arXiv subjects

Konstantin I. Morozov

Publications and source records attributed to Konstantin I. Morozov.

5 recordsLinked to original sources

arXiv2026

Ion Permeation in Nanoscale Films: Fundamental Limitation and Evaluation of Dielectric Properties

Nanoscale films play a central role in biology and osmotic separations. Their water/salt selectivity is often regarded as intrinsic property, favoring thinner membranes for faster permeation. Here we highlight and quantify a fundamental limitation arising from the dependence of ion self-energy on film thickness, governed by its ratio to Bjerrum length. The resulting relation factors out this dependence from intrinsic ion permeability, which agrees well with available data and enables evaluation of dielectric properties of ultrathin films, advancing understanding of ion transport in membranes.

cond-mat.soft↗

arXiv2025

Weak thermal fluctuations impede steering of chiral magnetic nanobots

Rotating magnetic field is an efficient method of actuation of synthetic colloids in liquids. In this Letter we theoretically study the effect of the thermal noise on torque-driven steering of magnetic nanohelices. Using a combination of numerical and analytical methods, we demonstrate that surprisingly a weak thermal noise can substantially disrupt the orientation and rotation of the nanohelix, severely impeding its propulsion. The results of Langevin simulations are in excellent agreement with the numerical solution of the Fokker-Planck equation and the analytical effective field approximation.

cond-mat.soft↗

arXiv2019

The role of symmetry in driven propulsion at low Reynolds number

We theoretically and experimentally investigate low-Reynolds-number propulsion of geometrically achiral planar objects that possess a dipole moment and that are driven by a rotating magnetic field. Symmetry considerations (involving parity, $\widehat{P}$, and charge conjugation, $\widehat{C}$) establish correspondence between propulsive states depending on orientation of the dipolar moment. Although basic symmetry arguments do not forbid individual symmetric objects to efficiently propel due to spontaneous symmetry breaking, they suggest that the average ensemble velocity vanishes. Some additional arguments show, however, that highly symmetrical ($\widehat{P}$-even) objects exhibit no net propulsion while individual less symmetrical ($\widehat{C}\widehat{P}$-even) propellers do propel. Particular magnetization orientation, rendering the shape $\widehat{C}\widehat{P}$-odd, yields unidirectional motion typically associated with chiral structures, such as helices. If instead of a structure with a permanent dipole we consider a polarizable object, some of the arguments have to be modified. For instance, we demonstrate a truly achiral ($\widehat{P}$- and $\widehat{C}\widehat{P}$-even) planar shape with an induced electric dipole that can propel by electro-rotation. We thereby show that chirality is not essential for propulsion due to rotation-translation coupling at low Reynolds number.

physics.flu-dyn↗

arXiv2014

Dynamics and polarization of superparamagnetic chiral nanomotors in a rotating magnetic field

Externally powered magnetic nanomotors are of particular interest due to the potential use for \emph{in vivo} biomedical applications. Here we develop a theory for dynamics and polarization of recently fabricated superparamagnetic chiral nanomotors powered by a rotating magnetic field. We study in detail various experimentally observed regimes of the nanomotor dynamic orientation and propulsion and establish the dependence of these properties on polarization and geometry of the propellers. Based on the proposed theory we introduce a novel "steerability" parameter $γ$ that can be used to rank polarizable nanomotors by their propulsive capability. The theoretical predictions of the nanomotor orientation and propulsion speed are in excellent agreement with available experimental results. Lastly, we apply slender-body approximation to estimate polarization anisotropy and orientation of the easy-axis of superparamagnetic helical propellers.

cond-mat.soft↗

arXiv2013

The chiral magnetic nanomotors

Propulsion of the chiral magnetic nanomotors powered by a rotating magnetic field is in the focus of the modern biomedical applications. This technology relies on strong interaction of dynamic and magnetic degrees of freedom of the system. Here we study in detail various experimentally observed regimes of the helical nanomotor orientation and propulsion depending on the actuation frequency, and establish the relation of these two properties with remanent magnetization and geometry of the helical nanomotors. The theoretical predictions for the transition between the regimes and nanomotor orientation and propulsion speed are in excellent agreement with available experimental data. The proposed theory offers a few simple guidelines towards the optimal design of the magnetic nanomotors. In particular, efficient nanomotors should be fabricated of hard magnetics, e.g., cobalt, magnetized transversally and have the geometry of a normal helix with a helical angle of 35-45 degrees.

cond-mat.soft↗