A. Mitus | Wrocław University of Technology (original) (raw)

Papers by A. Mitus

Research paper thumbnail of The liquid-liquid phase transition. I: Statistical-mechanics description

Acta Physica Polonica A, 1988

Research paper thumbnail of Kinetics of grating inscription in DR1:DNA-CTMA thin film: experiment and semi-intercalation approach

Nanobiosystems: Processing, Characterization, and Applications V, 2012

The semi-intercalation hypothesis 1-5 which states that an azo-dye Disperse Red 1 (DR1) molecule ... more The semi-intercalation hypothesis 1-5 which states that an azo-dye Disperse Red 1 (DR1) molecule intercalates in a specific way into a biopolymeric material made of DNA complexed with the cationic surfactant CTMA, has successfully explained the main experimental results 6 of laser dynamic inscription of diffraction gratings: short response time, low diffraction efficiency, single-exponential kinetics and flat wavelength dependence. 4 Recent experiments indicate that the inscription of the grating displays some features of non-exponential behavior. To understand this complex dynamics we characterize local environment of polymeric chains in Monte Carlo modelling by analyzing some features of local free-volume (void) distribution.

Research paper thumbnail of How to distinguish the local structures of the melts

Physics Letters A, 1987

ABSTRACT

Research paper thumbnail of Theory of crystal ordering: Hexagonal symmetry

Physics Letters A, 1983

Abstract Using the statistical-mechanics theory of crystal ordering, the case of the hexagonal sy... more Abstract Using the statistical-mechanics theory of crystal ordering, the case of the hexagonal symmetry of the local order parameter (the sixth-rank tensor) is studied. The crystals metastability interval is small: E = 0.04. The phase diagram is constructed and the explanation of non-existence of mesophase in hcp crystals is proposed.

Research paper thumbnail of The liquid-liquid phase transition

Physics Letters A, 1985

It is shown that a change in the local structure of a liquid may lead to a first-order liquid-liq... more It is shown that a change in the local structure of a liquid may lead to a first-order liquid-liquid phase transition. A simple phenomenological model describing this phenomenon is proposed.

Research paper thumbnail of Locating liquid-solid transitions in computer simulations based on local structure analysis

Journal of Physics: Condensed Matter, 1993

The concept of local structure in fluids is applied to a complex model fluid with classical trans... more The concept of local structure in fluids is applied to a complex model fluid with classical translations in two dimensions and two internal quantum states. We demonstrate the usefulness and efficiency of an analysis based on local structure parameters that allows ...

Research paper thumbnail of Molecular dynamics study of linear diatomic chain

The Journal of Chemical Physics, 1977

The molecular dynamics method is applied to a linear system of 64 diatomic molecules with periodi... more The molecular dynamics method is applied to a linear system of 64 diatomic molecules with periodic boundary conditions. The molecules interact via the sum of harmonic and quadrupole potentials. A pseudo phase transition from hindered to rotational diffusion is found. Results are given for energy, specific heat, equation of state, order parameter, dynamical structure factor, angular velocity correlation function, and relaxation times. At low temperature the peaks in the dynamical structure factor can be identified with translational and torsional phonons. They generally agree with the predictions of harmonic lattice dynamics. At high temperatures the existence of large quasielastic peaks indicates on the rotational diffusion of molecules. The model is tested by both the classical and quantum pseudoharmonic approximations.

Research paper thumbnail of Dynamical light scattering for DNA-CTMA:DR1 chains: wormlike semi-flexible model, coil size and persistence length

Recent experimental Dynamic Light Scattering (DLS) studies of the coil sizes of DNA-CTMA:Rh solut... more Recent experimental Dynamic Light Scattering (DLS) studies of the coil sizes of DNA-CTMA:Rh solutions have lead to numerical discrepancies with theoretical predictions amounting to one-two orders of magnitude.1 In this paper, which has partially character of a tutorial, we present the basic theoretical concepts underlying an analysis of the polymer coil sizes from DLS experiments. In particular, we discuss the limitations of those methods. We present a wormlike model of a polymer chain which is a promising candidate for inferring information about the spatial structure of the DNA chain from experimental data.

