Deformation Of Films Research Articles

Capillary deformation of ultrathin glassy polymer films by air nanobubbles

Confined glasses and their anomalous interfacial rheology raise important questions in fundamental research and numerous practical applications. In this Letter, we study the influence of interfacial air nanobubbles on the free surface of ultrathin high-molecular-weight glassy polystyrene films immersed in water, in ambient conditions. In particular, we reveal the counterintuitive fact that a soft nanobubble is able to deform the surface of a rigid glass, forming a nanocrater with a depth that increases with time. By combining in-situ atomic-force-microscopy measurements and a modified lubrication model for the liquid-like layer at the free surface of the glass, we demonstrate that the capillary pressure in the nanobubble together with the liquid-like layer at the free surface of the glass determine the spatiotemporal growth of the nanocraters. Finally, from the excellent agreement between the experimental profiles and the numerical solutions of the governing glassy thin-film equation, we are able to precisely extract the surface mobility of the glass. In addition to revealing and quantifying how surface nanobubbles deform immersed glasses, until the latter eventually dewet from their substrates, our work provides a novel, precise, and simple measurement of the surface nanorheology of glasses.

Deformation and dewetting of liquid films under gas jets

Abstract

Mechanochromic LLDPE Films Doped with NIR Reflective Paliogen Black.

The perylene bisimide derivative Paliogen Black (P-black) is proposed as a new chromogenic probe that shows visible (vis) and near-infrared (NIR) responses after mechanical solicitations of host linear low-density polyethylene (LLDPE) films. P-black is reported to display strong absorption in the vis spectrum and unusual reflective and cooling features in the NIR region. Uniaxial deformation of the 2.5, 5, and 10 wt% P-black/LLDPE films yields a dichroic absorption under polarized light with color variations attributed by the computational analysis to the distinct anisotropic behavior of the transition dipole moments of P-black chromophores. When LLDPE films are deformed, P-black aggregates reduce their size from ≈30-40µm to ≈5-10µm that, in turn, causes reflectivity losses of about 30-40% at the maximum elongation. This gives rise to warming of 5-6°C of the locally oriented film placed in contact with a black substrate under the illumination with an IR lamp for 5 s. These features combined with the high sensitivity of the vis-NIR response toward mechanical solicitations render P-black as a new solution to detect uniaxial deformations of plastic films through both optical and thermal outputs.

Star topology increases ballistic resistance in thin polymer films

Polymeric films with greater impact and ballistic resistance are highly desired for numerous applications, but molecular configurations that best address this need remain subject to debate. We study the resistance to ballistic impact of thin polymer films using coarse-grained molecular dynamics simulations, investigating melts of linear polymer chains and star polymers with varying number (2≤f≤16) and degree of polymerization (10≤M≤50) of the arms. We show that increasing the number of arms f or the length of the arms M both result in greater specific penetration energy within the parameter ranges studied. Greater interpenetration of chains in stars with larger f allows energy to be dissipated predominantly through rearrangement of the stars internally, rather than chain sliding. During film deformation, stars with large f show higher energy absorption rates soon after contact with the projectile, whereas stars with larger M have a delayed response where dissipation arises primarily from chain sliding, which results in significant back face deformation. Our results suggest that stars may be advantageous for tuning energy dissipation mechanisms of ultra-thin films. These findings set the stage for a topology-based strategy for the design of impact-resistant polymer films.

Continuous mechanical tuning of plasmonic nanoassemblies for tunable and selective SERS platforms

The continuous tuning of plasmonic nanoassembly’s structure is the key to manipulate their optical and catalytic properties. Herein, we report a strategy of using macroscopic deformation to continuously tune the structure and optical activity of massive plasmonic nanoassemblies that are embedded in elastic polymer matrix. Plasmonic gold nanoparticles (Au NPs) are assembled to nanochains (Au NCs) with defined length and further embedded into polyvinylpyrrolidone (PVP) matrix. The nanostructure and plasmonic properties of massive Au NCs in this Au NCs-PVP film can be simultaneously and continuously tuned, simply by reversible mechanical deformation of this elastic film. In this way, the surface-enhanced Raman scattering (SERS) enhancement factor of this film as a SERS substrate can be mechanically modulated in the range of 100 to 6.8 × 107. Meanwhile, the PVP matrix also serves as a selective diffusion barrier to eliminate the fluorescence interference of large biomolecules, which enables the Au NCs-PVP film as a convenient SERS substrate for quick and direct analysis of small molecule analytes in biological samples and food, avoiding the complicate and time-consuming sample pretreatment process.

