Stiff Film Research Articles

A simple route of providing a soft interface for PEDOT: PSS film metallic electrodes without loss of their electrical interface parameters

The work presents the development of a soft interface at PEDOT:PSS film without changing its electrical interface parameters. In the first step, PEDOT:PSS is electrodeposited on the commercial platinum electrode under the state-of-the-art conditions desirable for different electrochemical electrodes. Secondly, a pure hydrogel layer is deposited on the top of the electrodeposited PEDOT:PSS film under conditions that provide desirable mechanical properties (Young's modulus ∼10–20 kPa) and high permeability to ions from the solution. As a result, a PEDOT:PSS electrode with a soft interface desirable for different electrode applications is fabricated. The electrode exhibits electrical parameters at the same level as the state-of-the-art PEDOT:PSS film applied already for electrode applications. Moreover, the hydrogel layer additionally supports the polymeric film's electrochemical stability by inhibiting its oxidative degradation. The thickness of PEDOT film does not affect the overall electrochemical properties of the hydrogel electrode. The work shows that the specific choice of the hydrogel type and fabrication conditions allows to synthesis of the hydrogel interface on a stiff polymeric film, which does not block the ionic and electrical transfer. Moreover, the fabricated PEDOT:PSS electrode with hydrogel interface reveals interfacial impedance and potential window comparable or even better to the already published studies on PEDOT:PSS hydrogels.

Strong and tough semi-crystalline poly(aryl ether nitrile) with low coefficient of thermal expansion

The crystallization of poly (aryl ether nitrile) (PEN) has an essential impact on improving heat resistance, mechanical properties, chemical resistance, and dielectric properties. However, during the synthesis process, high crystallinity PEN is prone to precipitate out, which makes it difficult to carry out the synthesis reaction, which poses a significant challenge to synthesizing high crystallinity and high molecular weight PEN. In this work, hydroquinone (HQ) as the main phenolic monomer and 4,4′-biphenol (BP) as the second phenolic monomer were used to solve the technical difficulties in synthesis by copolymerization. The crystalline PEN with high molecular weight and significant crystallinity was obtained by regulating the molar ratio of BP to HQ. The effects of isothermal heat treatment on its crystalline, mechanical, and thermal properties were investigated. The influence laws of molecular chain structure and heat treatment process on the properties of PEN films were revealed. Among them, when the isothermal treatment temperature was 270 °C and the HQ: BP was 85:15, the mechanical strength reached 130 MPa, and the elongation at break could be up to an astonishing 50 %. Besides, the CTE value from 50 °C–150 °C is 40.84 ppm/°C, which is lower than most thermoplastics. Therefore, PEN with the HQ to BP molar ratio of 85:15 is suitable for large-scale production, providing new crystalline plastic specifications for high-performance special engineering plastics. A crystal bridge-tie chain model is summarized by the properties of HQ/BP-PEN films under different crystallization conditions, which provides an idea for preparing stiff and tough films.

Influence of a multilayer interlayer with a stiff core on the performance of laminated glass

Laminated safety glass is an important component of modern façade structures and is used when higher safety requirements are demanded. The interlayer increases the stiffness due to the available shear action, ensures the residual load-bearing capacity of the structure in the event of failure and holds broken pieces of glass in place. However, the stiffness and tensile strength of conventional interlayers such as EVA or PVB are known to strongly depend on time and temperature. This phenomenon is particularly critical for the behavior of glass panes during impact and after breakage when high tensile stresses occur in the interlayer. A film with higher stiffness, lower time and temperature dependence can be laminated between two layers of interlayer material to improve laminated glass behavior. Given the need to conserve resources and reduce weight, the question arises as to whether such an interlayer could also be used to meet the safety requirements for laminated glass made out of thin glass. In this study, the influence of a multilayer interlayer of EVA and a stiff core film of modified polyester (MPE) in glass laminates was examined. For this purpose, the material and composite behaviors were experimentally studied and evaluated. This article presents the test setup and the results. The focus is on comparing the properties of interlayers with and without MPE films. The results show that the impact strength of thin glass laminates is improved by the multilayer interlayer.

