1,721,035 research outputs found
An extrapolation procedure to obtain the total fringe number from Gouy fringe pattern data
No full textA rapid new procedure is described for getting the total no. of fringes J from Gouy fringe pattern data. This PQ method is exact and the results excellent (within 0.01 - 0.03 fringe) for ideal systems (Ωj = 0 for all j, Q0 = 0). Such systems include most binaries; for these, the diffusion coeff. is either const. or a polynomial function of concn. with small concn. differences. For multicomponent systems and some binaries, Q0 can be significantly different from 0. In these cases, the PQ method unambiguously gives the integer no. of fringes. If in addn. Q0/Q1 is larger than 2.0, then J obtained from a second extrapolation procedure is also good
Velocity correlation analysis in polymer-solvent mixtures
No full textThe subject of this article is the combined interpretation of intradiffusion and mutual-diffusion data for polymer-solvent mixtures in terms of integrals over velocity self-correlation functions and velocity cross-correlation functions. The combination of mutual-diffusion, intradiffusion, and activity data allows the evaluation of velocity-correlation coefficients (VCCs) and distinct-diffusion coefficients in systems containing one monodisperse solute. This study is the first attempt to extend these approaches to polymers that are polydisperse solutes. Because of the polydispersity, this correlation analysis may become critical for polymers. Its application to polydisperse samples requires the reduction of intradiffusion and mutual-diffusion coefficients to the same average. After such a reduction, the VCCs and distinct-diffusion coefficients are evaluated for a homologous series of poly(ethylene glycol)s (PEGs). Attractive PEG-PEG interactions depend on the chain length and concentration of PEG. In this analysis, network formation in PEG-water systems appears to be a smooth process
Velocity correlation analysis in polymer-solvent mixtures
No full textThe subject of this article is the combined interpretation of intradiffusion and mutual-diffusion data for polymer-solvent mixtures in terms of integrals over velocity self-correlation functions and velocity cross-correlation functions. The combination of mutual-diffusion, intradiffusion, and activity data allows the evaluation of velocity-correlation coefficients (VCCs) and distinct-diffusion coefficients in systems containing one monodisperse solute. This study is the first attempt to extend these approaches to polymers that are polydisperse solutes. Because of the polydispersity, this correlation analysis may become critical for polymers. Its application to polydisperse samples requires the reduction of intradiffusion and mutual-diffusion coefficients to the same average. After such a reduction, the VCCs and distinct-diffusion coefficients are evaluated for a homologous series of poly(ethylene glycol)s (PEGs). Attractive PEG-PEG interactions depend on the chain length and concentration of PEG. In this analysis, network formation in PEG-water systems appears to be a smooth process
Multicomponent diffusion in solutions where crystals grow
No full textThe correct study of diffusive time evolution of concentration boundaries in n-component systems requires the use of all the (n-1)(2) diffusion coefficients defined by Fick's law. However, to simplify the analysis, the so-called pseudo-binary approximation is very often used. This can lead to very misleading results. On the other hand, the possibility to predict the diffusional behaviour of rt-component systems from the properties of corresponding binaries and from the knowledge of the solute-solute cross-interactions should be a very important goal. If no "chemical" solute-solute interactions are present in solution, the diffusion coefficients depend only on the "hydrodynamic" or volumetric solute-solute interactions. This contribution, which is mostly reflected in the cross-diffusion coefficient values, is always present and assumes an important role in solutions containing macromolecular solutes. It is then very important in modelling the diffusion phenomena in systems where a protein can crystallise in the presence of polymeric solutes as precipitating agents. The present paper is devoted to the study of the hydrodynamic effects on the diffusion coefficients of poly(ethyleneglycol) samples, which is one of the widely precipitating agents used in the protein precipitation. A predictive model to evaluate the diffusion coefficients in the presence of the only hydrodynamic effect was applied with good success to the systems presented and to a literature system NaCl-lysozyme-water
Diffusion properties of cyclodextrins in aqueous solution at 25°C
No full textDiffusion, density, and viscosity data are collected for the systems α-cyclodextrin and β-cyclodextrin in water. Frictional coeffs. were computed with the help of literature activity data and a qual. discussion of their concn. dependence was attempted
Hydrophobic interactions of alkanols. A calorimetric study in water at 298.15 K
No full textEnthalpies of dilution in water of binary aqueous solutions of n-diols of increasing alkyl chain length are performed using a flow microcalorimeter. The pairwise enthalpic coefficients of these hydrophobic solutes depend mainly on the mutual positions of the -OH groups in the molecule. A rationalization of the excess enthalpies of positional isomers is attempted
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