Dewetting of Thin Polymer Films on Wrinkled Graphene Oxide Monolayers.

We investigated the effect of the morphological structure of a graphene oxide (GO) monolayer on the dewetting dynamics of the upper polymer thin films. The Langmuir-Schaefer (LS) technique was used to prepare a wrinkled GO ( wrGO) structure with a root mean square (rms) roughness of 22.7 Å. The dewetting behavior of poly(methyl methacrylate) (PMMA) thin films on the wrGO monolayers was perfectly prevented, whereas the PMMA thin films on a flat GO monolayer were dewetted at 203 °C. This wrinkle effect of the GO can be also obtained when the GOs monolayers are intercalated to the PMMA/polystyrene (PS) interface. In this multilayer, the flat GO monolayer at the interface between the PS and PMMA layers was spontaneously roughened with rms roughness of 46.9 Å after annealing and also prohibited the dewetting behavior. From the results, we found that to improve the compatibility of polymer blends by adding the two-dimensional nanosheets, it is important to control the morphological structure of the sheets at the interface, along with manipulation of the GO-polymer interactions.

Fabrication of Wettability-Patterned Surface for Cellular Micropatterning Using Step-Wise Ion Beam Processing.

In this study, the fabrication of a wettability patterned surface for cellular micropatterning was investigated using step-wise ion beam processing. A perfluorinated poly(ethylene-co-propylene) (FEP) film was first irradiated using accelerated Xe+ ions with 100 keV of energy at the low current density of 1 µA/cm² over the entire surface. Second, its confined regions were irradiated at the higher current density of 15 µA/cm² at various ion fluences through the pattern mask to generate patterns with big differences in wettability. From the analytic results, it was clearly verified that the step-wise irradiation induced effective chemical and morphological changes on the FEP surface, resulting in the successful formation of well-defined micropatterns with relatively hydrophilic and superhydrophobic surfaces. Moreover, the results of in-vitro cell culture showed well-resolved formation of 200 µm cell micropatterns on the wettability patterned FEP surface due to the individual effects of the relatively hydrophilic and superhydrophobic properties on the cell adhesiveness and proliferation.

Perpendicular Orientation of Diblock Copolymers Induced by Confinement between Graphene Oxide Sheets.

We have studied an orientation structure of self-assembled block copolymers (dPS-b-PMMA) of deuterated polystyrene (dPS) and poly(methyl methacrylate) (PMMA) confined between graphene oxide (GO) surfaces. The results of combination techniques, such as neutron reflectivity, time-of-flight secondary-ion mass spectrometry, grazing-incidence small-angle X-ray scattering, and scanning electron microscopy, show that self-assembled domains of the block copolymers in thin films near the GO sheets are oriented perpendicular to the surface of the GO monolayers, in contrast to the horizontal lamellar structure of the copolymer thin film in the absence of the GO monolayers. This is due to the amphiphilic nature of the GO, which leads to a nonpreferential interaction of both dPS and PMMA blocks. Double-sided confinement with the GO monolayers further extends the ordering behavior of the dPS-b-PMMA thin films. Continuous vertical orientation of the block copolymer thin films is also obtained in the presence of alternating GO layers within thick copolymer films.

Preparation of Conductive Carbon Films from Novolac Resins by Ion Beam Irradiation and Carbonization.

In this study, thin carbon films with good electrical properties were prepared using commercial novolac resins by ion beam irradiation and carbonization. Novolac films were irradiated with ion beams and then carbonized under inert atmosphere. Based on the FTIR and UV results, the novolac resins were found to be crosslinked by ion beam irradiation without any additives. The Raman and XRD results indicate that carbon films with pseudo-graphitic structures were formed by carbonization of the ion beam irradiated novolac films. The sheet resistance of the prepared carbon films decreased to 1.35 × 102 Ω/ with an increasing fluence. The prepared carbon films showed a good electrical conductivity of ∼2.34 × 102 S/cm.

