Wrinkle Morphology Research Articles

Computational model for tactile sensing system with wrinkle’s morphological change

ABSTRACTWe previously developed Wrin’Tac, a tactile sensing system that can select sensing modalities by changing its morphology. In this paper, we present a computational model to estimate a wrinkle’s morphology and predict the output of embedded sensing elements in both static indentation and sliding action cases. We evaluated the wrinkle shape and the posture of the sensing element by calculating its height. The wrinkle’s mechanical change is assessed by ascertaining its stiffness under vertical indentation by a spherical indenter. The output voltages of the sensor under static indentation are calculated by the proposed model, and the experimental values have error less than 10%, which validates the accuracy of our proposed model. For dynamic sliding action, this proposed model clarified the capability of wrinkle morphology in an evaluation of such sliding action’s characteristics as the sliding direction and velocity. We also identified the role of the wrinkle’s morphology in the sensor’s sensitivity under different conditions of dynamic sliding motion, implying that this sensing system may select suitable sensitivity for specific sensation tasks. We expect this work to pave the way for assessing the role of morphological changes to tactile sensation and developing soft active tactile sensing systems.

Morphology of wrinkles along the surface of turbulent Bunsen flames – Their amplification and advection due to the Darrieus–Landau instability

The morphological development of wrinkles along the surface of a Bunsen flame in a weakly-turbulent flow is investigated, with turbulence added solely to disturb the flame front. The resulting flame-flow interactions are examined using a hybrid Navier–Stokes/front-tracking methodology within the context of the hydrodynamic theory. Topological markers based on the skewness of curvature are introduced to distinguish between sub- and super-critical conditions, or the absence/presence of the Darrieus–Landau instability, respectively. We show that for sub-critical conditions disturbances created along the flame surface are dampened when convected downstream along the flame front, and the flame surface is only weakly perturbed. For super-critical conditions, on the other hand, disturbances of the flame front are amplified when advected downstream leading to a highly corrugated surface and a flame brush of increasing thickness. A measure of these dramatic changes is included in the mean local stretch rate which, when properly modulated by a Markstein length, directly affects the turbulent flame speed.

FRACTURE AND WRINKLE PATTERNS IN METAL FILMS DEPOSITED ON LIQUID MENISCUSES

Liquid meniscuses were prepared by spraying silicone oil drops with different sizes onto clean glass slides. Metal (iron) films with varied thicknesses were then deposited on the liquid meniscuses by direct current magnetron sputtering. The fracture and wrinkle behaviors of the films resulting from residual stresses are investigated in detail. It is found that cracks nucleate and propagate in the film during deposition owing to the thermal expansion of the liquid substrate. Subsequent cooling of the system creates a high compressive stress, resulting in the formation of various wrinkles in the film. The initiation and shape of the cracks are closely related to the film thickness and oil drop size. The wrinkle morphologies are dependent on the stress anisotropy induced by the liquid meniscus and crack edge.

One-step synthesis of bifunctional PEGDA/TiO2 composite film by photopolymerization for the removal of Congo red

Wrinkled structures can provide enlarged surface areas for some living organisms to ingest nutrients. Imitating biological wrinkle structures offers an efficient way to enhance the adsorption surface for removing hazardous pollutants in wastewater. In this work, poly-(ethylene glycol) double acrylate (PEGDA)/TiO2 composite film with tunable surface wrinkles was synthesized. TiO2 nanoparticles were evenly immobilized in the PEGDA hydrogel simply by a facile photopolymerization method within 700 ms. Various wrinkle morphologies were obtained by precisely controlling UV exposure time. The composite film was characterized by X-ray diffraction, scanning electron microscopy, diffuse reflection spectroscopy, etc. Congo red was chosen as a model pollutant to demonstrate the adsorption and degradation capacity of the composite film. The experimental results showed that the introduction of wrinkled polymer improved the dispersibility of TiO2 nanoparticles. The removal efficiency reached 100% after 180-min adsorption in the darkness and 180-min UV irradiation. The composite film exhibited a much higher enrichment and photocatalysis capacity than the pure TiO2 powder, and could be developed as a reusable film for the removal of the organic pollutants in wastewater.

