Diffusion Of Poly Research Articles

Charge Scaling in Classical Force Fields for Lithium Ions in Polymers.

Polymer electrolytes are of interest for applications in energy storage. Molecular simulations of ion transport in polymer electrolytes have been widely used to study the conductivity in these materials. Such simulations have generally relied on classical force fields. A peculiar feature of such force fields has been that in the particular case of lithium ions (Li+), their charge must be scaled down by approximately 20% to achieve agreement with experimental measurements of ion diffusivity. In this work, we present first-principles calculations that serve to justify the charge-scaling factor and van der Waals interaction parameters for Li+ diffusion in poly(ethylene glycol) (PEO) with bistriflimide (TFSI-) counterions. Our results indicate that a scaling factor of 0.79 provides good agreement with DFT calculations over a relatively wide range of Li+ concentrations and temperatures, consistent with past reports where that factor was adjusted by trial and error. We also show that such a scaling factor leads to diffusivities that are in quantitative agreement with experimental measurements.

Triggering Gaussian-to-Exponential Transition of Displacement Distribution in Polymer Nanocomposites via Adsorption-Induced Trapping.

In many disordered systems, the diffusion of classical particles is described by a displacement distribution P(x, t) that displays exponential tails instead of Gaussian statistics expected for Brownian motion. However, the experimental demonstration of control of this behavior by increasing the disorder strength has remained challenging. In this work, we explore the Gaussian-to-exponential transition by using diffusion of poly(ethylene glycol) (PEG) in attractive nanoparticle-polymer mixtures and controlling the volume fraction of the nanoparticles. In this work, we find "knobs", namely nanoparticle concentration and interaction, which enable the change in the shape of P(x,t) in a well-defined way. The Gaussian-to-exponential transition is consistent with a modified large deviation approach for a continuous time random walk and also with Monte Carlo simulations involving a microscopic model of polymer trapping via reversible adsorption to the nanoparticle surface. Our work bears significance in unraveling the fundamental physics behind the exponential decay of the displacement distribution at the tails, which is commonly observed in soft materials and nanomaterials.

Exciton diffusion in poly(3-hexylthiophene) by first-principles molecular dynamics.

Poly(3-hexylthiophene) (P3HT) is a polymer used in organic solar cells as a light absorber and an electron donor. Photogenerated excitons diffuse and dissociate into free charge carriers provided they reach the absorber boundaries. The device efficiency is therefore dependent on the exciton diffusion. Although measurements can be performed for example by time-resolved photoluminescence, a quantitative modeling is highly desirable to get an insight into the relationship between the atomic structure at finite temperature and the diffusion coefficient of the exciton. This is the objective of the present work, achieved by resorting to first-principles molecular dynamics in combination with the restricted open-shell approach to model the singlet excited state. The maximally localized Wannier functions and their centers are used to monitor and localize the electron and the hole along the dynamics. The resulting diffusion coefficient is in close agreement with available measurements.

Investigation of Hydronium Diffusion in Poly(vinyl alcohol) Hydrogels: A Critical First Step to Describe Acid Transport for Encapsulated Bioremediation

Bioremediation of chlorinated aliphatic hydrocarbon-contaminated aquifers can be hindered by high contaminant concentrations and acids generated during remediation. Encapsulating microbes in hydrogels may provide a protective, tunable environment from inhibiting compounds; however, current approaches to formulate successful encapsulated systems rely on trial and error rather than engineering approaches because fundamental information on mass-transfer coefficients is lacking. To address this knowledge gap, hydronium ion mass-transfer rates through two commonly used hydrogel materials, poly(vinyl alcohol) and alginic acid, under two solidification methods (chemical and cryogenic) were measured. Variations in hydrogel crosslinking conditions, polymer composition, and solvent ionic strength were investigated to understand how each influenced hydronium ion diffusivity. A three-way ANOVA indicated that the ionic strength, membrane type, and crosslinking method significantly (p < 0.001) contributed to changes in hydronium ion mass transfer. Hydronium ion diffusion increased with ionic strength, counter to what is observed in aqueous-only (no polymer) solutions. Co-occurring mechanisms correlated to increased hydronium ion diffusion with ionic strength included an increased water fraction within hydrogel matrices and hydrogel contraction. Measured diffusion rates determined in this study provide first principal design information to further optimize encapsulating hydrogels for bioremediation.