Theoretical modeling and experimental study of pressure fields of inclined airflow film

Air flotation rails are widely used in semiconductor production lines to produce an airflow film for handling components such as liquid crystal glass substrates. During transportation, the glass substrate deforms with a large curvature, which inclines the airflow film between each hole in the rail and substrate. This study theoretically and experimentally investigated the pressure field of an inclined airflow film. First, the radial velocity distribution of the inclined airflow film was derived, and a theoretical model of the radial velocity-dominated pressure distribution was developed that considered the inclination angle and central height of the film. Then, experiments were performed to measure the pressure fields of inclined airflow films with different inclination angles and central heights, and the results showed good agreement with the theoretical results. When the central height of the airflow film was fixed, the asymmetry of the pressure field increased as the inclination angle of the airflow film increased. On the other hand, when the inclination angle of the airflow film was fixed, the asymmetry of the pressure field decreased as the central height of the airflow film increased. Thus, considering the inclination angle of the velocity distribution can better embody the asymmetry of the pressure field of the inclined airflow film. These findings serve as important theoretical and experimental references for monitoring the deformation of airflow films.

Investigation on the creep behavior of PA6 film based on the fractional differential model

A fractional Burgers model was proposed to investigate the creep behavior of Polyamide 6 (PA6) film. The creep tests at various conditions were conducted on dynamic mechanical analysis (DMA) tester, and the strain-time ( ∊- t) curves of deformation were analyzed by the derived model. The results indicated that the fractional Burgers model had a better performance than the classical integer-order model in simulating the deformation of PA6 film. Parameters analysis showed that the stress facilitated the transformation from viscoelastic deformation to the viscoplastic one under ambient condition. Whereas, at the state of higher temperature, the deformation could be directly activated as the viscoplastic deformation. The softening effect of PA6 film was found to be related to the expansion of viscoplastic units during stretching. Also, the fluidity of the viscoelastic units was greater than that of the viscoplastic units. Through the analysis of dynamic rheological parameters, we speculated that the variation of loss factor may come from the evolution of viscoelastic units.

Temperature dependence of initial deformation and cracks of indium tin oxide film by quasi-continuous-wave laser irradiations

In this study, we investigated the temperature dependence of the initial deformation and cracks of indium tin oxide (ITO) thin films deposited on a fused silica substrate using a 1064-nm quasi-continuous-wave laser. We observed that the laser-induced morphology threshold of the film shows a dramatic thickness effect. The laser-induced morphology threshold of a 100-nm ITO film is four times that of a 300-nm ITO film. Initial laser-induced surface morphologies of the initial deformation and cracks will occur as long as temperature rises to about 520 K and 1250 K, respectively, irrespective of the thickness of a film. Experimental results indicate that a thin ITO film is more likely to tolerate laser irradiation because of lower absorptivity than a thicker ITO film. Studying the temperature effect helps clarify more about the laser annealing process, which is a promising process in improving the performance of the ITO films.

High temperature nanomechanical and nanotribological behavior of sub-5 nm nitrogen-doped carbon overcoat films

Elevated temperature tribological properties of ultra-thin nitrogen-doped carbon overcoat (NCOC) protective film for magnetic disks were investigated. NCOC with three different thicknesses (2.5, 3.5, and 4.5 nm) were examined in terms of both chemical and mechanical properties at temperatures up to 300 °C. The chemical changes were traced by XPS, revealing that the configuration of both carbon and nitrogen elements change partially from sp3- to sp2-hybridizations with exposure of NCOC samples to annealing. The friction coefficient, wear rate, and deformation of the NCOC films were measured using nanoscratch/wear experiments. Three sets of mechanical experiments verified the operating temperature and thickness dependence of the tribological behavior of the NCOC films. The NCOC samples show that the average wear depth is acceptably small after exposure to annealing, thus offering durable films for high temperature applications. Noteworthy, the permanent reduction in mechanical properties associated with annealing reduces in the presence of N dopants.

