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We present a dynamic density functional theory for modeling the effects of applied electric fields on the local structure of polymers with added salt (polymer electrolytes). Time-dependent equations for the local electrostatic potential and volume fractions of polymer, cation, and anion of added salt are developed using the principles of linear irreversible thermodynamics. For such a development, a field theoretic description of the free energy of polymer melts doped with salts is used, which captures the effects of local variations in the dielectric function. Connections of the dynamic density functional theory with experiments are established by relating the three phenomenological Onsager's transport coefficients of the theory to the mutual diffusion of electrolyte, ionic conductivity, and transference number of one of the ions. The theory is connected with a statistical mechanical model developed by Bearman and Kirkwood [J. Chem. Phys. 28, 136 (1958)] after relating the three transport coefficients to friction coefficients. The steady-state limit of the dynamic density functional theory is used to understand the effects of dielectric inhomogeneity on the phase separation in polymer electrolytes. The theory developed here provides not only a way to connect with experiments but also to develop multi-scale models for studying connections between local structure and ion transport in polymer electrolytes. [ABSTRACT FROM AUTHOR]

Polyethylene oxide (PEO) holds significant importance in the field of batteries due to its high processability, intrinsic properties, and potential for high ionic conductivity. Achieving simulation at different scales is crucial for gaining a comprehensive understanding of its properties and thus improving them. In this context, we conducted a comparative study on the molecular physical structure, thermodynamic, and dynamic properties of PEO using three distinct coarse-grained (CG) procedures and all-atom (AA) simulations. The three CG simulation procedures involved modeling with MARTINI forcefield, SPICA forcefield, and an IBI derived potential from AA simulations. The AA simulation has been performed using the class 2 pcff+ forcefield. The ensuing simulated densities align significantly with the literature data, indicating the reliability of our approach. The solubility parameter from the AA simulation closely corresponds to literature reported values. MARTINI and SPICA yield almost similar solubility parameters, consistent with the similar density predicted by both the forcefields. Notably, SPICA forcefield closely reproduces the intermolecular structure of atomistic systems, as evidenced by radial distribution function (RDF). It also comprehensively replicates the distribution of radius of gyration (Rg) and the end-to-end distance (Re) of the atomistic samples. IBI ranks second to SPICA in emulating the structural properties of the atomistic systems, such as Rg, Re, and RDF. However, IBI falls short in accurately representing the solubility parameter of the amorphous PEO samples, while MARTINI does not provide an accurate representation of the structural properties of the systems. The use of SPICA forcefield results in enhanced dynamics of the systems in comparison with IBI and MARTINI. [ABSTRACT FROM AUTHOR]

This study delves into the phenomenon of air cavity formation resulting from sphere-liquid impacts, a subject of enduring scientific interest with broad interdisciplinary applications. The actual cavity and air bubble volumes following cavity rupture are for the first time measured and analyzed, in correlation with the thinning of the air filament. Utilizing direct visualization and an original image processing technique, we introduce a method for these precise measurements. We have explored the dynamics of this phenomenon across various fluids, including sunflower oil, glycerin, and polyethylene oxide (PEO) viscoelastic solutions. Impact velocity and fluid properties dictate not only the topology of the air cavity but also the volume dynamics and the evolution of the air thread near cavity rupture. Experiments with PEO solutions show that increasing polymer concentration influences elasticity, resulting in narrower cavity interfaces and reduced air volume attached to the sphere after cavity rupture. The asymmetry of the air cavity is diminished with increasing viscosity and is amplified in the presence of fluid elasticity. Insights into cavity shapes generated by the impact of a spherical body in a liquid, and correlating cavity dynamics with fluid properties, contribute to advancing knowledge in various fields, from solid–fluid interaction and rheology to biomechanics and biology. [ABSTRACT FROM AUTHOR]

Microfluidic cytometry is an emerging technology for single-cell analysis and offers rich biochemical information about cells. Three-dimensional focusing of cells is a key function for microfluidic cytometry. However, the existing microfluidic chips have fixed geometries and are designed for specific cells, limiting the applicability of microfluidic cytometry. In this work, we develop the ultrastretchable microchannel for size-tunable three-dimensional elasto-inertial focusing of particles and cells. This channel can be modulated by stretching the chip, enabling the focusing of particles and cells with a wide range in sizes. The focusing performance of this ultrastretchable channel is characterized experimentally at different particle sizes, flow rates, polyethylene oxide concentrations, and stretch ratios, showing the great capability in three-dimensional focusing of particles. Finally, the applicability of our ultrastretchable microchannel to biological cells is verified by three-dimensional focusing of yeast cells and fibroblast cells (3T3 cells). The ultrastretchable microchannel is easy for mass production and can be integrated with optical sensing modules for downstream single-cell imaging and analysis. [ABSTRACT FROM AUTHOR]

We investigate the effect of liquid elasticity on the transient cavitation bubbles confined in a tube both experimentally and theoretically. In experiments, the tube-arrest apparatus is used to generate cavitation bubbles near the tube bottom with various polyethylene oxide solutions. Our experiments show that bubble dynamics, particularly the maximum bubble length, are significantly influenced by liquid elasticity. We establish a double oscillator model for the liquid column to explain the experimental results and predict the bubble dynamics over a broader range. Finally, we propose that the reciprocal of the cavitation number C a 2 and p r R / k determine the regimes of the liquid column separation, where p r is the reference pressure, R is tube radius, and k is the "stiffness coefficient" of the liquid column. Our work provides a quantitative scaling of the dynamics of large cylindrical cavitation bubbles in viscoelastic liquids during the transient process. [ABSTRACT FROM AUTHOR]

