Amorphous Polymers Research Articles

Nonlinear effects at the deformation of amorphous polymers in warm and frozen states

One of the important problems of the modern rheology of polymer materials, namely, the possibility of describing the deformation of amorphous polymers within the framework of linear rheological relationships between relative deformation and deforming stress or the need to use nonlinear rheological equations is considered. The criteria for distinguishing these approaches, namely, the determination of the corresponding critical values of the macro- and microphysical characteristics of the material and the conditions for carrying out the mechanical tests are also discussed. In particular, the difference between the influence of kinetic and thermodynamic nonlinear effects on the regularities of deformation processes of amorphous polymers in warm and frozen states was noted. The influence of nonlinear effects on the general shape and characteristics of individual stages of the “relative strain - deforming stress” diagram at deformation of polymer samples with specified values of strain rate and temperature is analyzed in detail. The results of the theoretical analysis were used for the physical interpretation of the general form and features of individual stages of the tensile test diagrams of amorphous polyimide films (V. D. Natsik, H. V. Rusakova, S. V. Lubenets, V. A. Lototskaya, and L. F. Yakovenko, Fiz. Nyzk. Temp. 49, 569 (2023) [Low Temp. Phys. 49, 521 (2023)]), empirical estimates for the rheological characteristics of this polymer were obtained.

Development And Characterization of Magnesium Ion Conducting Biopolymer Electrolyte Using Agar and Magnesium Nitrate Hexa Hydrate

The aim of the study was to develop an agar-based biopolymer electrolyte with varying concentrations of Mg(NO3)2.6H2O in double-distilled water as the solvent. To better understand the impact each concentration had on the biopolymer, a range of characterisation techniques were employed - XRD, FTIR, DSC, Ac impedance analysis and transference number measurement being amongst them. XRD was used to determine whether a crystalline or amorphous polymer resulted from the process. Agar and magnesium nitrate may form complexes, according to FTIR. Through the process of differential scanning calorimetery, researchers have pinpointed the glass transition temperatures for a biopolymer electrolyte with superior conductivity. In order to study its performance, a Mg2+ ion primary battery was built using a biopolymer membrane with a highest ionic conducting of 1.74 x 10-4 S cm-1. This electrolyte was comprised of 40% agar and 60% magnesium nitrate in water, and its ionic transference number of Mg2+ had been determined at 0.30 via Evan's methodology.

Advances in organic–inorganic nanocomposites for cancer imaging and therapy

Abstract “All in one” organic–inorganic nanocomposites with high biocompatibility and excellent physicochemical properties have recently attracted special attention in cancer imaging and therapy. Combination of organic and inorganic materials confers the nanocomposites with superior biocompatibility and biodegradability of organic materials, as well as magnetic, mechanical, and optical properties of inorganic materials. Increased endeavors have been made to produce diverse organic–inorganic nanocomposites and investigate their potential applications in cancer treatment. Thus, a systematic review of research progresses of diverse organic–inorganic nanocomposites in cancer imaging and therapy is indispensable. Following a brief overview of nanocomposites synthesis, classification, and functionalization, the current review is focused on comprehensively summarizing representatives of both organic–inorganic nanoscale nanocomposites (including organic-silica, organic-carbon, organic-quantum dots, organic-platinum family metals, organic-gold, organic metal oxides, and other nanocomposites) and organic–inorganic molecular nanocomposites (including metal-organic frameworks, organosilica nanoparticles, and amorphous metal coordination polymer particles), and further analyzing their working mechanism in cancer imaging and therapy. Finally, the challenges and future perspectives of organic–inorganic nanocomposites are addressed for promoting their developments and clinical application in cancer treatment.

Structural Modulation of Nitrogen-Rich Covalent Organic Frameworks for Iodine Capture.