Polydimethylsiloxane films engineered for smart nanostructures

Herein, we present organic molecular beam deposition to fabricate (sub-)micrometer-thin polydimethylsiloxane (PDMS) substrate-fixed films with a thickness homogeneity better than 2% on square centimeters. Their surface roughness and wrinkle morphology is controlled by the evaporation temperature, the growth rate, and the ultraviolet-light irradiation. The tailoring of the elastic modulus for the selected vinyl-functionalized PDMS nano-membranes is demonstrated. Both the surface morphology and mechanics are key parameters, which crucially determine the tissue-to-implant interactions for applications in bioelectronics. The cross-linked PDMS nano-membranes with elastic moduli of only a few hundred kPa are realized – a compliance similar to human soft tissues. The in situ characterization of their mechanical properties is presented based on their temperature sensitivity by spectroscopic ellipsometry and correlated to subsequently performed nano-indentation using a sophisticated atomic force microscopy instrument. Such soft sub-micrometer-thin elastomer membranes will become an essential component of dielectric elastomer transducers with strains comparable to human muscles, operated at the conventional battery voltages for future artificial muscles or skin implants.

Development and optimization of ciprofloxacin-loaded gelatin microparticles by single-step spray-drying technique

Polymeric particles are a versatile class of local or systemic drug delivery systems, used to improve drugs pharmacokinetics and pharmacodynamics along with patient compliance. Herein, we report a rapid, scalable, and optimized method to encapsulate ciprofloxacin (CPx), a poor water soluble antimicrobial agent, in gelatin microparticles by single step processing via spray-drying of an aqueous solution. The developed particles show mainly a wrinkle morphology with a unimodal distribution, with mean diameters ranging between 2 and 4 μm, depending on the processing conditions. The encapsulation of 1, 2 and 5 wt% CPx narrows the size distribution (1–3 μm). In vitro release experiments showed that up to 80% of encapsulated drug is released during the first 6 h, and the release kinetics was best fitted with the Korsmeyer-Peppas model, explained by the superimposition of drug diffusion and polymer chain relaxation. The minimal inhibitory concentrations against S. aureus and E. coli, obtained from pure and encapsulated ciprofloxacin, demonstrated that the spray-drying process does not inhibit the drug's bioactivity or the process feasibility. Thus, spray-drying of protein-drug particle systems is an advantageous method to produce microparticles with potential to lung delivery systems.

Structural hybridization of ternary (0D, 1D and 2D) composites as anodes for high-performance Li-ion batteries

We report herein on a novel structural hybridization strategy to synthesize a ternary composite (Fe,Co)3O4/Co3O4/rGO using a facile hydrothermal method for high-performance lithium-ion batteries (LIBs). In the as-fabricated hybrid structure, high-capacity (Fe,Co)3O4 sub-microparticles (zero-dimension) and Co3O4 nano-rods (one-dimension) are composited with highly conductive network of reduced graphene oxide (rGO) nano-sheets (two-dimension). Benefiting from the unique architecture, the volume expansion of (Fe,Co)3O4, Co3O4 during charging/discharging and their direct exposure to the electrolyte have been effectively alleviated by the spatially confining effects of rGO nano-sheets. On the other hand, the intrinsic wrinkle morphology of graphene nano-sheets was alleviated by the nano-rods support, leading to enhanced transportation mobility of electrons and ions. Furthermore, the formed hierarchical pores effectively increase the reaction sites and kinetics. As a result, the as-built electrode of the ternary composite shows remarkably cycling stability (1668.5 mAh g−1 for the first cycle and 80.97% capacity retention after 500 cycles at 1 A g−1) and rate capability (341.6 mAh g−1 at 10 A g−1), which are much superior to those of binary composites. The newly fabricated ternary composites as well as the structural hybridization strategy show great potentials in energy storage applications.

Fabrication of wrinkled graphene based on thermal-enhanced Rayleigh-Bénard convection for field electron emission

Graphene with atomic sharp edges have been widely studied to demonstrate that it is an ideal material for field electron emission (FEE). However, FEE performance of graphene film with wrinkled or crumpled tip-structures is still unknown. Here, we introduce a facile method to fabricate wrinkled graphene (WG) at the liquid-air interface. The graphene synthesized by chemical vapor deposition self-shrinks into WG on the surface of ethanol/deionized water solution. The morphology, height and distribution of wrinkles in WG can be conveniently controlled by modulating the vertical temperature gradient of the solution. According to the theoretical analysis, the self-assembly of WG is due to the energy transfer from the decreasing Gibbs free energy and the work done by Rayleigh-Bénard convection to the bending strain energy of WG. The substrate-independent formation of WG enables its direct transfer onto arbitrary hydrophilic surfaces to greatly enhance the hydrophobicity. Furthermore, the as-prepared WG shows more excellent FEE performance in comparison of the pristine graphene. The WG with higher wrinkles show a lower turn-on field, higher field enhancement factor and stable emission current. We believe that the method is potential to be universally applied in the manufacture of microstructures on other 2D materials for facilitating their practical applications.

