Detection of two glass transitions on triton X-100 under confinement
Résumé
Because of the strong tendency of Triton X-100 to crystallize, inclusion in a SBA-15 matrix of 5.7 nm in pore diameter was used as a means to suppress crystallization. Clear evidence that Triton X-100 exists under confinement in the amorphous and supercooled state is given by X-ray diffraction supported by differential scanning calorimetry and dielectric relaxation spectroscopy. From the thermogravimetric analysis, a loading degree of 50% (wt) was estimated; the decomposition of confined Triton X-100 follows a two-step profile, indicating that molecules are partitioned between bulklike and adsorbed, the latter fraction being in a higher proportion. This allowed the unequivocal detection by DSC of two well-resolved glass transitions (∼ 20 K apart), which is a remarkable result obtained by conventional calorimetric analysis in confined systems. The two molecular populations have different mobilities giving rise to two different dielectric relaxation processes: an αTr/SBA bulklike process associated with molecules located more in the center of the pores, slightly slowed down relative to bulk α-relaxation, and an S-process due to molecules absorbed at the walls with significantly hindered mobility. Moreover, an MWS process is detected due to interfacial polarization that builds up between the adsorbed Triton X-100 molecules and SBA pore walls whose temperature dependence seems to be correlated with the one of the S-process. The inclusion in SBA-15 revealed to be a good strategy to simultaneously avoid crystallization and achieve a long-term stabilization of the disordered form.
Mots clés
Calorimetric analysis
Confined systems
Dielectric relaxation spectroscopy
Interfacial polarization
Molecular population
Supercooled state
Temperature dependence
Two glass transition
differential scanning calorimetry
Glass
Glass transition
Molecules
Thermogravimetric analysis
X ray diffraction
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