Effects of constituting material and interfacial crack on mechanical response of nanoscale metallic bilayers – a quasi-continuum study

ABSTRACT The effects of the constituting material and an interfacial crack on the deformation and mechanical response of metallic bilayer films under tension are studied using quasi-continuum simulations in terms of atomic trajectories, stress distribution and the stress–strain curve. The simulation results show that bilayer films with identical constituting monolayers have higher tensile strength than that of those with different monolayers. For bilayer films with different monolayers, the layer interface acts as a barrier that resists dislocation propagation. Dislocation emission at a crack tip blunts the tip. Necking originates at the layer interface and develops on monolayers with relatively low strength. A rectangular crack is less likely to develop than a V-shaped crack.

Emergence of Highly Linearly Polarized Interlayer Exciton Emission in MoSe2/WSe2 Heterobilayers with Transfer-Induced Layer Corrugation.

The availability of accessible fabrication methods based on deterministic transfer of atomically thin crystals has been essential for the rapid expansion of research into van der Waals heterostructures. An inherent issue of these techniques is the deformation of the polymer carrier film during the transfer, which can lead to highly nonuniform strain induced in the transferred two-dimensional material. Here, using a combination of optical spectroscopy, atomic force, and Kelvin probe force microscopy, we show that the presence of nanometer scale wrinkles formed due to transfer-induced stress relaxation can lead to strong changes in the optical properties of MoSe2/WSe2 heterostructures and the emergence of linearly polarized interlayer exciton photoluminescence. We attribute these changes to local breaking of crystal symmetry in the nanowrinkles, which act as efficient accumulation centers for interlayer excitons due to the strain-induced interlayer band gap reduction. Surface potential images of the rippled heterobilayer samples acquired using Kelvin probe force microscopy reveal variations of the local work function consistent with strain-induced band gap modulation, while the potential offset observed at the ridges of the wrinkles shows a clear correlation with the value of the tensile strain estimated from the wrinkle geometry. Our findings highlight the important role of the residual strain in defining optical properties of van der Waals heterostructures and suggest effective approaches for interlayer exciton manipulation by local strain engineering.

Formation of half-period surface relief gratings in azobenzene containing polymer films

We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45° relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films.

Microphysics of Inelastic Deformation in Reservoir Sandstones from the Seismogenic Center of the Groningen Gas Field

Physics-based assessment of the effects of hydrocarbon production from sandstone reservoirs on induced subsidence and seismicity hinges on understanding the processes governing compaction of the reservoir. Compaction strains are typically small (ε < 1%) and may be elastic (recoverable), or partly inelastic (permanent), as implied by recent experiments. To describe the inelastic contribution in the seismogenic Groningen gas field, a Cam–clay-type plasticity model was recently developed, based on the triaxial test data obtained for sandstones from the Groningen reservoir (strain rate ~ 10−5 s−1). To underpin the applicability of this model at production-driven strain rates (10−12 s−1), we develop a simplified microphysical model, based on the deformation mechanisms observed in triaxial experiments at in situ conditions and compaction strains (ε < 1%). These mechanisms include consolidation of and slip on µm-thick clay films within sandstone grain contacts, plus intragranular cracking. The mechanical behavior implied by this model agrees favourably with the experimental data and Cam–clay description of the sandstone behavior. At reservoir-relevant strains, the observed behavior is largely accounted for by consolidation of and slip on the intergranular clay films. A simple analysis shows that such clay film deformation is virtually time insensitive at current stresses in the Groningen reservoir, so that reservoir compaction by these mechanisms is also expected to be time insensitive. The Cam–clay model is accordingly anticipated to describe the main trends in compaction behavior at the decade time scales relevant to the field, although compaction strains and lateral stresses may be slightly underestimated due to other, smaller creep effects seen in experiments.

Switchable Wettability and Adhesion of Micro/Nanostructured Elastomer Surface via Electric Field for Dynamic Liquid Droplet Manipulation.