Synthesis and characterization of nanocrystalline vanadium oxide thin films: electrochemical behavior by annealing in different atmosphere

Nanocrystalline vanadium oxide thin films were prepared using sol–gel dip-coating technique. The effect of heat treatment in different environment including air, N2, Ar, and O2 gas on the structural, optical, electrical, and electrochemical properties of nanocrystalline vanadium oxide thin films were investigated. The results indicated that the calculated average crystallite size was reduced by annealing in Ar environment. Scanning electron microscopy (SEM) images showed layered morphology on the surface of the film annealed in air atmosphere, whereas the film annealed under Ar and N2 ambient revealed granular and wrinkle morphology, respectively. This morphology altered to rather smooth surface by annealing in O2 environment. The optical bandgap of the films were found to be 1.75, 1.84, 2.08, and 2.10 eV annealed in air, O2, N2, and Ar environment, respectively. It was observed that the films annealed under Ar and N2 ambient had low resistivity (~ 0.2 Ω cm) and high carrier concentration, while the film annealed in nitrogen environment showed higher mobility of charge carrier. The electrochemical measurements showed that annealing under N2 ambient improved the intercalation of Li ions, leading a higher interfacial capacitance of 19.18 mF Cm−2, and decreased the charge transfer resistance due to surface defects created by heat treatment in nitrogen environment.

Voltage-Induced Wrinkling in a Constrained Annular Dielectric Elastomer Film

Wrinkles can be often observed in dielectric elastomer (DE) films when they are subjected to electrical voltage and mechanical forces. In the applications of DEs, wrinkle formation is often regarded as an indication of system failure. However, in some scenarios, wrinkling in DE does not necessarily result in material failure and can be even controllable. Although tremendous efforts have been made to analyze and calculate a variety of deformation modes in DE structures and devices, a model which is capable of analyzing wrinkling phenomena including the critical electromechanical conditions for the onset of wrinkles and wrinkle morphology in DE structures is currently unavailable. In this paper, we experimentally demonstrate controllable wrinkling in annular DE films with the central part being mechanically constrained. By changing the ratio between the inner radius and outer radius of the annular films, wrinkles with different wavelength can be induced in the films when externally applied voltage exceeds a critical value. To analyze wrinkling phenomena in DE films, we formulate a linear plate theory of DE films subjected to electromechanical loadings. Using the model, we successfully predict the wavelength of the voltage-induced wrinkles in annular DE films. The model developed in this paper can be used to design voltage-induced wrinkling in DE structures for different engineering applications.

Morphology and surface characteristic control of dimpled wrinkles using microscale water-soluble powders

We proposed a novel method for the morphological shape change of dimpled wrinkles using water-soluble powders to modify surface characteristics. Ultraviolet (UV)-curable resin was coated thinly on an aluminum plate and three water powders with 70, 100 and 200 μm in average diameters were dredged on each resin-layered plate. After a short exposure in UV light for less than 15 s on the plate and subsequent thermal curing, we observed microscale wrinkles with diverse morphological structures. Next, dimpled wavy structures were observed by dissolving water-soluble powders on the skin using water rinsing. Through experimental results, wrinkle morphology was affected by the powder size and resin layer thickness. Using this simple approach, various types of dimpled wavy structures can be realized and may be utilized in engineering applications, such as hydrophobicity control.

Controlling nested wrinkle morphology through the boundary effect on narrow-band thin films

We describe the formation of nested wrinkles created by the thermal mismatch between a narrow-band thin film and a compliant substrate. When a film is described as “narrow-band”, it literally means that the film band width is much shorter than its length; more precisely, it means that the width is comparable with the wavelength of the wrinkles. A silicon mask was used during film sputtering to create narrow-band films on poly (dimethylsiloxane) substrate, thus creating regular boundaries to steer local stresses and control wrinkle morphology. Disordered nano-scale wrinkles were found nested within highly ordered micro-scale sinusoidal wrinkles. The formation of nested wrinkles was explained through the amplitude and wavelength saturation of nano-scale wrinkles. The disordered morphology of nano-scale wrinkles and the highly ordered morphology of micro-scale wrinkles were explained by using the boundary effect.

