No abstract

Confined at the nanoscale level, polymers crystallize much slower than in bulk, and in some cases the formation of ordered structures results inhibited for extremely long experimental time scales. Here, we report on the thickness dependence of the cold crystallization of thin poly(l-lactide) (PLLA) films (<300 nm), capped between two aluminum (Al) layers. The crystallization kinetics was monitored by means of dielectric relaxation spectroscopy, following the reduction in dielectric strength during annealing in isothermal experiments. We exploited a recently developed analytical method assessing the impact of irreversible chain adsorption and permitting to disentangle finite size and interfacial effects. In line with previous literature, the conversion time increased upon reduction of the thickness and crystallization was inhibited in films thinner than 10 nm. Moreover, we analyzed the thickness dependence of the dielectric strength and obtained the gradient in segmental mobility inside our capped films. We conclude that irreversible adsorption of chains onto the Al electrodes ultimately leads to a reduction in molecular mobility compared to the bulk.

International audienceAn attractive methodology based on diazonium chemistry has been developed for the surface modification of polymers such as polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS). The grafting procedure involves the in situ formation of diazoates in basic aqueous solution. The reactivity of calix[4]arene-tetradiazonium salts and a classical aryldiazonium salt was examined through comparative studies on gold and polymer surfaces. The surfaces were analyzed with a combination of techniques such as AFM, XPS, and ellipsometry. The results highlighted the fact that the calix[4]arene molecules are grafted as a robust and uniform monolayer both on gold and polymer surfaces, allowing a fine control over surface modification. Furthermore, the chemical postfunctionalization of the grafted calixarene platforms equipped with carboxylic-pendant groups was successfully performed with either an amine or an alcohol. These results open real possibilities in the controlled immobilization on polymers of a wide variety of molecules of interest such as biomolecules or chromophores and in the tailoring of polymer properties

(1) IQFR-CSIC; (2) EM-CSIC Polymer nanospheres with different size distributions are prepared by two different methods: with and without the aid of an anionic surfactant. Calorimetric traces of these nanospheres show a different glass transition temperature, with respect to that of the bulk, which has been discussed in terms of an entropy model. The total confinement, imposed by the spherical geometry, leads to a limiting number of repeating polymer units in the sphere and thus to a reduction of the possible configuration states of the polymer chains. This is ultimately related to variations in the bulk value of the glass transition temperature. The model is evaluated against our calorimetric measurements as well as with the data available in the literature. Good agreement between data and model is found for many cases, proving that confinement can be related to reductions in the entropy of these nanosystems.