Bulk Polymer Research Articles

In-plane oxygen diffusion measurements in polymer films using time-resolved imaging of programmable luminescent tags

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10–7 cm2/s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Experimental Investigation and Computational Insights of Enhanced Rheological Stability of Water-Based Drilling Fluids by Microspherical Polymers

Summary 3D bulk polymer, as an alternative to linear polymer, has exhibited large potential in formulating high-performance water-based drilling fluids. Understanding the mechanism behind the enhanced rheological stability of drilling fluids by microspherical polymers is critical for designing and developing new high-performance drilling fluids. In this work, we conducted a pioneering investigation that integrated experimental techniques with computational modeling, to explore the enhancement mechanism involved in the targeted drilling fluids. Inverse emulsion polymerization experiments were first carried out to fabricate the microspherical polymer acrylic acid (AA), acrylamide (AM), and 2-acryloylamino-2-methyl-1-propanesulfonic acid [P(AA-AM-AMPS)], and then physicochemical properties of microspherical polymer were characterized. Subsequently, the performance of drilling fluids with microspherical polymer as an additive was systematically evaluated. Finally, molecular simulations were used to investigate the characteristics of chemical active sites, molecular conformation, and structural variation at various temperatures. The results showed that the final microspherical polymer has a core-shell structure, with an average size of 198.3 nm and a molecular weight of 6.2×106 g/mol. The 3D structure exhibits good thermal stability, and thermal decomposition occurs above 220°C. The drilling fluids formulated with the microspherical polymer showed better rheological stability in the medium-low (4–65°C) and medium-ultrahigh (40–240°C) temperature ranges, compared with the relevant drilling fluids with the parallel linear polymer. Analyses on electrostatic potentials (ESPs) and frontier molecular orbital (FMO) revealed that active groups within the confined sphere domain mainly include carbonyl C = O and amide -CO(NH2). Additionally, these active groups exhibit a hierarchical distribution in the outer molecular region. Analyses on the radius of gyration (Rg) and the radial distribution function g(r) further validated the core-shell structure of microspherical polymer and its temperature-resistant stability. Moreover, a new self-consistent structural compensation model was proposed to rationalize the structure-activity relationship of microspherical polymer in drilling fluids. The computational results align well with the experimental findings. This pioneering work will provide valuable information for both the synthesis of new functional additives and the formulation of tailored-performance drilling fluids.

Multiple Force-Triggered Downconverted and Upconverted Emission in Polymers Containing Diels-Alder Adducts.

Fluorescent mechanophores can indicate the deformation or damage in polymers. The development of mechanophores with multi-triggered response is of great interest. Herein, Diels-Alder (DA) adducts are incorporated into linear poly(methyl acrylate) PMA-BA and network poly(hexyl methacrylate) (PHMA) as mechanophores to detect the stress caused by ultrasound, freezing, and compression. The DA mechanophores undergo retro-DA reaction to release 9-styrylanthracene chromophore upon applying force, resulting in cyan fluorescence. The dissociation ratio of the DA mechanophore after pulsed ultrasonication of PMA-BA solution for 240 minutes is estimated to be 52 % by absorption spectra and 1H NMR. Additionally, the rate constant of mechanical cleavage is calculated to be 1.2×10-4 min-1⋅kDa-1 with the decrease in molecular weight from 69 to 22 kDa measured by gel permeation chromatography. Freezing of PHMA gels as well as compression of PHMA bulk samples turn-on the DA mechanophores, revealing the microscale fracture. Photon upconversion responses toward various force stimuli are also achieved in both polymer solutions and bulk samples by doping platinum octaethylporphyrin (PtOEP) or palladium meso-tetraphenyltetrabenzoporphyrin (PdTPTBP) sensitizers with multiple excitation wavelengths.

Characterizing ABS–copper chemistry-dependent adhesion: From the atomic to macro level

The electroplating of copper layers on acrylonitrile–butadiene–styrene (ABS) polymer surfaces is a common need in industrial applications. The development of new eco-friendly techniques to promote ABS–copper adhesion is crucial due to the harsh and expensive chemicals used in the existing processes. The initial path involves establishing a better understanding on chemistry-dependent ABS–copper adhesion mechanisms. By formulating the material with more functional groups, the adhesion between ABS and the coated copper layer was characterized through a multiscale approach. At the atomic scale, we performed ab initio density functional theory simulations to obtain the variations in the adsorption energy. At the nano and micro scales, we adopted atomic force microscopy to measure the adhesion forces on the bulk polymer surfaces. At the macro scale, we compared these adhesion results with both 90-degree peeling tests and finite element model analyses. This study presents the first comprehensive approach for bridging information gaps across the scales (from nano to macro) with computational and experimental data, facilitating the design of formulated ABS additives.