Computer vision distortion correction of scanning probe microscopy images

Since its inception, scanning probe microscopy (SPM) has established itself as the tool of choice for probing surfaces and functionalities at the nanoscale. Although recent developments in the instrumentation have greatly improved the metrological aspects of SPM, it is still plagued by the drifts and nonlinearities of the piezoelectric actuators underlying the precise nanoscale motion. In this work, we present an innovative computer-vision-based distortion correction algorithm for offline processing of functional SPM measurements, allowing two images to be directly overlaid with minimal error – thus correlating position with time evolution and local functionality. To demonstrate its versatility, the algorithm is applied to two very different systems. First, we show the tracking of polarisation switching in an epitaxial Pb(Zr0.2Ti0.8)O3 thin film during high-speed continuous scanning under applied tip bias. Thanks to the precise time-location-polarisation correlation we can extract the regions of domain nucleation and track the motion of domain walls until the merging of the latter in avalanche-like events. Secondly, the morphology of surface folds and wrinkles in graphene deposited on a PET substrate is probed as a function of applied strain, allowing the relaxation of individual wrinkles to be tracked.

Dynamic pattern of wrinkles in a dielectric elastomer.

A membrane of a dielectric elastomer may undergo electromechanical phase transition from the flat to wrinkled state, when the applied voltage reaches a critical value. The wrinkled region is observed to expand at the expense of the flat region during the phase transition. In this paper, we report on a dynamic pattern of wrinkles in a circular membrane of a dielectric elastomer. During phase transition, both the flat and wrinkled regions move interchangeably in the membrane. The radial prestretch is found to significantly affect electromechanical phase transition. For example, a membrane with a small prestretch can exhibit a dynamic pattern of wrinkles, which is essentially related to snap-through instability. However, a membrane with a large prestretch undergoes continuous phase transition, without exhibiting a dynamic pattern. An analytical model is developed to interpret these experimental phenomena. Finite element simulations are performed to predict the wrinkle morphology, especially the coexistence of flat and wrinkled regions. Both the theoretical calculations and finite element simulations are qualitatively consistent with the experiments. Additionally, we observe another type of electromechanical behavior involving a dynamic pattern of wrinkles with different wavelengths. The membrane first undergoes continuous transition from the flat to wrinkled state, followed by discontinuous transition from one wrinkled state to another. These results may inspire new applications for dielectric elastomers such as on-demand patterning of wrinkles for microfluidics and stretchable electronics.

Biobased Wrinkled Surfaces Induced by Wood Mimetic Skins upon Drying: Effect of Mechanical Properties on Wrinkle Morphology.

We previously developed biobased wrinkled surfaces based on wood mimetic skins in which microscopic wrinkles were fabricated on a chitosan film by immersion in a phenolic acid solution, horseradish peroxidase-catalyzed surface reaction, and drying. Here, we prepared a diverse range of wrinkled films by immersion treatment at 30, 40, 50, and 60 °C in p-coumaric acid and then investigated the correlation between wrinkle morphology and mechanical properties. Wrinkle wavelengths gradually decreased as the immersion temperature increased as well as the previous report. In order to clarify the mechanisms responsible for the different wrinkle morphologies, the films were subjected to elastic moduli measurement and GPC analysis after immersion treatment. These experiments provided evidence that the chitosan around the film surface decomposed along with the immersion process. The decomposition was accelerated by higher immersion temperature, suggesting that higher temperatures led to the formation of softer skins, inducing smaller wrinkles. In fact, wrinkle morphologies with this system were predominately determined by the hardness of the wood mimetic skins. This phenomenon is consistent with the fundamentals of surface wrinkling in nature. This study is the first to demonstrate that artificial wrinkling triggered by water evaporation can be controlled by precise control of the surface hardness of soft material.

Wrinkling Non-Spherical Particles and Its Application in Cell Attachment Promotion.

Surface wrinkled particles are ubiquitous in nature and present in different sizes and shapes, such as plant pollens and peppercorn seeds. These natural wrinkles provide the particles with advanced functions to survive and thrive in nature. In this work, by combining flow lithography and plasma treatment, we have developed a simple method that can rapidly create wrinkled non-spherical particles, mimicking the surface textures in nature. Due to the oxygen inhibition in flow lithography, the non-spherical particles synthesized in a microfluidic channel are covered by a partially cured polymer (PCP) layer. When exposed to plasma treatment, this PCP layer rapidly buckles, forming surface-wrinkled particles. We designed and fabricated various particles with desired shapes and sizes. The surfaces of these shapes were tuned to created wrinkle morphologies by controlling UV exposure time and the washing process. We further demonstrated that wrinkles on the particles significantly promoted cell attachment without any chemical modification, potentially providing a new route for cell attachment for various biomedical applications.

