Increasing Bulk Concentration Research Articles

EFFECT OF INSOLUBLE PARTICLES UPON SOLID INCLUSION LEVELS IN ICE FORMED ON A SUBCOOLED STAINLESS STEEL SURFACE

This study employed an insoluble solid particle, i.e. a potato starch used as an example, to investigate the impact of the concentration of such particles suspended in water (with solid loading of 5, 10, 20 and 30 wt%) upon the solid inclusion levels in ice layers formed on a sub-cooled smooth stainless steel plate surface. The effects of ice growth rate, bulk concentration and suspension velocity on insoluble solid inclusion, i.e. potato starch mass fraction, in ice layer were studied. The experiments, where potato starch is added into aqueous sucrose solutions or the reverse where sucrose is added into starch suspension, were also carried out to investigated effect of the starch particles on sucrose inclusion in ice and effect of solute (sucrose) on starch particle inclusion in ice. It has been found that solid inclusion in ice increases with increasing bulk concentration and average ice growth rate, at constant solution and coolant velocities, and increasing suspension velocity can help pure ice formation. The average distribution coefficient of sucrose in ice layer formed from sucrose solution does not appear to be affected by the addition of potato starch. However, the average distribution coefficient of potato starch in ice layer formed from suspension is influenced by sucrose concentration quite significantly.

Surface Composition of Biopolymer Blends Biospan-SP/Phenoxy and Biospan-F/Phenoxy Observed with SFG, XPS, and Contact Angle Goniometry

The surface compositions of two biopolymer blends, Biospan-SP/Phenoxy (BSP/PHE) and Biospan-F/Phenoxy (BF/PHE), have been studied using sum frequency generation (SFG), X-ray photoemission spectroscopy (XPS), and contact angle goniometry. BSP and BF are polyurethanes capped with poly(dimethylsiloxane) (PDMS) and fluoroalkyl (-(-CF{sub 2}-){sub n}-) as end groups, respectively. With contact angle goniometry, the surface tensions of pure BSP, BF, and PHE were found to be 26, 16, and 45 dyne/cm. For each of the blends, the polymer component with a lower surface concentration of the surface-active component increases sharply as its bulk concentration increases. For BSP/PHE (and BF/PHE) in air, the surface of the polymer blend is fully covered by BSP (and BF) at a bulk concentration of 3.5 wt % (and 1 wt %). The contact angle measurements and the XPS studies yield compatible results. Comparison of results for BSP/PHE, BS/PHE (published before), and BF/PHE polymer blends shows that the lower the surface energy of the surface-active component (surface tension: BF < BS < BSP), the easier it is for the component to segregate to the surface (the minimum bulk concentration to saturate the surface is BF (1 wt %) < BS (1.7 wt %) < BSP (3.5 wt %)). Aftermore » exposure to water, SFG spectra indicate that the surface layer of a polymer blend could be restructured. For BSP (3.5 wt %)/PHE, the hydrophobic end groups of BSP submerge while the hydrophilic polyurethane backbone emerges. For BF (1 wt %)/PHE, PHE emerges at the surface after exposure to water, but for BF (5 wt %)/PHE, the BF component dominates the surface in both air and water. Their results demonstrate the bifunctionality of polymer blends and show that the surface chemistry of polymer blends may be dominated by a minor component, while the mechanical stability of the polymer is controlled by the major component.« less

Fluorescence Analysis of Acridine Orange Adsorbate at the Water/ N -Heptane Interface, Bulk and Interface

The amphiphilic nature of 3, 6-bisdimethylaminoacridine (trivial name, acridine orange) can be used to characterize (polar/nonpolar) interfaces. This paper studies the properties of acridine orange and its dodecyl derivative at a solvent interface by internal reflection and tension determinations. In the case of absorbance measurements of crystallized acridine orange, the potenz value of the conventional acid dissociation constant pK a was found to be 9.6. A clear isosbestic point could be obtained after purification at a unique pH for different concentrations. In contrast, in the absorbance measurements of acridine orange dodecyl, no isosbestic point was observed; this was attributed to the free long dodecyl chain. The overlap in the absorbance spectrum and the normalized fluorescence spectrum was found in many solvents around 500 nm. Neutral species were more likely to transfer into organic phase upon shaking. For fluorescence measurements both steady-state and time-resolved spectra were investigated. Results showed that at the interface a bathochromic shift happened to the maxima. This means that chromophore species aggregated at the interface as the dimer or trimer or the macro oligomer. Fluorescence polarization in bulk was calculated and found to be ca. 0.4. For interfacial measurements a dynamic volume method was applied to obtain the interfacial tension. An extrapolated Gibbs plot was obtained. Increasing bulk concentration increased the concentration at the interface to a finite value representing saturation.