Developing efficient adsorbent materials for iodine scavenging is essential to mitigate the threat of radioactive iodine causing adverse effects on human health and the environment. In this context, we explored N-rich two-dimensional covalent organic frameworks (COFs) with diverse functionalities for iodine capture. The pyridyl-hydroxyl-functionalized triazine-based novel 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(pyridine-2-amine) (TTPA)-COF possesses high crystallinity (crystalline domain size: 24.4 ± 0.6 nm) and high porosity (specific BET surface area: 1000 ± 90 m2 g-1). TTPA-COF exhibits superior vapor-phase iodine adsorption (4.43 ± 0.01 g g-1) compared to analogous COF devoid of pyridinic moieties, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-COF. The high iodine capture by TTPA-COF is due to the enhanced binding affinity conferred by the extra pyridinic active sites. Furthermore, the crucial role of long-range order in porous adsorbents has been experimentally evidenced by comparing the performance of iodine vapor capture of TTPA-COF with an amorphous network polymer having identical functionalities. We have also demonstrated the high iodine scavenging ability of TTPA-COF from the organic and aqueous phases. The mechanism of iodine adsorption by the heteroatom-rich framework is elucidated through FTIR, XPS, and Raman spectral analyses. The present study highlights the need for structural tweaking of the building blocks toward the rational construction of advanced functional porous materials for a task-specific application.

Tailoring porous organic polymers with enhanced capacity, thermal stability and surface area for perfluorooctane sulfonic acid (PFOS) elimination from water environment

Perfluorooctane sulfonic acid (PFOS), a perfluoroalkyl substance, has engendered alarm over its presence in water sources due to its intrinsic toxicity. Hence, there is a pressing need to identify efficacious adsorbents capable of removing PFAS derivatives from water. To achieve this, batch adsorption studies under various circumstances were employed to tune amorphous polymer networks regarding their morphological configuration, heat durability, surface area and capacity to adsorb PFOS in water. A facile, one-pot nucleophilic substitution reaction was employed to synthesize amorphous polymer networks using triazine derivatives as building units for monomers. Notably, POP-3 exhibited a superlative adsorption capacity, with a removal efficiency of 97.8%, compared to 90.3% for POP-7. POP-7 exhibited a higher specific surface area (SBET) of 232 m2 g−1 compared to POP-3 with a surface area of 5.2 m2 g−1. Additionally, the study emphasizes the importance of electrostatic forces in PFOS adsorption, with pH being a significant element, as seen by changes in the PFOS sorption process by both polymeric networks under neutral, basic and acidic environments. The optimal pH value for the PFOS removal process using both polymers was found to be 4. Also, POP-7 exhibited a better thermal stability performance (300 °C) compared to POP-3 (190 °C). Finally, these findings indicate the ease with which amorphous polymeric frameworks may be synthesized as robust and effective adsorbents for the elimination of PFOS from waterbodies.

High-Quality Circularly Polarized Organic Afterglow from Nonconjugated Amorphous Chiral Copolymers.

Organic materials featuring circularly polarized luminescence (CPL) and/or afterglow emission represent an active research frontier with promising applications in various fields, but the achievement of high-performance CPL organic afterglow (CPOA) remains a huge challenge due to the intrinsic contradictions between the luminescent lifetime/dissymmetry factor (glum) and phosphorescent quantum efficiency (PhQY). Herein, we report a simple and universal approach to design efficient CPOA from amorphous copolymers by incorporating chiral chromophores into a nonconjugated clusterization-triggered emissive polymer with plenty of hydron-bonding interactions, followed by aggregation engineering using water dissolution and evaporation. With this chiral copolymerization and aggregation engineering (CCAE) strategy, high-performance CPOA polymers with PhQYs of up to 6.32%, ultralong lifetimes of over 650 ms, glum values of 3.54 × 10-3, and the highest figure-of-merit were achieved at room temperature. Given the impressive CPOA performance of these polymers, the applications in multilevel data anticounterfeiting and reversible displays with high stability were demonstrated. These findings through the CCAE strategy to overcome the inherent restraints of CPOA materials lay the foundation for the development of amorphous polymers with superior CPOA, significantly expanding the understanding of CPL and the design of organic afterglow materials.

