Liquid Polymer Research Articles

A Novel Poly(ε-Caprolactone)-Based Photo-Crosslinkable Liquid Copolymer as a Versatile Drug Delivery Platform

Background/Objectives: Hydrophobic semi-solid or liquid biodegradable polymers have shown unique advantages as injectable matrices for sustained release of a wide range of drugs. Here we report the design, synthesis, and characterization of a new low-melt liquid copolymer based on poly(ε-caprolactone) (PCL) and establish its utility as a versatile delivery platform. Methods: The copolymer, mPA20, consisting of short PCL blocks connected via acid-labile acetal linkages, was synthesized using a one-pot reaction and its properties were comprehensively characterized. Results: mPA20 is an amorphous, injectable liquid at physiological temperature and can undergo pH-sensitive hydrolytic degradation. mPA20 bearing methacrylate end groups can be photo-crosslinked into solid matrices with tunable mechanical properties. A hydrophobic fluorophore, Nile Red (NR), was solubilized in mPA20 without any solvent. Sustained release of NR into aqueous medium was achieved using mPA20, either as an injectable liquid depot or a photo-crosslinked solid matrix. Further, mPA20 self-emulsified in water to form nanodroplets, which were subsequently photo-crosslinked into nanogels. Both the nanodroplets and nanogels mediated efficient intracellular delivery of NR with no cytotoxicity. Conclusions: mPA20, a new photo-crosslinkable, hydrophobic liquid copolymer with pH-sensitive degradability, is highly adaptable as either an injectable or implantable depot or nanoscale carrier for the controlled release and intracellular delivery of poorly soluble drugs.

Recent developments on multiscale simulations for rheology and complex flow of polymers

AbstractThis review summarized the multiscale simulation (MSS) methods for polymeric liquids. Since polymeric liquids have multiscale characteristics of monomeric, mesoscopic, and macroscopic flow scales, MSSs that relate different hierarchical levels are adequate to reproduce flow properties accurately. Our review includes pioneering studies to the most advanced MSS studies on rheology predictions and flow simulations of polymeric liquids. We discuss two major types of MSS methods: the bottom-up and model-embedded MSS methods. The former method mainly connects all-atom molecular dynamics models and mesoscopic models to predict rheological properties. In contrast, the latter method, where a microscopic or mesoscopic model is embedded in a macroscopic computational domain, is designed to predict macroscopic flow properties. Finally, we also discuss MSS methods using machine learning techniques. Graphical abstract

Inverse parameter estimation for the white–metzner equation using extrudate diameter measurements

Abstract This study presents a method to determine the elastic modulus of the White–Metzner (WM) viscoelastic model, which is used to describe polymer melt flow. In processes involving polymeric liquids, elastic effects are essential for accurate simulations. In particular, phenomena such as melt swelling after extrusion and upon gate passage in injection molding are critical to process simulation. However, systematic procedures for material characterization remain underdeveloped since implementation of an appropriate material model is challenging due difficulties inherent in parameter determination. In this work, to account for the shear thinning behavior, which is essential when handling polymeric liquids in current processes, while also incorporating elastic properties, the WM equation was employed. The method employs the post-extrusion swelling phenomenon where the diameter of the extruded material expands after exiting the capillary die. It integrates melt swell measurements with numerical simulations based on the WM equation and highlights the importance of considering gravity in the simulation. A laser scanning microscope is used to measure the extruded diameter while adaptive multi-objective optimization identifies unknown parameters in the model to align the simulation results with the measured diameter. This approach successfully determined the elastic modulus of the PET-PEN copolymer, establishing a system for determining the viscoelastic properties of polymer melts.

From Anisotropic Molecules and Particles to Small-Scale Actuators and Robots: An Account of Polymerized Liquid Crystals

From Anisotropic Molecules and Particles to Small-Scale Actuators and Robots: An Account of Polymerized Liquid Crystals

Understanding Relaxation in the Kob-Andersen Liquid Based on Entropy, String, Shoving, Localization, and Parabolic Models.

We assess the validity of a range of models of glass formation based on molecular dynamics simulation results of the Kob-Andersen (KA) model system under a wide range of constant volume and constant pressure conditions. These models include the Adam-Gibbs model emphasizing configurational entropy, the string model emphasizing collective particle exchange motion, the shoving model emphasizing material elasticity, the localization model emphasizing dynamical free volume, and parabolic models based on the ideas of dynamic facilitation and, alternatively, the hypothesis that glass formation involves an avoided critical point. We demonstrate that these seemingly disparate models all provide a reasonable description of structural relaxation and diffusion data for the KA model system under all simulation conditions considered. Hence, the present study points to some unity in our understanding of the relationship between leading models of glass formation, supporting inferences drawn from previous studies of polymeric glass-forming liquids.

