Increasing Bulk Concentration Research Articles

ADSORFHON OF HUMAN IgG MOLECULES ONTO GLASS BEADS: REVERSIBLE AND IRREVERSIBLE ASPECTS

ABSTRACT Reversible and irreversible aspects of polyclonal IgG adsorption onto glass beads were studied using 125I radiolabeled proteins for bulk concentrations as low as 4× 10−4 mg ml−1. A true thermodynamic equilibrium was reached in the low bulk concentration domain, and a saturation of 0.1μg cm−2 was noticed for concentrations ranging from 0.03 to 0.37mg ml−1. The decrease of the amount of desorbed IgG's with increasing bulk concentrations in the plateau domain taken together with the impossibility to adjust desorption kinetics using a single exponential law, allowed us to propose an adsorption mechanism in which two protein populations i.e. rapidly (state B) and slowly (state C) desorbed molecules are involved

Influence of temperature on the ultrafiltration of silica sol in a stirred cell

The ultrafiltration of silica sol (average particle diameter of 18 nm) was studied in a stirred batch cell with an Amicon PM 10 membrane over the temperature range 293–323 K. With a stirrer speed of 400 rpm, the limiting flux and threshold pressure increased with increasing temperature and decreasing bulk concentration. The increasing temperature caused an increase in the mass transfer coefficients. The specific resistance of the gel layer was investigated in an unstirred cell. The specific resistance of the silica sol gel layer was in the range 2.8–10.4X10 14 m-kg −1. A rise in temperature caused the formation of a denser gel layer corresponding to increased specific resistance. The specific resistance was also found to increase with increasing bulk concentration of silica sol and with increasing pressure difference. The gel layer was found to be compressible, the specific resistance increasing with pressure difference to the power of 0.5–0.6.

Adsorption from a bidisperse polymer mixture

The adsorption of long linear polymer chains dissolved in a solvent made of shorter chains of similar chemical species is discussed. Various regimes that may befound and the crossovers when either the bulk concentration increases or the length of the smaller chains is increased are discussed.

The effects of concentration on partitioning of flexible chains into pores

Equilibrium partitioning between bulk solution and pores was investigated by computer experiment using the Monte Carlo technique. In a multichain athermal system, self-avoiding walks of up to 60 steps were generated on a simple cubic lattice with variable pore size and chain concentration. The results demonstrate that the constraints imposed by the pores and/or neighbouring chains reduce the chain entropy. The entropy related parameter, the partition coefficient K (the equilibrium pore-to-bulk concentration ratio) increases linearly with bulk concentration ø. A maximum concentration dependence of K was found for large pores characterized by a coil-to-pore dimension ratio λ of about 0.1–0.3. In this range the increase in bulk concentration brings about a dramatic enhancement of partitioning into pores. The results of computer experiments are compared with predictions of hard-sphere solutes theory and with static and gel-chromatographic measurements of the partitioning equilibrium. The implications of the concentration-dependent coefficient K for hindered transport of flexible polymers inside pores are briefly discussed.

Lysozyme adsorption at the air/water interface

The adsorption of reductively methylated chicken egg white lysozyme (EC 3.2.1.17) to the air/water interface has been measured by the radiotracer technique. This method enables direct determination of surface excess concentration as well as relative rates of adsorption and desorption. Improvements in calibration and radiolabeling techniques led to differences between the present results and previous lysozyme isotherms reported in the literature. The isotherm indicates monolayer saturation at low concentrations of bulk protein (below 2 × 10 −5 wt%) and multilayer adsorption at high concentrations (above 10 −3 wt%). At intermediate concentrations, an abrupt increase in surface concentration with increasing bulk concentration indicates a change in orientation of the adsorbed protein molecules. Adsorption experiments performed by sequential addition of protein to the bulk solution provide evidence that lysozyme molecules adsorbed at concentrations below the multilayer region do not exchange significantly with lysozyme molecules in the bulk solution. A kinetic model which incorporates the monolayer plateau, the multilayer adsorption, and the change of orientation of adsorbed lysozyme is presented.

Grain boundary segregation of boron and sulfur and its effect on ductility in rapidly solidified Ni-base L1 2 compounds

This paper reports a study of boron segregation in Ni 3Al, Ni 3Si, Ni 3Ge, and Ni 3Ga. Sulfur segregation in Ni 3Al is also considered. The results show that boron segregates in Ni 3Al and that the amount of segregation tends to increase as the bulk concentration of boron in the alloy increases. However, because the samples had not reached equilibrium during the heat treatment, there was some scatter in this correlation. Boron also segregated in Ni 3Si and Ni 3Ge, but there appeared to be no dependence of the amount of segregation on the bulk concentration. This result is not surprising because in these alloys the boron concentration was above the solubility limit. Boron segregation also occurred in Ni 3Ga and it appeared to increase with increasing bulk concentration. However, only a small amount of data was obtained for this system. Sulfur segregated in Ni 3Al and its concentration on the grain boundaries increased with increasing bulk concentration. It did not appear to compete with boron for grain boundary sites. Aluminum also segregated in Ni 3Al, but there was a large amount of scatter in the data. The plastic strain to failure measured for the samples of Ni 3Al did not correlate with the amount of boron segregation. In particular, we could not explain the fact that boron additions enhance grain boundary cohesion more effectively in Ni-rich alloys by an increase in boron segregation in these alloys. Stoichiometric alloys and Ni-poor alloys that were very brittle had boron segregation in equivalent amounts to that found in ductile Ni-rich alloys.

