Deformation Of Films Research Articles

UV ozone‐modified Fe3O4‐PDMS film for solvent‐driven soft actuators with controlled and multi‐stable deformations

AbstractIn recent years, solvent‐driven actuators have been capable of controlling deformations in response to external stimuli. However, a magnetic polydimethylsiloxane (PDMS) composite film with magnetic properties is traditionally developed using the micro‐electro‐mechanical system process. Although it has general actuation deformation, the composite film suffers from the problems of actuation and control. Here, this is done by co‐mixing PDMS and ferrosoferric oxide (Fe3O4) then waiting for curing and then undergoing ultraviolet‐ozone (UVO) surface treatment. By adjusting the time and orientation of the UVO treatment, a series of solvent‐driven actuators with multiform steady‐state structures (e.g., mono/bistable helix) is proposed. In addition, the deformation of the composite film under different geometrical parameters and surface constraints was visually predicted by incorporating finite element analysis methods. In addition, the controlled deformations of the composite film (such as box‐like, folded, and so on) are carried out by self‐morphing design. Finally, four bionic applications are also proposed to demonstrate the practical use of soft actuators based on Fe3O4‐PDMS films in bionic robots. This work provides new strategies for designing and fabricating programmable and controllable soft actuators and lays the foundation for a wide range of smart material applications.

Deformation Behavior of Microparticle-Based Polymer Films Visualized by AFM Equipped with a Stretching Device.

Understanding the structural changes and property alterations at the nanoscale and microscopic levels is critical to clarifying the deformation behavior and mechanical properties of polymer materials. Especially, in latex films composed of polymer nanoparticles, it is widely accepted that the remaining interfaces between microparticles in the film affect their brittleness. However, detailed information on nanoscale changes of latex films during deformation remains unclear due to technical difficulties in analyzing the microstructures under mechanical stress. In this study, we employed atomic force microscopy equipped with a uniaxial stretching device to visualize the surface structures of films composed of slightly cross-linked microparticles under elongation strain. The observations revealed that the latex film deforms in a nonaffine manner, which is attributed to the concurrent deformation of individual microparticles and the pull-out of interpenetration between them. Furthermore, by introducing a load-strain measurement mechanism to the stretching device, we compared the relationships between nanostructural changes, local property changes, and macroscopic deformation of microparticle-based films. The results suggest that loads are dominated by the deformation of microparticles and dissipate as the interpenetration of surface polymer chains between microparticles is pulled out.

Shape-Memory Property Acting as a Switch to Change the Surface Property of the Film

Shape-memory polyester films having functional groups were prepared and further grafted onto poly(N-isopropylacrylamide) (PNIPAAm) via atom-transfer radical polymerization. The grafting point of PNIPAAm was controlled by changing the composition of good and poor solvents. In the case of graft polymerization using only good solvents, the film swells, and polymerization proceeds not only from the surface but also from the internal polymerization initiation points. By increasing the proportion of poor solvents, PNIPAAm was grafted onto the surface of the film without swelling. The samples grafted to the interior regions of the film exhibited a decrease in the shape-memory recovery rate and recovery speed, whereas the samples grafted only to the surface of the film exhibited high shape-memory properties. Furthermore, contact-angle measurements revealed that the surface-grafted polymer exhibited changes in surface properties in response to film deformation. Because the deformation of the film is a large change, on the order of several millimeters, the deformation of the manually stretched film was shown to control molecular-level changes on the surface.

Ultrasensitive liquid sensor based on an embedded microchannel bulk acoustic wave resonator

The high-frequency and high-quality factor characteristics of bulk acoustic wave (BAW) resonators have significantly advanced their application in sensing technologies. In this work, a fluidic sensor based on a BAW resonator structure is fabricated and investigated. Embedded microchannels are formed beneath the active area of the BAW device without the need for external processes. As liquid flows through the microchannel, pressure is exerted on the upper wall (piezoelectric film) of the microchannel, which causes a shift in the resonant frequency. Using density functional theory, we revealed the intrinsic mechanism by which piezoelectric film deformation influences BAW resonator performance. Theoretically, the upwardly convex piezoelectric film caused by liquid flow can increase the resonant frequency. The experimental results obtained with ethanol solutions of different concentrations reveal that the sensor, which operates at a high resonant frequency of 2.225 GHz, achieves a remarkable sensitivity of 5.1 MHz/% (221 ppm/%), with an ultrahigh linearity of 0.995. This study reveals the intrinsic mechanism of liquid sensing based on BAW resonators, highlights the potential of AlN/Al0.8Sc0.2N composite film BAW resonators in liquid sensing applications and offers insights for future research and development in this field.

Effect of Epoxy Conductive Adhesive on Film Deformation During the Thermoforming Process for In‐Mold Electronic Devices

AbstractIn‐Mold Electronics (IME) is an innovative technology that allows the creation of 3D‐shaped electronic surfaces by combining printed electronics and In‐Mold Decoration (IMD). During the manufacturing process, the materials that integrate these devices, such as adhesive, must endure the transformation conditions of thermoforming. However, the adhesive rigidity may influence the deformation of the film during this process. In this study, both printed and hybridized samples are compared regarding their stretching and thickness reduction during the thermoforming process. The results indicate that the deformation of the hybridized samples differs from the printed ones, resulting in less stretching in areas near the adhesive, with stretching increasing as it steps away from where it is deposited. Thickness values are also affected, being greater around the adhesive and decreasing farther away. Therefore, the presence of the adhesive significantly impacts the behavior of the film during processing, a factor that must be considered in the design of IME devices to maximize the number of functional devices.

Analysis and Guideline for Determining Piezoelectric Coefficient for Films With Substrate Constraint.

Piezoelectric films including coatings are widely employed in various electromechanical devices. Precise measurement for piezoelectric film properties is crucial for both piezoelectric material development and design of the piezoelectric devices. However, substrate constraint on the deformation of piezoelectric films could cause significant impacts on the reliability and accuracy of the piezoelectric coefficient measurement. Through both theoretical finite element analysis (FEA) and experimental validation, here we have identified three important factors that strongly affect the measurement results: ratio of Young's modulus of substrate to piezoelectric film, ratio of electrode size to substrate thickness, and test frequency. Our investigations show that a relatively smaller substrate's Young's modulus to film, and a larger ratio of electrode size to substrate thickness would cause a larger substrate bending effect and thus potentially more significant measurement errors. Moreover, intense transversal displacement fluctuation can be excited at excessively high frequencies, leading to unreliable measurements. Various well-established piezoelectric measurement methods are compared with outstanding measurement issues identified for those commonly used piezoelectric films and substrates. We further establish the guidelines for piezoelectric coefficient measurements to achieve high reliability and accuracy, thus important to the wide technical community with interests in electromechanical active materials and devices.

Investigation on the creep mechanism of PA6 films based on quasi point defect theory

Polyamide 6 (PA6) films with significant α relaxation process was selected as the model system. The creep behavior and rheological mechanism during deformation in the amorphous regions of semi-crystalline polymers are systematically investigated by carrying out creep experiments. Based on the quasi point defect (QPD) theory, the complete physical process of PA6 film creep behavior from elasticity to viscoelasticity and viscoplasticity was analyzed and modeled from the perspective of structural heterogeneity. The results demonstrate that the creep deformation of PA6 film is a typical thermo-mechanical coupling and nonlinear mechanics process, and potential creep mechanisms corresponds to stress-induced local shear deformation enhancement and thermal activation-induced particle flow diffusion. The elastic-plastic transition involved in the creep deformation process of semi-crystalline polymer originates from the activation of quasi-point defective sites in the amorphous region, the expansion of sheared micro-domains and irreversible fusion. The generalized fractional Kelvin (GFK) model is proposed, and the physical meaning of parameters is explained by combining the quasi point defect theory and creep delay spectrum(L(τ)). Finally, the effectiveness of the GFK model and the QPD theory in studying the deformation behavior of PA6 films was validated by comparing experimental data with theoretical results, which theoretically reveals the structural evolution of PA6 film during creep process.

Analysis of Vibration Characteristics of Spatial Non-Uniform Tensioned Thin-Film Structures Based on the Absolute Nodal Coordinate Formulation.

