Fabrication Of Polymer Films Research Articles

Influence of Initial Film Properties in UVO-Mediated Patterning of an Elastomeric Film Using a TEM Grid.

Ultraviolet irradiation of a cross-linked polydimethylsiloxane (PDMS) Sylgard 184 film in the presence of atmospheric oxygen (UVO) through a bare transmission electron microscope (TEM) sample holding grid is a rather simple and widely utilized technique for creating micropatterned surfaces. The surface oxidation of a Sylgard 184 film due to UVO exposure is associated with densification and the formation of a silica-like surface layer, which under a TEM grid happens only over the exposed areas of the film, resulting in a physicochemical pattern. It is known that the depth (hD) of the features depends on the duration of UVO exposure (tE). In this article, we show for the first time that hD also depends on the initial film thickness (hF) and the cross-linker percentage (CL, ratio of part A to part B) in a Sylgard 184 thin film. We show that for a specific tE, hD progressively decreases with the reduction in hF. On the other hand, hD shows a nonmonotonic dependence with CL, resulting in patterns with maximum depth for CL ≈ 10.0%. We attribute this observation to the combined effect of resistance against the penetration of the propagation front by the rigid substrate as well as stress relaxation within the exposed parts of the film below the propagating front in films with higher CL values leading to the variation of hD. The observation reported here would allow the potential fabrication of polymer films with physicochemical patterns with feature height on demand by a one-step, facile technique.

R2R‐Based Continuous Production of Patterned and Multilayered Elastic Substrates with Liquid Metal Wiring for Stretchable Electronics

AbstractThe roll‐to‐roll (R2R) process for fabricating elastic substrates is essential for the social implementation of next‐generation stretchable devices with soft interfaces. In recent years, there is a growing demand for soft heterostructures with multiple monolithically patterned organic materials. However, a continuous processing technique for substrates with heterostructures patterned using highly stretchable wiring has not yet been developed. Conventional manufacturing methods for stretchable electronics lack production capacity. This study introduces an R2R‐based method for the continuous production of multilayered substrates composed of various elastic materials, integrated with liquid metal (LM) wiring, suitable for stretchable electronics. Continuous fabrication of polymer films is achieved with pattern areas as small as 0.78 mm2, using three different polymers varying in hardness. The R2R coating process, paired with liquid metal wiring dispensing printing, allows for the creation of lines as fine as 140 microns. This process supports the batch production of 15 stretchable hybrid devices at a time and enables the creation of large‐area devices up to 400 cm2. The fabrication technique developed herein holds promise for the future manufacturing of not only stretchable electronics but also cutting‐edge soft electronics like smart packaging. This is expected to be a factor leading to the commercialization of stretchable electronics.

НАБУХАНИЕ ПОЛИУРЕТАНОВЫХ ПЛЕНОК НА ОСНОВЕ АМИНОЭФИРОВ БОРНОЙ И ОРТОФОСФОРНОЙ КИСЛОТ В ВОДНЫХ РАСТВОРАХ СПИРТОВ

In this work we have carried out studies to determine the sorption capacity (swelling) of polymer polyurethane films based on amino esters of boric and orthophosphoric acids in pure components (water, isopropyl and ethyl alcohols) and water-alcohol mixtures (isopropanol-water, ethanol-water) at temperatures of 22, 40 and 60 °С. On the basis of the data on the sorption capacity of components through polymer films a preliminary assessment of the prospects of using the investigated polymers as a selective layer of pervaporation membranes is made. The changes in the volume-mass concentration of low-molecular-weight components in polymer films depending on the solvent concentration in the initial mixture and the temperature of the process have been determined experimentally. The obtained data are necessary for creating a mathematical model of the pervaporation separation process. The paper describes the developed methodology for the fabrication of polymer films based on amino esters of orthophosphoric and boronic acids. Hyperbranched polyols with high solubility and low characteristic viscosities were used as crosslinking agents in the synthesis of the studied polymers Experimental studies for water-alcohol mixtures were carried out in a wide range of alcohol concentrations (0-99 wt.%). The swelling dynamics of polymer films in water-alcohol mixtures and individual components were measured. For all films, a tendency of decreasing volume-mass concentration with increasing process temperature in isopropyl alcohol and water can be seen, but in ethyl alcohol the volume-mass concentration increases with exceeding the process temperature.

A Photomechanical Film in which Liquid Crystal Design Shifts the Absorption into the Visible Light Range.

