Abstract
The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C≡N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 Å (C14), below which it is not frozen. In addition, phase changes between α-type and β-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Δγ1/α = 22.4 mJ m-2 for the liquid/pore surface (ps) and α-type/ps, and Δγα/β = 3.17 mJ m-2 for α-type/ps and β-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol -1 compared to the bulk value of 12.7 kJ mol-1. The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.
| Original language | English |
|---|---|
| Pages (from-to) | 23162-23169 |
| Number of pages | 8 |
| Journal | Journal of Physical Chemistry B |
| Volume | 109 |
| Issue number | 49 |
| DOIs | |
| Publication status | Published - Dec 15 2005 |
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- Physical and Theoretical Chemistry
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Low temperature properties of acetonitrile confined in MCM-41. / Kittaka, Shigeharu; Iwashita, Takafumi; Serizawa, Akihiro; Kranishi, Miki; Takahara, Shuichi; Kuroda, Yasushige; Mori, Toshinori; Yamaguchi, Toshio.
In: Journal of Physical Chemistry B, Vol. 109, No. 49, 15.12.2005, p. 23162-23169.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Low temperature properties of acetonitrile confined in MCM-41
AU - Kittaka, Shigeharu
AU - Iwashita, Takafumi
AU - Serizawa, Akihiro
AU - Kranishi, Miki
AU - Takahara, Shuichi
AU - Kuroda, Yasushige
AU - Mori, Toshinori
AU - Yamaguchi, Toshio
PY - 2005/12/15
Y1 - 2005/12/15
N2 - The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C≡N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 Å (C14), below which it is not frozen. In addition, phase changes between α-type and β-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Δγ1/α = 22.4 mJ m-2 for the liquid/pore surface (ps) and α-type/ps, and Δγα/β = 3.17 mJ m-2 for α-type/ps and β-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol -1 compared to the bulk value of 12.7 kJ mol-1. The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.
AB - The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C≡N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 Å (C14), below which it is not frozen. In addition, phase changes between α-type and β-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Δγ1/α = 22.4 mJ m-2 for the liquid/pore surface (ps) and α-type/ps, and Δγα/β = 3.17 mJ m-2 for α-type/ps and β-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol -1 compared to the bulk value of 12.7 kJ mol-1. The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.
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U2 - 10.1021/jp052476g
DO - 10.1021/jp052476g
M3 - Article
C2 - 16375278
AN - SCOPUS:30544450481
VL - 109
SP - 23162
EP - 23169
JO - Journal of Physical Chemistry B Materials
JF - Journal of Physical Chemistry B Materials
SN - 1520-6106
IS - 49
ER -