Thin Polymer Films Research Articles

Synthesis and Characterization of Indolenine‐based Squaraine Dyes and their Photophysical Properties in Polymer Thin Films

Four squaraine dyes bearing various N substituents with different electron‐withdrawing abilities were synthesized in this study. The effects of these substituents on the photophysical properties and stabilities of the squaraine dyes were analyzed. Squaraine‐doped polymer films were fabricated using the synthesized squaraine dyes, and all films demonstrated excellent transmittances of ~100% in the non‐absorptive region, along with extremely low transmittances in the 630–640 nm wavelength region. The thermal stabilities of the squaraine films were evaluated after thermal treatment at elevated temperatures. The film fabricated using polysulfone, which possesses a high glass‐transition temperature, maintained an absorption of >97% after heat treatment, indicating its excellent thermal stability. Furthermore, all squaraine films maintained absorptions of >70% after 24 h of light irradiation, surpassing the photostabilities of conventional polymethine dyes. It was concluded that squaraine dyes are sufficiently effective and applicable for producing optical films, owing to their excellent optical properties and high stabilities.

Mechanisms of the Photomechanical Response in Thin-Film Dye-Doped Glassy Polymers.

This work aims to determine the mechanism of the photomechanical response of poly(Methyl methacrylate) polymer doped with the photo-isomerizable dye Disperse Red 1 using the non-isomerizable dye Disperse Orange 11 as a control to isolate photoisomerization. Samples are free-standing thin films with thickness that is small compared with the optical skin depth to assure uniform illumination and photomechanical response throughout their volume, which differentiates these studies from most others. Polarization-dependent measurements of the photomechanical stress response are used to deconvolute the contributions of angular hole burning, molecular reorientation and photothermal heating. While photo-isomerization of dopant molecules is commonly observed in dye-doped polymers, the shape changes of a molecule might not couple strongly to the host polymer through steric mechanical interactions, thus not contributing substantially to a macroscopic shape change. To gain insights into the effectiveness of such mechanical coupling, we directly probe the dopant molecules using dichroism measurements simultaneously while measuring the photomechanical response and find mechanical coupling to be small enough to make photothermal heating-mediated by the transfer of optical energy as heat to the polymer-the dominant mechanism. We also predict the fraction of light energy converted to mechanical energy using a model whose parameters are thermodynamic material properties that are measured with independent experiments. We find that in the thin-film geometry, these dye-doped glassy polymers are as efficient as any other material but their large Young's modulus relative to other organic materials, such as liquid crystal elastomers, makes them suitable in applications that require mechanically strong materials. The mechanical properties and the photomechanical response of thin films are observed to be significantly different than in fibers, suggesting that the geometry of the material and surface effects might play an important role.

Disulfide Glass: An Optical Polymer for Commodity Plastics, Precision Optics, and Photonics

AbstractThe development of an organic optical glass, termed, disulfide glass (DSG), is reported as a new polymer for commodity plastic optics and thin film photonic applications. This low‐cost thermoset polymer possesses excellent transparency across the visible and infrared spectrum comparable to the best optical plastic to date, poly(methyl methacrylate), while having superior refractive index (n ≈ 1.6). DSG can be fabricated into defect‐free, thick optical glass by bulk addition polymerization of two commodity monomers (sulfur monochloride, 1,3,5‐triallyl isocyanurate) via a new polymerization, sulfenyl chloride inverse vulcanization. The robust mechanical properties and optical clarity of DSG enable fabrication of precision optics (lenses, prisms) via diamond turn machining to demonstrate the manufacturability of DSG for commodity plastic optics. Finally, the synthetic modularity of DSG is demonstrated to form solution processable forms for the fabrication of thin film polymer photonic devices, negative tone polymer photoresists, and micropatterned arrays.

Confocal Raman Microscopy for Measuring In Situ Temperature-Dependent Structural Changes in Poly(Ethylene Oxide) Thin Films.

