Polymer Density Research Articles

A thermodynamic study on relationship between gas separation properties and microstructure of polyurethane membranes

The lattice fluid (LF) thermodynamic model and extended Vrentas’ free-volume (E-VSD) theory were coupled to study the gas separation properties of the linear thermoplastic polyurethane (TPU) membranes with different chemical structures by analyzing their microstructures. A set of characteristic parameters were extracted using the repeating unit of the TPU samples and led to prediction of reliable polymer densities (AARD < 6%) and gas solubilities. The viscoelastic parameters, which were obtained from the DMTA analysis, were also estimated the gas diffusion vs. temperature, precisely. The degree of microphase mixing based on the DSC analysis was in order: TPU-1 (4.84 wt%) < TPU-2 (14.16 wt%) < TPU-3 (19.92 wt%). It was found that the TPU-1 membrane had the highest degree of crystallinity, but showed higher gas solubilities and permeabilities because this membrane has the least degree of microphase mixing. These values, in combination with the gas permeation results, showed that the content of the hard segment along with the degree of microphase mixing and other microstructural parameters like crystallinity were the determinative parameters.

Controlled Interfacial Polymer Self-Assembly Coordinates Ultrahigh Drug Loading and Zero-Order Release in Particles Prepared under Continuous Flow.

Microparticles are successfully engineered through controlled interfacial self-assembly of polymers to harmonize ultrahigh drug loading with zero-order release of protein payloads. To address their poor miscibility with carrier materials, protein molecules are transformed into nanoparticles, whose surfaces are covered with polymer molecules. This polymer layer hinders the transfer of cargo nanoparticles from oil to water, achieving superior encapsulation efficiency (up to 99.9%). To control payload release, the polymer density at the oil-water interface is enhanced, forming a compact shell for microparticles. The resultant microparticles can harvest up to 49.9% mass fraction of proteins with zero-order release kinetics in vivo, enabling an efficient glycemic control in type 1 diabetes. Moreover, the precise control of engineering process offered through continuous flow results in high batch-to-batch reproducibility and, ultimately, excellent scale-up feasibility.

Scalable Polyimide-Organosilicate Hybrid Films for High-Temperature Capacitive Energy Storage.

High-temperature polymer dielectrics have broad application prospects in next-generation microelectronics and electrical power systems. However, the capacitive energy densities of dielectric polymers at elevated temperatures are severely limited by carrier excitation and transport. Herein, a molecular engineering strategy is presented to regulate the bulk-limited conduction in the polymer by bonding amino polyhedral oligomeric silsesquioxane (NH2 -POSS) with the chain ends of polyimide (PI). Experimental studies and density functional theory (DFT) calculations demonstrate that the terminal group NH2 -POSS with a wide-bandgap of Eg ≈ 6.6eV increases the band energy levels of the PI and induces the formation of local deep traps in the hybrid films, which significantly restrains carrier transport. At 200°C, the hybrid film exhibits concurrently an ultrahigh discharged energy density of 3.45Jcm-3 and a high gravimetric energy density of 2.74Jg-1 , with the charge-discharge efficiency >90%, far exceeding those achieved in the dielectric polymers and nearly all other polymer nanocomposites. Moreover, the NH2 -POSS terminated PI film exhibits excellent charge-discharge cyclability (>50000) and power density (0.39MWcm-3 ) at 200°C, making it a promising candidate for high-temperature high-energy-density capacitors. This work represents a novel strategy to scalable polymer dielectrics with superior capacitive performance operating in harsh environments.

Failure characteristics analysis of crushed-stone-reinforced polymer (CSRP) composites under compressive load based on meso-mechanics

Adding crushed stones into the polymer can effectively improve the stiffness and engineering properties of the polymer. In this study, a meso finite element model is established to explore the influence of the matrix polymer, interfacial transition zone (ITZ), and crushed stone on the mechanical properties of crushed-stone-reinforced polymer (CSRP) composites, and analyze the failure mechanism of CSRP. The results showed that the elastic modulus and compressive strength of the CSRP increased significantly with an increase in the matrix polymer density and decreased with an increase in the low-density ITZ (LDITZ) relative content or ITZ thickness. An increase in the crushed stone content can increase the elastic modulus of the CSRP. Polymer density and LDITZ primarily affected the development of CSRP cracks. The modulus and strength of the LDITZ were lower than those of the matrix polymer. The failure began at LDITZ under load in the low-density CSRP owing to the high LDITZ relative content. The polymer and crushed stone are split simultaneously under load in the high-density CSRP owing to the strong mechanical properties of the matrix polymer and the low LDITZ relative content.