Evidence of short chains in liquid sulfur.

High energy x-ray pair distribution function measurements show the average coordination number of the first shell in liquid sulfur is 1.86 ± 0.04 across the λ-transition, not precisely 2.0 as widely accepted. This indicates that upon melting, liquid sulfur does not comprise solely of S8 rings but also possesses a significant number of short chains. Intensities of the pre-peak and first diffraction peak of the x-ray structure factor and third peak height of the pair distribution function all show deviations at the λ-transition temperature Tλ, associated with the break-up of S8 rings and the start of oligomer polymerization. A significant number of non-bonded or loosely bonded "interstitial atoms," with an average coordination number of 0.20 ± 0.005, are also observed in the so-called "forbidden zone" between the first and second shells upon melting. The number of interstitial atoms is found to decrease to a minimum at the λ-transition, but the majority persist into the high temperature polymerized liquid. The existence of short chains and nearby interstitial atoms represent the two main factors required to initiate the S8-ring to chain transition, as proposed by recent molecular dynamics simulations.

Boosted electrochemical reduction detoxification and oxidation of clofibric acid by polymerized ionic liquid functionalized cathode: Parameter optimization and degradation mechanisms

The application of electrocatalytic degradation technology in the treatment of pharmaceuticals and personal care products (PPCPs) has attracted widespread attention currently. Through structure and properties characterization of catalysts we found that more uniformly distributed metal particles and excellent thermal stability were obtained by modification with poly(1-vinyl-3-butylimidazole hexafluorophosphate) ([(PV)BIM]PF6) on graphene to anchor the metal CoNi nanoparticles (CoNi/PILs-rGO). For assessing its application potential, the CoNi/PILs-rGO cathode in combination with Ti/RuO2/IrO2 anode to set up an experimental reaction system for the electrocatalytic degradation of clofibric acid (CA) simulated wastewater. Reactor settings for experimentation are optimized, and intermediates, alterations in toxicity during degradation, and active species are detected. The results of the single-factor experiment showed that the average removal rate of CA by the cathodic compartment was 97.18 % when the conditions were optimal. Two possible pathways of degradation are deduced from the CA intermediates, one is the C-Cl bond breaking in electrochemical reduction, and the other is that the C-O bond is directly broken by anodic reactive oxygen. Toxicity tests have shown that the anode produces some by-products that are more hazardous than the original chemical, while the cathode produces a dechlorination process that is ultimately more detoxifying.

Deformation localisation in stretched liquid crystal elastomers

We model within the framework of finite elasticity two inherent instabilities observed in liquid crystal elastomers under uniaxial tension. First is necking, which occurs when a material sample suddenly elongates more in a small region where it appears narrower than the rest of the sample. Second is shear striping, which forms when the in-plane director rotates gradually to realign and become parallel with the applied force. These phenomena are due to the liquid crystal molecules rotating freely under mechanical loads. To capture necking, we assume that the uniaxial order parameter increases with tensile stretch, as reported experimentally during polydomain-monodomain transition. To account for shear striping, we maintain the uniaxial order parameter fixed, as suggested by experiments. Our finite element simulations capture well these phenomena. As necking in liquid crystal elastomers has not been satisfactorily modelled before, our theoretical and numerical findings related to this effect can be of wide interest. Shear striping has been well studied, yet our computed examples also show how optimal stripe width increases with the nematic penetration depth measuring the competition between the Frank elasticity of liquid crystals and polymer elasticity. Although known theoretically, this result has not been confirmed numerically by previous nonlinear elastic models.

One-pot fabrication of bio-inspired shape-morphing bilayer structures

Soft bilayer structures capable of shape morphing in response to external stimuli have been commonly adopted in the design of soft robots, flexible electronics and many other smart systems. However, existing methods to fabricate such structures generally require multiple steps and may end up a weak interface between the two layers. Here, we report a one-pot fabrication strategy to generate elastomer-based shape-morphing bilayer structures with a seamless interface. Our strategy leverages on a recently developed bioinspired polymer-NaCl particle composite system which can undergo significant osmotic swelling in water. Bilayer structures are readily formed after the precipitation of NaCl particles in liquid polymers under gravity and the crosslinking of the polymers. The shape-morphing behavior of the fabricated bilayer structures can be well controlled by tuning the particle precipitation kinetics, NaCl content, and crosslinking level of the polymer matrix. More importantly, the bilayer structures fabricated using this strategy exhibit more complex shape-morphing responses than typical bilayer structures. Considering the wide applicability of NaCl particle-induced osmotic swelling of polymer composites, our one-pot bilayer formation strategy will greatly benefit many shape-morphing applications with a simplified fabrication workflow and enhanced configurational versatility.

