Polarity Matters: Dielectric Relaxation in All-<i>cis</i>-Multifluorinated Cycloalkanes

Theodoridis, A; Papamokos, George; Wiesenfeldt, Mario P.; Wollenburg, Marco; Müllen, Kläus; Glorius, Frank; Floudas, George

doi:10.1021/acs.jpcb.1c00100

Cited by 6 publications

(6 citation statements)

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“…Uniaxially stretched poly(vinylidene fluoride) (PVDF) and its random copolymers with trifluoroethylene (TrFE) having VDF content in the range from 50 to 80 mol % exhibit exceptional ferroelectric and piezoelectric properties. , These properties are attributed to the polar ferroelectric (FE) β-phase. Within the β-phase, the packing of molecular chains is in a planar all-trans conformation that orders all the fluorine atoms on one side of the chain and the hydrogen atoms on the other side, leading to a large spontaneous polarization. − The well-known Curie transition or Curie temperature ( T c ) refers to the transition from the low-temperature FE phase to a high-temperature paraelectric (PE) phase. The latter (PE) is characterized by conformationally disordered chains, packed in a hexagonal lattice .…”

Section: Introductionmentioning

confidence: 99%

P(VDF-TrFE) Copolymer Dynamics as a Function of Temperature and Pressure in the Vicinity of the Curie Transition

2022

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We report on the phase behavior and the respective dynamics in random P(VDF-TrFE) copolymers using standard and temperature-modulated differential scanning calorimetry, X-ray diffraction, and a combination of temperature-and pressuredependent dielectric spectroscopy measurements. Depending on the copolymer composition, the coexistence of three/four weakly ordered phases was identified in the vicinity of the Curie transition (T c ). With respect to the dynamics, we demonstrate that the segmental dynamics associated with the relaxation of constrained amorphous VDF segments at the crystal/amorphous "phase" can be used as a marker of the Curie transition. The corresponding segmental relaxation freezes at about 50 K above the lower liquid-toglass temperature associated with the freezing of amorphous segments away from the interface. Pressure-dependent dielectric measurements provided quantitative insight into (i) the molecular origin of the segmental processes (by employing the pressure sensitivity of relaxation times and the pressure coefficient of the respective T g 's), (ii) the nature of the phase transition at T c , and (iii) information about the stability of phases under the variation of temperature and pressure (through the T−P phase diagram). We show that T c increases linearly with pressure and is accompanied by small volume changes, implying a weakly f irst-order thermodynamic transition. Furthermore, pressure stabilizes the ferroelectric phase over a broader temperature range. This could extend the operating temperature range of ferroelectric devices based on P(VDF-TrFE) copolymers.

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Section: Introductionmentioning

confidence: 99%

P(VDF-TrFE) Copolymer Dynamics as a Function of Temperature and Pressure in the Vicinity of the Curie Transition

2022

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“…This fact indicates that two axial halogens are the ideal number to produce stability in the chairs in 1,2,3,4,5,6‐hexachloro‐ and 1,2,3,4,5,6‐hexafluorocyclohexanes. Regarding dipole moment, it is worth mentioning that the least stable structure (ζ for both HCH and HFH) has the highest dipole moment, an opposite behavior compared to multifluorinated cycloalkanes studied by Theodoridis and co‐workers [27] …”

Section: Resultsmentioning

confidence: 92%

“…Regarding dipole moment, it is worth mentioning that the least stable structure (ζ for both HCH and HFH) has the highest dipole moment, an opposite behavior compared to multifluorinated cycloalkanes studied by Theodoridis and co-workers. [27] A closer inspection of α e , ɛ e , and θ e is insightful since they differ in relative configurational energy but share the feature of two axial and four equatorial halogens. The conformers α e and ɛ e have their axial substituents in an antiparallel orientation,…”

Section: Conformational Analysismentioning

confidence: 99%

Theoretical Exploitation of 1,2,3,4,5,6‐Hexachloro‐ and 1,2,3,4,5,6‐Hexafluorocyclohexane Isomers as Biologically Active Compounds