Dynamic Wrinkling Instability of Elastic Films on Viscoelastic Substrates

Abstract The dynamic instability of stiff films on compliant substrates has received sustained attention due to the potential applications in flexible functional devices. Film/substrate system-based devices are increasingly utilized under dynamic conditions, including dynamic sensors, tunable optical components, anti-fouling surfaces, etc. To better design the dynamic characteristics of devices based on film/substrate systems, it is essential to establish a comprehensive dynamic model and find out the deterministic and non-deterministic instability domains of nonlinear dynamic wrinkling under time-varying biased loads. In this paper, a multi-level coupling time-varying parameter excitation dynamic model for films bonded on Kelvin viscoelastic substrates is developed. The damping effect on the nonlinear dynamic responses of wrinkled film/substrate systems under step, slope and biased sinusoidal axial time-varying excitations are analyzed. We revealed and analyze the nonlinear dynamic behavior of film/substrate systems, which are significantly influenced by the excitation frequency and viscous coefficients of substrates. Various response forms, such as excitation-following deterministic responses, chaotic responses, and double-period resonant responses, are observed. We analyzed the parametric excitation induced dynamic bifurcation of the time-varying energy barrier that causes the nonlinear dynamic phenomenon, and provided deterministic and non-deterministic dynamic response domains. Based on the theory and results, methods for generating responses of specific types are proposed, offering theoretical guidance for designing dynamic characteristics of devices based on film/substrate systems.

Surface wrinkling of a film coated to a graded substrate

We study the surface wrinkling of a stiff thin elastic film bonded to a compliant graded elastic substrate subject to compressive stress generated either by compression or growth of the bilayer. Our aim is to clarify the influence of the modulus gradient on the onset and surface pattern in this bilayer. Within the framework of finite elasticity, an exact bifurcation condition is obtained using the Stroh formulation and the surface impedance matrix method. Further analytical progress is made by focusing on the case of short wavelength limit for which the Wentzel–Kramers–Brillouin method can be used to resolve the eigenvalue problem of ordinary differential equations with variable coefficients. An explicit bifurcation condition is obtained from which the critical buckling load and the critical wavelength are derived asymptotically. In particular, we consider two distinct situations depending on the ratio β of the shear modulus at the substrate surface to that at infinity. If β is of O(1) or small, the parameters related to modulus gradient all appear in the higher-order terms and play an insignificant role in the bifurcation. In that case, it is the modulus ratio between the film and substrate surface that governs the onset of surface wrinkling. If, however, β≫1, the modulus gradient affects the critical condition through leading-order terms. Through our analysis we unravel the influence of different material and geometric parameters, including the modulus gradient, on the bifurcation threshold and the associated wavelength which can be of importance in many biological and technological settings.

Theoretical and numerical analysis of period-doubling bifurcation in sandwich systems

Period-doubling bifurcation will appear when a stiff film is embedded into a compliant matrix or constrained to a soft substrate and undergoes in-plane compression. Though period-doubling bifurcation in bilayer systems have received extensive investigation, the mechanism of intricate post-buckling phenomena in sandwich systems remains an open question due to the inherent high nonlinearity. In this paper, a theoretical model for period-doubling bifurcation in sandwich systems is established and verified by finite element simulations. The proposed theoretical model is generalized to neo-Hookean materials and transformed into an equivalent nonlinear oscillator through an internal-to-external force transformation. Theoretical analysis reveals that an increase in the degree of up-down symmetry suppresses period-doubling bifurcation. Especially, when both the substrate and superstrate are identical, the influence of nonlinear deformation partly reflected by even high terms on the pressure difference on the film disappears, as a result, a novel period-doubling-like pattern appears due to the competitive effects from both sides strike a balance.

Natural resin as a biosource and bio-based plasticizer for edible resin/ethylcellulose composite film preparation.

Nowadays, finding natural and inexpensive resources that can be easily used to make food films has been considered. Despite the widespread use of synthetic resins, natural resins are rarely used. Opopanax resin (OR) was used in this study as a new biosource to prepare the hydrophobic edible film. Ethylcellulose (EC) was blended well with the resin, allowing the formation of a composite film. Film preparation was possible using different amounts of OR and EC. It was interesting that OR had a plasticizing effect on EC film. While using up to 33% w/w glycerol could not produce an elastic EC film, using only 8.5% w/w OR produced a stiff and flexible EC film with lower water sensitivity. Fourier transform infrared (FTIR) spectroscopy analysis showed that the strength of C-O-C and CH bonds in OR + EC film was higher than in EC film. Despite the higher water sensitivity of OR-based composite films than EC-based composite films, they had lower water vapor permeability (WVP) and higher contact angle due to their smoother and more homogeneous film structures with lower porosity, confirmed by scanning electron microscopy (SEM) images. The mechanical properties showed that the film with the highest resin content had the lowest tensile strength (~ 0.4MPa) and the higher elongation at break (~ 67%) and, therefore, the highest flexibility. The use of natural resins as a biosource is a promising approach in food packaging to prepare hydrophobic films with desirable mechanical properties.