Relationship between Gel Mesh and Particle Size in Determining Nanoparticle Diffusion in Hydrogel Nanocomposites.

The diffusion of poly(ethylene glycol) methyl ether thiol (PEGSH)-functionalized gold nanoparticles (NPs) was measured in polyacrylamide gels with various cross-linking densities. The molecular weight of the PEGSH ligand and particle core size were both varied to yield particles with hydrodynamic diameters ranging from 7 to 21 nm. The gel mesh size was varied from approximately 36 to 60 nm by controlling the cross-linking density of the gel. Because high-molecular-weight ligands are expected to yield more compressible particles, we expected the diffusion constants of the NPs to depend on their hard/soft ratios (where the hard component of the particle consists of the particle core and the soft component of the particle consists of the ligand shell). However, our measurements revealed that NP diffusion coefficients resulted primarily from changes in the overall hydrodynamic diameter and not the ratio of particle core size to ligand size. Across all particles and gels, we found that the diffusion coefficient was well predicted by the confinement ratio calculated from the diameter of the particle and an estimate of the gel mesh size obtained from the elastic blob model and was well described using a hopping model for nanoparticle diffusion. These results suggest that the elastic blob model provides a reasonable estimate of the mesh size that particles "see" as they diffuse through the gel. This work brings new insights into the factors that dictate how NPs move through polymer gels and will inform the development of hydrogel nanocomposites for applications such as drug delivery in heterogeneous, viscoelastic biological materials.

Small molecule diffusion in poly-(olygo ethylene glycol methacrylate) based hydrogels studied by fluorescence correlation spectroscopy

Understanding just how solutes such as small molecules, polymers or proteins diffuse in “smart” hydrogels is a key factor in developing potential applications. In this work, we used fluorescence correlation spectroscopy (FCS) to study how structural parameters (length of side groups, network density) influence the diffusion of small dye molecules in poly (oligo (ethylene glycol) methyl ether methacrylates) (POEGMAs) hydrogels. Two diffusion components were found and attributed to (i) Fickian-like diffusion slowed only by steric effects, and (ii) diffusion slowed by interactions with the polymer. The relationship between the diffusion component (i) and the polymer concentration showed two regimes with different slopes in both hydrogels and solutions of non-crosslinked polymers, additionally studied for reference. The threshold between these regimes depended on the polymer hydrophilicity/hydrophobicity and the presence of cross-links. The release time of the model drug (ibuprofen) proved to be shorter in the case of denser hydrogel networks than for looser ones. This means that the drug affinity to the polymer network is the crucial parameter determining release processes, while the diffusion factor is of secondary and minor importance.

Long-Range Interactions Boost Singlet Exciton Diffusion in Nanofibers of π-Extended Polymer Chains

Raising the distance covered by singlet excitons during their lifetimes to values maximizing light absorption (a few hundred nm) would solve the exciton diffusion bottleneck issue and lift the constraint for fine (∼10 nm) phase segregation in bulk heterojunction organic solar cells. In that context, the recent report of highly ordered conjugated polymer nanofibers featuring singlet exciton diffusion length, LD, in excess of 300 nm is both appealing and intriguing [Jin, X.; et al. Science 2018, 360 (6391), 897-900]. Here, on the basis of nonadiabatic molecular dynamics simulations, we demonstrate that singlet exciton diffusion in poly(3-hexylthiophene) (P3HT) fibers is highly sensitive to the interplay between delocalization along the polymer chains and long-range interactions along the stacks. Remarkably, the diffusion coefficient is predicted to rocket by 3 orders of magnitude when going beyond nearest-neighbor intermolecular interactions in fibers of extended (30-mer) polymer chains and to be resilient to interchain energetic and positional disorders.

Gas sorption and diffusion in poly(dimethylsiloxane) (PDMS)/graphene oxide (GO) nanocomposite membranes

Gas solubility and diffusivity are reported for a series of poly(dimethylsiloxane) (PDMS)/graphene oxide (GO) nanocomposites. The nanocomposites were prepared via a crosslinking reaction between the amino-terminal end groups of the telechelic PDMS and epoxide groups on the surface of GO. Gas solubilities of N2, O2, CH4, and CO2 were measured at 35 °C over a range of pressures. Gas solubility in the nanocomposites was unaffected by GO at the maximum loading of 8 wt%. Therefore, a previously reported decrease in the nanocomposite permeability with increasing GO content was due to a reduction in diffusivity. The pure-gas selectivity of the nanocomposite was controlled by diffusivity selectivity, and both increased with increasing GO content. Based on Meares’ formula, correlations between diffusivity and the square of the kinetic diameter were observed for the nanocomposites. The slopes of these correlations increased progressively as a function of GO content, indicating the enhanced size-sieving ability of the nanocomposites.

