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1
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Monte Carlo Study of Chain Entanglements in Polymer Melt

100%
Sikorski A., Romiszowski P.
Acta Physica Polonica A
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2001
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vol. 100
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issue 4
477-484
EN
The new multibond algorithm for the Monte Carlo simulations of polymers developed for an isolated chain was extended for the case of dense polymer melts. Polymer chains were confined to a simple cubic lattice with excluded volume and no attractive interactions (good solvent conditions). The simulations were carried out by the means of the classical Metropolis scheme. The algorithm was verified by the analysis of static and dynamic properties of polymer melts. The dependence of the longest relaxation time and the self-diffusion coefficient on the chain length and the polymer concentration was discussed and the proper scaling laws were formulated. The number of entanglements, their distribution, and lifetimes were determined for different chain lengths and melt concentrations using the new algorithm.
2
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New Multi-Bond Algorithm for Monte Carlo Simulation of Lattice Chains

100%
Romiszowski P., Sikorski A.
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vol. 96
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issue 6
691-697
EN
The new algorithm for the Monte Carlo simulations of polymer lattice chains was developed. The model chains were constructed on a simple cubic lattice. The simulations were carried out on chains with and without excluded volume effect using the Metropolis scheme. The basic concept of the new algorithm is the multi-bond modification of the chain conformation instead of applying the classical set of elementary micromodifications. The correctness of the algorithm was verified by studying both static and dynamic properties of the chains. The new algorithm was found to be 3 to 8 times faster than the classical one.
3
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Properties of Confined Polymer Melts

80%
Sikorski A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 3
443-450
EN
Properties of simple models of confined linear polymer chains were studied by means of the Monte Carlo method. Model chains were built of united atoms (statistical segments) and embedded to a simple cubic lattice. Then polymers were put into a slit formed by two parallel impenetrable surfaces. Chain lengths were varied up to 800 segments and the density of the polymer melt was changed up to 0.5. A Metropolis-like sampling Monte Carlo algorithm was used to determine the static properties of this model. The influence of the size of the confinement, the polymer melt concentration and the chain length on the chain's size and the structure was studied. The universal behavior of all confined polymer linear chains under consideration was found and discussed.
4
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Casimir Force between Nanoparticles Immersed in a Crosslinked Polymer Blend

80%
El Fassi S., Benhamou M., Boughou M., Kaidi H., El Yaznasni M., Ridouane H.
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issue 4
606-612
EN
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.
5
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Photon Force-Induced Phase Transition Dynamics of Single Hydrogel Nanoparticles in Water

80%
Hosokawa C., Matsumura Y., Yoshikawa H., Iwai K., Masuhara H.
Acta Physica Polonica A
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2007
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vol. 112
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issue S
S-57-S-70
EN
We investigated laser-induced phase transition dynamics of μm sized single poly(N-isopropylacrylamide) hydrogel particles in water. Single poly(N-isopropylacrylamide) gel particles labeled with a polarity-sensitive fluorescent probe monomer were optically trapped by a focused laser beam and its fluorescence dynamics was analyzed. The fluorescence intensity of trapped single gel particles was increased with the trapping laser power, while the fluorescence peak wavelength was not changed. Temperature-induced changes of fluorescence properties of the single particle were confirmed to be similar to those of the bulk solution. These behaviors are well interpreted by considering that the fluorescence intensity and fluorescence peak reflect local interactions between the fluorescent probe and attaching (bound) water molecules and effective polarity determined by (free) water content in the particle, respectively. A change in the fluorescence peak wavelength after laser trapping was followed and its blue-shift was confirmed to occur within a few hundreds seconds, indicating that a single gel particle gradually attains to a globular state on this timescale, expelling initially free water molecules and then bound ones.
6
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Structure of Dense Polymer Systems Confined to a Slit

80%
Sikorski A.
Acta Physica Polonica A
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2006
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vol. 109
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issue 2
133-141
EN
The linear polymer chains were approximated as series of identical segments on a simple cubic lattice. The excluded volume was included into the model with no attractive interactions which corresponded to the good solvent conditions. The polymer chains were put into a slit formed by a pair of parallel surfaces. These walls were impenetrable for polymer segments and no other interactions between walls and chains were assumed. The models chains were studied by the means of the Monte Carlo method. The sampling algorithm was Metropolis-type and employing micromodifications of chain's conformation to sample efficiently the conformational space. The influence of the chain length, density of the polymer system, and the distance between the surfaces on the shape of macromolecules was studied. It was found that the decrease in the size of the slit and the decrease in the polymer density led to the formation of more spherical macromolecules. This is partially caused by the interpenetration of polymer chains.
7
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The Shape of Confined Polymer Chains

80%
Sikorski A.
Acta Physica Polonica A
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2003
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vol. 103
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issue 4
339-347
EN
The linear polymer chains were modeled on a simple cubic lattice. The excluded volume was included into the model while the system remained athermal (no attractive interactions) which simulated the good solvent conditions. The polymer chain was located between two parallel impenetrable walls and the distance between the walls was changing. No interaction between walls and polymer segments was assumed. These models of polymer chains were simulated by the means of the Monte Carlo method. In the sampling algorithm we used the micromodifications of chain's conformations to sample efficiently the conformational space. The size of the chain did not change monotonically for all lengths under consideration (up to 800 statistical segments). For distances between the plates close to the double value of chain's radius of gyration the size of the chain approached its minimum value. It was shown that scaling of chain dimensions with its length changed from N^{1.18} to N^{1.5} while the distance between the walls was decreasing. The behavior of the asymmetry of the chain was found to be analogous to that of the radius of gyration.
8
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Dependence of Order and Dynamics in Polymers and Elastomers under Deformation Revealed by NMR Techniques

61%
Stapf S., Kariyo S.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
247-259
EN
Uniaxial stretching and swelling are considered as two limiting cases of deformations of elastomers. Under both conditions, the molecular dynamics is changed with respect to the behavior that describes the undisturbed, equilibrium elastomer. Particularly the spectrum of segmental motions, which reveals itself in the frequency-dependence of the longitudinal NMR relaxation time, is discussed in this study, but also order effects expressed via the dipolar coupling strength are investigated. For stretched elastomers, a significant change of the relaxation dispersion is found for three different types of rubber; it is a consequence of a change of the mode spectrum of segmental motions that becomes obvious at low frequencies (below 1 MHz at room temperature). In swollen elastomers, on the other hand, a cross-over towards a behavior expected for semi-dilute solutions is found, and a comparison to solutions of uncross-linked polymers reveals a significant effect of the cross-links only in the kHz range. A much more pronounced difference between elastomers and polymer solutions, however, is found from double-quantum encoded NMR measurements where the residual order introduced by the presence of permanent cross-links is maintained even in the presence of solvent.
9
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Nematic ordering problem as the polymer problem of the excluded volume

61%
Yakunin A.
Open Physics
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2003
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vol. 1
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issue 2
355-362
EN
Based on a solution of the polymer excluded volume problem, a technique is proposed to estimate some parameters at the isotropic-nematic liquid crystal phase transition (the product of the volume fraction of hard sticks and the ratio of the stick length, L, to its diameter, D; the maximum value of this ratio at which one cannot regard the stick as hard). The critical exponents are estimated. The transition of a swelling polymer coil to ideal is revealed as the polymerization degree of a macromolecule increases. The entanglement concentration obtained agrees with experimental data for polymers with flexible chains. The number of monomers between neighbor entanglements is assumed to be the ratio L/D. A comparison of the theory with other ones and recent experimental data is made.
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