Concentration Polarization of Interacting Solute Particles in Cross-Flow Membrane Filtration

A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted. Copyright 1999 Academic Press.     

Effect of mild oxidation of natural graphite (NG7) on anode-electrolyte thermal reactions

The effect of mild oxidation of natural graphite (NG7) and some other parameters on the reaction between a fully lithiated graphite anode (Li _x C₆, x=1.0–1.1) and 1 M lithium hexafluoroarsenate in ethylene carbonate and diethyl carbonate electrolyte (1:2, v/v) were studied by differential scanning calorimetry (DSC). It was found that mild oxidation of the graphite suppressed the exothermic reaction of the fully lithiated anode with the electrolyte, most probably as a result of the formation of a more stable and chemically bonded solid electrolyte interphase. Separation and removal of the small graphite particles from the anode mixture suppressed this reaction further. It was also found that the copper current collector, the amount of electrolyte and binder as well as other parameters have a significant influence on the heat evolution as measured by DSC. Received: 11 October 1999 / Accepted: 1 March 2000     

Oxidation and aging of cellulose

Oxidation of cellulose by chlorine, bromine, hydrogen peroxide and ozone and the functional groups formed are reviewed. The roles of the pH and of the nature of the oxidant in the formation of carboxy- and keto-celluloses are discussed. The relationships between the functional groups, degradation and stability of the celluloses enable to predict the aging and storage behavior of the polymer. The “active” carbonyls are responsible for the peeling reaction and the formation of the yellow chromophore in alkaline solutions as well as for the reversion in color on aging. The nature of the yellow chromophore, its spectra at several pH values, its use for the characterization of cellulose, e.g. the rapid determination of the degree of polymerization and for the estimation of the primary and secondary degradation of the polymer and its stability on storage and aging are discussed. The parallelism between the yellowing and the reversion in color is reviewed.     

Sharp thresholds for the phase transition between primitive recursive and Ackermannian Ramsey numbers

We compute the sharp thresholds on g at which g-large and g-regressive Ramsey numbers cease to be primitive recursive and become Ackermannian.We also identify the threshold below which g-regressive colorings have usual Ramsey numbers, that is, admit homogeneous, rather than just min-homogeneous sets.     

Breakdown of colloid filtration theory: role of the secondary energy minimum and surface charge heterogeneities

The mechanisms and causes of deviation from the classical colloid filtration theory (CFT) in the presence of repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions were investigated. The deposition behavior of uniform polystyrene latex colloids in columns packed with spherical soda-lime glass beads was systematically examined over a broad range of physicochemical conditions, whereby both the fluid-phase effluent particle concentration and the profile of retained particles were measured. Experiments conducted with three different-sized particles in a simple (1:1) electrolyte solution reveal the controlling influence of secondary minimum deposition on the deviation from CFT. In a second series of experiments, sodium dodecyl sulfate (SDS) was added to the background electrolyte solution with the intent of masking near-neutrally charged regions of particle and collector surfaces. These results indicate that the addition of a small amount of anionic surfactant is sufficient to reduce the influence of certain surface charge inhomogeneities on the deviation from CFT. To verify the validity of CFT in the absence of surface charge heterogeneities, a third set of experiments was conducted using solutions of high pH to mask the influence of metal oxide impurities on glass bead surfaces. The results demonstrate that both secondary minimum deposition and surface charge heterogeneities contribute significantly to the deviation from CFT generally observed in colloid deposition studies. It is further shown that agreement with CFT is obtained even in the presence of an energy barrier (i.e., repulsive colloidal interactions), suggesting that it is not the general existence of repulsive conditions which causes deviation but rather the combined occurrence of "fast" and "slow" particle deposition.     

Propellanes. LXVI. Exo- and Endo-Diels-Alder adducts of 4-substituted 1,2,4-triazoline-3, 5-diones with various 1, 6-methano [10]annulenes

Relatively few exo-adducts have been obtained from the title compounds. Only one such mono-adduct, 3 , is known. Several exo-endo-bis-adducts have been obtained but the structure of one of these, 5 , has been proved unequivocally by X-ray structural determination.     

The chemistry of THPC–urea polymers and relationship to flame retardance on wool and wool-polyester blends. I. Chemistry of THPC–urea polymers

Polymer formation from THPOH-urea, THPOH-dichloropropanol-urea, and THPC-urea was studied. Order and rate of urea addition were shown to influence insoluble polymer yields as well as polymer structure. The polymers were characterized by elemental analyses and infrared spectroscopy, and predominant structures proposed. The structures were correlated with thermogravimetric and differential scanning calorimetry data and probable thermal decomposition paths.     

Fluorescence Polarization as a Functional Parameter in Monitoring Living Cells: Theory and Practice

The use of fluorescence polarization as a functional parameter in monitoring cellular activation calls for the reliable and accurate measurement of the fluorescence intensity and polarization (FI and FP) of microscopic objects. The relevant experimental parameters that enter such measurements are thoroughly discussed. The possibility of executing FP measurements properly by flow-through systems is compared with that of static cytometry. Remarks on the effects of high-power excitation on markers and cells conclude the paper.     

New approach to the effects of pressure dependence on sedimentation velocity experiments

A theory is developed for sedimentation velocity experiments when the sedimentation coefficient s_p depends on pressure P as s_p/s_o = (1 + γP)^?1, where γ is a constant. In contrast to the more usually analyzed from s_p/s_o = 1 ? γP, this model does not lead, in extreme cases, to a negative sedimentation rate. A theory is presented for homogeneous macromolecules sedimenting with no diffusion. It leads to estimations of s_o and γ from a knowledge of the point of maximum concentration gradient as a function of time. Results of these calculations are compared with accurate numerical solutions of the Lamm equation with diffusion included.     

Are HO radicals produced in the reaction of O(3P) with 1-C4H8?

The reaction of O(³P) with 1-C₄H₈ was examined in the presence of CO which scavenges HO radicals to produce CO₂. From the CO₂ quantum yield, an upper limit to the efficiency of HO production in the reaction of O(³P) with 1-C₄H₈ was found to be 0.02 at both 298° and 473°K.