17 research outputs found
Solvation forces in Ising films with long-range boundary fields: density-matrix renormalization-group study
Using the quasi-exact density-matrix renormalization-group method we
calculate the solvation forces in two-dimensional Ising films of thickness L
subject to identical algebraically decaying boundary fields with various decay
exponents p. At the bulk critical point the solvation force acquires a
universal contribution which is long-ranged in L due to the critical
fluctuations, a phenomenon known as the critical Casimir effect. For p = 2, 3
and 50, we study the scaling behaviour of the solvation force along the
pseudo-phase coexistence and along the critical and sub-critical isotherms.Comment: 9 pages, 6 figures, accepted to Molecular Physic
On the surface critical behaviour in Ising strips: density-matrix renormalization-group study
Using the density-matrix renormalization-group method we study the surface
critical behaviour of the magnetization in Ising strips in the subcritical
region. Our results support the prediction that the surface magnetization in
the two phases along the pseudo-coexistence curve also behaves as for the
ordinary transition below the wetting temperature for the finite value of the
surface field.Comment: 15 pages, 9 figure
Influence of Capillary Condensation on the Near-Critical Solvation Force
We argue that in a fluid, or magnet, confined by adsorbing walls which favour
liquid, or (+) phase, the solvation (Casimir) force in the vicinity of the
critical point is strongly influenced by capillary condensation which occurs
below the bulk critical temperature T_c. At T slightly below and above T_c, a
small bulk field h<0, which favours gas, or (-) phase, leads to residual
condensation and a solvation force which is much more attractive (at the same
large wall separation) than that found exactly at the critical point. Our
predictions are supported by results obtained from density-matrix
renormalization-group calculations in a two-dimensional Ising strip subject to
identical surface fields.Comment: 4 Pages, RevTeX, and 3 figures include
Interplay of complete wetting, critical adsorption, and capillary condensation
The excess adsorption in two-dimensional Ising strips subject to identical boundary fields, at both one-dimensional
surfaces decaying in the orthogonal direction as , is studied
for various values of and along various thermodynamic paths below the
critical point by means of the density-matrix renormalization-group method. The
crossover behavior between the complete wetting and critical adsorption
regimes, occurring in semi-infinite systems, are strongly influenced by
confinement effects. Along isotherms the asymptotic power law
dependences on the external bulk field, which characterize these two regimes,
are undercut by capillary condensation. Along the pseudo first-order phase
coexistence line of the strips, which varies with temperature, we find a broad
crossover regime where both the thickness of the wetting film and
increase as function of the reduced temperature but do not follow any
power law. Above the wetting temperature the order parameter profiles are not
slab-like but exhibit wide interfacial variations and pronounced tails. Inter
alia, our explicit calculations demonstrate that, contrary to opposite claims
by Kroll and Lipowsky [Phys. Rev. B {\bf 28}, 5273 (1983)], for critical
wetting transitions do exist and we determine the corresponding wetting phase
diagram in the plane.Comment: RevTeX 23 Pages and 17 figures, submitted to Phys. Rev.
The effect of partially fluorinated chain length on the mesomorphic properties of chiral 2’,3’-difluoroterphenylates
Modelling of the interactions between magnetic nanoparticles in aqueous solutions
The ability of magnetic nanoparticles and their aggregates to form larger structures or new materials is primarily based on the interactions between individual particles. The article analyzes the behavior of spherical nanoparticles Fe3O4 placed in an aqueous base solution as a result of their mutual interactions, i.e. repulsive (electrostatic forces) and attractive (van der Waals forces and dipolar magnetic forces) for the full range of parameter values. Considering the application of magnetic aqueous suspensions in industry or environmental research, the presented method allows for a preliminary selection of the parameters of the dispersed material and the solution so as to obtain a suspension with the desired properties
Effect of Magnetic Heating on Stability of Magnetic Colloids
Stable aqueous suspension of magnetic nanoparticles is essential for effective magnetic hyperthermia and other applications of magnetic heating in an alternating magnetic field. However, the alternating magnetic field causes strong agglomeration of magnetic nanoparticles, and this can lead to undesirable phenomena that deteriorate the bulk magnetic properties of the material. It has been shown how this magnetic field influences the distribution of magnetic agglomerates in the suspension. When investigating the influence of the sonication treatment on magnetic colloids, it turned out that the hydrodynamic diameter as a function of sonication time appeared to have a power-law character. The effect of magnetic colloid ageing on magnetic heating was discussed as well. It was shown how properly applied ultrasonic treatment could significantly improve the stability of the colloid of magnetic nanoparticles, ultimately leading to an increase in heating efficiency. The optimal sonication time for the preparation of the magnetic suspension turned out to be time-limited, and increasing it did not improve the stability of the colloid. The obtained results are important for the development of new materials where magnetic colloids are used and in biomedical applications
Orthoconic antiferroelectric liquid crystals containing biphenyl, terphenyl, or naphthyl mesogenic unit
Filtration of Nanoparticle Agglomerates in Aqueous Colloidal Suspensions Exposed to an External Radio-Frequency Magnetic Field
The study investigated the phenomenon of the fast aggregation of single-domain magnetic iron oxide nanoparticles in stable aqueous colloidal suspensions due to the presence of a radio-frequency (RF) magnetic field. Single-domain nanoparticles have specific magnetic properties, especially the unique property of absorbing the energy of such a field and releasing it in the form of heat. The localized heating causes the colloid to become unstable, leading to faster agglomeration of nanoparticles and, consequently, to rapid sedimentation. It has been shown that the destabilization of a stable magnetic nanoparticle colloid by the RF magnetic field can be used for the controlled filtration of larger agglomerates of the colloid solution. Two particular cases of stable colloidal suspensions were considered: a suspension of the bare nanoparticles in an alkaline solution and the silica-stabilized nanoparticles in a neutral solution. The obtained results are important primarily for biomedical applications and wastewater treatment