Research paper thumbnail of Beam Shaping by Using the Liquid Crystal Panel of a Commercial Display Device

Research paper thumbnail of Complex Dynamics of Photo-Switchable Guest Molecules in All-Optical Poling Close to the Glass Transition: Kinetic Monte Carlo Modeling

The Journal of Physical Chemistry B, 2018

We study theoretically the kinetics of non-interacting photo-switchable guest molecules (model az... more We study theoretically the kinetics of non-interacting photo-switchable guest molecules (model azo-dye) dispersed at low concentration in host (model polymer matrix) in the all-optical poling process close to the glass transition temperature T g. We modify kinetic Monte Carlo model used in our previous studies of nonlinear optical processes in host-guest systems. The polymer matrix is simulated using the bond-fluctuation model. The kinetics of multiple trans-cis-trans cycles is formulated in terms of transition probabilities which depend on local free volume in the matrix and its dynamics. Close to T g the build-up of polar order, monitored in terms of angular probability density functions, follows a power-law in time while the evolution of the nonlinear susceptibilities related to second harmonic generation effect follows the stretched-exponential law. This complex dynamics of guest molecules implies the presence of dynamic heterogeneities of the matrix in space and time which spread the complexity from the matrix to the otherwise simple dynamics of non-interacting guest molecules. A qualitative physical picture of mosaic-like states-intertwined areas of free-and hindered angular motion of guest molecules-is proposed and the role of related short and longer scales in space for the promotion of complex dynamics of guest molecules is discussed. A brief comparison of the theory to available experimental data is given.

Research paper thumbnail of Photoinduced (anomalous) dynamics of functionalized polymer chains: Applications for Surface Relief Grating modelling

SPIE Proceedings, 2017

Recently we have formulated a generic Monte Carlo model for the photoinduced build up of the dens... more Recently we have formulated a generic Monte Carlo model for the photoinduced build up of the density grating and surface relief grating (SRG) in a model polymer matrix functionalized with azo–dyes.1 Mass transport from illuminated to dark places was demonstrated and ascribed to a hypothetical complex dynamics of polymer chains in bond–fluctuation model. This paper constitutes a first step towards verification of this hypothesis: we characterize the motion of single functionalized chain dependent on the intensity of linearly polarized light illumination. We report various regimes of diffusion of the center of mass (CM) of the chain: subdiffusion, normal diffusion and superdiffusion. Presence/absence of those regimes depends on the light intensity and on the length of the chain. We report a surprising effect in the presence of light illumination: the longer the polymer chain the stronger superdiffusion sets in.

Research paper thumbnail of Towards modeling of random lasing in dye doped bio-organic based systems: ray-tracing and cellular automaton analysis

Nanobiosystems: Processing, Characterization, and Applications VIII, 2015

One of many photonic applications of biopolymers as functional materials is random lasing resulti... more One of many photonic applications of biopolymers as functional materials is random lasing resulting from an incorporation of highly luminescent dyes into biopolymeric matrix, which leads to a random but coherent light scattering in amplifying medium. In spite of numerous theoretical and experimental studies the origin of the coherence is still not clear and various scenarios are discussed. In particular, inhomogeneity of biopolymeric layers can hypothetically promote the feedback in the scattering of the emitted light resulting in coherent and incoherent random lasing. In this paper we analyze the light scattering in a model system of scattering centers of circular shapes and various dimensions using ray-tracing techniques. In the second part, which has mostly a tutorial character, we present the approach to the study of random lasing using a cellular automaton model of Wiersma et al.

Research paper thumbnail of Random lasing in dye doped bio-organic based systems: recent experiments and stochastic approach

SPIE Proceedings, 2014

ABSTRACT We review the results of recent experimental studies on random lasing phenomenon in biop... more ABSTRACT We review the results of recent experimental studies on random lasing phenomenon in biopolymeric matrices: DNA-CTMA and starch, loaded with different luminescent dyes (DCNP and Rh6G). New experimental results for DNA-CTMA:DCNP system are presented. The random lasing originates due to the light scattering induced by formation of microcrystals or clusters in the bulk of biosystem. We propose a simple model for light transport in the scattering medium accounting for the inhomogeneities in polymer matrices simulated using Monte Carlo method and present some preliminary results related to ray scattering.