Martins

Freitas

2022

ChemPhysChem

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Hexachlorocyclohexanes (HCHs) have been widely explored as biological compounds during the last century. However, most of them were banned due to their potential toxicity in humans, animals, and the environment. Revisiting HCHs to explore their biological activity while improving key features is valuable and may lead to a new class of pesticides that utilizes the biological response of HCHs without their toxic characteristics. In this sense, the fluorine atom can be a possible alternative since a large number of therapeutics and agrochemicals have been developed with this halogen in their structure. We have evaluated herein the conformational behavior of HCHs and their bioisosteric fluorinated compounds, namely, hexafluorocyclo-hexanes (HFHs), through quantum-chemical calculations. We also explored the potential of the HCH and HFH isomers as biological compounds by docking them inside three possible targets. It was demonstrated that HCH and HFH have similar ligand-protein interactions with three pockets: the picrotoxin and barbiturate sites of the GABA A receptor and the ryanodine receptor. The results support HFHs as possible alternatives for HCHs since the replacement of Cl with F does not forfeit the main ligand-protein interactions. Finally, we demonstrated that HFHs have a lower log P than HCHs by almost two logarithmic units. This result highlights the role of fluorine in distribution and bioaccumulation.

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“…Substituted cyclohexanes depend strongly on the stereochemistry of the synthesized compounds regarding their dipole moments. 28 Here, the syndiotactic trans-PCHC dimer has a low value of dipole moment because it is highly symmetric, and the existing electric dipoles cancel each other. On the contrary, the isotactic isomer does not have a highly symmetric structure, and its dipole moment is high (Cartesian coordinates of the minimized structures are available in the Supporting Information).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Their structures and their dipole moments are shown in Figure . Substituted cyclohexanes depend strongly on the stereochemistry of the synthesized compounds regarding their dipole moments . Here, the syndiotactic trans -PCHC dimer has a low value of dipole moment because it is highly symmetric, and the existing electric dipoles cancel each other.…”

Section: Results and Discussionmentioning

confidence: 99%

Dynamics of Poly(cyclohexene carbonate) as a Function of Molar Mass

Spyridakou

Gardiner

Papamokos

et al. 2022

ACS Appl. Polym. Mater.

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Stereoregular poly(cyclohexene carbonate) (PCHC) homopolymers were prepared via copolymerization of cyclohexene oxide and carbon dioxide (CO2) using (R,R)-(salcy)-CoCl and bis(triphenylphosphine)iminium chloride as a catalyst. The homopolymers had molar masses in the range of 4800–33,000 g mol–1 and relatively narrow dispersity after careful fractionation, as required for the molecular dynamics investigation. We employed differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, for investigating the thermal properties and the molecular dynamics, respectively. The segmental dynamics in the vicinity of the liquid-to-glass temperature was very complex. The dual segmental processes were inseparable by decreasing the temperature or by increasing the pressure. Based on DFT calculations of the dipole moment, they were ascribed to different stereo sequences of the PCHC backbone. The limiting glass temperature, T g, for very high molar masses was ∼125 °C. The high T g value obtained herein well justifies its application as a CO2-based alternative for polystyrene (PS) in a variety of materials based on block copolymers. Moreover, fragility increased with increasing molar mass with values intermediate to poly(styrene) and poly(cyclohexyl methacrylate). The flexible cyclohexyl group in PCHC undergoing intramolecular chair-to-chair conversion increases the packing ability and consequently decreases the fragility. PCHC is a brittle material because it lacks entanglements even for the higher molar masses investigated herein, which is relevant for application as a PS substitute. Within the investigated range of molar masses, the dependences of the terminal relaxation times, τΝΜ, and of the zero-shear viscosity, ηο, on the molar mass, M, are τΝΜ/τSM ∼ M 3.2 and ηο ∼ M 1.4, revealing an intermediate behavior between Rouse and entangled chains.

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Polarity Matters: Dielectric Relaxation in All-cis-Multifluorinated Cycloalkanes

Cited by 6 publications

References 61 publications

P(VDF-TrFE) Copolymer Dynamics as a Function of Temperature and Pressure in the Vicinity of the Curie Transition

P(VDF-TrFE) Copolymer Dynamics as a Function of Temperature and Pressure in the Vicinity of the Curie Transition

Theoretical Exploitation of 1,2,3,4,5,6‐Hexachloro‐ and 1,2,3,4,5,6‐Hexafluorocyclohexane Isomers as Biologically Active Compounds

Dynamics of Poly(cyclohexene carbonate) as a Function of Molar Mass

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