Surface Wrinkling Research Articles

A novel self-wrinkled polyurethane-acrylate wood coating with self-matting, anti-fingerprint performance and skin-tactile feeling via excimer lamp/UV curing.

Wrinkled surfaces exist widely in nature and organic living world, such as plants, insects, and skin. The optical, wettability and mechanical properties of materials can be enhanced by artificially preparing regular microstructure on the surface of materials. In this study, a novel self-wrinkled polyurethane-acrylate (PUA) wood coating with self-matting, anti-fingerprint performance and skin-tactile feeling curing by excimer lamp (EX) and ultraviolet (UV) was prepared. The wrinkles were formed on the surface of PUA coating at microscopic level after excimer and UV mercury lamp irradiation. The width and height of the wrinkles on the coating surface can be controlled to adjust the coating performance by changing the curing energy. When the PUA coating samples were cured by excimer lamp and UV mercury lamp with curing energy of 25-40 mJ cm-2 and 250-350 mJ cm-2, the excellent coating performances were observed. The gloss value of self-wrinkled PUA coating at 20° and 60° were less than 3 GU, while at 85° was 6.5 GU, which satisfied the demanding of matting coating. Besides, the fingerprints on the coating samples could disappear in 30 s and could still have anti-fingerprint performance after 150 times of anti-fingerprint tests. Furthermore, the pencil hardness, abrasion quantity and adhesion of self-wrinkled PUA coating were 3H, 0.045 g and 0 grade respectively. Finally, the self-wrinkled PUA coating has excellent skin-tactile feeling for touching. The coating can be applied to wood substrates, and has potential application in the field of wood-based panels, furniture and leather.

Numerical Simulation Analysis on Surface Quality of Aluminum Foam Sandwich Panel in Plastic Forming

The surface quality of an aluminum foam sandwich panel (AFSP) is very important for its appearance and application. This paper mainly studies the surface quality of AFSP after plastic forming. Combined with three-dimensional (3D) scanning technology, the normal deviation between the experimental AFSP and the target surface was obtained, and the surface quality parameters Sq, Sz and dmax were calculated to evaluate surface quality. The AFSP models with cubic-spherical (CS) and tetrakaidecahedral (TKD) as foam structures were established respectively. A series of numerical simulations of multi-point forming (MPF) were then carried out. Equivalent strain and deformation characteristics of spherical and saddle-shaped AFSP were discussed. The main surface defects produced by AFSP in plastic forming, such as surface wrinkle, the local straight face effect and surface dimpling were analyzed. Finally, MPF experiments were carried out, and it was found that the numerical simulation results were significantly corresponded to the experimental AFSP in terms of the degree and distribution of normal deviation and surface quality evaluation parameters. The TKD model was more consistent with the experimental results than the CS model. Moreover, the results show that the surface quality can be improved by thicker face sheets and smaller core cell sizes.

Light‐Responsive Polyblend Films with Reconfigurable Surface Micropatterns as Rewritable Information Storage Media

Comprehensive SummaryStimulus‐sensitive surfaces with tunable morphologies exhibit a wide range of applications in the fields of surface science and engineering. Herein, a cost‐effective yet practical strategy is proposed to fabricate photo‐sensitive patterning surface on film/substrate wrinkle system based on an azo‐containing polyblend. By manipulating the stress field of the bilayer system globally and/or locally upon the stress relaxation triggered by the reversible cis‐trans isomerization of the azobenzene, heating/cooling triggered surface wrinkles on the polyblend films could be tailor‐made with visible‐light‐irradiation. Notably, upon selective photo‐irradiation, bespoke surface patterns may be cyclically generated or eliminated, allowing these reconfigurable patterned polyblend surfaces to be used as rewritable information storage media for non‐ink printing. The as‐prepared photo‐printed information patterns with high‐resolution are shown to be rewritable for multiple cycles and legible for over 90 d in dark ambient conditions. This study not only provides a versatile strategy for flourishing the stimulus‐sensitive systems, but also sheds light on the stress relaxation‐triggered morphological evolution of the wrinkling polyblend films.