Electric Heating Performance of Pyrolyzed Photoresist Films Prepared by Proton Irradiation and Pyrolysis.

In this study, pyrolyzed photoresist films (PPFs) were prepared using commercial SU8 photoresist by proton irradiation and pyrolysis. SU8 thin films were irradiated with high-energy proton ions and then pyrolyzed in a tube furnace at 1000 °C under inert atmosphere. The carbonization yield of the PPFs increased with an increasing fluence due to the formation of more crosslinked network structures at a higher fluence. The electrical resistance decreased with an increasing fluence due to the higher remaining thickness and carbonization yield at a higher fluence. Therefore, the PPFs prepared at 1 × 1016 ions/cm2 showed the maximum temperature of 150 °C at 20 V and a high electric power efficiency of 1.57 mW/°C.

Effects of Silicone Oil on Electrowetting to Actuate a Digital Microfluidic Drop on Paper.

The effects of an immiscible, lubricating polydimethylsiloxane fluid, referred to as silicone oil, on the static deformation and on the dynamic motion of a water drop on paper induced by electrowetting were investigated. The deformation of a drop on a hydrophobic film of amorphous fluoropolymers top-coated with less hydrophobic silicone oil was much more predictable, reversible and reproducible than on the uncoated surface. In the dynamic tribological experiment for a sliding drop along an inclined surface, a significant decrease in the friction coefficient, with an unexpected dependency of the contact area, was observed. Based on the curve fitting analysis, the shear stress and the net friction force were estimated quantitatively. Because of the tribological effect and the reduced shear friction force of the oil film, the static and the dynamic electrowetting states of the water drop were enhanced.

Synthesis of a Graphene-Like Nanofilm from Polyacrylonitrile.

There are various different approaches in synthesizing graphene including chemical vapor deposition (CVD) and solid-phase method, where gas or solid type carbon source, to be converted into graphene, interacts with transition metals such as nickel and copper. When any thin nickel layer coated atop the polyacrylonitrile (PAN) film is pyrolyzed at a sufficiently high temperature, it is impossible to grow a continuous graphene film with a large area owing to dewetting, which has restricted the subsequent utilization in practical applications. Herein, we suggest a method to synthesize a continuous graphene-like nanofilm with a nickel coated thin PAN film through pyrolysis at 750 to 800 °C in a high-vacuum furnace without a reductive gas flow. The graphene-like nanofilm obtained was characterized using Raman spectroscopy, Raman mapping, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy.

The fabrication of patterned gold nanoparticle arrays via selective ion irradiation and plasma treatment.

A simple and facile method for the patterning of gold nanoparticles (GNPs) was described via selective ion irradiation and oxygen plasma etching. Thin Pluronic films containing HAuCI4 as the precursor of GNPs were selectively irradiated through a pattern mask with 200 keV proton ions to generate GNP-embedded Pluronic patterns. The Pluronic was then removed by an oxygen plasma etching process for the pattern formation of GNPs. Based on the results of the UV-Vis, FE-SEM, and EDX analyses, 50 µm negative-tone line patterns of the GNP-embedded Pluronic were successfully generated at a fluence of less than 1 x 10(16) ions/cm2. The changes in the morphology and elemental composition of the formed GNP-embedded Pluronic patterns with different time periods of oxygen plasma etching were investigated using an FE-SEM with an EDX. The experimental results demonstrated that the patterns of GNPs were effectively generated by the oxygen plasma etching of the formed GNP-embedded Pluronic patterns for 15 min. Furthermore, the XRD results revealed that GNPs in the patterns formed by ion irradiation were further grown during the subsequent oxygen plasma etching.

Direct patterning of poly(acrylic acid) on polymer surfaces by ion beam lithography for the controlled adhesion of mammalian cells.