Diffusion of poly (l-lactide) in activated metal organic frameworks; crystallization evidenced by ssNMR and subsequent shape memory effects

Shape-memory polymers are a class of materials that show dual or multi-shape competence. Here a solvent casting method was used to prepare composite films from Cu-BTC crystals in poly (l-lactide) (PLLA) to induce crystallization leading to a marked shape memory effect (SME). Extensive physico-chemical characterizations including solid-state NMR indicated that Cu-BTC triggered the crystallization of PLLA for ensuring the entropy needed for the shape memory behavior. The diffusion of polymeric chains inside pores of activated Cu-BTCs ensured interactions which increases the crystallinity as both simulation and experimental results show. Moreover, the segregation of Cu-BTC crystallites to small copper oxide particles due to the activation increases the volume of the crystalline region observed by microscopic images. We compared the identical features of composite prepared in the same method in where small molecule was encapsulated inside Cu-BTC with PLLA/5 wt% Cu-BTC; we were able to show that having the sharp transition of elastic to rubbery state in the vicinity of cold crystallization temperature in PLLA/5 wt% Cu-BTC provides Cu-BTC crystallites to act as netpoints. Moreover, the reinforcement accompanied by increased toughness demonstrates the combination of improved mechanical properties as well as SME of polymers which rarely have attained.

Effect of sodium salts on diffusion of poly(vinyl alcohol) in aqueous solutions

Abstract The Taylor dispersion technique has been used for measuring the tracer diffusion coefficients, D0Tracer, for poly (vinyl alcohol) (PVA) in aqueous systems containing two specific electrolytes (i.e., NaCl and Na2SO4) at three different concentrations (0.020, 0.050 and 0.10 mol dm−3), and at 25 °C. The selection of these salts has been based on the Hofmeister series of cations and anions, which order the ions with respect to the behavior of some macroscopic properties (such as, surface tension) and that can be interpreted as an effect salting-out or salting-in, depending if the target ions are strongly (kosmotropic) or a weakly hydrated (chaotropic). In this work, we have been used the combination of two kosmotropic ions (Na2SO4) and another one with a kosmotropic cation and a chaotropic anion (NaCl). These data, complemented by NMR measurements, permit us to have a better understanding about the effect of these sodium salts on transport and thermodynamic behaviour of PVA.

Solvation and diffusion of poly(vinyl alcohol) chains in a hydrated inorganic ionic liquid.

While the behavior of polyelectrolyte chains in aqueous salt solutions has been extensively studied, little is known about polar polymer chains in solvents with extremely high concentrations of inorganic ions, such as those found in ionic liquids (ILs). Here, we report on expansion, solvation and diffusion of poly(vinyl alcohol), PVA, chains in dilute solutions of a hydrated inorganic IL phase change material (PCM), lithium nitrate trihydrate (LNH). This solvent has an extremely high concentration of inorganic ions (≈18 M) with a low concentration of water molecules largely forming solvation shells of Li+ and NO3- ions, as shown using ATR-FTIR spectroscopy. Diffusion and hydrodynamic size of PVA chains of different molecular weights in this unusual solvent were studied using fluorescence correlation spectroscopy (FCS). A higher scaling exponent obtained from the molecular weight dependences of the diffusion coefficients of PVA chains as well as a lower overlap concentration (c*) of PVA in LNH solutions as measured by FCS suggest an expansion of the polymer coils in this solvent. We argue that enhanced solubility of PVA in LNH solutions is likely a result of increased rigidification of polymer chains due to the binding of solvated Li+ ions, which is demonstrated using 7Li NMR spectroscopy. We believe that an understanding of solvation and ion-binding capability can offer crucial insight into designing polymer-based shape stabilization matrices for inorganic PCMs.