Suppressive Photochromism and Promotive Mechanochromism of Rhodamine Mechanophore by the Strategy of Poly(methyl acrylate)/Polyurethane Interpenetrating Polymer Network.

As molecular design and the structure-property relationships of photochemical molecules established in the literature serve as a convenient reference for mechanophore exploration, many typical mechanophores suffer undesired responses to UV light or even sunlight in bulk polymers. We developed a strategy of a poly(methyl acrylate)/polyurethane (PMA/PU) interpenetrating polymer network (IPN) to suppress the photochromic property of the mechanophore and promote its mechanochromic property. A widely used rhodamine mechanophore (Rh-2OH) was first incorporated into polyurethane (P1). Then P1 was swollen in methyl acrylate and photopolymerized to prepare a PMA2.8/PU IPN (P2). Different from photo/force-responsive P1, P2 selectively responded to force because the low free volume in IPN greatly hinders photoisomerization of the rhodamine spirolactam, suggesting that a simple IPN strategy successfully resolves the giant problem of nonselective response to photo/force for photochromic mechanophores. Moreover, PMA/PU IPN enhanced the mechanical property, resulting in a higher mechanochemical activation ratio than PU, and the prestretching effect of PMA/PU IPN promoted the force sensitivity of rhodamine mechanophores significantly. We believe that the strategy can be applied to other mechanophores, promoting their application in more complicated environments.

Evaluation of the reusability of photocatalytic P25/PDMS membranes when hindering their hydrophobic recovery

Polydimethylsiloxane is a suitable photocatalyst support for wastewater treatment. However, as polydimethylsiloxane is hydrophobic it must be modified, to become hydrophilic prior to its application. Unfortunately, this modification is not permanent and polydimethylsiloxane materials can recover part of their original characteristics. Therefore, even though photocatalytic polydimethylsiloxane-based membranes exhibit a satisfactory performance in the abatement of pollutants, they present a low performance when reused. The main objective of this study was to develop methodologies that may improve the surface wettability of P25/polydimethylsiloxane materials to enhance their reusability. Thus, the following strategies were implemented to delay the hydrophobic recovery or decrease the water contact angle stabilization values of both polydimethylsiloxane and P25/polydimethylsiloxane membranes: increased amount of photocatalyst particles added to the matrix, prolongated curing process and finally storage/application of the material at low temperatures. According to the results, the followed approaches were effective in this regard. However, (i) the first two mentioned strategies led to the formation of photocatalysts agglomerates and, as such, the membranes exhibited a low photocatalytic activity compared to previous studies, and (ii) the last-mentioned strategy led to the inactivation of the photocatalyst. Therefore, it was concluded that an improvement in the surface wettability does not necessarily translate in an improvement of the materials performance, since it may affect other crucial characteristics. It was also concluded that the best results were achieved when P25 was attached to the surface of polydimethylsiloxane but no photocatalyst particles were added to the polymer bulk, when the curing process took four hours, and also when the photocatalytic process was conducted at 25 °C. With these conditions, the material exhibited a performance on the degradation of a mixture of three pollutants of, approximately, 55% in the first cycle, 35% in the second cycle and 30% in the third and fourth cycles.

The role of monomer geometry on the properties of polyolefins: A numerical study

AbstractWe explore the role of monomer geometry on the structural, dynamic, and thermodynamic properties of polyolefis by employing all‐atom molecular dynamic simulations. Specifically, we compare properties of atactic polyolefins in the molten state including polypropylene (aPP), a short‐chain branched polymer: poy(1‐hexene) (aPH), and a polymer having cyclic olefins: poly(vinyl cyclobutane) (aPVCB). We find polymers having the same chain mass and atom composition (hydrocarbon‐based molecules), but having different monomer architecture differ strongly in material properties. In particular, the polymer glass transition () and bulk modulus () show higher values for aPVCB in comparison to aPP and aPH. This increase is caused by having the carbon atoms in a cyclic structure, making aPVCB achieve higher mass and energy densities. By contrast, adding linear short side chains to polymer backbones causes a reduction in and , since side chains make backbones displace each other reducing their packing and thus their mass and energy densities. More broadly, our numerical results suggest that the incorporation of VCB monomers to linear polyolefins will enhance their properties, opening the possibility for designing a new set of materials.

