Gisbert Riess

Inhomogeneities and local chain stretching in partially swollen networks

According to classic single-chain theories of rubber elasticity such as the affine or phantom models, the length N and the state of stretching R/R0 of network chains are directly reflected in the magnitude of segmental orientation correlations, as quantified by a dynamic order parameter S ∝ R2/N (this relation holds for chains in the bulk and θ solvent). S can be determined by suitable NMR techniques, and is a viable molecular probe of the network structure, as it is directly proportional to the elasticity modulus. Furthermore, previous studies (see Saalwachter et al., Soft Matter, 2013, XX, XXX, in this issue for a review) have convincingly demonstrated the validity of the phantom model for the prediction of S in equilibrium-swollen networks. We here investigate changes in the degree of local chain stretching reflected in S as a function of the degree of (partial) swelling Q = V/V0 in different networks prepared in bulk and in states of increasing dilution. Previous work has already revealed a non-monotonic dependence of S on Q, indicating strongly subaffine local deformation in the early stages of swelling. The width of the distribution in S is also accessible, and increases significantly during the early stage of swelling, indicating the well documented presence of swelling heterogeneities. We find that beyond this early stage, the network chains deform affinely. A back-extrapolation of the affine deformation range to zero swelling allows for conclusions on the actual crosslink density of the networks corrected for the effect of topological or packing constraints, which we refer to as the “phantom reference state” of a bulk network. Deviations of the network elasticity from this state constitute non-classical contributions, possible origins of which are discussed.

Chapter 2 – Chemical/physical preprocessing of nanoclay particles

A number of concepts are shown to prepare novel modified montmorillonites. Transition metal cation–exchanged montmorillonites are prepared for the application as Zn2+ ion donor materials for crosslinking reactions, with emphasis on crosslinking XNBR latex. The main aim of the intercalation of Fe3+ ions is the immobilization of the UV reactive species to act as ion donor material for the photochemical crosslinking of polymers. As cation exchange reactions may also be employed to immobilize amino compounds with functional groups such as carboxylic-, mercapto-, or sulfonic acid moieties into the interlayer galleries of montmorillonite. The novel two-step process of acid activation and amino acid intercalation leads to increased organic content as well as repulsion of interlayer water. The obtained modified clay minerals may be utilized as water-based functional fillers or crosslinking agents for water soluble polymers and dispersions such as poly(vinyl alcohol), cellulose ethers, or lattices.

Novel silicone thermoplastic elastomers with tailored permeation properties

The paper deals with the synthesis and properties of thermoplastic silicone elastomers containing soft segments of dimethylsiloxane and hard urea segments. To determine structure-property relations, regarding to permeation properties, the chemical structure was varied. In this study, thermoplastic silicone elastomers, based on polydimethylsiloxane oligomers with amino groups and different diisocyanates, were synthesized. The polymers were characterized by nuclear magnetic resonance (NMR) and infrared (FTIR) spectroscopy. Thin membranes of thermoplastic silicone thermoplastic elastomers were prepared and investigated with respect to the permeation properties of organic solvents. Vials were filled with a mixture of an aromatic (toluene) and an aliphatic hydrocarbon (iso-octane) and were sealed with the polymer films. The weight loss of the vials was measured. The concentration of residual solvent mixture was detected by the relation of the peak area of the two solvents. This was investigated by the GC-MS-te...

Correction: Inhomogeneities and local chain stretching in partially swollen networks

Correction for ‘Inhomogeneities and local chain stretching in partially swollen networks’ by Walter Chasse et al., Soft Matter, 2013, 9, 6943–6954.

Index patterning of photoreactive polymers

Photoreactive polymeric materials have been investigated under one-photon (linear) and two photon (non linear) absorption conditions. A selected chromophore, 4-(N,N-diphenylamino)phenyl benzoate, was covalently attached to different polymer backbones (polystyrene, polynorbornene and polysiloxane). It is shown, that the predominant photoreaction of the chromophore is a photo-decarboxylation (extrusion of CO2) both for two-photon and one-photon conditions. The large increase in refractive index, which results from this reaction, allows the optical patterning of the polymeric systems by conventional and two-photon radiation processes. The materials were investigated by ellipsometry, UV-VIS and FT-IR spectroscopy, FT-IR and phase contrast microscopy. Under two-photon conditions, three-dimensional index structures were inscribed in the polymers, which can be used as optical waveguides.