The capture of moisture from the atmosphere through condensation has the potential to provide a sustainable source of water. Here, we investigate the condensation of humid air at low subcooling condition (11 °C), similar to conditions for natural dew capture, and explore how water contact angle and contact angle hysteresis affect the rates of water capture. We compare water collection on three families of surfaces: (i) hydrophilic (polyethylene oxide, MPEO) and hydrophobic (polydimethylsiloxane, PDMS) molecularly thin coatings grafted on smooth silicon wafers, which produce slippery covalently attached liquid surfaces (SCALSs), with low contact angle hysteresis (CAH = 6°); (ii) the same coatings grafted on rougher glass, with high CAH (20°–25°); (iii) hydrophilic polymer surfaces [poly(N-vinylpyrrolidone), PNVP] with high CAH (30°). Upon exposure to water, the MPEO SCALS swell, which likely further increases their droplet shedding ability. MPEO and PDMS coatings collect similar volume of water (around 5 l m−2 day−1), both when they are SCALS and non-slippery. Both MPEO and PDMS layers collect about 20% more water than PNVP surfaces. We present a basic model showing that, under low heat flux conditions, on all MPEO and PDMS layers, the droplets are so small (600–2000 µm) that there is no/low heat conduction resistance across the droplets, irrespective of the exact value of contact angle and CAH. As the time to first droplet departure is much faster on MPEO SCALS (28 min) than on PDMS SCALS (90 min), slippery hydrophilic surfaces are preferable in dew collection applications where the collection time frame is limited. [ABSTRACT FROM AUTHOR]

The present work attempts to systematically explore the surfactant sorption at liquid–liquid interfaces with coarse-grained models targeting thermodynamic properties of reference liquid solutions. We employ dissipative particle dynamics with soft-core forcefield tested against experimental data on micellization of surfactants in water, and the previous results are reproduced in this work. We consider three different nonionic surfactants: hexaethylene glycol monododecyl ether (C12E6), 2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol) known as Triton X-100 (TX-100), and two alkyl glucoside surfactants (CnG1) with n-alkane tail fragments and a saccharide hydrophilic head at decane–water and toluene–water interfaces. For TX-100, we composed a model based on the literature forcefield and found good agreement with the experimental critical micelle concentrations (CMCs). The head–head interactions are of different origins for different surfactant groups: entropic repulsion between ethylene oxide chains of C12E6 and TX-100, and more chemically specific and complex interactions between the maltose heads of alkyl glucosides. We interpret our results with the Redlich–Peterson equation of monolayer adsorption in order to relate the adsorption to the bulk concentration of the surfactant and the interfacial tension. The densities of the adsorbed monolayer at CMC mostly agree with the experimental data, and a reasonable agreement was obtained for the interfacial tension at CMC. At the same time, we found significant discrepancies between the simulated and experimental adsorption isotherms. We explain them by the oversimplified forcefield: when the parameters are fitted to the free energies of bulk solutions, they may not correctly reproduce the interfacial free energies. [ABSTRACT FROM AUTHOR]

This study experimentally observes the flow regimes of polyethylene oxide solutions in continuous, abrupt contraction–expansion microchannels. In dilute solutions (0.5 × 10−3–1.5 × 10−3 wt. %), the effects of flow rate, concentration, and cavity length on flow characteristics in the contraction and expansion parts of each cavity are analyzed, including quantified calculations of normalized vortex lengths and extension rates. The results indicate that polymer memory and scission affect the flow transitions. Memory effects enhance vortex growth and scission weakens flow, and these effects occur continuously within the channel. Increased flow rates and cavity lengths intensify polymer scission, accelerating the transitions from elastic instability to corner vortex, lip vortex, and then to steady vortex-free flows in the contraction parts and from steady vortex-free flows to lip and corner vortices in the expansion parts. The flow-regime transitions for concentrations from 0.01 to 0.4 wt. % for dilute and unentangled semi-dilute solutions at various flow rates are summarized in the Reynolds and Weissenberg number spaces. Polymer chains tend to become entangled in higher-concentration solutions, rendering the solution rigid and inducing complex flow regimes. [ABSTRACT FROM AUTHOR]

This research experimentally examines the influence of viscoelastic dilute water solutions of polyethylene oxide on Venturi cavitation. Variations in solutions are engineered to manipulate the viscoelastic properties that in turn affect cavitation patterns and attributes. The consequences of viscoelasticity and flow conditions on cavitation are quantified using dimensionless numbers, including the elasticity number (El), the Reynolds number (Re), and the pressure ratio (κ). The experiment identifies three distinct cavitation patterns in the solutions, with their transitions being impacted by alterations in El and κ. As El amplifies, the cavitation bubbles expand and get smoother, and the reentrant jet thickens and amplifies. The behavior of cavitation aligns with the model proposed by Zhang et al. [Phys. Fluids 31, 097107 (2019)], suggesting the critical role of the reentrant jet in the shedding of the cavity cluster. The study also substantiates that the reentrant jet intensifies with ascending El or Re. The collective influence of El, Re, and κ is discovered to shape the cavitation length and shedding frequency of cavity clusters. An increased El or a decreased Re reinforces the vorticity and the reentrant jet, which inevitably leads to a reduction in cavitation lengths and an uptick in the shedding frequency. Conversely, a larger El results in a more gradual response of the bubble to pressure alterations and pronounced rebounds, extending the cavitation length. [ABSTRACT FROM AUTHOR]

