Institute on Laser and Information Technologies

Shatura, Russia

Institute on Laser and Information Technologies

Shatura, Russia
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Nikitin A.N.,Institute on Laser and Information Technologies | Hutchinson R.A.,Queen's University | Hesse P.,University of Gottingen | Hesse P.,BASF
Macromolecular Chemistry and Physics | Year: 2013

The pulsed laser polymerization-high termination rate limit-size-exclusion chromatography (PLP-HTRL-SEC) technique is used to estimate the mode of termination (δ) for n-butyl methacrylate (n-BMA) polymerization at 30 °C. It is found that molecular mass distributions measured in these experiments are influenced by an unknown side reaction such as retardation or chain transfer that results in a marked decrease of intensity of the PLP peak. A new approach is developed to evaluate δ, with numerical experiments used to demonstrate the robustness of the methodology in the presence of retardation or chain transfer to agent. Application to the experimental n-BMA polymerization at 30 °C leads to an estimate for δ of 0.60 ± 0.03. The pulsed laser polymerization-high termination rate limit-size-exclusion chromatography (PLP-HTRL-SEC) method is extended to estimate the mode of termination (δ) even in the presence of side reactions such as retardation or chain transfer to agent. By applying this method for n-BMA polymerization at 30 °C, δ is estimated to be 0.60 ± 0.03. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nazarov M.M.,Institute on Laser and Information Technologies | Shkurinov A.P.,Moscow State University | Garet F.,University of Savoy | Coutaz J.-L.,University of Savoy
IEEE Transactions on Terahertz Science and Technology | Year: 2015

We excite surface plasmons (SPs) at the surface of highly doped Si using a prism coupler, and we study the propagation properties of these SPs in order to characterize the terahertz (THz) response of the doped semiconductor. Thanks to the long interaction length of the propagating SP with the substrate material, the method is more sensitive than classical THz time-domain spectroscopy in reflection or in transmission. Moreover, we propose a new technique based on measuring the SP signal, for which the delicate problem of accurately measuring the phase of the signal is solved. All of these different experiment techniques allow us to determine reliably the dielectric function of highly doped Si in the THz range. It appears that the experimentally determined values differ strongly from the ones calculated with a Drude model. © 2011-2012 IEEE.


Nikitin A.N.,Institute on Laser and Information Technologies | Hutchinson R.A.,Queen's University | Buback M.,University of Gottingen | Hesse P.,University of Gottingen
Macromolecular Chemistry and Physics | Year: 2011

Pulsed laser polymerization (PLP) with subsequent analysis of molecular mass distribution (MMD) is used to determine the rate coefficient of chain transfer to an agent A, ktrA, by varying pulse repetition rate such that the contributions of PLP-induced and chain-transfer-induced peaks to the MMD change to a significant extent. It is shown by simulation that the relative heights of these peaks may be used to estimate ktrA. The method is applied to evaluation of the rate coefficient of chain transfer to dodecyl mercaptan with butyl methacrylate polymerizations at -11, 0, 20 and 40°C. The Arrhenius parameters for this coefficient are determined to be: A(k trA) = (2.2 ± 0.6) × 106 L · mol -1 · s-1 and Ea(ktrA) = (22.1 ± 0.7) kJ · mol-1.(Figure Presented) © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nikitin A.N.,Institute on Laser and Information Technologies | Hutchinson R.A.,Queen's University | Wang W.,Queen's University | Kalfas G.A.,DuPont Company | And 2 more authors.
Macromolecular Reaction Engineering | Year: 2010

Butyl acrylate solution polymerization has been studied at 80-170 °C over a range of monomer and initiator levels. A PREDICI model has been developed to describe the experiments, taking into account chain backbiting, β-scission, and addition of macromonomer. The model is used to estimate Arrhenius parameters for the rate coefficients of β-scission [A(kβ) = (1.49 ± 0.28) × 109 s-1, Ea(kβ) = 63.9 ± 0.9 kJ · mol-1], for the ratio of the termination rate coefficients of secondary and midchain radicals Akt/kt t= 0.74± 0.08, Eaktkt t= - (11.2± 0.5)kJ mol-1 and for the constant of chain transfer to xylene [A(CtrS) = 107 ± 13, Ea(CtrS) = 35.4 ± 0.8 kJ · mol-1] by fitting simulated dependencies to the experimental data.Butyl acrylate solution polymerization has been studied at 80-170 °C over a range of monomer and initiator levels. To describe the experiments a PREDICI model has been developed allowing for the reactions of β-scission and addition of macromonomers. The Arrhenius parameters for the rate coefficients of midchain radicals termination, β-scission and the constant of chain transfer to xylene have been estimated from fitting of simulated dependencies to the experimental data. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Monyatsi O.,Queen's University | Nikitin A.N.,Institute on Laser and Information Technologies | Hutchinson R.A.,Queen's University
Macromolecules | Year: 2014

The radical propagation kinetics of vinyl acetate (VAc) has been studied by pulsed-laser polymerization coupled with analysis of the resulting polymer molar mass distributions. The significant increase in the apparent propagation rate coefficient observed with increasing pulse repetition rate is explained by the influence of the head-to-head defects formed during chain growth. Simulations that include head-to-head monomer addition are combined with an analysis of the experimental results to estimate the subsequent rate coefficients for reaction of the resultant radical as well as the propagation rate coefficient of normal head-to-tail addition. An analytical expression is derived for an averaged rate coefficient, kpav, for the system, with the best-fit Arrhenius parameters of ln(A/L mol-1 s-1) = 16.56 ± 0.35 and E/R= 2508 ± 108 K. © 2014 American Chemical Society .


