Bulk Concentration In Solution Research Articles

Studies on the Surface Adsorption of Binary Molten Salts.

The surface adsorption of eight binary molten salts, AgNO3-M1NO3(M1 = Li, Na, K, Rb), NaNO3-M2NO3 (M2 = K, Rb), Ca(NO3)2-CsNO3, and Cd(NO3)2-NaNO3, has been investigated. It is found that the surface tension and temperature of molten salts at constant pressure and mole fraction satisfy the same equation as that for pure liquid compounds reported in our previous works. The heats of phase transition from the bulk to the surface phase for eight molten salts are determined. The heats per unit area are all at the order of -10-2 J/m2. The phase transition is exothermic because the entropy in the surface phase is smaller than the entropy in the bulk phase. The ratio of the solute surface concentration to the solute bulk concentration is approximated as the first-order polynomials of the solute bulk concentration. Then, curves of the surface tension vs the solute bulk concentration are well fitted. The ratio (ΔcBs/ΔcBα) is used to interpret the changing trend of the surface tension with bulk concentrations of solute. It is also found that the surface tension of molten salts decreases linearly with the solute surface concentration.

Flattened and Wrinkled Encapsulated Droplets: Shape Morphing Induced by Gravity and Evaporation.

We report surprising morphological changes of suspension droplets (containing class II hydrophobin protein HFBI from Trichoderma reesei in water) as they evaporate with a contact line pinned on a rigid solid substrate. Both pendant and sessile droplets display the formation of an encapsulating elastic film as the bulk concentration of solute reaches a critical value during evaporation, but the morphology of the droplet varies significantly: for sessile droplets, the elastic film ultimately crumples in a nearly flattened area close to the apex while in pendant droplets, circumferential wrinkling occurs close to the contact line. These different morphologies are understood through a gravito-elastocapillary model that predicts the droplet morphology and the onset of shape changes, as well as showing that the influence of the direction of gravity remains crucial even for very small droplets (where the effect of gravity can normally be neglected). The results pave the way to control droplet shape in several engineering and biomedical applications.

Enhancement and mechanism of adsorptive particles on gas-liquid interfacial mass transfer

The aim of this paper is to study the enhancement mechanism of adsorptive particles on gas-liquid interfacial mass transfer. A quantitative model for predicting enhancement factor is proposed based on film model and interfacial non-equilibrium model, in which the enhancement factor depends mainly on the surface fractional coverage θ and the solute bulk concentration Cb, the interfacial concentration of liquid CI is dependent of the mass transfer coefficient kl and Cb, and usually is far from the equilibrium concentration with gas phase at the interface. The surface fractional coverage θ is a function of particle property and operating condition. The present model divided the enhancement into two regimes: particle-transport-controlled regime and surface-adsorption-controlled regime. The increase of gas-liquid mass transfer rate in the presence of adsorptive particles could mainly attributed to the surface adhesion of particles, the enhancement factor is an increasing function of surface fractional coverage θ but a decreasing function of the solute bulk concentration Cb, which well explains the effects of particles concentration and stirring intensity on enhancement factor. The prediction values of present model are at considerably good agreement with experimental data.

Solvent grain boundary diffusion in binary solid solutions: a new approach to evaluate solute grain boundary segregation

A new method to estimate solute grain boundary (GB) segregation from solvent GB diffusion measurements in binary solid solutions is proposed for the systems with restricted solubility and intermediate stoichiometric phases. The method is based on the model of complex formation: solvent atoms (A) interact with solute ones (B) at GB with the formation of AB chemical bond. A description of solvent GB diffusion is then given. Using such an approach, a new equation for the dependence of solvent GB diffusion coefficient on solute bulk concentration is derived for the systems with simple atomic attraction with AB complex formation in GB. Theoretical results predict non-linear dependence of solvent GB diffusion coefficient on solute bulk content, which is in agreement with earlier published experimental data regarding the ease of grain boundary diffusion in alloys of different chemical compositions. More importantly, the equation deduced permits to evaluate, on one hand, the characteristics of solute GB segregation from solvent GB diffusion measurements and, one the other hand, GB diffusion coefficient in pure solvent. Such a numerical data analysis for Fe–Sn system is in agreement with experimental results. In special cases, such an analysis can be done analytically.