Characteristic of Salvia officinalis L. Genotypes in the Steppe of South Ukraine

In this study gives the characteristic of Salvia officinalis L. genotypes (Lamiaceae)grown in the Southern Steppe of Ukraine. S. officinalis one of the most well-known plants from Salvia L. genus that is used as an aromatic, medicinal, and culinary herb. The plant raw material of this plant is characterized by numerous biological activities that allow use in the pharmacological industry. This plant is characterized by morphological polymorphism and the selection of new genotypes within S. officinalis has a polyfunctional meaning. The plant material of this study was the genotypes of S. officinalis (108-14, 109-14, 108-14-1, 108-14-2, and 113-16). It investigated 3d years of living plants at the flowering stage from the experimental collections of aromatic and medicinal plants in the Kherson region, v. Plodove (Institute of Climate Smart Agriculture of the National Academy of Agrarian Sciences of Ukraine). The height of plants of investigated genotypes was 65.02–86.37 cm, the diameter of the plant was 89.37–117.03 cm, the leaf length was 8.20–11.06 cm, the leaf width was 2.95–3.79 cm, the inflorescence length was 14.52–26.01 cm, the inflorescence diameter was 4.07–5.57 cm, the number of whorls in inflorescences was 8.12–10.55, and the number of flowers in the whorl was 10.02–12.14. The colour of the leaf surface, the character of the leaf surface (wrinkles), and colour of the flowers depended on genotype. The mass of raw from the shrub was determined from 350.11 to 560.27 g and the average mass of essential oil of one plant was from 1.37 to 2.01 g depending on genotype. The essential oil content in the herb, leaves, and inflorescences on dry mass was 1.0–1.5%, 1.09–1.79%, and 0.98–1.28%, respectively. In the herbs and leaves, minimal and maximal content of oil were found in genotypes 113–16 and 109–14, respectively. These results can be useful for further selective work within S. officinalis species and including other species of this genus.

A Bioinspired Triple‐Hierarchical Superhydrophobic Surface with Exceptional Robustness to Water Impingement

Bioinspired surfaces have great potential for self‐cleaning, condensation acceleration, and drag reduction. However, manufactured biomimetic surfaces typically feature only one or occasionally two length scales of surface topography and do not fully recapitulate the structure and function of natural textures. Herein, a triple‐hierarchical superhydrophobic surface (TriSS) inspired by water‐repellent lotus leaves is introduced, which consist of arrays of microprotrusions with various sizes, grooves between the protrusions, and a covering of nanoscale hairs. The TriSS surface is manufactured by forming an array of microdomes through photolithography and thermal reflow. These microstructures are transferred, by casting, to an elastomer, which is then augmented with surface wrinkles by the relaxation of biaxial stress in an oxidized surface layer. Conformal growth of a nanoporous zinc oxide film and fluorosilanization adds further surface detail. The TriSS surface achieves a sessile water contact angle up to 174.3 ± 0.3° and contact angle hysteresis down to 9.9 ± 0.3° via the very limited liquid–solid contact enabled by the surface topography. The surface also captures and retains a stable air layer, which resists water impingement even when submersed to 20 cm depth for more than 200 h. The TriSS process offers a scalable route to water repellence in industrial applications.

Circumferential Wrinkling of Elastic Cylinders With Negative Surface Tension

Abstract The present paper studies the critical condition for negative surface tension-driven circumferential wrinkling of soft cylinders based on the linearized Steigmann–Ogden model of surface elasticity. A simple negative surface tension-mode number relation is derived explicitly for arbitrary Poisson ratios of the cylinder and its surface layer and their shear modulus ratio, on which the critical surface residual strain and the associated mode number can be determined easily. For an incompressible solid cylinder with an incompressible thin surface layer, the critical values of surface residual strain and the mode number predicted by the present model are in good agreement with available numerical results based on the popular neo-Hooken nonlinear model for a wide range of material and geometrical parameters. In addition, the critical condition for circumferential wrinkling of the inner surface of a cylindrical hole within an infinite body is also derived. The present work addresses the key role of negative surface tension in circumferential wrinkling of soft cylinders and offers supporting evidence for the efficiency and accuracy of the linear Steigmann–Ogden model for the determination of the critical values for circumferential wrinkling.

