TY  - JOUR
A1  - Raman Venkatesan, Thulasinath
A1  - Gulyakova, Anna A.
A1  - Gerhard, Reimund
T1  - Influence of film stretching on crystalline phases and dielectric properties of a 70/30 mol% poly(vinylidenefluoride-tetrafluoroethylene) copolymer
JF  - Journal of advanced dielectrics
N2  - Polyvinylidene fluoride (PVDF)-based copolymers with tetrafluoroethylene (P(VDF-TFE)), trifluoroethylene (P(VDF-TrFE)) or hexafluoropropylene (P(VDF-HFP)) are of strong interest due to the underlying fundamental mechanisms and the potential ferro-, pyro- and piezo-electrical applications. Their flexibility and their adaptability to various shapes are advantageous in comparison to inorganic ferroelectrics. Here, we study the influence of stretching temperature on the crystalline phases and the dielectric properties in P(VDF-TFE) films by means of Dielectric Relaxation Spectroscopy (DRS), Fourier-Transform InfraRed spectroscopy (FTIR), Wide-Angle X-ray Diffraction (WAXD), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Especially, the effect of stretching and the influence of the temperature of stretching on the mid-temperature (T-mid) transition are studied in detail. The results show that stretching has a similar effect as that on PVDF, and we observe an increase in the fraction of ferroelectric beta-phase with a simultaneous increment in both melting point (T-m) and crystallinity (chi(c)) of the copolymer. While an increase in the stretching temperature does not have a profound impact on the amount of ferroelectric phase, the stability of the ferroelectric phase seems to improve - as seen in the reduction of the Full Width at Half Maximum (FWHM) of the WAXD peaks in both parallel and perpendicular directions to the molecular chain axis. The observation is also supported by the reduction of dissipation losses with an increase in stretching temperature - as seen in DRS measurements. Finally, both stretching itself and the temperature of stretching affect the various molecular processes taking place in the temperature range of the T-mid transition.
KW  - P(VDF-TFE) copolymer
KW  - dielectric properties
KW  - crystalline phases
KW  - film
KW  - stretching
KW  - mid-temperature transition
Y1  - 2020
U6  - https://doi.org/10.1142/S2010135X2050023X
SN  - 2010-135X
SN  - 2010-1368
VL  - 10
IS  - 5
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Mazurek, P.
A1  - Yu, L.
A1  - Gerhard, Reimund
A1  - Wirges, Werner
A1  - Skov, A. L.
T1  - Glycerol as high-permittivity liquid filler in dielectric silicone elastomers
JF  - Journal of applied polymer science
N2  - A recently reported novel class of elastomers was tested with respect to its dielectric properties. The new elastomer material is based on a commercially available poly(dimethylsiloxane) composition, which has been modified by embedding glycerol droplets into its matrix. The approach has two major advantages that make the material useful in a dielectric actuator. First, the glycerol droplets efficiently enhance the dielectric constant, which can reach astonishingly high values in the composite. Second, the liquid filler also acts as a softener that effectively decreases the elastic modulus of the composite. In combination with very low cost and easy preparation, the two property enhancements lead to an extremely attractive dielectric elastomer material. Experimental permittivity data are compared to various theoretical models that predict relative permittivity changes as a function of filler loading, and the applicability of the models is discussed. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44153.
KW  - crosslinking
KW  - dielectric properties
KW  - elastomers
KW  - sensors and actuators
Y1  - 2016
U6  - https://doi.org/10.1002/app.44153
SN  - 0021-8995
SN  - 1097-4628
VL  - 133
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -