Comparison of various measurements of microscopic friction in polymer solutions

Gisser, Daniel J.; Johnson, Bruce M.; Ediger, M. D.; Meerwall, E. D. von

doi:10.1021/ma00055a017

Cited by 41 publications

(52 citation statements)

References 9 publications

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“…The calculated exponents are 1.21 and 0.58 in the low-and high-molecular weight regions, respectively, at 418 K, and 1.59 and 0.65 at 318 K. They were 1.58 and 0.52 with the transition point at C 24 in a previous MD simulation study of N ¼ 27 n-alkane molecules [1] at 318 K, and the experimentally measured values are 1.88 and 0.91 with the transition point at C 22 at 318 K [5]. Assuming the log -log plots of D MY2 versus M of n-alkane at 618 and 518 K in Figure 5 as straight lines, the corresponding exponents are 0.48 and 0.72, respectively, and comparing these values with those for MY1 at the same temperatures, 0.28 and 0.50, we found that the smaller the probe is the smaller the exponent is.…”

Section: Resultssupporting

confidence: 56%

Molecular dynamics simulation study of probe diffusion in liquidn-alkanes

Yoo

Kim

Lee

2009

Molecular Simulation

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We performed molecular dynamics simulations for the probe diffusion and friction dynamics of Lennard-Jones (LJ) particles modelled for methyl yellow (MY) in liquid n-alkanes of C 12 -C 200 at temperatures of 318, 418, 518 and 618 K. Two LJ particles are chosen: MY1 with a mass of 114 g/mol, LJ parameters of s ¼ 4.0 Å and 1 ¼ 0.4 kJ/mol, and MY2 with a mass of 225 g/mol, s ¼ 6.0 Å and 1 ¼ 0.6 kJ/mol. We observed a clear transition in the power law dependence of MY2 diffusion on the molecular weight of n-alkanes at lower temperatures of 318 and 418 K. The sharp transitions occur near n-dotriacontane (C 32 ). However, no such transition is found for MY1 at all the temperatures and for MY2 at higher temperatures of 518 and 618 K. We also calculated the friction constants of both MY probe molecules in liquid n-alkanes. For the larger probe molecule (MY2), at lower temperatures, a large deviation of slope from the linear dependence of the friction of MY2 on the chain length of n-alkane is observed, which indicates a large reduction of friction in longer chains when compared with the shorter chains, enhancing the diffusion of the probe molecules (MY2).

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Section: Resultssupporting

confidence: 56%

Molecular dynamics simulation study of probe diffusion in liquidn-alkanes

Yoo

Kim

Lee

2009

Molecular Simulation

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“…In contrast, highly symmetric fluorescent compounds are ideal acceptors due to the extremely low f ISC from the T A to the ground state which results in triplets lifetimes up to several milliseconds, thus allowing for a large number of collision events before recombination. 41,49,50 Polycyclic aromatic hydrocarbons, such as DPA, PERY and BPEA, exhibit both f A E 1 and metastable triplet states suitable to enhance TTA. 51 In contrast to f A and f ISC , the yields f ET and f TTA depend also on the concentration (C A ) of the acceptor species.…”

Section: Francesco Meinardimentioning

confidence: 99%

“…The large energy gap between Soret and Q absorption bands allows to keep high BPEA f A thus avoiding re-absorption by the donor. [87][88][89][90] Furthermore, the large acceptor S A -T A singlet/triplet splitting permits acceptor sensitization even by using different donors, with an UC energy gain as large as 0.65 eV. 48,91,92 A system composed of aromatic hydrocarbons as acceptors paired to metallo-organic complexes as donors shows unbeaten performances up to now.…”

Section: Materials For Sucmentioning

confidence: 99%

Low power, non-coherent sensitized photon up-conversion: modelling and perspectives

Monguzzi

Tubino

Hoseinkhani

et al. 2012

Phys. Chem. Chem. Phys.