Effect of post-treatment on the microstructure and properties of Ti-27 Nb-5Zr-2Cr alloy prepared by laser powder deposition

A metastable titanium alloy of Ti-27 Nb-5Zr-2Cr (wt%) was fabricated by laser powder deposition (LPD), and the bulk samples were then treated with hot forging (HF) and hot forging + surface shot blasting (HF + SB). The microstructures and mechanical properties of the laser-deposited Ti-27 Nb-5Zr-2Cr alloy in LPD, LPD + HF, and LPD + HF + SB were investigated. The obtained results showed that the microstructure of the LPD specimen was composed of β phase and isothermal ω phase. Due to the exist of the isothermal ω phase, the alloy was significantly strengthened and the deformation twinning was suppressed completely. As a result, the LPD specimen exhibited high strength (yield strength 728 ± 72 MPa) but low plasticity (6 ± 1%); after hot forging, the isothermal ω phase transformed to β phase and the deformation twinning occurred during tensile deformation. The yield strength and tensile strength of LPD-HF specimen decreased by 45% and 29%, respectively, but the plasticity increased by 483% to 35 ± 2%. Shot blasting was used to introduce gradient nanostructures on the surface of LPD-HF-SB specimens, which suppressed surface wrinkling caused by deformation twinning while improving strength and plasticity. Compared with the LPD-HF specimen, the yield strength, tensile strength, and plasticity of the LPD-HF-SB specimen were increased by 18%, 8%, and 6%, respectively.

Liquid metal and Mxene enable self-healing soft electronics based on double networks of bacterial cellulose hydrogels

Liquid metal (LM) nanodroplets and MXene nanosheets are integrated with sulfonated bacterial nanocellulose (BNC) and acrylic acid (AA). Upon fast sonication, AA polymerization leads to a crosslinked composite hydrogel in which BNC exfoliates Mxene, forming organized conductive pathways. Soft conducting properties are achieved in the presence of colloidally stable core-shell LM nanodroplets. Due to the unique gelation mechanism and the effect of Mxene, the hydrogels spontaneously undergo surface wrinkling, which improves their electrical sensitivity (GF = 8.09). The hydrogels are further shown to display interfacial adhesion to a variety of surfaces, ultra-elasticity (tailorable elongation, from 1000 % to 3200 %), indentation resistance and self-healing capabilities. Such properties are demonstrated in wearable, force mapping, multi-sensing and patternable electroluminescence devices.

A dynamic supercritical carbon dioxide foaming method for fabricating wrinkled surface to enhance triboelectric nanogenerator performance

AbstractTriboelectric nanogenerator (TENG) is a promising energy harvester to overcome the energy depletion issue. The surface structure has been considered as an effective way to enhance the triboelectric performance. Herein, a dynamic supercritical carbon dioxide (scCO2) foaming method, which introduced a scCO2 flow field during scCO2 saturation, was proposed to fabricate thermoplastic polyurethane (TPU) foams with surface wrinkly structures. The size of the surface wrinkles could be regulated in the range of 1.8–10 μm by varying the foaming pressure. The surface wrinkled TPU film with wrinkle wave length of 2.4 μm demonstrated an excellent enhancement in output voltage (130%), current (180%), and maximum transfer charge (130%) when paired with surface structured polydimethylsiloxane film in a TENG. Due to the excellent durability and flexibility of the composing materials, the developed TENG showed outstanding stability in long‐term continuous operation. With a high power density of 0.5 W/m2 achieved on a 107 Ω external load, the flexible TENG could be used to charge capacitors, power light‐emitting‐diodes, and served as a self‐powered sensor to detect various human movement behaviors. This work provides a new path for the fabrication of surface wrinkled films for the sustainable development of high performance TENGs.