Manipulating the adhesion of electroless plated Cu film on liquid polymer crystal substrate for advanced microelectronic manufacturing

Manipulating the adhesion of electroless plated Cu film on liquid polymer crystal substrate for advanced microelectronic manufacturing

Methods of active friction control in the presence of lubricant compositions with mesogenic additives

Purpose of research. The aim of the study is to systematize the latest literature data related to the modulation of the friction coefficient by external fields when using lubricant compositions with liquid crystal mesogens and polymer composites.Methods. The article considers the methods of tribological tests using various schemes of friction pairs (cylinder-disk, pin-on-disk). Some commonly used methods of applying coatings to the elements of friction pairs are considered: ion beam-assisted deposition, chemical and physical thermal spraying, molecular layer deposition, photopolymerization, etc. Of the discussed methods of characterizing tribosystems, the following are indicated: dielectric spectroscopy, Raman scattering, polarization optical microscopy, nuclear-physical methods (positron annihilation spectroscopy and Xray diffraction).Results. The article systematizes modern trends in the development of modulated modes of operation of tribological circuits with lubricant compositions containing liquid crystals and polymer composites. The following approaches are used to implement active control of the friction coefficient: 1) modulation of friction by an electric field, 2) modulation of friction by a temperature field, and 3) modulation of friction on optical gratings under light irradiation. These approaches take into account the changed characteristics of the lubricant associated with the use of mesogenic additives, modes of exposure to electromagnetic and thermal fields, electrical characteristics, geometry of the surface of friction pairs, and provide the values of tribological characteristics (friction coefficient and wear) that are achieved as a result of friction modulation.Conclusion. A positive effect of mesogenic additives of liquid crystals and polymers on tribological characteristics with active control of the friction coefficient has been established: a decrease in the friction coefficient is observed, which helps to reduce material wear.

Fractionation of phenolic aldehydes by liquid–liquid extraction and polymer resin adsorption

ABSTRACT The extraction and adsorption characteristics of three phenolic aldehydes with high physicochemical similarity in lignocellulosic biomass hydrolyzate, which are fermentation inhibitors, were investigated. The extraction process considered both physical extraction with two organic solvents and reactive extraction with five basic extractants. In physical extraction, n-hexane was found to be the most suitable organic solvent for selectively separating 4-hydroxybenzaldehyde from the three phenolic aldehydes, and in reactive extraction, trioctylphosphine oxide was identified as the most suitable basic extractant for the selective separation of syringaldehyde. In the adsorption process, various neutral polymer resins and anion-exchange polymer resins were employed. Among them, the neutral polymer resin XAD16 was found to be the most suitable for selectively separating 4-hydroxybenzaldehyde. To efficiently separate and concentrate the three phenolic aldehydes with equal mass percentages, a proposed five-step fractionation process included the aforementioned extraction and adsorption techniques. By implementing n-hexane-based physical extraction in step 4 and NaOH solution-based back-extraction in step 5 of the fractionation process, the purities of 4-hydroxybenzaldehyde, vanillin, and syringaldehyde in the final solution increased from their initial 33.3% each to 67.6%, 69.8%, and 76.4%, respectively, at a volume ratio of the aqueous phase to the organic phase of 1:15.

METROLOGICAL ANALYSIS OF THE IMPACT OF THE ARRANGEMENT OF MODELS ON THE 3D PRINTER PLATFORM ON THE DIMENSIONAL ACCURACY OF MODELS MANUFACTURED USING PHOTO-CURING TECHNOLOGY - PJM

The paper presents the results of metrological tests and measurements of dimensional accuracy of models manufactured using the photo-curing additive technology of POLYJET MATRIX - PJM. The material from which the samples were manufactured was a liquid polymer resin with the commercial name MED610, which is characterized by a high degree of biocompatibility, which increases the validity of the research in medical and dental applications. The key parameter considered was the location of digital CAD models in selected places of the virtual building platform and it influence of dimensional accuracy. The research results showed a clear impact of the arrangement of models on the building platform on the accuracy of the produced models, both in terms of external and internal diameters.

Influence of Density and Pressure on Glass Formation in the Kob-Andersen Model.