Wrinkling of a thin film on a nematic liquid-crystal elastomer.

Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is subject to compression. Motivated by recent experiments [Agrawal et al., Soft Matter 8, 7138 (2012)]1744-683X10.1039/c2sm25734c that show how wrinkle morphology can be controlled by using a nematic elastomer substrate, we develop the theory of small-amplitude wrinkles of an isotropic film atop a nematic elastomer. The directors of the nematic elastomer are initially uniform. For uniaxial compression of the film along the direction perpendicular to the elastomer directors, the system behaves as a compressed film on an isotropic substrate. When the uniaxial compression is along the direction of nematic order, we find that the soft elasticity characteristic of liquid-crystal elastomers leads to a critical stress for wrinkling which is very small compared to the case of an isotropic substrate. We also determine the wavelength of the wrinkles at the critical stress and show how the critical stress and wavelength depend on substrate depth and the anisotropy of the polymer chains in the nematic elastomer.

Spontaneous wrinkling of soft matter by energetic deposition of Cr and Au

Wrinkling of stiff thin films deposited on compliant substrates is an effect that has been broadly investigated. However, wrinkling consequent to metal ion implantation has been less studied. In the work described here, we have explored the sub-micron wrinkling phenomena that spontaneously occur when metal ions (Au and Cr) are implanted with energy of a few tens of electron volts (49 eV for Au and 72 eV for Cr) into a compliant material (PDMS). This very low energy ion implantation was performed using a Filtered Cathodic Vacuum Arc technique, a process often referred to as energetic deposition or energetic condensation. For comparison, Au and Cr depositions with similar doses were also done using a sputtering technique (with lower particle energy of approximately 2 eV), and no wrinkle formation was then observed. In this way, we can discuss the role of ion energy in wrinkle formation. Depth profiles of the implanted material were calculated using the Tridyn computer simulation code for each metal, for several implantation doses. UV-vis absorption spectroscopy analysis confirmed the presence of metal nanoparticles. Atomic Force Microscopy imaging with spectral processing was used to compare the wrinkle morphology for each case investigated.

All-Solution-Processed Wrinkled Gold Nanoparticles As Sensors

Design and Methodology: Materials with feature sizes spanning the nano- and micro-scale range have been sought after by materials scientists and engineers to address specific functional demands unmet by bulk materials, in fields ranging from energy to sensors. Surface-enhanced Raman scattering (SERS) based sensors for molecular detection rely on nano- and micro-structuring of metallic substrates to amplify the intrinsically weak Raman signal, however fabricating SERS substrates can be tedious and time consuming. Our vision was to create a versatile and simple approach to fabricate SERS substrates. Wrinkling of a thin film on a compliant substrate is a rapid and inexpensive fabrication method for controllably creating materials with features covering several lengthscales.[1] Bioprocessing and biosensing devices have been fabricated using wrinkling with sputtered thin films,[2–4]however we sought to develop a method to create tunable wrinkled materials for SERS without the use of complex, vacuum-based deposition systems. First, a layer of gold nanoparticles was formed on an amino-silane treated heat-shrinkable substrate using self-assembly. Then, wrinkling of the nanoparticle layer was induced by heating the coated polymer substrate over its glass transition temperature, causing the footprint of the substrate to be reduced to 16% of the original area, while exerting a compressive force on the gold nanoparticle layer. The mechanical stress was relieved through the buckling of the gold nanoparticle layer on the surface of the substrate. Original Data and Results: The wrinkling behaviour of the gold nanoparticle film was assessed before shrinking, after shrinking uniaxially (by physically constraining two sides of the substrate), and after shrinking biaxially using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Well-ordered uniaxial and biaxial nanoparticle wrinkles were produced across the entire surface of the substrate. In order to control the wavelength and amplitude of the resulting wrinkles, nanoparticles of different diameters (~12 nm, ~18 nm, and ~36 nm) were deposited as the film layer. In addition, we assessed the effect of depositing multiple layers of ~12 nm nanoparticles on the resulting wrinkled structures. We observed that by increasing the diameter of the nanoparticles or by increasing the number of deposited nanoparticle layers, the wavelength and amplitude of the wrinkles could be controllably increased (Figure 1). These wrinkle structured nanoparticle surfaces were applied as SERS substrates, using 4-mercaptopyridine as the target analyte. By tuning the wavelength and morphology of the wrinkled structures, using different sized nanoparticles or multiple nanoparticle layers, the enhancement factor of the various SERS substrates was altered and optimized. Conclusions:We have developed a benchtop all-solution-processing method to create wrinkled metallic nano-/microstructures, tunable in size and morphology, on polymer substrates. By altering the nanoparticle diameters and number of deposited layers, we were able to control the amplitude and wavelength of the resulting wrinkled structures. Moreover, using physical constraints during the shrinking/wrinkling process allows for further regulation of the wrinkle morphology. We have demonstrated that these structures can used to create optical sensors as they were successfully applied as tunable SERS substrates to specifically detect a target analyte, and we envision these nanoparticle polymer composites finding other applications in chemical sensors, biosensors, and optoelectronics. [1] A. Schweikart, A. Horn, A. Böker, A. Fery, Adv. Polym. Sci. 2010, 227, 75. [2] S. M. Woo, C. M. Gabardo, L. Soleymani, Anal. Chem. 2014, 86, 12341. [3] C. M. Gabardo, A. M. Kwong, L. Soleymani, Analyst 2015. [4] A. Hosseini, L. Soleymani, Appl. Phys. Lett. 2014, 105, 074102. Figure 1