Liquid crystalline polymer networks (LCN) with azobenzene monomers bend reversibly under UV-light irradiation, combining photomechanical and photothermal effects. However, the harmful nature of UV-light limits their use in biology and soft robotics. Although visible light-absorbing tetra-ortho-fluoro-substituted azobenzenes exist, liquid crystalline monomers have never been prepared. Previously, such azobenzenes were added as photoactive additives (up to 10%) to otherwise passive liquid crystalline polymer networks. In this work, a molecular design of a liquid crystalline, polymerizable azobenzene switchable by visible light is presented. The monomer assembles in a highly fluid nematic phase, but polymerizes in a layered smectic C phase. The films are produced solely from the monomer without additional liquid crystalline components and are actuated with visible light. Bending experiments in air and under water differentiate photomechanical and photothermal effects. Remarkably, a 60µm splay aligned film maintains its deformation for hours, slowly reverting over days. Monomer liquid crystallinity is characterized using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and polarized optical microscopy (POM); polymer films are analyzed using WAXS and DSC on a homogeneously aligned film. The synthetic procedure is high yielding and polymer film fabrication is scalable, which enables the use of safe and efficient photomechanical LCNs in soft robotics, engineering and biology.

Facile fabrication of ultrastrong polyethylene nanocomposite films with low filler content via flow-driven graphene re-dispersion assisted crystallization

Fabrication of polymer films with superb mechanical properties is far from mature compared to that of fibers, hampering the further engineering applications of lightweight polymer materials. Herein, high density polyethylene (HDPE) films reinforced with re-dispersed or refined reduced graphene oxide (rGO) are prepared via a facile melt-stretching strategy. The incorporation of only 0.2 wt% rGO is demonstrated to endow the melt-stretched film (80× stretch ratio) with ultrahigh Young's modulus of 2.9 GPa and tensile strength of 162.2 MPa, which are comparable to many engineering plastics and also significantly superior to the existing HDPE/graphene composites. More importantly, these modulus and strength values are increased by 71 and 65% compared to the neat PE (80×), respectively, far more than the theoretical prediction with the mixing rule. Experimental characterizations indicate that the high-efficient mechanical enhancement is attributed to the strong synergy of melt stretching-driven crystallization and rGO re-dispersion or refinement in constructing the compact and robust shish-kebabs crystal network. Such microstructural characteristics greatly promote the load transfer along the covalently bonded molecular chains, and also from polymer to rigid fillers under loading. Furthermore, the excellent puncture resistance and thermo-mechanical properties of PE/rGO films have been demonstrated. This work provides a feasible way towards scalable manufacturing of high-performance polymer nanocomposite films from general plastics and carbonaceous nanomaterials.

Analyzing STEM Students’ Critical Thinking Performance: Literacy Study on the Polymer Film Fabrication Process Irradiated with Gamma Rays

The reliability of pedagogical practice is highly dictated by how it enhances science, technology, engineering, and mathematics (STEM) students’ critical thinking achievement. Adequate pedagogical practice is thus needed in line with the demands of STEM learning in the 21st century, namely achieving optimal critical thinking. This paper reports this pedagogical practice on a topic of polymer film fabrication irradiated with gamma rays. The specific objective was to analyze STEM students’ critical thinking performance in literacy of the aforementioned topic. It is an exploratory study with an experimental method. Only one treatment group was involved, they were STEM students attending the Material Physics Courses. By employing valid critical thinking instruments and adequate methods of analysis, the findings show that literacy on the assigned topic significantly improved STEM students’ CT skills. It was proven that the mean scores of CT indicators have increased in all aspects of the CT assessed. The statistical analysis confirmed that there were significant differences in the CT skills of STEM students between the observations before and after the learning process intervention. The implication of this study is that pedagogical interventions integrated with studies on advanced material modification technology could be effectively used for creating inspiring STEM learning, especially for training STEM students’ critical thinking ways.

Numerical study on oblique stretching of viscoelastic polymer film

• Numerical format for oblique stretching of viscoelastic film is established. • The application scenarios of the membrane hypothesis are expanded. • Detailed numerical procedure and a complete numerical case are provided. • The influence of the y -direction stretching on thickness uniformity is investigated. Oblique stretching is a special approach for the fabrication of polymer film whose product is mainly used in the optical display field, such as compensation films, retardation films, et al. Nonetheless, the previous research reports on oblique stretching processing are still lacking, and the related numerical research is almost blank. This contribution uses the FEM (finite element method) to simulate the oblique stretching process of viscoelastic polymer film for the first time. The differential viscoelastic PTT (Phan-Thien and Tanner) model, one of the most realistic constitutive models is chosen. Furthermore, the polycarbonate melt was rheologically characterized and used as input material parameters in our simulations. Based on the membrane hypothesis and stabilization algorithms like DEVSS (discrete elastic viscous stress splitting), the specific numerical scheme is derived and the algorithm implementation is summarized. Finally, a complete numerical example of oblique stretching is demonstrated and compared with symmetric stretching. Based on the simulation results, the evolution of thickness and the influence of the y -direction stretching on thickness uniformity are further investigated.

