Structure Of Polymer Films Research Articles

Electrically switchable bistable dual frequency liquid crystal light shutter with hyper-reflection in near infrared

ABSTRACTBistable light shutter based on dual frequency cholesteric liquid crystals (LCs) have attracted intensive interests due to low energy consumption. Herein, we demonstrated an electrically switchable bistable dual frequency LC light shutter with a hybrid structure of cholesteric LC and chiral polymer film. The fabricated device can be switched between planar state which is transparent and focal conic state which is opaque in visible light through voltage pulse while keeping hyper-reflection in near infrared light in both states. The increase of reflection in near infrared light dramatically reduces the interior heat from solar energy, thus making it quite useful in temperature control. In addition, the reflection of near infrared light can be further improved by using cholesteric LC with larger birefringence. The proposed device is useful in smart windows of automobiles, energy-saving buildings and other photonic applications.

Stable Molecular Photocathode for Solar-Driven CO2 Reduction in Aqueous Solutions

The performance of dye-sensitized photoelectrodes for artificial photosynthesis is typically limited by instability in aqueous solutions. We describe here a new molecular-based photocathode that integrates functional chromophore–catalyst assemblies for long-term solar-driven CO2 reduction in stabilized polymeric film structures. The assemblies include a silane surface-anchoring bridge, a ruthenium polypyridyl chromophore, and a rhenium-based molecular catalyst. They were prepared on nanocrystalline oxide films by silanization of the oxide and two-step electropolymerization of vinyl-derivatized precursors. The integrated photocathode was stable toward CO2 reduction for over 10 h with a Faradaic efficiency of ∼65%. The long-term stability arises from the silane surface-anchoring groups and the carbon–carbon bonds formed by electropolymerization between the three components. Transient absorption measurements on a nano-to-microsecond time scale show that the assemblies undergo rapid hole injection into the ox...

Preparation and Self‐Repairing of Highly Oriented Structures of Ultrathin Polymer Films

AbstractThin and ultrathin polymer films play an important role in a variety of applications, such as electronics, liquid crystal alignment, adhesion, and so on. It is well established that the properties of semicrystalline polymeric materials depend remarkably on their multiscale structures; for example, an increase of more than a factor of 100 has been reported for the electrical conductivity of doped and aligned conjugated macromolecules compared with their nonoriented counterparts. Consequently, sophisticated methods have been developed for preparing highly oriented polymer ultrathin films. It should be pointed out that the highly oriented crystalline structure of polymers can be maintained only at temperatures below their melting points. Otherwise, structure rearrangement will result in the loss of orientation and therefore the properties. Therefore, self‐repairing of highly oriented polymer structures is of great significance for the long‐term application of polymer thin films in some specific fields. In this review paper, the preparation and self‐repair of the highly oriented structure of polymer thin films is described in the hopes that this will afford useful information for further development of polymeric materials for advanced applications.

Light induced reversible structuring of photosensitive polymer films.

In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be “set in motion” like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices.

Effect of NiO NPs doping on the structure and optical properties of PVC polymer films

The goal of this study was to investigate the structure and optical properties of the prepared PVC/NiO nanocomposites. The samples were characterized via XRD, TEM, SEM, and UV–Vis spectrophotometer experimental measurements. The partial crystal structure of PVC/NiO nanocomposites and cubic structure of NiO nanoparticles were explored by X-ray diffraction. SEM exhibited the good distribution of the nanoparticles in PVC films. Linear optical parameters: refractive index and normalized absorption, increased whenever transmission and reflection reduced by adding NiO nanoparticles. Direct and indirect optical band gaps were obtained from Tauc’s formula, and it was found that both direct and indirect optical band gaps decrease as more NiO nanoparticles added. The direct optical band gap decreases from 5.20 to 5.15 eV. The optical conductivity increased by increasing the content of NiO nanoparticles. The dispersion parameters: oscillator energy $$E_{0}$$ , dispersion energy $$E_{\text{d}}$$ , plasma angular frequency $$w_{\text{p}}$$ , optical momentum of dispersion $$M_{ - 1}$$ and $$M_{ - 3}$$ , and static refractive index, were calculated by using Wemple and DiDominco model. The nonlinear optical susceptibility $$x^{(3)}$$ and nonlinear refractive index $$n_{2}$$ were evaluated from the linear optical parameters using semiempirical relation. The increasing in nonlinear parameters $$x^{(3)}$$ and $$n_{2}$$ suggest the use of PVC/NiO nanocomposites for nonlinear optical applications.

