with polar functional (CO). Due to this compatibility, with 10–30 wt% of HS2, the composite shows a homogeneous micrometer-scale dispersion of HS2 in the EVA matrix (avg. diameter (Davg) ~ 7 µm). The composite maintains the dispersion of the HS2 without significant coalescence or network formation up to 50 wt% of HS2 (Davg ~ 10 µm). Correspondingly, the storage modulus (G′ at 0.1 rad/s) of the composite increases linearly until the HS2 content reaches 40 wt%, after which it increases exponentially with an increase in the HS2 content. An EVA composite with 10–20 wt% HS2 shows increased ductility (from 1700% to 2000% elongation at break with 10 wt% HS2) without a decrease in the tensile strength due to the homogeneous dispersion. Even with higher concentration of HS2, the composite maintains its ductile behavior and retains its synergistic effect with EVA (~ 500% elongation at break with 70 wt% HS2). The compatibility of HS2 with EVA and their hydrophilic surface delay agglomeration or percolation formation of HS2 cells in a polymer. This study suggests that protein-rich HS2 is a promising biomass filler that disperses in a polymer to the micrometer scale without additional chemical treatment.

Differential surface partitioning for an ultrasensitive solid-state SERS sensor and its application to food colorant analysis

Solid-state SERS sensors are desirable point-of-care tools due to their portability. However, the level of SERS sensitivity achieved in liquid phase is rarely duplicated in the solid phase. We report herein the fabrication of a SERS sensor using alumina beads as the solid support and demonstrate its high SERS sensitivity with the model analyte 4-aminophenyl disulfide (4-APDS). The key to sensitivity is a hydrophilic-hydrophobic surface gradient constructed by sequentially coating with the surfactant cetyltrimethylammonium bromide and fluorous 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The surface gradient, together with chloride etching, allows the detection of 4-APDS at the low concentration of 10−15 M. The practicality of the sensor beads is evidenced by successfully tracking the SERS fingerprints of five food colorant standards in the SERS spectra of a popular candy product. These SERS sensor beads are easy to prepare, convenient to use, and highly responsive as a SERS platform for the analysis of colorants.

Water-stable Zn-based metal-organic framework with hydrophilic-hydrophobic surface for selective adsorption and sensitive detection of oxo-anions and pesticides in aqueous medium

Given the importance of surface-functionalized materials with improved adsorption and detection properties for targeted applications, we report herein the design and development of a water-stable luminescent Zn-based metal-organic framework (Zn-MOF) with the hydrophobic-hydrophilic surface property. The developed luminescent Zn(II)-MOF {[Zn(PA2-)(dmbpy)](DMF)}n was synthesized via a solvothermal method using pamoic acid (PA) and 5,5′-dimethyl-2,2′-bipyridine (dmbpy) with free functional groups (hydroxyl and methyl groups). Careful single-crystal structure analysis revealed a 3-dimensional hydrogen-bonded network with a one-dimensional channel and functionalized surface. The surface functionalization was achieved through rational choice of ligands bearing methyl and hydroxyl groups as suitable hydrophobic and hydrophilic functionalities respectively, leading to a stable MOF in the aqueous medium. The MOF was used as an adsorbent for selective adsorption of monovalent permanganate anion (MnO4-) over other polyvalent oxo-anions as well as an optical platform for the detection of oxo-anions (permanganate (MnO4-), dichromate (Cr2O72-) and chromate (CrO42-)) and pesticide (2,6-dichloro-4-nitroaniline (2,6-DCNA)) in the aqueous medium. Overall, a combination of luminescent nature and hydrophilic-hydrophobic surface property makes the developed Zn-MOF an interesting platform for environmental application.

Large-Scale Fabrication of Wettability-Controllable Coatings for Optimizing Condensate Transfer Ability.

Systematic regulation of hydrophilic regions plays a key role in optimizing the heterogeneous hydrophilic-hydrophobic surface for promoting condensate transfer ability (CTA) under subcooling or high-humidity conditions. In this work, we develop an operable method to fabricate wettability-controllable coatings by regulating the mass ratio of superamphiphobic and superamphiphilic powder (MRP). By investigating the synergic relationship between CTA and MRP, we display an interesting competition between condensation and detachment of condensates. The initial dewing rate associated with reflecting phase change heat transfer capacity could be continuously strengthened by promoting MRP, while the detachment capacity with respect to improving the long-term condensing rate can be limited by the excessive superamphiphilic microregions. Based on this, we have optimized the threshold of MRP for promoting the condensation heat transfer ability and the water harvesting efficiency with the values of 10:0-8:2 and 10:0-4:6, respectively. This work provides important guidance in designing and optimizing heterogeneous hydrophilic-hydrophobic surfaces for multiple industrial applications including heat management, water harvesting, and desalination.

Formation of double emulsion micro-droplets in a microfluidic device using a partially hydrophilic-hydrophobic surface.