Nikitin A.N.,Free University of Berlin | Nikitin A.N.,Institute on Laser and Information Technologies | Wulkow M.,CiT GmbH | Schutte C.,Free University of Berlin
Macromolecular Theory and Simulations | Year: 2013

The modeling approach called "numerical fractionation" has been incorporated into a PREDICI model to simulate crosslinking copolymerization. In order to take inhomogeneities of the considered copolymerization into account, the kinetic parameters of the model are proposed to be different for each generation of the numerical fractionation. Using this approach the chain-length dependence of the termination has been incorporated into the model so that even the method of moments could be applied to study crosslinking copolymerization. The styrene/m-divinylbenzene crosslinking copolymerization at low crosslinker content has been simulated. The chain-length dependence of the termination has been found to accelerate the gel point in monovinyl/divinyl copolymerization and must be taken into account for a correct description of the gel points. The modeling approach called "numerical fractionation" has been incorporated into a PREDICI model to simulate crosslinking copolymerization. The kinetic parameters of the model are proposed to be different for each generation of the numerical fractionation. The styrene/m-divinylbenzene copolymerization at low content of the crosslinker is simulated. The chain-length dependence of the termination is found to accelerate the gel point in monovinyl/divinyl copolymerization. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Kosarev I.N.,Institute on Laser and Information Technologies
Physics of Plasmas | Year: 2015

Interaction of femtosecond laser pulses with the intensities 1021, 1022W/cm2 with CH plastic foils is studied in the framework of kinetic theory of laser plasma based on the construction of propagators (in classical limit) for electron and ion distribution functions in plasmas. The calculations have been performed for real densities and charges of plasma ions. Protons are accelerated both in the direction of laser pulse (up to 1 GeV) and in the opposite direction (more than 5 GeV). The mechanisms of forward acceleration are different for various intensities. © 2015 AIP Publishing LLC.


Paulus F.,Free University of Berlin | Weiss M.E.R.,Free University of Berlin | Steinhilber D.,Free University of Berlin | Nikitin A.N.,Free University of Berlin | And 4 more authors.
Macromolecules | Year: 2013

We have investigated the anionic ring-opening multibranching polymerization for hyperbranched polyglycerol using slow monomer addition at 120 C. Different molecular masses were targeted, and the reaction mixture was probed at regular intervals for the experimental data. The resulting polymers were characterized by gel permeation chromatography, mass spectrometry, and NMR spectroscopy. A computational PREDICI model of the polymerization was developed to describe the experimental parameter dependencies. The rate coefficients were determined for the thermal and base-catalyzed, intra- and intermolecular reactions by fitting simulated number- and weight-average molecular weights to the experimental values. Although the main reaction was expected to be base-mediated, thermal propagation proved to play a crucial role in the dynamics of the investigated system. Both thermal and base-catalyzed self-initiation significantly increased the dispersity for targeting molecular masses exceeding 10 kDa, whereby the size of the growing polymer species was affected by polymerization kinetics. © 2013 American Chemical Society.


Weiss M.E.R.,Free University of Berlin | Paulus F.,Free University of Berlin | Steinhilber D.,Free University of Berlin | Nikitin A.N.,Free University of Berlin | And 3 more authors.
Macromolecular Theory and Simulations | Year: 2012

The ring-opening polymerization of glycidol at elevated temperatures is investigated. To improve the synthesis of dendritic polyether polyols, experiments are carried out without initiator to identify the influence of thermal side reactions. This results in a step-growth polymerization caused by the spontaneous combination of monomers. Kinetic parameters of the side reactions are estimated by fitting simulated number- and weight-average molecular weights to the experimental values measured at different reaction times during the polymerization. The reactions are conducted at three different temperatures of 90, 105, and 120 °C. It is shown that thermal side reactions lead to high dispersities of the final product and are highly sensitive to the reactor operating temperature. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Niziev V.G.,Institute on Laser and Information Technologies
Conference Proceedings - 5th International Conference on Advanced Optoelectronics and Lasers, CAOL' 2010 | Year: 2010

Several problems are considered in this review. Using our dipole wave theory of diffraction the analytical formulas for diffraction from a narrow ring for different polarization were obtained. They were used in the new wave numerical model of an open resonator. A number of parameters of mode formation were investigated. It was shown that multipass geometrical "modes" win in competition with single pass Laguerre-Gaussian (LG) non-main modes during the relaxation oscillations. A method has been suggested for description of the azimuthally (A) and radially (R) polarized modes that excludes any inherent contradictions and unjustified approximations. It allows the analytical calculation of the field components for these modes, including the longitudinal one. Generation of high power beams with axial symmetric polarization in stable resonator of industrial CO2-laser with diffraction gratings has been realized. The transformation of azimuthally polarized mode to R-polarized mode was demonstrated. R-polarized beam was successfully used for cutting metal. The principal scheme based on a modified Sagnac interferometer was proposed and investigated experimentally. This external cavity technique was used for generation of R- and A-polarized laser beam. © 2010 IEEE.

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