Preparation of a polymeric aggregate of unsaturated polystyrene with sawdust and studying its physical and mechanical properties

In this study a type of polymeric composites from melting poly Unsaturated polyester as a basic substance with powdered sawdust was prepared, studying some of it is mechanical properties, which was included: Impact Strength (I.), Yong modulus (E), hardness (B.) and compression Strength (C.). Polymeric composites before and after reinforcing were studied by comparison between them. It was noticed increasing resistance of Yong modulus (E), Impact Strength (I.), hardness (B.) and compression Strength (C.). Also, It is studied the effect of some acids like (, H2SO4, HNO3) with concentrations (0.5 N; 1N and 1.5N) respectively. Some physical properties were studied as absorbance and poly 's diffusion coefficient before and after reinforcing. The results showed increases in values of these properties with increasing concentration of acid and time of polymer's immersion in the acidic solution.

Enhanced Charge Injection Properties of Organic Field-Effect Transistor by Molecular Implantation Doping.

Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large-area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal-OSC interfaces, a non-ideal transfer curve feature often appears in the low-drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self-assembled monolayers and introducing charge injection layers. Here, a selective contact doping of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 -TCNQ) by solid-state diffusion in poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) to enhance carrier injection in bottom-gate PBTTT organic field-effect transistors (OFETs) is demonstrated. Furthermore, the effect of post-doping treatment on diffusion of F4 -TCNQ molecules in order to improve the device stability is investigated. In addition, the application of the doping technique to the low-voltage operation of PBTTT OFETs with high-k gate dielectrics demonstrated a potential for designing scalable and low-power organic devices by utilizing doping of conjugated polymers.

Atomistic Description of Ionic Diffusion in PEO–LiTFSI: Effect of Temperature, Molecular Weight, and Ionic Concentration

Understanding the ionic diffusion mechanism in polymer electrolytes is critical to the development of advanced lithium-ion batteries. We report here molecular dynamics-based characterization of structures and diffusion in poly(ethylene oxide) (PEO) with lithium and bis(trifluoromethysulfonyl)imide (TFSI) ions imbedded into the PEO structure. We consider a range of temperatures (360–480 K), molecular weights (43, 22, 10, and 2 chains with 23, 45, 100, and 450 EO monomers, respectively), and ion concentrations (r = 0.02, 0.04, 0.06, and 0.08 Li:EO) for which there is experimental data. The found dependence of the diffusion coefficients on these variables is in good agreement with experimental measurements. We then analyze how the diffusion performance depends on details of the atomistic diffusion mechanism, the motion of the Li and TFSI along the polymer chains and hopping between them, the role of polymer motion, the temperature dependence of the intrachain and interchain diffusion contributions to the tot...

Molecular Dynamics Simulations of Ionic Diffusion in PEO-LiTFSI Polymer Electrolyte: Effect of Temperature, Molecular Weight, and Ionic Concentration

Polymer electrolytes are promising materials for development of the next generation of energy storage devices, including lithium-ion polymer batteries, due to their exceptional chemical and mechanical stability, high energy density and long lifetimes. Understanding the ionic diffusion mechanism in polymer electrolytes is critical to the development of advanced lithium-ion batteries. A molecular dynamics-based characterization of structures and diffusion in poly(ethylene oxide) (PEO) with lithium and bis(trifluoromethy-sulfonyl-imide) (TFSI) ions imbedded into the PEO structure have been performed across a range of temperatures, molecular weights and ion concentrations, with relative ionic diffusion coefficients shown to be in good agreement with experimental measurements. To determine details of the atomistic diffusion mechanism, the chain coordination of Li atoms, polymer motion, and temperature dependences of the intrachain and interchain diffusion contributions into the total ionic diffusion coefficients on ionic concentration and molecular weight were analyzed. We find that the most diffusive Li atoms exhibit frequent interchain hopping, whereas the least diffusive Li atoms rather oscillate or “shift” coordination between two or more polymer chains. These shifts may actually reduce the segmental motion of the PEO-LiTFSI polymer, which is important for the fast lithium-ion diffusion. Good agreement between experiment and theory validates the approach and methodology used in this study and its further applications for predicting the structure and ionic conductivity of new advanced polymer materials for a new generation of electrochemical devices. Acknowledgement This work was supported by Bosch Energy Research Network Grant No. 13.01.CC11.