A comparative study on the speed-up dynamics of drop spreading on floating and glass-supported polystyrene thin films

The enhanced spreading of a 2D drop on a stiff and free-standing elastic thin film theoretically investigated by Shanahan (Rev. Phys. Appl. 1988, 23, 1031–1037) has not been studied and verified experimentally. To shed a light on this interesting problem, herein, we perform comparison studies on the spreading behavior of a silicone oil drop on stiff polystyrene thin films supported by two different substrates: glass vs. water. Scaling analysis on the time evolution of the contact radius for the drop spreading on the films of varied thickness (∼40 nm to ∼600 nm) reveals the difference on the dynamics for the drop spreading on glass-supported and floating films. Upon fitting the spreading data by using the spreading model developed by de Ruijter et al. (Langmuir 1999, 15, 2209–2216), we are able to identify the speed-up effect for the drop spreading on water supported floating films, which progressively decreases with film thickness and diminishes when the thickness is greater than ∼200 nm. The elastic driving force that is responsible for the speed-up of the drop spreading on the floating film is evaluated empirically, which is found to decay exponentially with contact radius of the drop. The pre-factor and the decay length of the decay function are determined by film thickness and drop volume, resepctively. Our findings expect to facilitate developing new theories with practical relevance on the spreading dynamics of a liquid drop on elastic films.

Starch films loaded with tannin: the study of rheological and physical properties

Recently, the research on innovative food packaging has been oriented toward biodegradable materials to lower the environmental impact generated by conventional plastics. The films often carry functional additives interacting with the matrix and modifying its physical properties. In this work tannin, a scarcely exploited active additive, was used to obtain potato starch-based films, and its content was optimized on the basis of mechanical and microscopic tests. Rheological measurements were adopted to evaluate the tannin-starch interaction and the microstructure of the film forming solutions (FFSs). Their thickness, color, thermal conductivity, elastic modulus (Eel), elongation at break (EAB), surface wettability and water solubility were evaluated. Furthermore, microstructure was investigated through Fourier-transform infrared spectroscopy (FTIR), polarized light (POM) and scanning electron microscopy (SEM).It was observed that all FFSs behave as weak gels and tannin addition weakens the gel structure and decreases the gelatinization temperature from about 60 °C to 57 °C. Plastic and deformable films (Eel = 1.96 MPa and EAB = 189 %) were obtained at low tannin fractions, whereas, at a higher concentration, stiffer films (Eel = 12 MPa and EAB = 10 %), with hydrophobic behavior were produced. Among the tested tannin fractions, an intermediate value of 1.7 % (w/w) was found to be promising for industrial purposes.

κ-Carrageenan/poly(vinyl alcohol) functionalized films with gallic acid and stabilized with metallic ions

Given the environmental issues caused by the extensive use of conventional petroleum-based packaging, this work proposes functional films based on commercial κ-carrageenan (κc), poly(vinyl alcohol) (PVA), and gallic acid (GA) prepared by the “casting” method. Metallic ions in the κc composition stabilized the films, supporting processability and suitable mechanical properties. However, the incorporated GA amount (6.25 and 10 wt%) in the films created from an aqueous κc solution at 3.0 % wt/v (κc3) prevented crystalline domains in the resulting materials. The κc3/GA6.25 and κc3/GA10 films had less tensile strength (8.50 ± 0.61 and 10.28 ± 0.65 MPa) and high elongation at break (2.36 ± 0.16 and 1.19 ± 0.17 %) compared to the other samples, respectively. Low κc contents (κc2.5/GA6.25 and κc2.5/GA10) promoted stiff films and less permeability to water vapor (5.36 ± 0.51 and 3.76 ± 0.02 [×10−12 g(Pa × m × s)−1], respectively. The κc/GA weight ratio also influenced the film wettability, indicating water contact angles (WCAs) between 55 and 74°. The surface wettability implies a low oil permeability and high water swelling capacity of up to 1600 %. The κc/GA also played an essential role in the film's antimicrobial action against Staphylococcus aureus and Escherichia coli. Thus, the κc3/GA10 film showed suitable physical, chemical, and biological properties, having the potential to be applied as food coatings.

