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Wyświetlanie 1-15 z 24
Tytuł:
Studies of Fractal Aspects of Cement
Autorzy:
Janik, J. A.
Kurdowski, W.
Podsiadły, R.
Samseth, J.
Powiązania:
https://bibliotekanauki.pl/articles/1952755.pdf
Data publikacji:
1996-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.12.Ex
82.70.Gg
Opis:
Small angle neutron scattering can be used to reveal the fractal nature of matter. The problems of fractal aspects of the structure of cement are related to those of fractal aspects of silica aerogels. Natural cement, when mixed with water, transforms after a series of chemical reactions (in a large part) into an amorphous phase called C-S-H. It is believed that the cationic sublattice composed of CaO$\text{}_{6}$ octahedrons constitutes the C-S-H structural basis, to which the SiO$\text{}_{4}$ tetrahedral chains are attached. It is a layer structure in which the cation sublattice determines the way of SiO$\text{}_{4}$ condensation. It is natural to expect that in this way one may obtain a really amorphous substance, since some tetrahedrons may be lacking, which leads to defects. We present here the results of a small angle neutron scattering and X-ray diffraction study of several samples with the pure C-S-H phase for which during the process of chemical synthesis various ratios of molar contents of CaO and SiO$\text{}_{2}$ were used (various C/S ratios). We obtained a gradual change of fractal characteristics with the change of C/S ratio.
Źródło:
Acta Physica Polonica A; 1996, 90, 6; 1179-1184
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Change of Free Volume in Polymer Gels As Studied by Positron Annihilation Lifetimes
Autorzy:
Ito, K.
Ujihira, Y.
Yamashita, T.
Horie, K.
Powiązania:
https://bibliotekanauki.pl/articles/2008070.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.70.Gg
Opis:
Variations of a free volume size of a poly(N-isopropylacrylamide) gel and a polyacrylamide gel during a volume phase transition induced by a change of external environment - temperature, solvent composition, pH, and ion strength, are described. The free volume size is probed by positron annihilation lifetime technique. Variations of the free volume size suggest that a nanoscopic environment of the gels is affected by the free volume of the solvent phase and an interaction between the polymer chain and the solvent molecule in the swollen state, and by the aggregation of the polymer chain and a balance of the interaction among the polymer chain and the solvent molecules in the collapsed state. It is revealed that the free volume size reflects the essential change of the nanoscopic environment in the gels which could induce the macroscopic volume phase transition.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 551-556
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Fractal Structure of C-S-H and Tobermorite Phases
Autorzy:
Janik, J. A.
Kurdowski, W.
Podsiadły, R.
Samseth, J.
Powiązania:
https://bibliotekanauki.pl/articles/2028897.pdf
Data publikacji:
2001-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.12.Ex
82.70.Gg
Opis:
The C-S-H I phase is the main component of the cement paste, which is a near-amorphous, highly porous gel. Due to high porosity of the sample in this phase we can observe a fractal nature of the volume pores distribution, similar to that observed for silica aerogels. The C-S-H I phase is thermodynamically unstable and crystallize to a tobermorite phase, forming crystal aggregates on the surface of the amorphous paste. The mixture of these two phases, formed in this way, have irregular volume and surface structures, both of which may exhibit the fractal nature. To study the fractal nature of the matter the small angle neutron scattering method is frequently used. We present here the results of small angle neutron scattering studies supported by the X-ray diffraction and scanning electron microscope observations of several samples with the common molar C/S ratio equal to 1. Some of the samples were autoclaved during various time periods to accelerate transformation of the C-S-H I phase to tobermorite. We observed the fractal properties of the volume structure of all samples under study. Moreover, we observed also the fractal behaviors of the surfaces of the samples which were autoclaved.
Źródło:
Acta Physica Polonica A; 2001, 100, 4; 529-537
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
$\text{}^{1}$H NMR and Rheological Studies of the Calcium Induced Gelation Process in Aqueous Low Methoxyl Pectin Solutions
Autorzy:
Dobies, M.
Kuśmia, S.
Jurga, S.
