Han Sup Lee

Irreversible extinction of ferroelectric polarization in P(VDF-TrFE) thin films upon melting and recrystallization

We observed the irreversible extinction of ferroelectric polarization in spun coated poly(vinylidene fluoride-co-trifluoroethylene) thin films upon melting and recrystallization. We investigate the alteration of the ferroelectric properties correlated with the preferred polymer crystal orientation with respect to the electrodes using grazing incident scattering, spectroscopy, and electron microscopes. Heat treatment above melting point gave rise to the significant reduction of the ferroelectric performance mainly caused by the modification of molecular orientation of polymer crystals whose c and b axes are perpendicular and parallel to the electrode surface, respectively, leading to almost zero effective electric field.

Graft polymerization of acrylamide onto poly(hydroxybutyrate-co-hydroxy- valerate) films

Graft polymerization of acrylamide onto poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)) film using benzoyl peroxide was studied, and the morphology and properties of grafted film were investigated. The effect of various polymerization conditions such as reaction time, monomer and initiator concentration on the graft% was studied. Graft% was increased initially with the increase of reaction time, monomer and initiator concentration, and levelled off above a certain level. Grafted films with different graft% and film thickness showed different internal structures. To elucidate the morphology of grafted film, characterization methods such as Fourier transform infra-red and X-ray photoelectron spectroscopy and dimensional change analysis were used. It was observed that grafting of polyacrylamide occurred well inside the film, not just being limited to the film surface. Swelling phenomena of grafted film in various solvent mixtures were also investigated in order to test the applicability of the grafted polymers to a permselectivity.