Crystallization from the melt is a critical process governing the properties of semi-crystalline polymeric materials. While structural analyses of melting and crystallization transitions in bulk polymers have been widely reported, in contrast, those in thin polymer films on solid supports have been underexplored. Herein, in situ Raman microscopy and self-modeling curve resolution (SMCR) analysis are applied to investigate the temperature-dependent structural changes in poly(ethylene oxide) (PEO) films during melting and crystallization phase transitions. By resolving complex overlapping sets of spectra, SMCR analysis reveals that the thermal transitions of 50 µm thick PEO films comprise two structural phases: an ordered crystalline phase and a disordered amorphous phase. The ordered structure of the crystalline PEO film entirely disappears as the polymer is heated; conversely, the disordered structure of the amorphous PEO film reverts to the ordered structure as the polymer is cooled. Broadening of the Raman bands was observed in PEO films above the melting temperature (67 °C), while sharpening of bands was observed below the crystallization temperature (45 °C). The temperatures at which these spectral changes occurred were in good agreement with differential scanning calorimetry (DSC) measurements, especially during the melting transition. The results illustrate that in situ Raman microscopy coupled with SMCR analysis is a powerful approach for unraveling complex structural changes in thin polymer films during melting and crystallization processes. Furthermore, we show that confocal Raman microscopy opens opportunities to apply the methodology to interrogate the structural features of PEO or other surface-supported polymer films as thin as 2 µm, a thickness regime beyond the reach of conventional thermal analysis techniques.

Sequential Infiltration Synthesis of Cadmium Sulfide Discrete Atom Clusters.

Exposure of soft material templates to alternating volatile chemical precursors can produce inorganic deposition within the permeable template (e.g. a polymer thin film) in a process akin to atomic layer deposition (ALD). While such sequential infiltration synthesis (SIS) processes have now been demonstrated for many metal oxides, we report an SIS process for a transition metal sulfide - CdS. Gas phase dimethyl cadmium and hydrogen sulfide precursors infiltrated into poly(4-vinylpyridine) thin films result in the 3D-nucleation of clusters consistent with a cubane-type Cd4S4 core that are variably terminated with methyl, thiol and hydroxy capping ligands. First principles models and simulation of few-atom Cd-based clusters are consistent with electronic and vibrational spectroscopy and grazing-incidence total X-ray scattering measurements of 3D-cluster-arrays synthesized at 80 °C. The direct synthesis of few-atom transition metal sulfide clusters within polymer thin films will provide a versatile new route to precision architectures for light-absorbing materials including solar energy harvesting and conversion applications.

Sequential Infiltration Synthesis of Cadmium Sulfide Discrete Atom Clusters

AbstractExposure of soft material templates to alternating volatile chemical precursors can produce inorganic deposition within the permeable template (e.g. a polymer thin film) in a process akin to atomic layer deposition (ALD). While such sequential infiltration synthesis (SIS) processes have now been demonstrated for many metal oxides, we report an SIS process for a transition metal sulfide – CdS. Gas phase dimethyl cadmium and hydrogen sulfide precursors infiltrated into poly(4‐vinylpyridine) thin films result in the 3D‐nucleation of clusters consistent with a cubane‐type Cd4S4 core that are variably terminated with methyl, thiol and hydroxy capping ligands. First principles models and simulation of few‐atom Cd‐based clusters are consistent with electronic and vibrational spectroscopy and grazing‐incidence total X‐ray scattering measurements of 3D‐cluster‐arrays synthesized at 80 °C. The direct synthesis of few‐atom transition metal sulfide clusters within polymer thin films will provide a versatile new route to precision architectures for light‐absorbing materials including solar energy harvesting and conversion applications.

Osteoblastic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells on P3HT Thin Polymer Film.