Powiązania:
https://bibliotekanauki.pl/articles/2043388.pdf
Data publikacji:
2005-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.70.Gg
87.15.By
87.15.Rn
82.56.-b
87.15.He
83.10.-y
87.15.La
Opis:
The $\text{}^{1}$H NMR relaxometry in combination with water proton spin-spin relaxation time measurements and rheometry have been applied to study the ionic gelation of 1% w/w aqueous low methoxyl pectin solution induced by divalent Ca$\text{}^{2+}$ cations from a calcium chloride solution. The model-free approach to the analysis of $\text{}^{1}$H NMR relaxometry data has been used to separate the information on the static (β) and dynamic (〈τ$\text{}_{c}$〉) behaviour of the systems tested. The $\text{}^{1}$H NMR results confirm that the average mobility of both water and the pectin molecules is largely dependent on the concentration of the cross-linking agent. The character of this dependency (β,〈τ$\text{}_{c}$〉 and T$\text{}_{2}$ vs. CaCl$\text{}_{2}$ concentration) is consistent with the two-stage gelation process of low methoxyl pectin, in which the formation of strongly linked dimer associations (in the range of 0-2.5 mM CaCl$\text{}_{2}$) is followed by the appearance of weak inter-dimer aggregations (for CaCl$\text{}_{2}$ ≥ 3.5 mM). The presence of the weak gel structure for the sample with 3.5 mM CaCl$\text{}_{2}$ has been confirmed by rheological measurements. Apart from that, the T$\text{}_{1}$ and T$\text{}_{2}$ relaxation times have been found to be highly sensitive to the syneresis phenomenon, which can be useful to monitor the low methoxyl pectin gel network stability.
Źródło:
Acta Physica Polonica A; 2005, 108, 1; 33-46
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Coincidence Doppler Broadening Spectroscopy to Hydrocarbons at Different Substance States
Autorzy:
Yu, R.
Suzuki, T.
Ito, Y.
Djourelov, N.
Kondo, K.
Shantarovich, V. P.
Powiązania:
https://bibliotekanauki.pl/articles/2042205.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
82.30.Gg
78.70.Bj
Opis:
Coincidence Doppler broadening spectroscopy was applied to study n-hexane (C$\text{}_{6}$H$\text{}_{14}$), cyclohexane (C$\text{}_{6}$H$\text{}_{12}$) and cyclohexanone (C$\text{}_{6}$H$\text{}_{10}$O), at solid, as well as liquid states. The experiments were performed in parallel with traditional positron annihilation lifetime spectroscopy. Significant positron trapping by oxygen was observed in cyclohexanone; the oxygen effect is stronger in liquid state than in solid one, which can possibly be attributed to positron solvation in polar solution. Coincidence Doppler broadening results for n-hexane and cyclohexane indicate an existence of higher energetic annihilation electrons in Ps-bubble forming liquids than that in solids.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 697-701
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Gelation Process of Toluene-Based bis-Urea in Cyclohexane Studied with Magnetic Resonance Imaging
Autorzy:
Tritt-Goc, J.
Boguszyńska, J.
Szwaj, M.
Boutellier, L.
Jadżyn, J.
Powiązania:
https://bibliotekanauki.pl/articles/2043392.pdf
Data publikacji:
2005-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.70.Gg
76.60.Pc
82.56.Lz
82.56.Na
Opis:
Magnetic resonance imaging was used for studies of the gelation and swelling processes of toluene-based bis-urea prepared in a form of cylindrical tablet and immersed in cyclohexane. The processes were investigated with the use of Bruker AVANCE (300 MHz) spectrometer equipped with a micro imaging probe head. The images were taken for cyclohexane protons within the bis-urea gel formed around the sample dry core at different intervals of the immersion. The mobility of the solvent molecules was estimated from the spatially resolved distribution of the spin-spin relaxation time T$\text{}_{2}$ and the spin densitiesρ, calculated on the basis of the images obtained. It was shown that the time-evolution of the thickness of the gel layer can be well described by the power equation with an exponent equal to 0.47 (±0.04), indicating the Fickian nature of the diffusion of cyclohexane molecules.
Źródło:
Acta Physica Polonica A; 2005, 108, 1; 81-87
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hydration of Hydroxypropylmethyl Cellulose: Effects of pH and Molecular Mass
Autorzy:
Tritt-Goc, J.
Kowalczuk, J.
Piślewski, N.
Powiązania:
https://bibliotekanauki.pl/articles/2043541.pdf
Data publikacji:
2005-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.70.Gg
76.60.Pc
Opis:
Magnetic resonance imaging was used to study the diffusion of a water solution of hydrochloric acid (HCl) and sodium hydrochloride (NaOH) into hydroxypropylmethyl cellulose matrices. Polymer in the form of a cylinder was hydrated in a water solvent of pH = 2, 7, and 12 at 37ºC and monitored at equal intervals with a 300 MHz Bruker AVANCE. The spatially resolved spin-spin relaxations times and spin densities, along with a change in the dimension of the glass core of the polymer were determined for hydroxypropylmethyl cellulose tablets as a function of hydration times. The data showed the effects of the pH solvent and of the molecular mass of the polymer on the swelling process, spin-spin relaxation time, and diffusion of solvent molecules into hydroxypropylmethyl cellulose matrices. The time dependence of the diffusion front, effective T$\text{}_{2}$, and proton-density ρ analysis clearly indicate a case II diffusion mechanism in the system composed of a water solution of hydrochloric acid (pH = 2) and hydroxypropylmethyl cellulose, whereas in the case of water solutions with pH = 7 and 12 the anomalous and case I diffusion are observed, respectively.