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.

Dehydration of iodide segregated by tetraalkylammonium at the air/solution interface studied by photoelectron emission spectroscopy

Photoelectron emission spectroscopy was used to detect iodide anion at the aqueous solution surface. The photoelectron emission threshold energies E t for the iodide segregated by tetraalkylammonium cations differ from those for solutions with surface inactive cations. The smaller E t values found for larger alkylammonium salt solutions seem to be due to dehydration of iodide at the surface layer. When tetrabutylammonium is used as the surfactant, the dehydration proceeds in a stepwise way with increasing bulk concentration.

Structural conformation of lysozyme layers at the air/water interface studied by neutron reflection

The adsorption of chicken egg white lysozyme at the air/water interface has been studied by specular neutron reflection. The variation of the total thickness of the lysozyme layer at the surface of water under varying solution conditions has been determined. The use of mixed H2O and D2O allowed the determination of the extent of immersion of the layer in water at all concentrations. The measured layer thickness combined with the globular dimensions of lysozyme suggests that the adsorbed lysozyme molecules retain their globular structure with no significant denaturation. Measurements were made over a lysozyme concentration range of 9×10-4 g dm-3 to 4 g dm-3 at pH 7 and at an ionic strength of 0.02 M. The thickness of the layer was determined by measuring neutron reflectivities in null reflecting water (NRW) where the signal is only from the adsorbed protein layer. Below 0.1 g dm-3 the surface coverage increases with bulk concentration but the thickness of the layer is constant at 30±3 A, suggesting that lysozyme is adsorbed sideways-on. As the bulk concentration increases, the layer thickness gradually increases to a value of 47±3 A2 at a bulk concentration of 1 g dm-3, suggesting that the molecules switch from sideways-on to longways-on orientations. The area per molecule at 1 g dm-3 was found to be 950±50 A2 which is close to the limit of 30×30 A2 for a saturated layer of longways-on molecules. The extent of mixing of the layer with water was determined directly by measuring reflectivity profiles in mixed H2O and D2O. A two layer model was found to be appropriate with an upper layer in air and a lower layer fully immersed in water. The thickness of the layer in air was found to vary from 15±5 Aat the lowest bulk concentration to 9±3 Aat the highest concentration studied. The results show that as the total layer thickness increases with bulk concentration the fraction of the layer immersed in water increases from 50 to 85%. At the highest concentration of 4 g dm-3 the adsorbed layer is better described by a two layer model consisting of a close packed top layer of thickness 47±3 Aand a loosely packed sublayer of 30±3 A.

Absorption and reaction of CO2 with 2,3-epoxypropyl phenyl ether using aliquat 336 AS catalyst

A kinetic study on the absorption and reaction of carbon dioxide with 2,3-epoxypropyl phenyl ether (phenyl glycidyl ether, PGE) in benzene solution has been carried out at room temperature in the presence of tricaprylylmethyl ammonium chloride (Aliquat 336) as catalyst. A simple method of measuring the absorbed volume of CO2 was proposed to obtain the reaction rate constant, and it was based on the film theory accompanied by a chemical reaction. The enhancement factor (β-NCO2/NCO2 o) increased with increasing bulk concentration of PGE and Aliquat 336. The flux of CO2 was proportional to the agitation speed.

Surface Crystallization and Phase Transitions of the Adsorbed Film of F(CF2)12(CH2)16H at the Surface of Liquid Hexadecane

The interplay of the surface freezing phenomenon of hexadecane (abbreviated as H 16 ) with the monolayer phase behavior of a semifluorinated alkane, 1-(perfluorododecyl)hexadecane F(CF 2 ) 12 (CH 2 ) 16 H (abbreviated as F 12 H 16 ), at the air/hexadecane solution interface was studied by measuring the surface tension of hexadecane solutions of F 12 H 16 as a function of temperature and bulk concentration under atmospheric pressure. Above the surface freezing temperature of H 16 , our system F 12 H 16 + H 16 exhibits gaseous, expanded, and condensed monolayer phases of F 12 H 16 . In the domain of the gaseous film the entropy of surface formation per unit area, Δs, is almost independent of temperature and bulk concentration, and its magnitude is similar to that of pure H 16 . In contrast, in the domain of the expanded film Δs decreases sharply with increasing bulk concentration. Thus, the expanded film of F 12 H 16 in the present system manifests a unique behavior, indicating the formation of an ordered structure comparable to that of a condensed film. At lower temperature, this evolution of surface phases of the amphiphile (F 12 H 16 ) is cut off by the surface freezing of H i6 . It appears that F 12 H 16 is effectively insoluble in the solid monolayer of H 16 and that the F 12 chains of the F 12 H 16 molecules form a close-packed film in the condensed state. The point at which the gaseous film coexists with the condensed phase of F 12 H 16 and the solid monolayer phase of H 16 represents a surface heteroazeotrope (surface eutectic) and is located at about 17.4 °C, i.e., ca. 0.2 K below the surface freezing of pure H 16 (17.64 °C).

Adsorption-induced surface ordering on solutions of rigid-rodlike molecules

A simple model is developed to describe the adsorption and the surface ordering in solutions of rigid-rodlike molecules. We focus here on the planar adsorption of the rigid rods restricting the orientations to two mutually orthogonal directions which are both parallel to the surface. When the bulk concentration increases, the adsorbed amount is increased and the adsorption isotherm has a kink at a bulk concentration φc, where the second-order isotropic–nematic transition (INT) takes place in a surface. Further increasing concentration, the adsorbed amount jumps at a bulk critical concentration φIN, where the first-order INT takes place in the bulk phase. For various values of the axial ratio of the rigid rods, the solvent conditions, and the adsorption energy, we examine the adsorption isotherms, the surface tensions, and the surface ordering. We also discuss the co-occurrences between the adsorption phenomena and the phase separation of a surface phase.

Ultrafiltration of non-newtonian fluids

The current study reports on a series of ultrafiltration experiments using newtonian and non-newtonian fluids (pectine, xanthan and polyacrylamide solutions). For non-newtonian pseudoplastic fluids, the shape of the plot of flux versus log(bulk concentration) is different to the linear decline in flux which would occur throughout. Moreover, we observed that the axial velocity exponent decreases with increasing bulk concentration. An empirical equation for the laminar mass transfer coefficient of a pseudoplastic fluid has been proposed which includes a Sieder and Tate type correction factor. The equation is a tool for understanding the decrease in axial velocity exponent with increasing bulk concentration. However, a comprehensive numerical model is necessary to get better agreement between observed and predicted axial velocity exponent and permeate flux.

A Model for the Galvanostatic Deposition of Nickel Hydroxide

A mathematical model is presented for the galvanostatic deposition of films in stagnant solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated species decreased drastically as the concentration of increased beyond 0.1 M. For example as the concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm2. At this high ratio of concentration to current density, a comparison with Faraday's law indicates that only 10% of the species generated at the surface led to deposition. It has been proposed that the inefficient use of electrochemically generated species is due to the presence of as an intermediate in the deposition process. As the bulk concentration increases, the concentration of at the electrode surface increases. A high concentration of the intermediate results in an increase in the diffusion rate of the species away from the electrode surface and thus a decrease in the deposition rate. Here, this hypothesis is tested by developing a model which includes the generation of from the electrochemical reduction of nitrate to ammonia and the diffusion and migration of , and . The model predictions agree well with previously reported mass deposition data collected using an electrochemical quartz crystal microbalance at different currents and over a range of concentrations. The present work confirms the role that plays in the deposition process and provides a fundamental framework for understanding the electrochemical impregnation of nickel electrodes.

A study of fouling in the ultrafiltration of passion fruit juice

The effects of operating variables on permeation flux and resistances for the ultrafiltration of passion fruit juice were studied. The experiments were carried out on a polysulfone hollow fibre membrane laboratory module. The results showed that flux increased with temperature from 30 to 40°C and then decreased at 50°C. At low temperatures (30 and 40°C) the flux-pressure curves followed the gel-polarization model. The results were different at 50°C where flux initially increased with pressure and then subsequently decreased. It was also observed that flux increased with increasing bulk flow rates and decreased with increasing bulk concentration, in accordance with concentration polarization models. Except for membrane resistance R m, which was constant, other resistances increased with pressure and juice concentration and decreased with flow rate. An increase of temperature reduced the values of R p,re, the reversible polarized layer resistance and R p,ir, the semi-reversible polarized layer resistance but enhanced R f, the fouling resistance. R p,re was the major resistance which controlled the permeation flux for low temperature operation. At high temperature (50°C) the reversible polarized layer changed to a cross-linked gel and R f was significantly increased.