The effect of physical aging on the viscoelastoplastic response of glycol modified poly(ethylene terephthalate)

For most amorphous polymers, their long term viscoelastic behaviour is greatly affected by physical aging, referring to the transition of their non-equilibrium structure towards equilibrium. This, in turn, affects their thermomechanical properties. In this study, we successfully applied a constitutive model, originally developed for semi-crystalline polyesters to assess the impact of physical aging on stress relaxation and creep in two glycol modified poly(ethylene terephthalate) grades, (poly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate) (PECT) and poly(ethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PETT). Both copolyesters are subject to annealing at Tg-20 °C for up to 504 h and subsequent uniaxial stress relaxation tests and, for PECT, creep tests. The results show that the annealing time has a significant influence on the viscoelastic behaviour increasing the resistance to creep and stress relaxation. The effect of physical aging on model parameters is described and analysed while it is found that the concentration of active polymer junctions decreases exponentially with annealing time. Generally, PETT and PECT showed almost identical viscoelastic behaviours at 30 °C, suggesting that the chemical structure of the glycol unit (2,2,4,4-tetramethyl-1,3-cyclobutanediol and 1,4-cyclohexylenedimethanol) does not have significant effect on their viscoelasticity. However, when stress relaxation is tested at increased temperatures, the structural effects are more apparent, demonstrating higher activation energies for PECT than those for PETT, describing the rate of the rearrangement of interchain interactions. Physical aging is also found to decrease these activation energies from 326.6 to 128.1 kJ mol−1 for PECT and from 262.7 to 78.5 kJ mol−1 for PETT.

Martensitic ternary FeCrMn thin films sputtered from austenitic AISI 202 stainless steel target: Phase transition and corresponding magnetic properties under the influence of deposition rate

The nanostructured materials exhibit quite different properties from their bulk counterparts. Therefore, in this work, phase transition from a commercial austenitic AISI 202 (Bulk FeCrMn) stainless steel to martensitic ternary FeCrMn thin films under variation of deposition rate were studied. The films were easily sputtered onto a flexible amorphous polymer substrate from the target by a DC magnetron. X-ray diffraction analysis showed that austenitic phase of the target converted into a mixture of martensitic and a very weak of austenitic phase of the films at the deposition rates of 0.04 and 0.06 nm/s. With a further increase of the deposition rate, martensitic phase in the films increased, and at the highest deposition rate, the film with 100 % martensite phase was obtained. According to magnetic analysis, austenitic target consists of paramagnetic and ferromagnetic components as oppose to the paramagnetic phase stated in the literature. The films obtained by sputtering of austenitic target have ferromagnetic character with an increasing saturation magnetization, MS as the deposition rate increases. The increase of the MS from 117 to 346 emu.cm−3 may be explained by the increase of the % martensite that may increase the ferromagnetic character. Also, the increase of the coercivity of the films from 31 to 196 Oe may have come from the increase of % martensite and the increase of grain sizes with increasing deposition rates which may induce the stress in the films. It is seen that the nanostructured ternary FeCrMn thin films exhibit quite different phase and corresponding magnetic properties from their bulk counterpart. With sputtering, martensitic phase transition of ternary FeCrMn thin films can be controlled by varying deposition rates. It presents a potential usage for data storage and micro electric-electronic devices on flexible substrates.

Raman Analysis of Orientation and Crystallinity in High Tg, Low Crystallinity Electrospun Fibers.

