52 research outputs found
Multinational enterprises, development and globalisation: some clarifications and a research agenda
Critical Casimir effect in classical binary liquid mixtures
If a fluctuating medium is confined, the ensuing perturbation of its
fluctuation spectrum generates Casimir-like effective forces acting on its
confining surfaces. Near a continuous phase transition of such a medium the
corresponding order parameter fluctuations occur on all length scales and
therefore close to the critical point this effect acquires a universal
character, i.e., to a large extent it is independent of the microscopic details
of the actual system. Accordingly it can be calculated theoretically by
studying suitable representative model systems.
We report on the direct measurement of critical Casimir forces by total
internal reflection microscopy (TIRM), with femto-Newton resolution. The
corresponding potentials are determined for individual colloidal particles
floating above a substrate under the action of the critical thermal noise in
the solvent medium, constituted by a binary liquid mixture of water and
2,6-lutidine near its lower consolute point. Depending on the relative
adsorption preferences of the colloid and substrate surfaces with respect to
the two components of the binary liquid mixture, we observe that, upon
approaching the critical point of the solvent, attractive or repulsive forces
emerge and supersede those prevailing away from it. Based on the knowledge of
the critical Casimir forces acting in film geometries within the Ising
universality class and with equal or opposing boundary conditions, we provide
the corresponding theoretical predictions for the sphere-planar wall geometry
of the experiment. The experimental data for the effective potential can be
interpreted consistently in terms of these predictions and a remarkable
quantitative agreement is observed.Comment: 30 pages, 17 figure
Visualization and Quantitative Analysis of Reconstituted Tight Junctions Using Localization Microscopy
Tight Junctions (TJ) regulate paracellular permeability of tissue barriers. Claudins (Cld) form the backbone of TJ-strands. Pore-forming claudins determine the permeability for ions, whereas that for solutes and macromolecules is assumed to be crucially restricted by the strand morphology (i.e., density, branching and continuity). To investigate determinants of the morphology of TJ-strands we established a novel approach using localization microscopy
Composition profiling in a binary polymer blend thin film using polarized neutron reflectivity
The concentration profile in an ultra-thin film (film thickness d =
435Â Ã…) of a high molecular mass poly(isoprene)/deuterated
poly(butadiene) blend is measured in the bulk system's miscible region
with a new polarized neutron reflectivity method. By using a buried
ferromagnetic layer inside the wafer and a polarized neutron beam, it
is possible to obtain the neutron specular reflection amplitude A
including its phase angle φ. Conventional reflectivity
measurements only determine the reflected intensity I=A2 which does
not contain information on the phase angle. Only the knowledge of the
phase angle allows an unambiguous determination of the neutron
scattering length density profile of the film. The scattering length
density profile thus obtained reveals poly(isoprene) segregating
symmetrically to the polymer/air and polymer/Si interfaces. The
adsorption profile at both interfaces can be approximately described
using an exponential- or tanh-function with a decay constant smaller
than the bulk correlation length
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