Thixotropy, antithixotropy, and viscoelasticity are three types of time-dependent dynamics that involve fundamentally different underlying physical processes. Here, we show that the three dynamics exhibit different signatures in hysteresis by examining the fingerprints of the simplest thixotropic kinetic model, a new antithixotropic model that we introduce here, and the Giesekus model. We start by showing that a consistent protocol to generate hysteresis loops is a discrete shear-rate controlled ramp that begins and ends at high shear rates, rather than at low shear rates. Using this protocol, we identify two distinguishing features in the resulting stress versus shear rate loops. The first is the direction of the hysteresis loops: clockwise for thixotropy, but counterclockwise for viscoelasticity and antithixotropy. A second feature is achieved at high ramping rates where all responses lose hysteresis: the viscoelastic response shows a stress plateau at low shear rates due to lack of stress relaxation, whereas the thixotropic and antithixotropic responses are purely viscous with minimal shear thinning or thickening. We establish further evidence for these signatures by experimentally measuring the hysteresis of Laponite suspensions, carbon black suspensions, and poly(ethylene oxide) solutions, each representing a historically accepted example of each class of material behavior. The signatures measured in experiments are consistent with those predicted by the three models. This study reveals different fingerprints in hysteresis loops associated with thixotropy, antithixotropy, and viscoelasticity, which may be helpful in distinguishing the three time-dependent responses. [ABSTRACT FROM AUTHOR]

Microfluidic manipulation of particles usually relies on their cross-stream migration. A center- or wall-directed motion has been reported for particles leading or lagging the Poiseuille flow of viscoelastic polyethylene oxide (PEO) solution via positive or negative electrophoresis. Such electro-elastic migration is exactly opposite to the electro-inertial migration of particles in a Newtonian fluid flow. We demonstrate here through the top- and side-view imaging that the leading and lagging particles in the electro-hydrodynamic flow of PEO solution migrate toward the centerline and corners of a rectangular microchannel, respectively. Each of these electro-elastic particle migrations is reduced in the PEO solution with shorter polymers though neither of them exhibits a strong dependence on the particle size. Both phenomena can be reasonably explained by the theory in terms of the ratios of the forces involved in the process. Decreasing the PEO concentration causes the particle migration to shift from the viscoelastic mode to the Newtonian mode, for which the magnitude of the imposed electric field is found to play an important role. [ABSTRACT FROM AUTHOR]

This communication presents a simple yet straightforward method for preparing water-in-water-in-water particle-stabilized double emulsions, also known as Pickering double emulsions. The approach involves using oppositely charged nanoparticles (OCNPs) in two distinct fluid phases, promoting self-assembly and the formation of aggregates with varying sizes and compositions. By enhancing the interfacial area through the adsorption of aggregates at the interface, this method increases the Gibbs detachment energy of particles between the two aqueous phases, forming stable double emulsions. Furthermore, we investigated the impact of the molecular weight of polyethylene oxide and dextran in the respective fluid phases and the mass ratio (M) of the OCNPs on double emulsion formation. The results demonstrate that the molecular weight of the polymers used in the aqueous phase is a critical parameter influencing the structural formation of the emulsion and the generation of double emulsions. Consequently, double emulsions are formed when equal molecular weight polymer mixtures are employed at an appropriate M, with the dispersed phase placed in the highly viscous continuous phase. The proposed method offers a one-step synthesis process, enabling easy preparation, and exhibits excellent stability for at least 30 days. This study represents the first reported approach for the one-step synthesis of multiple emulsions in an aqueous two-phase system utilizing a Pickering emulsion template. [ABSTRACT FROM AUTHOR]

New fluorescent materials with a low cost, hypotoxicity, and concealment are desired for the application of anti-counterfeiting. Herein, we report a CsCu2I3@Cs3Cu2I5 composite with a triple-mode photoluminescence (PL) feature by simply adjusting the excitation wavelengths, which are ascribed to the multiple excited states of different phases in the CsCu2I3@Cs3Cu2I5 composite. The broadband emission and high quantum yield (∼51%) of the composite originate from the structure-oriented self-trapped excitons effect of Cs3Cu2I5 and CsCu2I3 phases. Moreover, the incorporation of polyethylene oxide (PEO) into this composite improves the stability of CsCu2I3@Cs3Cu2I5@PEO against harsh environments. The CsCu2I3@Cs3Cu2I5@PEO composite has a slight decay of ∼5% of its initial PL intensity and only a 3.5% shift of the corresponding color coordinate after 30 days of storage. More importantly, its initial PL intensity shows only 10.3% decay under ultraviolet exposure for 200 h. Our work provides a promising approach to design materials for advanced anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Foldable electrochromic NiO films were achieved through plasma enhanced e-beam evaporation on indium-doped tin oxide coated polyethylene naphthalate two formic acid glycol ester substrates. These films displayed fast coloration and bleaching times of 3.3 and 0.5 s, respectively, and were highly transparent in the visible region. The electrochromic properties of the films were evaluated using cyclic voltammetry, chronoamperometry, and spectrophotometry in an aqueous alkaline electrolyte of 0.1 M KOH. The films exhibited a coloration efficiency of 23.1 cm2/C at 550 nm. The films maintained their functionality even after being folded 1000 times under concave conditions. [ABSTRACT FROM AUTHOR]

