S. Rohrsetzer

A new experimental method for determination of the repulsive force-distance relationship between disperse particles

A new method for determination of osmotic pressure in electrostatically stabilized monodisperse dispersion has been developed.From the measured pressure supposing different structures the particle-particle interaction as a function of particle distance has been derived. It was found that in the used homogeneous force field the average structure of the latex dispersion is cubic or slightly deformed cubic lattice.The theoretically calculated pair interaction force vs. particle distance functions have been compared with the experimental values.

Investigation of adsorbed polymer layers by flocculation of oppositely charged sols III. Effect of molecular mass of polymers

The stabilizing effect of water-soluble neutral polymers with different chemical structure and relative molecular mass on AgI sol has been studied. It was shown that the stabilizing effect of the polymers used is independent of the relative molecular mass of the polymer when equal amounts of the adsorbed polymers are compared with each other as stabilizers. The high stabilizing effect of polymers with high relative molecular mass is presumably due to the larger adsorbed amount.Among polyvinyl alcohol, polyvinyl pyrrolidone and methylcellulose, polyvinyl pyrrolidone exhibits the smallest stabilizing layer thickness at equal adsorbed amounts. According to our earlier results this is due to the fact that the polyvinyl pyrrolidone shows the strongest affinity for AgI surfaces, forming short loops or tails.

Surface properties of sol particles I. Dependence of peptizability of flocculated sols on the aging time

SummaryThe peptizability of floes of various sols was studied as a function of peptizer concentration and of the aging period of flocs. The order of peptizability of these sols correlates well with the order of other properties such as the kinetic stability, the recrystallization during drying and the resistance against freezing. The presented experimental technique appears to be suitable for a qualitative characterization of the rate of surface recrystallization of various sols. On the basis of the obtained results, the rate of recrystallization may be suggested as a factor determining the kinetic stability of relatively stable sols in addition to the height of the barrier of the repulsive potential.ZusammenfassungEs wurde die Peptisierbarkeit von Koagula verschiedener Sole in Abhängigkeit von der Peptisatorkonzentration und der Alterungszeit untersucht. Die Reihenfolge der Peptisierbarkeit stimmt in befriedigen dem Maße überein mit der von anderen Eigenschaften, wie z. B. der Stabilität der Sole, der Rekristallisationsfähigkeit der Teilchen unter dem Einfluß des Trocknens und der Beständigkeit gegen Frostkoagulation.Die beschriebene Methode ist auch anwendbar, um die Rekristallisationsgeschwindigkeit auf halbquantitative Weise zu charakterisieren. Aus den Ergebnissen haben wir gefolgert, daß für die Beständigkeit der verhältnismäßig stabilen Sole neben dem Verlauf der Potentialkurven auch die Rekristallisationsfähigkeit eine wichtige Rolle spielt.

Der Einfluß des Gefrierens auf die As2S3-Sole

Zusammenfassung1.Es wird die Einwirkung des Gefrierens auf die Eigenschaften der As2S3-Sole untersucht. Es wird festgestellt, daß die mit NaOH oder Na2S versetzten Sole beim Gefrieren nicht koagulieren, dagegen zeigen sie eine auffallende Farbänderung. Die ursprünglich gelben Sole wandeln sich nämlich in sehr beständige, tiefrot gefärbte Sole um.2.Die Intensität der roten Farbe nimmt im gefrorenen Zustand mit der Zeit zu. Die Bildungsgeschwindigkeit der roten Sole ist von der Temperatur abhängig und ändert sich entsprechend einer Maximumkurve.3.Das rote As2S3-Sol zeigt Thixotropie und Strömungsdoppelbrechung. Diese Eigenschaften sind auf die Bildung von anisodimensionalen Sekundärteilchen zurückzuführen. Es wird vorgeschlagen, die durch Gefrieren hervorgerufene orientierte Koagulation alsKryotropie zu bezeichnen.4.Bei höheren Temperaturen geht in den roten Solen eine Desaggregation vor sich, die roten Sole wandeln sich wieder in gelbe Sole mit nahezu ursprünglichen Eigenschaften um.

Investigation of adsorbed polymer layers by flocculation of oppositely charged sols

Measuring the flocculation of oppositely charged sols is a suitable method for investigating the stabilizing effect of thick adsorbed polymer layers since the values of the electrical attractive potential are much higher than those of the van der Waals-London attraction. In this case flocculation occurs at low electrolyte concentrations and thus the precipitation of the polymer that normally occurs at high electrolyte concentration can be prevented. These observations were proved by the mutual flocculation of positively charged Fe2O3-sol and negatively AgI-sol, in the presence of large amounts of adsorbed polyvinylalcohol. The total free energy of interaction has been calculated for 1.5 mg/m2 adsorbed polymer amount and for two electrolyte concentrations, and the results were in saticfactory agreement with the experimental values.

Surface properties of sol particles

SummaryThe adsorption of neutral macromolecules and ionic surfactants on various sols, as well as the effect of these substances on the stability of the sols were investigated. Sols having high recrystallization rate do adsorb both macromolecules and ionic surfactants; the adsorption isotherms are of the high affinity type. However, neutral macromolecules are not adsorbed at all by sols having low recrystallization rates. With these the adsorption isotherms of the ionic surfactants are of the Langmuir type.The stability of the arsenic trisulphide sol is affected by macromolecules and surfactants in a way differing from that of other sols examined. The As2S3-sol, too, has the highest recrystallization rate. In all cases the interfacial energy is supposed to be the determining factor.ZusammenfassungWir haben die Adsorption von neutralen Makromolekülen und ionischen Tensiden an verschiedenen Solen, sowie den Einfluß dieser Stoffe auf die Stabilität dieser Sole untersucht.Wir haben festgestellt, daß auf jenen Solen, deren Teilchen nur relativ wenig rekristallisieren, die Makromoleküle nicht, die Tenside dagegen adsorbiert werden; die Adsorptionsisotherme entspricht dem Langmuir-Typ. Demgegenüber adsorbieren jene Sole, welche eine große Rekristallisationsfähigkeit besitzen, sowohl die Makromoleküle wie auch die Tenside, wobei die Isothermen vom sog. Hochaktivitätstyp sind.Unter den untersuchten Solen besitzt das Arsentrisulfid die größte Rekristallisationsfähigkeit. Der Einfluß der Makromoleküle und der Tenside auf die Stabilität dieses Sols unterscheidet sich vom Einfluß auf die anderen untersuchten Sole.Die Korrelation zwischen den untersuchten Eigenschaften weist darauf hin, daß in allen Fällen die Grenzflächenenergie der Solteilchen der wichtigste Faktor ist.

Investigation of adsorbed polymer layers by flocculation of oppositely charged sols - II. Determination of relative stabilizing layer thickness

The stabilizing effect of water-soluble neutral polymers and of their 1∶1 (w/w) mixtures on the mutual flocculation of a positively charged Fe2O3 sol and a negatively charged AgI was investigated. The electrical attraction potential vs. particle surface separations curves were calculated at three different electrolyte concentrations. From these curves the approximate thickness of the adsorbed polymer layer required for the stabilization (slow flocculation) was constructed. These thicknesses are denoted as relative stabilizing layer thicknesses (Hst). The adsorbed polymer amounts required for the stabilization (equivalent stabilizing amounts,ast) have also been determined at three different electrolyte concentrations. TheHst vs.ast curves are characteristic both for the stabilizing effect of the different polymers and the changes of the stabilizing layer thickness with the adsorbed amount. Furthermore, they offer a possibility to calculate whether the stabilizing effect of the mixed polymer layers does, or does not, deviate from the values of the polymer components by assuming additivity.