Kinetic Study of the Diels-Alder Reaction between Maleimide and Furan-Containing Polystyrene Using Infrared Spectroscopy.

The Diels-Alder (D-A) reaction between furan and maleimide is a thermally reversible reaction that has become a vital chemical technique for designing polymer structures and functions. The kinetics of this reaction, particularly in polymer bulk states, have significant practical implications. In this study, we investigated the feasibility of utilizing infrared spectroscopy to measure the D-A reaction kinetics in bulk-state polymer. Specifically, we synthesized furan-functionalized polystyrene and added a maleimide small-molecule compound to form a D-A adduct. The intensity of the characteristic absorption peak of the D-A adduct was quantitatively measured by infrared spectroscopy, and the dependence of conversion of the D-A reaction on time was obtained at different temperatures. Subsequently, the D-A reaction apparent kinetic coefficient kapp and the Arrhenius activation energy Ea,D-A were calculated. These results were compared with those determined from 1H-NMR in the polymer solution states.

Enhancing solid-state photochromic performance of Stenhouse Adducts doped in bulk polymers by C3-Symmetric multipolar design

Here, we introduce a C3-symmetric molecular design strategy to develop a brand-new visible-light organic photoswitch, named tri-branched multipolar Stenhouse Adduct (TMSA). After doping TMSA into low glass transition polymers (i.e. thermoplastic urethane, TPU) via simple blending and solution casting, the resultant composite films exploit unique geometric and electronic effects of TMSA to afford markedly-improved photoswitching performance compared to those doped with dipolar donor-acceptor Stenhouse Adduct (DASA) counterparts with suppressed solid state photochromism. Importantly, they display good fatigue resistance over 50 photo-discoloration/thermal-recovery cycles with slow degradation, surpassing those literature-reported composites involving various DASAs (<30 cycles). As revealed by combined experiment and computation studies, the multi-dimensional electronic coupling in multipolar TMSA facilitates the thermal cyclization and non-planar branched structures of TMSA afford large free space in polymers for efficient molecular isomerization, while the promoting effect on TMSA isomerization induced by ester-rich polymer micro-environments is more pronounced relative to DASA counterpart.

One‐Stop Hybrid Printing of Bulk Metal and Polymer for 3D Electronics

One‐Stop Hybrid Printing of Bulk Metal and Polymer for 3D Electronics

A review of polymer surface modification by cold plasmas toward bulk functionalization

AbstractPlasma surface modification of polymers is a well‐established method applied to increase the surface energy of these materials, where the capacity of cold plasmas to generate free radicals and functionalize the surface with polar groups is widely reported in the literature. This article provides a comprehensive literature review on plasma surface treatment, plasma‐induced grafting, and plasma polymerization, evaluating how these techniques can be applied to modify the bulk properties of polymers. A novel process of plasma‐induced polymer bulk functionalization in the melt state is introduced, where an atmospheric pressure plasma jet could be applied to a continuous reactive extrusion process, enhancing the production of graft copolymers for compatibilization of polymeric blends and fiber composites.

Reinforcement of styrene‐acrylonitrile polymer bulk with glass nanofibers to introduce photoluminescent bricks

AbstractTransparent and mechanically reliable plastic was developed by reinforcing styrene‐acrylonitrile polymer (SAP) with electrospun glass nanofibers (EGN). The physical inclusion of strontium aluminate nanoparticles (SAN) produced long‐persistent photoluminescent and photochromic EGN@SAP bricks or smart windows. EGN were fabricated by electrospinning technique and incorporated as a toughening mediator into styrene‐acrylonitrile plastic to boost its mechanical properties. Transparency of EGN@SAP with the capacity to shift to green under ultraviolet (UV) illumination was verified using photoluminescence analysis and CIE Lab parameters. EGN@SAP with low content of SAN exhibited immediate reversibility of the photochromic feature, proving fluorescence emission. Afterglow emission from EGN@SAP embedded with high concentration of SAN persisted for longer time and was less easily reversed. After excitation at 365 nm, the emission peaked at 519 nm. Increasing the SAN content resulted in improved hydrophobicity and UV protection. Diameter measurements of SAN (6–14 nm) and EGN (75–300 nm) were taken utilizing transmission electron microscopy and scanning electron microscopy, respectively. EGN and EGN@SAP bricks were analyzed for their morphological characteristics using a variety of analytical techniques. The scratch resistance of EGN@SAP bricks containing SAN was enhanced in comparison to SAN‐free EGN@SAP bricks.

