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The logarithmic relaxation process and the critical temperature of liquids in nano-confined states

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ABSTRACT

The logarithmic relaxation process is the slowest of all relaxation processes and is exhibited by only a few molecular liquids and proteins. Bulk salol, which is a glass-forming liquid, is known to exhibit logarithmic decay of intermediate scattering function for the β-relaxation process. In this article, we report the influence of nanoscale confinements on the logarithmic relaxation process and changes in the microscopic glass-transition temperature of salol in the carbon and silica nanopores. The generalized vibrational density-of-states of the confined salol indicates that the interaction of salol with ordered nanoporous carbon is hydrophilic in nature whereas the interaction with silica surfaces is more hydrophobic. The mode-coupling theory critical temperature derived from the QENS data shows that the dynamic transition occurs at much lower temperature in the carbon pores than in silica pores. The results of this study indicate that, under nano-confinements, liquids that display logarithmic β-relaxation phenomenon undergo a unique glass transition process.

No MeSH data available.


The vibrational density-of-states for bulk salol and salol confined in Carbon pores (39 ± 1 Å) and Silica pores (40 ± 1 Å) at 100 K.
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f1: The vibrational density-of-states for bulk salol and salol confined in Carbon pores (39 ± 1 Å) and Silica pores (40 ± 1 Å) at 100 K.

Mentions: where is the Bose population factor35. The resulting vibrational density-of-states for bulk salol, salol confined in carbon pores (39 ± 1 Å) and silica pores (40 ± 1 Å) are shown in Fig. 1. The peak around 6 meV is associated with the translative vibrational motions (Boson peak)36. As compared to the bulk sample the translative vibrational motions of confined samples are much damped which is visible from the Fig. 1, indicating the reduction of this degree of freedom upon confinement and slowing down of translative vibrational motion. The suppression of this low energy translative vibrational motion of confined salol molecules must be due to strong hydrogen bond interactions between salol molecules and the surface of the nonporous matrix materials. In addition, the translational peak is less affected for salol in silica pores than that in carbon pores. This indicates that the porous silica material provides a much more hydrophobic environment for salol compared with carbon pores.


The logarithmic relaxation process and the critical temperature of liquids in nano-confined states
The vibrational density-of-states for bulk salol and salol confined in Carbon pores (39 ± 1 Å) and Silica pores (40 ± 1 Å) at 100 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037365&req=5

f1: The vibrational density-of-states for bulk salol and salol confined in Carbon pores (39 ± 1 Å) and Silica pores (40 ± 1 Å) at 100 K.
Mentions: where is the Bose population factor35. The resulting vibrational density-of-states for bulk salol, salol confined in carbon pores (39 ± 1 Å) and silica pores (40 ± 1 Å) are shown in Fig. 1. The peak around 6 meV is associated with the translative vibrational motions (Boson peak)36. As compared to the bulk sample the translative vibrational motions of confined samples are much damped which is visible from the Fig. 1, indicating the reduction of this degree of freedom upon confinement and slowing down of translative vibrational motion. The suppression of this low energy translative vibrational motion of confined salol molecules must be due to strong hydrogen bond interactions between salol molecules and the surface of the nonporous matrix materials. In addition, the translational peak is less affected for salol in silica pores than that in carbon pores. This indicates that the porous silica material provides a much more hydrophobic environment for salol compared with carbon pores.

View Article: PubMed Central - PubMed

ABSTRACT

The logarithmic relaxation process is the slowest of all relaxation processes and is exhibited by only a few molecular liquids and proteins. Bulk salol, which is a glass-forming liquid, is known to exhibit logarithmic decay of intermediate scattering function for the β-relaxation process. In this article, we report the influence of nanoscale confinements on the logarithmic relaxation process and changes in the microscopic glass-transition temperature of salol in the carbon and silica nanopores. The generalized vibrational density-of-states of the confined salol indicates that the interaction of salol with ordered nanoporous carbon is hydrophilic in nature whereas the interaction with silica surfaces is more hydrophobic. The mode-coupling theory critical temperature derived from the QENS data shows that the dynamic transition occurs at much lower temperature in the carbon pores than in silica pores. The results of this study indicate that, under nano-confinements, liquids that display logarithmic β-relaxation phenomenon undergo a unique glass transition process.

No MeSH data available.