Relationship between segmental dynamics and tracer diffusion of low mass compounds in polyacrylates

We studied the relationship between segmental dynamics of matrix polymers and tracer diffusion of low mass compounds by the use of forced Rayleigh scattering and dielectric spectroscopy. Specifically poly(methyl acrylate), poly(ethyl acrylate) and poly(n-butyl acrylate) were used as the polymer matrices and six azobenzene derivatives with various substituents as the diffusant. The temperature dependence of the tracer diffusion coefficient D was measured on methylyellow (MY)/polyacrylate blends at the MY concentration of 1 wt%. The results indicate that the temperature dependence of D is weaker than the dielectric loss maximum frequencies f_m for the α processes of the matrices. The effect of volume of the dye molecules on D was also investigated at 305 K. Comparison of the tracer diffusion coefficients among various dye/polymer systems indicates that log D in the same matrix decreases linearly with the molar volume of the dyes.     

Effect of penetrant size and shape on its transport through a thermoset adhesive: I. n-alkanes

The diffusion behaviors of a series of n-alkanes, ranging from C₆ to C₁₇, through a polyamide-type polymeric matrix have been investigated by means of mass uptake measurements. Since n-alkanes are known to display negligible interactions with the polymer matrix, this study serves to isolate the effects of penetrant size and shape on the transport process without undue interference from polymer-penetrant interactions. It is established that the diffusion of the n-alkanes through the polymer matrix studied is Fickian and proceeds via a Henry's law-type mechanism. The diffusion coefficients, D, are evaluated based on a thin-film approximation of the Fickian equation. The activation energies of diffusion, E_d, are determined from the temperature dependence of D, using the Arrhenius equation. Correlations between the Arrhenius terms, E_d and D₀, are also established which enable the prediction of diffusion coefficients for similar polymer-penetrant systems. It is also demonstrated by means of activation energy calculations and molecular simulations that the n-alkanes assume a linear geometry within the polymer matrix and diffuse along their long axes.     

Effect of cation doping on lattice and grain boundary diffusion in superplastic yttria-stabilized tetragonal zirconia

Lattice diffusion coefficients D_l and grain boundary diffusion D_gb coefficients of hafnium were studied for 0.5 and 1 mol% cation-doped yttria-stabilized tetragonal zirconia at the temperature range from 1283 to 1510 °C. The diffusion profiles were determined by two experimental techniques: secondary ion mass spectroscopy and electron microprobe analysis. Additionally the first principle calculations of the electronic states of Zr⁴⁺, dopant cations and O^2? anions and elastic properties in 3Y-TZP were performed. Superplastic strain rate versus stress and inverse temperature was also measured. For 1 mol% doped samples the significant increase of the grain boundary diffusion and superplastic strain rate was observed. Correlations between the calculated ionic net charges and D_gb indicate that enhancement of D_gb was caused by the reduction of ionic bonding strength between metal cation and oxygen anion in zirconia. The new constitutive equation for superplastic flow of yttria-stabilized tetragonal zirconia ceramics was obtained.     

Diffusion of rigid rodlike polymer in isotropic solutions studied by dissipative particle dynamics simulation

Dissipative particle dynamics (DPD) was employed to simulate the diffusion of rigid rodlike polymers in isotropic solutions. In a dilute solution range, the simulated diffusion behavior is in good agreement with that as described by the Kirkwood theory. In a semi-dilute range, the simulation shows that the DPD model adopting soft repulsive interactions can effectively reproduce the entanglement effect on both rotational and translational diffusions. The rotational diffusion coefficient D_r obeys the asymptotic scaling law D_r ∼ (νL³)⁻² (ν is the number of polymers per volume and L is the polymer length) for the large νL³, which corresponds to formation of a completely enclosed tube in the Doi-Edwards theory. The parallel translational diffusion coefficient D_‖ decreases with ν increase, which can be attributed to the friction effect of surrounding medium. The perpendicular translational diffusion coefficient D_⊥ decays more drastically with ν increase, which is caused by the topological constraint.     