PCPDTBT copolymer based high performance organic phototransistors utilizing improved chain alignment

Abstract In this article, we report single component thin film based organic phototransistors (OPTs) developed using the novel ribbon-floating film transfer method (ribbon-FTM). A low band-gap copolymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) has been employed to develop the photoactive thin films of the devices. The fabricated polymer films were highly anisotropic in nature. To investigate the effect of film anisotropy on the device performance, organic field effect transistors (OFETs) were fabricated in two configurations namely, parallel and perpendicular, wherein the polymeric chains were oriented in line and orthogonal to the transistor channel direction, respectively. Notable differences in charge carrier mobility and device on-off ratios were observed among the two sets of devices. An on-off ratio of 4.1 × 103 and an average mobility of 0.001 cm2/V were observed in case of the perpendicular oriented OFETs which were increased to 105 and 0.003 cm2/V for the parallel oriented OFETs. A probe into the contact resistance at the respective metal/polymer interfaces of the devices was carried out using the modified transmission line method (MTLM). 4 times lower contact resistance was observed in the parallel OFET which was anticipated to be responsible for its superior performance. Further, the fabricated devices were illuminated with monochromatic red light (Pin = 0.4 mW/cm2) to observe their performance as phototransistors. Appreciable values of photosensitivity (2 × 104) and photoresponsivity (17.6 A/W) were obtained for the parallel OPTs which were found to be much higher than those of the previously reported thin film based OPTs employing other materials fabricated through conventional film coating techniques. The results presented in this report are of key significance towards the development of highly sensitive and cost-effective phototransistors which can be used in opto-sensing and imaging applications.

Pearl-inspired polymer films with chiral nematic and multi-lamellar structures

ABSTRACT Structural coloured materials have been widely found in nature. More and more artificial materials were created based on structural colour. However, fabrication of polymer films with pearly lustre remains a challenging task. Herein, a strategy is reported to prepare broadband reflection polymer films based on the fluorophilic association. A monomer with a perfluorooctyl chain is synthesised. After photo-crosslinking a mixture of a chiral nematic liquid crystal and the fluorinated monomer, broadband reflection film with pearly lustre is obtained. The broadband reflection originates from the broad distribution of the helical pitch. The pearly lustre is caused by the periodically ordered layers formed by the microphase separation between hydrocarbon and fluorocarbon chains.A strategy for the preparation of color liquid crystal polymer film with pearly luster is developed. The Bragg-reflection color originates from the supramolecular helical structure of the cholesteric liquid crystal and the pearly luster originates from the multilayer structure formed by the fluorocarbon/hydrocarbon microphase separation

Tunable and Responsive Structural Color from Polymeric Microstructured Surfaces Enabled by Interference of Totally Internally Reflected Light

This report describes a straightforward and versatile approach to the fabrication of polymer films composed of microscale dome or well features that create structural color by interference from tot...

Tuning cavitation and crazing in polymer nanocomposite glasses containing bimodal grafted nanoparticles at the nanoparticle/polymer interface.

It is widely accepted that adding nanoparticles (NPs) into polymer matrices can dramatically alter the mechanical properties of the material, and that the properties at the NP/polymer interface play a vital role. By performing coarse-grained molecular dynamics simulations, we study the stress-strain behaviour of polymer/NP composites (PNCs) in a glassy state under a triaxial tensile deformation, in which the NPs are well dispersed in the system via bimodal grafting. A 'HOMO' system, in which the short grafted chains are chemically identical to the matrix polymer, and a 'HETERO' system, in which the short grafted chains interact weakly with the matrix, are investigated. Our simulations demonstrate that the HOMO system behaves very similarly to the pure polymer system, with quick cavitation and a drop in stress after the yielding point, corresponding to a craze deformation process. While in the HETERO system, weak interactions between the short grafts and the matrix polymer induce a low local modulus, therefore, rather homogeneous void formation and consequently a slower cavitation process are observed at the surface of the well dispersed NPs during the tensile deformation. As a result, the depletion effect at the NP surface eventually leads to NP re-assembly at large strains. Moreover, the HETERO system undergoes a shear-deformation-tended tensile process rather than the craze deformation found in the HOMO system. At the same time, the HETERO system is more ductile, with a much slower drop in stress after yielding than the HOMO system. In addition, the homogeneous generation of voids at small strain in the HETERO system can be utilized in the fabrication of polymer films with desirable separation abilities for gases or small molecules. We hope that these simulation results will be helpful for the property regulation of PNC materials containing polymer grafted NPs.