High‐Energy‐Density All‐Organic Dielectric Film via a Continuous Preparation Processing

AbstractDielectric polymers with high power density and breakdown strength (Eb) are indispensably used in electrostatic energy‐storing systems and devices. However, the discharged energy density (Ue) of dielectric polymers is severely limited due to the relatively low dielectric constant (K). Although current polymer composites improve K, this approach usually faces challenges in enhancing Ue due to the trade‐off relation between K and Eb and difficulties in scalable production of dielectric films. Here, a fully melt‐extrudable, meter‐scale, and high‐Ue ferroelectric polymer‐based all organic composite film comprising a poly(p‐phenylene terephthalamide)‐based fluxible polymer (denoted as f‐PPTA) is reported. The polymer composite with only 2 wt% of f‐PPTA presents a productivity of 12 m2 h−1 and an ultrahigh Ue of 20.7 J cm−3, which outperforms other extruded dielectric polymers reported in the literatures. Such enhancements of dielectric and capacitive properties have been comprehensively investigated and attributed to the crystallization behavior modulations and conformation changes induced by f‐PPTA. As a demonstration of real applications, the dielectric capacitors established based on the extruded films enable tens of times higher efficacy on powering electronic devices than biaxially oriented polypropylene capacitors, in addition to long‐term cyclic stability. This study opens up new avenue for the design and fabrication of high‐Ue polymer dielectrics that are totally compatible with industrial production.

Sorption of CO2, CH4 and Their Mixtures in Amorphous Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO).

Sorption of pure CO2 and CH4 and CO2/CH4 binary gas mixtures in amorphous glassy Poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) at 35 °C up to 1000 Torr was investigated. Sorption experiments were carried out using an approach that combines barometry with FTIR spectroscopy in the transmission mode to quantify the sorption of pure and mixed gases in polymers. The pressure range was chosen to prevent any variation of the glassy polymer density. The solubility within the polymer of the CO2 present in the gaseous binary mixtures was practically coincident with the solubility of pure gaseous CO2, up to a total pressure of the gaseous mixtures equal to 1000 Torr and for CO2 mole fractions of ~0.5 mol mol-1 and ~0.3 mol mol-1. The Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) modelling approach has been applied to the Non-Random Hydrogen Bonding (NRHB) lattice fluid model to fit the solubility data of pure gases. We have assumed here that no specific interactions were occurring between the matrix and the absorbed gas. The same thermodynamic approach has been then used to predict the solubility of CO2/CH4 mixed gases in PPO, resulting in a deviation lower than 9.5% from the experimental results for CO2 solubility.

Experimental investigation on the compressive mechanical properties of the non-aqueous reacting polymer with AE and DIC techniques

As a new type of non-excavation repair material, non-aqueous reacting polymer (NARP) is increasingly adopted in rehabilitation engineering. Properly evaluating the compressive mechanical properties of NARP with different densities is crucial for optimizing the repair design in engineering practices. However, due to a lack of experiments, the mechanism of the compressive mechanical properties of NARP influenced by the density is still not clear, and the constitutive model applicable for NARP with a wide range of density has also not been established yet. In this study, the compression characteristics of NARP with different densities under uniaxial compressive loading were comprehensively investigated, by using the acoustic emission (AE) and digital image correlation (DIC) techniques. Consequently, a statistical damage constitutive model considering the effect of density was established. The results showed that both the compressive yield strength and the elastic modulus of the NARP were strongly correlated with the density, and the correlated relationships can be characterized by two separate quadratic polynomial functions. The damage pattern of the NARP mainly changed from a ductile mode with low-density (ρ < 0.4 g/cm3) to a brittle mode with high-density (ρ > 0.4 g/cm3). The high-density NARP tends to exhibit a significant compressive brittleness. The AE signals were detected throughout the uniaxial compression experiments and the released AE activity was stronger at the same strain with a higher polymer density. Both the pre- and post- yield stages of NARP materials with different densities can be well characterized by using the proposed statistical damage model, being capable of considering the effect of density. The findings on the deformation and damage mechanism, together with the established constitutive model, have significant implications for the design of NARP in engineering practices.

