arXiv subjects

Carlos Mattea

Publications and source records attributed to Carlos Mattea.

4 recordsLinked to original sources

arXiv2026

Dynamics of ring polymer melts: Memory function approach

We investigated the static and dynamic properties of a Rouse ring polymer modified by introducing an effective, spherically symmetric, attractive potential of entropic nature and a memory function describing the effect of dynamic entanglement. Renormalized Rouse formalism is used to approximate the time dependence of the memory matrix. The results obtained are in good agreement with existing experimental data and the results of computer simulations of ring polymer ring with , , where N_e is the number of Kuhn segments in linear polymer melts between neighboring entanglements and , the number of Kuhn segments. For large molecular weights, a refined self-consistent approximation is proposed to describe the time dependence of the memory function. It is shown that this approximation allows us to describe an exponential decrease in the self-diffusion coefficient with molecular weight of the rings, i.e., the effect of dynamic localization.

cond-mat.soft↗

arXiv2025

The Rouse ring chain with attractive harmonic potential of spherical symmetry

The static and dynamic properties of a cyclic Rouse chain modified by the introduction of an effective, spherically symmetric, attracting potential of entropic nature is studied. It is shown that a relatively weak potential can lead to a strong contraction of the polymer chain: the radius of gyration becomes much smaller compared to the size of free cyclic chain. The pronounced decrease in the terminal relaxation time of cyclic macromolecules compared to the Rouse relaxation time leads to a lengthening of the time interval for the transition to the normal, i.e. the Fickian, diffusion regime, generating a pseudo-plateau at increasing molecular mass for the time dependence of segmental mean squared segmental displacement.

cond-mat.soft↗

arXiv2019

Molecular velocity auto-correlations in glycerol/water mixtures studied by NMR MGSE method

Molecular dynamics in binary mixtures of water and glycerol was studied by measuring the spectrum of water velocity auto-correlation in the frequency range from 0.05 to 10 kHz by using the NMR method of modulated gradient spin echo. The method shows that the diversity of diffusion signature in the short spin trajectories provides information about heterogeneity of molecular motion due to the motion in the micro-vortexes of hydrodynamic fluctuation, which is especially pronounced for the mixtures with the low glycerol content. As concentration of glycerol increases above 10vol%, a new feature of spectrum appears due to interaction of water molecules with the clusters formed around hydrophilic glycerol molecules. New spectrum exposes a rate thickening of molecular friction, according to Einstein-Smoluchowski-Kubo formula, which inhibits rapid molecular motions and creates the conditions for a slow process of spontaneously folding of disordered poly-peptides into biologically active protein molecules when immersed in such a mixture.

cond-mat.stat-mech↗

arXiv2010

Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.

cond-mat.soft↗