Structural relaxation as a forked road to crystallization and glass transition of vapor-deposited amorphous molecular systems

Ishii, Kikujiro; TAKEI, Masaki; Yamamoto, Masatsugu; Nakayama, Hideyuki

doi:10.1016/j.cplett.2004.09.074

Cited by 11 publications

(14 citation statements)

References 16 publications

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“…On the other hand, as already mentioned in the above section, the SCLs of the four compounds were found to crystallize when the temperature was raised into a certain region characteristic to each compound. This change was confirmed by the appearance of Bragg peaks in the X-ray diffraction patterns 16,17,26 and changes in Raman spectra, 17,26 and was also visually detected by an abrupt increase in laserlight scattering. Thus, the temperature boundary between SCL and crystalline regions was determined for all samples, as shown with another dashed line in each part of Figure 1.…”

Section: Stability Of the Glass Against The Thermal Motion Ofmentioning

confidence: 55%

“…As has been described in our previous papers, 4,14,15,17 laser light reflected from the sample on a metal substrate showed a periodic change in intensity as sample thickness increased via constant-rate vapor deposition. This was due to changing conditions of the light interference in the sample.…”

Section: Resultsmentioning

confidence: 84%

“…In our previous paper, 17 we defined the temperature T r at which the V m evolution changes from normal thermal expansion to an evolution accompanying a rapid structural relaxation. We marked this point on each fringe in Figure 1 with an open circle.…”

Section: Stability Of the Glass Against The Thermal Motion Ofmentioning

confidence: 99%

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Behavior of Glass and Supercooled Liquid Alkylbenzenes Vapor-Deposited on Cold Substrates: Toward the Understanding of the Curious Light Scattering Observed in Some Supercooled Liquid States

Ishii¹,

Nakayama²,

Moriyama³

et al. 2009

Bulletin of the Chemical Society of Japan

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Ethylbenzene (EB) films prepared on cold metal substrates by vapor deposition in vacuum show a curious light scattering in the supercooled liquid (SCL) state when the temperature is raised at a constant rate. To investigate the cause of this phenomenon, we examined the behavior of similarly prepared samples of a series of alkylbenzenes. We found that the vapor-deposited glass of propylbenzene (PB) and isopropylbenzene (IPB) showed a deposition-temperature (T d ) dependence of the initial molar volume (V m ) on deposition similar to EB glass. Interestingly, the samples of the three compounds, which were formed initially as glasses with V m much larger than that of SCL at the same temperature, exhibited the curious light scattering when they transformed to SCL states after the temperature elevation to above their glass-transition temperature, while the corresponding samples with initial V m smaller than that of SCL did not exhibit this light scattering. On the basis of these observations, a hypothesis on the cause of the light scattering in the SCL state is proposed in relation to structural transformation between different SCL states. A microscopic mechanism of the formation of a high-density glass with V m smaller than that of SCL is briefly discussed by referring to the observations of toluene samples which showed a slightly different T d dependence of V m and did not show the curious light scattering in the SCL state.We have studied the structure and relaxation behavior of amorphous molecular systems prepared by vapor deposition on cold metal substrates. 16 The samples were films with a thickness of about 10¯m. Such amorphous samples usually tend to crystallize when they are annealed with temperature elevation. 16 However, vapor-deposited amorphous samples of certain compounds undergo a glass transition and transform into supercooled liquid (SCL) states by temperature elevation without experiencing crystalline states. 710 Similar phenomena have been known for a variety of bulk amorphous materials prepared by liquid quenching.1113 Such special amorphous states are called glasses by analogy with conventional glass. A common structural feature of these glass-forming molecular compounds is their flexibility which permits various intra-and intermolecular conformations and hinders crystallization.We found that glass samples of ethylbenzene (EB) and related alkylbenzenes could be prepared by vapor-deposition with good reproducibility. We studied the properties of these materials using laser light interference in film samples.14,15 One of the remarkable observations during these studies was that the density and relaxation behavior of the glass state systematically depended upon the vapor-deposition temperature (T d ). 15 Glass samples deposited at a T d much lower than the glass-transition temperature (T g ) had a lower density than that estimated for the SCL state at the same temperature. In this paper, we call such a glass "low-density glass" (LDG). In contrast, glass samples deposited at a T d close to T g sometim...

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Section: Stability Of the Glass Against The Thermal Motion Ofmentioning

confidence: 55%

Section: Resultsmentioning

confidence: 84%

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Behavior of Glass and Supercooled Liquid Alkylbenzenes Vapor-Deposited on Cold Substrates: Toward the Understanding of the Curious Light Scattering Observed in Some Supercooled Liquid States

Ishii¹,

Nakayama²,

Moriyama³

et al. 2009

Bulletin of the Chemical Society of Japan

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“…On the basis of the above observations, we have schematically shown [14] a diagram on the structural changes of vapor-deposited amorphous molecular systems as is partly reproduced in Fig. 3.…”

Section: Discussionmentioning

confidence: 96%

“…To explore the relation between the direct crystallization and glass transition, we have studied the behaviors of the systems made of two compounds [13,14]. The compounds chosen were chlorobenzene that undergoes direct crystallization from its neat amorphous state and toluene or ethylbenzene that undergo glass transitions from their neat glass states.…”

Section: Discussionmentioning

confidence: 99%

Formation and stability of amorphous molecular systems: As the prototype of functional amorphous organic materials

Ishii

Nakayama

2007

Journal of Non-Crystalline Solids

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Microstructure Evolution during Crystallization of Vapor‐Deposited Hexanitroazobenzene Films

Knepper

Browning

Wixom

et al. 2012

Propellants Explo Pyrotec

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Vapor‐deposited hexanitroazobenzene (HNAB) films were observed to form a dense amorphous structure that crystallizes to a mixture of the HNAB‐II polymorph and an unidentified structure over a period ranging from hours to weeks depending on the ambient temperature. Films crystallized at various temperatures were characterized using scanning electron microscopy, atomic force microscopy, X‐ray diffraction, and Raman spectroscopy to measure the impact of crystallization temperature on resultant microstructure. Crystallization temperature was observed to have different effects on film microstructure over two temperature regimes. At temperatures below approximately 65 °C, increases in temperature led to a greater fraction of the film forming the HNAB‐II polymorph and caused subtle changes in morphology. However, at higher temperatures, a thin surface layer was observed to form prior to crystallization, which led to films composed primarily of the unknown crystal structure with conspicuous differences in morphology.

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Structural relaxation as a forked road to crystallization and glass transition of vapor-deposited amorphous molecular systems

Cited by 11 publications

References 16 publications

Behavior of Glass and Supercooled Liquid Alkylbenzenes Vapor-Deposited on Cold Substrates: Toward the Understanding of the Curious Light Scattering Observed in Some Supercooled Liquid States

Behavior of Glass and Supercooled Liquid Alkylbenzenes Vapor-Deposited on Cold Substrates: Toward the Understanding of the Curious Light Scattering Observed in Some Supercooled Liquid States

Formation and stability of amorphous molecular systems: As the prototype of functional amorphous organic materials

Microstructure Evolution during Crystallization of Vapor‐Deposited Hexanitroazobenzene Films

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