Ralf Zimehl

Coagulation of latex dispersions in the presence of some organic compounds

Abstract Three different types of polystyrene latices were prepared. Latex 1 prepared without emulsifier is a “classical” latex that behaves like common hyd The salt stability of the dispersions responds sensitively to the surface structure and is greatly influenced by some organic compounds (acetone, aceta The properties of type-2 latices depend on the concentration of the radical initiator during the preparation. Latices prepared at low initiator concent

SOME ASPECTS OF POLYMER COLLOIDS. I, PREPARATION AND PROPERTIES OF DIFFERENT TYPES OF LATEX PARTICLES

The boundary region separating a latex particle from the surrounding medium has a great influence on the properties of latex dispersions. Four types of polystyrene and polystyrene/comonomer latices differing greatly in the structure of the boundary region were prepared. The first part of a series of papers reports on the preparation of the various latex dispersions. Mean particle sizes were obtained from simple turbidity measurements, quasi-elastic light scattering, and electron micrographs. The behavior of the particles in the centrifugal force field is a simple tool for detecting aggregation tendencies that are not directly related to salt stability. The BET-surface area agrees with the area calculated from the mean particle size when a sharp boundary and smooth surface is developed between the particle and the surrounding medium. In the case of particles with extended boundary regions (core/shell particles or particles with hairy envelopes), film formation reduces the specific surface area. Removal of soluble oligomers and polymers from the boundary region during subsequent treatments (purification and centrifugation before freeze-drying) can increase the surface area considerably.

Sorption of binary liquid mixtures on polymer networks Part I. Determination of surface excess isotherms and free energy functions

Two groups of polymer networks (polymer resins) are investigated by selective liquid sorption fromn-propanol-water mixtures. Group 1 consists of gel polymerized polar (hydrophilic) ion exchangers which swell in the binary liquid mixture. Group 2 consists of non-polar, non-swelling, macroporous resins. The free energy isotherms accompanying the sorption processes are calculated from the excess isotherms and the bulk activities. The adsorption excess free energies reveal the differences in polarity of the polymer network.

Oberflächenpotential und elektrokinetisches Potential

Die Ladungen an der Oberflache eines Teilchens erzeugen ein Potential ψ, das unmittelbar an der Grenzflache den Wert ψ 0 hat und zur Losung hin abfallt. Weit weg vom Teilchen ist ψ = 0 (Kap. 2.3.1). Wie sich das Potential mit zunehmendem Abstand von der Grenzflache andert, hangt von der Verteilung der Ionen zwischen Grenzflache und Losung ab. Modelle, die diese Verteilung beschreiben, wurden bereits diskutiert (Kap. 2.3.2, 9.4).

Herstellung und Eigenschaften von Emulsionen

Emulsionen sind disperse Systeme, bei denen eine flussige Phase (dispergierte Phase, innere Phase) in eine andere flussige Phase (koharente Phase, ausere Phase) verteilt ist (Becher, 1983, 1985, 1988; Lissant, 1974, 1984; Shah, 1985; Rieger, 1986; Myers, 1988; Stache, 1990; Heusch, 1993). Das Phasenvolumen-verhaltnis φ ist der Quotient aus dem Volumen V i der inneren Phase und dem der auseren:

Adsorption aus binären Flüssigkeitsmischungen

\phi = V_i /V_a .

Elektrostatisch stabilisierte Dispersionen (DLVO-Theorie)

(7.1)

Kolloidale Verteilungen und ihre technische Bedeutung

Die Stabilitat elektrostatisch stabilisierter Dispersionen wird durch die elektrostatische Abstosung V R und die Van-der-Waals-Anziehung V A bestimmt. Die Potentialkurve V T = V A + V R einer stabilen Dispersion zeigt eine Energiebarriere V m (Kap. 2.6; Abb. 2.13–2.15), die mit steigendem Salzgehalt abnimmt. Wenn V T,max unter 15 kT absinkt, wird die Dispersion instabil und koaguliert. Die dazu notwendige kritische Koagulationskonzentration c K des Salzes hangt empfindlich von der Wertigkeit υ des Gegenions ab.