Abstract
An investigation of the glass transition of the antiferroelectric smectic CA* phase and cold crystallization of (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluoro- butoxy)heptyl-1-oxy]benzoate (denoted as 3F7FPhH6) by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy is presented. The fragility index mf = 72, classifying 3F7FPhH6 as a glassformer with intermediate fragility, was obtained from the temperature dependence of the α-process relaxation time, measured upon cooling. Duplication of the α-process was observed exclusively upon heating, before the onset of cold crystallization, and is connected with the pre-transitional effect. The presence of two crystal phases likely influences the kinetics of cold crystallization; the idea stems from a comparison with previous results for the 3F7HPhF6 and 3F7HPhH7 compounds. Additionally, the presence of the smectic Cα* sub-phase in a narrow temperature range was proved based on the differential scanning calorimetry and broadband dielectric spectroscopy results, as well as the fractal dimension analysis of the textures obtained by polarizing optical microscopy.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
We report results regarding the vitrification of the phase and kinetics of the isothermal cold crystallization on subsequent heating for (S)-4 -(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy)heptyl1-oxy]benzoate, denoted in short as 3F7HPhH6
For 3F7HPhH6, instead, the cold crystallization investigated by differential scanning calorimetry (DSC) does not show the Arrhenius dependence of τcr ( T ), and both nucleation and diffusion have an equal impact on the crystallization kinetics
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. SmCA phase was reported, even for slow cooling (1 K/min or at an even lower rate, enough to avoid crystallization) [12,13,14,15,16,17,18] It allows for the obtainment of glass with anisotropic properties, whose practical application was already proposed both for smectic and nematic glassformers [19,20,21,22,23]. We report results regarding the vitrification of the phase and kinetics of the isothermal cold crystallization on subsequent heating for (S)-4 -(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy)heptyl1-oxy]benzoate, denoted in short as 3F7HPhH6 This compound belongs to a family of
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