Poly(acrylic acid) (PAA)-patterned polystyrene (PS) substrates were prepared by ion beam lithography to control cell behaviors of mouse fibroblasts and human embryonic kidney cells. Thin PAA films spin-coated on non-biological PS substrates were selectively irradiated with energetic proton ions through a pattern mask. The irradiated substrates were developed with deionized water to generate negative-type PAA patterns. The surface characteristics of the resulting PAA-patterned PS surface, such as surface morphology, chemical structure and composition and wettability, were investigated. Well-defined 100 µm PAA patterns were effectively formed on relatively hydrophobic PS substrates by ion beam lithography at higher fluences than 5 × 10(14) ions/cm(2). Moreover, based on the in vitro cell culture test, cells were adhered and proliferated favorably onto hydrophilic PAA regions separated by hydrophobic PS regions on the PAA-patterned PS substrates, and thereby leading to the formation of well-defined cell patterns.

Design of a Bioinspired Robust Three-Dimensional Cross-Linked Polymer Binder for High-Performance Li-Ion Battery Applications.

Si has the highest theoretical capacity (4200 mA h g-1) among conventional anode materials, such as graphite (372 mA h g-1), but its large volume expansion leads to deterioration of the battery performance. To overcome this problem (issue), we investigated the use of polysaccharide-based 3D cross-linked network binders for Si anodes, in which the polysaccharide formed an effective 3D cross-linked network around Si particles via cross-linking of polysaccharide with citric acid (CA). Sodium alginate (SA), a natural polysaccharide extracted from brown algae, is a suitable binder material for Si anodes because its abundant hydroxyl (-OH) and carboxyl (-COOH) groups form hydrogen and covalent bonds with the -OH groups present on the Si surface. We found that CA-cross-linked (CA-SA) could effectively prevent the volume expansion of Si anodes through the formation of 3D cross-linked network structures. In addition, the CA-SA binders provide enhanced adhesion strength, enabling the fabrication of more robust electrodes than those prepared using binders with linear structures ("linear binders"). In particular, the fabricated Si-based electrode (high mass loading of 1.5 mg cm-2) with CA-SA binder exhibited outstanding areal capacity (∼2.7 mA h cm-2) and excellent cycle retention (∼100% after 100 cycles).

Patterning of TiO2 particles on poly(dimethyl siloxane) films by using proton irradiation and liquid-phase deposition process.

Micropatterning of titanium dioxide (TiO2) on the surface of thin poly(dimethyl siloxane) (PDMS) films was described by means of proton irradiation and liquid-phase deposition (LPD) techniques. The surface of thin PDMS films was irradiated with accelerated proton ions through a pattern mask in the absence or presence of oxygen in order to create hydrophilically/hydrophobically patterned surfaces. The results of the surface analysis revealed that the PDMS films irradiated at the fluence of 1 x 10(15) ions cm-2 in the presence of oxygen showed the highest hydrophilicity. The LPD of TiO2 particles on the patterned PDMS film surface showed a selective deposition of TiO2 on the irradiated regions, leading to well defined TiO2 micropatterns. The crystal structure of the formed TiO2 films was found to be in an anatase phase by X-ray diffraction analysis. This process can be applied for patterning various metal and metal oxide particles on a polymer substrate.

Passive Daytime Radiative Cooling by Thermoplastic Polyurethane Wrapping Films with Controlled Hierarchical Porous Structures.

Invited for this month's cover is a combined work of the Korea Research Institute of Chemical Technology together with the Chungnam National University, the University of California, Irvine, and Chung-Ang University. The cover shows the effective thermal management of a vehicle interior through the wrapping of stretchable passive radiative cooling film. Thermoplastic polyurethane (TPU) cooler film with a hierarchical porous structure shows a dramatic cooling effect compared to commercial paint in sunny, hot weather. The Research Article itself is available at 10.1002/cssc.202201842.

Passive Daytime Radiative Cooling by Thermoplastic Polyurethane Wrapping Films with Controlled Hierarchical Porous Structures.