Hydrogen etching of chemical vapor deposition-grown graphene domains

In this paper we analyze the reason of the etching trenches in chemical vapor deposition (CVD) graphene domain and study the influence factor in the distribution and morphology of wrinkles. Graphene is synthesized on Cu substrate. The Cu substrate is annealed at 1050℃ for 60 min with 1000 sccm Ar and 200 sccm H2. After annealing, 500 sccm Ar, 20 sccm H2, and 1 sccm dilute CH4 (mixed with Ar) are introduced into the CVD system for graphene growth. Hydrogen etchings of graphene are conducted with flows of 500 sccm Ar and 200 sccm H2 at atmospheric pressure, and etching are performed at 950 and 1050℃. The striated and reticular etching trenches are observed after etching via optical microscope and scanning electron microscope. Every graphene domain is divided into island structures by these etching trenches. However, the edge of graphene domain is not etched and the size of domain is not changed. Electron backscatter diffraction (EBSD) is conducted to analyze the different morphologies of etching trenches. According to the EBSD analysis, the etching trench is closely associated with the Cu crystal orientation. Different Cu planes result in differences in mode, shape, and density of the etching trench. We conduct a verification experiment to judge whether the etching trenches are caused by the gaps between graphene and Cu substrate or by the hydrogenation of wrinkles. The graphene domains grown on Cu substrate with the same growth condition are etched immediately after growth without cooling process. We select graphene which grows across the Cu grain boundary, via optical microscope. A small number of regular hexagons are observed in graphene surface and the region of Cu boundary, but no etching trench is found. As the graphene growing across Cu boundary is the suspending graphene and there is no etching trench, we consider that the gap between graphene and Cu species is not a significant factor of forming etching trench. For comparison, the etching trenches are observed in the graphene domains with cooling process. Thus, the trench formation is bound up with the cooling process after growth, which can lead to the wrinkle formation on the graphene surface, giving rise to a large thermal expansion coefficient difference between the graphene and Cu species. As a major type of structural imperfection, wrinkles can show that enhanced reactivity is due to hydrogenation because of high local curvature. So we consider that the trench formation is caused by the hydrogenation of wrinkles. Then the as-grown graphene domains are transferred to SiO2 substrate and atomic force microscope (AFM) is employed to measure the surface appearance of graphene. The AMF image shows lots of wrinkles in the graphene surface. The morphology and density of wrinkles are similar to those of the etching trenches extremely. Thus, the AFM testing result provides another evidence to prove that the etching trenches are related to the hydrogenation of wrinkles. From the above we can draw some conclusions. Numerous trenches are observed in the graphene domains after etching, and the trench patterns are closely associated with the Cu crystal orientation. A different Cu crystal orientation leads to variations in mode, shape, and density of the etching trench. We prove that the etching trenches are caused by the hydrogenation on wrinkles formed in the cooling down process instead of the gap between Cu and graphene. This hydrogen etching technology is a convenient way to detect the distribution and morphology of wrinkles. Furthermore, it provides a reference for improving the quality of CVD graphene.