期刊
ACS NANO
卷 4, 期 2, 页码 841-848出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn9014517
关键词
ultrathin polymer films; nanocomposites; confinement effects; glass transition; thermal expansivity; dilatometry; free volume
类别
资金
- FWO (Fonds Wetenschappelijk Onderzoeks - Vlaanderen)
The temperature and thickness dependence of the thermal expansivity of ultrathin thin films of poly(tert-butylstyrene) capped between aluminum layers revealed an unusual and intriguing confinement scenario. Below 50 nm, both the glass transition temperature and the thermal expansion coefficients decreased. Such a mixed behavior implies an enhancement of the molecular mobility, without the presence of any free surface, but dead layers, On the basis of a careful analysis of averaged quantities measured by capacitive dilatometry, we deduced a profile of thermal expansivity that explains our experimental data and previous observations in polymer nanocomposites. The effect of density-conformation coupling in proximity of a nonattractive interface allows the coexistence of an immobilized fraction in direct contact with the metal and an excess of thermal expansivity, arising from the long-range effects of packing frustration penetrating inside the bulk-like core of the film.
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