Novel Theories for Modeling the Surface Stabilization and Dendrite Suppression for Lithium-Metal Anode Based on Piezoelectric Effect

During electrodeposition, a small perturbation can cause the metal surface to lose its stability and form dendrite. Lithium dendrite is a key barrier that has impeded the commercialization of lithium metal batteries as well as fast charging. We find a piezoelectric mechanism to suppress dendrites, whose effect measured by over-potential can easily be 106 stronger than mechanically blocking dendrite with a stiff film. We first expanded the classical electrochemical reaction kinetics by incorporating the effect of stress and thin film piezoelectricity. We then developed a novel theory that couples the fields of electrochemistry, piezoelectricity and thin film mechanics. We then developed a rigorous stability analysis approach to reveal the effect of surface tension, mechanical blocking and piezoelectric mechanism on the stability of electrodeposition. We finally developed a theoretical expression of the critical wavelength, which provides useful guidance on achieving stable electrodeposition for various systems [1].We further developed a theory for a bulk porous piezoelectric medium which couples electrochemistry, piezoelectricity, and mechanics. Specifically, we derived a piezoelectric overpotential, which reveals a fundamental relation to surface charge density, dielectric property of the medium, electrolyte concentration and diffusivity, and the reaction coefficient. Our simulation results show that piezoelectric medium can effectively suppresses electrodeposition on any protrusion, leading to a flat, dendrite-free surface [2].

Biodegradable composite films based on mucilage from Opuntia ficus-indica (Cactaceae): Microstructural, functional and thermal properties

This study evaluated the feasibility of using cactus mucilage (CM) to elaborate biobased composite films blended with styrene-butadiene rubber latex (SBL). The CM was extracted and precipitated with ethanol (CMET) and isopropanol (CMIS). Mucilage-based films were formulated using three levels of mucilage (4, 6, and 8 wt%). The microstructure, thickness, moisture content, density, water contact angle, water vapor permeability, film solubility, thermal stability, and toughness of mucilage films blended with SBL (SBL/CMET and SBL/CMIS) were measured. The properties of mucilage-based films varied systematically, depending on the concentration of mucilage. The addition of SBL to CM film produces compatible, hydrophobic, flexible, and stiffer films with low moisture contents and good barrier properties. The mucilage film incorporated with 6 wt% CMET and CMIS reached the highest Young's modulus of 1512 ± 21 and 1988 ± 55 MPa, respectively. The DSC of produced films reveals that the Tg of SBL/CMIS is lower than that of SBL/CMIS. The synthesized films were structurally stable at high temperatures. The biodegradability of the composite films buried in the ground shows that the produced films are 100 % biodegradable after 40 days. Thus, CM blended with SBL can benefit specific applications, especially food packaging.

Highly Robust and Strain-Resilient Thin Film Conductors Featuring Brittle Materials.

Stretchable conductors with stable electrical conductivity under various deformations are essential for wearable electronics, soft robots, and biointegrated devices. However, brittle film-based conductors on elastomeric substrates often suffer from unexpected electrical disconnection due to the obvious mechanical incompatibility between stiff films and soft substrates. We proposed a novel out-of-plane crack control strategy to achieve the strain-insensitive electrical performance of thin-film-based conductors, featuring conductive brittle materials, including nanocrystalline metals (Cu, Ag, Mo) and transparent oxides (ITO). Our metal film-based conductors exhibit an ultrahigh initial conductivity (1.3 × 105 S cm-1) and negligible resistance change (R/R0 = 1.5) over wide strain range from 0 to 130%, enabled by film-induced substrate cracking and liquid metal-induced electrical self-repairing. They could function well under multimodal deformations (stretching, bending, and twisting) and severe mechanical damage (cutting and puncturing). We demonstrated the strain-resilient electrical functionality of metal film-based conductors in a flexible light-emitting diode display that shows high mechanical compliance.

