Glass transition properties of PMMA thin shells deposited on rodlike calcium carbonate particles

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Rodlike capsules consisting of a calcium carbonate core and a thin shell of poly(methyl methacrylate) (PMMA) were synthesized. The shell thickness d ranged from 8 to 93 nm, and the degree of crosslink Xc for the polymer shell ranged from 0 to 7.0wt%, where Xc is defined as the mass content of the crosslink monomer (ethylene glycol dimethacrylate). The glass transition temperature Tg and the length scale for dynamic heterogeneity at the glass transition ξ(Tg) for the polymer thin shells were evaluated by temperature-modulated differential scanning calorimetry. It was found that Tg is not altered from the bulk value for d ≥ ca. 20 nm for both filled and hollow shells. The thinnest non-crosslinked shell (d = 8 nm) exhibited a lowered Tg from the bulk value. As for ξ(Tg), no distinct dependence on d was observed for non-crosslinked filled shells. Correlation between ξ(Tg) and Tg was also revealed, which is interpreted in terms of the concept of cooperatively rearranging region.