Partner: H.A. Stone

Princeton University (US)

Recent publications
1.Richter Ł., Żuk P.J., Szymczak P., Paczesny J., Bąk K.M., Szymborski T., Garstecki P., Stone H.A., Hołyst R., Drummond C., Ions in an AC electric field: strong long-range repulsion between oppositely charged surfaces, PHYSICAL REVIEW LETTERS, ISSN: 0031-9007, DOI: 10.1103/PhysRevLett.125.056001, Vol.125, No.5, pp.056001-1-5, 2020
Abstract:

Two oppositely charged surfaces separated by a dielectric medium attract each other. In contrast we observe a strong repulsion between two plates of a capacitor that is filled with an aqueous electrolyte upon application of an alternating potential difference between the plates. This long-range force increases with the ratio of diffusion coefficients of the ions in the medium and reaches a steady state after a few minutes, which is much larger than the millisecond timescale of diffusion across the narrow gap. The repulsive force, an order of magnitude stronger than the electrostatic attraction observed in the same setup in air, results from the increase in osmotic pressure as a consequence of the field-induced excess of cations and anions due to lateral transport from adjacent reservoirs.

Affiliations:
Richter Ł.-other affiliation
Żuk P.J.-IPPT PAN
Szymczak P.-University of Warsaw (PL)
Paczesny J.-other affiliation
Bąk K.M.-other affiliation
Szymborski T.-other affiliation
Garstecki P.-Institute of Physical Chemistry, Polish Academy of Sciences (PL)
Stone H.A.-Princeton University (US)
Hołyst R.-other affiliation
Drummond C.-other affiliation
2.Gupta A., Żuk P.J., Stone H.A., Charging dynamics of overlapping double layers in a cylindrical nanopore, PHYSICAL REVIEW LETTERS, ISSN: 0031-9007, DOI: 10.1103/PhysRevLett.125.076001, Vol.125, No.7, pp.076001-1-6, 2020
Abstract:

The charging of electrical double layers inside a cylindrical pore has applications to supercapacitors, batteries, desalination and biosensors. The charging dynamics in the limit of thin double layers, i.e., when the double layer thickness is much smaller than the pore radius, is commonly described using an effective RC transmission line circuit. Here, we perform direct numerical simulations (DNS) of the Poisson-Nernst-Planck equations to study the double layer charging for the scenario of overlapping double layers, i.e., when the double layer thickness is comparable to the pore radius. We develop an analytical model that accurately predicts the results of DNS. Also, we construct a modified effective circuit for the overlapping double layer limit, and find that the modified circuit is identical to the RC transmission line but with different values and physical interpretation of the capacitive and resistive elements. In particular, the effective surface potential is reduced, the capacitor represents a volumetric current source, and the charging timescale is weakly dependent on the ratio of the pore radius and the double layer thickness.

Affiliations:
Gupta A.-Government Tulsi Degree College (IN)
Żuk P.J.-IPPT PAN
Stone H.A.-Princeton University (US)
3.Słowicka A.M., Stone H.A., Ekiel-Jeżewska M.L., Flexible fibers in shear flow approach attracting periodic solutions, PHYSICAL REVIEW E, ISSN: 2470-0045, DOI: 10.1103/PhysRevE.101.023104, Vol.101, No.2, pp.023104-1-14, 2020
Abstract:

The three-dimensional dynamics of a single non-Brownian flexible fiber in shear flow is evaluated numerically, in the absence of inertia. A wide range of ratios A of bending to hydrodynamic forces and hundreds of initial configurations are considered. We demonstrate that flexible fibers in shear flow exhibit much more complicated evolution patterns than in the case of extensional flow, where transitions to higher-order modes of characteristic shapes are observed when A exceeds consecutive threshold values. In shear flow, we identify the existence of an attracting steady configuration and different attracting periodic motions that are approached by long-lasting rolling, tumbling, and meandering dynamical modes, respectively. We demonstrate that the final stages of the rolling and tumbling modes are effective Jeffery orbits, with the constant parameter C replaced by an exponential function that either decays or increases in time, respectively, corresponding to a systematic drift of the trajectories. In the limit of C→0, the fiber aligns with the vorticity direction and in the limit of C→∞, the fiber periodically tumbles within the shear plane. For moderate values of A, a three-dimensional meandering periodic motion exists, which corresponds to intermediate values of C. Transient, close to periodic oscillations are also detected in the early stages of the modes.

Affiliations:
Słowicka A.M.-IPPT PAN
Stone H.A.-Princeton University (US)
Ekiel-Jeżewska M.L.-IPPT PAN
4.Kuei S., Słowicka A.M., Ekiel-Jeżewska M.L., Wajnryb E., Stone H.A., Dynamics and topology of a flexible chain: knots in steady shear flow, NEW JOURNAL OF PHYSICS, ISSN: 1367-2630, DOI: 10.1088/1367-2630/17/5/053009, Vol.17, pp.053009-1-15, 2015
Abstract:

We use numerical simulations of a bead–spring model chain to investigate the evolution of the conformations of long and flexible elastic fibers in a steady shear flow. In particular, for rather open initial configurations, and by varying a dimensionless elastic parameter, we identify two distinct conformational modes with different final size, shape, and orientation. Through further analysis we identify slipknots in the chain. Finally, we provide examples of initial configurations of an 'open' trefoil knot that the flow unknots and then knots again, sometimes repeating several times.

Keywords:

knots, low Reynolds number flows, multipole method

Affiliations:
Kuei S.-Princeton University (US)
Słowicka A.M.-IPPT PAN
Ekiel-Jeżewska M.L.-IPPT PAN
Wajnryb E.-IPPT PAN
Stone H.A.-Princeton University (US)
5.Nunes J.K., Sadlej K., Tama J.I., Stone H.A., Control of the length of microfibers, LAB ON A CHIP, ISSN: 1473-0197, DOI: 10.1039/C2LC40280G, Vol.12, pp.2301-2304, 2012

Conference abstracts
1.Słowicka A.M., Stone H.A., Ekiel-Jeżewska M.L., Periodic motions of flexible fibers in shear flow, Bulletin of the American Physical Society, ISSN: 0003-0503, Vol.62, No.14, pp.221-221, 2017
2.Słowicka A.M., Stone H.A., Wajnryb E., Ekiel-Jeżewska M.L., Three modes of the dynamics of flexible fibers in shear flow, ICTAM XXIV, 24th International Congress of Theoretical and Applied Mechanics, 2016-08-21/08-26, Montréal (CA), pp.1142-1143, 2016
Abstract:

Dynamics of a single non-Brownian flexible fiber in shear flow at low Reynolds number is investigated numerically. Initially, the fiber is straight and at the equilibrium. For different initial orientations and values of bending stiffness, three generic scenarios are observed: the fiber tends to: align along the vorticity direction, tumble within the plane perpendicular to vorticity, or perform a periodic motion superposed with translation along the flow.

Keywords:

Stokes equations, flexible fibers, shear flow

Affiliations:
Słowicka A.M.-IPPT PAN
Stone H.A.-Princeton University (US)
Wajnryb E.-IPPT PAN
Ekiel-Jeżewska M.L.-IPPT PAN