Diffusivity of gases and main-chain cooperative motions in plasticized poly(vinyl chloride)

Permeability and time-lag measurements for H₂ and CO in poly(vinyl chloride) (PVC) plasticized with tricresyl phosphate show that the apparent diffusion coefficients at first decrease as the plas-ticizer concentration is increased. The diffusion coefficients then increase as the additive concentration is raised above 15 wt %. These changes in the apparent diffusion coefficients can be related to the behavior of a variety of mechanical properties and are attributed to antiplasticization and plasticization effects of low and high concentrations of tricresyl phosphate, respectively. The antiplasticization-plasticization effects reflect altered molecular motions of the polymer. Carbon-13 NMR rotating-frame relaxation rate measurements show directly that the cooperative main-chain molecular motions of PVC are reduced when the additive acts as an antiplasticizer and are increased when the polymer is plasticized. Both the apparent diffusion coefficient and the rotating-frame relaxation rate have a similar dependence on additive concentration. An application of the molecular theory of diffusion of Pace and Datyner accounts qualitatively for the way in which additives alter the average chain interaction energy, cooperative polymer main-chain motions, and the diffusion coefficients of gaseous penetrants.     

磺化聚芳醚酮砜/聚吡咯复合型直接甲醇燃料电池用质子交换膜的制备与性能研究

以高磺化度的磺化聚芳醚酮砜(SPAEKS)和吡咯(Py)为原料,通过原位聚合的方法制备了含有不同吡咯含量的SPAEKS/PPy复合膜.红外谱图表明SPAEKS聚合物中的磺酸基团与聚吡咯(PPy)中的亚氨基基团之间形成了强烈的相互作用.扫描电镜照片显示PPy能够均匀地分散在SPAEKS聚合物基体中,没有发生团聚现象.通过对复合膜的性能测试发现PPy的引入提高了复合膜的热稳定性,降低了复合膜的吸水率,改善了其水溶胀性.同时膜中水的脱附系数下降,提高了膜的保水能力.SPAEKS/PPy-3复合膜的甲醇渗透系数达到了1.18×10-7cm2/s,明显低于纯SPAEKS膜的8.52×10-7cm2/s,而其质子传导率虽有所降低,但在25℃和80℃仍然分别达到了0.039S/cm和0.061S/cm,能够满足质子交换膜对质子传导率的要求.研究结果表明,聚吡咯与SPAEKS中磺酸基的摩尔比为0.99的复合膜有望在直接甲醇燃料电池中得到应用.     

PREPARATION AND PROPERTIES OF SPAES-TiO_2 HYBRID MEMBRANES FOR DIRECT METHANOL FUEL CELL

Sulfonated poly(arylene ether sulfone)(SPAES) copolymer with degree of sulfonation of 1.0 was synthesized and characterized.A series of SPAES-TiO_2 hybrid membranes with various contents of nano-sized TiO_2 particles were prepared and characterized through sol-gel reactions.Scanning electron microscopy(SEM) images indicated the TiO_2 particles were well dispersed within polymer matrix.These composite membranes were evaluated for proton exchange membranes(PEMs) in direct methanol fuel cell(DMFC).These mem...     

Mobility-sensitive fluorescence probes for quantitative monitoring of water sorption and diffusion in polymer coatings

The fluorescent molecular rotor probes 4-tricyanovinyl-[N-(2-hydroxyethyl)-N-ethyl]-aniline, tricyano-4-(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10^-8 cm²/s in poly(vinyl acetate), and a value of 6 × 10^-9 cm²/s in a room-temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. © 1995 John Wiley & Sons, Inc.     

Ion-selective electrodes based on metalloporphyrins for gibberellic acid determination in agricultural products

This work describes the construction, evaluation and analytical application of electrodes selective to the gibberellate anion for the determination of gibberellic acid in agricultural products. Several types of PVC membrane electrodes without internal reference solution were prepared using the manganese(III) complex of meso -tetraphenylporphyrin (TPP) as ionophore and dibutyl phthalate (DBP), as plasticizer. The incorporation of lipophilic chemical species as additives, was also carried out aiming the evaluation of the response characteristics of the electrodes. To accomplish the analysis of commercial agricultural products a selective membrane composed of 28.0% (w/w) of PVC, 66.0% (w/w) of plasticizer and 6% (w/w) of ionophore was used, with no additive. This potentiometric unit presented a linear response between 10^-4 and 10^-1 mol L^-1 in gibberellate, a slope of about ⫙ mV dec^-1 and a reproducibility of about ǃ mV day^-1. The potentiometric analysis of gibberellic acid in commercial products was carried out by direct potentiometry and the results obtained were compared with those provided by HPLC.     

Formation of manganese solid solutions in single crystals of ZnGeP2

Process of the solid-phase diffusion of manganese into single crystals ZnGeP² are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn²⁺ concentration of 10¹⁸ cm^-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP² at a diffusion annealing temperature was determined.     

