Critical point in ferroelectric Langmuir-Blodgett polymer films

The ferroelectric critical point has been found in a ferroelectric polymer by exploring the influence of the electric field on the paraelectric-ferroelectric phase transition. Dielectric and pyroelectric measurements on 30-monolayer-thick films of the crystalline copolymer poly(vinylidene fluoride-trifluoroethylene) grown by Langmuir-Blodgett deposition show a single hysteresis loop below the zero-field phase transition temperature $T_{c0\mathrm{}}=80\mathrm{}\pm 10°\mathrm{C},$ double hysteresis loops between $T_{c0\mathrm{}},$ and the critical temperature $T_{\mathrm{cr}}=145\mathrm{}\pm 5\mathrm{}\mathrm{°}\mathrm{C},$ and no hysteresis above $T_{\mathrm{cr}}$ where the critical electric field is $E_{\mathrm{cr}}{=0.93\mathrm{}\pm 0.1\times 10}^9\mathrm{}\mathrm{V}/\mathrm{m}.$