Search results for "ion temperature"
showing 10 items of 220 documents
Shear Effects on the Phase Diagrams of Solutions of Highly Incompatible Polymers in a Common Solvent. 1. Equilibrium Behavior and Rheological Propert…
1997
Phase diagrams (cloud points, tie lines, critical compositions) and viscosities of homogeneous solutions were determined at temperatures ranging from 20 to 100 °C for three representatives of the ternary system cyclohexanone/polystyrene/poly(n-butyl methacrylate) [CHO/PS/PBMA] in preparation of a study on shear influences. An only moderate increase of the two-phase region observed upon heating (LCST behavior) witnesses little heat effects upon mixing. Tie lines which are nearly parallel to the PS/PBMA edge of the Gibbs phase triangle indicate comparable solvent quality of CHO for both polymers. The quantitative mathematical description of the equilibrium behavior-required for a theoretical …
α,ω-Functionalized poly-N-isopropylacrylamides: controlling the surface activity for vesicle adsorption by temperature
2003
The synthesis of alpha,omega-end-functionalized copolymers of N-isopropylacrylamide and N-(3-dimethylaminopropyl)acrylamide was performed. Monomer ratios of 100:0, 96:4, and 81:19 were investigated. The lower critical solution temperature (LCST) of these polymers was determined by cloud-point measurements and by microcalorimetric measurements. The LCST increased from 32 over 37 to 47 degrees C as the hydrophobicity increased with increasing amount of comonomer N-(3-dimethylaminopropyl)acrylamide. The polymers could successfully be adsorbed onto gold surfaces. Finally, vesicle adsorption onto these self-assembled polymer films on flat gold surfaces was investigated as the vesicle solution te…
Cooperative High-Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion
2016
Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz)(Au(CN)2)2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6%) and contraction (ca. 9.6%) of the lattice. Negative thermal expansion along th…
Mechanical behaviour of Mater-Bi/wood flour composites: a statistical approach
2008
Interest in biocomposites (lignocellulosic filled biopolymers) started in the 90s, due to environmental advantages, related to the full biodegradability of both matrix and filler, economical issues (organic fillers usually come from sawmill or agriculture wastes) and aesthetical issues (wood filled biopolymers could be particularly pleasant if used for indoor furnishing and automotive interior). In this work, a method for a systematic study of the properties of Mater-Bi®/wood flour composites is presented. A two-level full factorial model was built. It allows investigating the effects of multiple operative variables on the observed properties, their contributions, their optimal combinations…
Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution
2004
Abstract The cloud-point temperatures (Tcl’s) of trans-decahydronaphthalene (TD)/polystyrene (PS, Mw=270 kg/mol) solutions were determined by light scattering measurements over a range of temperatures (1–16 °C), pressures (100–900 bar), and compositions (4.2–21.6 vol% polymer). The system phase separates upon cooling and the Tcl was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud…
The Crystalline State of Macromolecular Substances
1974
Unlike low molecular weight substances, high polymers do not crystallize completely. However long the crystallization process is continued, they still consist of a mixture of crystalline and non crystalline regions. In the undrawn material, these regions form larger units which are known as spherulites. Questions that are of special interest concern the arrangement of the chains in the noncrystalline regions, the causes of chain folding, and the imperfections in the crystals. The incomplete crystallization is a consequence of kinetic inhibitions. This can be deduced from the fact that the crystalline fraction increases with rising crystallization temperature. If polymerization is carried ou…
Infrared spectroscopic study of a phenyl benzoate side group—methacrylate main chain polymeric liquid crystal
1994
Abstract The temperature dependence of the infrared dichroism of a side chain polymeric liquid crystal was investigated for two homogeneously oriented samples, one aligned with a PVA coating and the other aligned by a magnetic field. From the apparent order parameters, it was found that the rotation of the mesogenic side group was restricted. Not only the rigid part of the side group, but also the alkyl chains were found to be partly ordered. Realignment of the side groups was observed in the case of the magnetically aligned sample at the smectic-nematic transition temperature. Unlike the other absorption bands, the C˭O bond vibration band shifted to higher wavenumbers with increasing tempe…
Temperature-Responsive Surface Coatings Based on Poly(methylsilsesquioxane)-hybrid Polymers
2007
The present paper presents a new method to build up temperature-responsive surfaces. First a poly(silsesquioxane)-block-poly(N-isopropyl-acrylamide) (PMSSQ-b-PNIPAM) was successfully synthesized using RAFT polymerization. Spin-coating or dip-coating of PMSSQ-b-PNIPAM onto glass surfaces resulted in temperature-responsive surfaces. Surface ATR FT-IR measurements proofed the successful surface modification using PMSSQ-b-PNIPAM. IR fine structures of PNIPAM and PMSSQ could be assigned, respectively. In capillary rise experiments a change of the meniscus height measured at temperatures below or above LCST was observed, indicating a different wetting behavior. Thus, a simple spin- or dip-coating…
Rheological behavior of a semirigid liquid crystal polymer
1993
The rheological behavior of liquid crystal polymers is still far from completely clarified from both experimental and theoretical points of view. In this paper, the shear flow and the non-isothermal elongation flow behavior of a semi-rigid liquid crystal copolyester is discussed. The viscosity strongly decreases when the test temperature is increased above the crystal-nematic transition temperature; below this temperature the viscosity is very high. The thermal history strongly affects the shear viscosity. The elongational flow behavior depends also on temperature. Above the crystal-nematic transition temperature and the mesophase is easily spinnable, whereas below this temperature, the spi…
Polar relaxation mode in pure and iron-doped barium titanate
1989
A dielectric relaxation peak is reported in ${\mathrm{BaTiO}}_{3}$ and in ${\mathrm{BaTi}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{O}}_{3}$. It is nearly monodispersive, centered in the ${10}^{8}$-Hz range, and slowest at the transition temperature ${T}_{c}$\ensuremath{\simeq}413 K from the cubic to the tetragonal phase. Iron doping lowers ${T}_{c}$ and slows down this relaxation mode.