Harry P. Gregor

Studies on ion-exchange resins. IV. Selectivity coefficients of various cation exchangers towards univalent cations

Abstract 1. 1. The thermodynamic theory of ion-exchange processes predicts that the selectivity coefficient is determined by the ratio of the exchange ion activity coefficients in the resin phase, by differences in ionic volumes and by the thermodynamic osmotic pressure. 2. 2. The variation in selectivity coefficient with ionic composition of the resin phase appears to be, in the case of the alkali metal cations, primarily a pressure-volume effect. In the case of the quaternary ammonium ions, ion activity variations, resulting from adsorption of the organic ions on the resin matrix, appear to oppose the pressure-volume effects. 3. 3. The effects of temperature and concentration of the resin phase are consistent with the concept of ion hydration as it affects the pressure-volume term. The constancy of ionic activity ratios for the alkali metal cations is in accord with the Bjerrum, Harned, Stokes-Robinson theory. 4. 4. The selectivity coefficients are not a function of the ionic strength of the equilibrative solutions. In the absence of adsorption effects, the smaller ion is preferred. 5. 5. Selectivity coefficients for a pair of cations can be calculated from selectivity coefficient values for each of these ions with a third reference ion. This indicates that the thermodynamic osmotic pressure varies only slightly with different exchange cations for a given resin, and supports the view that the ionic activity coefficients are determined chiefly by the nature and concentration of the ion and not by interaction between the ions. 6. 6. Adsorption effects of the quaternary ammonium ions are more pronounced in the case of low capacity resins, due to the larger ratio of organic to polar groups.

Studies on ion-exchange resins. II. Volumes of various cation-exchange resin particles☆☆☆

Abstract 1. 1. The volume and composition of a number of cation-exchange resins, measured under various experimental conditions, have been described. For a particular resin, the volume increases with the (hydrated) ionic volume of the exchange cation (except where ion-pair formation takes place). This phenomenon is discussed in terms of the Bjerrum, Harned, Stokes-Robinson theory. 2. 2. The swelling of resins having different degrees of cross-linking is described in terms of an osmotic model. Various sulfonated polystyrene—divinylbenzene resins are compared. 3. 3. The swelling and composition of a resin phase containing more than one species of exchange cation is described. Net partial molar volumes are calculated. 4. 4. The deswelling of resins in concentrated electrolytic solutions is described, and the mean ionic activity coefficient of the movable electrolyte within the resin phase calculated. This activity coefficient decreases sharply as the concentration in the external solution phase decreases.

Composition of stearic and behenic acid monolayers from sodium-containing substrates

Monomolecular films of stearic and behenic acid were formed on substrates 0.1 M in sodium chloride, sodium bicarbonate, or sodium phosphate. The film was removed by skimming and its composition determined by infrared analysis. On all substrates only the pure acids could be detected by pH < 6. At pH 6–10 a mixture of the acid and the sodium salt was observed. The apparent pKa of the acids in the monolayer was 3–4 units higher than the estimated value in the bulk solution. The Gouy-Chapman theory was applied to these results and the true pKa was calculated to be 5.6–6.5, reasonably close to the bulk value. It was concluded that the binding of sodium ions to the monolayer is almost entirely ionic.

Studies on ion-exchange resins. V. Water vapor sorption☆

Abstract 1. 1. Water vapor sorption studies on a series of ion-exchange resins are presented. The systems investigated include sulfonic acid cation-exchange resins of various degrees of cross-linking, a carboxylic acid resin, and a quaternary ammonium anion-exchange resin. 2. 2. Some direct calorimetric measurements of heats of sorption are presented. Free energies, heats of sorption, and entropies are calculated. 3. 3. The sorption behavior of sulfonic acid resins is compared with that of sulfuric acid. It is concluded that the sulfonic acid groups are osmotically inactive. For the sulfonic acid resins, variations in sorption with ionic state are discussed and interpreted. The partial molal volumes of the hydrated resin systems are studied. 4. 4. The behavior of the cross-linked polystyrene sulfonic acid resins is discussed from the point of view of simple, strong electrolytes in aqueous media. This interpretation is valid for the range 0–75% relative humidity; the influence of cross-linking makes itself felt above this point.

Studies on ion-exchange resins. Capacity of sulfonic acid cation-exchange resins

Abstract 1. 1. The preparation of a series of sulfonated polystyrene-divinyl-benzene cation-exchange resins is described. 2. 2. Exchange capacities are found to be identical to all inorganic and organic univalent cations studied, with the possible exception of the tetra-(n)-butylammonium ion. The divalent cation capacities are slightly larger in every case. 3. 3. Studies of rates of uptake are presented, and diffusion coefficients calculated. The rate of uptake is correlated with both the ionic volume and the degree of cross-linking of the resin structure.

