Coagulation Conditions Research Articles

Low angle light scattering technique for the study of coagulation

A new low angle light scattering technique for the measurement of absolute coagulation rate constants of monodisperse spherical sols has been developed. Measurements have been made on a series of polystyrene latices under both rapid and slow coagulation conditions. The results were compared with calculated values which incorporate (i) a hydrodynamic correction due to Spielman and Honig et al., (ii) an estimate of the electrostatic repulsion between the particles based on constant potential calculations and electrophoretic measurements and (iii) an estimate of the van der Waals attraction based on the Hamaker theory. From the rapid rate measurements (accurate to within ± 13%) the value of the Hamaker constant is expected to lie within the range, 3 × 10–21 to 1.6 × 10–21 J. The slow coagulation results suggest that the van der Waals attraction is salt dependent: in 0.2 M NaCl the measured Hamaker constant is ∼4 × 10–21 J which is the value expected from the classical Hamaker theory, in 0.09 M NaCl agreement between theory and experiment requires this value to have increased to 1.1 × 10–20 J. These findings are in qualitative agreement with the recent theoretical predictions of Parsegian and Ninham which are based on the macroscopic Lifshitz theory of van der Waals interactions.

Interaction of two parallel colloidal plates in an electrolyte mixture of univalent and divalent ions

We consider the electric double layer interaction energy per unit area of two, equally charged, parallel, colloidal plates at separation 2 h in an aqueous electrolyte mixture containing univalent and divalent ions. The Gouy-Chapman model of the double layer is used and the potential ψ0 at the plates is assumed independent of plate separation. An expression is obtained for the interaction energy which is based on the assumption that the potential at the plane midway between the plates is the sum of the potentials produced by each of the plates in the absence of the other (linear super-position approximation). This provides a good approximation to the interaction energy at large separations which is proportional to exp (−2 κh) where 1/κ is the Debye-Huckel thickness of the diffuse layer. This approximation is the leading term in an expansion for the interaction energy, the second term of which is also obtained. The formulae for the general electrolyte mixture are applied to the two particular electrolytes, of valency types 1−1 + 2−2 and 1−1 + 2−1, where the first valency of each electrolyte in a mixture refers to the coagulating ion oppositely charged to the plates. Introducing the Hamaker-van der Waals interaction energy between infinitely thick plates, both the methods of zero potential barrier and of zero force are used to define the coagulation conditions in the D.L.V.O. theory of colloid stability. Plots between the coagulating concentrations of the two binary electrolytes in each mixture are obtained for values of ψ0 in the range 0–100 mV. For ψ0≲25 mV the 1−1 + 2−2 mixture shows additivity but with further increase in ψ0 this changes to sensitization. With the 1−1 +2−1 mixture, approximate additivity is obtained at ψ0≲50 mV and at higher ψ0 some superadditivity at the 2−1 end and sensitisation at the 1−1 end set in. Although the linear superposition approximation produces mutual antagonism at the 2−1 end for the higher potentials, this is completely eliminated for ψ0≲100 mV when the second term in our expansion for the energy is included.

Effect of Ionic Environment and Temperature on the Coagulation of Color‐Causing Organic Compounds With Ferric Sulfate

In an earlier paper, a direct relationship between the color of a raw water and the optimum conditions required to remove that color were shown. By the use of extensive mobility determinations correlated with jar tests, the optimum conditions for color removal from soft surface waters were found to be a function of the raw water color. The work reported here should serve to expand the usefulness of these relationships, as it elucidates the effect of ionic environment and temperature on the optimum coagulation conditions.

Coagulation Control

This article discusses a number of methods that have been developed for more precisely identifying good coagulation. The most common method of monitoring coagulation is by the use of jar tests and visual observation. The electrophoretic cell method involves measuring the charge on particles by observing their rate of movement toward electrodes. The streaming current detector can yield the same qualitative information as the electrophoretic cell. The main focus of the article is the pilot filter coagulant control system, used either to indicate coagulation conditions or to control them automatically.

Rheological behavior of some acrylic fibers dissolved and spun in the ZnCl2 system

AbstractConcentrated solutions of Acrilan 16 and 1656, Creslan 58 and 61, Orlon 42, and several experimental acrylic copolymers were prepared by dissolution of the staple fibers in 60% ZnCl2. The solutions were investigated rheologically. It was shown that a 3.5‐power relationship between the log of the Newtonian viscosity and the log of the molecular weight held for these solutions. Their elastic behavior as exhibited by the Barus effect was shown to be a function of shear stress and independent of molecular weight or composition. The ZnCl2 solutions of the acrylic fibers were spun under a harsh and a mild condition of coagulation. On physical and beinding properties of the fibers, mild coagulation has an effect similar to an increase in the content of the minor component of the copolymer. The loop properties and shrinkage of Turbo‐stretched fibers are shown to be mainly functions of their composition.