Diffusion des additifs du polyethylene—V: Influence sur le vieillissement du polymere

Diffusion measurements of additives in polyethylene suggest that the main problem for stabilizing this polymer is that of the compatibility of antioxydants. The results of natural ageing (exposure to natural environment) on the antioxydant content of samples, in which diffusion and solubility were studied, confirm that the lifetime of a sample is closely connected with the migration of stabilizers. It seems that the determining factors are the antioxydant solubility and then the diffusion coefficient. Generally, the other factors are of negligible importance. After 6 months, a sample does not retain additive of low solubility but additive of high solubility is still present after 2 years.     

Repeated migration of additives from a polymeric article in food simulants

The migration of three additives from polypropylene samples into a series of five liquid food simulants was investigated at 60 °C in a repeated migration regime. This regime was simulated by 20 migration periods each of 8 h and using initially additive free food simulants. Between these migration periods the bare samples were stored in an air conditioned room at around 23 °C for 16 h at working days and for 64 h during weekends. An asymptotic decrease of the additive level in the food simulants in the successive migration periods, from a maximum values towards zero, was observed when the additives easily solve in the food simulants. In contrast when the additives solve poorly in the food simulants this additive level decrease is almost linear and shows a slow decrease rate. In the first case the leaching/migration of the additives is controlled mainly by their diffusion in the matrix of the polymer. In the latter case this process is controlled mainly by the partitioning of the additives between the polymer and food simulants. Two approaches were used to model theoretically these results.In the first approach the mass transport equation was solved by using as input parameters overestimated diffusion and partitioning coefficients as estimated for polypropylene homopolymer, the used food simulants and the three additives according to the recommendations of a practical guidance document in support of migration modelling as stipulated in the Regulation (EU) 10/2011. As expected the results of these calculations overestimate the vast majority of the migration levels determined experimentally. However there are also situations in which this approach leads to underestimations of the real migration levels.In the second approach numerical fitting was applied with the same equation and using the diffusion and partition coefficients as adjustable parameters to obtain a best-fit between experimental and calculated results. It was found that the so obtained “realistic” diffusion coefficients are all lower than the overestimated ones mentioned above. Moreover these “realistic” coefficients depend not only on the nature of the additive but also on the nature of the food simulant in contact with the polymer. This suggests that interaction of food simulants with the polypropylene occurs, which changes the properties of the polymer and thus the mobility of the additive molecules in its matrix. For the “realistic” partition coefficients it was found that they all are higher than the conservative ones mentioned above. Using these “realistic” parameters a good fit between calculated and experimental migration results was found.     

Evaluation of the dynamic properties of polymer latex particles interacting with quartz interface by evanescent wave dynamic light scattering

The diffusion behavior of polymer latex particles in dispersion near the quartz interface has been estimated by evanescent wave dynamic light scattering (EVDLS) technique. The diffusion coefficient of the particles was measured as a function of the distance between the particle and interface. The apparent diffusion coefficient estimated by EVDLS was small for particles near the interface and increased upon increasing the distance from the interface, and then saturated at a certain value which is close to the value expected for free-motion. The range of the distance over which diffusion was affected by interaction with the interface depended on the added salt concentration. This means that the diffusion of the particle is influenced by an electrostatic interaction between the particle and quartz interface in addition to the hydrodynamic effect near the wall. This range was found to be more than 800?nm at 0?M salt condition but about 400?nm at 10^-4 and 10^-3?M salt conditions. Hence it is appropriate to say that the hydrodynamic effect reaches up to 400?nm and the electrostatic effect is longer ranged, more than 800?nm, for the system studied here. The EVDLS technique is a very powerful tool for quantitative estimations of the dynamic behavior of the particle near the interface and for estimation of the range where the wall effect is dominant. EVDLS will give us an answer to the question of “where is the ‘interface’ and where is the ‘bulk’?”.     

Characterisation of soot particulates from fire retarded and nanocomposite materials, and their toxicological impact

Polyamide 6 (PA 6) and polypropylene (PP) containing fire retardants, nanofillers or a combination of both additives have been investigated using the steady state tube furnace (ISO TS 19700). The samples were tested under three different fire conditions, to determine the effect of additives on the soot production or toxic product yields. The particle size distribution of the soot was investigated with a cascade impactor, and the separated soot fractions examined by SEM. The predicted deposition based on aerodynamic size of particulates in the human respiratory tract shows clear differences between the pure polymer and its additive counterparts. In all ventilation conditions the virgin polymer produces the least amount of soot, both the additives used (fire retardant and nanoclay) increase the amount of soot, mainly within 0.5-1.0 μm range, for each fire condition. A large contribution to the total soot mass originated particles smaller than 0.5 μm.     