Diffusion in polyacrylamide gels

Using a novel sorption technique, the diffusion of some series of solutes in polyacrylamide gels has been investigated with regard to: (a) molecular size of solute; (b) concentration of solute and gel polymer; and (c) temperature. The approach used also yields the partition coefficient pertaining to sorption equilibrium. The ratio, $\text{D}\text{D}{}_{\mathrm{o}}$, where D_o refers to diffusion in the pure solvent, is found to reflect in part the characteristic interactions between solute and gel polymer. The temperature results indicate that the apparent activation energy for solute diffusion is approximately independent of the polymeric component for dilute gels.     

Dielectric,transport and thermal properties of clay based polymer‐ nanocomposites

The polymer nanocomposite films (PNC) with varying amounts of organically modified sodium montmorillonite (DMMT) clay in poly(methyl methacrylate) (PMMA) based polymer matrix were prepared by solution cast technique. Dielectric measurements were carried out on these films as a function of frequency at 30°C and 100°C. The addition of clay significantly improved the ionic conductivity. Transport parameters, such as the diffusion coefficient (D), number density (n) and mobility (μ) of charge carriers were determined using a new approach, which is based on impedance spectroscopy. The temperature‐dependent dc conductivity, relaxation and mobility plots obey the Arrhenius rule. The results suggest that the higher ionic conductivity of these PNC films at elevated temperature is not only due to increased mobility of ions, but it is accompanied by a significant increase in carrier concentration. Analysis of DSC thermogram reveals a very high percentage of amorphous content for all samples. A good correlation among dielectric permittivity, carrier concentration, mobility and ionic conductivity has also been observed. POLYM. ENG. SCI., 58:220–227, 2018. © 2017 Society of Plastics Engineers     

Water Sorption and Diffusion in Poly-(3-Hydroxybutyrate) Films

For improved understnding of the transport of low-molecular substances' in moderately hydrophobic polymers, the temperature dependence of water vapor sorption and diffusion in poly-(3-hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption and diffusion kinetics were determined by a quartz McBain's vacuum microbalance technique in the temperature range 303-333 K. The water molecule interaction with the polymer matrix was analyzed for wet PHB films by the Fourier transform infrared spectroscopy technique. Water sorption isoterms are interpreted as a superposition of free water sorption estimated by the Flory-Huggins equation and water immobilized on car-bony 1 groups of PHB. The immobilization effect was described by a Lmgmuir-type equation. The dependence of diffusivity on water concentration was described in the framework of Fujita's immobilization model in which the growing function D _w versus C _w characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and water immobilization (42 kJ/mol) as well as the activation energy of water diffusion coefficients (71 kJ/mol) in noncrystalline areas of PHB were determined.     

Cyclic wet drying of an epoxy coating using an ionic liquid

The barrier protection of an organic coating for a metallic substrate is compromised by the transport of water, oxygen and ions from the environment to the metal/coating interface. Metallic outdoor structures are exposed to the weather and undergo cyclic wetting and drying conditions. In the absence of holidays, the transport of water is diffusion limited. The diffusion coefficients associated with water ingress D_in and egress D_out are indicators of the wetting and drying rates, respectively, of the coating. Gravimetric and capacitance methods are used for the measurement of D_in whereas D_out measurement has been limited to the gravimetric method. The objective of this paper is to demonstrate the application of a recently reported method that employed a hydrophilic room temperature ionic liquid to monitor the capacitance changes associated with the egress of water from which D_out was calculated. Experimental results associated with cyclic dilute NaCl wetting and ionic liquid drying are presented for an epoxy coating on an AA 2024-T3 substrate that was subjected to 50 cycles. The D_in and D_out values were calculated using a short-time approximate solution and a series solution to Fick's second law. Presented electrochemical impedance spectra associated with the ends of wet and dry stages of the cycles were analyzed using an equivalent circuit model that separated the bulk coating and metal/coating characteristics.     