The effect of the conditions of coagulation and orientational stretching on the size of the structural elements and the physicomechanical properties of cellulose hydrate fibres

The effect of the conditions of coagulation and orientational stretching on the size of the structural elements and the physicomechanical properties of cellulose hydrate fibres

Stoichiometry of the Coagulation of Color‐Causing Organic Compounds With Ferric Sulfate

The basic objectives of this study were to gain a better understanding of the stoichiometry of the coagulation of organic color with ferric sulfate and to develop quantitative relationships that would permit the prediction and control of optimum coagulation conditions for efficient color removal. The primary objectives of this work were: to utilize the newer techniques of microelectrophoresis in a critical study of coagulation phenomena and stoichiometry as specifically applied to color removal with ferric sulfate; and, to determine whether microelectrophoresis could be applied as a practical method for determining optimum coagulation conditions in water treatment plants.

Studies on the Properties and Formation of Quick Clays

AbstractIn a natural clay, the occurrence of a high sensitivity, i.e. a high quotient between the shear strength of the undisturbed and remolded soils respectively, under undrained conditions, is connected to thixotropic effects and to “quickness”.The general composition of the soils in which quick clay occurs is described, and mention is made of the occurrence of non-argillaceous rock fragments in a matrix of clay particles. Mite is the main clay mineral. Quickness occurs both in salt-leached, marine deposited clays and in clays deposited in fresh water. The pore water of these clays is low in electrolytes and undecomposed organic material. It is found that quick clays often occur near peat and similar humic deposits. Also briefly discussed is the internal stress distribution in natural clays under various consolidation conditions, the structure of quick clays and their conditions of formation. The consistency of clays is considered, as is the stability and coagulation conditions of suspensions. This is followed by a commentary on physico-chemical effects contributing to the formation of quick clays under natural conditions, and a discussion of the salt-leaching theory and the theory on the effect of peptizing agents.In the discussion, the author draws parallels between the coagulation and the thixotropic phenomena, and between the stability and dispersion of suspensions and the quickness.

The Influence of Coagulation Variables on the Structure and Physical Properties of an Acrylic Fiber

During the coagulation step in the wet spinning process, a concentrated, highly viscous polymer solution is transformed into protofibers which require further processing before they acquire textile fiber properties. The structure of these protofibers is strongly influenced by coagulation conditions, and this structure, in turn, influences the extent to which desirable properties can be developed in the finished product. In this study, the effect of several coagulation variables on the structure of protofibers preserved by freeze drying has been determined and related to the further processability and final properties of the fibers. Coagulation temperature, coagulation bath composition, extrusion rate, and take-up rate are shown to influence the cross-sectional shape, initial density, and void structure of the protofibers. Higher initial fiber density and more homogeneous internal structure permit the development of higher strength at lower stretches, higher elongation at a given strength level, high maximum strength and modulus at high stretch ratios, and improved fatigue and abrasion behavior.

The Kinetics of the Coagulation of Latex of Hevea Brasiliensis and the Separation of the Hydratant Acid

Abstract In the present work, an attempt is made to study the process of coagulation of Hevea brasiliensis latex, so familiar to every rubber expert, from a general colloid-chemical point of view, and to ascertain the physical conditions under which the kenetic phenomena take place. Hevea Brasiliensis Latex as a Physical System In “The Electrometric Determination of the Hydrogen Ion Concentration in the Latex of Hevea brasiliensis and Its Applicability to Technical Problems” the true character of Hevea brasiliensis latex as a physical system and the phenomena which take place during coagulation of this system are discussed in the light of investigations and observations of various rubber experts. Latex is a dispersion composed of polydispersed rubber hydrocarbon, serum components, and water. The rubber component consists of microscopically visible solid or semi-solid particles, in Brownian movement, and judged by the degree of affinity of rubber for water these particles are unquestionably lyophobic. Since the serum components are in a colloidal state, they are present as sols or emulsions, and they impart to the latex its lyophilic properties. It is possible, however, to choose the conditions of coagulation so that, for a given concentration of dispersed substances and at a given temperature, the dispersion will be predominantly lyophobic or lyophilic. This dual standard leads to the conclusion that Hevea brasiliensis latex is a pseudo-lyophilic dispersion. In saying this, it should be noted that, although the dispersion has several lyophilic properties, it is nevertheless essentially a lyophobic system, the properties of which become manifest under the right conditions.