Electrospun fibers of amorphous or low-crystallinity polymers typically exhibit a low molecular orientation that can hamper their properties and application. A key stage of the electrospinning process that could be harnessed to mitigate the loss of orientation is jet rigidification, which relates closely to the solvent evaporation rate. Here, we establish quantitative Raman methods to assess the molecular orientation and crystallinity of weakly crystalline poly(2,6-dimethyl-1,4-phenylene oxide) fibers with varying diameters. Our findings demonstrate that solvent volatility can be leveraged to modulate the orientation and crystallinity through its impact on the effective glass transition temperature (Tg,eff) of the polymer jet during the electrospinning process. Specifically, a highly volatile solvent yields a higher and more sustained orientation (median ⟨P2⟩ of 0.53 for diameters < 1.0 µm) because its fast evaporation rapidly increases Tg,eff above room temperature. This vitrification early along the jet path promotes the formation of an oriented amorphous phase and a moderate fraction of strain-induced crystals. Our data reveals that a high Tg is a crucial parameter for reaching high orientation in amorphous or low-crystallinity polymer systems.

Functionalized semi‐crystalline polyethylene with polar groups at branch end enabled by bulky cationic palladium catalysts

AbstractTransition metal‐catalyzed copolymerization of ethylene with polar monomers is the most direct and efficient way to prepare polar functionalized polyethylene. Generally, the classical Brookhart type α‐diimine Pd(II) catalysts produced hyperbranched functionalized polyethylene with polar groups at the branch ends, which turns out to be amorphous polymer materials. In this contribution, we described the synthesis and characterization of three bulky diarylmethyl α‐diimine ligands and the corresponding Pd(II) complexes. Lightly branched (21–27/1000C) polyethylenes with high molecular weights (317.8–640.0 kg/mol) and high melting points (94–101°C) were prepared using these Pd(II) complexes at high activities (well above 105 g/mol.h). The resulting polyethylene materials exhibited high stress (23.8‐34.3 MPa) and high strain (559–839%) at break values with typical properties of thermoplastics. Polar functionalized semi‐crystalline polyethylenes with moderate incorporation ratios (0.35–2.99 mol%) and high melting points (84–109°C) were prepared using complexes Pd1‐3 in the copolymerization of ethylene with several polar comonomers (methyl acrylate and 10‐undecenoic acid and 10‐methyl undecanoate). The 1H and 13C NMR spectral analysis revealed that these polar functionalized polyethylenes have a low branching density (19–34/1000C) and are predominantly methyl‐branched, with polar groups located at the end of the branches. In addition, the 4‐methoxy group on the ligands in this work would facilitate the insertion of polar monomers in the copolymerization of ethylene with various polar monomers.

Comparing molecular weight models for polymer degradation with ball-mill grinding

Kinetics studies provide important insight into the parameters that influence the degradation of polymers during ball-mill grinding (BMG). One of the simplest ways to calculate degradation rate constants is by fitting molecular weight data (the molecular weight typically decreases with increasing grinding time) with a molecular weight model. Most molecular weight models were developed for ultrasonic or other degradation processes, and a robust evaluation of their suitability for BMG had previously not been conducted. In this report, we evaluate the performance of six different molecular weight models in fitting the degradation data from polystyrene (PS) samples with varying initial molecular weight. We use fit statistics and rate constant trends to identify three molecular weight models that appear to be suitable phenomenological models for the degradation of PS with BMG. We also use these models to probe the generality of the glass transition temperature as a kinetic parameter in amorphous polymer degradation. This work highlights the importance of using a suitable molecular weight model, as they can influence the reactivity trends that are observed.

Unravelling the Molecular Structure and Confining Environment of an Organometallic Catalyst Heterogenized within Amorphous Porous Polymers.

The catalytic activity of multifunctional, microporous materials is directly linked to the spatial arrangement of their structural building blocks. Despite great achievements in the design and incorporation of isolated catalytically active metal complexes within such materials, a detailed understanding of their atomic-level structure and the local environment of the active species remains a fundamental challenge, especially when these latter are hosted in non-crystalline organic polymers. Here, we show that by combining computational chemistry with pair distribution function analysis, 129 Xe NMR, and Dynamic Nuclear Polarization enhanced NMR spectroscopy, a very accurate description of the molecular structure and confining surroundings of a catalytically active Rh-based organometallic complex incorporated inside the cavity of amorphous bipyridine-based porous polymers is obtained. Small, but significant, differences in the structural properties of the polymers are highlighted depending on their backbone motifs.