Hierarchically Patterned Elastomeric and Thermoplastic Polymer Films through Nanoimprinting and Ultraviolet Light Exposure.

The surface relief structure of polymer films over large areas can be controlled by combining nanoscale imprinting and microscale ultraviolet–ozone (UVO) radiation, resulting in hierarchical structured surfaces. First, nanoscale patterns were formed by nanoimprinting elastomer [poly(dimethylsiloxane) (PDMS)] films with a pattern on a digital video disk. Micron-scale patterns were then superimposed on the nanoimprinted PDMS films by exposing them to ultraviolet radiation in oxygen (UVO) through a transmission electron microscopy grid mask having variable microscale patterning. UVO exposure leads to conversion and densification of PDMS to SiOx, leading to micron height relief features that follow a linear scaling relation with pattern dimension. Further, the pattern scopes are shown to collapse into a master curve by normalized feature values. Interestingly, these relief structures preserve the nanoscale features. In this paper, the influence of the self-limiting PDMS densification, wall stress at the boundary of micro-depression, and UVO exposure energy is studied in control of the micro-depression scale. This simple two-step imprinting process involving both nanoimprinting and UV radiation allows for facile fabrication of the dimension adjustable micro–nano hierarchically structures not only on elastomer films but also on thermoplastic polymer films. Coarse-grained molecular dynamics simulations were performed to correlate the surface tension and elastic properties of polymeric materials to the deformation of the pattern structure.

Structural, topographical, and mechanical characteristics of purified polyhydroxyoctanoate polymer

ABSTRACTInsight into the topographic and mechanical properties of biomaterials allows for efficient selection of a material for a specific application. Here, atomic force microscopy (AFM) and force spectroscopy were exploited to reveal the topographic and mechanical characteristics of charcoal‐purified, solvent‐cast polyhydroxyoctanoate (PHO) film. The root mean square surface roughness of a PHO surface derived from ethyl acetate, acetone, or chloroform solution was 13.2, 11.5, or 30.9 nm, respectively, for 100 μm2 AFM images. The distribution of the local Young's modulus had a maximum of 25.4, 14.1, and 12.6 MPa for PHO films obtained from ethyl acetate, acetone, and chloroform solution, respectively. The positron annihilation spectroscopy measurements allowed us to determine the free volume in the polymer film structure (9.38%). Moreover, a number of additional techniques (X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, NMR, infrared spectroscopy, and polarized light microscopy) were used to reveal PHO features. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47192.

Impact of Endometallofullerene on P84 Copolyimide Transport and Thermomechanical Properties.

Novel polymer composite materials, including unique nanoparticles, contribute to the progress of modern technologies. In this work, the endohedral fullerene C60 with incapsulated iron atom (endometallofullerene Fe@C60) is used for modification of P84 copolyimide. The impact of 0.1, 0.5, and 1 wt % endometallofullerene on the structure and physicochemical properties of polymer films is studied through scanning electron microscopy, thermogravimetric analysis, and thermomechanical tests. Transport properties are estimated through sorption and pervaporation techniques toward methanol and methyl acetate mixture. The inclusion of endometallofullerene into the copolyimide matrix improves membrane permeability and selectivity in the separation of methanol—methyl acetate mixtures. The maximal effect is achieved with a composite containing 0.5 wt % Fe@C60. The developed composites are effective for energy and resource saving purification of methyl acetate by pervaporation.

Piezoelectric MEMS with tactile stimulation and displacement sensing functions

For the application of bidirectional communication between a human activity monitoring system and a human using tactile sensation, a tactile MEMS device is developed. To obtain the displacement and provide energy to the human skin, a driving actuator and a displacement sensor are integrated. The tactile device is based on a cantilever with a lamination structure of polymer and Pb(Zr,Ti)O3 thin films. The characterization of the device showed that the sensor output agreed well with the tip displacement. For the touch experiment of the device, the frequency response demonstrates hardening-spring-like behavior. By using a piecewise linear system model, the behavior is analyzed. The experimental results and analytical model showed similar tendencies. These results indicate a potential application of the stiffness sensor of an object.

