Search results for "Concentration"
showing 10 items of 1906 documents
CO2 as a C1-organic building block: Electrocarboxylation of aromatic ketones. A quantitative study of the effect of the concentration of substrate an…
2006
The purpose of this work is to establish and discuss quantitative relationships between the selectivity in preparative scale electrolysis and intrinsic and operational parameters for the electrocarboxylation of aromatic ketones. For the investigated ketones, under appopriate experimental conditions the selectivity of the process is mainly determined by the competition between carboxylation and protonation, de-halogenation reactions (when an halogenated ketone is involved), and possibly dimerizations involving the electrogenerated radical anion. A simple model was proposed to account for these unwanted side paths which allows to predict the dependence of the selectivity as a function of the …
Behaviour of modified and unmodified polybutadienes in the semidilute regime
1997
Abstract The association behaviour of polybutadiene modified with 4-phenyl-l,2,4-triazoline-3,5-dione was studied in semidilute solution through static (SLS) and dynamic light scattering (DLS). The results were compared with the unmodified polybutadiene, whose behavior in semidilute solution was also studied as function of the molecular weight. At higher concentrations a small-angle excess scattering in SLS and a slow mode motion in DLS were observed both for modified and unmodified polybutadienes suggesting the presence of large clusters. Increasing the polymer concentration, the mass fraction of the slow motion increases up to values near 1, indicating a proximity to the gel point. For po…
Maleic diamide polymerizable surfactants. Applications in emulsion polymerization
2003
Abstract A series of new polymerizable non-ionic and ionic surfactants (surfmers) with amides groups on both sides of the C=C double bonds have been prepared upon reaction of maleic isoimide carrying a long alkyl chain (or a benzyl group) with a hydrophilic amine derivative. Their critical micellar concentration (CMC) was measured with a surface tensiometer. They have been engaged in batch emulsion polymerization of styrene, and semi-batch seeded copolymerization of styrene and butyl acrylate, giving stable latexes during the polymerization process, and upon extraction with ethanol, showing a high rate of incorporation at the particle surface. However these surfmers do not confer good steri…
Counterion transport numbers of poly(acrylic acid)-grafted porous ion-exchange membranes as determined from current step measurements
1997
Abstract The effect of an electric current on the concentration polarization of the external bathing solutions and the permselectivity of poly(acrylic acid)-grafted porous ion-exchange membranes has been studied. The experimental approach is based on the transient behavior of the total electric potential drop through the membrane cell when a current step is imposed from external nonpolarizable electrodes. When this voltage drop is recorded as a function of time, a transition time characteristic of each membrane system is obtained. From this time, the counterion transport number for the salt solution (KClH2O) in the membrane can be obtained. The theoretical modeling is based on the time-dep…
Calcium effect on enhanced biological phosphorus removal.
2006
The role of calcium (Ca) in enhanced biological phosphorus removal and its possible implications on the metabolic pathway have been studied. The experience has been carried out in an SBR under anaerobic–aerobic conditions for biological phosphorus removal during 8 months. The variations of influent Ca concentration showed a clear influence on the EBPR process, detecting significant changes in YPO4. These YPO4 variations were not due to influent P/COD ratio, pH, denitrification and calcium phosphate formation. The YPO4 has been found to be highly dependent on the Ca concentration, increasing as Ca concentration decreases. The results suggest that high Ca concentrations produce “inert” granul…
The effect of pH on polymorph formation of the pharmaceutically active compound tianeptine.
2012
The anti-depressant pharmaceutical tianeptine has been investigated to determine the dynamics of polymorph formation under various pH conditions. By varying the pH two crystalline polymorphs were isolated. The molecular and crystal structures have been determined to identify the two polymorphs. One polymorph is an amino carboxylic acid and the other polymorph is a zwitterion. In the solid state the tianeptine moieties are bonded through hydrogen bonds. The zwitterion was found to be less stable and transformed to the acid form. During this investigation an amorphous form was identified.
Competing salt effects on phase behavior of protein solutions: tailoring of protein interaction by the binding of multivalent ions and charge screeni…
2014
The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher multivalent ion concentrations. This effect is found to be reflected in the protein interactions, as accessed via small-angle X-ray scattering. Two simulation schemes (a Monte Carlo sampling of the counterion binding configurations using the detailed protein structure and an analytical coarse-grain…
Synthesis, properties and processability of a new class of semirigid liquid crystalline copolyesteramides
1995
Abstract A new family of semirigid main chain liquid crystalline polymers (LCPs), referred to as SBAN, characterized by fairly good processability and mechanical properties, and improved thermal resistance, have been synthesized by the melt polycondensation of sebacic acid (S), 4,4′-dihyhxybiphenyl (B), 4-aminobenzoic acid (A), and 2-hydroxy-6-naphthoic acid (N), in a wide range of compositions. The molar concentration of the A ahd N units, in these LCPs must be kept lower than ca 40 and 60%, respectively, in order to avoid the formation of homopolymeric blocks, which impair spinnability. The presence of A units grants the formation of hydrogen bonds between neighboring macromolecules, and …
Dependence of Coefficient of volumetric thermal expansion (CVTE) of glass fiber reinforced (GFR) polymers on the glass fiber content
2007
In a Glass Fiber Reinforced (GFR) polymer, the coefficient of volumetric thermal expansion CVTE (determined as a sum of the coefficients of linear thermal expansion CLTE’s for the three principal directions) is sometimes much smaller than the value predictable on the basis of well acquainted models, such as Chow model, taking into account fibers anisotropy and aspect ratio.
Effect of random copolymer additives on the interfacial tension between incompatible polymers
1998
Interfacial tensions γ were measured for mixtures of poly(methylphenylsiloxane) (4 kg/mol) and poly(dimethylsiloxane) (24 kg/mol) in the absence and in the presence of small amounts of the random copolymer poly(dimethylsiloxane-ran-methylphenylsiloxane) (89 mol-% of dimethylsiloxane units, 28 kg/mol) from 25 to 110°C. Approximately 1 wt.-% of the copolymer additive suffices to reduce γ from ca. 2.2 to 1.6 mN/m. The time dependence of the apparent γ value in the course of the attainment of equilibria also indicates surface acivity. The hypothesis is formulated that the efficiency of the random copolymer for a reduction of γ is bound to the condition that it is only sparingly soluble in both …