Flows through contraction geometries (contraction flows) are found in many fields involving fluids, but they are poorly understood because they have two inseparable aspects as a whole: shear flow and elongational flow. In this paper, we focus on the center line of the contraction flow where the shear component vanishes because of the symmetry of the flow field and clarify elongational properties of liquids using the data obtained to date. First, we show images of contraction flows of water and dilute polymer solutions, and then, the continuity equation is used to obtain expressions for the center-line velocity. The expressions represent either the exponential contraction flow (ECF) or linear contraction flow (LCF) and agree well with experimental results obtained to date. It is suggested that the Deborah number plays an important role in deciding ECF or LCF. For dilute solutions of polyethylene oxide and polyacrylamide, the ratio of the elongational viscosity (μe) to the shear viscosity (μs) is found to be high, of the order of 104 and 103, respectively. On the other hand, molten polyethylene and 5.0-wt. % polyisobutylene in hydrocarbon tetradecane have greatly different values of μe and μs, but their values of μe/μs do not differ much from four. We propose a novel relaxation velocity number (RV) and find that the exponent ai of the ECF velocity-profile is correlated with log10RV for water, polymer solutions, and molten polyethylene. Furthermore, the expressions agree with experimental data for wet spinning. We propose a novel spinning model for the contraction flow of polymer solutions. [ABSTRACT FROM AUTHOR]

Selected configuration interaction plus perturbation theory approaches have long been used to solve both the electronic and vibrational Schrödinger equations. In the last few years, many new selection algorithms have been developed for these approaches and applied to solve the electronic Schrödinger equation, but these algorithms have seen little to no use for solving the vibrational Schrödinger equation. Herein, we adapt one of the recently developed approaches, the adaptive sampling configuration interaction (ASCI) method, to calculate the vibrational excitations of molecules. The vibrational ASCI method has accuracy comparable to other high-accuracy approaches for solving the vibrational Schrödinger equation while requiring only modest computer resources. We study two different approaches for calculating excited states with vibrational ASCI and benchmark the method on acetonitrile and ethylene oxide. Finally, we demonstrate the applicability of the vibrational ASCI method to large systems by calculating the 128 lowest energy vibrational states of naphthalene, which has 48 vibrational degrees of freedom. [ABSTRACT FROM AUTHOR]

This article is devoted to the study of polymer layers of amphiphilic homopolymers tightly grafted to a flat surface at the nodes of a square lattice. It was shown that, due to the amphiphilicity of monomer units containing groups with different affinities, in a selective solvent, such layers form lamellae perpendicular to the grafting surface. The period of the lamellae depends on the grafting density and the quality of the solvent. The results are presented in the form of a state diagram in variables "the energy of attraction of the side groups" (effective solvent quality) and "the distance between the grafting points" (inversely proportional to the square root of the grafting density). The diagram contains the regions of stability of lamellae with significantly different periods, and a transitional area with a parking garage structure. The diagram is constructed by calculating the layer-by-layer structure factor and the angle of inclination of the lamellae in the slice. The calculations were performed for different sizes of the simulation box, and the most commensurate size was determined by a special procedure for each grafting density. The results may be interesting not only to specialists in polymer science but also to all those who investigate the processes of self-organization and rearrangement in dense systems. [ABSTRACT FROM AUTHOR]

Diblock polymer micelles dispersed in an aqueous environment are being actively investigated for various applications, but there is only a qualitative understanding of the effect of the chemical structure on the micelle hydration and water dynamics as these properties are difficult to assess experimentally. Using all-atom molecular dynamics simulations, we investigate aqueous solutions of three comparable in size diblock copolymer micelles with core-forming blocks of different hydrophobicity: polybutadiene (PB), polycaprolactone (PCL), and polytetrahydrofuran (pTHF) with the same hydrophilic block, polyethylene oxide (PEO). We found that core-block hydrophobicity and ability to form hydrogen bonds with water strongly affect the water dynamics near the core: water molecules spend considerably less time in contact with the PB block than with PCL and pTHF blocks. We obtained polymer and solvent volume fraction profiles and determined that the interfacial width systematically increases with a decrease of core block hydrophobicity with water penetration into the core being negligible for PB-PEO and PCL-PEO micelles, while for pTHF-PEO micelles the interface is more diffuse and there is a noticeable penetration of water (17% by volume). For PCL-PEO micelles, which are commonly used in biomedical applications, we also investigated tetrahydrofuran (THF) penetration into the micelles from mixed THF:water solution at early stages of micelle dissolution. We found an inhomogeneous solvent distribution with a maximum of THF volume fraction in the interfacial core-corona region and partial exclusion from the PEO corona, which slows down micelle dissolution. These results can have important implications for micelle stability and use in biomedical applications. [ABSTRACT FROM AUTHOR]