Effects of alkyl side chain length of low bandgap naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐based copolymers on the optoelectronic properties of polymer solar cells

ABSTRACTTwo donor‐π‐acceptor (D‐π‐A) type naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NT)‐based conjugated copolymers (CPs), namely, PBDT‐TT‐DTNT‐HD and PBDT‐TT‐DTNT‐OD, containing different side chain length (2‐hexyldecyl, HD and 2‐octyldodecyl, OD) anchoring to thiophene π‐bridge between the two‐dimensional (2D) 5‐((2‐butyloctyl)thieno[3,2‐b]thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐TT) unit and NT moiety are developed and fully characterized. The resultant two copolymers exhibited broader absorption in wide range of 300–820 nm and obviously deepened EHOMO of approximately −5.50 eV. The effects of side chain length on film‐forming ability, absorption, energy levels, aggregation, dielectric constant (ɛr), mobility, morphology, and photovoltaic properties are further systematically investigated. It was found that the side chain length had little impact on solution‐processability, absorption, energy levels, and aggregation in CB solution of resultant CPs. However, tinily increasing side chain length promoted to form the more ordered structure of neat polymer film even if the corresponding ɛr decreased. As a result, the side‐chain‐extended PBDT‐TT‐DTNT‐OD:PC71BM‐based device achieved 32% increased FF than that of PBDT‐TT‐DTNT‐HD:PC71BM and thus the PCE was significantly raised from 3.99% to 5.21%, which were benefited from 2 times higher SCLC hole mobility, more favorable phase separation, and improved exciton dissociation. These findings could provide an important and valuable insight by side chain modulation for achieving efficient PSCs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2059–2071

Near-Surface Structure of Plasma Polymer Films Affects Surface Behavior in Water and its Interaction with Proteins

Using low pressure plasma polymerization, nano-scaled oxygen-rich plasma polymer films (CO) were deposited onto pristine silicon wafers as well as on nitrogen-containing plasma polymer (CN) model surfaces. We investigate the influence of the nature of the substrate as well as a potential sub-surface effect emerging from the buried CO/CN interface, just nanometers below the surface. X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry revealed two important phenomena that occurred during the deposition of the terminal CO layer: (1) a strong degree of oxidation, already for 1 nm nominal thickness, and (2) a gradual transition in chemical composition between the two layers, clearly indicating that effectively a vertical chemical gradient results, even when a two-step coating process was applied. Such terminal gradient film structures were used to study film stability in aqueous environments. Molecular rearrangements were scrutinized in the top-surface in contact with water and we found that the top-surface chemistry and wetting properties of the oxygen-rich termination layer matched those of thick CO reference coatings. Nevertheless, the adsorption of green fluorescent protein (GFP) was observed to be sensitive to the CO terminal layer thickness. Namely, an enhanced protein adsorption was observed for 1–2 nm thick CO layers on CN, whereas a significantly reduced protein adsorption was seen on ≥ 3 nm thick CO terminal layers. We conclude that both, surface and sub-surface conditions significantly affect protein adsorption as opposed to the traditional consideration of surface properties alone.

Direct casting of a PDMS substrate holder from a structured polymer film for lab-on-a-foil bonding

Lab-on-a-foil devices have recently attracted increasing attention, in which a thin and flexible polymer film is used as the substrate material. However, to protect the special three dimensional microfluidic structures on the polymer film from collapsing during the bonding process, a very elaborate substrate holder is required. In this work, we propose the use of a PDMS plate as the substrate holder for lab-on-a-foil bonding. The PDMS substrate holder is directly cast from the structured polymer film, hence it can perfectly match the polymer film and protect the microfluidic structures. This method is straightforward and low-cost, and obviates the difficulties of measuring the dimensions of the structured polymer film. Meanwhile, the stickiness of PDMS makes the positioning of the structured polymer film on the surface of the holder much easier, and the low modulus of PDMS contributes to obtaining a uniform bonding. As a demonstration, with the help of a PDMS substrate holder, a 240-μm-thick thermoformed polypropylene film was bonded with a 100-μm-thick aluminium foil to make a lab-on-a-foil device for gene expression analysis. The bonding qualities were examined, and the performances of the device were tested.

