Surface Energy Difference Research Articles

Grafted Nanoparticle Surface Wetting during Phase Separation in Polymer Nanocomposite Films.

Wetting of polymer-grafted nanoparticles (NPs) in a polymer nanocomposite (PNC) film is driven by a difference in surface energy between components as well as bulk thermodynamics, namely, the value of the interaction parameter, χ. The interplay between these contributions is investigated in a PNC containing 25 wt % polymethyl methacrylate (PMMA)-grafted silica NPs (PMMA-NPs) in poly(styrene-ran-acrylonitrile) (SAN) upon annealing above the lower critical solution temperature (LCST, 160 °C). Atomic force microscopy (AFM) studies show that the areal density of particles increases rapidly and then approaches 80% of that expected for random close-packed hard spheres. A slightly greater areal density is observed at 190 °C compared to 170 °C. The PMMA-NPs are also shown to prevent dewetting of PNC films under conditions where the analogous polymer blend is unstable. Transmission electron microscopy (TEM) imaging shows that PMMA-NPs symmetrically wet both interfaces and form columns that span the free surface and substrate interface. Using grazing-incidence Rutherford backscattering spectrometry (GI-RBS), the PMMA-NP surface excess (Z*) initially increases rapidly with time and then approaches a constant value at longer times. Consistent with the areal density, Z* is slightly greater at deeper quench depths, which is attributed to the more unfavorable interactions between the PMMA brush and SAN segments. The Z* values at early times are used to determine the PMMA-NP diffusion coefficients, which are significantly larger than theoretical predictions. These studies provide insights into the interplay between wetting and phase separation in PNCs and can be utilized in nanotechnology applications where surface-dependent properties, such as wettability, durability, and friction, are important.

Composite of aromatic polythiourea/BaTiO3 nanowires with high energy density and high discharge efficiency for energy storage applications

Ceramic/polymer nanocomposites have shown great potential in high energy storage density capacitors for pulsed power applications. However, due to the difference in surface energy between inorganic fillers and polymers, the discharge energy density and efficiency of nanocomposites are limited. In this article, the BaTiO3 (BT) nanowires (NWs) modified with dopamine (Dopa) was introduced into aromatic polythiourea (ArPTU) polymer matrix as composite for high-performance dielectrics. This is a new path about the introduction of a high dielectric constant ceramic into high dipole moment linear polymers (HDMLP), which produces the polymer composite with high energy storage density and high discharge efficiency. The composite ArPTU/BT NWs shows an energy density of 7.5 J cm−3 and high efficiency more than 90% is obtained under an electric field of 250 MV m−1. It also has been found that the modification of BT NWs with the Dopa reduces the dielectric loss of composite effectively due to the good synergistic effective between ArPTU and BT NWs, and high stability of composite for energy storage is also achieved. This work provides an effective solution for achieving high energy storage density and high discharge efficiency in polymer dielectrics for practical capacitor applications.

Nb Texture Evolution and Interdiffusion in Nb/Si-Layered Systems.

In this paper, we present a detailed study on the microstructure evolution and interdiffusion in Nb/Si-layered systems. Interlayer formation during the early stages of growth in sputter-deposited Nb-on-Si and Si-on-Nb bilayer systems is studied in vacuo using a high-sensitivity low-energy ion-scattering technique. An asymmetric intermixing behavior is observed, where the Si-on-Nb interface is ∼2× thinner than the Nb-on-Si interface, and it is explained by the surface-energy difference between Nb and Si. During Nb-on-Si growth, the crystallization of the Nb layer occurs around 2.1 nm as-deposited Nb thickness with a strong Nb(110)-preferred orientation, which is maintained up to 3.3 nm as-deposited Nb thickness. A further increase in the Nb layer thickness above 3.3 nm results in a polycrystalline microstructure with a reduced degree of texture. High-resolution cross-sectional transmission electron microscopy imaging is performed on Nb/Si multilayers to study the effect of the Nb layer texture on interdiffusion during low-temperature annealing. Nb/Si multilayers with amorphous 2 nm Nb layers and strongly textured 3 nm thick Nb layers, with limited grain-boundary pathways for diffusion, show no observable interdiffusion during annealing at 200 °C for 8 h, whereas in a Nb/Si multilayer with polycrystalline 4 nm thick Nb layers, a ∼1 nm amorphous Nb/Si interlayer is formed at the Si-on-Nb interface during annealing.