The objective of this paper is to propose a surface modification method for preparing PDMS microfluidic devices with partially hydrophilic–hydrophobic surfaces for generating double emulsion droplets. The device is designed to be easy to use without any complicated preparation process and also to achieve high droplet encapsulation efficiency compared to conventional devices. The key component of this preparation process is the permanent chemical coating for which the Pluronic surfactant is added into the bulk PDMS. The addition of Pluronic surfactant can modify the surface property of PDMS from a fully hydrophobic surface to a partially hydrophilic–hydrophobic surface whose property can be either hydrophilic or hydrophobic depending on the air- or water-treatment condition. In order to control the surface wettability, this microfluidic device with the partially hydrophilic–hydrophobic surface undergoes water treatment by injecting deionized water into the specific microchannels where their surface property changes to hydrophilic. This microfluidic device is tested by generating monodisperse water-in-oil-in-water (w/o/w) double emulsion micro-droplets for which the maximum droplet encapsulation efficiency of 92.4% is achieved with the average outer and inner diameters of 75.0 and 57.7 μm, respectively.

Wetting transition of a nanodrop on switchable hydrophilic-hydrophobic surfaces

The dynamic modulation of contact angle on switchable hydrophilic-hydrophobic surfaces is one of the important factors in designing miniaturized optical devices. A spreading and retention of a nano water droplet placed on an insulator surface covering two planar electrode layers and perpendicularly in contact with a conductive tip is studied using atomistic molecular simulation. The change in the droplet shape is initiated by modifying interaction energy between the insulator atoms and the water molecules. The contact angle analysis shows a unique dependence on the nature of the underlying substrate. Time correlation function analysis based on the calculation of variation of the height of the drop’s center of mass with time estimates the rate of relaxations for wetting-dewetting behavior subject to the condition of surface hydrophilic and hydrophobic nature. For the hydrophilic case, the relaxation rate of the drop is found to be twice slower than the hydrophilic one. The difference in the rate of relaxations is analyzed by considering the effects of the frictional force on the contact line motion of the drop. Friction coefficients are calculated on the basis of continuum hydrodynamic (HD) and molecular kinetic theory (MKT) theories. The dependence of the friction coefficients on the surface properties depicts the strong dominance of the liquid-substrate friction on the drop’s perimeter motion based on molecular kinetic theory.

Oxygen inhibition induced hydrophilic-hydrophobic surface for self-assembled droplet microarrays

Hydrophilic-hydrophobic surface is vital for the study of the wettability behavior of microdroplets. In this paper, a method for preparation of hydrophilic-hydrophobic patterned surface is proposed based on the oxygen inhibition effect. Oxygen inhibition is very common in photo-cured process, and usually should be avoided for its adverse effect on curing quality. However, it also results in numerous nanostructures naturally formed on the cured layer surface, and the density and sizes of the nanostructures can be modulated conveniently by adjusting the exposure time. Based on this phenomenon, the cured layer surface having hydrophobicity can be processed. The contact angle system is used to measure the contact angle of the cured layer surface, and the morphology of the cured layer surface is measured in detail by atomic force microscopy and scanning electron microscope.The hydrophobic layer is only 1.5 $$\upmu $$ m thick. By combining maskless lithography, patterned surface with nanostructures can be easily formed in just one step without any special treatment. This helps us to generate highly controllable hydrophilic-hydrophobic surface effectively in a very simple and low-cost way. With this method self-assembled droplet microarrays are successfully achieved. The results offer a new idea for the control of surface wettability and may find wide potential applications in microfluidics.

Hybrid Hydrophilic-Hydrophobic CuO@TiO2-Coated Copper Mesh for Efficient Water Harvesting.

Fresh water scarcity has been a worldwide problem to be solved urgently. Inspired by the outstanding hydrophobic-hydrophilic patterns on the back of Namib desert beetles, hierarchical CuO@TiO2-coated surface with alternating hydrophilic-hydrophobic chemistry patterns were fabricated utilizing the photocatalysis of titanium dioxide through ultraviolet irradiation. The results indicated that the as-prepared hybrid dual-coated copper mesh enhanced the fog-collection efficiency compared with the uniformly superhydrophobic or superhydrophilic surface. This enhancement can be regulated by controlling the deposition cycle times of TiO2 multilayers on CuO and UV irradiation time. The best water harvesting behavior was determined at the deposition cycle times of 10 times and UV irradiation time of 4 h. This work findings offer new insights into the fabrication of hybrid hydrophilic-hydrophobic surfaces for highly efficient water harvesting.

Assessment of the Hydrophilic-Hydrophobic Balance of Alumina Oxidized at Different Temperatures via H<sub>2</sub>O and C<sub>4</sub>H<sub>10</sub> Vapor Adsorption

The hydrophilic-hydrophobic surface area of alumina powder (Al2O3) oxidized at different temperatures was determined on the base of adsorption of water and butane vapor at 25°C. In the order to study the influence of thermal oxidation upon hydrophilic/hydrophobic character of the surface, samples of Al2O3 were characterized using granulometry, SEM and BET surface area measurement. SEM results showed that the thermal treatment does not affect the morphology of the Alunima. However, the increase of treatment temperature from 250 to 900°C results in changing of the hydrophilic-hydrophobic balance of Al2O3 surface.

Flexible Photodetector Arrays Based on Patterned CH3 NH3 PbI3- x Clx Perovskite Film for Real-Time Photosensing and Imaging.

The quest for novel deformable image sensors with outstanding optoelectronic properties and large-scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as-prepared perovskite arrays for photosensing and imaging. Large-scale growth controllable CH3 NH3 PbI3- x Clx arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two-step sequential deposition method with the developed Al2 O3 -assisted hydrophilic-hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 1011 Jones), large on/off current ratio (up to 1.2 × 103 ), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real-time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.