Search results for "solu"

Tailoring Properties of Carbon Nanotube Dispersions and Nanocomposites Using Temperature-Responsive Copolymers of Pyrene-Modified Poly(N-cyclopropyla…

2010

Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Stimuli-responsive polymers show conformational changes with an applied external stimulus (pH, temperature, light, etc.). The dispersion of carbon nanotubes by thermoresponsive polymers is shown to enable the macroscopic properties of aqueous suspensions to be tailored as a function of temperature. This work presents the synthesis, characterization, and use of temperature-responsive poly(N-cyclopropylacrylamide) (PNCPA) polymers containing 1, 3, and 5 mol % pyrene-bearing repeat units to tailor the dispersion state of single-walled carbon n…

Bitterness and astringency of flavan-3-ol monomers, dimers and trimers

1999

Intensity of astringency and bitterness of seven flavonoid compounds was evaluated by a time-intensity (TI) procedure. Eighteen trained judges rated intensity continuously from ingestion, through expectoration at 10 s until extinction of the sensation. The seven stimuli included two flavan-3-ol monomers, (+)-catechin and (−)-epicatechin, three dimers and two trimers synthesised from catechin or epicatechin by condensation with (+)-dihydroquercitin. As the degree of polymerisation increased, maximum bitterness intensity (Imax) and total duration (Ttot) decreased whereas astringency Imax increased. The monomers were significantly higher in bitterness at Imax than the dimers, which were signif…

Uptake and retention of calcium, iron, and zinc from raw legumes and the effect of cooking on lentils in Caco-2 cells

2006

Abstract This study examined calcium, iron, and zinc uptake in Caco-2 cells (retention plus transport) from white beans, chickpeas, and lentils subjected to prior in vitro gastrointestinal digestion and the effect of cooking (traditional and industrial—ready to eat) on the uptake of these minerals from lentils. The highest cell uptake of calcium, iron, and zinc corresponded to raw chickpeas, which had the lowest soluble oxalate content and intermediate phenolic and tannin contents. From these results, raw chickpeas would be the best dietary source of calcium, iron, and zinc, although consumption in this form (ie, raw) is low. Cooking affects the calcium, iron, and zinc contents of lentils a…

Barrier, structural and mechanical properties of bovine gelatin-chitosan blend films related to biopolymer interactions

2014

BACKGROUND The increased use of synthetic packaging films has led to a high ecological problem due to their total non-biodegradability. Thus, there is a vital need to develop renewable and environmentally friendly bio-based polymeric materials. Films and coatings made from polysaccharide polymers, particularly chitosans and gelatins have good gas barrier properties and are envisaged more and more for applications in the biomedical and food fields, as well as for packaging. In this study a casting method was used to develop an edible plasticised film from chitosan and gelatin. Aiming to develop a blend film with enhanced properties, the effects of mixing chitosan (CS) and gelatin (G) in diff…

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

2000

The kinetics of the anionic polymerization of methyl methacrylate in presence of N,N,N', -tetramethylethylenediamine (TMEDA) in THF are investigated using 1,1-diphenyl-hexyllithium as initiator in a temperature range between -20°C and 0°C in a flow-tube reactor. The rate constants of propagation determined in the presence of TMEDA are compared to those obtained in the absence of a chelating agent. For propagation, the reaction order with respect to active centers is found to be 0.5 in both cases which indicates that the chelation of the lithium cation does not effectively perturb the aggregation of the enolate ion pair. Both the rate constants of propagation via non-aggregated ion pairs, k …

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.

The Efficiency of Polymer Fractionation at Lower Critical Solution Temperatures

1978

The efficiency of a single fractionation step (i.e. of the partition of a given polymer sample between the coexisting phases which form when its solution demixes) is governed by the variation of the mass ratio of the individual P-mers with chain length. These dependences have been measured for the system dimethoxymethane/diethylether/ polystyrene which exhibits lower critical solution temperatures by means of the Baker-Williams method and by means of g.p.c. Their comparison with the results of previous investigation on systems showing upper critical solution temperatures reveals no thermodynamic differences in the aptitude of upper and lower critical solution temperatures for fractionation …

Cylindrical polyelectrolyte-comb-surfactant complexes

2006

Abstract Quaternized polymer combs based on poly(2-vinylpyridine-macromonomers) and the surfactant sodium dodecylsulfate are employed in the synthesis of a novel cylindrical polyelectrolyte-comb-surfactant complex (PECSC). The complex formed has 1:1 stoichiometry with respect to the ratio of dodecylsulfate to pyridinium units. It is soluble in organic solvents such as 2-butanol or chloroform. Characterization of single particle properties of the complex in organic solution is possible and yields a radius of gyration of 〈Rg〉z = 78.4 nm, a hydrodynamic radius of 〈1/Rh〉z−1 = 51.4 nm and a cross-sectional radius of Rg,cross = 3.9 nm in chloroform. The characteristic ratio γ = 〈Rg〉z/〈1/Rh〉z−1 de…

1984

Influence de la structure de chaine sur le type de phase et relation entre la masse moleculaire et les temperatures de transition

Phases and phase transitions of (NaCl)1?x(NaCN)x

1985

(NaCl)1−x(NaCN)x mixed crystals with CN-concentrationsx of 0.87, 0.76, 0.71 and 0.65 have been investigated by X-ray powder diffraction. Apart from the cubic room temperature phase, a rhombohedral and an orthorhombic phase have been identified. In addition a glass state has been observed which is characterized by a strong broadening of the cubic powder lines. The phase diagram shows a wide coexistence gap between the non-cubic phases and the glass state.