Surface effects on the spherical indentation of biological film/substrate structures

Micro-/nano-indentation has been the most popular technique to extract the mechanical characteristics of biological cells and tissues. However, due to surface effects and the existence of substrates, conventional contact models are unable to determine the accurate elastic modulus of biological samples by analyzing the measured load-indent depth data. In this study, the spherical indentation of the film/substrate structure considering the surface energy and large deformations is investigated. The hyperelasticity of biological films and substrates is considered through neo-Hookean constitutive model, and the surface effect is incorporated using the finite element method. The explicit formulas for the relations between load and indent depth are presented for films with two orders of magnitude modulus mismatch to the substrate. It is found that the modulus mismatch between film and underlying substrate would lead to an overestimation of modulus for the film on a stiffer substrate, but an underestimated modulus for that on a softer substrate if the conventional Hertzian theory is directly adopted in the analysis. Moreover, for indentation at micro-/nano-scale, the surface energy would pronouncedly reduce the indent depth under a given load and lead to a seemingly stiffer film. Our results provide the explicit expressions to accurately predict the spherical indentation response of biological film/substrate structures.

Dextran-Chitosan Composites: Antioxidant and Anti-Inflammatory Properties.

This study presents the development of new formulations consisting of dextran (Dex) and chitosan (Ch) matrices, with fillings such as chitosan stearate (MCh), citric acid, salicylic acid, or ginger extract. These materials were characterized using Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and mechanical tests, and evaluated for antioxidant properties, including scavenging activities, metal chelation, and ferric ion reducing power, as well as anti-inflammatory properties, measuring the binding affinity between serum albumin and the bioactive substances, which can influence their bioavailability, transport, and overall anti-inflammatory effect. Compounds in ginger such as 6-gingerol reduce inflammation by inhibiting the production of inflammatory substances, such as prostaglandin, cytokines, interleukin-1β, and pro-inflammatory transcription factor (NF-κB) and, alongside citric and salicylic acids, combat oxidative stress, stabilizes cell membranes, and promote membrane fluidity, thereby preserving membrane integrity and function. Incorporating chitosan stearate in chitosan:dextran samples created a dense, stiff film with an elastic modulus approximately seventeen times higher than for the chitosan:dextran matrix. The Dex:Ch:MCh sample exhibited low compressibility at 48.74 ± 1.64 kPa, whereas the Dex:Ch:MCh:citric acid:salicylic acid composite had a compact network, allowing for 70.61 ± 3.9% compression at 109.30 kPa. The lipid peroxidation inhibitory assay revealed that Dex:Ch:MCh:citric acid had the highest inhibition value with 83 ± 0.577% at 24 h. The study highlights that adding active substances like ginger extract and citric acid to Dex:Ch composites enhances antioxidant properties, while modified chitosan improves mechanical properties. These composites may have potential medical applications in repairing cell membranes and regulating antioxidant enzyme activities.

Elastic moduli of polyelectrolyte multilayer films regulate endothelium-blood interaction under dynamic conditions

A broad spectrum of biomaterials has been explored in order to design cardiovascular implants of sufficient hemocompatibility. Most of them were extensively tested for the ability to facilitate repopulation by patient cells. It was shown that stiffness, surface roughness, or hydrophilicity of polyelectrolyte films have an impact on adhesion, proliferation, and differentiation of cells. At the same time, it is still unknown how these properties influence cell functionality and as a consequence interactions with blood components under dynamic conditions. In this study, we aimed to determine the impact of chemical cross-linking of Chitosan (Chi) and Chrondroitin Sulphate (CS) on endothelium-blood cross-talk. We have found that the morphology of the endothelium monolayer was not altered by changes in coating properties. However, free radical generation by endothelial cells varied depending on the elastic properties of the coating. Simultaneously, we have observed a significant decrease in the level of adhering and circulating active platelets as well as aggregates when the endothelium monolayer was formed on stiffer films than on the other coating variants. Moreover, the same type of films has promoted significantly higher adhesion of blood morphotic elements when they were not functionalized by endothelium. The observed changes in hemocompatibility indicate the importance of a design of coatings that will promote cellularization in vivo in a relatively short time and which will regulate cell function.