Thermosensitive nanosized micelles from cholesteryl-modified hydroxypropyl cellulose as a novel carrier of hydrophobic drugs

The thermosensitive micelles based on the two series of cholesteryl-modified hydroxypropyl cellulose (series 1 and 2, respectively) were used as a promising drug carrier. The polymers 1a and 2a with side chain substitution degrees D _Chol?=?0.7 and 2.1?mol% were selected for micelle preparation, respectively. Polymeric micelles were prepared by the co-solvent evaporation method. The aqueous self-assembly of the polymers was studied using fluorescence analysis and transmission electron microscopy (TEM). The critical micelle concentrations (CMCs) values of the various D _Chol of polymers were evaluated in the range of ca. 0.13?C0.29?g/L which decreased with the increase of D _Chol in both series. Furthermore, the CMC values displayed a downtrend profile, with increasing the temperature. The polymer 1a with less D _Chol had lower CMC than that of polymer 2a. By using the naproxen as a hydrophobic model drug, the drug-loaded micelles were prepared. The TEM image of naproxen-loaded micelles of polymer 1a with 40?% drug-loading efficiency and 8?% loading capacity showed that micelles were regularly spherical in shape with a mean diameter of 70?nm. The unmodified HPC exhibited a lower critical solution temperature (LCST) of more than 41?°C in water, while polymeric micelles in aqueous solution presented an LCST of 38.7?°C. A drug release study was performed by dialysis method in phosphate-buffered solution at 25, 37 and 40?°C, respectively. The release kinetics of naproxen from the polymeric micelles revealed a thermosensitivity, since its release rate was higher at 40?°C than at 25?°C.     

Concentration dependence of the diffusion coefficient in polymer solution and molecular weight distribution determined by the diffusion method

The effects of the concentration dependence of the diffusion coefficient of a polymer solution (polystyrene in benzene and cyclohexane) in determining molecular weight distribution by the diffusion method are briefly discussed. The value of the ratio D_m0/D_A0 in a good solvent was found to be close to 1.0 for a polydisperse polymer and less than 1.0 for monodisperse polymers. Molecular weight distribution curves of the polydisperse sample were obtained by the diffusion method in cyclohexane and benzene, respectively. The molecular weight distribution curve obtained for the polymer used in benzene solution looked as if the polymer had a narrow molecular weight distribution. The phenomena cited above were interpreted in the light of the concentration dependence of the diffusion coefficient of polymer solutions.     

Synthesis and characterization of polyurethane cationomer/MMT hybrid composite

BACKGROUND: The development of polymeric nanocomposites incorporating intercalated or exfoliated layered silicate clays into the organic matrix has been substantially motivated by the significant improvements induced by the presence of the inorganic component. Moreover, understanding and controlling the dispersion of inorganic layers into segmented polyurethane matrices by means of ionic interactions, and exploiting these interactions to enhance physicomechanical behaviour, could be of great interest in the field of polymer nanocomposites. RESULTS: New cationic polyurethane elastomers were prepared starting from poly(butylene adipate)diol (M_n = 1000 g mol^?1), 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol and N‐methyldiethanolamine or N,N′‐β‐hydroxyethylpiperazine, used as potential quaternizable moieties. The characterization of the polymers was achieved using specific analyses employed for the macromolecular samples (Fourier transform infrared and ¹H NMR spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography). An extension of our research on polymers reinforced with organically modified montmorillonite (OM‐MMT) in order to prepare hybrid composites with improved properties was performed and the resulting materials were characterized using TGA, X‐ray diffraction, atomic force microscopy and scanning electron microscopy. Also, the mechanical properties of the cationic polyurethane/OM‐MMT composites were investigated in comparison with the pristine ionic/non‐ionic polymers and their composites containing non‐ionic polymer blended with OM‐MMT or ionic polymer and unmodified MMT. CONCLUSION: The insertion of the organically modified clay into the polymeric matrix gave an improvement of the mechanical properties of the polyurethane composites, especially the tensile strength and stiffness of the hybrid materials. Copyright © 2009 Society of Chemical Industry     