Enhancing surface segregation with cyclic polymer additives: A facile approach to surface modification

The preferential surface segregation of one component of a polymer blend has been used for the controlled modification of the surface properties. Unlike other modification methods, this technique is simple and does not require any complex modeling or additional processing steps for surface modification. Most surface segregation studies are based on the interaction between the chain ends of the additive and bulk polymer at the surface. However, additives with cyclic topologies without chain ends have not been used. In this study, an additive platform with cyclic topology without a chain end was designed for surface modification. A series of cyclic additives were synthesized via ring-expansion cationic polymerization. X-ray photoelectron spectroscopy analysis of the cyclic polymer additive showed approximately 1.5 times higher surface segregation than the linear polymer when blended with polyurethane. In addition, the surface segregation behavior depending on the molecular weight and pendant length of the cyclic polymer additive was investigated. Moreover, the monomer, allyl vinyl ether, enabled the addition of functional groups to the cyclic additive and the addition of perfluoroalkyl pendant groups was performed, revealing a promising antifouling effect in the adsorption of a plasma protein. The high performance and versatility of the cyclic architectural polymer additives extend the scope of the surface segregation field and can replace existing biomedical coatings.

Excitonic one-photon absorption of one- and two-dimensional C60 polymers: Insights from many-body first-principles calculations

By solving the many-body Bethe–Salpeter equation, we explored the excitonic one-photon absorption of one- and two-dimensional C60 polymers. We studied seven polymeric structures including C60-chain, two structures with quasi-tetragonal phases (qTP1 and qTP2), and four structures with quasi-hexagonal phases (qHP1, ML-qHP2, BL-qHP2, and bulk-qHP2). The one-photon excitonic transitions were analyzed in detail relative to the independent particle transitions. Significant red-shifts (0.4 and 0.2 eV for ML-qHP2 and BL-qHP2, respectively) were observed in the excitonic one-photon absorption of low-dimensional polymers compared to bulk polymers. The red-shift can be related to the dimensional and interlayer dependences of screening effect which lead to different binding energies (0.61, 0.44, and 0.27 eV for ML-qHP2, BL-qHP2, and bulk-qHP2, respectively). For two qHPs (i.e., qHP1 and ML-qHP2), different connection modes between C60 molecules lead to different types (direct and indirect for qHP1 and ML-qHP2, respectively) of electronic band gap, and they also have different spectral profiles due to different hole and electron densities of excitons. Finally, the C60-chain formed by [2 + 2] cycloadditions has a direct band gap of 2.09 eV which is desirable for applications in photoelectric devices based on the solar spectrum.

Mechanical reinforcement from two-dimensional nanofillers: model, bulk and hybrid polymer nanocomposites.

Thanks to their intrinsic properties, multifunctionality and unique geometrical features, two-dimensional nanomaterials have been used widely as reinforcements in polymer nanocomposites. The effective mechanical reinforcement of polymers is, however, a multifaceted problem as it depends not only on the intrinsic properties of the fillers and the matrix, but also upon a number of other important parameters. These parameters include the processing method, the interfacial properties, the aspect ratio, defects, orientation, agglomeration and volume fraction of the fillers. In this review, we summarize recent advances in the mechanical reinforcement of polymer nanocomposites from two-dimensional nanofillers with an emphasis on the mechanisms of reinforcement. Model, bulk and hybrid polymer nanocomposites are reviewed comprehensively. The use of Raman and photoluminescence spectroscopies is examined in light of the distinctive information they can yield upon stress transfer at interfaces. It is shown that the very diverse family of 2D nanofillers includes a number of materials that can attribute distrinctive features to a polymeric matrix, and we focus on the mechanical properties of both graphene and some of the most important 2D materials beyond graphene, including boron nitride, molybdenum disulphide, other transition metal dichalcogenides, MXenes and black phosphorous. In the first part of the review we evaluate the mechanical properties of 2D nanoplatelets in "model" nanocomposites. Next we examine how the performance of these materials can be optimised in bulk nanocomposites. Finally, combinations of these 2D nanofillers with other 2D nanomaterials or with nanofillers of other dimensions are assessed thoroughly, as such combinations can lead to additive or even synergistic mechanical effects. Existing unsolved problems and future perspectives are discussed.

Novel thermal initiator systems for radical induced cationic frontal polymerization

Frontal polymerization is an extremely efficient and rapid method for producing bulk polymers, characterized by a self-sustaining curing front that propagates throughout the resin.