Interaction and stability of adsorbed ferritin clusters on hydrophobic quartz surfaces

Ferritin adsorption on a hydrophobic quartz surface was measured at different bulk concentrations and adsorption times. The initial slope of the isotherms increases with increasing bulk concentration. The pair correlation function, g( r), was obtained from the spatial distribution of adsorbed ferritin molecules on a quartz surface. The potential of average force was found to be around 1.4 kT, and clusters that are kept together by this potential are found to be stable only for less than a second. Ferritin molecules adsorbed on a hydrophobic quartz surface at low concentration (1 mg l −1) were found to interact at distances up to 5 radii. A theoretical model describing the kinetics of adsorption, desorption and cluster dissociation on an ideal surface was also derived.

Kinetics of Adsorption of Lysozyme and Bovine Serum Albumin at the Air–Water Interface from a Binary Mixture

The kinetics of adsorption of lysozyme and bovine serum albumin (BSA) at the air–water interface from binary bulk mixtures have been studied. An increase in BSA concentration in bulk phase caused a decrease in the extent of adsorption of lysozyme and an exponential decrease in its apparent diffusion coefficient; the lag time for its adsorption, however, decreased progressively with increasing bulk concentration of BSA. The ratio of BSA to lysozyme in the mixed monolayer increased with increasing ratio of BSA to lysozyme in the bulk phase. However, the unit cell dimensions occupied by BSA and lysozyme in the mixed monolayer were the same as those in single-component monolayers, suggesting that both BSA and lysozyme adsorbed independently, and the thermodynamic state of one protein was not modified by the other protein at the interface. Analysis of variations in interfacial composition of mixed monolayers formed at various bulk concentration ratios of the proteins indicated that adsorption of these proteins from the binary bulk phase did not follow a Langmuir-type competitive adsorption mechanism. Sequential adsorption experiments showed that although bulk phase BSA abruptly stopped adsorption of lysozyme, it could not displace lysozyme already adsorbed at the interface. In contrast, bulk phase lysozyme could neither stop adsorption of BSA nor displace adsorbed BSA. Critical analysis of these results indicated that adsorption of BSA and lysozyme from binary mixtures followed a kinetically controlled, noncompetitive adsorption mechanism. The interfacial composition of the mixed protein layer was primarily, if not solely, determined by the rate of arrival of each protein at the interface and unoccupied unit cells available at the interface at the time of arrival.

Grain Boundary Segregation of Phosphorus and Boron in Extra-Low Carbon Steels

Grain boundary segregation of P and B in extra-low carbon cold-rolled steel sheet containing from 0.01 and 0.15 mass% P and up to 38 mass ppm B after annealing at 1123 K was investigated by Auger electron spectroscopy (AES). AES measurements on the intergranular fracture surfaces of the specimen indicate that the Auger peak intensity ratio (PIR) of P increased and that of B decreased with increasing bulk concentration of P, and that PIR of P markedly decreased, while that of B increased with a B addition of up to 10 ppm. In the bulk concentration range of B of more than 10 ppm, however, these ratios hardly changed. The segragation behavior was nearly the same between specimens annealed for 20 s and 500 s, indicating that the segregation of P and B was in an equilibrium state. Calculations of the grain boundary coverages of P and B indicate that (1) the segregation free energy of B was about twice that of P, (2) the coverage of B was larger than that of P in the specimen with B concentration of more than 10 mass ppm, and (3) the total coverage of P and B was nearly constant in the specimen with B concentration of more than 10 mass ppm. It is concluded that the improvement in secondary workability of P-added steel sheet by also adding B is attributable to the segregation of less P and more B on the grain boundary, resulting in enhanced grain boundary cohesion.

Surface composition of machined leaded brass

AbstractESCA and RBS were used to obtain quantitative information on the thickness and nature of the surface layers formed on machined brasses containing 1–3% lead. The results show that the brass surface is strongly enriched in lead. The amount of this element accumulated on the surface increases with increasing bulk concentration. Lead appears to be present as islands partially covering the brass surface and having variable thicknesses up to several hundred Å. The outermost layer of the islands is mainly a Pb hydroxycarbonate, under which PbO and Pb metal can be detected. Between the islands, the brass surface is covered by a layer of zinc oxide covering the CuZn metallic phase. The accumulation of Pb at the surface is attributable to a smearing effect caused by the machining cool.

