Structural Relaxation in Nanometer Thin Layers of Glycerol

Capponi, Simona; Napolitano, Simone; Behrnd, N.-R.; Couderc, Gaitan; Hulliger, Jürg; Wübbenhorst, Michael

doi:10.1021/jp108151p

Cited by 36 publications

(34 citation statements)

References 22 publications

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“…Glycerol films with thickness in the range between 10 and 130 nm showed a tremendous enhancement in the dielectric strength, over three times higher than the value measured for bulk glycerol films deposited well above the glass transition temperature T g [16]. This behavior is indeed consistent with the concept of a liquid state having enhanced medium range order (MRO) and enhanced BOO, with respect to the ordinary liquid phase (OL).…”

Section: Experimental Evidence Of the Mrcossupporting

confidence: 75%

1D Confinement Stabilizes Non-equilibrium Liquid Phase with Enhanced Orientational Order

Capponi

Napolitano

Wübbenhorst

2015

Non-Equilibrium Phenomena in Confined Soft Matter

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Recent models of the glass transition rationalize the relevant features of vitrification by introducing the concept of medium range order in supercooled liquids. In particular, a crucial role is assigned to the orientational order induced by intermolecular bonding (bond orientational order, BOO). Although this idea is very appealing, severe difficulties limit the experimental determination of the BOO in molecular liquids: because of the small difference in entropy and in form factor between the isotropic liquid and the phase rich in orientational order, calorimetry and scattering techniques cannot be used to assess the BOO. In this chapter we describe an innovative model to investigate BOO via broadband dielectric spectroscopy. We verified that ultrathin films of polyols deposited by physical vapor deposition below their glass transition temperature show an extraordinary enhancement in bond orientational, indicated by a huge enhancement of the dielectric strength with respect to the bulk values. Hint of an underlying phase transition was found from a liquid phase enriched in bond orientational order, with a metastable character, towards an ordinary liquid phase. The kinetic stability of the metastable phase could be tuned by varying the deposition conditions and the molecular size. The impact of film thickness and of the presence of a solid substrate on the persistence of enhanced BOO were also investigated. We demonstrate that confinement stabilizes the non-equilibrium character of our supercooled liquids with enhanced orientational order.

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Section: Experimental Evidence Of the Mrcossupporting

confidence: 75%

1D Confinement Stabilizes Non-equilibrium Liquid Phase with Enhanced Orientational Order

Capponi

Napolitano

Wübbenhorst

2015

Non-Equilibrium Phenomena in Confined Soft Matter

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“…1), exceeding by more than threefold the value measured for bulk glycerol films deposited well above T g (ref. 30). Such a large value cannot be rationalized by a mere increase in density, which would prompt non-physical changes, nor by a larger effective dipole moment, due to a very unlikely perfectly planar orientation in the direction of the electric field.…”

Section: Resultsmentioning

confidence: 96%

“…Films of glycerol, threitol and xylitol (degree of purity 499%, purchased from Aldrich), were prepared by organic molecular beam deposition directly on the IDE 30,39,40 , which made it possible to probe their dielectric response. The bulk material was heated above its melting temperature in a crucible connected, via a pneumatic valve, to a vacuum chamber maintained at a pressure pB10 -8 mbar.…”

Section: Methodsmentioning

confidence: 99%

“…Further isothermal measurements were performed on glycerol films of different thicknesses (9,15,18,26,30,55, 89 nm): the temperature of the IDE was varied in the same range as above, but in steps of 5 K. The sample was held at each annealing temperature for 2 h. The conversion rate into the OL phase, v, was estimated by fitting isothermal scans with linear decays v ¼ Dl/(t À t 0 ), where Dl is the fraction of transformed film, and t 0 indicates the onset of measurement. The value of Dl is obtained from the time evolution of the dielectric strength under the assumption that De is the sum of the contribution of the two liquid phases averaged over their volume fractions according to We ruled out the possibility that the larger values of De and of t observed in the medium-range crystalline order phase are actually induced by the presence of water or other contamination in the films.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Supercooled liquids with enhanced orientational order

2012

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The nature of the glass transition, the transformation of a liquid into a disordered solid, still remains one of the most intriguing unsolved problems in materials science. Recent models rationalize crucial features of vitrification with the presence of medium-range ordered regions coexisting with the isotropic liquid. Here, in line with this prediction, we report an extraordinary enhancement in bond orientational order in ultrathin films of supercooled polyols, grown by physical vapour deposition. By varying the deposition conditions and the molecular size, we could tune the kinetic stability of the liquid phase enriched in bond orientational order towards conversion into the ordinary liquid phase. We observed a strong increase in the dielectric strength with respect to the ordinary supercooled liquid and slower structural dynamics, suggesting the existence of a metastable liquid phase with improved orientational correlations.

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“…Dielectric spectroscopy is a very advantageous noninvasive technique for monitoring the annealing process of ultrastable glasses, 37,38 partly due to its sensitivity and broad frequency range. 39 Because the transformation times are long compared with the structural or α relaxation time of the conventional liquid at the annealing temperature, the complete loss spectrum can be recorded multiple times in the course of the annealing process.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of glass-forming liquids. XVI. Observation of ultrastable glass transformation via dielectric spectroscopy

Chen

Sepúlveda²,

Ediger³

et al. 2013

The Journal of Chemical Physics

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Articles you may be interested inThe transformation of vapor-deposited ultrastable glasses of indomethacin (IMC) into the supercooled liquid state near T g is monitored by means of dielectric spectroscopy. Films with thickness between 400 and 800 nm are deposited on differential interdigitated electrode cells and their loss profiles are measured during isothermal annealing using a dual-channel impedance technique for frequencies between 0.03 and 100 Hz. All dielectric loss spectra observed during the transformation process can be explained by a volume fraction of the supercooled liquid that increases linearly with time. From the early stages of the transformation to the liquid that is formed via complete annealing of the ultrastable glass, the average dielectric relaxation time as well as the distribution of relaxation times of the liquid component are identical to those of the conventional liquid obtained by cooling the melt. The dependence of the transformation rate on the film thickness is consistent with a growth front mechanism for the direct conversion from the ultrastable glass to the equilibrium supercooled liquid. We conclude that the IMC liquid recovered from the ultrastable glass is structurally and dynamically identical to the conventional supercooled state.

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Structural Relaxation in Nanometer Thin Layers of Glycerol

Cited by 36 publications

References 22 publications

1D Confinement Stabilizes Non-equilibrium Liquid Phase with Enhanced Orientational Order

1D Confinement Stabilizes Non-equilibrium Liquid Phase with Enhanced Orientational Order

Supercooled liquids with enhanced orientational order

Dynamics of glass-forming liquids. XVI. Observation of ultrastable glass transformation via dielectric spectroscopy

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