Due to their lightweight characteristics, spatial thin-film structures can generate vibrations far exceeding their film thickness when subjected to external loads, which has become a key factor limiting their performance. This study examines the vibration characteristics of tensioned membrane structures with non-uniform elements subjected to impacts in air, leveraging the Absolute Nodal Coordinate Formulation (ANCF). This model takes into account the wrinkling deformation of thin films under pre-tension and incorporates it into the dynamic equation derived using the absolute node coordinate method. A detailed discussion was conducted on the influence of non-uniform elements, situated at different locations and side lengths, on the vibration characteristics of the thin film. The analytical results obtained from the vibration model were compared with the experimental results, validating the effectiveness of the vibration model. This provides a theoretical foundation for the subsequent vibration control of thin films.

Enhanced hydrate formation at the liquid CO2-brine interface with shear flow for solid CO2 sequestration

The hydrate-based CO2 sequestration provides an alternative solution for reducing CO2 emissions. However, the hydrate film that forms preferentially at the CO2-water interface can severely restrict hydrate conversion rate. How to enhance CO2 hydrate formation remains a crucial question. Here, we constructed static and shear flow contact models of liquid CO2 and brine in a cubic cavity and investigated their hydrate growth behavior at different subcoolings from perspectives of morphology and kinetics. For static contact, nucleation usually occurs at the CO2-brine interface, and high subcooling increases the degree of hydrate film wrinkling and the CO2 hydrate formation amount. The shear flow can delay the explosive growth of hydrates and tends to nucleate in bottom water; meanwhile, the continuous flow causes the overall extrusion deformation of hydrate film until the injection hole is blocked. Compared to static contact, this forced CO2-H2O contact caused by film deformation enhanced the CO2 hydration amount by 2.68–3.62 times at the subcoolings of 6.94–3.25 K. Increasing the flow rate can further delay hydrate appearance and enhance hydrate growth. We also speculate on the hydration patterns of CO2 in sediment pores under static and flowing conditions, and think that maintaining long-term flow can be an effective means to improve CO2 hydrate storage and prevent blockage occurring in the pore throat. Our work provides new insights into the growth behavior of CO2 hydrate for future CO2 storage in submarine sediments.

(Invited) In Situ and Operando Scattering Studies on Quantum Dot-Based Devices

Colloidal quantum dots (QDs) made e.g. of PbS are attractive for various optoelectronic applications due to their tunable band gap with a large absorption wavelength range from the visible to the near-infrared region. Moreover, due to the high intrinsic permittivity, the exciton binding energy of PbS is smaller than in cadmium chalcogenide QDs and polymer materials, which is beneficial for devices driven by charge carrier generation and transport, e.g. photovoltaics and photodetectors.In this work, we introduce wet chemical deposition methods beyond spin coating such as printing and spray deposition of QDs as a facile and potentially large-scale deposition method for high-performance photodetectors. The inner structures including the inter-dot distance of neighboring QDs and the structure, in the deposited QD solids, are studied by grazing-incidence small-angle X-ray scattering (GISAXS). In addition, the facet orientation of the QDs in the QD solids is characterized by grazing-incidence wide-angle X-ray scattering (GIWAXS). In particular, in situ GISAXS/GIWAXS studies during film formation are able to provide detailed information about the complex kinetic processes [1,2]. Operando GISAXS/GIWAXS studies on QD-based devices such as solar cells bring an in-depth understanding of the degradation mechanisms, which is key for improving the device stability and thereby bringing these novel materials into real-world applications [3]. Superlattice deformation in QD films on flexible substrates via uniaxial strain is followed in situ with GISAXS, providing a fundamental understanding of the impact of strain on the performance of flexible devices based on QD films, such as wearable electronics and next-generation solar cells on flexible substrates [4]. Nanoscale Horiz. 5, 880-885 (2020)Nano Energy 78, 105254 (2020)Energy Environ. Sci. 14, 3420-3429 (2021)Mater. Horizon 8, 383-395 (2023)

Novel flexible magnetoelastic biosensor based on PDMS/FeSiB/QD composite film for the detection of African swine fever virus P72 protein.

