Institute of Fundamental Technological Research
Polish Academy of Sciences

Staff

Paweł Sznajder, PhD

Department of Biosystems and Soft Matter (ZBiMM)
Division of Complex Fluids (PFPZ)
position: senior specialist
telephone: (+48) 22 826 12 81 ext.: 421
room: 322
e-mail:
ORCID: 0000-0002-6916-0884

Doctoral thesis
2019-12-09 Stan stacjonarny sedymentującej zawiesiny przy małej liczbie Reynoldsa i dużej liczbie Pecleta  (UW)
supervisor -- Prof. Bogdan Cichocki, PhD, UW
 

Recent publications
1.  Sznajder P., Cichocki B., Ekiel-Jeżewska M., Lack of Plasma-like Screening Mechanism in Sedimentation of a Non-Brownian Suspension, SYMMETRY, ISSN: 2073-8994, DOI: 10.3390/sym14010063, Vol.14, No.1, pp.63-1-10, 2022

Abstract:
We investigate qualitatively a uniform non-Brownian sedimenting suspension in a stationary state. As a base of our analysis we take the BBGKY hierarchy derived from the Liouville equation. We then show that assumption of the plasma-like screening relations can cancel some long-range terms in the hierarchy but it does not provide integrable solutions for correlation functions. This suggests breaking the translational symmetry of the system. Therefore a non-uniform structure can develop to suppress velocity fluctuations and make the range of correlations finite.

Keywords:
non-Brownian sedimentation, stability, BBGKY hierarchy, hydrodynamic screening, correlation functions, low-Reynolds-number hydrodynamics

Affiliations:
Sznajder P. - IPPT PAN
Cichocki B. - University of Warsaw (PL)
Ekiel-Jeżewska M. - IPPT PAN
2.  Słowicka A.M., Xue N., Sznajder P., Nunes J.K., Stone H.A., Ekiel-Jeżewska M.L., Buckling of elastic fibers in a shear flow, NEW JOURNAL OF PHYSICS, ISSN: 1367-2630, DOI: 10.1088/1367-2630/ac43eb, pp.1-16, 2021

Abstract:
Three-dimensional dynamics of flexible fibers in shear flow are studied numerically, with a qualitative comparison to experiments. Initially, the fibers are straight, with different orientations with respect to the flow. By changing the rotation speed of a shear rheometer, we change the ratio A of bending to shear forces. We observe fibers in the flow-vorticity plane, which gives insight into the motion out of the shear plane. The numerical simulations of moderately flexible fibers show that they rotate along effective Jeffery orbits, and therefore the fiber orientation rapidly becomes very close to the flow-vorticity plane, on average close to the flow direction, and the fiber remains in an almost straight configuration for a long time. This ``ordering'' of fibers is temporary since they alternately bend and straighten out while tumbling. We observe numerically and experimentally that if the fibers are initially in the compressional region of the shear flow, they can undergo a compressional buckling, with a pronounced deformation of shape along their whole length during a short time, which is in contrast to the typical local bending that originates over a long time from the fiber ends. We identify differences between local and compressional bending and discuss their competition, which depends on the initial orientation of the fiber and the bending stiffness ratio A. There are two main finding. First, the compressional buckling is limited to a certain small range of the initial orientations, excluding those from the flow-vorticity plane. Second, since fibers straighten out in the flow-vorticity plane while tumbling, the compressional buckling is transient - it does not appear for times longer than 1/4 of the Jeffery period. For larger times, bending of fibers is always driven by their ends.