We systematically study glass formation in the well-known Kob-Andersen model over a wide range of densities and pressures as a basis for judging the "universality" of glass formation through a comparison to a recent systematic study of model polymeric glass-forming liquids. Our purpose is to establish general characteristics of glass formation, to identify new relations, and to discern which properties of glass-forming liquids are material-specific and which are "universal." To this end, we analyze a number of characteristic properties of glass formation, such as the structural relaxation time, self-diffusion coefficient, viscosity, characteristic temperatures, and fragility. We also consider a suite of properties presumably related to dynamic heterogeneity in an attempt to better understand its relation to structural relaxation. We demonstrate that the glassy dynamics in the Kob-Andersen model exhibit many of the essential trends observed in polymeric glass-forming liquids, pointing to a remarkable "universality" of many aspects of glass formation.

On the non-linearity of rheological film condensation

Condensation of non-Newtonian fluids is a less explored research field but has tremendous potential in the industry. We propose a mathematical theory to model the behaviour of non-Newtonian film condensation on vertical surfaces. The simple theory can contribute to understanding the operation of many engineering appliances using motor oils, polymeric liquids, and fuels. The well-known power-law model approximates the viscosity of condensate. We vary the power-law index (n) within 0.8≤n≤1.2 to encompass the behaviour of shear-thinning, Newtonian and shear-thickening films, while the flow consistency index (μ0) remains constant throughout the study. Since the film flow is gravity-driven, stream-wise advection is expected to dominate over cross-stream advection. We, however, establish the subtle role of cross-stream advection within the thin condensate film. We have identified a thinner film, a lower condensate drainage rate and a greater average heat transfer coefficient (hm) as an influence of the cross-stream advection. An exclusion of cross-stream advection transforms temperature distribution across the film from non-linear to linear. The linear temperature distribution is unrealistic for Ja≥0.5. We illustrate approximately 5% error incurred for neglecting cross-stream advection in estimating hm at Ja=0.81 and n=0.8. The error increases with a further decrease in n values or an increase in the Ja. The exclusion of cross-stream advection affects the film-thickness and average heat transfer disproportionately in shear-thinning and shear-thickening regimes. Finally, we propose mathematical expressions to estimate heat transfer coefficient and Nusselt number, which would be helpful for field engineers.

Lithium Plating Using a Thermoplastic Vulcanizate Electrolyte

Lithium metal anodes have generated significant interest due to their high theoretical capacity. However, issues such as dendrite growth or cell failure caused by lithium loss with either liquid electrolytes or solid polymer electrolytes (SPEs) have hindered its widespread commercialization. In this work, we report on the electrochemical characterization of symmetric Li-SPE-Li cells made with a thermoplastic vulcanizate electrolyte, PCl:HNBR LiTFSI. Full plating of the lithium metal (LiM) electrode was achieved at 100 μA.cm−2 in pressurized pouch cells. This was confirmed ex situ using scanning electron microscopy which showed the absence of dendrites. The Sand equation was employed at higher current densities to determine that the lithium diffusion coefficient at 60 °C is 1.7 × 10−8 cm2.s−1. The calculated threshold current density j* was approximately 200 μA.cm−2. The determination of the theoretical current density limit may provide critical information for the understanding of the behavior of cathode materials during cycling with lithium metal. Cell failure at high polarization or from short circuiting was experimentally confirmed in symmetric Li-Li cells where 100 cycles were performed at a current density below j* with 0.1 mAh.cm−2 of charge per cycle, while 0.5 mAh.cm−2 of charge rapidly induced cell failure.

Tailoring the PVDF membrane surface with polyoxypropylene-polyoxyethylene brush via in-situ grafting for enhanced oil/water emulsion separation

Membrane technology has been widely applied in oil-water separation owing to low energy consumption and high separation efficiency, but membrane fouling is a fatal factor affecting membrane performance and service life. Inspired by polyether nonionic detergents, a liquid surfactant polymer with polyoxypropylene-polyoxyethylene (PPO-PEO) segments was tailored to the surface of polyvinylidene fluoride (PVDF) membrane via in-situ grafting to improve its antifouling and oil-water separation properties. Firstly, in order to activate the inert surface of the PVDF membrane, poly(styrene-co-maleic anhydride) (SMA) was blended with PVDF to prepare the MA@PVDF as membrane substrate. Then, PPO-PEO brushes were grafted onto the surface of the substrate by an alcoholysis reaction to fabricate the PPO-PEO@PVDF membrane. The chemical structure and the surface morphology of the PPO-PEO tailored PVDF membrane surface were characterized, and the separation performance for oil/water emulsion was explored. The results show that the optimized grafting amount of PPO-PEO on the PVDF membrane is up to 476.2±3.0mg·g-1, and the pure water flux of the corresponding PPO-PEO@PVDF membrane is 191.3±4.0L·m-2·h-1, which is more than 20 times higher than that of the control PVDF membrane (around 7L·m-2·h-1). The water wetted PPO-PEO brushes on the surface of the PVDF membrane can hinder the adhesion of oily substances, and the separation efficiency of the PPO-PEO@PVDF membrane for kerosene/water emulsion reaches 91.7±0.6%, which is much higher than that of the MA@PVDF membrane without PPO-PEO brushes. The PPO-PEO tailored PVDF membrane provides useful strategies for the surface modification of membranes with enhanced performances of antifouling and oil-water separation.