Research paper thumbnail of Monte Carlo simulation of the Fréedericksz transition in nematic liquid crystals

Advanced Materials for Optics and Electronics, 1997

ABSTRACT

Research paper thumbnail of k-vector angular correlations in negative refraction for TM polarization in nanosphere dispersed liquid crystal (NDLC) metamaterial

SPIE Proceedings, 2013

ABSTRACT We study the behavior of refracted angle for k-vector at the interface of uniaxial aniso... more ABSTRACT We study the behavior of refracted angle for k-vector at the interface of uniaxial anisotropic media in the case of nanosphere dispersed liquid crystal (NDLC) matematerial. Finite Element (FE) calculations (COMSOL Multiphysics) are used to trace the propagation of the electromagnetic wave. Preliminary results on the influence of incident angle on refracted angle wave-vector are presented.

Research paper thumbnail of <title>Toward cloaking in nanosphere dispersed liquid crystal (NDLC) metamaterial</title>

Liquid Crystals XV, 2011

We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) mate... more We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry for TM polarization. The system consists of six layers of NDLC with different values of ordinary refractive index. Finite element calculations (COMSOL Multiphysics) show that scattering from the hidden object is strongly limited in the presence of the cloak.

Research paper thumbnail of Optimization of cloak effect in nanosphere dispersed liquid crystal metamaterial

Liquid Crystals XVI, 2012

ABSTRACT In this paper the concept and design of infrared cloaking using nanosphere dispersed liq... more ABSTRACT In this paper the concept and design of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry is presented for TM polarization of incident light. The influence of material losses on the cloaking efficiency is discussed. The loss can be tuned by changing design parameters.

Research paper thumbnail of Grating inscription in DR1:DNA-CTMA thin films: theory and experiment

Nanobiosystems: Processing, Characterization, and Applications VI, 2013

ABSTRACT Recent experimental results indicate that the inscription of gratings in DR1:DNA-CTMA th... more ABSTRACT Recent experimental results indicate that the inscription of gratings in DR1:DNA-CTMA thin films displays some features of non-exponential grating amplitude growth with time.1 The origin of this behavior is hypothetically assigned to a complex distribution of local voids in a polymeric matrix1, 2 which strongly influences the dynamics of grating inscription modelled using the semi-intercalation hypothesis.3-7 We discuss critically those topics, review the theoretical methods used for modelling of the grating inscription and point-out a hypothetical relation to complex systems. New experimental results of holographic DTWM recording of the gratings in DNA-CTMA:DR1 and PS:DR1 are presented. The two observed types of dynamics are hypothetically assigned to various distributions of local voids in corresponding polymeric matrices.

Research paper thumbnail of Infrared cylindrical cloak in nanosphere dispersed liquid crystal metamaterial

Optics Letters, 2012

We present a design of an infrared cylindrical cloak using nanosphere dispersed nematic liquid cr... more We present a design of an infrared cylindrical cloak using nanosphere dispersed nematic liquid crystal (NLC) metamaterial following the approach of Smith&#39;s group [Science 314, 977 (2006)]. Cloaking conditions require spatial distribution of liquid crystal birefringence with constant extraordinary index of refraction and radially dependent ordinary index of refraction. An approximate analytical formula for the latter is derived. Finite element (FE) simulations confirm the cloaking effect. Owing to the tunable birefringence of the liquid crystal component, such cloaking material offers the interesting possibilities of real-time control of invisibility. The possibility of experimental realization is briefly discussed.

Research paper thumbnail of Monte–Carlo simulations of refractive index changes in nematic liquid crystal upon spatially nonuniform illumination

Optics Communications, 2000

We study the influence of a spatially modulated light intensity on the refractive index of a nema... more We study the influence of a spatially modulated light intensity on the refractive index of a nematic liquid crystal, using Monte–Carlo simulations with a generalized version of the Lebwohl–Lasher hamiltonian. We have considered a model of 2D liquid crystal cell in which one of the electrodes is covered by a photoconducting polymeric layer. The index profiles along the cell thickness are calculated and compared with experimental data.