Affiliations:
Słowicka A.M. - IPPT PAN
Xue N. - other affiliation
Sznajder P. - IPPT PAN
Nunes J.K. - other affiliation
Stone H.A. - Princeton University (US)
Ekiel-Jeżewska M.L. - IPPT PAN
3.  Szczytko J., Vaupotic N., Madrak K., Sznajder P., Górecka E., Magnetic moment of a single metal nanoparticle determined from the Faraday effect, PHYSICAL REVIEW E, ISSN: 1539-3755, DOI: 10.1103/PhysRevE.87.033201, Vol.87, No.3, pp.033201-1-6, 2013

Abstract:
Optical properties of a composite material made of ferromagnetic metal nanoparticles embedded in a dielectric host are studied. We constructed an effective dielectric tensor of the composite material taking into account the orientational distribution of nanoparticle magnetic moments in external magnetic field. A nonlinear dependence of the optical rotation on magnetic field resulting from the reorientation of nanoparticles is demonstrated. The theoretical findings were applied to the magneto-optical experimental data of cobalt ferromagnetic nanoparticles embedded in a dielectric liquid host. The dependence of the Faraday rotation on Co-based ferromagnetic nanoparticles was measured as a function of the external magnetic field, varying the size of nanoparticles and the wavelength of light. The proposed approach enables quantitative determination of the magnetic moment and the plasma frequency of a single nanoparticle, and from this the size of the nonmagnetic shell of magnetic nanoparticles.

Affiliations:
Szczytko J. - other affiliation
Vaupotic N. - other affiliation
Madrak K. - other affiliation
Sznajder P. - other affiliation
Górecka E. - other affiliation
4.  Serafin K., Oracz J., Grzybowski M., Koperski M., Sznajder P., Zinkiewicz Ł., Wasylczyk P., Measurement of the mass of an object hanging from a spring-revisited, European Journal of Physics, ISSN: 0143-0807, DOI: 10.1088/0143-0807/33/1/011, Vol.33, pp.129-134, 2012

Abstract:
In an open competition, students were to determine the mass of a metal cylinder hanging on a spring inside a transparent enclosure. With the time for experiments limited to 24 h due to the unexpectedly large number of participants, a few surprisingly accurate results were submitted, the best of them differing by no more than 0.5% from the true value with a relative uncertainty of less than 1%.

Affiliations:
Serafin K. - other affiliation
Oracz J. - other affiliation
Grzybowski M. - other affiliation
Koperski M. - other affiliation
Sznajder P. - other affiliation
Zinkiewicz Ł. - other affiliation
Wasylczyk P. - other affiliation
5.  Sznajder P., Piętka B., Szczytko J., Łusakowski J., Bardyszewski W., Resonant plasmon response of a periodically modulated two-dimensional electron gas, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.122.1090, Vol.122, No.6, pp.1090-1092, 2012

Abstract:
We report the theoretical study of the optical response of a periodically modulated two-dimensional electron gas. The density of states is calculated within the first order of the perturbation theory and the effects of the short-range disorder are explained and discussed. We demonstrate that the magnetic field values corresponding to the characteristic narrowing of the density of states width are given by the zeros of the subsequent Laguerre polynomials. The observed increase of the density of states at the edges are interpreted as van Hove singularities. The broadening effects are shown to modify and smear out the observed effects with increasing temperature above 2 K. The plasmon dispersion relation is discussed in terms of the random phase approximation. Small changes in plasmon dispersion relation related to the periodic modulation were predicted.

Affiliations:
Sznajder P. - other affiliation
Piętka B. - other affiliation
Szczytko J. - other affiliation
Łusakowski J. - other affiliation
Bardyszewski W. - other affiliation

Conference abstracts
1.  Ekiel-Jeżewska M.L., Słowicka A.M., Xue N., Sznajder P., Nunes J., Stone H.A., Buckling and temporal order of flexible fibers in shear flows, Bulletin of the American Physical Society, ISSN: 0003-0503, Vol.66, pp.M27.9, 2021

Patents
Filing No./Date
Filing Publication
Autors
Title
Protection Area, Applicant Name
Patent Number
Date of Grant
pdf
402159
2012-12-20
BUP 13/2014
2014-06-23
Szczytko J., Górecka E., Vaupotic N., Madrak K., Sznajder P., Osewski P., Turski H., Pociecha D.
Sposób wyznaczania wartości namagnesowania nanocząstek magnetycznych oraz urządzenie do wyznaczania wartości namagnesowania nanocząstek magnetycznych
PL, Uniwersytet Warszawski
222392
WUP 07/2016
2016-07-29

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