Dynamic control of liquid wetting behavior on smart surfaces has attracted considerable concern owing to their important applications in directional motion, confined wetting and selective separation. Despite much progress in this regard, there still remains challenges in dynamic liquid droplet manipulation with fast response, no loss and anti‐contamination. Herein, a strategy to achieve dynamic droplet manipulation and transportation on the electric field adaptive superhydrophobic elastomer surface is demonstrated. The superhydrophobic elastomer surface is fabricated by combining the micro/nanostructured clusters of hydrophobic TiO2 nanoparticles with the elastomer film, on which the micro/nanostructure can be dynamically and reversibly tuned by electric field due to the electric field adaptive deformation of elastomer film. Accordingly, fast and reversible transition of wetting state between Cassie state and Wenzel state and tunable adhesion on the surface via electric field induced morphology transformation can be obtained. Moreover, the motion states of the surface droplets can be controlled dynamically and precisely, such as jumping and pinning, catching and releasing, and controllable liquid transfer without loss and contamination. Thus this work would open the avenue for dynamic liquid manipulation and transportation, and gear up the broad application prospects in liquid transfer, selective separation, anti‐fog, anti‐ice, microfluidics devices, etc.

Evolution of defects, morphologies and fundamental growth characteristics of CVD diamond films induced by nitrogen addition

Diamond is a very promising material with exceptional properties for many high value-added applications especially due to the incorporation of impurities. As one of the most important impurities, nitrogen is widely found in natural and synthetic diamonds, and the control of nitrogen-related defects in diamond is definitely at the spotlight for its potentials in room temperature quantum applications. Since chemical vapor deposition (CVD) is one of the most promising techniques for diamond doping and realization of defect control, it is thus crucial to investigate the nitrogen impurities in as-grown CVD diamond. In this work, single-crystal diamonds were grown with different nitrogen concentration and the evolution of defects, morphologies and fundamental growth characteristics of the CVD diamond films was explored by various modern analysis and detection methods. It could be concluded that the introduction of nitrogen could result in an evident increase in supersaturation of the growth radicals at the growth interface, which would eventually distinctly promote the (100)-oriented diamond growth. In consequence, single-crystal diamonds of high crystalline quality and few carbonaceous impurities could be achieved at high growth rates with appropriate amounts of nitrogen addition. As the nitrogen concentration increased, the structure and content of the defects would evolve as well with the domination of point defects, probably leading to lattice deformation in the as-grown diamond films. The surface morphologies of the nitrogen-doped CVD diamond films could also be distinctly altered with the compromise between the development of step bunching process and the occurrence of two-dimensional growth, which would eventually lead to variations of the surface roughness and uniformity of the as-grown diamond films.

A fully sustainable, self-poled, bio-waste based piezoelectric nanogenerator: electricity generation from pomelo fruit membrane

A self-powered system is very much essential aspect in the recent trend to improve the working efficiency of the portable and wearable devices. Here, we have reported a fully sustainable, self-poled, bio-compatible, and bio-waste based piezoelectric energy harvester which has been made of Pomelo Fruit Membrane (PFM). PFM based piezoelectric generator (PFMBPEG) could generate ~ 6.4 V output voltage and ~ 7.44 μA output current directly, only by finger tapping on the device and registers a power density of ~ 12 μW cm−2 whereas, the same piezoelectric generator can generate ~ 15 V output voltage, 130 μA output current, and power density of ~ 487.5 μW cm−2 by using a full wave rectifier. The sensitivity and energy harvesting competence of the generator have also been assessed by attaching this nanogenerator into various parts of human body (as energy sources) such as wrist, elbow, finger, throat, jaws, leg and putting the device into ultrasonic bath and in every case, it could successfully generate voltage. Therefore, this bio-waste based energy harvester can be used as a power source for the different potable and wearable electronic goods where a small amount of energy is required, specifically in the biomedical applications (i.e., health monitoring, power source for the implantable devices and so on). Finally, mechanical stability the developed piezoelectric generator has been evaluated by cyclic bending test and it has been observed that there is no significant deformation of the PFM film even after 100 cycles.

