Search results for "Concentration"
showing 10 items of 1906 documents
Experimental studies of the rheological behavior of a demixing biopolymeric sol
1995
Experimental data are presented concerning a large transient viscosity surge occurring in the course of spinodal demixing of agarose aqueous solutions. The study includes the effects of water perturbation by minor proportions of compatible cosolutes. Three observations are noteworthy. One concerns an upward or downward shift of the spinodal temperature, caused by cosolutes, which agrees with their expected modulation of solvent-induced forces. The second concerns the time of appearance of the viscosity surge. This is observed to follow a critical law, with an exponent independent of polymer concentration and solvent perturbation. The third concerns the inverse-power-law dependence of the vi…
1991
The polysoaps [CH 2 C(Me)(CO 2 R)] n (R=(CH 2 ) 11 N + Me 2 (CH 2 ) 3 SO 3 − , (CH 2 ) 11 N + Me 2 CH 2 CH 2 OH) are studied. Their aqueous solution properties are strongly influenced by added salts; the surface activity can be modified efficiently by an appropriate choice of ions. The interactions of salts and polyzwitterions observed in solution can be extended to the behaviour in bulk. It enables the preparation of uniform, non crystalline blends containing up to equivalent amounts of inorganic salt and polyzwitterions
Molecular surfaces: An advantageous starting point for the description of composition-dependent viscosities applied to polymer solutions
1999
The viscosity of polymer/solvent systems is modeled as a function of composition under the premises that the dissipation of energy is taking place at the molecular interfaces and that the friction between solvent and solute varies with composition due to a change in the flow mechanism (drainage of coils). The simple expression obtained in this manner contains three system-specific parameters: a geometric factor γ, which accounts for the differences of the surface to volume ratios of the components; a hydrodynamic parameter α, which measures the friction between solute and solvent in the case of fully draining polymer coils; and β, which corrects for changes in the friction between unlike mo…
On the biochemical classification of yeast trehalases: Candida albicans contains two enzymes with mixed features of neutral and acid trehalase activi…
2009
Abstract Two enzymes endowed with trehalase activity are present in Candida albicans . The cytosolic trehalase (Ntc1p), displayed high activity in exponential phase regardless of the carbon source (glucose, trehalose or glycerol). Ntc1p activity was similar in neutral (pH 7.1) or acid (pH 4.5) conditions, strongly inhibited by ATP, weakly stimulated by divalent cations (Ca 2+ or Mn 2+ ) and unaffected in the presence of cyclic AMP. The Ntc1p activity decreased in stationary phase, except in glycerol-grown cultures, but the catalytic properties did not change. In turn, the cell wall-linked trehalase (Atc1p) showed elevated activity in resting cells or in cultures growing on trehalose or glyc…
Die zweifache unterdrückung der polymerisation einiger bis(methacrylsäureester) mittels radikalischer additionsreaktionen
1973
Aus Hydrochinon, Resorcin, Dihydroxydiphenylen und Dihydroxynaphthalinen wurden mit Methacrylsaurechlorid Bis(methacrylsaureester) hergestellt. Setzte man diese in siedendem Benzol mit groser Verdunnung gelosten Ester dem Angriff von Radikalen aus α.α′-Azoisobuttersauredinitril (Primarradikale) aus, dessen Uberschus in Beziehung zum Ester mindestens zwanzigfach molar war, so erhielt man mittels saulenchromatographischer Trennung Verbindungen, bei denen je olefinische Doppelbindung zwei Primarradikale addiert waren (unterdruckte Polymerisation). Die Struktur dieser Produkte wurde mittels Elementaranalyse, Molekulargewichtsbestimmung, IR- und 1H-NMR-Spektren bewiesen. Demnach kann die Polymer…