Recent studies have revealed the air-cushioning effect of droplet impact upon various surfaces and although pure water droplets have extensively been studied, the air entrainment dynamics for aqueous polymeric droplets was the focus of this study. Herein, droplets of low to moderate Weber numbers, We ∼ O (1 − 10) , displayed air film thickness gradients which was strongly influenced by the viscoelastic properties of the aqueous polymeric droplets in the dilute to the semidilute unentangled regimes. Aqueous polyethylene oxide droplets impacting a smooth thin oil film surface formed a submicrometer air layer, moments prior to impact, which was tracked by a high-speed total internal reflection microscopy technique. The radial changes in the air film thickness were related to the polymer concentration, thus providing an alternative tool for comparing the rheometer-derived overlap concentrations with a contactless optical technique. [ABSTRACT FROM AUTHOR]

The attenuation characteristic of a semiconductor laser and green laser beam power with various polymer nanocomposites including PbS, TiO2, V2O5, and CuO are investigated experimentally. Various polymeric nanocomposites with the same concentration of different nanoparticles were prepared using a solution casting technique. The distance between the sample and detector as well as the sample and laser source, and the laser beam incident angle on the surface of the sample are found to be important factors to obtain robust measurements of the attenuation of the semiconductor and green laser beam power. The nanocomposite thin film doped with CuO has more laser beam power attenuation compared to the other prepared nanocomposite thin films. Polymer nanocomposites have various applications, e.g., cut-off laser filters, optical limiting laser, and laser beam power attenuation. [ABSTRACT FROM AUTHOR]

In this work, we present results of coarse-grained simulations to study the encapsulation of prilocaine (PLC), both neutral and protonated, on copolymer bilayers through molecular dynamics simulations. Using a previously validated membrane model, we have simulated loaded bilayers at different drug concentrations and at low (protonated PLC) and high (neutral PLC) pH levels. We have characterized key structural parameters of the loaded bilayers in order to understand the effects of encapsulation of PLC on the bilayer structure and mechanical properties. Neutral PLC was encapsulated in the hydrophobic region leading to a thickness increase, while the protonated species partitioned between the water phase and the poly(ethylene oxide)-poly(butadiene) (PBD) interface, relaxing the PBD region and leading to a decrease in the thickness. The tangential pressures of the studied systems were calculated, and their components were decomposed in order to gain insights on their compensation. In all cases, it is observed that the loading of the membrane does not significantly decrease the stability of the bilayer, indicating that the system could be used for drug delivery. [ABSTRACT FROM AUTHOR]

In the context of modifying the extensional rheology of agricultural sprays to improve retention of sprays on plants, here we characterize the extensional rheology of dilute solutions of polyethylene oxide (PEO). Specifically, we examine the influence of pH and ionic strength, which vary significantly among agricultural sprays, as well as binary mixtures of two different nominal molecular weights of the polymer additive. Because PEO is nonionic, common intuition would predict that varying the pH and/or adding salt ions would have a minimal or negligible effect. However, the results presented here show a significant, complex, nonmonotonic, and ion-specific trend that is systematically documented for the first time. The role of shear degradation when mixing the polymer solutions is ruled out, and the data suggest that specific ion-polymer interactions appear to be more likely than changes in the solvent quality for producing this unexpected trend. We discuss some possible mechanistic explanations for the trend and highlight the potential impacts on product formulation as well as the need for improved theory of polymer physics. [ABSTRACT FROM AUTHOR]

The deuteron transverse relaxation properties of polyethylene oxide melts of four different molecular weights, covering the range from the onset of entanglements to the regime of fully entangled chains, are investigated using Hahn echo decays over an extensive time interval up to ten times the effective transverse spin relaxation time. The results are compared to predictions based on the Rouse and reptation formalisms, taking into account the dynamical heterogeneity of linear polymer chains produced by the end segments. The experimental results can be described qualitatively by a combination of both models, with the contribution of reptation dynamics increasing with growing chain length. The transition is continuous, rather than being characterized by sharp regime boundaries. Up to a molecular weight of 300.000 g/mol, the predicted limit of pure reptation dynamics is not yet reached. Quantitative deviations from the predicted decays as computed by numerical procedures become observable toward the long-time limit of the Hahn echo decays and are being discussed in terms of shortcomings of the available reptation theories. [ABSTRACT FROM AUTHOR]

The displacement flow of an organic Newtonian fluid by a pure viscoelastic aqueous solution is experimentally investigated inside a circular microchannel of 200 μm. Displacement is commonly encountered in many industrial applications, from cleaning and decontamination to enhanced oil recovery. In this study, a pure viscoelastic fluid with no shear-thinning properties (known as Boger fluid) made up of polyethylene oxide, polyethylene glycol, and zinc chloride is used to displace an immiscible organic liquid (silicone oil). The results were compared against those from displacement with a Newtonian fluid of similar density and viscosity as the viscoelastic one. High-speed imaging is used to track both the residual film thickness of the organic phase and the interface deformations during displacement. It is found that the Boger fluid displacing phase produces a thinner displaced phase film compared to the Newtonian fluid, particularly at high capillary numbers. A correlation is proposed for the film thickness, which includes the Weissenberg number for the viscoelastic case. After the displacement front, the interface becomes unstable with two modes of instability identified. In the case of the Boger fluid, the two modes of instability are core shifting, which is also present in the Newtonian case, and a periodic instability from the elastic stresses during displacement. Additionally, the shape of the interfacial instabilities switches freely from asymmetric to axisymmetric ones throughout the flow. The frequency of the periodic instabilities increases with the displacing phase flow rate. It was also found that microchannel bends downstream of the observation point affect the shape and frequency of the instabilities. [ABSTRACT FROM AUTHOR]