New insight into surface tension inverted curvature for liquid-liquid and solid-liquid binary mixtures: The special case of hexamethylenetetramine in water

Surface tension of most binary liquid systems decreases concavely up with increasing solute concentration. In a lesser extent, surface tension curvature is inverted and decreases concavely down. In this report, inverted curvature is explained through a Modified Extended Langmuir (MEL) isotherm that relates solute bulk concentration and surface coverage through a single lyophobic parameter β, and through the Volmer-Margules (VM) model developed by our group that provides activity coefficients from surface tension data. According to the MEL isotherm, inverted curvature is due to the weak adsorption of the solute at low concentrations, making the surface coverage a concave up function of solute bulk concentration. The MEL model was tested with different liquid-liquid binary mixtures and with the liquid-solid system of water+hexamethylenetetramine (HMT), with partial miscibility hindering its description. The VM model fits HMT surface tension data remarkably well, providing similar activity coefficients to those obtained from isopiestic data. The activity coefficient at infinite dilution of HMT in water is smaller than one, ratifying the weak adsorption of HMT due to its affinity to water in bulk solution. The positive Gibbs adsorption energy computed from the VM model confirms the conclusions, providing a new meaning to the inverted curvature.

Prediction of Permeate Flux During Ultrafiltration of Polysaccharide in a Stirred Batch Cell

Ultrafiltration of polysaccharide macromolecule has been carried out in a stirred batch cell using a fully retentive membrane over a wide range of operating conditions. An unsteady state mass transfer model in conjunction with resistance-in-series model is developed using film theory. The proposed model is used to predict the transient permeate flux decline behavior in gel controlled ultrafiltration. This model is also able to quantify the variation of bulk volume as well as the bulk concentration of solute with time. The variation of viscosity as a function of solute concentration is included in the model. A model parameter is used in this model and is evaluated by optimizing the experimental flux profiles with calculated flux profiles. The model predictions are successfully compared with the experimental data. A parametric study has been performed to observe the effect of different process parameters on the filtration performance in terms of transient permeate flux decline behavior. The proposed model in general will provide a better understanding of gel controlled ultrafiltration.

Structure and optical properties of plant cell wall bio-inspired materials: Cellulose–lignin multilayer nanocomposites

Interfacial affinity between lignin model compound (dehydrogenation polymer [DHP]) and cellulose nanocristals (CN) was studied before building a nanocomposite cellulose/lignin in multilayer form by spin-coating method. The adsorption isotherm of DHP was measured by ellipsometry at the liquid/CN film interface and showed that the surface concentration of adsorbed DHP increases with the bulk concentration in solution. The DHP appeared as globular structures on cellulosic film, as observed by AFM. Spreading a dense lignin layer on CN film gave rise to the disappearance of the InfraRed resonance bands related to the DHP aromatics. The film obtained from alternate layers of cellulose/DHP was transparent in visible light and had weak absorption in UV wavelengths. Optical properties measured in the visible wavelength range by ellipsometry and spectrophotometry indicated that beyond six bilayers (cellulose/DHP), the composite exhibits antireflexion properties.

Superficial segregation in nanoparticles: From facets to infinite surfaces

We compare the superficial segregations of the Cu-Ag system for a nanoparticle and for surfaces that are structurally equivalent to each of its facet. Based on a lattice-gas model and within a mean-field formalism, we derive segregation isotherms at various temperatures in the canonical ensemble, i.e., for a given overall solute concentration, and in the semigrand canonical ensemble, i.e., for a given bulk solute concentration. If both processes are very similar for high temperatures, they differ substantially at lower temperatures. Due to the finite-size effect and the indirect coupling between facets and edges, the relative position of the phase transitions of the facets and the corresponding surfaces is inversed when displayed as a function of the solute bulk concentration. Moreover, we show that working in the semigrand canonical ensemble is a much more efficient way to study this phenomenon, although nanoparticles are "canonical" objects in essence.

A generalized correlation of solute inclusion in ice formed from aqueous solutions and food liquids on sub‐cooled surface

AbstractSolute inclusion in an ice layer formed on a smooth stainless steel surface under sub‐cooled flow conditions has been studied experimentally. The effects of ice growth rate, solution velocity and bulk concentration of solute on the solute inclusion in the ice layer have been investigated using a controlled flow surface crystallizer (CFSC). For several aqueous solutions (sucrose, NaCI, glycol, fructose), food liquids (skim milk, whole milk, orange juice) and particulate suspension (potato starch particles), the effective molecular weights were calculated and their effects on solid inclusion determined. This effect was then conveniently related to the freezing point depression (FPD) of each liquid tested. A generalized empirical correlation has been established for all the liquids tested.

A theoretical investigation on non-equlibrium grain boundary segregation 1The research was sponsored by the National Natural Science Foudation of China and National Advance Materials Committee of China. 1

