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Under Preparation

1. Charged macromolecules interaction mediated by saline solution

2. Electrostatic interaction between polyelectrolytes

3. Effect of Nanoparticles in isotropic to smectic E phase transitions

Recent Publications

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We present a derivation of the screening length for a solution containing a charge-regulated macroion, eg protein, with its counterions. We show that it can be obtained directly from the second derivatives of the total free energy by taking recourse to the “uncertainty relation” of the Legendre transform, which connects the Hessians or the local curvatures of the free energy as a function of density and its Legendre transform, ie, osmotic pressure, as a function of chemical potentials. Based on the Fowler–Guggenheim–Frumkin model of charge regulation, we then analyze the “screening resonance” and the “overscreening” of the screening properties of the charge-regulated macroion solution.  https://doi.org/10.1063/5.0187324

On the nature of screening in Voorn–Overbeek type theories

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By using a recently formulated Legendre transform approach to the thermodynamics of charged systems, we explore the general form of the screening length in the Voorn–Overbeek-type theories, which remains valid also in the cases where the entropy of the charged component(s) is not given by the ideal gas form as in the Debye–Hückel theory. The screening length consistent with the non-electrostatic terms in the free energy ansatz for the Flory–Huggins and Voorn–Overbeek type theories, derived from the local curvature properties of the Legendre transform, has distinctly different behavior than the often invoked standard Debye screening length, though it reduces to it in some special cases.

https://doi.org/10.1063/5.0091721

Model of metameric locomotion in smooth active directional filaments with curvature fluctuations

Locomotion in segmented animals, such as annelids and myriapods (centipedes and millipedes),  is generated by a coordinated movement known as metameric locomotion, which can be also  implemented in robots designed to perform specific tasks. We introduce a theoretical model, based on  an active directional motion of the head segment and a passive trailing of the rest of the body  segments, in order to formalize and study the metameric locomotion. The model is specifically  formulated as a steered Ornstein-Uhlenbeck curvature process, preserving the continuity of the curvature along the whole body filament, and thus supersedes the simple active Brownian model, which would be inapplicable in this case.

( see more 10.1209/0295-5075/ac3ac2)

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04

Ordering of adsorbed rigid rods mediated by the Boussinesq interaction on a soft substrate

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Orientational ordering driven by mechanical distortion of soft substrates plays a major role in material transformation processes such as elastocapillarity and surface anchoring. We present a theoretical model of the orientational response of anisotropic rods deposited onto a surface of a soft, elastic substrate of finite thickness. We show that anisotropic rods exhibit a continuous isotropic–nematic phase transition, driven by orientational interactions between surface deposited rods. This interaction is mediated by the deformation of the underlying elastic substrate and is quantified by the Boussinesq solution adapted to the case of slender, surface deposited rods. From the microscopic rod–rod interactions, we derive the appropriate Maier–Saupe mean-field description, which includes the Boussinesq elastic free energy contribution due to the substrate elasticity, derive the conditions for the existence of a continuous orientational ordering transition, and discuss the implication of results in the soft (bio)system context.  https://doi.org/10.1063/5.0022556

Demixing of active particles in the presence of external fields

Self-propelled active particles are inherently out of equilibrium as they collect energy from their surroundings and transform it into directed motion. A recent theoretical study suggests that binary mixtures of active particles with distinct effective diffusion coefficients exhibit dynamical demixing when their diffusion coefficients differ by more than one order of magnitude. Here, we show that this difference may be reduced drastically in the presence of external fields even when the response to the field is the same for both species. We investigate this demixing as a function of the ratio of the diffusion coeffcients and discuss the implications of the results for active systems.

https://doi.org/10.1063/1.4992797

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