Surface wrinkles enhancing electromagnetic interference shielding of copper coated polydimethylsiloxane: A simulation and experimental study

Herein, the sandwiched copper/polydimethylsiloxane/copper (Cu/PDMS/Cu) composites with periodic micro-wrinkles were fabricated by a Cu sputtering deposition on the surface of the stretched PDMS substrates. The effect of Cu micro-wrinkles on electromagnetic interference shielding effectiveness (EMI SE) was evaluated by a simulation and experimental study via tuning pre-stretching strain and thickness of PDMS substrates. The results show that the EMI SE values increase with the increase of pre-stretching strain of substrates due to the formation of more micro-wrinkles on the surface. The shielding mechanism of the sandwiched Cu/PDMS/Cu composites with micro-wrinkles was also discussed in this study. The micro-wrinkles can induce the heterogeneous distribution of surface electrons, and then enhance conductive loss and multiple scattering of electromagnetic waves (EMW) on the surface. In addition, the micro-wrinkles also increase the surface area of the composites which enhance the Salisbury screen effect and then reduce the reflection of microwaves.

Patterned Aluminum/Polydimethylsiloxane-Laminated Film for a Solvent-Driven Soft Actuator with Programmable and Multistable Shape Morphing.

Recently, soft actuators capable of deforming in predictable ways under external stimuli have attracted increasing attention by showing great potential in emerging industries. However, limited efforts are being spent on the untethered actuators with multistable deformations. Also, there is a lack of mechanically guiding design principles for multistable structures. Here, the patterned aluminum/polydimethylsiloxane (Al/PDMS)-laminated films with surface wrinkles are fabricated by magnetron sputtering the Al layer on the PDMS substrate. By tuning the geometric parameters and surface constraints of the patterned Al/PDMS-laminated films, a series of solvent-driven actuators with multiform stable configurations (such as monostable arc, multistable cylinder, and monostable/bistable spiral) are proposed. The deformation mechanism is revealed using a linear elastic theory. Combined with the finite element analysis method, the deformations of Al/PDMS-laminated films with different surface constraints and geometric configurations are visually predicted. Besides, we modulate the deformation of different parts of the Z-shaped actuators by tuning the surface constraints in different regions of the Z-shaped Al/PDMS bilayer films to achieve multiple stable deformations in a single actuator. The concept offers a huge design scope for reconfigurable soft robots. Finally, two bionic applications are proposed to demonstrate the practical applications of the soft solvent-driven actuator based on the patterned Al/PDMS films in artificial muscles and bionic robotics. This work provides a strategy for the design and fabrication of programmable and controllable soft actuators, laying the foundation for a wide range of applications in smart materials.

Random wrinkle structures for spectrum preserved warm white organic light emitting diodes

Surface wrinkles of mesoscopic size were formed by a single photocuring process of an in-house synthesized linear liquid pre-polymer. The linear relationship between the amplitude and the period of the wrinkles indicates the presence of constant compressive strain during the wrinkling process. The stiffness ratio of the hard film to the soft foundation decreases as the initial film becomes thinner, providing a quantitative measure for estimating the wrinkle size. As an application, mesoscopic wrinkles were investigated as optical structures for enhanced light outcoupling and angular spectral stability of red, green, blue, and white organic light emitting diodes.

Surface Wrinkling for Flexible and Stretchable Sensors (Small 42/2022)

Surface Wrinkling In article number 2203491, Qingshan Wei, Yong Zhu, Seung Goo Lee, and co-workers summarize the recent advances in flexible and stretchable sensors based on surface wrinkling, which provides an effective alternative to improve both sensing performance and mechanical deformability of sensors. The detailed fundamental mechanics of wrinkle formation, geometry control strategies, fabricating methods, and practical applications are widely discussed.