MRI on a new polymeric multichannel membrane for ultrafiltration

Membrane ultrafiltration in new polymeric multi-channel membranes designed for in-out filtration was investigated to get insights into structure, flow and filtration properties. The apparent novelty of the membrane concerns the geometry and configuration of the feed channels.In-situmagnetic resonance imaging (MRI) allows non-invasive and non-destructive investigations with adequate spatial and time resolution. The structure of the new polymeric membrane was measured with an in-plane spatial resolution of 35 µm/pixel revealing first the polymer density distribution over the 19-channel membrane and second the wettability of the fiber and its cavities of different dimensions. MRI was also used to answer questions about flow and consequently feed distribution in the channels. Finally,in-situfiltration of an aqueous solution of sodium alginate was observed which led to deposit formation at the channel’s inner surfaces. The kinetics of this deposit formation was quantified. Backwashing and flushing gave insight into the cleanability of the channels.

Structural Modifications of Polyethylenimine to Control Drug Loading and Release Characteristics of Amorphous Solid Dispersions.

Crystalline drugs with low solubility have the potential to benefit from delivery in the amorphous form. The polymers used in amorphous solid dispersions (ASDs) influence their maximum drug loading, solubility, dissolution rate, and physical stability. Herein, the influence of hydrophobicity of crosslinked polyethylenimine (PEI) is investigated for the delivery of the BCS class II nonsteroidal anti-inflammatory drug flufenamic acid (ffa). Several synthetic variables for crosslinking PEI with terephthaloyl chloride were manipulated: solvent, crosslinking density, reactant concentration, solution viscosity, reaction temperature, and molecular weight of the hyperbranched polymer. Benzoyl chloride was employed to cap amine groups to increase the hydrophobicity of the crosslinked materials. Amorphous deprotonated ffa was present in all ASDs; however, the increased hydrophobicity and reduced basicity from benzoyl functionalization led to a combination of amorphous deprotonated ffa and amorphous neutral ffa in the materials at high drug loadings (50 and 60 wt %). All ASDs demonstrated enhanced drug delivery in acidic media compared to crystalline ffa. Physical stability testing showed no evidence of crystallization after 29 weeks under various relative humidity conditions. These findings motivate the broadening of polymer classes employed in ASD formation to include polymers with very high functional group concentrations to enable loadings not readily achieved with existing polymers.

Surface Mechanical Properties and Topological Characteristics of Thermoplastic Copolyesters after Precisely Controlled Abrasion.

Due to the high probability of surface-to-surface contact of materials during routine applications, surface abrasion remains one of the most challenging factors governing the long-term performance of polymeric materials due to their broad range of tunable mechanical properties, as well as the varied conditions of abrasion (regarding, e.g., rate, load, and contact area). While this concept is empirically mature, a fundamental understanding of mechanical abrasion regarding thermoplastics remains lacking even though polymer abrasion can inadvertently lead to the formation of nano-/microplastics. In the present study, we introduce the concept of precision polymer abrasion (PPA) in conjunction with nanoindentation to elucidate the extent to which controlled wear is experienced by three chemically related thermoplastics under systematically varied abrasion conditions. While depth profiling of one polymer reveals a probe-dependent change in modulus, complementary results from positron annihilation lifetime spectroscopy confirm that the polymer density changes measurably, but not appreciably, with depth over the depth range explored. After a single PPA pass, the surface moduli of the polymers noticeably increase, whereas the corresponding increase in hardness is modest. The dependence of wear volume on the number of PPA passes is observed to reach limiting values for two of the thermoplastics, and application of an empirical model to the data yields estimates of these values for all three thermoplastics. These results suggest that the metrics commonly employed to describe the surface abrasion of polymers requires careful consideration of a host of underlying factors.