Bone defects restoration has always been an arduous challenge in the orthopedic field due to the limitations of conventional grafts. Bone tissue engineering offers an alternative approach by using biomimetic materials, stem cells, and growth factors that are able to improve the regeneration of bone tissue. Different biomaterials have attracted great interest in BTE applications, including the poly(3-hexylthiofene) (P3HT) conductive polymer, whose primary advantage is its capability to provide a native extracellular matrix-like environment. Based on this evidence, in this study, we evaluated the biological response of human adipose-derived mesenchymal stem cells cultured on P3HT thin polymer film for 14 days. Our results suggest that P3HT represents a good substrate to induce osteogenic differentiation of osteoprogenitor cells, even in the absence of specific inductive growth factors, thus representing a promising strategy for bone regenerative medicine. Therefore, the system provided may offer an innovative platform for next-generation biocompatible materials for regenerative medicine.

Side-chain engineering of two-dimensional polymer thin films for high-performance organic non-volatile memories

The impact of side chains on the memory performance of charge-trapping layers in 2D polymer thin films with identical backbones but differing side chains was investigated.

A high-temperature resistant curved conformal thin-film polymer derived SiCN temperature sensor based on screen printing

A high-temperature resistant curved conformal thin-film polymer derived SiCN temperature sensor based on screen printing

Synthesis and characterization of polypyrrole polymer thin film and the effect of adding silver nanoparticles (PPY/AgNPs)

In this research, a chemical oxidative polymerization process was used to prepare polypyrrole (PPY). The characterization of polypyrrole thin films pure and dopped with silver nanoparticles (AgNPs) at different weight ratios of AgNPs (i.e., 5, 10, and 15 wt%) was studied. The thin films were prepared via the drop casting method and flung down on a clean glass substrate at room temperature. Using FT-IR, XRD, and AFM, the system and facet morphology of the thin films were investigated. FTIR analysis of undoped PPY powder revealed distinctive vibrational frequencies of PPY undoped. Strong absorption bands at 3653 cm-1 (N-H stretching), 2342 cm-1 (nitridation), and peaks at 1542, 1459 cm-1 (C=C, C=N vibrations) were observed. Other peaks at 1176 cm-1 (C-N stretching), 1039, 964 cm-1 (C-H vibrations), 893, 782 cm-1 (C-H bend deformation), 670 cm-1 (C-C deformation), and 590 cm-1 (polypyrrole presence) were identified. The results showed that the FT-IR spectra of pure ppy and the spectra of PPY/AgNPs composites were similar. The single XRD data also showed that ppy is amorphous and The distinctive peak of polypyrrole was found at (2θ) 24.35◦, indicating the short-range arrangement of PPy chains the interlayer distance (d) between the measured value of spacing for PPY was 3.6599 A0. Additionally, By using AFM, the parameters Ra, R.M.S, and G.S. were determined for PPY doped AgNPs thin films. These values increased with higher doping percentages. For undoped PPY thin film, values were (2.557nm, 3.299nm, 33.40nm) while for doped films with 5%, 10%, and 15% AgNPs, values were (3.397nm, 4.859nm, 46.12nm), (9.328nm, 11.90nm, 66.33nm), and (13.87nm, 19.28nm, 86.89nm) respectively. the AFM results for all thin films of PPY undoped and composites doped with silver nanoparticles (PPY/AgNPs) demonstrated that the values of grain size (G.S.) and root-mean-square (R.M.S.) roughness average (Ra) increase as the number of AgNPs increases.

Influence of Water Sorption on Ionic Conductivity in Polyether Electrolytes at Low Hydration.