Efficient Sensing of Selected Amino Acids as Biomarker by Green Phosphorene Monolayers: Smart Diagnosis of Viruses (Adv. Theory Simul. 10/2022)

Surface Wrinkling versus Global Buckling Instabilities in Thin Film-Substrate Systems In article 2200357, Panigrahi, Hussain and coworkers have used density functional theory simulations to explore the potential applications of green phosphorene monolayers as efficient nanobio-sensors.

Non-Equilibrium Growth of Surface Wrinkles Emerging in an SiO2/Si Stack during Si Melting Induced by UV Nanosecond Pulsed Laser Annealing

UV nanosecond pulsed laser annealing (UV-NLA) is demonstrating clear benefits in the emerging 3D-integrated electronic devices, where the allowed thermal budget is strictly limited to preserve underlying device performance. A possible drawback of UV-NLA is that melting a solid substrate covered by a dielectric layer, which can be found in typical CMOS device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in thermally-grown SiO2/Si structures to systematically investigate the formation of wrinkles. A classical analytical model adopted from literature shows a good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value is rapidly increasing for a thinner (roughly less than 50 nm) SiO2 film, whereas it becomes closer to unity for a thicker (roughly greater than 50 nm) SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The impact of the as-grown SiO2 film stress on the growth of wrinkles is also investigated, improving the statistics of the measurements. The results do not show any significant impact possibly because of the degree of the as-grown SiO2 film stress being negligible compared to the SiO2 shear modulus.

Formation of surface wrinkles and creases in constrained dielectric elastomers subject to electromechanical loading

This paper investigates issues that have arisen in experimental and theoretical studies of the stability of a dielectric elastomeric layer bonded to a stiff substrate and subject to a voltage difference across the top and bottom conducting surfaces of the layer. The role of equi-biaxial pre-stretch of the layer prior to bonding to the substrate is a central factor in the investigation. The focus is the competition between wrinkling and creasing and how this competition is affected by pre-stretch. A finite element model of the system is employed to generate wrinkling bifurcation and advanced post-bifurcation solutions in the form of localized modes, either crease-like or groove-like depending on the pre-stretch. The constitutive model includes elastic compressibility, but the formulation produces accurate solutions for nearly incompressible materials which coincide with the neo-Hookean solid in the incompressible limit. The numerical simulations reveal that localized crease solutions exist at voltages below the critical voltage for wrinkling bifurcation for equi-biaxial pre- stretches below about 2.4. In this range, the wrinkling bifurcation is highly unstable, creasing rather than wrinkling can be expected, and a discontinuous transition is predicted with a finite energy barrier that may be overcome due to the presence of surface defects. With an equi-biaxial pre-stretch greater than 2.4, a continuous transition is predicted with no energy barrier, forming a localized groove due to nonlinear interactions among the unstable wrinkling modes.

Controlled surface topography of nanofilm by local strain modulation in mechanical transfer process

The mechanical transfer of nanofilms has been successfully established based on interfacial delamination behaviors. However, controlling the formation of surface cracks and wrinkles in nanofilms during mechanical transfer processes remains a challenge. Here, we demonstrate the controlled surface topography of nanofilms using local strain in the mechanical transfer process. A single cantilever beam (SCB) fracture mechanics test is performed using a specimen composed of an elastomer receiver–Au nanofilm–Si donor structure to investigate the variation in the surface topography of a transferred nanofilm with respect to the receiver thickness, loading angle, and loading rate. The results indicate that owing to the reduction of the tensile strain at the crack tip, the crack density in the nanofilm decreases when a thick elastomer, high loading angle, and low loading rate are applied during the transfer process. Furthermore, beyond the reduction in the tensile strain, the use of a rigid receiver generates a compressive strain at the crack tip, resulting in wrinkles in the nanofilm without cracks. The mechanisms of surface cracking and wrinkling are elucidated by analyzing the strain distribution at the crack tip via numerical simulation. We believe that this study can potentially contribute to advancements in mechanical transfer technology.