Equilibrium surface segregation of interstitials on bcc (001) surfaces

The surface segregation of interstitials X on free (001) surfaces of a body-centered cubic metal lattice M is studied by means of Monte Carlo modeling. It is assumed that interstitially dissolved X atoms occupy irregularly shaped octahedral bulk interstices characteristic of the bcc structure. Pairwise nearest and more distant neighbor couplings between adjacent M and X atoms ϕ MX (i) are used to calculate binding energies for X atoms at the various bulk and surface sites. Additional repulsive interactions between adjacent X atoms ϕ XX (i) are considered. Monte Carlo simulations are performed for three different sets of interaction parameters ϕ XX (i) .In all these cases the fourfold hollow sites of the bcc (001) surface are the most stable coordination sites. Ideal behavior in the bulk and at the surface is found if all interaction energies ϕ XX (i) = 0 . For slightly repulsive nearest and next nearest neighbor interactions ϕ XX (1) , ϕ XX (2) < 0 X atoms on the fourfold hollow sites of the surface still behave ideal while deviations from ideal behavior are observed in the bulk for concentrations x≳0.01. With additional repulsive fourth nearest neighbor interactions ϕ XX (4) < 0 c(2 × 2) ordering is induced at the surface for coverages θ ≈ 0.5. In this case interstitials segregated at fourfold hollow sites also display nonideal behavior. The excess Gibbs free energy of segregation ΔG Seg xs is evaluated according to the Langmuir-McLean equation. In the case of ϕ XX (1) , ϕ XX (2) = 0 we find − ΔG Seg xs = | ϕ MX (1) | . For ϕ XX (1) , ϕ XX (2) < 0 and low bulk concentrations x ≲ 0.01 there is still Langmuir-McLean behavior, i.e. − ΔG Seg xs = | ϕ MX (1) | = const , but with increasing bulk concentrations strong positive deviations from ideal behavior are found, − ΔG Seg xs = ƒ(θ,T) | ϕ MX (1) | . In contrast, negative deviations − ΔG Seg xs < | ϕ MX (1) | are observed in the case of c(2 × 2) ordered surface phases ( ϕ XX (4) < 0 ), which strongly depends on surface coverage.

Molecular surface tailoring of biomaterials via pulsed RF plasma discharges.

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2 content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

Adsorption of sodium dodecylsulphate on mercury as an example of micellization within a multilayer interphase

The adsorption of sodium dodecylsulphate from aqueous electrolytic solutions on a polarized mercury electrode was studied by means of differential capacitance measurements over a wide range of concentration and potential, and in the presence of different supporting electrolytes with different ionic strengths. An interpretation of the differential capacitance vs. applied potential curves is given, based on theoretical treatments developed previously. It is shown that at concentrations below the cmc, two-dimensional aggregates are formed on the electrode surface within a polarization region which is bounded by two capacitance peaks at extreme positive and negative polarizations. This film is not particularly stable and is transformed into a compact layer at polarizations close to the potential of maximum adsorption, resulting in a capacitance pit. With increasing bulk concentration the aggregation process extends across the interphase and at least two layers of aggregates—micelles are formed at concentrations around and above the cmc. This three-dimensional aggregation is characterized by the appearance of deformed and/or split capacitance peaks which determine the polarization region wherê this phenomenon occurs.

Sb surface segregation during heavy doping of Si(100) grown at low temperature by molecular beam epitaxy

Sb surface segregation and doping during Si(100) molecular beam epitaxy at low temperature have been studied by depth profiling with secondary ion mass spectrometry, x-ray photoelectron spectroscopy, and conductivity measurements. We find that at a growth temperature near 320 °C complete donor activation and doping densities near 5×1020 cm−3 are obtainable. For temperatures between 320–500 °C, measurements point to the existence of distinct surface segregation regimes. For dilute surface and bulk Sb concentrations the measurements reveal a region where the surface segregation is constant and bulk and surface concentrations are linearly related. For bulk concentrations near the solid solubility limit, the surface segregation increases rapidly with increasing bulk concentration for temperatures between 350–450 °C. Finally, for Sb-saturated surfaces the surface segregation actually decreases, and doping levels exceeding the solid solubility limit are possible.