Heterogeneous relaxation dynamics of nano-confined salol probed by DMA

Schranz, W.; Puica, M. R.; Koppensteiner, J.; Kabelka, H.; Kityk, A. V.

doi:10.1209/0295-5075/79/36003

Cited by 15 publications

(20 citation statements)

References 49 publications

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“…Our findings compare well with experimental results on the dynamics of "conventional" liquid condensates [8,84,[98][99][100][101][102][103] confined in nanoporous media. In particular, the observation of distinct core and shell molecular mobilities is also in good agreement with experimental studies on pore-confined liquid crystalline systems presented in the past [7, 58-66, 69, 70], most prominently with the work by Aliev et al discussed in the introduction.…”

Section: Discussionsupporting

confidence: 86%

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillarycondensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-deGennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mobility in comparison to the unstretched liquid state of the complete filling. The strengths of the slow and fast relaxations provide local information on the orientational order: The thermotropic behaviour in the core region is bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at the P-N transition. By contrast, the interface ordering exhibits a continuous evolution at the P-N transition. Thus, the phase behaviour of the entirely filled liquid crystal-silica nanocomposite can be quantitatively described by a linear superposition of these distinct nematic order contributions.

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Section: Discussionsupporting

confidence: 86%

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

et al. 2015

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“…a crossover from relaxed to unrelaxed behaviour in the real part Y 0 and a peak behaviour in Y 00 [11]. As usual, with increasing measurement frequency, the curves shift to higher temperatures.…”

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confidence: 61%

“…Since most of the DMA measurements of salol in confinement have already been published in a sequence of recent papers [11][12][13]; here we will present only a summary of the main results.…”

Section: Salol In Mesoporous Confinementmentioning

confidence: 99%

“…A typical result is shown in Figure 11. The data were fitted assuming a spatial dependence of the relaxation time (r) across the pore radius and a Vogel-Fulcher dependence of the relaxation time, very similar to the procedure for salol and toluene, as described in detail in [11][12][13].…”

Section: Phase Transitions 753mentioning

confidence: 99%

“…Very recently, we have studied [11][12][13][14] the glass-freezing behaviour of various molecular glass-forming liquids (salol, ortho-terphenyl (OTP), toluene) in mesoporous geometries of Vycor and Gelsil at different pore sizes (2-10 nm) using a dynamic mechanical analyzer in the frequency range 0.1-100 Hz.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamic mechanical analysis of confined glass-forming liquids

Koppensteiner¹,

Schranz²

2010

Phase Transitions

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Decoupling between the Interfacial and Core Molecular Dynamics of Salol in 2D Confinement

et al. 2015

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Dielectric spectroscopy and differential scanning calorimetry (DSC) were applied to study the molecular dynamics and thermal properties of a low-molecular-weight glass-forming liquid, salol (phenyl salicylate), confined in anodic aluminum oxide membranes of different pore diameters (100−13 nm). On increasing the geometrical confinement, the glass transition temperature shifts toward lower temperatures, while at the same time broadening of the shape of the structural relaxation is observed. This was attributed to the interplay between surface and confinement effects leading to the transition from Vogel−Fulcher− Tammann-like to Arrhenius-like dependence of the structural relaxation times. We have noticed that the temperature of such crossover agrees with the endothermic process detected by DSC. Combined dielectric and calorimetric data have indicated that this phenomenon is related to the decoupling of the dynamics of molecules attached to the pore walls and those at the center. The enhancement of the structural relaxation of the core molecules increases with decreasing pore size possibly due to changes in the packing density. This finding gives a new insight into the behavior of glass-forming liquids under confinement and helps in the understand of the characteristic shift of the dynamic glass transition temperature with decreasing of the pore diameter. ■ INTRODUCTIONManipulation with the physicochemical properties of the materials at the nanoscale, for instance confined polymers, gives an opportunity to obtain unique morphologies that can find promising applications in nanotechnology as miniaturized sensors, magnetic labels, tissue implants, and so on. 1−3 Therefore, the effects at the nanoscale is a very active research area. For example, under confinement on the nanometer scale, the properties of various materials are affected mostly by the finite size and their interactions with the interfaces or confining surfaces. Numerous studies have shown that the melting/ freezing temperature, solid−solid transition, surface free energy, glass transition, and molecular mobility 4,5 are strongly affected by one or two-dimensional confinement. These changes are hotly discussed in the context of varying pore sizes 6−8 or film thicknesses. 9,10 In addition, the strength and the type of interactions between the confined molecules and pore walls (or a substrate) play a key role and have an important impact on the basic physical properties of different materials and potential applications. 11 Despite the intensive studies, the behavior of glass-forming liquids under confinement is still very puzzling. It is very difficult to rationalize or generalize it, because of the variety of theoretical concepts and experimental results that scatter a lot depending on the confining environment or surface interactions. 12,13 According to literature data, the glass transition temperature T g can decrease, increase, or even remain unaffected under nanoconfinement. 6,14−16 The influence of the spatial restriction on T g can be discussed in t...

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Heterogeneous relaxation dynamics of nano-confined salol probed by DMA

Cited by 15 publications

References 49 publications

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

Dynamic mechanical analysis of confined glass-forming liquids

Decoupling between the Interfacial and Core Molecular Dynamics of Salol in 2D Confinement

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