Structure, composition and enhanced magnetic properties of novel ternary multicore-shell Ni–Co–Cr nanoclusters prepared by one-step inert gas condensation method

We have synthesized ternary Ni–Co–Cr nanoclusters using one step method by simultaneous sputtering of metallic targets through inert gas condensation (IGC) deposition process. The difference in surface energy between the component atoms creates a preferential surface phase leading to the formation of multi core/shell structures. Surface structure and composition analysis reveal metallic and oxide phases characterized by extraordinary 1.43 μm periodicity strong magnetic stripe domains with weak magnetic force microscopy signal attenuation up to a lift height value of 2.5 μm. In addition, the ternary nanoclusters exhibit strong ferromagnetic behavior below the blocking temperature of 139 K with coercivity of 700 Oe at 4 K. The enhanced magnetic properties are attributed to Volmer-Weber growth mechanism and pave a facile way for preparing ternary core/shell magnetic structures needed for applications which require strong magnetic anisotropy along their growth direction.

Amplifying Surface Energy Difference toward Anisotropic Growth of All‐Inorganic Perovskite Single‐Crystal Wires for Highly Sensitive Photodetector

AbstractIt is a great challenge to directly grow super long all‐inorganic perovskite monocrystalline wires due to the weak surface energy difference among the low index facets. Here, a one‐pot solution process to grow the aspect ratio over 105 of monocrystalline CsPbBr3 perovskite wires (PWs) and yield up to 70% is reported. A chemical potential dependent surface energy difference amplification strategy is proposed to regulate the surface energy of growing and grown surfaces accordingly to the anisotropic growth of CsPbBr3. The anisotropic growth of wires is derived from the regulation of anti‐solvent diffusion kinetic and the mass transfer kinetic control of the metal halide salts. This experiment demonstrates a 50 times amplification of surface energy difference. As‐produced PWs present a high photodetection responsivity up to 4923 A W−1, external quantum efficiency exceeding 13 784%, and detectivity over 3.6 × 1013 Jones. This work not only reveals the mechanism of surface energy dominated anisotropic growth for CsPbBr3 PWs, but also elucidates the important role of kinetics regulation during the growth process, which may open a new window for the low‐dimensional crystal growth of ionic compounds.

Balance of surface energy difference between wetting and dewetting regions for patterning solution-processed organic light-emitting diode

Solution-processed organic light-emitting diodes (S-OLEDs) are potential candidates for next-generation wearable electronics due to the simple processing capability, high scalability, and mechanical flexibility. As a demand for the high-resolution OLEDs is given rise to realize the natural images in the eyewear displays, developing efficient methods for producing solution-processed organic patterns has been vital to achieve the practical S-OLEDs. Despite considerable effort to develop the fine organic patterns, an incomplete understanding of the effect of the surface wetting nature on the precise pattern formation inevitably restricts the resolution of the S-OLEDs. Herein, we present the physical picture of forming solution-processed high-resolution organic patterns using wetting phenomena. For macroscale patterns larger than 50 μm, the surface energy difference between the wetting and dewetting regions are critical for governing the pattern fidelity. In contrast, the microscale patterns with a feature size lower than 10 μm are produced by the subtle interplay between the surface energy difference and wettability following the Cassie state of the substrate. High-resolution line patterns with a width of 5 μm of the S-OLED are fabricated by balancing the surface energy difference and wettability of the substrate. The patterned S-OLED exhibits a high-pattern fidelity and stable electro-optical performance without any detrimental effects.

Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles.