Chemical structure and surface morphology evolution of glow discharge polymer films by Ar‐ions intermittent etching

The Ar‐ions intermittent‐etching technique was successfully incorporated during the deposition of glow discharge polymer (GDP) films. The ionic components and ion energy distributions (IEDs) of C4H8/H2 and C4H8/H2/Ar plasma were diagnosed by an energy‐resolved mass spectrometer, respectively. The Fourier transform infrared spectroscopy, scanning electron microscope, and white‐light interferometer were used to studying the chemical structure, surface morphology, and roughness of the GDP films, which are deposited with the various time of Ar‐ions intermittent etching. With the introduction of Ar into the chamber, the intensity of the CH absorption peaks becomes weak and the large‐mass CH species were ionized and dissociated from the mass spectrometer results. The surface roughness of GDP films are decreased with Ar‐ions intermittent etching, the lowest surface roughness (Rq) is only 33.6 nm when the intermittent cycle is 60 minutes/15 minutes. The highest sp3CH3 (sym) absorption peaks are attributed to samples also with 60‐minute/15‐minute intermittent cycle, which shortens the length of the carbon chain and reduces the probability of the cluster formations.

Selective electrochemical sensor based on the electropolymerized p-coumaric acid for the direct determination of l-cysteine

Novel electrochemical sensor based on poly(p-coumaric acid) electrodeposited on the surface of multi-walled carbon nanotubes modified glassy carbon electrode (poly(p-coumaric acid)/MWNT/GCE) has been developed for the direct determination of l-cysteine. Poly(p-coumaric acid) has been obtained by potentiodynamic electrolysis under the optimized conditions (0.10 mM p-coumaric acid in 0.1 M NaOH using 5 cycles in the potential window of 0–1.0 V and the scan rate of 25 mV s−1) providing highest voltammetric response of l-cysteine. Sensor surface has been studied by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The porous structure of polymeric film provides 6.9-fold increase in effective surface area and 4.2-fold lower charge transfer resistance in comparison to GCE. Under conditions of DPV, the sensor response is linear in the ranges of 7.5–50 and 50–1000 μM of l-cysteine with the detection and quantification limits of 1.1 and 3.6 μM, respectively. The excellent sensor selectivity to l-cysteine in the presence of glucose, uric and ascorbic acids, dopamine, l-tyrosine and S-containing substances (homocysteine, glutathione, l-methionine, l-cystine and α-lipoic acid) has been observed. Applicability of the sensor to real samples analysis has been shown on example of human urine.

Synthesis of bactericidal polymer coatings by sequential plasma-induced polymerization of 4-vinyl pyridine and gas-phase quaternization of poly-4-vinyl pyridine

Plasma-based technology is an alternative to produce universal polymer coatings with the appropriate requirements of robustness and stability for antibacterial applications. Here, we proposed a sequential two-step alternative to synthesize antibacterial polymer coatings. A non-isothermal plasma reactor, operated at atmospheric pressure (Patm) and room temperature (Troom), was used to induce free radical polymerization of 4-vinyl pyridine (4VP) on high-density polyethylene (PE). In a subsequent step, the poly-4VP (P4VP) films were treated with a bromoethane/He gas stream to produce quaternized P4VP (P4VPQ) films. Chemical structure of polymer films was validated by infrared and UV–visible spectroscopy, and morphology was evaluated by optical and atomic force microscopy; scanning electron microscopy was used to determine films thickness, which was then used to estimate the surface charge density. The bactericidal capacity was determined with a standard test by using Escherichia coli. Both types of films had an estimated charge density in the order of 1016 positive charges per cm2; P4VP films removed about 95–99% of bacteria, whereas 4PVPQ films eliminated 100%. The methodology proposed for the synthesis of antibacterial polymer coatings is simpler, faster, and more environmentally friendly than other plasma-based methods; operation at Troom and Patm may also have a significant effect on the economics and the ease of implementation of the process at commercial scale. The suggested approach may facilitate the development of new universal coatings, and operating plasma conditions could be extrapolated for engineering antibacterial coatings in industrial areas where bacterial attachment is of concern.

Investigation of the flow structure in thin polymer films using 3D µPTV enhanced by GPU

To understand the effects of inhomogeneous drying on the quality of polymer coatings, an experimental setup to resolve the occurring flow field throughout the drying film has been developed. Deconvolution microscopy is used to analyze the flow field in 3D and time. Since the dimension of the spatial component in the direction of the line-of-sight is limited compared to the lateral components, a multi-focal approach is used. Here, the beam of light is equally distributed on up to five cameras using cubic beam splitters. Adding a meniscus lens between each pair of camera and beam splitter and setting different distances between each camera and its meniscus lens creates multi-focality and allows one to increase the depth of the observed volume. Resolving the spatial component in the line-of-sight direction is based on analyzing the point spread function. The analysis of the PSF is computational expensive and introduces a high complexity compared to traditional particle image velocimetry approaches. A new algorithm tailored to the parallel computing architecture of recent graphics processing units has been developed. The algorithm is able to process typical images in less than a second and has further potential to realize online analysis in the future. As a prove of principle, the flow fields occurring in thin polymer solutions drying at ambient conditions and at boundary conditions that force inhomogeneous drying are presented.