African swine fever (ASF) is a highly contagious and severe hemorrhagic disease caused by the African swine fever virus (ASFV). The continuous spread of ASFV affects the safety of the global meat supply; therefore, the establishment of sensitive and specific detection methods for ASFV has become an important hot spot in food safety. Herein, we developed a flexible magnetoelastic (ME) biosensor based on PDMS/FeSiB/QDs composite films for the detection of ASFV P72 protein. Based on the high luminescence performance of CsPbBr3 quantum dots and the excellent magnetoelastic effect of FeSiB, flexible ME biosensors convert stress signals generated by antibody-antigen-specific binding into optical and electromagnetic signals. The nanostructures covalently linked by quantum dots and PDMS provide biomodification sites for ASFV P72 antibodies, simplifying the functionalization modification process compared to the case of conventional biosensors. The deformation of the PDMS film is amplified, and the conversion of surface stress signals to electrical signals is enhanced by exposing the biosensor to a uniform magnetic field. The experimental results proved that the flexible ME biosensor has a wide linear range of 10 ng mL-1-100 μg mL-1, and the detection limit is as low as 0.079 ng mL-1. Moreover, the flexible ME biosensor also shows good stability, sensitivity and specificity, confirming the potential for early disease screening.

Contact/non-contact control of electromagnetic shielding performances of flexible graphite nanoplatelet/carbonyl iron-polylactic acid/carbonyl iron shape memory composite film

To cope with the complex electromagnetic interference and electromagnetic pollution environment, it is necessary to develop the electromagnetic interference shielding products with adjustable shielding efficiency. One of the solutions is to modulate the shielding efficiency by changing a shape of the products. In this work, the polylactic acid-graphite nanoplatelets Janus films with both high and modulated shielding efficiency were prepared by hot pressing method. The shape-memory organic polymer Polylactic Acid (PLA) was used as the base material, whose morphology can be adjusted by changing the ambient temperature. The highly conductive Graphite Nanoplatelets (GNPs) was used as efficient electromagnetic shielding layer. And, a small amount of carbonyl iron particles (CIP) was added into the Janus films to enhance the conductivity of GNPs layer, while realize the pre-deformation state of PLA layer under the non-contact magnetic force. As the GNPs layer thickness increased, the maximum electromagnetic shielding performance of the Janus film reached around 68 dB in the frequency range of 8–26.5 GHz. The surface temperature of the Janus film can be regulated by applying contact current and non-contact light irradiation, to realize the deformation of the Janus film. The electromagnetic shielding performance of Janus film can be manually adjusted to a certain expected value (10–50 dB) by controlling the applied current and irradiation time. The GNPs-PLA Janus films can be applied in complex electromagnetic environments and have enormous research value and development potential in the field of controllable electromagnetic interference shielding.

Simulating plate and shell structures with anisotropic resolution using adaptive smoothed particle hydrodynamics

When simulating plate and shell structures characterized by large aspect ratios, reduced-dimensional models are frequently employed due to their notable reduction in computational overhead in contrast to traditional isotropic full-dimensional models. However, in scenarios involving variations in the thickness direction, where adequate resolution in this dimension is required, reduced-dimensional models exhibit limitations. To capture variations in the thickness direction while simultaneously mitigating computational costs, an anisotropic full-dimensional model, integrated with an adaptive smoothed particle hydrodynamics method (ASPH), is developed for simulating behaviors of plate and shell structures in this study. The correction matrix, which is applied to ensure the first-order consistency, is modified accordingly by incorporating the nonisotropic kernel into it within the total Lagrangian framework of ASPH. A series of numerical examples, along with a specific application concerning the deformation of a porous film due to nonuniform internal fluid pressure in the thickness direction, are conducted to assess the computational accuracy and efficiency of the proposed ASPH method. Comparative analyses of our results against reference data and traditional isotropic SPH solutions demonstrate close agreements, affirming the suitability of the present ASPH method across various scenarios.

Analysis of Thermoelastic Contact of Gas-Lubricated Rough Sealing Faces.