Self-Organized States from Solutions of Active Ring Polymers in Bulk and under Confinement.

In the present work, we study, by means of numerical simulations, the structural and dynamical behavior of a suspension of active ring polymers in bulk and under lateral confinement. At high activity, when changing the distance between the confining planes and the polymers' density, we identify the emergence of a self-organized dynamical state, characterized by the coexistence of slowly diffusing clusters of rotating disks and faster rings moving in between them. We further assess that self-organization is robust in a range of polymer sizes, and we identify a critical value of the activity, necessary to trigger cluster formation. This system has distinctive features resembling at the same time polymers, liquid crystals, and active systems, where the interplay between activity, topology, and confinement leads to a spontaneous segregation in an initially one-component solution.

One‐Stop Hybrid Printing of Bulk Metal and Polymer for 3D Electronics

Additive manufacturing (AM), so‐called 3D printing, has reshaped manufacturing technologies with attractive alternatives to the traditional centralized, subtractive‐based mass production. Further functionalities like multimaterial AM (MMAM) are essential for mainstream manufacturing. With MMAM of electrical traces, the traditional printed circuit board can be transformed to freeform 3D electronics using the entire volumetric space. Although research groups attempt MMAM for freeform 3D electronics, achieving easy integration of the electrical traces with high conductance into dielectric substrates in a streamlined and simplified process remains challenging. Herein, an in‐house developed printer, named Synkròtima, is demonstrated for one‐stop printing of 3D dielectric parts with fully embedded and structured conductive features via drop‐on‐demand printing of molten metal for the first time. Printed traces show 12 times lower electrical resistance of at 230 μm linewidth than the lines from conductive inks. Printed traces with 100 μm dot spacing reveal exemplary shape fidelity with a standard deviation of only 7 μm. Quantitative estimation of adhesion of metal traces to dielectric reveals a mean shear‐off force of 7.20 N which is half of what is obtained for reflow soldered electronics. Demonstrators with embedded functional electrical circuits, directly interconnected components, and 3D out‐of‐plane metal structures are printed via Synkròtima.

PhyNEO: A Neural-Network-Enhanced Physics-Driven Force Field Development Workflow for Bulk Organic Molecule and Polymer Simulations.

An accurate, generalizable, and transferable force field plays a crucial role in the molecular dynamics simulations of organic polymers and biomolecules. Conventional empirical force fields often fail to capture precise intermolecular interactions due to their negligence of important physics, such as polarization, charge penetration, many-body dispersion, etc. Moreover, the parameterization of these force fields relies heavily on top-down fittings, limiting their transferabilities to new systems where the experimental data are often unavailable. To address these challenges, we introduce a general and fully ab initio force field construction strategy, named PhyNEO. It features a hybrid approach that combines both the physics-driven and the data-driven methods and is able to generate a bulk potential with chemical accuracy using only quantum chemistry data of very small clusters. Careful separations of long-/short-range interactions and nonbonding/bonding interactions are the key to the success of PhyNEO. By such a strategy, we mitigate the limitations of pure data-driven methods in long-range interactions, thus largely increasing the data efficiency and the scalability of machine learning models. The new approach is thoroughly tested on poly(ethylene oxide) and polyethylene glycol systems, giving superior accuracies in both microscopic and bulk properties compared to conventional force fields. This work thus offers a promising framework for the development of advanced force fields in a wide range of organic molecular systems.

A continuum-micromechanical model for crazing in glassy polymers under cyclic loading

A micromechanics-inspired constitutive model is developed to describe the deformation behaviour of fibrillated material within crazes in glassy polymers subjected to cyclic loading. In a finite strain setting, the model accounts for the morphology change taking place by the drawing of material from the intact bulk polymer into craze fibrils and their transition from primitive to mature fibrils. Building on previous research, fibril drawing is described as a viscoplastic process. A novel contribution of this study is the incorporation of viscoelastic deformation of existing fibrils, which is motivated by experimental observations. This new perspective allows for creep recovery, especially during the unloading phases of cyclic deformation.A parameter study which pays special attention to the role of the characteristic times scales of fibril drawing and fibril creep in relation to the imposed loading rate illustrates the performance of the model. Since the model is designed as an input to cohesive fracture simulations in glassy polymers, its response under monotonic loading is analysed and compared to existing crazing models. Of primary interest, however, is the model behaviour under cyclic loading which is investigated for different loading scenarios up to fibril failure. The study highlights the complex interplay between the two viscous mechanisms and how they influence the local deformation behaviour of the craze matter as well as the number of cycles until failure.