429

577

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In the last few years, non-coherent sensitized photon up-conversion (SUC) in multi-component systems has been developed to achieve significantly high quantum yields for various chromophore combinations at low excitation powers, spanning from the ultraviolet (UV) to near infrared (NIR) spectrum. This promising photon energy management technique became indeed suitable for wide applications in lighting technology and especially in photovoltaics, being able to recover the sub-bandgap photons lost by current devices. A full and general description of the SUC photophysics will be presented, with the analysis of the parameter affecting the photon conversion quantum yield and the quantities which define the optimal working range of any SUC system, namely the threshold and saturation excitation intensity. It will be shown how these quantities depend on intrinsic photophysical properties of the moieties involved and on the SUC solid host matrix. The model proposed represents a powerful tool for evaluation of a newly proposed system, and its reliability will be discussed in respect to an optimized system with SUC yield of 0.26 ± 0.02. The results obtained will outline the research guidelines which must be pursued to optimize the SUC efficiency for its perspective technological applications.

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“…As the molecular weight of the matrix is increased further, we can expect a transition from the oligomer to the "polymer" (Rouse) regime where the molecular weight dependence of the probe diffusion disappears. It has been shown experimentally that the diffusion of small molecules in polymer solutions of sufficiently large molecular weight is nearly independent of the molecular weight or viscosity of the polymers [31]. erefore, D MY in the high-molecularweight polymer must be larger than that extrapolated from the oligomer regime.…”

Section: Log(d) Vs Log(m)mentioning

confidence: 99%

Diffusion and Friction Dynamics of Probe Molecules in Liquid n-Alkane Systems: A Molecular Dynamics Simulation Study

Lee

2019

Journal of Chemistry

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We present a molecular dynamics simulation study of the probe diffusion and friction dynamics of Lennard-Jones particles in a series of liquid n-alkane systems from C12 up to C400 at 318 K, 418 K, 518 K, and 618 K, to investigate the power law dependence of self-diffusion of polymer liquids on their molecular weights. Two LJ particles MY1 with a mass of 114 g/mol and MY2 with a mass of 225 g/mol are used as probes to model methyl yellow. We observed that a clear transition in the power law dependence of n-alkane self-diffusion on the molecular weight (M) of n-alkane, Dself∼M−γ, occurs in the range C120∼C160 at temperatures of 318 K, 418 K, and 518 K, corresponding to a crossover from the “oligomer” to the “Rouse” regime. We also observed that a clear transition in the power law dependence of the diffusion coefficient DMY2 on the molecular weight (M) of n-alkane, DMY2∼M−γ, occurs at low temperatures. The exponent γ for DMY2 shows a sharp transition from 1.21 to 0.52 near C36 at 418 K and from 1.54 to 0.60 near C36 at 318 K. However, no such transition is found for the probe molecule MY2 at temperatures of 518 K and 618 K and for MY1 probe at temperatures of 418 K, 518 K, and 618 K, but the power law exponent γ for MY1 at 318 K shows instead a linear or a rather slow transition. The dependence of the probe diffusion (DMY2) on the matrix molecular weight (M) reflects a significant change of the matrix dynamics associated with the probe diffusion: a crossover from the “solvent-like” to the “oligomer” regime. As the molecular weight of n-alkane increases, the ratio of Dself/DMY2 becomes less than 1 and the probe molecules encounter, in turn, two different microscopic frictions depending on MMY/Mmatrix and the temperature. It is believed that a reduction in the microscopic friction on the probe molecules that diffuse at a rate faster than the solvent fluctuations leads to large deviations of slope from the linear dependence of the friction of MY2 on the chain length of the n-alkane at 318 K and 418 K.

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Comparison of various measurements of microscopic friction in polymer solutions

Cited by 41 publications

References 9 publications

Molecular dynamics simulation study of probe diffusion in liquidn-alkanes

Molecular dynamics simulation study of probe diffusion in liquidn-alkanes

Low power, non-coherent sensitized photon up-conversion: modelling and perspectives

Diffusion and Friction Dynamics of Probe Molecules in Liquid n-Alkane Systems: A Molecular Dynamics Simulation Study

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