Tensile behaviors of Ti3C2Tx (MXene) films

As the most representative member of a new emerging family of 2D material, titanium carbides or nitrides (MXenes), Ti3C2Tx and its 2D assembly format, Ti3C2Tx film, have displayed outstanding performance in a broad range of practical applications. However the mechanical behaviors of Ti3C2Tx films are rarely reported. We report a systematic study of the tensile behavior of Ti3C2Tx films. Ti3C2Tx films with various thicknesses (2–17 µm) were prepared by the vacuum filtration method. Quasi-static tension and cyclic tension tests were performed to investigate the deformation and fracture mechanism of Ti3C2Tx films. It was found that: (1) the relative sliding between Ti3C2Tx flakes is the dominant deformation mechanism of Ti3C2Tx films. Cyclic loading-releasing in tension suppresses the inter-layer sliding of Ti3C2Tx flakes effectively and thus the tensile strength of thicker Ti3C2Tx film (5 µm) film improves from 57 MPa to 67 MPa. (2) The mechanical properties of Ti3C2Tx films are found to be thickness dependent. When the film thickness increases from 2.3 to 17 µm, the tensile strength and elastic modulus drop from 61 to 36 MPa and from 17 to 8 GPa, respectively. This is interpreted as more structural defects presented in the through-the-thickness direction as film thickness is increased. (3) Moderate ultrasonication pretreatment (30 min) reduces the Ti3C2Tx flake size significantly while improving the compactness of the Ti3C2Tx film; and the resulting Ti3C2Tx film shows a linear stress-strain relationship without plastic-like deformation. As a result, the tensile strength of 5 µm thick Ti3C2Tx film is enhanced to 85 MPa; (4) Structural defects of the Ti3C2Tx film have significant effects on both the brittle-like fracture behavior and the distribution of tensile strength.

The shape and dynamics of deformations of viscoelastic fluids by water droplets

Many studies on the deformation of soft films by liquids confirmed the increase in the radius of the deformation and the decrease in the apparent contact angle. However, due to the thinness, the dynamics of the deformation could not be observed until the thermodynamic equilibrium. Thus, the dynamics on thick soft materials was studied until equilibrium to contrast the effect of different interfacial energy between different soft materials and water. Therefore, we prepared two different polymeric fluids with similar rheology by cross-linking monomers, yet with different contact angles with water. Sometime after water droplets were placed on these thick polymers, 3D profiles of the deformation were recorded. Though the effect of the surface tension was not verified, the same trend in the dynamics was observed as with thin films, except for the decrease in the radius after the initial increase. The three-phase boundaries (TPBs) were found not at the apex of the ridges formed during the transition to equilibrium. By calculating the surface tensions and angles of each interface at the equilibrium, we found that the temporary imbalance among surface tensions induced the slip of the TPBs toward the center of water droplets, thus dislocating the TPBs and decreasing the radius.

Phase composition, crystalline structure and piezoelectric properties of thin films of polyvinylidene fluoride obtained by the spin-coating method

The regularities of the formation of the structural state and the piezoelectric properties of PVDF films with a thickness of about 170 nm, obtained by spin-coating on glass substrates, are studied. Using the methods of IR spectroscopy, X-ray diffraction, and Raman spectroscopy, the dependences of the ratio of crystalline α- and β-phases on the initial acceleration and maximum substrate rotation speed are established. The optimal values of these parameters are found that provide the maximum concentration of the β phase (∼ 60 %) with spontaneous electric polarization. It was shown that in the films studied, the value of the piezoelectric coefficient d33, determined by the method of piezoresponse force microscopy, can take anomalously large values (up to 74 pm/V). This is due to the fixing effect of the glass substrate, which provides significant residual deformation of the polymer films.

Towards a Deeper Understanding of Creep and Physical Aging Behavior of the Emulsion Polymer Isocyanate.

Information of the relaxation behaviors of polymer film is crucial to judge the durability of emulsion polymer isocyanate (EPI) as a structural adhesive for bonding timber-based products. A sequence of tensile creep tests and free volume evaluation of the cured EPI adhesive films during isothermal condition were carried out by dynamic mechanical analysis and positron annihilation lifetime spectroscopy, respectively. It is the first time to explore the creep response and physical aging of the EPI film, as well as associated microstructural evolution. The results indicate that the creep characteristics of the glassy EPI coating intimately depend upon the crosslinker and elapsed time, and the ideal momentary creep master curve can be constructed in terms of modified horizontal shifting method. Furthermore, the relaxation process is found to be dominated by vacancy diffusion mechanism. In addition, increasing the polymeric isocyanate content can significantly enhance the resistance to creep deformation of EPI films, but also accelerate the physical aging process. Due to a higher packing degree of pure polymer films, the EPI films with aqueous emulsified isocyanate exhibit much better relaxation resistance compared to that with general isocyanate crosslinker.