Current research has focused on effective solutions to mitigate global warming and the accelerating greenhouse gas emissions. Compared to most cooling methods requiring energy and resources, passive daytime radiative cooling (PDRC) technology offers excellent energy savings as it requires no energy consumption. However, existing PDRC materials encounter unprecedented problems such as complex structures, low flexibility, and performance degradation after stretching. Thus, this study reports a porous structured thermoplastic polyurethane (TPU) film with bimodal pores to produce high-efficiency PDRC with efficient solar scattering using a simple process. The TPU film exhibited an adequately high solar reflectivity of 0.93 and an emissivity of 0.90 in the atmospheric window to achieve an ambient cooling of 5.6 °C at midday under a solar intensity of 800 W m-2 . Thus, the highly elastic and flexible TPU film was extremely suitable for application on objects with complex shapes. The radiative cooling performance of 3D-printed models covered with these TPU films demonstrated their superior indoor cooling efficiency compared to commercial white paint (8.76 °C). Thus, the proposed design of high-efficiency PDRC materials is applicable in various urban infrastructural objects such as buildings and vehicles.

Preparation and Electrochemical Characterization of Si@C Nanoparticles as an Anode Material for Lithium-Ion Batteries via Solvent-Assisted Wet Coating Process.

Silicon-based electrodes are widely recognized as promising anodes for high-energy-density lithium-ion batteries (LIBs). Silicon is a representative anode material for next-generation LIBs due to its advantages of being an abundant resource and having a high theoretical capacity and a low electrochemical reduction potential. However, its huge volume change during the charge-discharge process and low electrical conductivity can be critical problems in its utilization as a practical anode material. In this study, we solved the problem of the large volume expansion of silicon anodes by using the carbon coating method with a low-cost phenolic resin that can be used to obtain high-performance LIBs. The surrounding carbon layers on the silicon surface were well made from a phenolic resin via a solvent-assisted wet coating process followed by carbonization. Consequently, the electrochemical performance of the carbon-coated silicon anode achieved a high specific capacity (3092 mA h g-1) and excellent capacity retention (~100% capacity retention after 50 cycles and even 64% capacity retention after 100 cycles at 0.05 C). This work provides a simple but effective strategy for the improvement of silicon-based anodes for high-performance LIBs.

Reversibility of electrowetting on hydrophobic surfaces and dielectrics under continuous applied DC voltage.

Various properties of electrowetting such as reversibility, reproducibility and mobility have been investigated experimentally. A conductive water drop on a thin hydrophobic film of amorphous fluropolymers coated on the counter electrode showed unexpectedly the poor reversibility under the discontinuous voltage, so called the contact angle hysteresis. The hysteresis could not been completely suppressed by inserting additionally a thick parylene-C film which has the high dielectric constant and no pinholes. However, both the reversibility and the reproducibility have been enhanced under the continuous voltage starting from the highest absolute electric potential.

Patterning of polymer nanocomposite resists containing metal nanoparticles by electron beam lithography.

Poly(vinyl pyrrolidone) (PVP)-stabilized silver nanoparticles (NPs) were used as a new nanocomposite resist for electron beam lithography. A nanocomposite resist prepared by reducing silver nitrate in an alcoholic PVP solution was patterned by using a scanning electron microscope equipped with a nanometer pattern generation system. Well-defined negative tone patterns with a good sensitivity of 200 microC/cm2 and a contrast of 2.83 were obtained using the prepared nanocomposite resist. In addition, the changes in the morphology and structure of the resist patterns with a thermal treatment temperature were investigated by a FE-SEM with an EDX. The results revealed that the patterns of Ag NPs were formed through sintering the formed resist patterns at above 300 degrees C.

Fabrication of silicon nanowire for detecting p-amyloid (1-42) by nanoimprint lithography.