Hierarchical honeycomb-patterned polydimethylsiloxane films with tunable nanostructures

The preparation of hierarchical nanoporous films is of great significance for their potential applications, but the development of a facile method to synthesize such films method remains a great challenge. In the current work, hierarchically honeycomb-patterned polydimethylsiloxane (PDMS) films with unique nanostructures were synthesized by simply depositing an acid solution, specifically consisting of a mixture of H2SO4, HNO3, and DI water, on PDMS films displaying regular concave structures. During the post-processing, secondary extrusions were generated on the surfaces of such PDMS films, leading to the formation of highly hierarchical honeycomb-shaped patterns. In the synthesis, the composition of the acid solution played a critical role in the formation and growth of the secondary extrusions. The morphological evolution of the PDMS films during the post-processing proceeded along different pathways depending on the experimental conditions of the process. Based on our results and observations, a plausible mechanism explaining the formation of the hierarchical honeycomb-shaped patterns and the morphological evolution during the synthesis was proposed. The developed approach provides a simple route for fabricating polymer films with unique hierarchical honeycomb-shaped patterns and without the need for any expensive or sophisticated lithographic patterning instruments.

Isomerization behavior of spiropyran-based compounds upon X-ray irradiation

We investigated the isomerization behavior of 1,3,3-trimethylindolino-6’-nitrobenzopyrylospiran (6-nitro BIPS) upon X-ray irradiation with the aim of developing tissue equivalent imaging sensor materials. We fabricated polymer films incorporated with 6-nitro BIPS. Also, we investigated the effect of the addition of the organic phosphor, b-PBD. Increase in the absorbance at 580 nm was observed at X-ray irradiation doses in the range 1–20 kGy. The increase of the absorbance as function of the dose is enhanced 1.5 times by the addition of b-PBD at 5.0 wt%. These results indicate that 6-nitro BIPS exhibits photochromism with direct excitation by X-rays, and that the photochromism behavior can be sensitized by the fluorescence from b-PBD.

Stabilization and Antifouling of Polymer Films on a Planar Surface by CO2 Pressurization.

In this article, we study the dewetting phenomenon of a polymer and carbon dioxide (CO2) mixture on a planar surface by combining density functional theory and the string method. It is found that dewetting is a first-order discontinuous phase transition. When the pressure is lower than the completely dewetting pressure (Pd), CO2 stabilizes the polymer films. The density fluctuation of the polymer decreases significantly with the inclusion of CO2. When the pressure is above Pd, the polymer film is depleted far away from the surface, leaving a thick layer of pure CO2 in the region near the surface. Pd is proportional to the surface energy strength. The CO2 molecules enhance the density fluctuation of the polymer during the dewetting process. The polymer-rich phase at the triple point dewets to a CO2-rich vapor film, as the CO2-rich liquid film near the surface is metastable. These results have promising application in the industry of fabricating polymer films and antifouling polymers on attractive surfaces.

Fabrication of Polymer Film Immobilizing Pd Nano Particles by Plasma-Assisted Method and Evaluation of its Catalytic Activity

We describe the development of a novel palladium catalyst supported on a durable hydrophilic surface fabricated by the plasma-assisted method. Pd nano particles were immobilized on the polymer film possessing a durable hydrophilic surface (LDPE-Pd film). Two kinds of LDPE-Pd film possessing different Pd density were prepared to estimate the chemoselective hydrogenation. Stilbene and 4-nitroaniline were readily hydrogenated with LDPE-Pd film, indicating that the temperature and density of Pd on film might be very important for chemoselectivity.

Fabrication of Polymer Film with Extraordinary Conductive Anisotropy by Forming Parallel Conductive Vorticity‐Aligned Stripes and Its Formation Mechanism

In this work, anisotropic conductive film (ACF) is fabricated by shear‐flow induced assembly. It is found that an appropriate content of carbonaceous filler is needed for forming well‐ordered parallel vorticity‐aligned stripes and the content depends on the category of the filler. Interestingly, the lowest aspect ratio carbon black (CB) with lowest electrical conductivity is the best candidate for fabricating ACF. The film with CB stripes shows excellent conductive anisotropy: the electrical resistivity in the direction parallel to the CB stripes is almost eight orders of magnitude lower than that in the perpendicular direction. The formation mechanism of the vorticity‐aligned stripe is also investigated by the rheological measurement and the study of morphological evolution. It is found that the coalescence of dispersed phase or aggregates dominates the formation and growth of the stripe and negative value of the first normal stress difference drives the stripe to align along the vorticity direction. image