Study on the failure mechanism between polyurethane grouting material and concrete considering the effect of moisture by digital image correlation

The bond resistance between polyurethane (PU) grouting material and concrete consists of adhesion, friction, and mechanical interlocking and is crucial to the repaired concrete structures. During the repair of the leakage and subsidence of underground concrete pipelines by PU grouting material, the chemical adhesion between PU and concrete interfaces may be influenced by moisture caused by the pipeline leakage and groundwater. In this paper, shear tests and the digital imaging correlation (DIC) method were used to study the effect of moisture on the shear bond performance and failure process of the PU-concrete interface before and after grouting PU with different densities. The results reveal that the differences in bond strength, shear strain and horizontal displacement between the interfaces are significantly reduced with the polymer density, especially for moistened interfaces before grouting and testing. Finally, a finite element model was employed to simulate the bond strength between PU and concrete and validated based on the test results.

Enhanced piroctone olamine retention from shampoo for superior anti-dandruff efficacy.

Dandruff is a pervasive chronic condition which negatively impacts quality of life. Effective treatment requires efficient delivery of scalp benefit agents that control commensal scalp Malassezia levels. Delivery of benefit agents from shampoos requires balancing many technical parameters to achieve the desired outcome without sacrificing secondary parameters, such as cosmetic attributes. To develop formulation technologies that increase the shampoo delivery efficiency of the scalp benefit agent piroctone olamine (PO). Increased delivery should result in increased anti-dandruff efficacy. Micellar Stability and Association parameters were quantified via dynamic surface tension and nuclear magnetic resonance (NMR) diffusion parameters, respectively. PO delivery has been assessed in vivo both on the scalp surface and follicular infindibula using extraction procedures and analytical analysis. Clinical anti-dandruff efficacy was assessed for an advanced delivery technology prototype in comparison to standard delivery technology. Shampoo prototypes have been developed that increase the delivery efficiency of PO. Both surfactant and polymer coacervate-based approaches have been developed. Decreased micellar stability results in weaker association between PO and micelles, resulting in more efficient PO retention on the scalp surface and delivery to the infundibula. Increased charge density of cationic polymers optimizes coacervation enabling improved PO delivery as well. Increased PO delivery has been shown clinically to result in higher anti-dandruff efficacy as measured by both visible flakes and underlying biomarkers. Increased efficiency PO delivery shampoos have been developed by optimization of both surfactant and coacervate parameters. The increased deposition efficiency results in significantly more products with significantly greater anti-dandruff efficacy.

Sediment matters as a route of microplastic exposure: A call for more research on the benthic compartment

Microplastics (MPs) are ubiquitous in the marine environment. Here, most MPs are expected to sink, either due to polymer density or environmental processes, such as biofouling, leading to sediment being proposed to act as a final sink for marine MPs. There is a discrepancy between the anticipated accumulation of MPs in the sediment compartment and the MP experiments conducted, since most MP effect studies have been conducted with pelagic species using water-only exposures. Here we address fundamental questions in relation to MP pollution to close the knowledge gap related hereto. A systematic literature search was performed to address these questions. We found that benthic invertebrates ingest MPs and that, even though these organisms evolutionary are adapted to handle particles, adverse effects may be observed upon ingestion of MPs. The analysis further revealed that there is a major knowledge gap on the impacts of sediment-associated MPs in marine, benthic invertebrates. To facilitate further and structured research within this topic, we recommend more studies with emphasis on the sediment as an important exposure pathway, and to focus on sediment-associated MP effects on benthic invertebrates. We recommend studies with ecological relevant exposure concentrations and ecological relevant exposure durations with emphasis on impacts on population- and community-level to reduce the knowledge gap within this central area of MP pollution research.

