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Small angle neutron scattering study of the micelle structure of amphiphilic block copolymers
The amphiphilic block copolymers of vinyl ether were prepared by living cationic polymerization. The partially deuterated copolymers for SANS experiments were especially synthesized by introducing deuterated phenyl units in the hydrophobic chain. SANS measurements were performed for aqueous solutions of these copolymers by changing H{sub 2}O/D{sub 2}O ratios. The SANS profiles indicate that the micelles in the present system exhibit a core-shell structure and that the size and shape of micelles are largely dependent on the length of hydrophobic chain. The micelle of shorter hydrophobic chain was found to be nearly spherical, whereas the micelle of longer hydrophobic chain was confirmed to have an ellipsoidal shape
Independent Ion Migration in Suspensions of Strongly Interacting Charged Colloidal Spheres
We report on sytematic measurements of the low frequency conductivity in
aequous supensions of highly charged colloidal spheres. System preparation in a
closed tubing system results in precisely controlled number densities between
1E16/m3 and 1E19/m^3 (packing fractions between 1E-7 and 1E-2) and electrolyte
concentrations between 1E-7 and 1E-3 mol/l. Due to long ranged Coulomb
repulsion some of the systems show a pronounced fluid or crystalline order.
Under deionized conditions we find s to depend linearily on the packing
fraction with no detectable influence of the phase transitions. Further at
constant packing fraction s increases sublinearily with increasing number of
dissociable surface groups N. As a function of c the conductivity shows
pronounced differences depending on the kind of electrolyte used. We propose a
simple yet powerful model based on independent migration of all species present
and additivity of the respective conductivity contributions. It takes account
of small ion macro-ion interactions in terms of an effectivly transported
charge. The model successfully describes our qualitatively complex experimental
observations. It further facilitates quantitative estimates of conductivity
over a wide range of particle and experimental parameters.Comment: 32 pages, 17 figures, 2 tables, Accepted by Physical Review
Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination
When an azobenzene-containing polymer film is exposed to a non-uniform
illumination, a light-induced mass migration process may be induced, leading to
the formation of relief patterns on the polymer free surface. Despite a
research effort of many years and several proposed models many aspects of this
phenomenon remain not well understood. Here we report the appearance of
spiral-shaped relief patterns on the polymer under the illumination of focused
Laguerre-Gauss beams, having helical wavefront and an optical vortex at their
axis. The induced spiral reliefs are sensitive to the vortex topological charge
and to the wavefront handedness. These findings are unexpected, because the
"doughnut"-shaped intensity profile of Laguerre- Gauss beams contains no
information about the wavefront handedness. We propose a model that explains
the main features of this phenomenon from the surface-mediated interference of
the longitudinal and the transverse components of the optical field. These
results may find applications in optical micro- and nanolithography and
optical-field.Comment: Open Access at Journal Reference homepag