Search PubMed⌕ Search

Biomedical subjects

P Ziherl

Publications and source records attributed to P Ziherl.

7 recordsLinked to original sources
PubMed2002

Foam analogy in charged colloidal crystals.

We model charged colloidal suspensions using an analogy with foams. We study the solid-solid phase transitions of these systems as a function of particle volume fraction and ionic strength. The screened-Coulomb interaction is replaced by an interaction between walls of the Voronoi cells around each particle. We fit the surface charge to reproduce the phase diagram for the charged suspension studied by Sirota et al. [Phys. Rev. Lett. 62, 1524 (1989)]. With this fit parameter we are able to calculate the elastic moduli of the system and find good agreement with the available data.

Journal Article↗
PubMed2000

Soap froths and crystal structures

We propose a physical mechanism to explain the crystal symmetries found in macromolecular and supramolecular micellar materials. We argue that the packing entropy of the hard micellar cores is frustrated by the entropic interaction of their brushlike coronas. The latter interaction is treated as a surface effect between neighboring Voronoi cells. The observed crystal structures correspond to the Kelvin and Weaire-Phelan minimal foams. We show that these structures are stable for reasonable areal entropy densities.

Journal Article↗
PubMed2000

Pseudo-casimir structural force drives spinodal dewetting in nematic liquid crystals

We analyze theoretically the fluctuation-induced force in thin nematic films subject to competing surface interactions, and we find that the force is attractive at small distances and repulsive otherwise. The results provide a consistent interpretation of a recent study of spinodal dewetting of 5CB on a silicon wafer [F. Vandenbrouck et al., Phys. Rev. Lett. 82, 2693 (1999)], implying that this experiment can be regarded as the first observation of the pseudo-Casimir effect in liquid crystals.

Journal Article↗
PubMed2000

Structural force in a presmectic liquid

The structural interaction in a presmectic film is analyzed theoretically using the Cartesian rather than the polar representation of the smectic order parameter. This representation diagonalizes the phenomenological Hamiltonian of the ordering and leads to a unified description of the mean-field interaction-first studied by de Gennes [Langmuir 6, 1448 (1990)]-and the fluctuation-induced interaction. The fluctuation-induced interaction turns out to be short-range, attractive, and unaffected by the apparent bidomain structure of the film, which controls the oscillatory mean-field interaction.

Journal Article↗
PubMed2000

Pseudo-Casimir effect in nematic liquid crystals in frustrating geometries

We study theoretically the fluctuation-induced structural force in nematic systems frustrated by external fields. We focus on the uniform director structure in the hybrid-aligned film characterized by opposing surface fields and in the Freedericksz cell where frustration arises from competing bulk and surface fields. We find that frustration gives rise to several interesting features of the interaction, including a crossover from attraction at small distances to repulsion at large distances. The fluctuation-induced interaction is enhanced substantially by frustration, the enhancement being progressively stronger on approaching the transition from uniform to distorted structure. At the structural transition the interaction diverges and we show that the pretransitional singularity is universal.

Journal Article↗