Biomimetic fabrication of polymer film with high adhesive superhydrophobicity by duplicating locust wing surface

Locust is a common flying insect. Locust wings were used as biomimetic templates to fabricate multi-functional polymer(polydimethylsiloxane, PDMS) films by soft lithography. The microstructure and wettability of the natural and artificial locust wing surfaces were investigated by means of a scanning electron microscope(SEM) and a video-based contact angle meter. The natural locust wing surface exhibits complicated hierarchical structures and high adhesive superhydrophobicity(contact angle 152°). The prepared polymer film faithfully reproduces the surface microstructures of the bio-template, and displays a good hydrophobicity and high adhesion(contact angle 144°). The complex wettability of the natural and artificial locust wing surfaces ascribes to the cooperative effect of hydrophobic composition and multi-dimensional rough microstructures. This work not only promotes our understanding of the wetting mechanism on bio-surfaces, but offers an inexpensive and effective approach for biomimetic fabrication of multi-functional interfacial materials.

Superhydrophobic anti-ultraviolet films by doctor blade coating

This article reports a scalable technology for fabricating polymer films with excellent water-repelling and anti-ultraviolet properties. A roll-to-roll compatible doctor blade coating technology is utilized to prepare silica colloidal crystal-polymer composites. The silica microspheres can then be selectively removed to create flexible self-standing macroporous polymer films with crystalline arrays of pores. The void sizes are controlled by tuning the duration of a reactive ion etching process prior to the removal of the templating silica microspheres. After surface modification, superhydrophobic surface can be achieved. This study further demonstrates that the as-prepared transparent porous films with 200 nm of pores exhibit diffraction of ultraviolet lights originated from the Bragg's diffractive of light from the three-dimensional highly ordered air cavities.

The synergistic effect of nanotopography and sustained dual release of hydrophobic and hydrophilic neurotrophic factors on human mesenchymal stem cell neuronal lineage commitment.

A combination of nanotopography and controlled release is a potential platform for neuronal tissue engineering applications. Previous studies showed that combining both physical and chemical guidance was more effective than individual cues in the directional promotion of neurite outgrowth. Nanotopography can direct human mesenchymal stem cells (hMSCs) into neuronal lineage, while controlled release of neurotrophic factors can deliver temporally controlled biochemical signals. Hypothesizing that the synergistic effect will enhance neuronal lineage commitment of hMSCs, a fabrication method for multiple neurotrophic factors delivery from a single nanopatterned (350 nm gratings), poly-ɛ-caprolactone (PCL) film was developed and evaluated. Our results showed a synergistic effect on hMSC differentiation cultured on substrates with both nanotopographical and biochemical cues. The protein/drug encapsulation into PCL nanopatterned films was first optimized using a hydrophilic model protein, bovine serum albumin. The hydrophobic retinoic acid (RA) molecule was directly incorporated into PCL films. To achieve sustained release, hydrophilic nerve growth factor (NGF) was first encapsulated within polyelectrolyte complexation fibers before they were embedded within the nanopatterned PCL film. Our results showed that nanotopography on the fabricated polymer films remained intact, while release of bioactive RA and NGF was sustained over a period of 3 weeks. Under the combinatorial effect of physical and biochemical cues, we observed an enhanced upregulation of neuronal genes such as microtubule-associated protein 2 (MAP2) and neurofilament light (NFL) as compared with sustained delivery of individual cues and bolus delivery. Quantitative polymerase chain reaction analysis showed that MAP2 and NFL gene upregulation in hMSCs was most pronounced on the nanogratings with sustained release of both RA and NGF. The fabricated platforms supported the sustained delivery of multiple neurotrophins, including both hydrophobic and hydrophilic therapeutic agents, while providing surface patterning versatility for application in neural regeneration and tissue engineering.

Fabrication of organic interfacial layers by molecular layer deposition: Present status and future opportunities

To keep pace with the miniaturization of next generation devices in applications such as electronics, biotechnology, and energy, their constituent polymer thin films must meet challenging requirements such as providing simultaneously ultrathin and conformal coatings. Traditional polymer deposition methods may not be suitable, and as a result, new fabrication methods are needed. Molecular layer deposition (MLD), as an analog to atomic layer deposition, provides precise control over many polymer film properties, such as thickness, composition, morphology, and conformality. Hence, MLD can be a powerful and novel method for fabrication of polymer films. This review article introduces the variety of polymer films that have been developed using MLD together with important film growth characteristics and properties. Examples of MLD polymer applications are provided as well. Finally, challenges and outlooks of the MLD technique are discussed.