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316(5-6) (2000), 343-348
A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly( p- phenylene vinylene) (PPV) alternating with poly(thiophene acetic acid) (PTAA). Quenching is caused by a photo-induced electron transfer between the excited PPV (donor, D) and the PTAA (acceptor, A). The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers, As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate can be described as k = Z exp(- beta r) where r is the distance between D and A. (C) 2000 Elsevier Science B.V. All rights reserved.

[50] Controlled Synthesis of Stable Poly(Vinyl Formamide-Co-Vinyl Amine)/Silica Hybrid Particles by Interfacial Post-Cross- Linking Reactions

I. Voigt, F. Simon, H. Komber, H. J. Jacobasch and S. Spange

Colloid Polym. Sci. 278(1) (2000), 48-56

The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA). and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4'-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/ silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state C-13 cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods.

[51] Synchronous Alternate Multilayered Adsorption of Poly(4-Vinyl-N- N-Butylpyridinium) Cations and Poly(Styrene Sulfonate) Anions on Polystyrene Colloidal Spheres

T. Okubo and M. Suda

Colloid Polym. Sci. 278(4) (2000), 380-384

Alternate multiple adsorbed layers of up to six macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on monodispersed polystyrene colloidal spheres above the critical concentration of the macroions, m*. The m* value is the minimum number of macroions needed to reverse the sign of the zeta potential of the spheres in the first adsorption step. Alternate sign reversal in the zeta potential and expansive-contractive thickness changes are observed on the repeated and alternate addition of macrocations first and macroanions next. When the macroanions are added first, sign reversal in the zeta potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type adsorption also occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of macrocations and macroanions in the multiple-adsorbed layers occurs only when the conformational rigidities with the multiple electrostatic and hydrophobic attraction and/or repulsion between macrocations and macroanions are delicately balanced.

[52] From Langmuir Monolayers to Nanocapsules

H. Möhwald

Colloid Surf. A