Responsive Structural Colors Derived from Geometrical Deformation of Synthetic Nanomaterials

Responsive structural colors generated by the geometrical deformation of synthetic nanomaterials with a periodic skeleton corresponding to light wavelength through interference, diffraction, and scattering are recognized as extremely valuable information conversion methods. However, there lacks systematic generalization regarding the responsive structural colors generated from the response deformation of micro–nano structures. In this review, the recent progress on synthetic structural color materials (SCMs) and their size effects on color conversion are summarized and discussed. Different deformable micro–nano structures, such as microspheres, inverse opals, surface wrinkles, nano‐/micropillars, layered stacks, and others, have been summarized. Their common feature is the variation in structural color produced by the deformation of nanostructures, but the difference lies in the deformation mechanism and response to stimuli. It is aimed to figure out the relationship and mechanism between stimuli deformation and the variable structural color of the corresponding nanostructures, inspiring the creation of the next generation of intelligent SCMs. Finally, perspectives on the development of responsive SCMs derived from the geometrical deformation of synthetic nanomaterials are presented. Several potential stimuli‐deformable micro–nano structures are discussed. It is believed that stimuli deformation is a powerful tool for the fabrication of high‐performance responsive SCMs to advance photonic technology.

Visual hydrogenation of palladium membranes on an elastic substrate and their applications in hydrogen sensing

AbstractThe study of metal‐hydrogen interaction is essential for hydrogen‐related applications. Due to the small permittivity variation of palladium (Pd), it is difficult to visualize its hydrogenation processes. Soft substrates can release the expansion stress of Pd membrane and form wrinkling during hydrogenation, which can be utilized to track the hydrogen diffusion. Here, we investigate the hydrogenation processes of Pd membranes with various shapes and sizes on polydimethylsiloxane (PDMS) substrates. It was found that the Pd membranes priorly wrinkles from the edges during hydrogenation and the saturation time of hydrogen absorption reduces with the decreasing size of Pd membranes. With these measurements, we fabricate a high‐performance optical hydrogen sensor consisted of a Pd nanostripe array on PDMS. Due to the transition from specular reflection to scattering during the surface wrinkling of the Pd nanostripe, when exposed to 4% hydrogen gas mixed with nitrogen gas, the sensor shows a high‐reflectance contrast of more than 800% with the absolute reflectance change exceeding 32% over the visible band, and the response time t90 is about 1.5 seconds. These results suggest that the Pd membranes on an elastic substrate is a promising platform for visualization of hydrogen diffusion and hydrogen detection.

Analysis of inhibition mechanisms of Streptococcus agalactiae by Siganus oramin L‐amino acid oxidase

In a previous experiment, an L-amino acid oxidase (LAAO) from the serum of Siganus oramin (SR) had a strong inhibitory effect on Streptococcus agalactiae. But we did not know inhibition mechanisms of SR-LAAO against S. agalactiae. In this study, after S. agalactiae was treated with SR-LAAO and hydrogen peroxide (H2O2) at the minimal bactericidal concentration, scanning and transmission electron microscopy showed that there are differences in cell size, degree of surface wrinkle and internal dissolution. These observations suggested that H2O2 can cause more serious damage to S. agalactiae than SR-LAAO. The metabolites of S. agalactiae that has been treated with SR-LAAO or H2O2 were analysed and compared. A total of 438 positive ion metabolites were detected and 129 were significantly different between SR-LAAO and H2O2. We detected 351 negative ion metabolites, of which 104 were significantly different. It should be noted that in the differential amino acid analysis, L-ergothioneine was the most significantly up-regulated amino acid in the H2O2 treatment group, which suggested that it may be related to the function of SR-LAAO. Direct mixing of L-ergothioneine and SR-LAAO did not extend the inhibition zone, which suggested that ergothioneine could not react directly with SR-LAAO, to enhance the antibacterial ability. However, the results of challenge experiments and the qRT-PCR experiment proved that ergothioneine can up-regulate the expression of SR-LAAO and reduce the mortality of S. agalactiae-challenged zebrafish. This study further revealed the antibacterial mechanism of fish LAAO and provided a foundation for future research.