Swelling of alkylammonium, montmorillonites

Adsorption on a series of primary n-alkylammonium bentonites was studied by simultaneous gravimetric determination of the adsorption isotherm and X-ray diffraction measurement of the c-spacing. All adsorbates gave typical Type II isotherms. BET plots were linear in the region P/P[subscript o] = 0.10 - 0.35 and v[subscript m] values were calculated. X-ray diffraction of the dry clay showed that the amine chains lay flat on the clay surface in two layers. Polar adsorbates, such as water, and nonpolar adsorbates, as n-heptane, did not cause any change in the c-spacing. However alcohols, adsorbates with both polar and nonpolar characteristics, caused a separation of the clay platelets to a distance corresponding to the calculated length of the amine ion, indicating that alcohol adsorption caused a rearrangement of the amine ions from their original prone position to an extended upright orientation. It was postulated that two adsorption processes were involved in the expansion, adsorption of the polar portion of the alcohol molecule on the oxygen surface of the clay platelet, possibly by hydrogen bond formation, and van der Waals bonding between the nonpolar part of the alcohol molecule and the amine chain. Adsorption of several other polar organic compounds was also satisfactorily explained. The effects of adsorbing polar and nonpolar compounds together was investigated and it was found that this also caused an expansion of the clay platelets

Polymer Nanostructures by Forced Assembly: Process, Structure,

Summary: The process of micro-and nanolayer coextrusion of polymeric systems with good layer uniformity is described. Coextrusion through a series of layer multiplying die elements has enabled the production of films containing tens to thousands of layers with individual layer thicknesses from the micro-to the nanoscale. Improvements in layer uniformity are discussed through optimization of layer multiplier die design, selection of viscosity matched polymer systems, and incorporation of surface layer capabilities. Design of 'uneven' split layer multiplication dies has enabled the coextrusion of layered films with a wide variety of layer thickness distributions having up to a 10Â difference in the individual film layer thicknesses. Coextrusion of layered polymer films with individual layer thicknesses down to the nanoscale has resulted in the production of novel systems with improved properties. Nanolayered polymer films were utilized to develop an all-plastic polymer laser, to fabricate gradient refractive index lenses, and to investigate gas barrier enhancement of crystalline polymer nanolayers confined to induce a high aspect ratio, in-plane, single-crystal-like lamellar structure

Die verkehrte Zeit/ bey Der Tugend Lobs-würdigen Jungfer Annen Sophien Hiltnerin/ Hn. Christian Hiltners/ Fürstlichen Sächsischen wohlbestalten Hof- und Kunstgärtners allhier zu Weimar/ und Fr. Magdalenen Sophien Hiltnerin/ ältesten wohlgearteten Jungfer Tochter/ welche den 4. Maji des 1700ten Jahrs bey Volckreicher Versammlung zu ihrem Ruhe-Cämmerlein gebracht wurde

DIE VERKEHRTE ZEIT/ BEY DER TUGEND LOBS-WÜRDIGEN JUNGFER ANNEN SOPHIEN HILTNERIN/ HN. CHRISTIAN HILTNERS/ FÜRSTLICHEN SÄCHSISCHEN WOHLBESTALTEN HOF- UND KUNSTGÄRTNERS ALLHIER ZU WEIMAR/ UND FR. MAGDALENEN SOPHIEN HILTNERIN/ ÄLTESTEN WOHLGEARTETEN JUNGFER TOCHTER/ WELCHE DEN 4. MAJI DES 1700TEN JAHRS BEY VOLCKREICHER VERSAMMLUNG ZU IHREM RUHE-CÄMMERLEIN GEBRACHT WURDE Die verkehrte Zeit/ bey Der Tugend Lobs-würdigen Jungfer Annen Sophien Hiltnerin/ Hn. Christian Hiltners/ Fürstlichen Sächsischen wohlbestalten Hof- und Kunstgärtners allhier zu Weimar/ und Fr. Magdalenen Sophien Hiltnerin/ ältesten wohlgearteten Jungfer Tochter/ welche den 4. Maji des 1700ten Jahrs bey Volckreicher Versammlung zu ihrem Ruhe-Cämmerlein gebracht wurde ([1]) Titelseite ([1]) Text ([1]

Predicting long-term creep failure of bimodal polyethylene pipe from short-term fatigue tests

Abstract Short-term fatigue testing was used to predict long-term creep failure of a bimodal polyethylene (BMPE) pipe with superior creep resistance. The stepwise crack propagation was studied by increasing the R-ratio (defined as the ratio of the minimum to the maximum stress intensity factor in the fatigue loading cycle) at 50°C from 0.1 approaching creep (R = 1). Crack growth rate (da/dt) was related to the maximum stress intensity factor K I,max and R-ratio by a power law relationship The correlation in crack growth kinetics allowed for extrapolation to creep fracture from short-term fatigue testing. The temperature dependence of crack growth rate was contained in the prefactor B 0 . A change in slope of the Arrhenius plot of B 0 at 67°C indicated that at least two mechanisms contributed to crack propagation, each dominating in a different temperature region. This implied that a simple extrapolation to ambient temperature creep fracture from elevated temperature tests might not be reliable