Research paper thumbnail of The liquid-liquid phase transition. I: Statistical-mechanics description

Acta Physica Polonica A, 1988

Research paper thumbnail of Kinetics of grating inscription in DR1:DNA-CTMA thin film: experiment and semi-intercalation approach

Nanobiosystems: Processing, Characterization, and Applications V, 2012

The semi-intercalation hypothesis 1-5 which states that an azo-dye Disperse Red 1 (DR1) molecule ... more The semi-intercalation hypothesis 1-5 which states that an azo-dye Disperse Red 1 (DR1) molecule intercalates in a specific way into a biopolymeric material made of DNA complexed with the cationic surfactant CTMA, has successfully explained the main experimental results 6 of laser dynamic inscription of diffraction gratings: short response time, low diffraction efficiency, single-exponential kinetics and flat wavelength dependence. 4 Recent experiments indicate that the inscription of the grating displays some features of non-exponential behavior. To understand this complex dynamics we characterize local environment of polymeric chains in Monte Carlo modelling by analyzing some features of local free-volume (void) distribution.

Research paper thumbnail of How to distinguish the local structures of the melts

Physics Letters A, 1987

ABSTRACT

Research paper thumbnail of Theory of crystal ordering: Hexagonal symmetry

Physics Letters A, 1983

Abstract Using the statistical-mechanics theory of crystal ordering, the case of the hexagonal sy... more Abstract Using the statistical-mechanics theory of crystal ordering, the case of the hexagonal symmetry of the local order parameter (the sixth-rank tensor) is studied. The crystals metastability interval is small: E = 0.04. The phase diagram is constructed and the explanation of non-existence of mesophase in hcp crystals is proposed.

Research paper thumbnail of The liquid-liquid phase transition

Physics Letters A, 1985

It is shown that a change in the local structure of a liquid may lead to a first-order liquid-liq... more It is shown that a change in the local structure of a liquid may lead to a first-order liquid-liquid phase transition. A simple phenomenological model describing this phenomenon is proposed.

Research paper thumbnail of Locating liquid-solid transitions in computer simulations based on local structure analysis

Journal of Physics: Condensed Matter, 1993

The concept of local structure in fluids is applied to a complex model fluid with classical trans... more The concept of local structure in fluids is applied to a complex model fluid with classical translations in two dimensions and two internal quantum states. We demonstrate the usefulness and efficiency of an analysis based on local structure parameters that allows ...

Research paper thumbnail of Molecular dynamics study of linear diatomic chain

The Journal of Chemical Physics, 1977

The molecular dynamics method is applied to a linear system of 64 diatomic molecules with periodi... more The molecular dynamics method is applied to a linear system of 64 diatomic molecules with periodic boundary conditions. The molecules interact via the sum of harmonic and quadrupole potentials. A pseudo phase transition from hindered to rotational diffusion is found. Results are given for energy, specific heat, equation of state, order parameter, dynamical structure factor, angular velocity correlation function, and relaxation times. At low temperature the peaks in the dynamical structure factor can be identified with translational and torsional phonons. They generally agree with the predictions of harmonic lattice dynamics. At high temperatures the existence of large quasielastic peaks indicates on the rotational diffusion of molecules. The model is tested by both the classical and quantum pseudoharmonic approximations.

Research paper thumbnail of Dynamical light scattering for DNA-CTMA:DR1 chains: wormlike semi-flexible model, coil size and persistence length

Recent experimental Dynamic Light Scattering (DLS) studies of the coil sizes of DNA-CTMA:Rh solut... more Recent experimental Dynamic Light Scattering (DLS) studies of the coil sizes of DNA-CTMA:Rh solutions have lead to numerical discrepancies with theoretical predictions amounting to one-two orders of magnitude.1 In this paper, which has partially character of a tutorial, we present the basic theoretical concepts underlying an analysis of the polymer coil sizes from DLS experiments. In particular, we discuss the limitations of those methods. We present a wormlike model of a polymer chain which is a promising candidate for inferring information about the spatial structure of the DNA chain from experimental data.