High internal phase emulsions and edible films with high methoxyl pectin and pea protein isolate or sodium caseinate

Structuring of sunflower oil by forming HIPEs in the presence of high methoxyl pectin (HMP) and pea protein isolate (PPI) or sodium caseinate (SC) was evaluated first. Initially, emulsions with protein: polysaccharide ratios of 2:1 and 6:1 and two different pectin concentrations (0.5 and 1% wt) were formed and compared with emulsions with just protein, with the former exhibiting greater viscosity and stability. All emulsions exhibited pseudoplastic behaviour with the higher biopolymer concentrations leading to increased emulsion viscosity. The type of protein was significant for stability only for the initial pectin concentration of 0.5% wt. Then, SC and PPI emulsions with a protein: polysaccharide ratio of 6:1 for both pectin concentrations were selected for HIPE formation. The formed HIPE for both proteins had a great oil loss (83–95%), showing that the used combination of biopolymers did not lead to the formation of a structured system. Subsequently, edible films formed by drying the aqueous dispersions of the previously selected protein-polysaccharide binary systems were studied. All films had the same density. The greater total biopolymer concentration led to thicker, heavier, stronger and stiffer films with greater water vapour permeability and opacity. SC films were thicker, heavier, stronger, stiffer and brighter than PPI films, with lower moisture content and opacity. Overall, the used protein affected the studied properties of the films, indicating differences in the formed network.

Buckling of a Stiff Thin Film Embedded Between Two Compliant Substrates

Layered structures consisting of stiff thin films and compliant matrixes are widely observed in flexible electronics, geology and composite materials. In this work, through analytic modelling and numerical simulations, we investigate the buckling instability of a stiff thin film embedded between two compliant substrates under uniaxial compression. Considering the shear stresses at the film/substrate interfaces and the finite geometry change of the film, the critical compressive strain, buckling wavelength and amplitude of sinusoidal wrinkles are analytically derived by the energy method. The analytic predictions agree well with the results obtained by finite element analysis. The post-buckling morphology may be sinusoidal or multiple-period, depending on the compressive strain and the modulus ratio of two compliant substrates. Our results aid in understanding the buckling of compliant substrate/film/compliant substrate tri-layer structures.

The effect of different molecular weight chitosan on the physical and mechanical properties of plasticized films

Packaging materials based on biodegradable polymers are a viable alternative to replacing conventional plastic packaging of fossil origin. The main two factors affecting functionality and performance are the molecular weight and the type of plasticizer used in these materials. The goal of this research was to modify unfractionated plasticized chitosan films to improve the physical and mechanical characteristics of the original unfractionated chitosan films. Chitosan extracted from local shrimp shells was zone-refined to produce five distinct chitosan fractions with molecular weights ranging from 1.089×105 to 5.605×105 g/mole. The unfractionated and fractionated chitosan films plasticized with 1:3 poly(vinyl alcohol) and 2:1 maleic acid were prepared by casting from their 2% acetic acid solutions. They were examined by FT-IR and were found to be comparable to the native chitosan spectrum, indicating that the primary backbone of the chitosan structure was unaltered. Therefore, the effects of molecular weight fractions and the type of plasticizer on the physical and mechanical properties were investigated. Examining the films’ surface topography by atomic force microscopy revealed that increasing the molecular weight of chitosan fractions from 2.702×105 to 5.605×105 g/mole affects the surface morphology of the chitosan: poly(vinyl alcohol) (1:3) film. This was accompanied by an increase in the surface roughness of the resulting film from 0.953 to 2.82, and for chitosan: maleic acid from 0.509 to 1.62. It was found that the tensile strength and Young’s modulus of the cast films decreased and the percent elongation at break of the plasticized fractionated chitosan films was increased, implying that less stiff films were obtained with fractionated chitosan. The outcome of this work suggests that the biodegradable fractionated chitosan blend film is a promising packaging material and that poly(vinyl alcohol) is the most suitable plasticizer for this formulation.

Buckling‐Pattern‐Based Characterization of Stiff Membrane on Soft Film

Stiff and soft bilayer systems are commonly used in industrial and biological applications. A classical stiff/soft bilayer film is an oxygen-plasma-treated polydimethylsiloxane (PDMS) film. After treatment, the PDMS film surface is oxidized, and then the stiff oxide surface layer and residual soft PDMS layer jointly constitute bilayer films, which are crucial materials in the fields of flexible electronics and buckling behavior studies. However, the oxidized surface layer is not properly recognized because of the complexity of the oxidization transition induced by the oxygen plasma. Here, its atomic composition and ratio are experimentally determined. A calculation approach to calculate its thickness and modulus based on the buckling behaviors of bilayer films is proposed. An accurate modulus of the oxide layer, 34.6 GPa, is obtained. Furthermore, this method can be used to characterize various stiff films in bilayer systems, which shows great potential for applications in many fields.