Zur methodik thermischer diffusionsmessungen von makromolekülen in lösung

Abstract

ZUSAMMENFASSUNG:Die experimentellen und theoretischen Grundlagen der Konzentrationsdiffusion, thermischen Diffusion und Thermodiffusion werden zusammengestellt. Bei der thermischen Diffusion war es bisher nicht moglich, wie bei den iibrigen Diffusionsversuchen, den Konzentrationsverlauf kontinuierlich einwandfrei zu verfolgen. Der Temperaturgradient des reinen Losungsmittels ergibt eine zu grone h d e r u n g des Brechungsindex. Es wird daher eine Zelle beschrieben, die diesen Temperaturgradienten mittels ekes Umkehrprismas eliminiert. AuBerdem wird eine Vorrichtung zur Gewinnung einer scharfen Anfangsgrenzschicht zwischen Losung und Losungsmittel angegeben. Die Apparatur wird zur Messung des thermischen Diffusionskoeffizienten von Polystyrol in Toluol benutzt. SUMMARY:Experimental and theoretical foundations of concentration diffusion, thermal diffusion and thermodiffusion are given. Diffusion and thermodiffusion is usually observed continually. For thermal diffusion this was hitherto not possible in a satisfactory manner owing the great difference of index of refraction resulting from the temperature gradient of the pure solvent. A cell is described eliminating this effect by means of a reversal prism. Moreover an apparatus is given, which creates a sharp starting boundary between solution and solvent by shifting in combination with sharpening, The cell is used to measure the thermal diffusion coefficients of polystyrene in toluene. Die ersten Diffusionsmessungen fuhrte F I C K~) 1855 aus. Fast zur gleichen Zeit entdeckte LUDWIG~) 1856 den Thermodiffusionseffekt, den

An evaluation of column thermal diffusion as a means of polymer characterization

“…Drickamer's theory of polymer thermal diffusion (12) The calculated thermal diffusion coefficients presented in Table VIII are of the same order of magnitude as the few data available in the literature (14)(15)(16). With regard to the usefulness of column thermal diffusion for molecular weight characterization of linear homologous high polymers, the following conclusions may be made:…”

“…where c is the concentration. The concentration gradient established in a thermal diffusion cell is the result of a balance between the separation tendency due to thermal diffusion and the resultant remixing due to ordinary diffusion, and therefore it is apparent that a, and not D' alone, determines the steady state separation, The cell method has been modified to provide a direct measure of the thermal diffusion coefficient D' through observation of the rate of motion of the boundary between layers of solution and solvent in a temperature gradient (14)(15)(16).…”

Thermal field-flow fractionation of polymers with exponential temperature programming

“…For highly retained components L= CtR(Rv0) d£ = 6PvoM~a f£R(l/AT)d£ (12) Jt=o Jt=o when ft " ve/v0 ~to/tfl ~ (13) with L = channel length (cm), t0 = solvent peak-elution time, vs = velocity of the solute migration down the channel (cm/s), and vQ = L/t0.…”

“…Data from the refractive (RI) index detector in Figure 12 produced results that were more easily interpreted, relative to UV detection at 215 nm, because of reduced Thermal Field Flow Fractionation of Polymers 2311 V0 Figure 12. Molecular weight characterization of Lucite 40 acrylic resin by TDE-TFFF.…”