Ion-containing polymers are subject to a wide range of hydration conditions across electrochemical and water treatment applications. Significant work on dry polymer electrolytes for batteries and highly swollen membranes for water purification has informed our understanding of ion transport under extreme conditions. However, knowledge of intermediate conditions (i.e., low hydration) is essential to emerging applications (e.g., electrolyzers, fuel cells, and lithium extraction). Ion transport under low levels of hydration is distinct from the extreme conditions typically investigated, and the relevant physics cannot be extrapolated from existing knowledge, stifling materials design. In this study, we conducted ion transport measurements in LiTFSI-doped polyethers that were systematically hydrated from dry conditions. A semiautomated apparatus that performs parallel measurements of water uptake and ionic conductivity in thin-film polymers under controlled humidity was developed. For the materials and swelling range considered in this study (i.e., <0.07 g water/g dry polymer electrolyte), ionic conductivity depends nonlinearly on water uptake, with the initial sorbed water weakly affecting conductivity. With additional increases in swelling, more significant increases in conductivity were observed. Remarkably, changes in conductivity induced by water sorption were correlated with the number of water molecules per lithium ion, with the normalized molar conductivity of different samples effectively collapsing onto one another until this unit of hydration exceeded the solvation number of lithium ions under aqueous conditions. These results provide important knowledge regarding the effects of trace water contamination on conductivity measurements in polymer electrolytes and demonstrate that the lithium-ion solvation number marks a key transition point regarding the influence of water on ion transport in ion-containing polymers.

The Influence of Alkyl Spacers and Molecular Weight on the Charge Transport and Storage Properties of Oxy-Bithiophene-Based Conjugated Polymers.

Conjugated polymers (CPs) with polar side chains can conduct electronic and ionic charges simultaneously, making them promising for bioelectronics, electrocatalysis and energy storage. Recent work showed that adding alkyl spacers between CP backbones and polar side chains improved electronic charge carrier mobility, reduced swelling and enhanced stability, without compromising ion transport. However, how alkyl spacers impact polymer backbone conformation and, subsequently, electronic properties remain unclear. In this work, we design two oxy-bithiophene-based CP series, each featuring progressively extended alkyl spacer lengths and two distinct molecular weight (MW) distributions. Using operando characterisations, we evaluate the (spectro)electrochemical and swelling properties of the polymer thin films, and their performance in organic field-effect transistors and organic electrochemical transistors. Surprisingly, alkyl spacers negatively impact the hole mobility of our polymers, with higher MW amplifying this effect. Using molecular dynamics simulations, we show that it is thermodynamically favourable for adjacent non-polar alkyl spacers to aggregate in polar electrolytes, leading to backbone twisting. Further spectroscopic measurements corroborate this prediction. Our findings demonstrate the active interactions between side chain structure, MW and electrolyte/solvent polarity in influencing polymer performance, underscoring the importance of considering solvation environment effects on polymer conformation when designing new mixed conducting CPs for electrochemical applications.

The Influence of Alkyl Spacers and Molecular Weight on the Charge Transport and Storage Properties of Oxy‐Bithiophene‐Based Conjugated Polymers

AbstractConjugated polymers (CPs) with polar side chains can conduct electronic and ionic charges simultaneously, making them promising for bioelectronics, electrocatalysis and energy storage. Recent work showed that adding alkyl spacers between CP backbones and polar side chains improved electronic charge carrier mobility, reduced swelling and enhanced stability, without compromising ion transport. However, how alkyl spacers impact polymer backbone conformation and, subsequently, electronic properties remain unclear. In this work, we design two oxy‐bithiophene‐based CP series, each featuring progressively extended alkyl spacer lengths and two distinct molecular weight (MW) distributions. Using operando characterisations, we evaluate the (spectro)electrochemical and swelling properties of the polymer thin films, and their performance in organic field‐effect transistors and organic electrochemical transistors. Surprisingly, alkyl spacers negatively impact the hole mobility of our polymers, with higher MW amplifying this effect. Using molecular dynamics simulations, we show that it is thermodynamically favourable for adjacent non‐polar alkyl spacers to aggregate in polar electrolytes, leading to backbone twisting. Further spectroscopic measurements corroborate this prediction. Our findings demonstrate the active interactions between side chain structure, MW and electrolyte/solvent polarity in influencing polymer performance, underscoring the importance of considering solvation environment effects on polymer conformation when designing new mixed conducting CPs for electrochemical applications.

