Critical solution concentration

The passivating action of an aqueous solution within porous concrete can be changed by various factors (see Section 5.3.2). The passive film can be destroyed by penetration of chloride ions to the reinforcing steel if a critical concentration of ions is reached. In damp concrete, local corrosion can occur even in the presence of the alkaline water absorbed in the porous concrete (see Section 2.3.2). The Cl content is limited to 0.4% of the cement mass in steel-concrete structures [6] and to 0.2% in prestressed concrete structures [7]. 

Physical and Chemical Properties - Physical State at 15 C and I atm. Solid Molecular Weight 169.87 Boiling Point at 1 atm. Decomposes Freezing Point 414, 212,485 Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity 4.35 at 19 °C (solid) Veqtor (Gas) Density Not pertinent Ratio of Specific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat of Combustion Not pertinent Heat of Decomposition Not pertinent. Health Hazards I ormation - Recommended Persorial Protective Equipment Goggles or face shield rubber gloves Symptoms Following Exposure Concentrated solution will produce irritation, ulceration. 

Nature of the metal surface The critical concentration of an anion required to inhibit the corrosion of iron may increase with increasing surface roughness. Thus, Brasher and Mercer" showed that the minimum concentration of benzoate required to protect a grit-blasted steel surface was about 100 times greater than that required to protect an abraded surface. However, surface preparation had little effect on the critical inhibitive concentrations for chromate" or nitrite " The time of exposure of the iron surface to air after preparation and before immersion may also affect the ease of inhibition by anions. There is evidence """ that the inhibition by anions occurs more readily as the time of pre-exposure to air increases. Similarly, if an iron specimen is immersed for some time in a protective solution of an inhibitive anion, it may then be transferred without loss of inhibition to a solution of the anion containing much less than the critical inhibitive concentration . ... 

Sodium tungstate solutions have provided data for the testing of Equation 7-6. These data, obtained in the authors laboratory, show that absorption effects can be calculated for a series of solutions in which the calculated critical thickness (Equation 6-8) decreases from 0.4 cm for water, the solvent, to only 0.1 cm for the most concentrated solution tested. In order not to confuse the issue here, the details of the cor-... 

Studies of the structure and molecular size of wheat AX [41] revealed that they are shear-thinning and exhibit two critical concentrations, which correspond to the onset of coil overlapping. The existence of three domains provided the evidence for the formerly suggested rigid, rod-Uke conformation of AX in solution. In a recent study [116], the previously reported conflicting suggestions on the conformation of AX were discussed. 

In reversible polymerization, the critical concentration is equal to the equilibrium dissociation constant for polymer formation. This parameter is therefore independent of the number of polymers in solution. Confirmation comes from smdying reversible polymerization of ADP-actin when sonic vibration is applied to a solution of F-ADP-actin filaments at equilibrium with G-ADP monomers, no change is observed in the proportion of G- and F-actin (Carlier et al., 1985). Therefore, the only effect of sonic vibration is to increase the number of filaments without affecting the rates of monomer association to and dissociation from filament ends. 

Because ATP hydrolysis on F-actin takes place with a delay following the incorporation of ATP-subunits, and because in the transient F-ATP state filaments are more stable than in the final F-ADP state, polymerization under conditions of sonication can be complete, within a time short enough for practically all subunits of the filaments to be F-ATP. At a later stage, as Pj is liberated, the F-ADP filament becomes less stable and loses ADP-subunits steadily. The G-ADP-actin liberated in solution is not immediately converted into easily polymerizable G-ATP-actin, because nucleotide exchange on G-actin is relatively slow, and is not able to polymerize by itself unless a high concentration (the critical concentration of ADP-actin) is reached. Therefore, G-ADP-actin accumulates in solution. A steady-state concentration of G-ADP-actin is established when the rate of depolymerization of ADP-actin (k [F]) is equal to the sum of the rates of disappearance of G-ADP-actin via nucleotide exchange and association to filament ends. [G-ADP]ss in this scheme is described by the following equation (Pantaloni et al., 1984) ... 

The configuration of a system in which percolation may occur is classically treated as one in which the ingredients do not move. Considerable work has been devoted to these static models, leading to numerical solutions of the critical concentrations and cluster sizes associated with a percolation threshold. 

Most pectin solutions behave like Newtonian liquids below a pectin concentration of about 1 % (w/w). Onogi (1966) derived the critical concentration of polymer solutions from plotting the double logarithmic curves of viscosity (ii) against concentration at constant shear rates. Each curve consists of two straight lines intersecting at the critical concentration. At higher... 

The measurement of the concentration dependence of the changes in surface potential was also used to find critical concentration for forming a micellar solution. Near this critical concentration, one can observe a very strong fall in A%. ... 

Studies of the adsorption of surface active electrolytes at the oil-water interface provide a convenient method for testing electrical double layer theory and for determining the state of water and ions in the neighborhood of an interface. The change in the surface amount of the large ions modifies the surface charge density. For instance, the surface ionic area of 100 per ion corresponds to 16, /rC/cm. The measurement of the concentration dependence of the changes of surface potential were also applied to find the critical concentration of formation of the micellar solution [18]. 

Simha [53] made the first attempts to model the transition from a dilute to a concentrated solution. He assumed that in the range from lscaling laws a theory has been developed which allows for the prediction of the influence of Mw c and the solvent power on the screening length [54,55]. This theory is founded on the presumption that above a critical concentration, c, the coils overlap and interpenetrate. Furthermore it is assumed that in a thermody-... 

The longest mode (p=l) should be identical to the motion of the chain. The fundamental correctness of the model for dilute solutions has been shown by Ferry [74], Ferry and co-workers [39,75] have shown that,in concentrated solutions, the formation of a polymeric network leads to a shift of the characteristic relaxation time A,0 (X0=l/ ycrit i.e. the critical shear rate where r becomes a function of y). It has been proposed that this time constant is related to the motion of the polymeric chain between two coupling points. 

Below a critical concentration, c, in a thermodynamically good solvent, r 0 can be standardised against the overlap parameter c [r)]. However, for c>c, and in the case of a 0-solvent for parameter c-[r ]>0.7, r 0 is a function of the Bueche parameter, cMw The critical concentration c is found to be Mw and solvent independent, as predicted by Graessley. In the case of semi-dilute polymer solutions the relaxation time and slope in the linear region of the flow are found to be strongly influenced by the nature of polymer-solvent interactions. Taking this into account, it is possible to predict the shear viscosity and the critical shear rate at which shear-induced degradation occurs as a function of Mw c and the solvent power. 

If the polymer concentration c is lower than c, the critical concentration of chain overlapping, one can express the viscosity q of the solution by ... 

It is now well known that the addition of Ca2+ in aqueous solutions of these copolymers induces phase separation with precipitation of a phase constituted by a polymer-Ca complex. From turbidity measurements, it is possible to define a critical concentration ca above which this phenomenon occurs(23-25). 

Under good solvent conditions the dynamics of semi-dilute solutions was investigated by NSE using a PDMS/d-benzene system at T = 343 K and various concentrations 0.02 c < 0.25. The critical concentration c as defined by (112) is 0.055. 

Fig. 17 B/E-p dependence of the critical temperatures of liquid-liquid demixing (dashed line) and the equilibrium melting temperatures of polymer crystals (solid line) for 512-mers at the critical concentrations, predicted by the mean-field lattice theory of polymer solutions. The triangles denote Tcol and the circles denote T cry both are obtained from the onset of phase transitions in the simulations of the dynamic cooling processes of a single 512-mer. The segments are drawn as a guide for the eye (Hu and Frenkel, unpublished results)...

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