Coagulation conditions and bacterial efficiency of preliminary water treatment

Coagulation conditions and bacterial efficiency of preliminary water treatment

Experimental Studies of Water Purification: IV. Observations on the Effects of Certain Modifications in Coagulation Sedimentation on the Bacterial Efficiency of Preliminary Water Treatment in Connection with Rapid Sand Filtration: B. Observed Effect of Certain Modifications in the Conditions of Coagulation

Experimental Studies of Water Purification: IV. Observations on the Effects of Certain Modifications in Coagulation Sedimentation on the Bacterial Efficiency of Preliminary Water Treatment in Connection with Rapid Sand Filtration: B. Observed Effect of Certain Modifications in the Conditions of Coagulation

Some Observations on Rubbers with Low Nitrogen Content

Abstract Rubber has been prepared protein-free, although not entirely nitrogen-free, by digesting latex with caustic soda, as recommended by Pummerer and Pahl. Rubbers with a nitrogen content of from 0.004–0.0096 per cent have been prepared by a slight modification of the original procedure. This rubber can be compounded and cured to give good quality vulcanizates, which compare very favorably with the controls. Protein-free rubber, when acetone-extracted, becomes nitrogen-free. This can still be vulcanized, although it cures slowly. The rate of cure of rubber from protein-free latex is affected very little by the pH of the coagulating medium whereas with full-nitrogen rubber rate of cure varies considerably with change in pH value at the time of coagulation. It was also found that protein-free rubber could be racked. Data on the preparation, coagulation and nitrogen content as well as the vulcanization results of protein-free rubber are presented. The observations lead to the conclusion that protein is not the key to the explanation of the physical properties of rubber. Rubber cannot be prepared absolutely nitrogen-free by the method of Pummerer and Pahl, even though the treatment of the latex with caustic is continued twice as long as they recommend. The residual 0.004 to 0.009 per cent of nitrogen is not protein nitrogen, since it is removable by acetone extraction and the amount of nitrogen falls so low as to be unmeasurable with accuracy by the exact method used in this research—i. e., colorimetric determination with Nessler???s solution. The authors note with satisfaction that Pummerer has come to exactly the same conclusion. Comparison of the results of vulcanizing protein-free rubber with those of the controls and with the results of the previous research shows that the rate of cure is constant under different conditions of coagulation and that the quality of the nitrogen-poor vulcanizates compares very well with the controls and with the earlier mentioned work described by Dinsmore. It appears, therefore, that the variation in cure and quality as noted by Dinsmore was due entirely to some particular condition of the rubber protein brought about by the varying pH values existing at the time of coagulation. Protein-free rubber, after acetone extraction, is practically nitrogen-free and cures slowly to give vulcanizates of lower quality than is obtained with the protein-free rubber. It should be remembered, however, that, as stated above, this effect may not be due entirely to the absence of nitrogen. Definite conclusions on this phase of the question must be withheld until more experiments are made. The evidence presented shows that protein-free rubber can be compounded and cured to give good quality products. Hence the protein is not an essential factor in producing the physical properties of vulcanized rubber. The condition of the protein does affect the rate of cure and so exerts an indirect effect upon the quality of the rubber.

On the Coagulation of Blood 1

BRÜCKE's researches on the conditions of coagulation of blood have shown that, on the one hand, contact with foreign bodies makes blood coagulate, and, on the other, that contact on all sides with the fresh vascular wall obviates coagulation (Durante). Lacker has proved the influence of foreign bodies on blood-coagulation by microscopic observation of coagulation in its first stages. In partial contradiction to these results was the observationof Grünhagen that blood, when received into glycerine, and so long as it did not mix, remained liquid. To determine the nature of these influences the following experiments were made. Blood was drawn under oil from the carotid artery of a dog, and let stand at ordinary indoor- temperature; after twenty-four hours it was not coagulated. Then the blood was drawn into a vessel smeared inside with vaseline, and it too did not coagulate. When it was stirred with an oiled glass rod, no fibrin was separated; but when, even after several hours, part of this blood was poured into an ungreased vessel, it coagulated in a few minutes. Moreover, contact with an un greased glass rod sufficed to make the blood in the greased vessel coagulate outwards from the rod.