TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Gulyakova, Anna A. A1 - Frübing, Peter A1 - Gerhard, Reimund T1 - Relaxation processes and structural transitions in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) relaxor-ferroelectric terpolymers as seen in dielectric spectroscopy JF - IEEE transactions on dielectrics and electrical insulation N2 - Dielectric relaxation processes and structural transitions in Poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films with two different monomer compositions were investigated in comparison with Poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer films as reference material. Differential Scanning Calorimetry was employed to assess annealing effects on phase transitions and crystalline structure, while relaxation processes were investigated by means of Dielectric Relaxation Spectroscopy, the results of which indicate the existence of two separate dispersion regions, denoted as processes A and B, respectively. Process A appears at a certain temperature independent of frequency, but is strongly influenced by the crystallisation temperature and the CFE content, while peak B shows typical features of a relaxation process and is less influenced by crystallisation temperature and CFE content. Furthermore, peak B is related to the glass transition which is more pronounced in the terpolymer than in P(VDF-TrFE). A closer analysis indicates that the addition of CFE and thermal annealing gradually shift the ferro-to-paraelectric transition in P(VDF-TrFE) to lower temperatures, while the phase transition is transformed more and more into a relaxation. KW - P(VDF-TrFE-CFE) terpolymer KW - relaxor-ferroelectric polymer KW - dielectric relaxation spectroscopy KW - Curie transition KW - differential scanning calorimetry Y1 - 2018 U6 - https://doi.org/10.1109/TDEI.2018.007440 SN - 1070-9878 SN - 1558-4135 VL - 25 IS - 6 SP - 2229 EP - 2235 PB - Institut of Electrical and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Raman Venkatesan, Thulasinath A1 - Gulyakova, Anna A. A1 - Frübing, Peter A1 - Gerhard, Reimund T1 - Electrical polarization phenomena, dielectric relaxations and structural transitions in a relaxor-ferroelectric terpolymer investigated with electrical probing techniques JF - Materials research express N2 - Dielectric Relaxation Spectroscopy (DRS) and Thermally Stimulated Depolarization Current (TSDC) measurements were employed to study dielectric-relaxation processes, structural transitions and electric-polarization phenomena in poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films. Results from DRS confirm the existence of two separate dispersion regions related to a para-to-ferroelectric phase transition and to the glass transition. The dipolar TSDC peak correlates with the loss peak of the ? relaxation that represents the glass transition. The electric polarization calculated from the dipolar TSDC peak (glass transition) shows a non-linear electric-field dependence and saturates at high electric poling fields. As the observed behaviour is essentially the same as that of the electric polarization obtained from direct polarization-versus-electric-field hysteresis measurements, TSDC experiments are also suitable for studying the polarization in relaxor-ferroelectric polymers. A saturation polarization of 44 mC m(?2) was found for an electric field of 190 MV m(?1). KW - P(VDF-TrFE-CFE) terpolymer KW - relaxor-ferroelectric polymers KW - dielectric relaxation spectroscopy KW - thermally stimulated depolarization current KW - electrical polarization hysteresis Y1 - 2019 U6 - https://doi.org/10.1088/2053-1591/ab5352 SN - 2053-1591 VL - 6 IS - 12 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Thayumanasundaram, Savitha A1 - Raman Venkatesan, Thulasinath A1 - Ousset, Aymeric A1 - Van Hollebeke, Kim A1 - Aerts, Luc A1 - Wubbenhorst, Michael A1 - Van den Mooter, Guy T1 - Complementarity of mDSC, DMA, and DRS Techniques in the Study of T-g and Sub-T-g Transitions in Amorphous Solids BT - PVPVA, Indomethacin, and Amorphous Solid Dispersions Based on Indomethacin/PVPVA JF - Molecular pharmaceutics N2 - Recently, glasses, a subset of amorphous solids, have gained attention in various fields, such as polymer chemistry, optical fibers, and pharmaceuticals. One of their characteristic features, the glass transition temperature (T-g) which is absent in 100% crystalline materials, influences several material properties, such as free volume, enthalpy, viscosity, thermodynamic transitions, molecular motions, physical stability, mechanical properties, etc. In addition to T-g, there may be several other temperaturedependent transitions known as sub-T-g transitions (or beta-, gamma-, and delta-relaxations) which are identified by specific analytical techniques. The study of T-g and sub-T-g transitions occurring in amorphous solids has gained much attention because of its importance in understanding molecular kinetics, and it requires the combination of conventional and novel characterization techniques. In the present study, three different analytical techniques [modulated differential scanning calorimetry (mDSC), dynamic mechanical analysis (DMA), and dielectric relaxation spectroscopy (DRS)] were used to perform comprehensive qualitative/quantitative characterization of molecular relaxations, miscibility, and molecular interactions present in an amorphous polymer (PVPVA), a model drug (indomethacin, IND), and IND/PVPVA-based amorphous solid dispersions (ASDs). This is the first ever reported DMA study on PVPVA in its powder form, which avoids the contribution of solvent to the mechanical properties when a selfstanding polymer film is used. A good correlation between the techniques in determining the T-g value of PVPVA, IND, and IND/ PVPVA-based ASDs is established, and the negligible difference (within 10 degrees C) is attributed to the different material properties assessed in each technique. However, the overall T-g behavior, the decrease in T-g with increase in drug loading in ASDs, is universally observed in all the above-mentioned techniques, which reveals their complementarity. DMA and DRS techniques are used to study the different sub-T-g transitions present in PVPVA, amorphous IND, and IND/PVPVA-based ASDs because these transitions are normally too weak or too broad for mDSC to detect. For IND/PVPVA-based ASDs, both techniques show a shift of sub-T-g transitions (or secondary relaxation peaks) toward the high-temperature region from -140 to -45 degrees C. Thus, this paper outlines the usage of different solid-state characterization techniques in understanding the different molecular dynamics present in the polymer, drug, and their interactions in ASDs with the integrated information obtained from individual techniques. KW - amorphous solids KW - PVPVA KW - indomethacin KW - ASDs KW - dynamic mechanical KW - analysis KW - dielectric relaxation spectroscopy KW - sub-T-g relaxations KW - relaxation dynamics Y1 - 2022 U6 - https://doi.org/10.1021/acs.molpharmaceut.2c00123 SN - 1543-8384 SN - 1543-8392 PB - American Chemical Society CY - Washington ER -