Perovskite films modified by a polymer will largely enhance the open circuit voltage (VOC) and cannot increase the short-circuit current (JSC) and fill factor (FF). In order to further optimize perovskite films, an ionic conducting polymer containing diblock-polymers of polyethylene oxide (PEO)150–polyphenylene oxide (PPO)30 and alkali metal salts of KBr was incorporated into perovskite films. The hydrophilic PEO blocks will coordinate with polar cations and form uniform heterostructure interfaces to passivate defects at grain boundaries (GBs). The transport of alkali metal ions in polymers will increase the conductivity of perovskite films. The synergistic effects of polymers and KBr can significantly enhance the photovoltaic response. The entirely functionalized perovskite GBs can also improve the tolerance of perovskite films against environmental stress. Aside from that, the glycine solution was deposited onto SnO2 films to passivate interface defects and further improve device performance. The improved charge transport dynamics and the suppressed charge recombination kinetics were determined using different characterization techniques. The optimized photoelectric conversion efficiency is 22.89% (a VOC of 1.166 V, a JSC of 24.30 mA cm−2, and a FF of 0.808) under a reverse scan. This work provides a feasible method to further optimize perovskite films and improve device performance. [ABSTRACT FROM AUTHOR]

The intrinsic ionic conductivity of polyethylene oxide (PEO)-based block copolymer electrolytes is often assumed to be identical to the conductivity of the PEO homopolymer. Here, we use high-field 7Li nuclear magnetic resonance (NMR) relaxation and pulsed-field-gradient (PFG) NMR diffusion measurements to probe lithium ion dynamics over nanosecond and millisecond time scales in PEO and polystyrene (PS)-b-PEO-b-PS electrolytes containing the lithium salt LiTFSI. Variable-temperature longitudinal (T1) and transverse (T2) 7Li NMR relaxation rates were acquired at three magneticfield strengths and quantitatively analyzed for the first time at such fields, enabling us to distinguish two characteristic time scales that describe fluctuations of the 7Li nuclear electric quadrupolar interaction. Fast lithium motions [up to O(ns)] are essentially identical between the two polymer electrolytes, including sub-nanosecond vibrations and local fluctuations of the coordination polyhedra between lithium and nearby oxygen atoms. However, lithium dynamics over longer time scales [O(10 ns) and greater] are slower in the block copolymer compared to the homopolymer, as manifested experimentally by their different transverse 7Li NMR relaxation rates. Restricted dynamics and altered thermodynamic behavior of PEO chains anchored near PS domains likely explain these results. [ABSTRACT FROM AUTHOR]

β-detected NMR (β-NMR) has been used to study the molecular-scale dynamics of lithium ions in thin films of poly(ethylene oxide) (PEO) containing either lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoroacetate (LiTFA) salts at monomer-to-salt ratios (EO/Li) of 8.3. The results are compared with previous β-NMRmeasurements on purePEOandPEOwith lithium triflate (LiOTf) at the same loading [McKenzie et al., J. Am. Chem. Soc. 136, 7833 (2014)]. Activated hopping of 8Li+ was observed in all of the films above ∼250 K, with the hopping parameters strongly correlated with the ionicity of the lithium salt rather than the polymer glass transition temperature. The preexponential factor increases exponentially with ionicity, while the activation energy for hopping increases approximately linearly, going from 6.3±0.2 kJ mol-1 in PEO:LiTFA to 17.8±0.2 kJ mol-1 in PEO:LiTFSI. The more rapid increase in the pre-exponential factor outweighs the effect of the larger activation energy and results in 8Li+ hopping being fastest in PEO followed by PEO:LiTFSI, PEO:LiOTf and PEO:LiTFA. [ABSTRACT FROM AUTHOR]

This paper presents a new model for polymersomes developed using a poly(ethylene oxide)- poly(butadiene) diblock copolymer bilayer. The model is based on a coarse-grained approach using the MARTINI force field. Since no MARTINI parameters exist for poly(butadiene), we have refined these parameters using quantum mechanical calculations and molecular dynamics simulations. The model has been validated using extensive molecular dynamics simulations in systems with several hundred polymer units and reaching up to 6 μs. These simulations show that the copolymer coarse grain model self-assemble into bilayers and that NPT and NPNγT ensemble runs reproduce key structural and mechanical experimental properties for different copolymer length chains with a similar hydrophilic weight fraction. [ABSTRACT FROM AUTHOR]

Forming polymeric core–sheath nanofibers is gaining prominence owing to their numerous potential applications, most notably in functional scenarios such as antiviral filtration, which is attracting significant attention due to the current COVID pandemic. This study has successfully designed and constructed a novel pressurized gyration vessel to fabricate core–sheath polymer nanofibers. Several water-soluble and water-insoluble polymer combinations are investigated. Both polyethylene oxide and polyvinyl alcohol were used as the core while both poly(lactic acid) (PLA) and poly(caprolactone) (PCL) were used as the sheath; PLA and PCL were used as core and sheath, in different instances; respectively. The fluid behavior of the core–sheath within the vessel was studied with and without applied pressure using computational fluid dynamics to simulate the core–sheath flow within the chamber. A high-speed camera was used to observe the behavior of jetted solutions at core–sheath openings, and the best scenario was achieved using 6000 rpm spinning speed with 0.2 MPa (twice atmospheric) applied pressure. The surface morphology of core–sheath fibers was studied using a scanning electron microscope, and focused ion beam milling assisted scanning electron microscopy was used to investigate the cross-sectional features of the produced fibers. Laser confocal scanning microscopy was also used to verify the core–sheath structure of the fibers, which were further characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Thus, using a variety of polymer combinations, we show, both theoretically and experimentally, how core–sheath fibers evolve in a vessel that can serve as a scalable manufacturing pressurized gyration production process. [ABSTRACT FROM AUTHOR]