Mass transfer kinetics on the heterogeneous binding sites of molecularly imprinted polymers

The mass transfer kinetics of the L- and D-Fmoc-Tryptophan (Fmoc-Trp) enantiomers on Fmoc-L-Trp imprinted polymer (MIP) and on its reference polymer (NIP), were measured using their elution peak profiles and the breakthrough curves recorded in frontal analysis for the determination of their equilibrium isotherms, at temperatures of 40, 50, 60, and . At all temperatures, the isotherm data of the Fmoc-Trp enantiomers on the MIP were best accounted for by the Tri-Langmuir isotherm model, while the isotherm data of Fmoc-Trp on the NIP were best accounted for by the Bi-Langmuir isotherm model. The profiles of the elution bands of various amounts of each enantiomer were acquired in the concentration range from 0.1 to 40 mM. These experimental profiles were compared with those calculated using the best values estimated for the isotherm parameters and the lumped pore diffusion model (POR), which made possible to calculate the intraparticle diffusion coefficients for each system. The results show that surface diffusion contributes predominantly to the overall mass transfer kinetics on both the MIP and the NIP, compared to external mass transfer and pore diffusion. The surface diffusion coefficients (D_s) of Fmoc-L-Trp on the NIP does not depend on the amount bound (q) while the values of D_s for the two Fmoc-Trp enantiomers on the MIP increase with increasing q at all temperatures. These positive dependencies of D_s on q for Fmoc-Trp on the MIP were fairly well modeled by indirectly incorporating surface heterogeneity into the surface diffusion coefficient. The results obtained show that the mass transfer kinetics of the enantiomers on the imprinted polymers depend strongly on the surface heterogeneity.     

Synthesis of small-band gap poly(3,4-ethylenedioxythiophene methine)s using acidic ionic liquids as catalyst

Poly(3,4-ethylenedioxythiophene methine)s were synthesized in the presence of acidic ionic liquids for the first time. The polymers were obtained in good yields and viscosities ranging which were soluble in most common solvents such as NMP, THF, CH₂Cl₂, p-dioxane, chloroform, etc. The polymer structures were confirmed by FT-IR, UV–Vis-NIR, ¹H-NMR spectra, elemental and thermogravimetric analysis techniques. The thermal gravimetric analysis showed that the polymers had a fairly good thermal stability. The optical and electrochemical band gaps of the synthesized polymers were 1.16–2.3 and 1.7–2.05 eV, respectively. The electrochemical impedance spectroscopy studies were shown that polymers conductivity was greatly increased after doping of polymers with iodine.     

High frequency mass transfer responses with polyaniline modified electrodes by using new ac-electrogravimetry device

For many years, polyaniline films have appeared to be one of the most studied conducting polymers. At the same time, ac-electrogravimetry has been used as a powerful technique for different polymer films but in general for slow perturbation rates. Two reasons for that: on the one hand, high frequency mass transfer responses are not expected and on the other hand, the electronic interfaces dedicated for ac-electrogravimetry are not prepared to follow, without distortion, high rate frequency shifts, faster than a few hertz. This paper shows that high ionic transfer responses can be detected by using a new ac-electrogravimetry concept. The experiments conducted with PANI tried to verify whether high frequency responses in conducting polymers are possible or not. The main interest of the new device is to reach the high frequency values directly and to demonstrate an ionic transfer contribution at 1 kHz which was not predicted with old systems.     

Correlation aspects of the selective gas permeabilities of polymeric materials and membranes

Although the solubility and diffusivity of each gas in each polymer are temperature- and may be pressure-dependent properties of every system nevertheless regular trends are noted when either many gases are studied in a single polymer or a single gas is studied in many polymers. Several empirical though scientifically based correlations of such data have been proposed which are at best semi-quantitative. In this paper improved correlations are described to correlate data on diffusivities D and the related energies of activation, and solubilities S and related heats of solution of gases in polymers. The procedures rely on determining an effective Lennard-Jones force constant and molecular diameter for each gas, which parameters hold in all polymers above T_g and, with slightly smaller diameters for the multiatomic gases, in all polymers below T_g. Each polymer is characterized by four temperature-dependent parameters, two for diffusivity and two for solubility, which hold with all gases. Rules are given for determining these parameters. It is demonstrated that D is correlated to within ±20% and S to ±30%. The procedure described may be used to predict D and S, and hence permeabilities, in cases where data do not already exist. The values and ratios of the predicted permeabilities are a valuable guide when seeking polymers for separating gas mixtures by membrane processing.     