Based on the concept that mobile solute-vacancy complexes migrating to grain boundaries (vacancy sink) is responsible for the non-equilibrium grain boundary segregation of solute atoms in an alloy, analytical expressions describing such a segregation process are presented. The driving force for the segregation is a decrease in the free energy of the system caused by the annihilation of vacancies at grain boundaries during cooling from an initial temperature. From the theoretical expressions, a sufficient condition for the non-equilibrium segregation to occur is determined to be that D s f /D p <1 (D s f and D p are diffusion coefficients for free solute atoms and solute-vacancy complexes, respectively). Besides, the expressions predict that the grain boundary segregation enrichment increases with a decrease in the ratio D s f /D p , the vacancy formation energy or the cooling rate (above a critical cooling rate) and an increase in the initial temperature or the binding energy of complexes, while the relative enrichment of solute atoms at grain boundaries decreases with an increase in the bulk concentration of solutes. Furthermore, an analytical relationship for the critical cooling rate giving the maximum grain boundary enrichment is also presented. The relationship exhibits that the critical cooling rate increases with an increase in the diffusion coefficient for solutes or complexes, the initial temperature or the binding energy of complexes and a decrease in vacancy formation energy, while it is independent of the bulk concentration of solute. On the other hand, the calculated results are compared with the computer simulations done by Karlsson in boron-doped Austenite . Although good agreement between the two studies on the characteristics of the non-equilibrium grain boundary segregation behavior is achieved, real segregation profiles of solutes can only be calculated quantitatively by the functional expression without spending much computation time.

Solute inclusion in ice formed from sucrose solutions on a sub-cooled surface—an experimental study

Solute inclusion levels in ice layers formed on a smooth stainless steel plate surface under sub-cooled flow conditions were studied. Sucrose solutions with solute concentrations up to 30 wt% were used. The effects of ice growth rate and solute concentration on solute inclusion (i.e. solute mass fraction) were investigated. It was found that solute inclusion in ice increases with increasing bulk concentration of solute and average ice growth rate and decreasing solution velocity. The solute inclusion, as labelled by the distribution coefficient, can be correlated well using a simple empirical equation. At low concentrations and low ice growth rates, the formation of ice with less than 100 ppm impurity was found to be possible.

Thermogravimetric Measurement of the Distribution Coefficients of Maltooligosaccharides upon a Cation-exchange Resin.

Thermogravimetry under nitrogen atmosphere was applied to measure the distribution coefficients of maltooligosaccharides upon a cation-exchange resin. Thermal degradation of the solute occurred at about 200°C and its weight decreased gradually with increases in temperature, while that of the resin occurred above 350°C. The solute distributed in the resin also degraded at that temperature. Thus, it was demonstrated that thermogravimetry was applicable to measurement of the distribution coefficient. The coefficients determined by this method coincided well with those determined by the conventional method. Because the amount of solute distributed in the resin became large when the bulk concentration of solute was high, the thermogravimetric determination of the amount was more accurate. Thus, this technique was useful for the measurement of the coefficient at higher bulk concentrations of solute.

The effects of temperature on the spherical crystallization of salicylic acid

The effects of temperature on the spherical crystallization of salicyclic acid were investigated. An ethanolic solution of salicylic acid held at 40 °C was introduced into a well-dispersed mixture of chloroform and water at 5 to 30 °C. By increasing the temperature, larger agglomerates with less spherical forms composed of larger crystals were obtained. The mass growth rate of the agglomerated crystals was described by the mass transfer-controlled kinetics. The growth rate coefficient at 30 °C was significantly smaller than those at 10 and 20 °C. The linear growth rate of the agglomerated crystals increased with increasing temperature, but did not depend upon the solute bulk concentration.

In situ adsorption of bovine submaxillary mucin at the mica/aqueous solution interface

An in situ adsorption measurement method at the mica/protein solution interface is described. An apparatus especially constructed for this purpose permits direct and continuous measurement of total adsorption (reversible and Irreversible) of 14 C-labelled proteins. Bovine submaxillary mucin (BSM), extracted from salivary glands, was acetylated with (CH 3, 14CO) 2 O. The results show the increase of BSM adsorbed on mica surfaces with its concentration in solution and adsorption time. Pseudo plateaux are obtained for all concentrations studied, Indicating the formation of thick layers. The loosely bound fraction of adsorbed mucin is proportional to the bulk concentration in solution. The amount of BSM adsorbed increases in the neighbourhood of the isoelectric point of BSM (pH 3).

Motion of a particle generated by chemical gradients Part 1. Non-electrolytes

When a particle is placed in a fluid in which there is a non-uniform concentration of solute, it will move toward higher or lower concentration depending on whether the solute is attracted to or repelled from the particle surface. A quantitative understanding of this phenomenon requires that the equations representing conservation of mass and momentum within the fluid in the vicinity of the particle are solved. This is accomplished using a method of matched asymptotic expansions in a small parameter L/a, where a is the particle radius and L is the length scale characteristic of the physical interaction between solute and particle surface. This analysis yields an expression for particle velocity, valid in the limit L/a → 0, that agrees with the expression obtained by previous researchers. The result is cast into a more useful algebraic form by relating various integrals involving the solute/particle interaction energy to a measurable thermodynamic property, the Gibbs surface excess of solute Γ. An important result is that the correction for finite L/a is actually O(Γ/C∞a), where C∞ is the bulk concentration of solute, and could be O(1) even when L/a is orders of magnitude smaller.