Tuning Morphology and Melting Temperature in Polyethylene Films by MAPLE

The control of structure and thermal stability in semicrystalline polymer films remains an important challenge in applications ranging from solar energy devices to packaging films. Here, we demonstrate the ability to dramatically alter the morphology and melting temperature (Tm) of low-molecular-weight linear polyethylene (PE) by employing an innovative vapor-assisted deposition process termed matrix assisted pulsed laser evaporation (MAPLE). We report the ability to tune Tm of PE films by 20 °C by simply adjusting the deposition temperature during MAPLE processing. This unique capability stems from the ability of MAPLE to exploit confined crystallization during thin film growth. In addition, we demonstrate the ability to exploit MAPLE to design PE films that exhibit the same Tm as their melt-crystallized analogues but have an ∼25% higher degree of crystallinity. Our investigation offers new insights into how confinement effects in polymer crystallization can be utilized in the emerging field of polymer f...

Directed Self-Assembly in "Breath Figure" Templating of Melamine-Based Amphiphilic Copolymers: Effect of Hydrophilic End-Chain on Honeycomb Film Formation and Wetting.

Amphiphilic copolymers are widely used in the fabrication of hierarchically honeycomb-structured films through a "breath figure" (BF) process because the hydrophilic block plays a key role in stabilising water templating. However, the hydrophilic monomers reported are mainly confined to acrylic acid and its derivatives, which largely limits understanding of the formation of BF arrays and the introduction of additional functions on porous films. The relationship between polymer composition, film microstructure and surface properties are also less documented. Herein, a novel melamine-based hydrophilic moiety, N-[3-({3-[(4,6-bis{[3-(dimethylamino)propyl]amino}-1,3,5-triazin-2yl)amino]propyl}(methyl)amino)propyl]methacrylamide (ANME), was incorporated into polystyrene (PS) chains by combining atom-transfer radical polymerisation and post-modification to afford three well-defined end-functionalised PS-PANME derivatives. These polymers were used to fabricate honeycomb films through the BF technique. Both inner and outer microstructures of the films were characterised by optical microscopy, AFM and SEM. Polymer hydrophilicity is enhanced upon increasing the PANME content, which results in variation of the film microstructure and porosity, and provokes a transition from Cassie-Baxter to Wenzel behaviour. Furthermore, the surface wettability of as-prepared honeycomb films and corresponding pillared films is mainly governed by film morphology, rather than by the properties of the polymers. Knowledge of the relationships between polymer composition and film structure, as well as surface wettability, is beneficial to design and prepare hierarchically porous films with desirable structures and properties.

Large Area Polymer Composite Films Embedded with Colloidal Quantum Dots for Efficient White Light Generation

A large‐area (30 × 30 cm2) polymer film, embedded with green‐ and red‐emitting colloidal semiconductor quantum dots (QDs) to generate white light excited by blue light emitting diodes (LEDs), is fabricated. To prevent reabsorption and nonradiative energy transfer between QDs causing a significant redshift of the desired final color, the polymer film structure comprised of separated green and red emitting composite layers is explored. As a result, high‐quality white light generation is demonstrated by placing these composite films on a blue LED platform.

Manipulation of Crystallization Sequence in PEO-b-PCL Films Using Solvent Interactions

The physical structure of polymer films is important for understanding the observed macroscopic properties. In crystalline–crystalline block copolymers, the hierarchical nature of assembly is even more influential. Controlling this assembly process is crucial for tailoring film properties. In materials where crystallization of each block occurs nearly simultaneously, the ability to manipulate crystallization order is desirable. Poly(ethylene oxide)-b-poly(e-caprolactone) (PEO-b-PCL) films were monitored via ATR-FTIR to determine the crystallization order during drying from varying solvents. PCL crystallized first from most solvents except toluene and ethyl acetate, where PEO nucleation occurred first. Moreover, after melting the sample to remove solvent–polymer interaction effects, PCL was first to crystallize from the melt, as has been previously reported. Differences in the films’ morphologies based on crystallization order were observed using polarized optical microscopy. These results demonstrate that...