The interdiffusion of counterions in a cation-exchange membrane with metal chelation in solution phase.

Some water-soluble metal-chelating agents are introduced into a Donnan dialyzer as the strip agent for the enrichment of nickel ion. The interdiffusion fluxes of Ni2+-Na+ and Ni2+-H+ are found to increase with increasing capability of chelating agent. Experimental results of ion-exchange equilibria indicate that the nickel uptake on the strip-side, membrane-solution interface is reduced in the presence of chelator, which explains the promotion of interdiffusion rate. Effects on the interdiffusion fluxes due to various types of chelating agents, concentrations of chelating agents, concentrations of counterions, and pH value are investigated. In the presence of strong EDTA ligand, the inter-diffusion process is found to be feed-side, film- and membranediffusion controlled. The integral interdiffusion coefficient of counterions in the ion-exchange membrane are obtained from stirred cell data. An increase of interdiffusion activation energy with increasing bulk concentrations of nickel ion in feed solution is observed.

Effect of concentration on the rejection coefficients of rigid macromolecules in track-etch membranes

To test theoretical predictions that the membrane rejection coefficient ( R) for rigid macromolecules should decrease with increasing bulk concentration, R was measured at volume fractions of 0.001 and 0.033–0.080 for Ficoll (a crosslinked polysaccharide) and bovine serum albumin (a globular protein) in track-etch polycarbonate membranes having uniform capillary pores. The membranes were characterized by scanning electron microscopy and hydraulic permeability measurements, yielding pore radii of 15–36 nm. R decreased with concentration for all membrane—solute combinations, in fair agreement with a hydrodynamic model of hindered transport in pores. For any given solute and pore size, however, R in either dilute or concentrated solutions was significantly larger than anticipated by the theory. This last finding can be interpreted in terms of a greater effect of macromolecule adsorption on rejection properties than on hydraulic permeability.

A model for counterion binding to ionic micellar aggregates

A model for the interface between an ionic surfactant aggregate and the surrounding electrolyte is developed to incorporate the binding of counterions at the surface. The model considers discrete ionic headgroups and ionic headgroup-bound counterion pairs and the interactions among them which introduce a nonrandomness into their distribution over the interface. The effect of the double layer is included by an improved approximate solution to the nonlinear Poisson-Boltzmann equation. Our approach allows calculation of the work of formation of the interface, from which an equation can be derived predicting the degree of dissociation of surface groups. This is applied to micelles formed by the sodium alkyl sulfates. The calculated degree of dissociation decreases significantly with increasing bulk concentration of counterions and is sensitive to the shape and size of the aggregate. For sodium dodecyl sulfate at zero added salt it is about 0.35 for spherical micelles and 0.12 for rodlike micelles. A comparison of different approximations for the dissociation reveals that the discrete structure of the interface must be taken into account if this quantity is to be predicted over the entire range of counterion concentrations.

Effects of saturating metabolic uptake on space profiles and tracer kinetics.

Vascular and steady-state lengthwise concentrations evolving in tissue as a consequence of saturable uptake processes are explored when there is no effective barrier between blood and tissue, when there is one effective barrier (the liver), and when barriers are present at both capillary and cell membrane. Falling exponential profiles develop at low-input concentrations and grade over into much smaller linear decreases at high concentrations. Uptake behind an effective barrier produces a step-down in concentration. With no effective barriers, a tracer impulse propagates to the outflow in a delayed fashion, reversible binding to the enzymic removal mechanism increasing its space of distribution and delaying it further and irreversible uptake diminishing its area. As bulk concentration is increased, proportional tracer uptake diminishes and ultimately approaches zero. With barriers in the system, tracer output consists of an impulse damped by cell entry, followed by outflow recovery of material that has escaped cell uptake. Increase in bulk concentration is found to saturate the uptake mechanism, with a proportionate increase in the returning material.

