We report on salt-dependent interaction potentials of a single charged
particle suspended in a binary liquid mixture above a charged wall. For
symmetric boundary conditions (BC) we observe attractive particle-wall
interaction forces which are similar to critical Casimir forces previously
observed in salt-free mixtures. However, in case of antisymmetric BC we find a
temperature-dependent crossover from attractive to repulsive forces which is in
strong contrast to salt-free conditions. Additionally performed small-angle
x-ray scattering experiments demonstrate that the bulk critical fluctuations
are not affected by the addition of salt. This suggests that the observed
crossover can not be attributed alone to critical Casimir forces. Instead our
experiments point towards a possible coupling between the ionic distributions
and the concentration profiles in the binary mixture which then affects the
interaction potentials in such systems.Comment: 5 pages, 4 Figure
Digital video-microscopy measurements are reported of both elastic bandstructures and overdamped phonon decay times in two-dimensional colloidal crystals. Both quantities together allow to determine the friction coefficients along various high symmetry directions in q-space. These coefficients contain valuable information on the hydrodynamic forces acting between the colloidal particles. We find Stokes-like friction for phonons near the edge of the first Brillouin zone and vanishing friction coefficients for long wavelength phonons. The effect of this wavelength dependence in real-space is further investigated by simulating a crystal with constant friction (Langevin simulation) and comparing experimentally measured and simulated particle auto-correlation functions.
A transition metal‐free method for the cycloisomerization of propargylic amides to oxazoles was developed. The reaction utilizes in situ generated hydrogen chloride in hexafluoroisopropanol (HFIP). With the aid of Design of Experiments optimization a wide range of substrates was transformed into the desired oxazoles. The method allows product formation without side reactions eliminating the need for extensive work‐up and purification.
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