Nanocrystalline anatase TiO2 is a robust model anode for Li insertion in batteries. The influence of nanocrystal size on the equilibrium potential and kinetics of Li insertion is investigated with in operando spectroelectrochemistry of thin film electrodes. Distinct visible and infrared responses correlate with Li insertion and electron accumulation, respectively, and these optical signals are used to deconvolute bulk Li insertion from other electrochemical responses, such as double-layer capacitance, pseudocapacitance, and electrolyte leakage. Electrochemical titration and phase-field simulations reveal that a difference in surface energies between anatase and lithiated phases of TiO2 systematically tunes the Li-insertion potentials with the particle size. However, the particle size does not affect the kinetics of Li insertion in ensemble electrodes. Rather, the Li-insertion rates depend on the applied overpotential, electrolyte concentration, and initial state of charge. We conclude that Li diffusivity and phase propagation are not rate limiting during Li insertion in TiO2 nanocrystals. Both of these processes occur rapidly once the transformation between the low-Li anatase and high-Li orthorhombic phases begins in a particle. Instead, discontinuous kinetics of Li accumulation in TiO2 particles prior to the phase transformations limits (dis)charging rates. We demonstrate a practical means to deconvolute the nonequilibrium charging behavior in nanocrystalline electrodes through a combination of colloidal synthesis, phase field simulations, and spectroelectrochemistry.

Self-Formation of Superhydrophobic Surfaces through Interfacial Energy Engineering between Liquids and Particles.

The superhydrophobic surface has been used in ultradry surface applications, such as the maritime industry, windshields, non-sticky surfaces, anti-icing surfaces, self-cleaning surfaces, and so forth. However, one of the main hurdles for the production of superhydrophobic surfaces is high-cost fabrication methods. Here, we report a handy process of self-synthesis fabrication of superhydrophobic surfaces with daily supplies. Driven by the physics of biscuit dunking, we introduce a method to self-synthesize superhydrophobic surfaces from daily supplies by coating a substrate with a liquid (liquids of paraffin from candles or polydimethylsiloxane) and subsequently sprinkling powders (food-desiccant silica, alumina, sugar, salt, or flour). A mechanistic study revealed that the capillary force, governed by surface energy difference, liquid viscosity, and powder pore size, draws the liquid solution into the porous channels within the powders. The entire surface of powders, in turn, is covered with the low-surface-energy liquid to maintain the porosity, creating a 3D porous nanostructure, resulting in a water contact angle over 160°. This work provides a scientific understanding that technological developments are closely related to the science that can be seen in our daily lives. Also, we believe that further intensive studies extended from this work could enable to home-fabricate a superhydrophobic surface, such as a bathtub and sink in bathrooms and a cooking area and sink in kitchens.

Universal and Switchable Omni-Repellency of Liquid-Infused Surfaces for On-Demand Separation of Multiphase Liquid Mixtures.

Mixtures of immiscible liquids are commonly found in the scenarios of environmental protection and many industrial applications. Compared to widely explored water-oil mixtures, small differences in the surface energy of organic liquids, especially for those in multiphase mixtures, make their separation a formidable challenge. Here, a family of versatile coatings based on the reactions between plant polyphenols and 3-aminopropyl triethoxysilane is introduced to regulate the wetting behavior of substrates by forming stable liquid-infused interfaces. The key finding is that when a coated substrate is prewetted with a liquid forming a stable liquid-infused interface, it becomes repellent to any other immiscible liquids. This phenomenon is independent of the surface energy of the initial wetting liquid. This exclusive wetting behavior can lead to distinctive repellency toward almost any liquid by the infusion of an immiscible liquid, even if the difference of surface energy and dielectric constant of a liquid pair is as small as 2.0 mJ m-2 and 1.8, respectively, resulting in universal and switchable omni-repellency. Of particular importance is that the as-prepared coating makes possible the on-demand separation of multiphase liquid mixtures by both continuous membrane filtration and static absorption, presenting a green and cost-effective approach to addressing this major environmental and industrial challenge.

Preparation and evaluation of a UV-curing hydrophilic semi-IPN coating for medical guidewires

Guidewires have crucial roles in intravascular, critical care, and urological applications. In recent years, the demand for guidewires with lower friction surfaces has arisen for medical applications. Among various surface lubrication strategies for guidewires, the most promising is the use of a hydrophilic coating. However, obtaining a hydrophilic coating on guidewires with strong adhesion remains difficult owing to the surface energy difference between the substrate and hydrophilic coating. Herein, we present a UV-curing semi-interpenetrating polymer network coating for medical thermoplastic polyurethane (TPU)-sheathed nitinol guidewires. A polyurethane acrylate (PUA) was synthesized and cured as a transition layer on the TPU substrate to provide strong adhesion. Then, polyvinyl pyrrolidone (PVP) and polyethylene glycol diacrylate (PEGDA) permeated into the PUA layer and cured to form the composite coating. The PUA–PEGDA–PVP coating exhibited excellent lubricity and satisfactory adhesion force. The surface coefficient of friction decreased to approximately 0.02 after modification with the coating, and the coating was stable during long-term soaking in water and repeated friction. In vitro toxicity tests revealed that the coating had good biocompatibility. Thus, our PUA–PEGDA–PVP coating has the potential for application as super-lubricity guidewires and other medical devices.