Studien zum Vorgang der Wasserstoffübertragung, 47.Elektroreduktion von 1,4-Benzoldicarbonitril, 1,4-Diacetylbenzol und Terephthalaldehyd
1978
Die Elektroreduktion von 1,4-Benzoldicarbonitril in Gegenwart von Essigsaure fuhrt bei einem Stromdurchgang von 4.5 Faraday-aquivalenten/mol in 80proz. Ausbeute zu 4-Amino-methylbenzonitril (1). Bei Anwendung von 6 Faraday-aquivalenten/mol konnen geringe Mengen an 4-Methylbenzonitril (2) nachgewiesen werden. Bei der praparativen Elektroreduktion von 1,4-Diacetylbenzol in Gegenwart unterschiedlicher Mengen an Essigsaure entstehen 4-(1-Hydroxyethyl)acetophenon (3), 1,1′-(1,4-Phenylen)diethanol (4) sowie polymere Pinakole 5 in den in Tabelle 1 angegebenen Mengen. Terephthalaldehyd wird in Gegenwart von Essigsaure zu 4-Hydroxymethylbenzaldehyd (6), Terephthalalkohol (7) und einem polymeren Pina…
Determination of fluoride after direct separation from acid medium by collection of its volatile compounds
1989
A method is proposed for determination of fluoride by separation in acid medium followed by ion-selective electrode measurement. The separation is done at temperatures up to 200 °C, without any previous treatment of the sample, in a PTFE reactor designed to ensure the complete absorption of volatile fluoride compounds. The distillation variables (temperature, time and acid concentration) have been optimized and the interference of other various species in the separation step has been studied. The method has been applied to geological samples. The results obtained are statistically satisfactory.
Der acidolytische abbau von polyoxymethylenen. 18. Mitt. über polyoxymethylene
1962
Beim acidolytischen Abbau von Polyoxymethylendihydraten wurden gaschromatographisch folgende Substanzen identifiziert: Formaldehyd, Wasser, Methanol, Ameisensauremethylester sowie Tri- und Tetraoxymethylen. Die Ausbeute an cyclischen Oligomeren und das Verhaltnis Trioxan/Tetraoxymethylen hangen von der Saure, der Saurekonzentration und der Reaktionszeit ab. Es wird ein Abbaumechanismus vorgeschlagen und diskutiert. In the acidic degradation of polyoxymethylenes the following substances are obtained and identified by gas chromatography: formaldehyde, water, methanol, methyl formate, and also tri- and tetraoxymethylene. The yields of the cyclic oligomers and the ratio trioxane/tetraoxymethyle…
Effects of non-ionic micelles on transient chaos in an unstirred Belousov-Zhabotinsky reaction.
2001
The behaviour of the Ce(IV)-catalyzed Belousov-Zhabotinsky (BZ) system has been monitored at 20.0 degrees C in unstirred batch conditions in the absence and presence of different amounts of the non-ionic micelle-forming surfactants hexaethylene glycol monodecyl ether (C10E6) and hexaethylene glycol monotetradecyl ether (C14E6). The influence of the non-ionic surfactants on both the kinetics of the oxidation of malonic acid (MA) by Ce(IV) species and the behaviour of the BZ reaction in stirred batch conditions has also been studied over a wide surfactant concentration range. The experimental results have shown that, in unstirred batch conditions, at surfactant concentrations below the critic…
1976
A radical mechanism is proposed for the formation of the 1,2-polymer 2 in the “spontaneous” polymerization of 4-vinylpyridinium salts 4-VP.HX (X=NO3, ClO4, HSO4, I) in aqueous solution on the basis of strong inhibition by oxygen and other radical inhibitors. Quantitative investigation of the influence of oxygen on the formation of the 1,2-polymer allowed the derivation of a formal kinetic scheme for the initiation and polymerization steps which is consistent with a free radical mechanism. Dependence of the average molecular weight of 2 on monomer concentration is in agreement with this model. Dependence of the inhibition time on the oxygen concentration as well as an acceleration of the fin…