A Brillouin light scattering study of the λ transition in liquid sulphur

Scarponi, F.; Fioretto, D.; Crapanzano, Laura; Monaco, G.

doi:10.1080/14786430601032402

Cited by 4 publications

(6 citation statements)

References 17 publications

(25 reference statements)

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“…contrary, both M ′ and M ′′ display a continuous smooth decreasing trend across the λ-transition [18,19] testifying a decrease of the structural relaxation time (the orthodox behaviour in ordinary liquids), and not the increase expected on the basis of the Maxwell relation. The situation becomes even more puzzling considering ultrasonic experiments [15,20,21] performed in the 1-10 MHz window, where the timescale of the probe is much longer than the 10 ns expected for the relaxation time.…”

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Origin of theλTransition in Liquid Sulfur

et al. 2007

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Developing a novel experimental technique, we applied photon correlation spectroscopy using infrared radiation in liquid Sulphur around T λ , i.e. in the temperature range where an abrupt increase in viscosity by four orders of magnitude is observed upon heating within few degrees. This allowed us -overcoming photo-induced and absorption effects at visible wavelengths -to reveal a chain relaxation process with characteristic time in the ms range. These results do rehabilitate the validity of the Maxwell relation in Sulphur from an apparent failure, allowing rationalizing the mechanical and thermodynamic behavior of this system within a viscoelastic scenario. PACS numbers: 62.60.+v,64.70.Ja,62.10.+s, Common wisdom holds that liquids become less viscous as the temperature is raised. On a microscopic ground, indeed, viscosity can be regarded as arising from continual brushing of molecules which are close to each other. On increasing temperatures the more vigorous thermal motion of the molecules is expected to render such mutual friction progressively less effective. This naive description provides a qualitative interpretation of the decrease in viscosity normally observed in almost all substances as the temperature increases. There exist, however, a few remarkable exceptions exhibiting complex behavior, which can be regarded as extreme examples of how critically viscosity depends upon molecular interactions. Specifically, there are ranges of temperatures in which the viscosity of Sulphur exhibits anomalous temperature dependence. In the liquid state, just above melting (T m =119 o C), eight-membered rings (S8) are the most abundant species, and the viscosity slightly decreases with temperature as normally expected, reaching values as low as 0.01 Pa·s at T = 157 o C. Further increase of temperature causes a dramatic increase of viscosity [1], accompanied by gross changes in optical [2,3,4] and thermodynamic [5,6] properties, which, at T ≈185 o C, reaches a maximum value of 100 Pa·s. Beyond this temperature, a gradual viscosity decrease is observed. Although this phenomenon, known as λ-transition (T λ = 159 o C), has been tackled for more than 150 years, its comprehension is still far from being reached: to rationalize this puzzling temperature dependence of viscosity, indeed, a liquid-liquid transition from a monomeric (i.e. a S8 rings liquid) to a polymeric phase has been invoked [7,8]. The temperature dependence of the mass fraction of S atoms participating in the polymeric component turns out to be a central parameter for extracting information on many thermodynamic aspects of the λ-transition [9,10]. This phenomenon has been classified as a living polymerization [11] transition that essentially involves two steps, the initiation (formation of diradicals through opening of S8 rings) and propagation (concatenation of species to form long polymeric chains). Thermo-chemical models were developed in the past [12,13,14] to relate the transport properties of liquid sulphur to the underlying polymerization phenomenon. T...

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Origin of theλTransition in Liquid Sulfur

et al. 2007

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“…Fig. 6 displays the temperature dependence of the sound velocity in the glassy phase together with that measured in the MHz [7,27,28], GHz [13] and THz [12] frequency ranges in the liquid phase on crossing the λ transition. The differences in the liquid sulfur data corresponding to different frequencies are due to the effect played by the structural relaxation process.…”

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“…Recently, the polymeric phase of sulfur has been investigated by means of inelastic X-ray scattering (IXS) and Brillouin light scattering (BLS) techniques and by infrared photon correlation spectroscopy [12][13][14]. A slow relaxation process has been found in the millisecond time scale.…”

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Brillouin light scattering study of polymeric glassy sulfur

Ruta

Monaco

Scarponi

et al. 2011

Journal of Non-Crystalline Solids

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“…Figure displays the temperature dependence of the sound velocity measured in the GHz and THz frequency range in the glassy state together with that measured in the MHz, − GHz, and THz frequency ranges in the liquid phase on crossing the λ transition. The differences observed in the liquid phase have been already discussed; therefore, we keep our attention on the comparison between the high frequency sound velocity in the polymeric liquid sulfur and the one measured in the corresponding glassy state.…”

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“…Temperature dependence of the sound velocity v L of the longitudinal acoustic excitations. The values measured in the glassy state in the GHz (blue circles) and THz (magenta stars) frequency range are reported together with those measured in the liquid phase in the MHz (empty violet triangles and green hexagons), − in the BLS (empty purple circles), and in the IXS (red squares) frequency range. The orange empty circle has been calculated from the relation v 0 ( T g ) = 1/[ρ( T g )χ T 0 ( T g )] 1/2 using the values of χ T 0 ( T g ) obtained from eq .…”

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Nonergodicity Factor, Fragility, and Elastic Properties of Polymeric Glassy Sulfur

et al. 2011

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We present a detailed investigation of the vibrational dynamics of glassy sulfur (g-S). The large frequency range spanned in this study has allowed us to carefully scrutinize the elastic properties of g-S and to analyze their relation to various features of both the glassy and the liquid state. In particular, the acoustic properties of g-S present a quasi-harmonic behavior in the THz frequency range, while at lower frequency, in the GHz range, they are affected by a strong anharmonic contribution. Moreover, the high frequency (THz) dynamics of g-S does not present signatures of the elastic anomalies recently observed in a number of glasses. Despite this apparent contradiction, we show that this finding is not in disagreement with the previous ones. Finally, by considering the correct long wavelength limit of the density fluctuations in the glassy state, we estimate the continuum limit of the nonergodicity factor and we investigate recently proposed relations between the fast dynamics of glasses and the slow dynamics of the corresponding viscous melts.

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A Brillouin light scattering study of the λ transition in liquid sulphur

Cited by 4 publications

References 17 publications

Origin of theλTransition in Liquid Sulfur

Origin of theλTransition in Liquid Sulfur

Brillouin light scattering study of polymeric glassy sulfur

Nonergodicity Factor, Fragility, and Elastic Properties of Polymeric Glassy Sulfur

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