Efficiency enhancement of organic light-emitting diodes via a self-assembled moth-eye nanopatterned hole-transporting layer.

A moth-eye nanopatterned hole-transporting layer (ME-HTL) is proposed to enhance the device efficiency of organic light-emitting diodes (OLEDs), which is fabricated via spontaneous phase separation during spin-coating between poly(N-vinylcarbazole) (PVK) and poly (9,9-dioctylfluorene) (PFO) induced by their surface energy difference. Meanwhile, film morphology characteristics confirm the conformal deposition of the following organic layers and metal electrode on the ME-HTL, indicating the extension of ME nanostructure over all layers in OLEDs. Finally, owning to the disruption of the internal waveguide light at the organic layer/anode interface and the suppression of surface plasmonic loss at organic layer/cathode interface, this device architecture obtained a current efficiency of 78.9 cd/A, with an enhancement factor of 40%. This approach takes the advantage of manufacturing compatibility on behalf of solution-process and thus can be a promising strategy to reduce the production cost of OLEDs.

Bottlebrush Copolymer as Surface Neutralizer for Vertical Alignment of Block Copolymer Nanodomains in Thin Films.

Herein we designed bottlebrush copolymers for use as a neutral additive to block copolymer (BCP) thin films in which they are segregated to the interfaces via architectural effects and produce nonpreferential interfaces to induce perpendicular orientation of BCP microdomains. Two BCP systems were employed, a conventional poly(styrene-b-methyl methacrylate) (PS-b-PMMA) with relatively low χ and similar surface energies between blocks, and a high χ poly(styrene-b-methacrylic acid) (PS-b-PMAA) with distinct surface energies. The bottlebrushes, with either short side-chains of PS-r-PMMA or PS-r-PMAA random copolymers, were synthesized via ring-opening metathesis polymerization (ROMP). Remarkably, it was observed that the top and bottom interfaces of both BCP films were enriched with bottlebrush copolymers, regardless of the surface energy difference between blocks, hence, vertically oriented microdomains were achieved for both BCP systems. This can be attributed to the screening of polymer interactions by a good solvent during the spin-casting process, allowing architectural effects to play a role in surface segregation of bottlebrush copolymers, as confirmed by contact angle measurements and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). We believe that this concept can be further extended to various applications that require polymer films with functional surfaces.

Acrylic polymer treatment on Nylon fibers improves color strength and durability in thermal transfer printing

Digital inkjet printing technology includes fabric inkjet printing and thermal transfer printing. Fabric inkjet printing method has been applied to various materials such as cotton, nylon, silk, polyester, PE, PP, PU, etc. Thermal transfer printing has been applied to polyester or nylon that as resistant to heat by printing heat and pressure. In dying nylon using the thermal transfer printing technology, however, there has been an outstanding issue on a complete transfer of black ink to the nylon fabric; in particular, blue dye which is a component dye of a black ink is hardly fixed at nylon fabric. Here, we found that treating nylon fabrics with acrylic polymers enables a complete transfer of black inks without a loss of transfer of component dyes including blue dye, showing 11 % enhancement of color strength compared to that of the neat control. Moreover, we reveal that surface energy difference between polymer-coated nylon fabric and the ink is closely related to color strength and fastness of inks to the polymer-treated nylon fabric, demonstrating PMAe which has the closest surface energy to that of black ink shows the highest color strength (470) and fastness (average 4 grade). Our results may open a new avenue to dying nylon.