The Addition of MoO3 or SiO2 Nano-/Microfillers Thermally Stabilized and Mechanically Reinforce the PVDF-HFP/PVP Polymer Composite Thin Films

The properties of thin polymer films are influenced by the size of the fillers, their morphology, the surface properties and their distribution/interaction in the polymer matrix. In this work, thin polymer composite films with MoO3 or SiO2 nano and micro fillers in PVDF-HFP/PVP polymer matrix were successfully fabricated using the solvent casting method. The effects of different types, sizes and morphologies of the inorganic fillers on the crystallization of the PVDF-HFP polymer were investigated, as well as the effects on the thermal and mechanical properties of the composites. Scanning electron microscopy, ATR-FTIR spectroscopy, differential scanning calorimetry, nanoindentation and uniaxial mechanical tests were used for characterization. The results showed that MoO3 nanowires thermally stabilized the polymer matrix, induced crystallization of the PVDF-HFP polymer in all three polymorphs (α-, β-, γ-phase) and formed a geometrical network in the polymer matrix, resulting in the highest elastic moduli, hardness and Young’s modulus.

A Spectral Method for Rapidly Determining the Linear Birefringence of Thin Polymer Films.

A rapid and simple spectral method for determining the linear birefringence of thin anisotropic films, using the channeled spectra, is proposed in this article. Two channeled spectra must be recorded for a transparent system containing a thick anisotropic layer and a thin stretched polymer film, when the two anisotropic uniaxial layers have parallel and perpendicular optical axes, respectively. The sum and difference of the two channeled spectra indicate (by the positions of the maxima and minima in the resulting channeled spectra) the phase difference introduced by the thin polymer film. One must measure with precision only the thickness of the polymer film in order to compute the linear birefringence of the thin polymer film, using the position of the maxima and minima of the sum and difference. The experimental data obtained for poly (vinyl alcohol)-PVA-and poly (ethylene terephthalate)-PET-films attest to the applicability of the proposed method to the uniaxial transparent polymeric thin films.

Periodically Ordered Wrinkles in Gradient Patterned Polymer Stripes.

We demonstrated a versatile and robust strategy to create spatially defined periodic wrinkles in gradient striped polymer films through the coupled process of controlled evaporative self-assembly (CESA) and mechanically driven surface wrinkling. The mechanical properties of patterned-gradient polymer thin films were investigated by wrinkling methodology in a fast and simple manner. Understanding of the complex wrinkles can provide insights into the growth mechanism of most biological species that can be explained by competition between bending and stretching energies, e.g., leaves with gradient thickness range from the central area to edges. Furthermore, it also benefits a wide range of micro-to-nanotechnologies that strongly depend on the mechanical stability and performance of thin polymer membranes for semiconductor applications.

Potentiality of chitosan/titanium oxide nanocomposite for removing iron and chromium from hydrous solutions.

The present study involved the preparation of a nano-polymer based on shrimp wastes as a biodegradable chitosan nanoparticle (Cs) incorporated into titanium oxide nanoparticles (TiO2) in an aqueous medium and carried on the specific polymer to form thin films. The spectroscopic properties of chitosan/TiO2/Polymer thin films were estimated by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The fabricated films were then examined for their potential to eliminate iron (Fe) and chromium (Cr) from solutions. The adsorption efficiency was also evaluated along various contact times. In general, the results illustrated that the heavy metals removal increases with increasing the different ratios of chitosan and TiO2 nanoparticles incorporated in polymer thin films. Removal efficiency increased with an increase in contact time. More than 70% of Fe and Cr ions were removed in the first 30min of contact time using different thin films examined. The maximum removal for metal ions after 90min for the pest thin film (0.08 TiO2) was 97.1 and 88.8% for Fe and Cr, whereas the lowest thin film removal efficiency (PVC) was 29.5 and 8.07% for Fe and Cr, respectively. In conclusion, the fabricated thin film composed of polyvinylidene chloride and chitosan plus 0.08 g titanium oxide nanoparticles had a heavy metal removal capacity three times greater than that of basic polyvinylidene chloride.