Amorphous Macromers as Potential Organic Matrix in Dental Composites

Objectives: Assess the thermal and hydrolytic stability of patented macromer- based dental polymer matrices and composites Methods: Polymer matrices and composites based on a patented material (IP:343192) containing hybrid amorphous macromers co-polymerized with one of the 4 different dimethacrylates was prepared and the thermal and photo-thermal behavior were assessed. Diffusivity resistance and cross-link density of polymers were assessed. Sorption (𝑆(𝑡), 𝑀𝑔%(𝑡) 𝖠 𝑆%(𝑡)and solubility (𝑆𝐿(𝑡) 𝖠 𝑆𝐿%(𝑡) of composites in chloroform (CHCl3), tetrahydrofuran (THF), carbon tetrachloride (CCL) and acetone (Ace) for varying durations (1h, 24h 1mo), and deionized water for 120h were determined. Results: Dual Tg were noticed for both the matrices and composites; matrices containing BisGMA (G) and UDMA (U) as the dimethacrylate co-polymer showed significantly lower𝑆𝐿(𝑡). Matrix containing TEGDMA (T) as the dimethacrylate co-polymer showed the least 𝑆(𝑡). Matrix containing BisEMA (E) had the highest cross-link density. photo-DSC of composites showed a Degree of Conversion of 97% at lower enthalpies (15-28J/g). None of the composites showed water solubility. All materials showed solubility in acetone with U being the least. Sorption and solubility in other organic solvents was lower and occurred only at longer immersion time. Conclusions: Amorphous hybrid macromer-based polymer matrices and composites show promising thermal and hydrolytic behavior.

Role of surface hydrophilicity on MR relaxivity of PEG coated- gadolinium oxide nanoparticles

The magnetic resonance (MR) contrast enhancement capabilities of gadolinium oxide nanoparticles (GONPs) have high dependency on its surface chemistry- as the solution properties such as colloidal stability and hydrodynamic diameter of nanoparticles which are prime regulatory parameter for MR relaxivity, are all governed by grafting density of surface material. However, the purification of synthesized surface coated nanoparticles, without compromising the surface properties, remains a major challenge. Among the various cleaning methods, dialysis is often used to remove the unwanted by-products produced during synthesis. However, the effect of dialysis time may significantly impact the surface properties and hence, the MR contrast properties of such nano-formulations. The aim of the present study is to evaluate the effect of dialysis time on surface chemistry and MR contrast enhancement properties of GONPs by comparing the proton relaxivity data. Ultra-small polyethylene glycol (PEG)-coated GONPs with an average particle diameter of 17 nm were synthesized using polyol method. The impact of dialysis time has been investigated systematically on the size distribution, hydrophilicity, magnetic properties, polymer grafting density and relaxometric properties of the as synthesized GONPs. A significant impact of dialysis time was observed on surface chemistry and hence, on the MR relaxivity of synthesized NPs. We evidenced a dramatic decrease in the proton relaxivities of GONPs with increase in dialysis time, which correlated well with the observed decrease in the grafting density of surface polymer. The results clearly indicate that the proton relaxivity of GONPs of similar size and same coating material depends on the surface coating thickness and hydrophilicity of the coating polymer. Overall, it is essential to optimize the accurate time duration of dialysis treatment as the prolonged dialysis may have negative effect on the relaxation times and hence on MR contrast enhancement properties of GONPs. This study is a strategic pathway to fine-tune the dialysis treatment of as-synthesized surface-capped GONPs for pre-eminent MR contrast imaging.

Interfacial microstructure of neutral and charged polymer brushes: A density functional theory study.

Polymer density functional theory (PDFT) is a computationally efficient and robust statistical mechanics theory for capturing the interfacial microstructure of grafted polymer brushes (PBs). Undoubtedly, the intramolecular and intermolecular interactions in PDFT (e.g., hard-core interactions and direct Coulomb interactions) are greatly affected by the grafting behavior of PBs. However, the combination of these interactions with the physical constraints on grafting behavior remains unclear and there is a remarkable difference in the density profile of grafted PB between PDFT and simulation. Herein, we propose a PDFT to study neutral and charged grafted PBs by incorporating the physical constraints of end-grafted PBs into the excess free energies due to intramolecular and intermolecular interactions. This PDFT has been successfully validated where the density distributions of neutral and weakly charged PBs predicted by the PDFT are in excellent agreement with the results of the Monte Carlo and molecular dynamics simulations. In addition, the significant contribution of grafting behavior to the free energy of PB systems is presented. Consequently, this work provides a powerful and accurate theoretical method to reveal the interfacial microstructure of grafted PBs.