Enhanced pool boiling heat transfer on soft liquid metal surface

Pool boiling is a high-efficient energy transfer method through the gas-liquid phase transition. It has the characteristics of small heat transfer temperature difference and high heat flux density. The current enhancement of boiling heat transfer is realized mainly through modifying the solid heating surface. So far, there has been no report on the study of pool boiling heat transfer on soft surfaces. Therefore, in this work the pool boiling heat transfer performances of ethanol on the copper surface and soft liquid metal surface are investigated experimentally. The experimental results indicate that soft surface can effectively reduce the wall superheat corresponding to the onset of boiling (ONB). In saturation boiling, the superheat of the wall surface at ONB is reduced by nearly 12 ℃, while the heat transfer coefficient is improved by 149%. It is found that soft surface enhances pool boiling heat transfer performance significantly by increasing nucleate site density, reducing the bubble departure diameter, and increasing bubble departure frequency. Unlike the copper surface, the soft surface deforms elastically under the action of the vertical component of surface tension <i>γ</i><sub>lv</sub>sin<i>θ</i> at the three-phase contact line of the vapor bubble. From the perspective of surface energy analysis, the difference in surface energy Δ<i>E</i><sub>LM</sub> between before and after bubble departure on soft liquid metal surface is smaller than in smooth surface Δ<i>E</i><sub>CS</sub>. The potential barrier of the soft surface is smaller than of the copper surface, and the buoyancy required for bubble separation is small, and the bubble is easy to separate. Elastocapillary wave and bubble jet phenomenon on the soft surface are observed particularly, which are generated on liquid metal under the action of elastic restoring force. The fluctuation of elastocapillary wave contributes to the enhancement of heat and mass transfer in thermal boundary layer and the generation of residual nucleation site. The residual bubble grows up rapidly and coalesces with the rising large bubble, forming bubble jet phenomenon. Elastocapillary wave and bubble jet contribute to the enhancement of pool boiling heat transfer on soft liquid metal surface.

Анализ влияния плазменной активации на энергию поверхности волокон сверхвысокомолекулярного полиэтилена, на прочность волокон и армированных волокнами композитов

Completely saturated chemical bonds in ultrahigh-molecular-weight polyethylene (UHMWPE) fibers — are a reason for their low surface energy (FSE), i.e. inert properties. Elongated crystal structure of UHMWPE molecules ensures high anisotropic tensile strength of the fibers. An inertness is a problem for utilization these fibers in high-strength composites production. Surface energy (SE) difference of the fibers and a binder in fiber/matrix system hinders chemical interaction at interphase boundary and worsens fiber wettability. Increase in their FSE is a topical task for this problem decision. Necessary condition of FSE increase is the integrity of molecule structure, lying under modified surface. Low temperature, nonequilibrium plasma (LTP) treatment in a medium of argon and argon/propane mixture, used in this work for plasma activation of fibers’ surface, permits to abide by this condition. However, plasma ion bombardment during a process of activation can modify interior crystal structure and, as a result, decrease their strength. The rovings SK75 (Holland) and D800 (China) were used for study of the properties of UHMWPE fibers after plasma treatment. Activation effect on FSE, strength, and fibers’ wetting by water and epoxy binder before and after ageing was studied. Capillary wetting of the fibers by distilled water used for FSE evaluation. The data of filaments surface structure and their diameter change at maximal load, obtained by optical microscope study, were used for the analysis of FSE and epoxy matrix effect on the strength of fiber/matrix systems. Essential distinction of SK75 and D800 fibers properties is ascertained. Negative effect of fibers’ and matrix’s stiffness, as well as increased FSE of stiff fibers on the strength of fiber/matrix system is revealed.

Self-propelled sessile droplets on a superheated and heterogeneous wetting surface

In this study, we investigated self-propelled sessile droplet evaporation on superheated surfaces with mixed wetting patterns. The primary reason for droplet motion was an increase in surface temperature and the difference in surface energy, which affected the moving contact line and moved droplets close to the wetting regions and then out to the heating surface. In this study, we observed that increases in temperature significantly influenced the changes in surface adhesion force. The force balance equation was used to demonstrate the existence of a moment of droplet movement. In addition, temperature data demonstrated energy conservation behaviour. The heterogeneous wetting surface exhibited greater differences in energy because of the energy expended during liquid–vapour phase transition and droplet movement.

Facet-Dependent Photodegradation of Methylene Blue by Hematite Nanoplates in Visible Light.