Research paper thumbnail of Beam Shaping by Using the Liquid Crystal Panel of a Commercial Display Device

Research paper thumbnail of Complex Dynamics of Photo-Switchable Guest Molecules in All-Optical Poling Close to the Glass Transition: Kinetic Monte Carlo Modeling

The Journal of Physical Chemistry B, 2018

We study theoretically the kinetics of non-interacting photo-switchable guest molecules (model az... more We study theoretically the kinetics of non-interacting photo-switchable guest molecules (model azo-dye) dispersed at low concentration in host (model polymer matrix) in the all-optical poling process close to the glass transition temperature T g. We modify kinetic Monte Carlo model used in our previous studies of nonlinear optical processes in host-guest systems. The polymer matrix is simulated using the bond-fluctuation model. The kinetics of multiple trans-cis-trans cycles is formulated in terms of transition probabilities which depend on local free volume in the matrix and its dynamics. Close to T g the build-up of polar order, monitored in terms of angular probability density functions, follows a power-law in time while the evolution of the nonlinear susceptibilities related to second harmonic generation effect follows the stretched-exponential law. This complex dynamics of guest molecules implies the presence of dynamic heterogeneities of the matrix in space and time which spread the complexity from the matrix to the otherwise simple dynamics of non-interacting guest molecules. A qualitative physical picture of mosaic-like states-intertwined areas of free-and hindered angular motion of guest molecules-is proposed and the role of related short and longer scales in space for the promotion of complex dynamics of guest molecules is discussed. A brief comparison of the theory to available experimental data is given.

Research paper thumbnail of Photoinduced (anomalous) dynamics of functionalized polymer chains: Applications for Surface Relief Grating modelling

SPIE Proceedings, 2017

Recently we have formulated a generic Monte Carlo model for the photoinduced build up of the dens... more Recently we have formulated a generic Monte Carlo model for the photoinduced build up of the density grating and surface relief grating (SRG) in a model polymer matrix functionalized with azo–dyes.1 Mass transport from illuminated to dark places was demonstrated and ascribed to a hypothetical complex dynamics of polymer chains in bond–fluctuation model. This paper constitutes a first step towards verification of this hypothesis: we characterize the motion of single functionalized chain dependent on the intensity of linearly polarized light illumination. We report various regimes of diffusion of the center of mass (CM) of the chain: subdiffusion, normal diffusion and superdiffusion. Presence/absence of those regimes depends on the light intensity and on the length of the chain. We report a surprising effect in the presence of light illumination: the longer the polymer chain the stronger superdiffusion sets in.

Research paper thumbnail of Towards modeling of random lasing in dye doped bio-organic based systems: ray-tracing and cellular automaton analysis

Nanobiosystems: Processing, Characterization, and Applications VIII, 2015

One of many photonic applications of biopolymers as functional materials is random lasing resulti... more One of many photonic applications of biopolymers as functional materials is random lasing resulting from an incorporation of highly luminescent dyes into biopolymeric matrix, which leads to a random but coherent light scattering in amplifying medium. In spite of numerous theoretical and experimental studies the origin of the coherence is still not clear and various scenarios are discussed. In particular, inhomogeneity of biopolymeric layers can hypothetically promote the feedback in the scattering of the emitted light resulting in coherent and incoherent random lasing. In this paper we analyze the light scattering in a model system of scattering centers of circular shapes and various dimensions using ray-tracing techniques. In the second part, which has mostly a tutorial character, we present the approach to the study of random lasing using a cellular automaton model of Wiersma et al.

Research paper thumbnail of Random lasing in dye doped bio-organic based systems: recent experiments and stochastic approach

SPIE Proceedings, 2014

ABSTRACT We review the results of recent experimental studies on random lasing phenomenon in biop... more ABSTRACT We review the results of recent experimental studies on random lasing phenomenon in biopolymeric matrices: DNA-CTMA and starch, loaded with different luminescent dyes (DCNP and Rh6G). New experimental results for DNA-CTMA:DCNP system are presented. The random lasing originates due to the light scattering induced by formation of microcrystals or clusters in the bulk of biosystem. We propose a simple model for light transport in the scattering medium accounting for the inhomogeneities in polymer matrices simulated using Monte Carlo method and present some preliminary results related to ray scattering.