Melt crystallization of syndiotactic polypropylene in nanolayer confinement impacting structure

a b s t r a c t Layer multiplying coextrusion technique was used to fabricate films with hundreds of alternating layers of a crystallizable polymer, syndiotactic polypropylene (sPP), and an amorphous polymer, polycarbonate (PC). Atomic force microscopy and wide-angle X-ray scattering revealed the absence of any oriented crystal morphology of sPP in the extruded layered films. An approach of isothermal melt recrystallization of sPP nanolayers revealed the formation of oriented lamellae under the rigid confinement of hard glassy PC layers. X-ray scattering data showed that sPP crystallized as stacks of single crystal lamellae oriented parallel to the layers at high crystallization temperatures. As the crystallization temperature decreased, on-edge lamellar orientation was preferred. Formation of in-plane lamellae was attributed to heterogeneous bulk nucleation, while nucleation of on-edge lamellae was initiated at substrate interface. It was observed that as the layers thickness reduced, the orientations of both in-plane and on-edge lamellae became sharper. Detailed analysis of crystal orientations in 30 and 120 nm sPP layers was carried out. Melt recrystallization of 30 nm layers revealed formation of in-plane lamellae above 90 C and mainly on-edge lamellae below 70 C. At intermediate temperatures, formation of mixed crystals was reported. In 120 nm layers, crystallization temperature of 100 C was required to form in-plane crystals, while onedge lamellae were formed below 90 C. We also investigated crystallization onset for on-edge and in-plane lamellar nucleation. Although, the two crystal fractions were significantly affected as a function of crystallization temperature, it was noticeable that both crystal habits were initiated at the same time. The results suggested that the relative growth rates of in-plane and on-edge crystal orientations was responsible for different fractions of the two crystal orientations at a given crystallization temperature. Oxygen transport properties of melt recrystallized sPP layers were measured. When the melt recrystallization temperature increased from 85 to 105 C in 120 nm sPP layers, at least one order of magnitude enhancement in the barrier properties was observed. It was evident from the X-ray data that the amount of in-plane crystal fraction increased with increasing crystallization temperature. In-plane crystals acted as impermeable platelets to oxygen flux resulting in improved gas barrier properties. A similar effect was observed in 30 nm sPP layers over a temperature range of 60e105 C. A correlation between in-plane crystal fraction and the oxygen permeability was obtained from X-ray and oxygen transport data analysis. It was shown that the permeability decreased exponentially with increasing inplane crystal fraction

Complement-mediated leukocyte adhesion on poly(etherurethane ureas) under shear stress in vitro

Blood-contacting biomaterials may activate the complement cascade, thus promoting leukocyte adhesion to the biomaterial surface. We hypothesize that the extent of complement activation is modulated by biomaterial formulation and the presence of fluid shear stress. To investigate this hypothesis, we tested base poly(etherurethane ureas) formulated with or without Santowhite® antioxidant, a nucleophilic additive. We found that adherent leukocyte densities decreased with increasing shear stress. Moreover, leukocyte adhesion was decreased significantly further by Santowhite® additive under shear stress but not under static conditions. Monocytes showed a higher propensity for adhesion than did neutrophils under shear and static conditions. Under static conditions, adherent cells on the Santowhite®- containing polyurethane had a slightly more activated morphology than those on the base polyurethane. Cell adhesion under shear stress was significantly decreased when C3 or fibronectin was depleted from the suspension medium. Santowhite® additive increased Factor B adsorption to the test surface while shear stress increased Factor H adsorption. The combination of Santowhite® additive and shear stress increased the adsorption of both Factor B and Factor H and the serum protein S-terminal complement complex levels, but it did not further increase the state of activation of adherent cells. We conclude that leukocyte adhesion on poly(etherurethane urea) surfaces is sensitive to the levels of shear stress and that both C3 and fibronectin are required to maintain adhesion in the presence of shear stress. The low state of cellular activation and increased Factor H adsorption may explain the decreased adherent leukocyte density on the Santowhite®-containing polyurethane. | It has been observed that the extent of complement activation resulting from blood contacting biomaterials may be modulated by biomaterial formulation and the presence of fluid shear stress. This hypothesis is investigated by testing base poly(etherurethane ureas) formulated with or without Santowhite antioxidant, a nucleophilic additive. Adherent leukocyte densities were found to decrease with increasing shear stress, while leukocyte adhesion was further decreased by Santowhite additive under shear stress but not under static conditions. Adherent cells on the Santowhite containing polyurethane had a slightly more activated morphology than those on the base polyurethane under static conditions.Link_to_subscribed_fulltex

Structure and transport properties of polyethylene terephthalate and poly(vinylidene fluoride-co-tetrafluoroethylene) multilayer films

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