Fe(100)面上へのイオウの偏析と2次元化合物の析出

The segregation behavior of sulfur has been investigated on Fe(100) surface by AES and LEED in the temperature range from 873 to 1123 K. The bulk concentration of sulfur in specimens was varied from 17 to 100 wt ppm, which covered the areas both below and above the solubility limit of sulfur in α-Fe. In the area below the solubility limit, the equilibrium surface concentration of sulfur was about 30 at%, which was independent of the annealing temperature and the bulk concentration of sulfur. The surface structure c(2×2) was observed on the sulfur-segregating surface for all specimens. In the area above the solubility limit, the surface concentration of sulfur amounted to about 40 at% for some specimens, but the scattering of data between specimens was larger. From these results, it was concluded that the two-dimensional surface phase of Fe2S precipitates on Fe(100) surface below the solubility limit of sulfur and that the additional precipitation of bulk phase FeS occurs on the surface above the solubility limit. The thermodynamical consideration was given on the two-dimensional surface phases, and the attempt was made to construct the equilibrium phase diagram containing the surface phases. The qualitative representation of Fe(100)-S system has been given: (1) When the bulk concentration of sulfur is very small, the surface phase is in the state of solid solution, and the surface concentration increases with an increase in bulk concentration; McLean-type segregation. (2) If the bulk concentration exceeds a critical value (less than 1 wt ppm), the two-dimensional surface phase Fe2S precipitates, and the surface concentration of sulfur remains almost constant until the bulk concentration arrives at the bulk solubility limit (100 wt ppm at 1073 K). (3) Above this concentration, the three-dimensional FeS precipitates and coexists with the surface phase Fe2S on the surface.

Adsorption maxima from solutions of ionic surfactants. A thermodynamic analysis

By regarding adsorbed and dissolved surfactant as independent species whose chemical potentials are equal at equilibrium, general expressions are derived which specify the conditions for the Gibbs surface excess of surfactant, Γ, and the contribution from an adsorbed monolayer, Γm, to exhibit maxima with increasing surfactant concentration. These conditions do not appear to be thermodynamically or otherwise forbidden and lead to the conclusion that situations may arise in which the total number density of solute in an interfacial region decreases with increasing bulk concentration. An example based on a simplified model is used to show that the appropriate conditions might be fulfilled in practice by some micellar solutions of ionic surfactants. Similar reasoning could also apply to surfactant binding on polymers.

The effects of temperature and concentration on counter-ion interdiffusion in anion exchange membrane.

The apparent interdiffusion of counter-ions in anion exchange membrane Selemion ASV was investigated. The experimental results show that the rate of interdiffusion is controlled by combined film diffusion and membrane diffusion at low flow rate, but controlled by membrane diffusion alone at high flow rate. The relationships between the apparent interdiffusion coefficient and temperature can be expressed by the Arrhenius equation for various systems. The apparent interdiffusion coefficient arid interdiffusion activation energy for various systems have the ordersDOH-Br>DOH-C1>DOH-NO3>DOH-I ?? DOH-SO4 AND EOH-Br SbOH-C1 SbOH-I, respectively. The interdiffusion of counter ions is independent of the kinds of co-ions at low concentration of the solution. There are an increase of integral interdiffusion coefficient and a decrease of interdiffusion activation energy with increasing bulk concentration of the electrolyte solution.

Concentration dependence of currents through single sodium-selective pores in frog skin

Many transport processes in biological membranes show a saturation of transport rate when the concentration of the transported ions or molecules is sufficiently increased. Saturation will result when at high concentrations a translocation step which does not directly depend on bulk concentration becomes rate limiting, and it is expected for all multi-step translocation mechanisms. However, a possible alternative explanation for saturation is a regulatory process which decreases the number of translocating channels in response to an increase in bulk concentration of the transported species. In the frog epidermis, Na+ uptake from the extracellular space into the epithelial cytosol occurs through Na+-selective, passively conducting channels located in the apical membrane of the cells directly below the cornified outer cell layer. Saturation of transport occurs with increasing outer Na+ activity ([Na]o): the net Na+ current1,2, membrane conductance2,3 and unidirectional Na+ influx4 increase only subproportionally with [Na]0. The apical Na+ current can transiently be larger than the saturation value, suggesting that a fixed upper single channel transport rate is not responsible for the saturation, and it has, therefore been suggested that in this case saturation occurs through a [Na]o-dependent decrease in channel density2. The Na+-translocation process can be investigated by a statistical evaluation of spontaneous transport fluctuations. The reversible transport blocker amiloride can be used to induce random fluctuations of the Na+ current at the apical membrane. The power density spectrum of these fluctuations is of the lorentzian type and permits an estimation of the Na+ current which passes through individual translocators in the time intervals between blocks5. We have recorded the current fluctuations at different [Na]o values and different amiloride concentrations in the [Na]o range in which saturation of total Na+ current is observed. We report here that the density of the conducting pores decreases with increasing [Na]o.