All‐Atom Molecular Dynamics Simulation of Structure and Diffusion of Hydrophilic Antistatic Agents in Polypropylene

Glycerol monostearate (GMS) is an additive widely used in plastic industry for its good ability to improve the wettability and antistatic property of polymer surfaces. Based on GMS, we propose five additives of different polarity by attuning the number of oxyethyl groups. All‐atom molecular dynamics simulations of these additives in polypropylene (PP) matrix are carried out at temperatures of 300 K, 350 K and 400 K. Detailed molecular conformations are obtained and analyzed. Due to the gauche effect of the dihedral angles, the polar parts of these additives form helix structures. The diffusion coefficient of the additives depends on their molecular conformations and decreases monotonously with increasing polarity. These results are expected to be helpful in rational design of hydrophilic antistatic agents in polymeric materials.     

Mobility of Spherical Probe Objects in Polymer Liquids

We use scaling theory to derive the time dependence of the mean-square displacement ?Δr(2)? of a spherical probe particle of size d experiencing thermal motion in polymer solutions and melts. Particles with size smaller than solution correlation length ξ undergo ordinary diffusion (?Δr(2) (t)? ~ t) with diffusion coefficient similar to that in pure solvent. The motion of particles of intermediate size (ξ < d < a), where a is the tube diameter for entangled polymer liquids, is sub-diffusive (?Δr(2) (t)? ~ t(1/2)) at short time scales since their motion is affected by sub-sections of polymer chains. At long time scales the motion of these particles is diffusive and their diffusion coefficient is determined by the effective viscosity of a polymer liquid with chains of size comparable to the particle diameter d. The motion of particles larger than the tube diameter a at time scales shorter than the relaxation time τ(e) of an entanglement strand is similar to the motion of particles of intermediate size. At longer time scales (t > τ(e)) large particles (d > a) are trapped by entanglement mesh and to move further they have to wait for the surrounding polymer chains to relax at the reptation time scale τ(rep). At longer times t > τ(rep), the motion of such large particles (d > a) is diffusive with diffusion coefficient determined by the bulk viscosity of the entangled polymer liquids. Our predictions are in agreement with the results of experiments and computer simulations.     

A new method of growing crystalline networks in polymer matrices by simultaneous CT complex formation and in situ crystallization

A new method of preparing conductive polymer composites by growing crystalline networks of conductive additives in polymer matrices (reticulate doping) is described. The method consists of treating the polymer containing molecularly dispersed donor additive with acceptor/solvent vapors. In the swollen polymer layer simultaneously CT complex formation and crystallization takes place which for proper conditions leads to the formation of a network of the CT complex crystallites, making the film surface-conducting. The preparation and properties of surface conductive films using several electron donors and an iodine acceptor are described. The films obtained show surface resistivities of 10⁴–10⁶ ohm and are generally stable under ambient conditions.     

The equilibrium and kinetic rigidity of additive poly(trimethylsilyltricyclononenes) with one and two Si(CH<Subscript>3</Subscript>)<Subscript>3</Subscript> groups in monomer unit

The homologous series of additive poly[3-(trimethylsilyl)tricyclononene-7] with two heminal substituents Si(CH₃)₃ in the side cycle of the monomer unit is studied for the first time via the methods of viscometry and static and dynamic light scattering in the range of molecular masses of (29–770) × 10³. The scaling ratios for the intrinsic viscosity and the coefficient of translational diffusion of macromolecules in toluene at 298 K are obtained, and the equilibrium rigidity of the polymer chain is determined. The hydrodynamic and conformation properties of the polymer are compared to an analog with only one Si(CH₃)₃ substituent in the monomer unit. It is found that the introduction of the second side substituent in the heminal position increases the equilibrium rigidity of the additive poly[3-(trimethylsilyl)tricyclononene-7] by 1.4 times and has a far stronger effect on the kinetic rigidity of the polymer. With the use of the ¹Н NMR relaxation method, it is shown that the mobility of side groups of the polymer with two substituents decreases significantly and the correlation times of hydrogen atoms of Si(CH₃)₃ groups exceed some 20 times the corresponding values for the analog with one Si(CH₃)₃ group in the monomer unit cycle.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.     

Do additives shift the LCST of poly (<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) by solvent quality changes or by direct interactions?

The phase transition of thermoresponsive poly(N-isopropylacrylamide) is studied under the influence of additives considered as model substances for drugs. A series of aromatic compounds with similar structures, mainly benzaldehydes, is chosen. The lower critical solution temperature (LCST) is determined by differential scanning calorimetry and ¹H-NMR. All additives cause a down shift of the LCST, which depends on additive molecular structure and concentration. Since the LCST shifts are not correlated to hydrophobicity or solubility of the additive, the detailed substitution pattern is discussed as the controlling factor. The question whether LCST shifts can be explained by either the additives affecting the solvent quality or by specific interactions of additives with the polymer is addressed by LCST determination in dependence on polymer concentration. Though both factors are relevant, specific additive-polymer interactions are shown to play a major role in controlling the LCST.     