Bottom-up self-assembly of nanofibers in a chemical method is presented using the surfactant mixture of cetyltrimethylammonium bromide (CTAB) and Pluronics as the anisotropic micellar templates. Fully fluorinated perfluorooctanoic acids with highly hydrophobic C–F chains are imported for constructing exceptionally long nanofibers. Ag(I) provides robustness of the materials by the complexation with ethylene oxides in Pluronic copolymers. Fluorocarbons reside in the PPO (polypropylene oxide) blocks in Pluronic polymers and accordingly in reverse Pluronics, they are placed in the surrounding regions of nanofibers. During the segregation of water from hydrophobic cores, self-assembly is assumed to be driven by hydrophobic interactions among alkyl chains of CTAB, fluoroalkyl chains of perfluorooctanoic acids, and dehydrated methyl groups of PPO blocks in Pluronics. Nanofibers with relatively high aspect ratios were obtained when Pluronic copolymers with low number average molecular weights (Mn), such as L-31 (Mn ∼ 1100) and L-64 (Mn ∼ 2900), were used. Heterogeneous catalytic activities were monitored in the reduction reactions of 4-nitrophenol, and the nanorods prepared from Pluronic 31R1 show the best catalytic performances with a rate constant of 0.002 35 s−1. The roles of fluorine or C–F groups in perfluorooctanoic acids are believed to be the disruption of hydrogen bonding between water and polyethylene oxide groups, and the phase separation of nanofibers from the aqueous environment by the dehydration of hydrophobic cores. [ABSTRACT FROM AUTHOR]

Pulsed field gradient nuclear magnetic resonance spectroscopy and dielectric relaxation spectroscopy have been utilized to investigate lithium dynamics within poly(ethylene oxide) (PEO)-based lithium sulfonate ionomers of varying ion content. The ion content is set by the fraction of sulfonated phthalates and the molecular weight of the PEO spacer, both of which can be varied independently. The molecular level dynamics of the ionomers are dominated by either Vogel-Fulcher-Tammann or Arrhenius behavior depending on ion content, spacer length, temperature, and degree of ionic aggregation. In these ionomers the main determinants of the self-diffusion of lithium and the observed conductivities are the ion content and ionic states of the lithium ion, which are profoundly affected by the interactions of the lithium ions with the ether oxygens of the polymer. Since many lithium ions move by segmental polymer motion in the ion pair state, their diffusion is significantly larger than that estimated from conductivity using the Nernst-Einstein equation. [ABSTRACT FROM AUTHOR]

We use atomistic simulations to probe the ion conductivities and mechanical properties of polyethylene oxide electrolytes containing Al2O3 nanoparticles. We specifically study the influence of repulsive polymer-nanoparticle and ion-nanoparticle interactions and compare the results with those reported for electrolytes containing the polymorph β-Al2O3 nanoparticles. We observe that incorporating repulsive nanoparticle interactions generally results in increased ionic mobilities and decreased elastic moduli for the electrolyte. Our results indicate that both ion transport and mechanical properties are influenced by the polymer segmental dynamics in the interfacial zones of the nanoparticle in the ion-doped systems. Such effects were seen to be determined by an interplay between the nanoparticle-polymer, nanoparticle-ion, and ion-polymer interactions. In addition, such interactions were also observed to influence the number of dissociated ions and the resulting conductivities. Within the perspective of the influence of nanoparticles on the polymer relaxation times in ion-doped systems, our results in the context of viscoelastic properties were consistent with the ionic mobilities. Overall, our results serve to highlight some issues that confront the efforts to use nanoparticle dispersions to simultaneously enhance the conductivity and the mechanical strength of polymer electrolyte. [ABSTRACT FROM AUTHOR]

We have studied structure, ion transport, and relaxation dynamics in polyethylene oxide/poly (vinylidene fluoride-hexafluoropropylene)-lithium bis(trifluoromethane)sulfonimide blend polymer electrolytes embedded with 1-propyl-3-methyleimidazoliuum bis(trifluromethyle-sulfonyl)imide ionic liquid. Structural property and ion–polymer interaction of polymer electrolytes have been studied using X-ray diffraction and Raman spectroscopy. The addition of ionic liquid decreases glass transition temperature and reduces crystalline phase in the polymer matrix. It is also observed that surface becomes smooth with increase of ionic liquid content. The temperature dependence of the Li ion conductivity follows Vogel–Tammann–Fulcher type behaviour when a sufficient amount of ionic liquid is added to polymer matrix. The electric modulus has been studied using Havriliak–Negami function for the understanding of ion dynamics. The modulus data have been analyzed using non-exponential Kohlrausch–Williams–Watts function. It is observed that the nonexponential parameter β is quite lower than unity, suggesting existence of a non-exponential relaxation. The temperature dependence of the relaxation time also follows Vogel–Tammann–Fulcher relation for compositions with higher ionic liquid content. [ABSTRACT FROM AUTHOR]