Ultraviolet nanoimprint lithography (UV-NIL) is a high volume and cost-effective patterning technique with sub-10 nm resolution. It has great potential as a candidate for next generation lithography. Using UV-NIL, nanowire patterns were successfully fabricated on a four-inch silicon-on-insulator (SOI) wafer under moderate conditions. The fabricated nanowire patterns were characterized by FE-SEM. Its electrical properties were confirmed by semiconductor parameter analysis. Monoclonal antibodies against beta-amyloid (1-42) were immobilized on the silicon nanowire using a chemical linker. Using this fabricated silicon nanowire device, beta-amyloid (1-42) levels of 1 pM to 100 nM were successfully determined from conductance versus time characteristics. Consequently, the nanopatterned SOI nanowire device can be applied to bioplatforms for the detection of proteins.

Patterned immobilization of biomolecules on a polymer surface functionalized by radiation grafting.

Patterned graft polymerization of a functional monomer on a hydrophobic polymer surface was proposed for biomolecule patterning. A poly(vinylidene fluoride) (PVDF) film surface was selectively activated by ion implantation through a pattern mask and acrylic acid (AA) was then graft polymerized onto the activated regions of the PVDF surfaces. The peroxide concentration on the implanted surface depended on the fluence, which had a considerable effect on the grafting degree of AA. Afterwards, amine-functionalized biotin and probe DNA were immobilized on the poly(acrylic acid)-grafted regions of the PVDF surfaces. Specific binding of biotin with streptavidin and hybridization of probe DNA with complimentary DNA proved successful protein and DNA patterning and well-defined 50 microm dot-type patterns of the streptavidin and DNA were obtained. These results confirmed the potential of this strategy for patterning of various biomolecules.

Photothermal Fabrics for Efficient Oil-Spill Remediation via Solar-Driven Evaporation Combined with Adsorption.

Oil spill rapidly destroys aquatic system and threatens humans, requiring fast and efficient remedy for removal of oil. The conventional remedy employs water-floating oil adsorbents whose volume should be large enough to accommodate all oil ingredients. Here, we suggest a new concept for efficient oil-spill remediation, which combines solar-driven evaporation of light oil components and simultaneous adsorption of heavy oil components, namely, solar-driven evaporation of oil combined with adsorption (SEOA). To design photothermal oil absorbents for the efficient SEOA, we designed carbonaceous fabrics with high photothermal heating performance and oil-adsorption capacity by carbonizing nonwoven cotton fabrics. For three model organic solvents of octane, decane, and dodecane floating on water, the fabrics, respectively, accelerated the evaporation in factors of 2.0, 4.4, and 2.3 through photothermal heating under simulated sunlight condition. For the 1.18 mm thick crude oil floating on water, 70 and 77 wt % of crude oil were evaporated within 2 and 16 h, respectively, with the photothermal fabrics, whereas only 22 and 34 wt % was evaporated in the absence of the fabrics, indicating the dramatic enhancement of oil removal by solar-driven evaporation. The remaining heavy oil components were accommodated in the pores of the fabrics, removal of which showed an additional 18 wt % reduction; that is, a total 95 wt % of the crude oil was removed. The oil-treatment capacity is as high as 110 g g-1, which has never been achieved with conventional oil adsorbents to the best of our knowledge. We believe that our combinatorial SEOA approach potentially contributes to minimizing the environmental disaster through a fast and efficient oil-spill remediation.

Simple and biocompatible micropatterning of multiple cell types on a polymer substrate by using ion implantation.

A noncytotoxic procedure for the spatial organization of multiple cell types remains as a major challenge in tissue engineering. In this study, a simple and biocompatible micropatterning method of multiple cell types on a polymer surface is developed by using ion implantation. The cell-resistant Pluronic surface can be converted into a cell-adhesive one by ion implantation. In addition, cells show different behaviors on the ion-implanted Pluronic surface. Thus this process enables the micropatterning of two different cell types on a polymer substrate. The micropatterns of the Pluronic were formed on a polystyrene surface. Primary cells adhered to the spaces of the bare polystyrene regions separated by the implanted Pluronic patterns. Secondary cells then adhered onto the implanted Pluronic patterns, resulting in micropatterns of two different cells on the polystyrene surface.