Spectroscopic studies of spin-coated dye-in-polymer films. On the relationship between compatibility and aggregation of small molecules in polymer matrices

Dye-in-polymer (DIP) films of various concentrations of I (a p-N,N-dialkyl-aminobenzylidenemalononitrile derivative) in four polymers of different dye-polymer compatibilities have been prepared by spin-coating technique using a wide range of coating speeds (600–8000 rpm). The aggregation of dye molecules in polymer matrix was studied by electronic spectroscopy. The dye-polymer compatibility of various DIP systems was examined by d.s.c. Our results indicate that there exists a staturated concentration of I in each polymer and this saturated concentration decreases as the dye-polymer compatibility decreases, e.g. it decreases from ～20% in poly(vinyl acetate) and in poly(isobutyl methacrylate) to ～10% in styrene/isobutyl methacrylate (8:2) copolymer to ～5% in polystyrene. At dye concentrations lower than this saturated concentration, the degree of dye aggregation is not sensitive to varying spin-coating speeds. At dye concentrations higher than this saturated concentration, the degree of dye aggregation depends on the degree of dye-polymer incompatibility and on the spin-coating speed. The significance of the present work in solvent coating technology of small molecule/polymer systems, in general, will be discussed. Finally, the T_g's of various DIP systems were found not to correlate with the dye concentration (by weight). This is attributable to the strong dye-dye interaction of I inside the polymer matrix.     

Diffusion of hairy polymeric micelles in a homopolymer solution

Polystyrene-block-poly(4-vinylpyridine) (PS-b-PVP) forms hairy micelles with PVP and long PS block as the core and corona in toluene, respectively. Diffusion of the micelles in solution in the presence of poly(methyl methacrylate) (PMMA) or polystyrene homopolymer (h-PS), from dilute to semidilute, has been investigated by laser light scattering (LLS). Our results indicate the micelles only exhibit translational diffusion with characteristic Γ = Dq² in PMMA dilute and semidilute solutions, where Γ, D and q are characteristic line width, translational diffusion coefficient and scattering vector, respectively. PMMA concentration dependence of D reveals that the micelle diffusion follows a “stretched exponential” scaling law, similar to that of a hard sphere in the presence of matrix polymer. This is because the PS corona is incompatible with PMMA and no entanglement between them occurs. In contrast, in h-PS solution, due to the overlap and entanglement between the PS corona and h-PS matrix, the micelles exhibit diffusion with characteristic of Γ ∝ q^α, where α = 2-2.6. For the same matrix polymer concentration, the micelles exhibit a faster diffusion in PMMA solution than that in h-PS solution, especially in semidilute solutions. The fact further indicates that the overlap and entanglement between the corona and h-PS matrix restrict the micelle motion.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

A theory of case II diffusion

A theory is proposed to explain the transport behaviour of organic penetrants in glassy polymers in terms of two basic parameters: the diffusivity of the penetrant, D, and the viscous flow rate of the glassy polymer, $\text{1}\text{η}{}_0$. The rate controlling process for transport in these systems is considered to be diffusion of solvent down an activity gradient coupled with time-dependent mechanical deformation of the polymer glass in response to the swelling stress. The theory combines these two factors and is able to predict a wide range of observed transport phenomena from Fickian diffusion kinetics at one extreme to so-called Case II and Super-Case II behaviour at the other. The existence of a sharp front separating swollen and unpenetrated polymer is shown to result from the concentration dependence of the viscous flow rate.