An atomistic-continuum concurrent statistical coupling technique for amorphous materials using anchor points

A generalized framework for anchor point based concurrent coupling of finite element method (FEM) and molecular dynamics (MD) domains, incorporating previous related methods, is presented. The framework is robust and is agnostic of material crystallinity and atomistic description. The method follows an iterative approach to minimize the total energy of the coupled FEM-MD system, while maintaining displacement constraints between the domains. Two distinct forms of the coupling method are discussed in detail, differing in the nature of the constraint, both of which are able to make use of specialized MD solvers such as LAMMPS with little or no modification. Both methods make use of springs that join groups of atoms in the MD to the FEM domain. Method 1, termed ‘Direct Coupling’, couples MD anchor points directly to the FEM domain in a force-based manner and has the added advantage of being able to couple to specialized FEM solvers such as ABAQUS. Method 2 couples the MD to the FEM domain in a more ‘soft’ manner using the method of Lagrange multipliers and least squares approximation. The relative performance of these two methods are tested against each other in a uniaxial tension test using a graphene monolayer at 300 K temperature and a block of thermosetting polymer EPON862 at low temperature, showing comparable results. Convergence behaviour of the two coupling methods are studied and presented. The methods are then applied to the fracture of a centre-cracked graphene monolayer and compared with results from an identical pure MD simulation. The results corroborate the effectiveness of the developed method and potential use as a plug-and-play tool to couple pre-existing specialized FEM and MD solvers. Future work will focus on applying these methods to simulate elevated-temperature amorphous polymer models and their brittle fracture.

High-throughput computation and machine learning of refractive index of polymers

Refractive index (RI) of polymers plays a crucial role in the design of optoelectronic devices, including displays and image sensors. We have developed a framework for (1) high-throughput computation of RI values for computationally synthesized amorphous polymer structures based on a generalized polarizable reactive force-field (ReaxPQ+) model, which is orders-of-magnitude faster than quantum-mechanical methods; (2) prediction of composition–structure–RI relationships based on a machine-learning model based on graph attention neural network; and (3) computation of frequency-dependent RI combining ReaxPQ+ and Lorentz-oscillator models. The framework has been tested on a computational database of amorphous polymers.

On the modeling of cavitation and yielding in rubber-toughened amorphous polymers: Fully implicit implementation and optimization-based calibration

In the present contribution, a finite strain visco-elastic visco-plastic (three-dimensional) constitutive model is proposed to predict the nonlinear response of neat, porous and rubber-toughened amorphous polymers. In this context, a well-known nucleation law is modified and coupled with a nucleation criterion to suppress nucleation under compression and shear loadings, as well as to identify its material parameters directly. The growth of both the nucleated and initial voids is ruled by a modified version of the Gurson’s potential, ensuring the coherence in the energy dissipation between the macro and microscales. The post-yield strain hardening of the material is modeled with the well-established eight-chain model. A fully implicit integration algorithm is formulated under the infinitesimal strains functional format, and both constitutive state update and consistent tangent modulus are properly established. A three-stage optimization-based calibration procedure is designed to identify the model’s material parameters efficiently. This decoupled calibration strategy is only possible due to the well-defined influence of the model’s material parameters in the numerical response. The predictive capability of the proposed constitutive model is validated against literature results for polycarbonate and three rubber-filled polycarbonate blends. Moreover, the numerical response of the model is assessed under different triaxial states and is further compared with the homogenized response of a Representative Volume Element of the voided-amorphous polymer microstructure. The results highlight that the model can capture the typical behavior of amorphous polymers, namely yield stress, strain-softening and strain hardening under different loading conditions, as well as the decrease of stress associated with the increase of the void volume fraction. The additional numerical analyses conducted, validated some constitutive assumptions. The efficiency of the calibration procedure and the overall numerical strategy is also demonstrated.

