Die adsorption von makromolekülen. I. Über eine neue meßmethode

Abstract

ZUSAMMENFASSUNG:Es wird eine statische Methode beschrieben, die die Adsorption und Desorption von Polymeren an Folien und Membranen aus Losungen zu verfolgen gestattet. Aus den erhaltenen Adsorptionszeitkurven konnen die adsorbierten Mengen, die Adsorptionsgeschwindigkeiten und die diesen entsprechenden Aktivierungsenergien ermittelt werden.Im einzelnen werden Adsorptionsgleicbgewichte von Polyvinylacetat, Polyithylenglykol, Polyvinylpyrrolidon, Polyvinylalkohol und Polymethacrylsiureester an verschiedenen Adsorbentien in Abhlingigkeit von der Konzentration, dem Molekulargewicht und der Temperatur untersucht.Die Form der Isothermen weicht von den bisher beschriebenen insofern ab, als -bis auf eine Ausnahme -im me5baren Bereich keine Sattigung der Adsorbensobedichen beobachtet wurde und die adsorbierten Mengen betrlchtlich hoher d s bisher beschrieben gefunden wurden.Die Desorption verliiuft in den untersuchten Systemen ohne nennenswerten wigbaren Ruckstand (Ausnahme : Polyvinylacetat aus Butanon an Cellophan). SUMMARY:A statical method is described, which allows to observe directly the adsorption and desorption of polymers on foils and membranes from solutions. Amounts adsorbed, adsobtion rates and the corresponding activation energies may be evaluated from the experimental time-adsorption diagrams. Values for the adsorption equilibrium of polyvinyl acetate, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol and polymethacrylic ester on different adsorbents in dependence of polymer concentration, molecular weight of polymer and temperature were analysed.The amounts adsorbed are considerably higher than those found by others. Except in one case saturation was never reached. Adsorption-desorption shows almost negligibly hysteresis. (Exception: polyvinyl acetate from butanone on sheet-cellulose).,

Adsorption of ionizable polymers on ionic surfaces: poly(acrylic acid)

“…If one assumes that all extinction coefficients are similar in magnitude, then one can write .XAg ^ (12) Cta' = C., + Cb (13) Ca" = Cf + Cta (14) where C and a" are the repeating-unit concentration and degree of ionization in the original solution, respectively, and a' is the degree of ionization in the adsorbed layer. Substituting eq 10,11, 13 and 14 into eq 12, one obtains the expression XAa -(Ca'QqLpu ^pls(eb ~~ef) (15) Equation 15 justifies the use of (8) as an indication of trends in the extent of the adsorbate's interaction with the surface. XAa is equal to the carboxylate ion absorbance of the powder-liquid slurry (Apla).…”

Surface Properties as Physico-Chemical Phenomena

“…The sensitivity values given in Table 2 (21) are valid under these conditions. The radiation emission of labelled compounds can be determined by radiographic methods (29) on distinctly localized sites.…”

“…A more recent and promising approach to surface area determination is the use of radioisotopes (21,24,25,26) (Table 2). Table 2 Most important β radioisotopes for labelling of compounds, according to K chler (21) Radioisotopes Radioisotopes can be used advantageously not only for surface area determinations but also for the study of a multitude of chemical and physical surface or interfacial phenomena, e. g., in metallurgy for the investigation of surface and grain boundary conditions, diffusion, corrosion, contamination, lubrication, and wear, and in surface finishing and adhesion of various materials.…”

Adsorption Kinetics of Amphipathic Polystyrene-block-polybutadiene onto Silicon Wafer and Polystyrene Planar Surfaces

“…Since the amount of adsorbed block copolymers increases with temperature, it follows that the adsorption proceeds with an increase in enthalpy, and this differs from the conventional adsorption of low molecular substances; that is, heat is evolved. However, in many other cases involving the adsorption of polymers on solid substrates a considerable increase in polymer adsorption with temperature was also observed. , From the temperature dependence of the adsorption, one can calculate the thermal effect of the adsorption, which is a complex function of the intrinsic heat of adsorption, i.e., the heat of interaction of the polymer with the substrate, (−Δ ), and the sum of the heat of desorption of the solvent molecules from the substrate surface, (−Δ ), the heat of interaction of polymer chains with the solvent, (−Δ ), and the heat of interaction of polymer chains in aggregates (clusters or micelles) in bulk, (−Δ ); i.e., The overall negative heat of adsorption (positive values for enthalpies) indicates that the last three terms of the equation are larger than the first. The spontaneous adsorption process, involving an increase in the enthalpy of the system, should be accompanied by an entropy gain that is appreciably greater than the enthalpy to ensure a negative value of the free energy change during adsorption.…”