Research paper thumbnail of Monte Carlo simulation of the Fréedericksz transition in nematic liquid crystals

Advanced Materials for Optics and Electronics, 1997

ABSTRACT

Research paper thumbnail of k-vector angular correlations in negative refraction for TM polarization in nanosphere dispersed liquid crystal (NDLC) metamaterial

SPIE Proceedings, 2013

ABSTRACT We study the behavior of refracted angle for k-vector at the interface of uniaxial aniso... more ABSTRACT We study the behavior of refracted angle for k-vector at the interface of uniaxial anisotropic media in the case of nanosphere dispersed liquid crystal (NDLC) matematerial. Finite Element (FE) calculations (COMSOL Multiphysics) are used to trace the propagation of the electromagnetic wave. Preliminary results on the influence of incident angle on refracted angle wave-vector are presented.

Research paper thumbnail of <title>Toward cloaking in nanosphere dispersed liquid crystal (NDLC) metamaterial</title>

Liquid Crystals XV, 2011

We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) mate... more We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry for TM polarization. The system consists of six layers of NDLC with different values of ordinary refractive index. Finite element calculations (COMSOL Multiphysics) show that scattering from the hidden object is strongly limited in the presence of the cloak.

Research paper thumbnail of Optimization of cloak effect in nanosphere dispersed liquid crystal metamaterial

Liquid Crystals XVI, 2012

ABSTRACT In this paper the concept and design of infrared cloaking using nanosphere dispersed liq... more ABSTRACT In this paper the concept and design of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry is presented for TM polarization of incident light. The influence of material losses on the cloaking efficiency is discussed. The loss can be tuned by changing design parameters.

Research paper thumbnail of Grating inscription in DR1:DNA-CTMA thin films: theory and experiment

Nanobiosystems: Processing, Characterization, and Applications VI, 2013

ABSTRACT Recent experimental results indicate that the inscription of gratings in DR1:DNA-CTMA th... more ABSTRACT Recent experimental results indicate that the inscription of gratings in DR1:DNA-CTMA thin films displays some features of non-exponential grating amplitude growth with time.1 The origin of this behavior is hypothetically assigned to a complex distribution of local voids in a polymeric matrix1, 2 which strongly influences the dynamics of grating inscription modelled using the semi-intercalation hypothesis.3-7 We discuss critically those topics, review the theoretical methods used for modelling of the grating inscription and point-out a hypothetical relation to complex systems. New experimental results of holographic DTWM recording of the gratings in DNA-CTMA:DR1 and PS:DR1 are presented. The two observed types of dynamics are hypothetically assigned to various distributions of local voids in corresponding polymeric matrices.

Research paper thumbnail of Infrared cylindrical cloak in nanosphere dispersed liquid crystal metamaterial

Optics Letters, 2012

We present a design of an infrared cylindrical cloak using nanosphere dispersed nematic liquid cr... more We present a design of an infrared cylindrical cloak using nanosphere dispersed nematic liquid crystal (NLC) metamaterial following the approach of Smith&#39;s group [Science 314, 977 (2006)]. Cloaking conditions require spatial distribution of liquid crystal birefringence with constant extraordinary index of refraction and radially dependent ordinary index of refraction. An approximate analytical formula for the latter is derived. Finite element (FE) simulations confirm the cloaking effect. Owing to the tunable birefringence of the liquid crystal component, such cloaking material offers the interesting possibilities of real-time control of invisibility. The possibility of experimental realization is briefly discussed.

Research paper thumbnail of Monte–Carlo simulations of refractive index changes in nematic liquid crystal upon spatially nonuniform illumination

Optics Communications, 2000

We study the influence of a spatially modulated light intensity on the refractive index of a nema... more We study the influence of a spatially modulated light intensity on the refractive index of a nematic liquid crystal, using Monte–Carlo simulations with a generalized version of the Lebwohl–Lasher hamiltonian. We have considered a model of 2D liquid crystal cell in which one of the electrodes is covered by a photoconducting polymeric layer. The index profiles along the cell thickness are calculated and compared with experimental data.