Fast Water Diffusion and Long-Term Polymer Reorganization during Nafion Membrane Hydration Evidenced by Time-Resolved Small-Angle Neutron Scattering.

We report a small-angle neutron scattering study of liquid water sorption in Nafion membranes. The swelling of hydrophilic domains was measured on the nanoscale by combining in situ time-resolved and long-term static experiments, yielding kinetic curves recorded over an unprecedented time scale, from hundreds of milliseconds to several years. At low water content, typically below 5 water molecules per ionic group, a limited subdiffusive regime was observed and ascribed to nanoconfinement and local interactions between charged species and water molecules. Further ultrafast and thermally activated swelling due to massive liquid water sorption was observed and analyzed by using Fick's equation. The extracted mutual water diffusion coefficients are in good agreement with pulsed field gradient NMR self-diffusion coefficient values, evidencing a water diffusion-driven process due to concentration gradients within the Nafion membrane. Finally, after completion of the ultrafast regime, the kinetic swelling curves exhibit a remarkable long-term behavior scaling as the logarithm of time, showing that the polymer membrane can continuously accommodate additional water molecules upon hydration stress. The present nanoscale kinetics results provide insights into the vapor-versus-liquid sorption mechanisms, the nanostructure of Nafion, and the role of polymer reorganization modes, highlighting that the membrane can never reach a steady state.

Inside the structure of a nanocomposite electrolyte membrane: how hybrid particles get along with the polymer matrix.

Hybrid materials remain the target for a fruitful range of investigations, especially for energy devices. A number of hybrid electrolyte membranes consisting of inorganic and organic phases were then synthesized. Mechanical, solvent uptake and ionic transport properties were studied with the key point being the characteristic length scale of the interaction between the phases. A group of nanocomposite membranes made of polystyrenesulfonic acid-grafted silica particles embedded in a Poly(Vinylidene Fluoride-co-HexaFluoroPropene) (PVdF-HFP) matrix was studied by combining neutron and X-ray scatterings on the nanometer to angstrom scale. This approach allows for the variation in the morphology and structure as a function of particle loading to be described. These studies showed that the particles aggregate with increasing particle loading and these aggregates swell, creating a physical interaction with the polymer matrix. Particle loadings lower than 30 wt% induce a slight strain between both of the subphases, namely the polymer matrix and the particles. This strain is decreased with particle loading between 20 and 30 wt% conjointly with the beginning of proton conduction. Then the percolation of the aggregates is the beginning of a significant increase of the conduction without any strain. This new insight can give information on the variation in other important intrinsic properties.

Three-dimensional analysis of Nafion layers in fuel cell electrodes.

Proton exchange membrane fuel cell is one of the most promising zero-emission power sources for automotive or stationary applications. However, their cost and lifetime remain the two major key issues for a widespread commercialization. Consequently, much attention has been devoted to optimizing the membrane/electrode assembly that constitute the fuel cell core. The electrodes consist of carbon black supporting Pt nanoparticles and Nafion as the ionomer binder. Although the ionomer plays a crucial role as ionic conductor through the electrode, little is known about its distribution inside the electrode. Here we report the three-dimensional morphology of the Nafion thin layer surrounding the carbon particles, which is imaged using electron tomography. The analyses reveal that doubling the amount of Nafion in the electrode leads to a twofold increase in its degree of coverage of the carbon, while the thickness of the layer, around 7 nm, is unchanged.

Poly(p-phenylene sulfone)s with high ion exchange capacity: ionomers with unique microstructural and transport features.

Poly(phenylene) ionomers which contain merely sulfone units (-SO(2)-) connecting the phenyl rings and in which each phenyl ring is sulfonated (-SO(3)H) have been characterized with respect to their microstructural and transport properties. The high degree of sulfonation leads to the development of a microstructure characterized by very narrow hydrated, hydrophilic domains which are well connected on longer scales. These features together with high absolute water uptakes at given relative humidities and the high charge carrier concentration corresponding to the high ion exchange capacity (IEC approximately 4.5 milli equivalent g(-1)) result in very high proton conductivities but also low water transport coefficients (water diffusion and presumably also electroosmotic drag and permeation). Compared to the transport properties of Nafion, these trends increase with increasing water content and with increasing temperature. For a relative humidity of RH = 30% and a temperature of T = 135 degrees C, the proton conductivity is found to be seven times higher than the conductivity of Nafion under the same conditions. Highly sulfonated poly(p-phenylene sulfone) polymers are water soluble and brittle in the dry state, but their transport properties together with their high hydrolytical and morphological stability renders this type of ionomer an interesting constituent of polymer electrolyte membrane (PEM) fuel cell membranes able to operate at high temperature and low humidification.

Characterization of porous structure through the dynamical properties of ions confined in sulfonated polyimide ionomers films.

The structure of sulfonated PolyImide (sPI) ionomer membrane has been investigated via the transport properties of ions confined inside. Transport coefficients of N(CH(3))(4)(+) and Na(+) ions have been determined by several techniques in order to get a range of time/space scale as wide as possible: a method using radiotracers, conductivity, pulsed field gradient NMR and NMR quadrupolar relaxation rates determination. For N(CH(3))(4)(+), the self-diffusion has been measured in the direction of membrane plan (parallel) and in the perpendicular direction (transverse), whereas for Na(+) only transverse self-diffusion has been measured. The conductivity of both ions has been measured in the transverse direction. The results show a anisotropic and multiscale structure with a separation phase between hydrophilic and hydrophobic domains that is not well-defined.