The expression of specific crystal facets in different nanostructures is known to play a vital role in determining the sensitivity toward the photodegradation of organics, which can generally be ascribed to differences in surface structure and energy. Herein, we report the synthesis of hematite nanoplates with controlled relative exposure of basal (001) and edge (012) facets, enabling us to establish direct correlation between the surface structure and the photocatalytic degradation efficiency of methylene blue (MB) in the presence of hydrogen peroxide. MB adsorption experiments showed that the capacity on (001) is about three times larger than on (012). Density functional theory calculations suggest the adsorption energy on the (001) surface is 6.28 kcal/mol lower than that on the (012) surface. However, the MB photodegradation rate on the (001) surface is around 14.5 times faster than on the (012) surface. We attribute this to a higher availability of the photoelectron accepting surface Fe3+ sites on the (001) facet. This facilitates more efficient iron valence cycling and the heterogeneous photo-Fenton reaction yielding MB-oxidizing hydroxyl radicals at the surface. Our findings help establish a rational basis for the design and optimization of hematite nanostructures as photocatalysts for environmental remediation.

Inherent Dipole Layer Formation Driven by Surface Energy at Nonplanar Dielectric Interface

This work investigates the correlation between dipole formation and surface energy at a nonplanar dielectric interface on a Si nanowire (NW) by means of molecular dynamics simulations. According to the atom and charge distribution obtained by simulations, the built-in electric field and potential are calculated at the dielectric interface based on the Poisson equation. It is found that the built-in potential is dependent on the diameter of the Si NW, which is attributed to the dependence of the surface energy difference on the surface curvature of the dielectric heterointerface, driving atom diffusion and leading to a dipole layer at the interface. The impact of the built-in potential on the threshold voltage of a transistor with a multigate configuration is discussed as well.

Gas adsorbate-induced Au atomic segregation and clustering from Cu(Au)

Surface compositional and phase segregation in an alloy can change its functionality, especially for applications where surface structure and chemistry play a vital role. For instance, the surface status of alloy catalysts significantly affects their catalytic performance for both heterogeneous and electrochemical processes. Surface segregation is believed to be driven by the difference in surface energy to reduce the total free energy of the alloy. However, the atomistic processes during the segregation process remain elusive, especially for gas molecule-induced segregation, where both structural and chemical reordering may occur. Herein, we achieved in-situ atomic-scale visualization of the surface segregation behaviors of a solid solution Cu(Au) alloy under the CO gas by an aberration-corrected environmental transmission electron microscope. CO-induced Cu(Au) surface ordering structures largely change the surface chemistry of the alloy. Further gas exposure at elevated temperature could facilitate Au atom diffusion through a specific “atomic channel” structure for dealloying and clustering on the surface. The segregated Au nanoparticles show rich phase and morphological dynamics interacting with the alloy surface, where the gas adsorption also plays an important role. These atomic insights provide direct evidence for the surface segregation and dealloying mechanisms of bimetallic alloys, and highlight the role of gas adsorbate in these surface processes.

Behavior of enrichment and migration path of Cu–Ag–Pd–Bi–Pb in the recovery of waste multilayer ceramic capacitors by eutectic capture of copper

Recycling waste multilayer ceramic capacitors (MLCCs) has attracted much attention owing to its rich metal resource and environment pollution. Existing recycling processes have deficiencies in environmental protection, efficiency and metal purity. Capture technology is promising with advantages of efficient enrichment and less pollution, which was applied to recycle metals in this study. In order to study the mechanism for it, the behavior of enrichment and migration of metals in the recovery of waste MLCCs by eutectic capture of copper was discussed. The recovery rates of Ag, Pd and Bi were 87.53%, 100% and 100%, respectively. Alloy (Cu–Ag–Pd–Bi–Pb) and recyclable slag were obtained. There were three phases of Ag, Cu–Pd and Bi–Pb with the analysis of morphology and composition for the alloy. Then the capture mechanism was revealed. The slag and metal separated due to differences in chemical bonds, surface energy, density and viscosity. The interaction of metals was analyzed through phase diagrams and density functional theory. Pd tended to enter Cu phase. Ag and Cu existed as two phases. Bi and Pb neither entered Ag nor Cu phase based on phase diagrams and formation energy. This study provides a theoretical basis for the application of capture technology in metal enrichment.