Dynamics of H-bonded liquids confined to nanopores

Gorbatschow, W.; Arndt, M. B.; Stannarius, Ralf; Kremer, Friedrich

doi:10.1209/epl/i1996-00175-8

Cited by 116 publications

(104 citation statements)

References 20 publications

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“…29,30 In the untreated pores there are strong H-bonding interactions between the pore walls and the propylene glycol molecules at the interface, which increases their relaxation time. When the pores are treated in specific ways, these interactions are reduced and the relaxation then becomes slightly faster than in the bulk.…”

Section: -5mentioning

confidence: 99%

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Power¹,

Vij²,

Johari³

2007

The Journal of Chemical Physics

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To gain insight into the effects of liquid-liquid phase separation on molecular relaxation behavior we have studied an apparently homogeneous mixture of 5-methyl-2-hexanol and isoamylbromide by dielectric spectroscopy over a broad temperature range. It shows two relaxation regions, widely separated in frequency and temperature, with the low-frequency relaxation due to the alcohol and the high-frequency relaxation due to the halide. In the mixture, the equilibrium dielectric permittivity s of the alcohol is 41% of the pure state at 155.7 K and s of isoamylbromide is ϳ86% of the pure state at 128.7 K. The difference decreases for the alcohol component with decreasing temperature and increases for the isoamylbromide component. The relaxation time of 5-methyl-2-hexanol in the mixture at 155.7 K is over five orders of magnitude less than in the pure state, and this difference increases with decreasing temperature, but of isoamylbromide in the mixture is marginally higher than in the pure liquid. This shows that the mixture would have two T g 's corresponding to its of 10 3 s, with values of ϳ121 K for its 5-methyl-2-hexanol component and ϳ108 K for its isoamylbromide component. It is concluded that the mixture phase separates in submicron or nanometer-size aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own s and decrease markedly.

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Section: -5mentioning

confidence: 99%

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Power¹,

Vij²,

Johari³

2007

The Journal of Chemical Physics

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“…51 In mesopores ͑7.5-2.5 nm͒ of a sol-gel glass matrix this rate either decreases or increases depending on whether the pores are treated with hexamethyldisiloxane ͑this replaces dangling -OH groups on the pore walls with trimethylsilyl groups͒ or not. 52,53 In the untreated pores, H-bonding interactions between the SiO 2 pore walls and propylene glycol are strong, which increases , but weaker in the treated pores and then becomes slightly shorter than in the bulk. A more recent differential scanning calorimetry ͑DSC͒ study has shown that T g of another H-bonded liquid, glycerol, confined to hexagonal mesoporous silica with pore sizes of 26.4-2.6 nm ͑un-treated to maintain formation of interfacial -OH bonds͒ increases with decreasing pore size as a result of increasing importance of these interface effects, while T g of a non-H bonded liquid ͑o-terphenyl͒ is reduced by ϳ20 K for the smallest pore size.…”

Section: -6mentioning

confidence: 99%

Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture

Power

Vij

Johari

2007

The Journal of Chemical Physics

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The effects of liquid-liquid phase separation on molecular relaxation of an apparently homogeneous mixture of 1-propanol and isoamylbromide has been studied by dielectric spectroscopy over a broad frequency and temperature range, and its crystallization kinetics investigated in real time. The mixture shows two widely separated relaxation processes, as before, with the faster relaxation due to the orientational diffusion of isoamylbromide and the slower due to that of 1-propanol. In the mixture, the scaled contribution to permittivity from orientation polarization, ⌬ , of isoamylbromide is about the same as in the pure state, but that of 1-propanol decreases by a factor of ϳ3 at 120 K. As the temperature is decreased, this difference remains constant. The relaxation time, , of isoamylbromide and its distribution parameter remains the same as for the pure liquid, but that of 1-propanol is longer and increases with decrease in T, becoming ϳ130 times the pure liquid's value at 119 K. This is in contrast to the finding for an isomeric heptanol, whose had decreased. Extrapolation suggests that at T Ͼ 151 K, of 1-propanol in the mixture may become less than that in the pure liquid ͑the isoamylbromide component crystallizes before this temperature could be reached͒. This indicates that T g corresponding to of 10 3 s for 1-propanol in the mixture would be higher than in the pure liquid. Crystallization of the two components in the mixture occurs at different rates and 1-propanol remains partially uncrystallized while isoamylbromide completely crystallizes.of any remaining liquid isoamylbromide does not change in the presence of crystallized states while of residual liquid 1-propanol in the mixture is reduced. The mixture phase separates in submicron or nanosize aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own s decreases and increases. Consequences of the finding for various relaxation mechanisms are briefly described.

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“…rM is the mean van der Waals radius of the molecules. Taken from [9] Figures 6a-c show the relaxation rates of the α-relaxation of the bulk and confined liquids. No effect of confinement is observed on the relaxation rates of PG and BG in 7.5 nm and 5.0 nm pores.…”

Section: H-bond-forming Liquids In Zeolitic and Nanoporous Mediamentioning

confidence: 99%

“…The broadening is interpreted as being caused by interactions of the molecules with the surface [3]. The lubrication [9] hinders the formation of H bonds to the solid wall of the nanoporous ambience, hence decoupling its dynamics.…”

Section: H-bond-forming Liquids In Zeolitic and Nanoporous Mediamentioning

confidence: 99%

“…Confining geometries [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] can be realized in various ways: by containing the system under study in zeolites, in nanoporous sol-gel glasses, in mesoporous membranes, in blockcopolymers, etc. With its extraordinary dynamic range (in frequency and intensity), broadband dielectric spectroscopy enables one to unravel the subtle interplay between surface and confinement effects and to contribute to the solution of basic questions, such as for instance -is there an inherent length scale of cooperativity in glass-forming liquids and how does it vary with temperature, …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular Dynamics of Liquids in Confinement

Kremer

Stannarius

2004

Molecules in Interaction With Surfaces and Interfaces

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Abstract. Surface and confinement effects may have substantial effects on the molecular and collective dynamics of liquids. Within this chapter, we describe the confinement effects on the dynamical modes of isotropic liquids. Characteristic for many systems is the formation of surface layers with a retarded dynamics. Proper treatment of the adsorber walls ("lubrication") can reduce or completely remove such layers. In glass-forming liquids, the limiting space can lead to the suppression of the formation of collectively reorienting clusters in the liquid, and consequently to an acceleration of the dynamics compared to the bulk liquid. The combination of retarding and accelerating effects in a system where molecular migration between the boundary layers and the core is effective is describes in a dynamic model that calculates the influences of molecular exchange on dielectric spectra.

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Dynamics of H-bonded liquids confined to nanopores

Cited by 116 publications

References 20 publications

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture

Molecular Dynamics of Liquids in Confinement

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