TY - JOUR
T1 - An electrospray technique for hyperquenched glass calorimetry studies
T2 - Propylene glycol and di-n-butyl phthalate
AU - Wang, Li Min
AU - Borick, Steve
AU - Angell, Charles
N1 - Funding Information:
This work was supported by the NSF under Solid State Chemistry Grant No. DMR 0082535. The authors have profited from stimulating discussions with Andreas Heuer, Jeppe Dyre, Martin Goldstein, and Francesco Sciortino.
PY - 2007/11/1
Y1 - 2007/11/1
N2 - We describe an electrospray technique for in situ preparation, for differential scanning calorimetry study, of samples of molecular liquids quenched into the glassy state on extremely short time scales (hyperquenched). We study the cases of a hydrogen-bonded liquid, propylene glycol, PG and a Van der Waals liquid, di-n-butyl phthalate DBP. Using a fictive temperature method of obtaining the temperature dependence of enthalpy relaxation, we show that the electrospray method yields quenching rates of ∼105 K/s, while the more common method, dropping a sealed pan of sample into liquid nitrogen, yields only 120 K/s. These hyperquenched samples start to relax, exothermically, far below the glass temperature, at a temperature (0.75Tg) where the thermal energy permits escape from the shallow traps in which the system becomes localized during hyperquenching. This permits estimation of the trap depths, which are then compared with the activation energy estimated from the fictive temperature of the glass and the relaxation time at the fictive temperature. The trap depth in molar energy units is compared with the 'height of the landscape' for PG, the quasi-lattice energy of the liquid based on the enthalpy of vaporization, and the single molecule activation energy for diffusion in crystals. The findings are consistent with the mechanism of relaxation invoked in a current model of relaxation in glassforming liquids. In the case of di-n-butyl phthalate we investigate the additional question of sub-Tg annealing effects. We find the 'shadow' glass transition, (an annealing prepeak) seen previously only in multicomponent mineral and metallic glasses. The phenomenon is important for understanding microheterogeneities in viscous liquid structures.
AB - We describe an electrospray technique for in situ preparation, for differential scanning calorimetry study, of samples of molecular liquids quenched into the glassy state on extremely short time scales (hyperquenched). We study the cases of a hydrogen-bonded liquid, propylene glycol, PG and a Van der Waals liquid, di-n-butyl phthalate DBP. Using a fictive temperature method of obtaining the temperature dependence of enthalpy relaxation, we show that the electrospray method yields quenching rates of ∼105 K/s, while the more common method, dropping a sealed pan of sample into liquid nitrogen, yields only 120 K/s. These hyperquenched samples start to relax, exothermically, far below the glass temperature, at a temperature (0.75Tg) where the thermal energy permits escape from the shallow traps in which the system becomes localized during hyperquenching. This permits estimation of the trap depths, which are then compared with the activation energy estimated from the fictive temperature of the glass and the relaxation time at the fictive temperature. The trap depth in molar energy units is compared with the 'height of the landscape' for PG, the quasi-lattice energy of the liquid based on the enthalpy of vaporization, and the single molecule activation energy for diffusion in crystals. The findings are consistent with the mechanism of relaxation invoked in a current model of relaxation in glassforming liquids. In the case of di-n-butyl phthalate we investigate the additional question of sub-Tg annealing effects. We find the 'shadow' glass transition, (an annealing prepeak) seen previously only in multicomponent mineral and metallic glasses. The phenomenon is important for understanding microheterogeneities in viscous liquid structures.
KW - Calorimetry
KW - Enthalpy relaxation
KW - Fragility
KW - Glass transition
KW - Structural relaxation
KW - Thermodynamics
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U2 - 10.1016/j.jnoncrysol.2007.04.041
DO - 10.1016/j.jnoncrysol.2007.04.041
M3 - Article
AN - SCOPUS:34548780340
SN - 0022-3093
VL - 353
SP - 3829
EP - 3837
JO - Journal of Non-Crystalline Solids
JF - Journal of Non-Crystalline Solids
IS - 41-43
ER -