Źródło:
Acta Physica Polonica A; 2005, 108, 1; 197-205
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Free-Volume Studies in Polycaprolactone/Poly(propylene oxide) Urethane/Urea Membranes by Positron Lifetime Spectroscopy
Autorzy:
Ferreira Marques, M.
Gordo, P.
de Lima, A.
Queiroz, D.
Norberta de Pinho, M.
Major, P.
Kajcsos, Zs.
Powiązania:
https://bibliotekanauki.pl/articles/1812490.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.41.+e
78.70.Bj
82.30.Gg
Opis:
Positron annihilation lifetime spectroscopy was used to study the free volume parameters in polypropylene oxide-based tri-isocyanate terminated prepolymer/polycaprolactone diol bi-soft urethane/urea membranes (PU/PCL) with PCL content from 5 up to 25 wt%. Positron annihilation lifetime spectroscopy measurements carried out in the temperature range 298-324 K mirrored the phase separation of the various soft and hard segments present in the membranes. The size and amount of free volume holes determined by positron annihilation lifetime spectroscopy appear to be correlated with the $CO_2$ gas permeability through the membranes.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1359-1364
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Is a Molecular Adiabatic Approximation Appropriate to Positronic Atoms and Molecules?
Autorzy:
Mohallem, J.
Powiązania:
https://bibliotekanauki.pl/articles/1812542.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.-k
36.10.Dr
78.70.Bj
82.30.Gg
Opis:
The adiabatic approximation to positronic atoms and molecules was considered as an option to the computationally unfeasible methods that treat all particles in a common footing, in two different approaches communicated in the 37th PSPA. Here we present further assessment and comparison of the two approaches as a way of evaluating the potential of adiabatic or, as we found preferable, molecular approaches.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1465-1469
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron and Positronium Annihilation in Polymers Studied by Age-Momentum Correlation Spectroscopy
Autorzy:
Sato, K.
Murakami, H.
Ito, K.
Hirata, K.
Kobayashi, Y.
Powiązania:
https://bibliotekanauki.pl/articles/1812549.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
82.30.Gg
42.70.jk
Opis:
Positron (e⁺) and positronium (Ps) annihilation processes in polymers are studied by positron age-momentum correlation spectroscopy, which can sensitively probe momentum distributions of e⁺, p-Ps, and o-Ps. For polyether sulfone and ethylene tetrafluoroethylene copolymer belonging to oxygen-containing polymers (O group) and fluorine-containing polymers (F group), respectively, significant effects of positron trapping by polar element are observed. The Doppler profile of o-Ps pick-off annihilation is strongly influenced by F atoms, giving rise to anomalous broadening. The results are discussed together with our previous data of the S-I₃ correlation in order to explore the feasibility of chemical analysis around the free volumes by age-momentum correlation spectroscopy.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1511-1516
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Casimir Force between Nanoparticles Immersed in a Crosslinked Polymer Blend
Autorzy:
El Fassi, S.
Benhamou, M.
Boughou, M.
Kaidi, H.
El Yaznasni, M.
Ridouane, H.
Powiązania:
https://bibliotekanauki.pl/articles/1535673.pdf
Data publikacji:
2010-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.25.Hq
64.75.+g
82.70.Gg
Opis:
We consider a crosslinked polymer blend made of two polymers of different chemical nature. We suppose that such a system incorporates small colloidal particles, which prefer to be attracted by one polymer, close to the spinodal temperature. This is the so-called critical adsorption. As assumption, the particle diameter, $d_0$, is considered to be small enough in comparison with the size of microdomains (mesh size) ξ* ~ $an^{1//2}$, with a - the monomer size and n - the number of monomers between consecutive crosslinks. The critical fluctuations of the crosslinked polymer mixture induce a pair-potential between particles located in the non-preferred phase. The purpose is the determination of the Casimir pair-potential, $U_2 (r)$, as a function of the interparticle distance r. To achieve calculations, use is made of an extended de Gennes field theory that takes into account the colloid-polymer interactions. Within the framework of this theory, we first show that the pair-particle is attractive. Second, we find for this potential the exact form: $U_2(r)//k_{B}T = - A_{H}(d_0//r)^2 exp(-r//ξ*) - B_{H}(d_0//r)^4 exp(-2r//ξ*)$, with the known universal amplitudes $A_{H}$ > 0 and $B_{H}$ > 0 (the Hamaker constants). This expression clearly shows that the pair-potential differs from its homologue with no crosslinks only by the two exponential factors exp(-r/ξ*) and exp(-2r/ξ*). The main conclusion is that the presence of reticulations reduces substantially the Casimir effect in crosslinked polymer blends.