Adsorption of phenolic compounds on polymeric ionic liquids: Adsorption isotherms interpretation and thermodynamic study

This study describes the thermodynamic assessment and steric interpretation of the 4-nitrophenol (4-NP) and 4-chlorophenol (4-CP) adsorption on polymeric ionic liquids (PILs) using advanced statistical physics model. A monolayer model with a single energy level was employed to elucidate the adsorption mechanisms of these phenolic compounds. The results showed that the orientation of 4-NP and 4-CP on the surface of this adsorbent was a combination of parallel and non-parallel configurations at the tested adsorption temperatures. The values of the adsorption capacities at saturation were 484.7 and 406.7 mg/g for4-NP and 4-CP, respectively. The modelling results indicated that more active sites from PILs surface were involved in the removal of 4-nitrophenol than those required for the 4-chlorophenol adsorption. The calculation of adsorption energies confirmed that the adsorption of 4-NP and 4-CP on PILs was exothermic and driven by physical forces involving hydrogen bonds and van der Waals forces. Three thermodynamic functions were analyzed to complete the macroscopic analysis of the adsorption mechanism for these relevant phenolic contaminants.

Preparation and evaluation of polymeric ionic liquid functionalized microparticles as the efficient adsorbent for pipette tip solid phase extraction of sulfonamides

Sulfonamides (SAs) residues are commonly found in environmental samples, which is highly concerning for public safety and environmental protection. The detection of SAs is quite important but challenging. In this work, a kind of polymeric ionic liquid functionalized microparticles (PIL-FM) was synthesized via a simple free radical polymerization reaction, and applied as the adsorbent for pipette tip solid phase extraction (PT-SPE) of three SAs from river water, milk powder and honey samples. The adsorption performance of PIL-FM on SAs were evaluated using adsorption kinetics and adsorption isotherms, and the results showed that PIL-FM had the best selectivity for SMZ with the maximum adsorption capacity was as high as 45.05 mg·g−1. The extraction process was optimized and the adsorption mechanism was preliminarily discussed. PIL-FM has the excellent selectivity for SAs mainly because of the strong π-π interaction, and the electrostatic repulsion between them in the elution step also has a positive impact. Under optimal conditions, combined with HPLC, this PT-SPE method had wide linearity (0.2–100 μg·L−1, R2 ≥ 0.9998) and low limits of detection (0.06–0.08 μg·L−1). The intra-day and inter-day repeatability were found to be 3.7 %–4.6 % and 4.5 %–6.2 %, respectively. The suggested PT-SPE method is simple, low cost, rapid, and efficient to extract SAs, and can be applied for the monitoring of SAs residues in the aquatic environment and in food.

Closure to the PRISM equation derived from nonlinear response theory.

Nonlinear response theory is employed to derive a closure to the polymer reference interaction site model equation. The closure applies to a liquid of neutral polymers at melt densities. It can be considered a molecular generalization of the mean spherical approximation (MSA) closure of Lebowitz and Percus to the atomic Ornstein-Zernike (OZ) equation and is similar in some aspects to the reference "molecular" MSA (R-MMSA) closure of Schweizer and Yethiraj to PRISM. For a model binary blend of freely-jointed chains, the new closure predicts an unmixing critical temperature, Tc, via the susceptibility route that scales linearly with molecular weight, N, in agreement with Flory theory. Predictions for Tc of the new closure differ greatest from those of the R-MMSA at intermediate N, the latter being about 40% higher than the former there, but at large N, both theories give about the same values. For an isotopic blend of polyethylene, the new and R-MMSA closures predict a Tc about 25% higher than the experimental value, which is only moderately less accurate than the prediction of atomic OZ-MSA theory for Tc of methane. In this way, the derivation and its consequences help to identify the ingredients in a theory needed to properly model the equilibrium properties of a polymeric liquid at both short and long lengthscales.