Liquid Oil Trapped inside PVA Electrospun Microcapsules.

Electrospinning makes it possible to obtain solid fibers, in addition to core-shell fibers, using coextrusion. However, an exhaustive control of parameters allows the core-shell fibers from emulsion electrospinning to be obtained. The solvent in the outer surface tends to evaporate and the polymer density increases, moving the emulsion drops towards the center, which in turn promotes coalescence, thus creating the core. The aim of this work was to avoid coalescence and obtain a net of nanofibers entrapping oil microcapsules. We obtained an emulsion oil in water (O/W), with polyvinyl alcohol (W) and two essential oils (O), sage and thyme. An electrospinning process was used to place the microcapsules of oil inside a net of nanofibers. The electrospun veil was characterized by organoleptic testing, SEM microscopy, FTIR spectroscopy, DSC thermal analysis, and pressure tests. Organoleptic testing, FTIR spectroscopy, and DSC thermal analysis demonstrated the presence of the oil, which was retained in the spheres observed by SEM microscopy, while pressure tests revealed that the oil remained in a liquid state. Furthermore, we demonstrated a strong relationship between the emulsion size and the final microcapsules created, which are slightly larger due to the shell formation. The size of the emulsion determines whether the spheres will be independent or embedded in the nanofibers. Furthermore, the nanofiber diameter was considerably reduced compared to the nanofibers without the oil.

Effect of molecular weight distribution on the thermal adhesion of polystyrene and PMMA brushes

The effect of the molecular weight distribution (MWD) and graft density of polymer brushes on the adhesion strength of flat substrates was investigated using polystyrene (PS) and poly(methyl methacrylate) (PMMA) brushes with variations in the molecular weight, MWD, and graft density. Two silicon wafers covered with polymer brushes were bound in a 0.5 cm2 contact area using 5 μL of toluene and a pinchcock Hoffman clamp and then annealed at 408 K in a vacuum oven for 3 h. PS brushes with a MWD narrower than Mw/Mn = 1.20 yielded an adhesion strength lower than 0.1 MPa. In contrast, PS brushes having a broad MWD (Mw/Mn = 1.3–1.4) were successfully joined to afford a lap shear adhesion strength of 1.2 MPa despite high graft density due to the intermixing of longer chains of the opposite brushes. Similar results were also obtained in the case of PMMA brush.

Greatly enhanced energy density in polymer nanocomposites coated with high-k perovskite nanosheets

Polymer dielectric materials with high energy storage density are vital component in advanced electronic devices. However, the increase of conduction loss at relatively high electric field will lead to film failure and hinder the exploration of high energy density in the dielectric polymer. Herein, a general strategy is proposed to effectively enhance the breakdown strength and energy density by coating wide bandgap Ca2Nb3O10 nanosheets on the surface of the polyvinylidene fluoride film using Langmuir-Blodgett and spray coating technologies. The coating layers of Ca2Nb3O10 nanosheets exhibit high insulation feature, and therefore, suppress the leakage current density of the nanocomposite film, resulting in remarkably enhanced breakdown strength of 710 MV/m and discharged energy density of 25.1 J/cm3, with a satisfactory charge–discharge efficiency of 78%. Our work may provide a scalable, and yet effective route to tailor the energy storage density of polyvinylidene fluoride-based polymers.

Entrainment and vertical mixing of aquatic microplastics in turbulent flow: The coupled role of particle size and density.

Diversity in microplastics' characteristics, including their size, affects their transport and distribution in aquatic systems. Furthermore, turbulent induced mixing is often considered dominant in the dispersion of sediments and contaminants in marine and freshwater systems, which is also affected by particle size. The aim of this study is to investigate the effect of microplastics' size and polymer density on their mixing behaviour in response to turbulent structures. Using sediment analogy, several parameters are defined to describe entrainment patterns of microplastic particles of common polymers. Our results indicate that the level of mixing of microplastics in turbulent flow can vary several orders of magnitude. While large particles' vertical motion may be dominated by gravitational settling or rising, the motion of fine microplastics is mainly governed by the ambient turbulent flow. Our findings provide a plausible explanation for the presence of fine microplastics in remote areas.