SYNTHESIS AND STUDY OF THE PROPERTIES OF EPOXYCYCLOCARBONATES BASED ON ACRYLATE-VINYL COPOLYMERS

A method of synthesis of acrylate-vinyl copolymers based on glycidyl methacrylate and styrene at different molar ratios and epoxy cyclocarbonates based on them was developed. Synthesis of styrene-glycidyl methacrylate (СP GMA/St) copolymers was carried out by the method of thermally initiated radical polymerization in steel reactors in the presence of 1% azo-bis-isobutyronitrile initiator at a temperature of 65 °C for 10 hours. The number of epoxy groups in the synthesized СP GMA/St, determined by the potentiometric titration method, naturally decreases with a decrease in the molar ratio of GMA/styrene. The synthesis of СP GMA/St epoxycyclocarbonates was carried out in a high-pressure autoclave by passing CO2 through the reaction mixture of a solution of KP in toluene with a catalyst (tetrabutylammonium bromide 5%) with stirring at a temperature of 110–120 °C, a pressure of (4-5) atm. The structure of СP and ECC was confirmed by IR spectroscopy. No bands of double bonds are observed in the IR spectra of СP GMA/St, there are vibration bands characteristic of oligostyrene and vibration bands of C=O, C–O–C and epoxy groups. During the formation of ECC, new vibration bands of cyclocarbonate groups with a maximum of 1802 cm-1 appear, changes are observed in the absorption region of C–O–C groups (1100–1300) cm-1, and the vibration bands of epoxy groups with a maximum of 843 cm-1 decrease. The study of relaxation transitions in acrylate-vinyl copolymers GMA/St and epoxy cyclocarbonates based on them using the DSC method showed that all samples are amorphous single-phase polymers. After changing the background, the excessive enthalpy observed during the first heating disappears, and the glass transition temperature shifts towards higher temperatures, which indicates the formation of a denser and thermodynamically balanced structure. The thermostability of the synthesized GMA/St copolymers and epoxy cyclocarbons was investigated by the method of thermogravimetry. It was established that all the obtained substances have one stage of weight loss and are heat resistant, since weight loss begins at a temperature above 240 °C. In the future, the obtained epoxycyclocarbonates will be used for the synthesis of polyurethanes by the non-isocyanate method.

Kinetic criterion for triple-shape memory effect in amorphous polymers undergoing heterogeneous glass transitions

The triple-shape memory effect (triple-SME) in amorphous polymers arises from the heterogeneous glass transitions of different components. However, due to the complex composition and structural relaxation of triple-shape memory polymers (triple-SMPs), existing models struggle to characterize the shape memory temperature range for each component and its dependence on thermal history. This presents a challenge in developing a kinetic criterion to judge the occurrence of the triple-SME. To address this issue, we propose a kinetic phase transition model to predict the shape memory temperature range for each transition phase in triple-SMPs under different thermal histories. By combining the Tool-Narayanaswamy-Moynihan (TNM) model with the Adam-Gibbs theory, the effect of cooling rate during programming on subsequent triple-SME is investigated. Subsequently, the effectiveness of the proposed model is evaluated by applying it to predict the shape memory performance and thermomechanical behavior of SMPs with dual- and triple- SMEs under different thermal histories. Using this modeling strategy enables the calculation of the critical isothermal shape recovery time for each transition phase under different thermal histories, effectively preventing shape recovery overlap. Consequently, the proposed model is expected to provide theoretical guidance for designing SMPs with triple-SME and promoting their application in engineering.

In vitro enzymatic degradation of the PTMC/cross-linked PEGDA blends.