This paper presents atomistic molecular dynamics simulation studies of lithium bis(trifluoromethane) sulfonylimide (LiTFSI) in a blend of 1-ethyl-3-methylimidazolium (EMIm)-TFSI and poly(ethylene oxide) (PEO), which is a promising electrolyte material for Li- and Li-ion batteries. Simulations of 100 ns were performed for temperatures between 303 K and 423 K, for a Li:ether oxygen ratio of 1:16, and for PEO chains with 26 EO repeating units. Li+ coordination and transportation were studied in the ternary electrolyte system, i.e., PEO16LiTFSI · 1.0 EMImTFSI, by applying three different force field models and are here compared to relevant simulation and experimental data. The force fields generated significantly different results, where a scaled charge model displayed the most reasonable comparisons with previous work and overall consistency. It is generally seen that the Li cations are primarily coordinated to polymer chains and less coupled to TFSI anion. The addition of EMImTFSI in the electrolyte system enhances Li diffusion, associated to the enhanced TFSI dynamics observed when increasing the overall TFSI anion concentration in the polymer matrix. [ABSTRACT FROM AUTHOR]

The reverse Pluronic, triblock copolymer 17R4 is formed from poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO): PPO14 - PEO24 - PPO14, where the number of monomers in each block is denoted by the subscripts. In water, 17R4 has a micellization line marking the transition from a unimer network to self-aggregated spherical micelles which is quite near a cloud point curve above which the system separates into copolymer-rich and copolymer-poor liquid phases. The phase separation has an Ising-like, lower consolute critical point with a well-determined critical temperature and composition. We have measured the heat capacity as a function of temperature using an adiabatic calorimeter for three compositions: (1) the critical composition where the anomaly at the critical point is analyzed, (2) a composition much less than the critical composition with a much smaller spike when the cloud point curve is crossed, and (3) a composition near where the micellization line intersects the cloud point curve that only shows micellization. For the critical composition, the heat capacity anomaly very near the critical point is observed for the first time in a Pluronic/water system and is described well as a second-order phase transition resulting from the copolymer-water interaction. For all compositions, the onset of micellization is clear, but the formation of micelles occurs over a broad range of temperatures and never becomes complete because micelles form differently in each phase above the cloud point curve. The integrated heat capacity gives an enthalpy that is smaller than the standard state enthalpy of micellization given by a van't Hoff plot, a typical result for Pluronic systems. [ABSTRACT FROM AUTHOR]

Microscopic modeling of surfactant systems is expected to be an important tool to describe, understand, and take full advantage of the micellization process for different molecular architectures. Here, we implement a single chain mean field theory to study the relevant equilibrium properties such as the critical micelle concentration (CMC) and aggregation number for three sets of surfactants with different geometries maintaining constant the number of hydrophobic and hydrophilic monomers. The results demonstrate the direct effect of the block organization for the surfactants under study by means of an analysis of the excess energy and entropy which can be accurately determined from the mean-field scheme. Our analysis reveals that the CMC values are sensitive to branching in the hydrophilic head part of the surfactant and can be observed in the entropy-enthalpy balance, while aggregation numbers are also affected by splitting the hydrophobic tail of the surfactant and are manifested by slight changes in the packing entropy. [ABSTRACT FROM AUTHOR]

The Rouse model can be regarded as the standard model to describe the dynamics of a short polymer chain under melt conditions. In this contribution, we explicitly check one of the fundamental assumptions of this model, namely, that of a uniform friction coefficient for all monomers, on the basis of MD simulation data of a poly(ethylene oxide) (PEO) melt. This question immediately arises from the fact that in a real polymer melt, the terminal monomers have on average more intermolecular neighbors than the central monomers, and one would expect that exactly these details affect the precise value of the friction coefficient. The mobilities are determined by our recently developed statistical method, which provides detailed insights into the local polymer dynamics. Moreover, it yields complementary information to that obtained from the mean square displacement (MSD) or the Rouse mode analysis. It turns out that the Rouse assumption of a uniform mobility is fulfilled to a good approximation for the PEO melt. However, a more detailed analysis reveals that the underlying microscopic dynamics are highly affected by different contributions from intra- and intermolecular excluded volume interactions, which cannot be taken into account by a modified friction coefficient. Minor deviations occur only for the terminal monomers on larger time scales, which can be attributed to the presence of two different escape mechanisms from their first coordination sphere. These effects remain elusive when studying the dynamics with the MSD only. [ABSTRACT FROM AUTHOR]

The dependence on volume fraction φ of the Flory-Huggins interaction parameter Xwp(φ) describing the free energy of mixing of polymers in water is obtained by exploiting the connection of Xwp(φ) to the chemical potential of the water, for which quasi-chemical theory is satisfactory. We test this theoretical approach with simulation data for aqueous solutions of capped PEO (polyethylene oxide) oligomers. For CH3(CH2-O-CH2)mCH3 (m = 11), Xwp(φ) depends strongly on φ, consistent with experiment. These results identify coexisting water-rich and water-poor solutions at T = 300 K and p = 1 atm. Direct observation of the coexistence of these two solutions on simulation time scales supports that prediction for the system studied. This approach directly provides the osmotic pressures. The osmotic second virial coefficient for these chains is positive, reflecting repulsive interactions between the chains in the water, a good solvent for these chains. [ABSTRACT FROM AUTHOR]