Effects of forced flow, noncondensables, and variable properties on film condensation of pure and binary vapors at the forward stagnation point of a horizontal cylinder

An analytical investigation of the effects of forced flow, noncondensable gas, and variable thermophysical properties on laminar film condensation of pure and binary vapors at the forward stagnation point of a horizontal cylinder is presented. Condensation heat transfer results are obtained for a broad range of parameters including the oncoming bulk velocity ( u ∞ = 1–100 ft/s), saturation pressure ( P ∞ = 49–760 Torr), wall-to-bulk temperature difference ( T ∞ − T w = 0.3–40° F), mass fraction noncondensable gas ( m 1,∞ = 0.01–0.15), and cylinder radius ( R = 0.25–1.5 in.). As expected, the deleterious effects of noncondensable gas on q/ q Nu ( q Nu is the classical Nusselt solution for pure vapor) under quiescent conditions are markedly less severe with forced flow. (For steam-air mixtures, with 0.01 ⩽ m 1, ∞ ⩽ 0.15, q/ q Nu approximately doubles as u ∞ increases from 1 to 10 ft/s.) As was true for the flat plate results of Minkowycz and Sparrow, q/ q Nu passes through a maximum as T ∞ − T w increases; here, the maxima occur at higher T ∞ − T w and are more pronounced. For binary film condensation of steam-methanol mixtures, it is found that q/ q Nu ( q Nu is the classical Nusselt solution for pure steam) sharply decreases with increasing bulk concentration of (more volatile) methanol; the effect is similar to that for noncondensable gas. Guided by the numerical results, a simplified theory is developed which is in good agreement with the heat and mass transfer conductances.

Adsorption of Surface Active Substance at Aqueous Surface Using Tritium Labeled Compounds: Adsorption from Mixed Aqueous Solution of Sodium Dodecylsulfate and Dodecanol

Abstract Adsorbed amount of sodium dodecylsulfate (SDS) and n-dodecanol (DOH) at the gas-solution interface of their mixed aqueous solution was directly measured as a function of bulk concentration of DOH by the radiotracer method. For this purpose the surface radioactivity of the mixed solution in which either SDS or DOH was labeled with tritium, was counted by using a 2π window-less gas-flow counter. It was found that the adsorbed amount of DOH rapidly increases with increasing bulk concentration of DOH, while that of SDS gradually decreases. The adsorption of DOH and desorption of SDS are not a simple 1 : 1 replacement. A maximum total adsorption of about 13×10−10 mol/cm2, which exceeds the amount of close-packed monolayer adsorption extends over a wide range of concentration studied. It was suggested that the adsorbed film consists of mixed monolayer or double layers. The latter film is composed of mixed monolyaer of SDS and DOH with adsorbed layer of SDS beneath. The molar ratio of adsorbed amount of DOH to SDS in the surface became unity, when the ratio of the bulk concentration of DOH to SDS was about one hundredth, which shows a stronger adsorption tendency of DOH than that of SDS.

Measurement of the adsorption of surface-active agents at a solution/air interface by a radiotracer method

The adsorption of a water-soluble surface-active agent at the solution/air interface has been measured by taking advantage of the soft beta-radiation from the radioactive isotope of sulphur, 35 S. The method depends upon the fact that, because of 'self-absorption ’ of the radiation by the solution, and because the molecules of a surface-active agent are preferentially adsorbed at the interface, the radioactivity above a solution containing such an agent labelled with radiosulphur should be higher than that from a solution (e. g., of sodium sulphate) in which no surface adsorption occurs. Carefully purified di- n -octyl sodium sulphosuccinate and sodium sulphate were each synthesized with 35 S. Measurements on solutions of these showed that the radiotracer technique permitted a successful quantitative determination of the adsorption. Counting rates over the solutions of agent were 1.1 to 20 times those of the corresponding sodium sulphate, and for some 29 different solutions covering a range of specific activities (1 x 10 12 to 5 x 10 9 ) counts/min./mol.) and of concentrations (0.1 to 150 x 10 -8 mol./ml.) a well-defined adsorption isotherm resulted. The surface excess obtained from the tracer measurements agreed with that calculated from surface-tension measurements by the Gibbs equation if it was assumed that no Na + and only H + were associated with the long-chain ions adsorbed in the interface. The radioactivity measurements suggested further that, after the agent had formed a uni-molecular layer, a further increase in bulk concentration caused further adsorption at the interface. An interesting aspect is that the rate of adsorption was followed in the low concentration ranges. The method promises to be useful for studying the kinetics of such adsorption processes. The radiotracer method outlined above seems to be generally applicable to surface phenomena involving adsorbed layers, either mono- or multimolecular in nature. Although this paper describes the use of 35 S, it is evident that other radioisotopes having sufficiently soft radiation, such as 14 C, 45 Ca, 59 Fe, etc., could be employed. Moreover, the method appears to open considerable possibility for examining interaction in surface layers.