[Pulmonary regulation of fibrinogen levels in acquired heart defects with pulmonary hypertension]. / Reguliatsiia legkimi kontsentratsii fibrinogena pri priobretennykh porokakh serdtsa s legochnoi gipertoniei.

Fibrinogen levels and aortic and pulmonary-artery blood pressure were measured in 143 patients with acquired heart diseases and pulmonary hypertension and in 60 control patients. The lungs were shown to participate in the regulation of fibrinogen levels both in the controls and patients with heart diseases, as reflected in the deposition-balance-mobilization phases by positive, zero, negative arterio-venous difference of fibrinogen levels. The association between the metabolic and hemodynamic functions of the lungs is particularly obvious, if pressure gradients (pulmonary-capillary and bronchial perfusion ones), making for blood inflow into the alveolar-capillary region, are examined.

[Some aspects of the management of patients with epilepsy in pregnancy]. / Zu einigen Aspekten der Betreuung von Epilepsiepatientinnen während der Schwangerschaft.

The care of pregnant epileptics calls for a high measure of personal attention and material expenditure. Above all, it means close cooperation between the epileptic specialist, the obstetrician, and the clinical pharmacologist. The need for this collaboration, and its effectiveness, are demonstrated by means of practical examples, with special consideration of blood level.

[Role of tests of the total pressure of gases (O2 and CO2) in blood plasma in studying gaseous homeostasis in man]. / Rol' testov po summarnomu davleniiu gazov (O2 i CO2) v plazme krovi pri izuchenii gazovogo gomeostaza u cheloveka.

Sixty essentially healthy subjects were examined manometrically with blood withdrawn from the coronary sinus, pulmonary artery, aorta, veins of the right kidney and the right liver lobe. Together with the traditional parameters of the gas contents and gradients of plasma, it is proposed to use tests measuring additive O2 and CO2 parameters. It has been demonstrated that the above organs can be discriminated using tests that are additive with respect to the gas pressure. It is emphasized that the tests proposed here, when used in addition to the traditional ones, allow identification of the gas and non-gas parameters of homeostasis as a single system of tests to assess the human body function.

Daily glucose and insulin rhythms in diabetic dogs on the artificial beta cell.

The circadian periods of plasma glucose, insulin and alpha-amino nitrogen (alpha-AN) were studied in fed and fasting normal and diabetic dogs which were fed either beef or beef supplemented with carbohydrates (CH). The diabetics were either withdrawn from insulin supply or treated with an artificial beta cell (ABC) or infused a constant insulin dose (CI).--There was a significant daily glucose rhythm in normal fasting animals and in fasting diabetics on CI or on insulin withdrawal. In the fed controls, the phase of the rhythms depends on carbohydrate content of food. In CH-free fed controls the insulin maxima were related to alpha-AN but in CH-fed controls they were related to glycemia. Due to the mechanism of ABC-provided insulin dosage, the phases of glucose and of insulin oscillations were correlated in all diabetics on ABC. Thus even if the mean glucose level is normalized by ABC the intrinsic phase relations remain altered.--It is concluded that the daily glucose periodicity is based on endogenous rhythms in glucose production and utilization and is essentially independent of current insulin provision. But it is governed by the meals as main "Zeitgebers" and modified by the actual insulin supply.

[Effect of hydrocortisone on some indices of cardiac activity and of the greater circulation in acquired heart defects]. / Vliianie gidrokortizona na nekotorye pokazateli serdechnoi deiatel'nosti i krovoobrashcheniia bol'shogo kruga u bol'nykh priobretennymi porokami serdtsa

The catheterization technique was used to study the effect of 100 mg of water soluble hydrocortisone "Russel" upon the cardiac activity and greater circulation in patients with acquired heart diseases. Hydrocortisone was found to produce different effects upon the cardiac output and tonicity of the greater circulation vessels--increases or decreases them, or does not change at all. The varying dynamics of these indices serves as a manifestation of the optimizing effect of hydrocortisone on the cardiovascular system, depends on the initial values of the parameters in question, and is directed towards normalizing the oxygen consumption in the body (its blood flow). No direct correlation was found between the cardiac output and the pressure in the ventricles in patients with acquired heart diseases prior to and following hydrocortisone administration.

[The relationship between the state of the pulmonary circulation and indices of cerebral gas exchange in patients with acquired heart defects]. / Pokazateli gazoobmena mozga u bol'nykh s priobretennymi porokami serdtsa v sviazi s sostoianiem legochnoi gemi

The author studied the state of hemeostasis in normals and in patients with acquired heart insufficiency. By means of bloody methods of triple probe samples of the blood inflow and outflow from the brain, and by biochemical methods they also studied 22 normals and 100 patients with acquired heart insufficiency for interrelations between the gas metabolism indices and acid-base equilibrium of the central pulmonary hemodynamics. As a results it was established that the brain blood flux in patients with acquired heart insufficiency in different degrees of pulmonary hypertension is adequate to the metabolic requirement of the brain in oxygen and corresponds to identical indices in normals. There was no relation between the state of pulmonary circulation and brain circulation.