Theory of Selective Uptake of Ions of Different Size by Polyelectrolyte Gels—Experimental Results with Potassium and Quaternary Ammonium Ions and Methacrylic Acid Resins

A model has been developed to predict the selectivity of polyion gels for one counterion over another of a different size. The model, essentially an extension of the Kagawa—Gregor model is based on purely electrostatic interactions between the gel and the counterions and takes into account their differing distances of closest approach. This model was tested against experimental data involving cross‐linked polymethacrylic acid with Li+, Me4N+, and Et4N+ ions exchanging for K+; it was found to predict these selectivities to a good degree of accuracy, particularly with the unhydrated quaternary ammonium ions. The model correctly predicts the variation of selectivity with counterion size ratio and also correctly predicts the variation of selectivity with counterion concentration ratio. Discrepancies between theory and experiment attributable to pressure—volume effects were also evaluated and remaining differences were ascribed to adsorption phenomena.

The electrochemistry of permselective membranes. III. The electrical resistance of permselective collodion membranes in solutions of various electrolytes

Abstract 1. 1. A study was made of the time required in which final, stable electrical resistances are established with three electrolytes—potassium chloride, lithium chloride, potassium sulfate—across three types of permselective oxidized collodion membranes, being originally in the acidic state. These periods vary from 15 min. to many hours. Equilibration is reached somewhat faster with membranes of higher porosity. A large noncritical ion does not seem to retard the establishment of the equilibrium to a significant extent. A large critical ion, however, seems to slow down equilibration. The concentration of the solution in contact with the membrane seems to be of little significance. The establishment of final, stable resistances requires much longer periods than those necessary for reaching final, stable concentration potentials under comparable conditions. 2. 2. The final, stable resistances of four types of permselective collodion membranes equilibrated with solutions of six electrolytes at three concentrations, 0.1, 0.01, and 0.001 N , were measured and tabulated. The data are evaluated as to the differences of the various types of membranes, the influence of the concentration on membrane resistance, and the influence of the nature of the electrolyte. A comparison is also made of the concentration function of the resistance of the same membranes equilibrated with solutions of different electrolytes; and of the concentration function of the resistance of different membranes with solutions of the same electrolytes. 3. 3. Certain shortcomings of the permselective oxidized collodion membranes, their deficiency in mechanical strength, and mainly their weak acid character are discussed, and possible ways of improving them are indicated.

The electrochemistry of permselective protamine collodion membranes. III. The electrical resistance of several types of permselective protamine collodion membranes in solutions of various electrolytes

Abstract 1. 1. The periods of time required in which final, stable electrical resistances are established with three electrolytes—potassium chloride, potassium iodate, and magnesium chloride—across three types of permselective protamine collodion membranes vary from about 15 min. to many hours, being somewhat longer, for unknown causes, than in the case of the analogous permselective collodion membranes. The influence of the ionic properties of the electrolytes with which the membranes are equilibrated on the rates of equilibration closely resembles that observed with the permselective oxidized collodion membranes. 2. 2. The final, stable resistances of three types of permselective protamine collodion membranes equilibrated with solutions of six electrolytes at six concentrations were measured and tabulated. The data are evaluated as to the differences of the various types of membranes, the influence of the concentration on membrane resistance, the influence of the nature of the electrolyte, and various concentration functions. The regularities found are strictly analogous with those observed with permselective oxidized collodion membranes. 3. 3. The experimental data on equilibrium resistance of permselective collodion and protamine collodion membranes given in this and in the preceding paper are discussed jointly from the point of view of the basic concept of the fixed charge theory of electrochemical membrane behavior. Various complications which arise with real membranes which are heteroporous and have inhomogenous pores are sketched. Certain cases of membrane behavior under limiting conditions as to concentration of the adjacent solutions, the nature of the critical ions, etc., are discussed and compared to the experimental results. 4. 4. The direction of further fruitful investigations on membrane resistance is pointed out and the increasing number of points of close contact and even of overlapping between the physical chemistry of membranes and studies on ion exchangers is indicated.

Ion-mediated water flow. II. Anomalous osmosis.

SummaryAnomalous osmotic water flows may be the basis of the hypotonicity of gastric juice sampled at low rates of secretion. The anomalous osmotic flows of water produced by the exchange of hydrogen and a series of cations across the three membranes used in the electroosmotic studies (Paper I) have been obtained. The solvent flow results in part from the momentum imparted by the moving ions to the water contained in the membrane matrix. The physical parameters that regulate the rate of bi-ionic exchange and the accompanying anomalous osmotic solvent flows are: the hydration states of the membranes; the molarities of the membranes and the mobilities of the exchanging ions which are a function of ion size. Each ion in the exchange produces a flow of liquid. Assuming that the ions do not interact with one another in the membrane, the anomalous osmotic flux was assumed to be the sum of the water flows produced by each permeant ion. The anomalous osmotic flux produced by a bi-ionic exchange was calculated from electroosmotic coefficients ([EO]cation and [EO]Cl) and the ion-exchange rates. The calculated values were all 10 to 60% less than the observed values. Part of these differences may have resulted from concentration gradients in unstirred boundary layers adjacent to the membrane which caused an osmotic flow of water in the direction of net water movement. As in the stomach, the sodium-hydrogen exchange produced a hypotonic solution.