Fire retardancy of melamine and zinc aluminum layered double hydroxide in poly(methyl methacrylate)

The thermal and fire properties of PMMA modified with various loadings of melamine or zinc aluminum undecenoate LDH were evaluated using TGA, DTA and cone calorimetry. The additives were characterized by X-ray diffraction, TGA, FT-IR and elemental analysis. While the two additives are very effective with this polymer, a higher loading of melamine (30%) is required to reach a good reduction in PHRR (47%) relative to the pure polymer, while with the LDH, 10% loading is enough to obtain a similar reduction. The combinations of these additives in PMMA reveal that the time to PHRR and the amount of smoke produced are the key differences, with melamine increasing the first parameter and leading to less smoke production relative to LDH-rich PMMA systems at similar total additive loadings. Analysis of the residue shows that melamine is completely lost during combustion while the LDH forms ZnO and ZnAl₂O₄.     

Microgel Capsules Tailored by Droplet‐Based Microfluidics

Microgel capsules are micrometer‐sized particles that consist of a cross‐linked, solvent‐swollen polymer network complexed with additives. These particles have various applications, such as drug delivery, catalysis, and analytics. To optimize the performance of microgel capsules, it is crucial to control their size, shape, and content of encapsulated additives with high precision. There are two classes of microgel‐capsule structures. One class comprises bulk microcapsules that consist of a polymer network spanning the entire particle and entrapping the additive within its meshes. The other class comprises core–shell structures; in this case, the microgel polymer network just forms the shell of the particles, whereas their interior is hollow and hosts the encapsulated payload. Both types of structures can be produced with exquisite control by droplet‐based microfluidic templating followed by subsequent droplet gelation. This article highlights some early and recent achievements in the use of this technique to tailor soft microgel capsules; it also discusses applications of these particles. A special focus is on the encapsulation of living cells, which are very sensitive and complex but also very useful additives for immobilization within microgel particles.     

The influence of different additives and the mode of their addition on the sintering behavior and the properties of semiconducting barium titanate ceramics

The influence of different additives (TiO₂, TiO₂/SiO₂, CaO/TiO₂/SiO₂, 2BaO/TiO₂/2SiO₂) and the mode of their incorporation (spray drying: series 1; mixed-oxide method: series 2) on the sintering behavior and the microstructural and electrical properties of n-doped BaTiO₃ ceramics has been investigated. The incorporation of the additives from their aqueous solution by spray drying produces a homogeneous distribution of the additive in the BaTiO₃ matrix powder by coating the BaTiO₃ particles. This homogeneous distribution significantly lowers the activation energy for the densification process compared with that of the powders of series 2. Dynamic and isothermal dilatometric measurements revealed that the sintering process is considered as a classical solid phase sintering followed by recrystallization of the BaTiO₃ matrix particles by a eutectic melt. The densification process is dominated by sliding processes. These sliding processes are caused by the amorphous layer of the additive and by the defect-rich grain boundary layers of the BaTiO₃ grains generated intermediately by diffusion processes and reactions of the matrix material with the additive forming the secondary phases Ba₂TiSi₂O₈ and Ba₄Ti₁₃O₃₀, respectively. In series 1, ceramics with a homogeneous microstructure and useful electrical properties (e.g. low resistivity at room temperature) were already produced at a sintering temperature of 1280°C (with SiO₂-containing additives) due to the homogeneous distribution of the additive. The ceramics of series 2 sintered at the same temperature could only be obtained in poor quality. At higher sintering temperatures the differences between the two series vanished.     

Triclosan-loaded with high encapsulation efficiency into PLA nanoparticles coated with β-cyclodextrin polymer

The purpose was to prepare triclosan-loaded polylactic acid nanoparticles containing β-cyclodextrin polymer shell, evaluate triclosan release from the particles using Franz diffusion cells and to study the stability of the particles in presence of a model protein, bovine serum albumin. The nanoparticles were prepared by a solvent displacement process. The nanoparticles were characterized by their size, encapsulation efficiency and morphology. They were of spherical shape with hydrodynamic diameter of about 100 or 200 nm depending on the polylactic acid used. Their high encapsulation efficiency (~90%) indicated that triclosan is easily incorporated into the nanoparticles. The nanoparticles displayed slow and sustained triclosan release patterns (diffusion coefficient about 10^?22 m²/s) and the β-cyclodextrin polymer coating was stable under simulated physiological conditions. All these data indicated that these novel core–shell nanoparticles might provide a promising carrier system for controlled release of triclosan and other hydrophobic drugs after systemic administration.