0000000000121710
AUTHOR
Bernd Stühn
Interaction between a water-in-oil microemulsion and a linear-dendritic poly(propylene oxide)–polyglycerol block copolymer
We present small angle scattering and dielectric spectroscopy results on the influence of an amphiphilic diblock copolymer on the structure and dynamics of a microemulsion. We use a water-in-oil (w/o) droplet microemulsion based on the anionic surfactant AOT (sodium bis(2-ethylhexyl) sulfosuccinate), that forms spherical water droplets coated by a monolayer of AOT dispersed in the continuous oil matrix. The studied polymer consists of a hydrophobic poly(propylene oxide) (PPO) block and a hydrophilic hyperbranched polyglycerol with 74 glycerol units (NG74). Combining small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) we find that the droplet structure is preserved …
Thermodynamic and neutron diffraction studies of the nucleation of solid4He on graphite
The nucleation of solid layers of4He on the surface of exfoliated graphite (Grafoil) was investigated by thermodynamic and neutron diffraction measurements. The thermodynamic measurements consisted of recording isopycnals in the vicinity of the melting curve. The isopycnals show a rounding in comparison to the bulk ones, which can be explained by a continuous solidification of4He on the surface of graphite in a layer-by-layer mode in the van der Waals field of the substrate. Moreover, we found a hysteresis behavior of the isopycnals, probably due to defect states in the solidified film. The thickness of the solid film is estimated by means of a simple solidification model. The neutron diffr…
Modulated magnetic structures of ErPb3, HoPb3, ErTl3 and HoTl3
Neutron diffraction experiments have been carried out on the magnetically ordered phases of ErPb3, HoPb3, ErTl3 and HoTl3. The magnetic moments were found to be sinusoidally modulated with a propagation vector of (0, 0.2, 0.5) for the Pb-compounds and (0.38, 0.38, 0.16) for the Tl-compounds.
Chemical structure and internal diffusion within polymer chains in the melt
The single chain dynamics of polydimethylsiloxane in the melt is studied by means of quasielastic neutron scattering. For this polymer the wave vector range 0.03 A−1≦q≦0.30 A−1 covers the regime of universal modes as well as local diffusive processes. A model is described which incorporates the specific chemical structure of the macromolecule and allows to interpret our data in the full wave vector regime. The only parameter which enters the model, the monomer diffusion constantDm, is found to be (1.2±0.2)·10−5 cm2s−1.
Mesogen-Initiated Linear Polyglycerol Isomers: The Ordering Effect of a Single Cholesterol Unit on “Sticky” Isotropic Chains
Synthesis, thermal properties, and the liquid crystalline (LC) order of polymers consisting of a single mesogenic cholesterol unit and flexible, linear polyglycerol (PG) or poly(glyceryl glycerol) (PGG) chains have been investigated. Incorporation of the single mesogen has been achieved by using cholesterol directly as an initiator for the oxyanionic ring-opening polymerization (ROP) of ethoxyethyl glycidyl ether (EEGE) or isopropylidene glyceryl glycidyl ether (IGG). The controlled polymerization allowed the synthesis of a series of peculiar rod–coil type polyethers with molecular weights of 600–2300 g/mol, representing a degree of polymerization (DPn) of 4–30 for both PG and PGG with the …