Introduction: Poly(1,3-trimethylene carbonate) (PTMC) is a flexible amorphous polymer with good degradability and biocompatibility. The degradation of PTMC is critical for its application as a degradable polymer, more convenient and easy-to-control cross-linking strategies for preparing PTMC are required. Methods: The blends of poly(trimethylene carbonate) (PTMC) and cross-linked poly(ethylene glycol) diacrylate (PEGDA) were prepared by mixing photoactive PEGDA and PTMC and subsequently photopolymerizing the mixture with uv light. The physical properties and in vitro enzymatic degradation of the resultant PTMC/cross-linked PEGDA blends were investigated. Results: The results showed that the gel fraction of PTMC/cross-linked PEGDA blends increased while the swelling degree decreased with the content of PEGDA dosage. The results of in vitro enzymatic degradation confirmed that the degradation of PTMC/cross-linked PEGDA blends in the lipase solution occurred under the surface erosion mechanism, and the introduction of the uv cross-linked PEGDA significantly improved the resistance to lipase erosion of PTMC; the higher the cross-linking degree, the lower the mass loss. Discussion: The results indicated that the blends/cross-linking via PEGDA is a simple and effective strategy to tailor the degradation rate of PTMC.

Amorphous solid dispersions of curcumin in a poly(ester amide): Antiplasticizing effect on the glass transition and macromolecular relaxation dynamics, and controlled release

In order to exploit the pharmacological potential of natural bioactive molecules with low water solubility, such as curcumin, it is necessary to develop formulations, such as amorphous polymer dispersions, which allow a constant release rate and at the same time avoid possible toxicity effects of the crystalline form of the molecule under scrutiny. In this study, polymer dispersions of curcumin were obtained in PADAS, a biodegradable semicrystalline copolymer based on 1,12-dodecanediol, sebacic acid and alanine. The dispersions were fully characterized by means of differential scanning calorimetry and broadband dielectric spectroscopy, and the drug release profile was measured in a simulated body fluid. Amorphous homogeneous binary dispersions were obtained for curcumin mass fraction between 30 and 50%. Curcumin has significantly higher glass transition temperature Tg (≈ 347 K) than the polymer matrix (≈274-277 K depending on the molecular weight), and dispersions displayed Tg’s intermediate between those of the pure amorphous components, implying that curcumin acts as an effective antiplasticizer for PADAS. Dielectric spectroscopy was employed to assess the relaxation dynamics of the binary dispersion with 30 wt% curcumin, as well as that of each (amorphous) component separately. The binary dispersion was characterized by a single structural relaxation, a single Johari-Goldstein process, and two local intramolecular processes, one for each component. Interestingly, the latter processes scaled with the Tg of the sample, indicating that they are viscosity-sensitive. In addition, both the pristine polymer and the dispersion exhibited an interfacial Maxwell-Wagner relaxation, likely due to spatial heterogeneities associated with phase disproportionation in this polymer. The release of curcumin from the dispersion in a simulated body fluid followed a Fickian diffusion profile, and 51% of the initial curcumin content was released in 48 h.

Optimization of Gas-Sensing Properties in Poly(triarylamine) Field-Effect Transistors by Device and Interface Engineering.

In this study, we investigated the gas-sensing mechanism in bottom-gate organic field-effect transistors (OFETs) using poly(triarylamine) (PTAA). A comparison of different device architectures revealed that the top-contact structure exhibited superior gas-sensing performance in terms of field-effect mobility and sensitivity. The thickness of the active layer played a critical role in enhancing these parameters in the top-contact structure. Moreover, the distance and pathway for charge carriers to reach the active channel were found to significantly influence the gas response. Additionally, the surface treatment of the SiO2 dielectric with hydrophobic self-assembled mono-layers led to further improvement in the performance of the OFETs and gas sensors by effectively passivating the silanol groups. Under optimal conditions, our PTAA-based gas sensors achieved an exceptionally high response (>200%/ppm) towards NO2. These findings highlight the importance of device and interface engineering for optimizing gas-sensing properties in amorphous polymer semiconductors, offering valuable insights for the design of advanced gas sensors.