Źródło:
Acta Physica Polonica A; 2010, 118, 4; 606-612
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hydrodynamic Memory in the Motion of Charged Brownian Particles across the Magnetic Field
Autorzy:
Tóthová, J.
Lisý, V.
Powiązania:
https://bibliotekanauki.pl/articles/1535477.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.40.Jc
05.10.Gg
75.47.-m
82.70.Dd
Opis:
An exact solution of the Langevin equation is given for a charged Brownian particle driven in an incompressible fluid by the magnetic field, taking into account the hydrodynamic aftereffect. The stochastic integro-differential Langevin equation is converted to a deterministic equation for the particle mean square displacement. We have found the mean square displacement and other time correlation functions describing the particle motion. For the motion along the field the known results from the theory of the hydrodynamic motion of a free Brownian particle are recovered. The correlation functions across the field contain at long times the familiar Einstein terms and additional algebraic tails. The longest-lived tail in the mean square displacement is proportional to $t^{1//2}$. At short times the motion is ballistic and independent of the magnetic field.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 1051-1053
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Algorithm for Preliminary Analysis of Viscosity Behaviour of Some Aqueous Poly(ethylene oxide) Gels
Autorzy:
Todica, M.
Pop, C.
Udrescu, L.
Pop, M.
Powiązania:
https://bibliotekanauki.pl/articles/1505153.pdf
Data publikacji:
2011-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.70.Dd
82.70.Gg
82.70.Kj
Opis:
The dependence of the viscosity on temperature and shear rate was observed for some poly(ethylene oxide) gels with different polymeric concentrations. An algorithm of analysis of experimental data, based on the Arrhenius and power law models, and a mathematical function describing the dependence of the viscosity on temperature and shear rate are proposed.
Źródło:
Acta Physica Polonica A; 2011, 119, 6; 880-884
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Aluminum-Doped Zinc Oxide Thin Films Prepared by Sol-Gel and~RF Magnetron Sputtering
Autorzy:
Wu, G.
Chen, Y.
Lu, H.
Powiązania:
https://bibliotekanauki.pl/articles/1504062.pdf
Data publikacji:
2011-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.15.Cd
82.70.Gg
77.55.hf
Opis:
Zinc oxide (ZnO) thin films have become technologically important materials due to their wide range of electrical and optical properties. The characteristics can be further adjusted by adequate doping processes. In this paper, aluminum-doped zinc oxide thin films have been prepared on glass substrates using a sol-gel route and the radio-frequency magnetron sputtering process. The stoichiometry could be easily adjusted by controlling the nanosized precursor concentration and the thickness by dip-coating cycles. On the other hand, the mixed $N_2O//Ar$ plasma gas provided adequate N doping for the RF sputtering process. The results showed the low electrical resistivity of 21.5 Ω cm with the carrier concentration of - 3.21 × $10^{18} cm^{-3}$ for the n-type aluminium-doped zinc oxide film. They were 34.2 Ω cm and + 9.68 × $10^{16} cm^{-3}$ for the p-type aluminium-doped zinc oxide film. The optical transmittance has been as high as 85-90% in the 400-900 nm wavelength range. The aluminium-doped zinc oxide (2 at.% Al) films exhibited the hexagonal wurzite structure with (002) preferred crystal orientation. The electrical characteristics were depicted by the gradual increase in N and NO that occupy the oxygen vacancies.
Źródło:
Acta Physica Polonica A; 2011, 120, 1; 149-152
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Microstructure and Dynamics of Magnetic Iron Nanoparticles Aggregates in Protein Gels
Autorzy:
Konik, K.
Fornal, P.
Okła, D.
Stanek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1490101.pdf
Data publikacji:
2012-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.75.Jn
83.60.Np
61.25.H-
82.70.Gg
Opis:
The 60 nm metallic iron nanoparticles and its aggregates in gelatine gel were studied by means of optical microscopy, X-ray microtomography, atomic force scanning microscopy and the Mössbauer spectroscopy. The isolated nanoparticles in gel exhibit fast bounded diffusion described by Brownian movement. In the external magnetic field these magnetic particles form spectacular linear aggregates whose local dynamical and magnetic properties were determined from the Mössbauer spectra.
Źródło:
Acta Physica Polonica A; 2012, 121, 2; 457-463
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 24

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