In this work, the melting-point depression and molecular dynamics of hexamethyldisilane confined within five controlled pore
glasses, with mean diameters ranging from 7.9 to 23.9 nm, are studied by high-field (9.4 T) nuclear magnetic resonance (NMR),
and the results are discussed with reference to the bulk substance. The melting-point depression in pores with radius
R follows the simplified Gibbs-Thompson equation Δ
T=
k
p/(
R−
s) with a
k
p value of 74 K · nm and an
s value of 1 nm. To our knowledge, this is the first time the
k
p value of hexamethyldisilane is reported. Proton spin-lattice relaxation times (
T
1), spin-spin relaxation times (
T
2), and diffusivities (
D) are reported as a function of temperature. The confinement in the pores gives rise to substantial changes in the molecular
dynamics and the phase behavior. The line-shape measurements reveal a two-phase system assigned to a relatively mobile component
at the pore walls and a crystalline solid at the center of the pores. However, the
T
2 measurements show that the mobile phase also embraces a minor component attributed to nonfrozen liquid in pockets or micropores.
The diffusivity of the major narrow-line component is approximately three orders of magnitude larger than that in the plastic
bulk phase, reflecting fast diffusion of mobile molecules. Below the melting region,
T
1 of the narrow line is significantly shorter than
T
1 of the broad line, suggesting that the molecular reorientation is more hindered close to the surface than at the center of
the pore.
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