Polymers in Physics, Chemistry and Biology: Behavior of Linear Polymers in Fractal Structures.

We start presenting an overview on recent applications of linear polymers and networks in condensed matter physics, chemistry and biology by briefly discussing selected papers (published within 2022-2024) in some detail. They are organized into three main subsections: polymers in physics (further subdivided into simulations of coarse-grained models and structural properties of materials), chemistry (quantum mechanical calculations, environmental issues and rheological properties of viscoelastic composites) and biology (macromolecules, proteins and biomedical applications). The core of the work is devoted to a review of theoretical aspects of linear polymers, with emphasis on self-avoiding walk (SAW) chains, in regular lattices and in both deterministic and random fractal structures. Values of critical exponents describing the structure of SAWs in different environments are updated whenever available. The case of random fractal structures is modeled by percolation clusters at criticality, and the issue of multifractality, which is typical of these complex systems, is illustrated. Applications of these models are suggested, and references to known results in the literature are provided. A detailed discussion of the reptation method and its many interesting applications are provided. The problem of protein folding and protein evolution are also considered, and the key issues and open questions are highlighted. We include an experimental section on polymers which introduces the most relevant aspects of linear polymers relevant to this work. The last two sections are dedicated to applications, one in materials science, such as fractal features of plasma-treated polymeric materials surfaces and the growth of polymer thin films, and a second one in biology, by considering among others long linear polymers, such as DNA, confined within a finite domain.

Dependence of Charge Transport on the Degree of Ordering in Semicrystalline Conjugated Polymers

AbstractThe influence of ordering inside the crystalline regions of semi‐crystalline polymer thin films on charge transport is investigated by analyzing the electric field dependence of mobility calculated using Monte Carlo simulation. The degree of ordering inside the ordered regions is varied by changing the overlap between the hopping transport sites. Negative field dependence of mobility extending to higher electric field strengths along with an increase in the mobility are observed upon increasing the overlap between transport sites inside the ordered region. These observations are attributed to the variation in the charge transport, which affects the transit time that not only decreases but also shows a gradual shift from negative to positive field dependence at lower electric field strengths (∼&lt;3 × 105 V/cm). Variations in the transit time are explained using the variation in the field dependence of hops performed by the carrier inside the ordered and disordered regions. Field dependence of mobility is also simulated with ballistic charge transport inside the ordered regions. At low concentrations of ordered regions (COR), higher carrier mobility is attained with hopping transport (∼&lt;70%). Ballistic transport provides higher mobility at higher COR (∼&gt;70%). This suggests that a very high order inside the ordered region may not necessarily provide higher mobility.

Development of an environmentally friendly pre-treatment for electroless metallisation of glasses

ABSTRACT In recent years, the growing need for materials that have high thermal resistance, non-flammability, high radioactive resistance and durability is the reason for the development of new technologies for electroless metallisation of glasses. The most important operation is surface roughening, which is usually carried out in etching solutions containing HF acid, which is harmful to the environment and to health and safety at work. In this regard, the aim of the present research is the creation of an environmentally friendly technology for electroless metallisation of glasses. Тhe samples were pre-treated in two ways: one group was covered with a thin polymer film (Plastik 70 special glue or epoxy resin, thinned with dimethylformamide), and the other was degreased and treated with a solution of (3 aminopropyl) trimethoxysilane (APTS) at different concentrations and under different conditions. All samples were activated with a colloidal activator, after which copper or nickel-phosphorus coatings were deposited by electroless plating.