Electropolymerization and characterization of ionic diffusion in poly(diphenyldithieno[3,2‐b;20,30‐d]thiophene)

AbstractPoly(diphenyldithieno[3,2‐b;20,30‐d]thiophene) was synthesized by electropolymerization on Pt quartz crystal and on an indium tin oxide electrode by cyclic voltammetry. Ionic diffusion through the electronic conducting film (for the p‐doping process) was studied by cyclic voltammetry coupled to a quartz crystal microbalance (E‐QCM) and electrochemical impedance spectroscopy (EIS), using different electrolyte salts such as LiTFSI, LiClO4 or LiCF3CO2. The molar ratio of insertion/expulsion of anions and cations was estimated from E‐QCM. By comparison between E‐QCM and EIS, the intrinsic ionic diffusion mechanisms in the electronic conducting film were highlighted depending on the salts used in acetonitrile. Moreover, the different mechanisms are in good agreement with the molar ratio of anion/cation insertion/expulsion. © 2018 Society of Chemical Industry

Thermally assisted self‐healing polyurethane containing carboxyl groups

ABSTRACTSelf‐healing polymer is a kind of intelligent material with the capability to repair damage automatically. In this paper, a type of polyurethane containing carboxyl groups is reported that demonstrates thermally assisted healing effects. This polymer can be healed even 72 h after cutting and also has a repeatable healing property. The self‐healing efficiency can reach 90% when comparing the tensile strength of the healed sample to the original sample. Carboxyl content plays an important role in the self‐healing property; polyurethane with no carboxyl groups cannot be healed. The mechanism of self‐healing showed that hydrogen bonding interactions between carboxyl groups and diffusion of poly(ethylene glycol) chains contribute to the self‐healing behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45929.

Microstructure and model solute transport properties of transglutaminase-induced soya protein gels: effect of enzyme dosage, protein composition and solute size

The diffusion of poly(ethylene glycol) (PEG) in transglutaminase (TGase) cross‐linked soya protein gels as affected by enzyme dosage and protein composition was investigated. PEG with different molecular weights (Mw) varying from 6000 to 400 000 g mol⁻¹ was selected. Results of this study revealed that the time‐related release of PEG from gel slices was found to be controlled by Fickian diffusion process. For PEG with Mw 6000 g mol⁻¹, the diffusion coefficients (D) were independent on the enzyme dosage and protein composition. However, for PEG with Mw ≥ 20 000 g mol⁻¹, there were strong dependences of diffusion on the solute size and on the gel network microstructure revealed by scanning electron microscopy (SEM), where more density gel network with smaller pores resulted in lower D of PEG. Lower D values of PEG with Mw ≥ 20 000 g mol⁻¹ were obtained in gels induced by 2 U g⁻¹ TGase, and the D values increased with increasing 11S ratio in gels. Moreover, data also showed that the diffusion of PEG with larger size was more sensitive to the variation of gel network.

Grafted polymer chains suppress nanoparticle diffusion in athermal polymer melts.

We measure the center-of-mass diffusion of poly(methyl methacrylate) (PMMA)-grafted nanoparticles (NPs) in unentangled to slightly entangled PMMA melts using Rutherford backscattering spectrometry. These grafted NPs diffuse ∼100 times slower than predicted by the Stokes-Einstein relation assuming a viscosity equal to bulk PMMA and a hydrodynamic NP size equal to the NP core diameter, 2Rcore = 4.3 nm. This slow NP diffusion is consistent with an increased effective NP size, 2Reff ≈ 20 nm, nominally independent of the range of grafting density and matrix molecular weights explored in this study. Comparing these experimental results to a modified Daoud-Cotton scaling estimate for the brush thickness as well as dynamic mean field simulations of polymer-grafted NPs in athermal polymer melts, we find that 2Reff is in quantitative agreement with the size of the NP core plus the extended grafted chains. Our results suggest that grafted polymer chains of moderate molecular weight and grafting density may alter the NP diffusion mechanism in polymer melts, primarily by increasing the NP effective size.

Molecular Tracer Diffusion in Nondilute Polymer Solutions: Universal Master Curve and Glass Transition Effects

Using fluorescence correlation spectroscopy, we investigated the diffusion dynamics of a molecular probe in solutions of polystyrene and polybutadiene with different molar masses (Mw) and molecular architectures (stars, combs) over a broad concentration range (c). Whereas the tracer diffusion coefficient D was found to be insensitive to variations in Mw and architecture, the obtained master plot D(c) was polymer-specific, reflecting additional friction effects related to the concentration-dependent glass transition temperature Tg(c). This effect is fully suppressed for the same probe diffusion in poly(dimethylsiloxane) solutions with very low and virtually concentration-independent Tg. Hence, a universal master curve of D vs c can be obtained when Tg(c) is accounted for.