Search results for "Scanning"
showing 10 items of 1808 documents
Determining the selective impregnation of waterlogged archaeological woods with poly(ethylene) glycols mixtures by differential scanning calorimetry
2012
The differential scanning calorimetry (DSC) technique was demonstrated to be a reliable and fast tool for the investigation of the selective impregnation of archaeological woods with poly(ethylene) glycols (PEGs) mixtures. To this aim, waterlogged archaeological woods were impregnated by using aqueous mixtures of PEG 4000 and PEG 400 as well as mixtures of these polymers in the melt state. The efficiency of the treatments was also estimated by determining the total consolidant content entrapped into the cavities of degraded wood by means of DSC and thermogravimetry.
Effect of the crystallization on the phase transitions IV ⇐ III and IV ⇐ II of ammonium nitrate
1993
Abstract The solid state phase transition path of ammonium nitrate is influenced by the manner of crystallization. Slow crystallization from water gives ideal crystals, which behaved differently from crystals prepared by rapid crystallization from the melt.
Phase behavior and elastic properties of a slightly crosslinked liquid crystalline main-chain polymer
1990
A liquid crystalline main-chain polymer was slightly crosslinked by a reaction withα, ω-difunctionalized oligo-siloxanes. Crosslinking does not disturb the liquid crystalline phases, which are identified by x-ray measurements as smecticB and smecticA phases. Measurements of the elastic properties of the crosslinked sample show rubber-like elasticity, even in the liquid crystalline phases. A difference of 7 K was found between cooling and heating for the smecticA/isotropic transition from DSC and mechanical measurements.
Study of the micro-phase separation in LC-polymers with paired mesogens
1990
Differential scanning calorimetry and miscibility investigations were used to study the micro-phase separation of liquid-crystalline dimesogenic side-group polysiloxanes. Diluted co-polysiloxanes exhibit two glass transition temperatures and an unusual miscibility behavior. The observed biphasic character is compared with that of certain amphiphilic systems.
A kinetic study of the formation of smectic phases in novel liquid crystal ionogens
2013
[EN] A multi-rate non-isothermal kinetic analysis of the isotropic-melt to liquid crystalline phase transition of novel liquid crystalline ionogenic copolymers, LCIs, the 10-(4-methoxyazobenzene-4'-oxy)decyl methacrylate]-co-2-(acrylamido-2-methyl-1-propanesulfonic acid)s, 10-MeOAzB/AMPS, copolymers, has been performed by means of calorimetric experiments. An analytical methodology which includes the study of the phase transition rate parameter, the determination of the activation energies by using Kissinger and Flynn-Wall-Ozawa models, and the study of the phase transition kinetics by the use of the Avrami theory, has been applied. The formation of the mesophases from the isotropic state o…
Surface plasmon near-field imaging of very thin microstructured polymer layers.
2004
We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the…
Poly(carbonate) copolymers with a tailored number of hydroxyl groups from glycidyl ethers and CO2
2014
Functional poly(carbonate)s with multiple hydroxyl functionalities have been prepared by copolymerization of carbon dioxide (CO2) with glycidyl methyl ether (GME) and benzyl glycidyl ether (BGE) in various ratios, using a diethylzinc–pyrogallol catalyst system. Subsequent catalytic hydrogenation was employed for removal of the benzyl protecting groups at the polymer backbone. A series of copolymers with varying comonomer fractions from 0 to 100% was obtained. The copolymers possessed a broad range of molecular weights from 9000 to 30 000 g mol−1 and showed polydispersities Mw/Mn between 2.4 and 3.6. The materials were characterized via1H and 13C NMR, SEC and differential scanning calorimetr…
Crystalline CO2 -Based Aliphatic Polycarbonates with Long Alkyl Chains
2018
Carbon dioxide (CO2 ) is an easily available, renewable carbon source and can be utilized as a comonomer in the catalytic ring-opening polymerization of epoxides to generate aliphatic polycarbonates. Dodecyl glycidyl ether (DDGE) is copolymerized with CO2 and propylene oxide (PO) to obtain aliphatic poly(dodecyl glycidyl ether carbonate) and poly(propylene carbonate-co-dodecyl glycidyl ether carbonate) copolymers, respectively. The polymerization proceeds at 30 °C and high CO2 pressure utilizing the established binary catalytic system (R,R)-Co(salen)Cl/[PPN]Cl. The copolymers with varying DDGE:PO ratios are characterized via NMR, FT-IR spectroscopy, and SEC, exhibiting high molecular weight…
Branched polymers starting from ethylene-vinyl acetate copolymers
1995
Abstract Polyethylene-graft-poly-2-phenyl-2-oxazoline, polyethylene-graft-poly-2-methyl-2-oxazoline and polyethylenegraft-poly(ethylene oxide) were prepared using poly(ethylene-co-vinyl chloroformate) as macroinitiator or polyfunctional precursor. The vinyl acetate groups of ethylene-vinyl acetate copolymer were hydrolyzed, the corresponding alcohol functions were converted into chloroformate, which in turn was used for grafting of oxazolines. Comb-like polymers with hydrophilic poly(ethylene oxide) grafts with definite length were synthesized as well. The resulting graft copolymers were characterized by GPC, IR, and 1 H-NMR spectroscopy and differential scanning calorimetry.
Synthesis and characterization of water-swellable?,?-polyasparthydrazide derivatives
1995
α, β-polyasparthydrazide (PAHy) was crosslinked by glutaraldehyde to form water-swellable materials possessing a three-dimensional molecular network. Different crosslinking degrees were prepared varying glutaraldehyde/PAHy ratio and samples containing 5-fluorouracil were obtained by incorporating the drug into the polymer networks during the crosslinking reaction. All samples were characterized by swelling tests, thermal, x-ray and SEM analysis. Their microstructure was observed through scanning electron microscopy. Furthermore, for samples containing the anticancer drug,in vitro release studies were performed in pH 7.4 buffer solution.