Friction and wear are the main failure sources of face seals. When the surfaces of sealing rings exhibit greater roughness, the level of friction might increase and lead to sealing failure. Therefore, in this paper, based on the elastic contact hypothesis of rough and wavy surfaces and the influence of temperature on the elastic modulus of materials, a thermoelastic contact lubrication model of a gas-lubricated end seal is established. The novelty and advantage of this study is that it takes the effect of surface roughness into consideration during thermoelastic analysis of gas-lubricated seals. The film pressure, temperature, contact force and deformation of a gas spiral groove-faced seal are numerically determined. The influence of surface roughness on the contact distribution, deformation and temperature of the end-face seal at different speeds and pressures is analyzed. The film thickness increases as the rotational speed increases from 1 rpm to 2000 rpm, while the contact pressure sharply decreases from 0.25 kPa to 0. The analysis shows that the roughness contact mainly happens on the inner side of the rings due to convergent distortion of the seal faces, which easily causes partial wear of the seal faces. Moreover, it can also be found that the spiral grooves on the sealing surface can produce obvious hydrodynamic pressure effect due to the function of shear speed when the speed increases to 2000 rpm, while the film temperature increases from 293.3 K to about 306 K. The greater surface roughness results in a larger temperature rise under low-rotational-speed and lower-seal-pressure conditions, which further increases the risk of severe wear or even failure of the seal faces.

Bioinspired film-terminated ridges for enhancing friction force on lubricated soft surfaces

Enhancing friction force in lubricated, compliant contacts is of particular interest due to its wide application in various engineering and biological systems. In this study, we have developed bioinspired surfaces featuring film-terminated ridges, which exhibit a significant increase in lubricated friction force compared to flat samples. We propose that the enhanced sliding friction can be attributed to the energy dissipation at the lubricated interface caused by elastic hysteresis resulting from cyclic terminal film deformation. Furthermore, increasing inter-ridge spacing or reducing terminal film thickness are favorable design criteria for achieving high friction performance. These findings contribute to our understanding of controlling lubricated friction and provide valuable insights into surface design strategies for novel functional devices.

Mode Transition Of A Flexible Film Motion In The Circular Cylinder Wake

The fluid-structure interaction between a flexible film and the wake of a circular cylinder is an abstract of a series of natural phenomena like flag flapping and fish swimming. Diverse patterns of both solid deformation and fluid dynamics arise in this coupling system as the nondimensional parameters are varied. In our recent experiments, we find that beyond the extensively studied periodic coupling process, irregular processes also emerge in this system under specific conditions. However, due to the complexity inherent in the irregular coupling processes, no in-depth investigation into this topic is available yet. In this work, we delve into the irregular aperiodic flutter of a flexible film behind a circular cylinder in the uniform flow as well as the related irregular evolution of flow structures. Two representative cases of film streamwise length (L/D) pertinent to the irregular process, specifically L/D=3 and L/D=4, have been investigated experimentally in the wind tunnel with time-resolved synchronized measurements of both film deformation and flow field. Continuous wavelet transform and virtual dye visualization are employed to extract the time-frequency characteristics of film motion and Lagrangian coherent structures in the flow fields during the film’s irregular flutter, respectively. It is determined that the irregular flutter is aperiodic in terms of the overall view, but it also encompasses transient quasi-periodic stages as its motion modes alter. Hence, we term this irregular flutter as the “hybrid flutter” state. In the quasi-periodic stages of the hybrid flutter, the large-scale vortex structures are periodically formed on the surfaces of the film and evolve in the wake as a Kármán vortex street. The periodic formation of large-scale vortices exerts periodic alternating force on the film, which, therefore, leads to the quasi-periodic flutter of the film with the second-order mode. By comparison, the aperiodic stage entails the significant extension of the separated shear layers in such a way that the whole film is enveloped by the shear layers; then, large-scale vortices are formed downstream of the film’s trailing edge. In this scenario, no periodic force is acted on the film; as a result, the film flutters aperiodically with the first-order mode.

A mechanical nano sensor based on magnetic-mediated sensitization for 5-HT detection

The real-time detection of neurotransmitters had attracted more attention due to the potential to provide vital information for pathology research, disease diagnosis, and clinical efficacy evaluation. Here, a magnetic-mediated nano sensor was developed to improve sensitivity for detection of serotonin (5-HT). The PDMS membrane doped with magnetic particles serves as a conversion element, enhancing the deformation of the thin film caused by surface stress under the action of a magnetic field and amplifying the resistance response signal of the nano sensor. The 5-HT detection associated with neurotransmitter diseases serve as a proof of concept revealing the magnetic sensitization. The detection limit of the 5-HT was decreased to 3.21 nM in the linear range of 5–500 nM, which was lower than that of the nano sensor without magnetic field. The clinical 5-HT samples were also been accurately detected, indicating a positive application potential of the as-prepared magnetic-mediated nano sensor. All these results reveal the high sensitivity and practicality of the as-prepared magnetic-mediated nano sensor and provide a new method for neurotransmitter diseases diagnosis.

Effect of the dynamic contact angle on electromagnetically driven flows in free liquid films

We study the effect of a dynamic contact angle on an electromagnetically driven flow in a horizontal free electrolyte film stretched between two coaxial cylindrical electrodes and placed in a uniform magnetic field. The flow dynamics and film deformation are described using the reduced hydrodynamic model derived in the lubrication approximation in [A. Pototsky and S. A. Suslov, J. Fluid Mech., 984, A75 (2024)]. The linearized molecular kinetic model is used to relate the dynamic and static contact angles to the wetting-line friction coefficient. Steady azimuthal flow is found for arbitrary static contact angles. Linear stability of the base azimuthal flow with respect to azimuthally invariant perturbations is studied using the numerical continuation method. We find that the flow stability is highly sensitive to variations of the wetting-line friction coefficient and the static contact angle. The least stable azimuthal flow is found for the frictionless contact line corresponding to a free film that remains perpendicular to the surface of the electrodes. The azimuthal flows are found to experience a supercritical Hopf bifurcation upon which they transition to a stable oscillatory dynamic regime characterized by alternating squeezing and swelling of the film near the inner and outer electrodes.

Dynamics of sphere impact on a suspended film with glycerol and surfactant

Understanding the dynamics and inherent mechanisms of sphere impact on suspended films is important for improving sphere-film separation techniques. In this study, we conducted experiments to investigate the dynamics of sphere impact on suspended films and examine typical phenomena. We revealed the effects of dynamic viscosity and surface tension of films by altering the glycerol content (G) and the relative surfactant concentration (C*) and elucidated the characteristics of film deformation, sphere trajectory (hs), and contact time (tc). Moreover, we obtained the influences of sphere and film properties on bubble volume (Vbub) by analyzing force balance. The results indicate that three modes are observed and divided using the dimensionless energy parameter E* = Ek0/(ΔEfs + Evis) based on energy analysis, considering the sphere kinetic energy (Ek0), film surface energy increment (ΔEfs), and viscous dissipation (Evis): satisfying E* < 1, retention occurs; satisfying 1 < E* < 127.7(Ds/Df)2 (where Ds is the sphere diameter, Df is the film diameter), bubble entrainment passing appears; satisfying E* > 127.7(Ds/Df)2, non-bubble entrainment passing emerges. During retention, increasing G and C* causes film surface elasticity and hs to present a trend of first rising and then falling. For passing, the increase in G reduces deformability, leading hs to decrease, while increasing C* makes the film more susceptible to deformation, causing hs to increase. In addition, a film vibration period (τf) is introduced to measure tc, satisfying tc > 2τf for retention, while satisfying tc < τf/3 for passing. Inspection of the relationship between film deformation and falling height indicates that Vbub enlarges with increasing Ds and C* but shrinks with increasing G and release height Hs0.

Effect of plasticizers on the rheological properties of xanthan gum - starch biodegradable films

The effect of plasticizers, namely glycerol, sorbitol, and citric acid, on the structural and mechanical properties of biodegradable films obtained from xanthan gum (XG) and starch was studied. The plasticizing effect of glycerol, sorbitol, and citric acid on XG-starch films is justified by the destruction of intermolecular contacts between starch and XG macromolecules and the redistribution of hydrogen bonds in the system as a result of the hydrotropic action of plasticizer molecules. The use of glycerol proved to be the most effective for regulating the deformation of films, while the use of sorbitol to preserve strength. The dependence of the film roughness on the type and concentration of plasticizers was characterized. The smallest values of protrusions on the surface of XG-starch films were found in the presence of sorbitol. Considering the effect of the concentration of plasticizers on the stickiness of the surface of XG-starch films and their structural and mechanical properties, 1.5 % concentration of glycerol, sorbitol and citric acid was determined as optimal.