AC Conductivities of Neopentylglycol and 2‐Amino‐2‐Methyl‐1,3‐Propanediol

Abstract

Neopentylglycol (NPG) and 2-amino-2-methyl-l,3-propanediol (AMPL) are potential thermal energy storage materials which undergo energetic solid-state phase transformations. Both NPG and AMPL have monoclinic low temperature a-phase and cubic high temperature ~-phase structures. These polymorphic changes in structure occur at 41 and 80~ for NPG and AMPL, respectively. Below the a --> ~/transition, these compounds are dielectric materials with conductivities on the order of 10 -8 S/m (at 22~ and 10 -9 S/m (at 25~ for NPG and AMPL, respectively. The lack of appreciable conductivity in the low temperature phase is consistent with charge transport via low temperature structural reorientation. There is a significant increase in the conductivity through the a --> ~ phase transition with a maximum of 10 6 S/m (at 82.05~ for NPG and 10 -~ S/m (at 133.25~ for AMPL in the high temperature phase. The conductivities in both the a-and ~/-phases have been found to be thermally activated. The temperature dependent conductivity follows the Arrhenius equation with the activation energy of the a ---> ~ transition being larger in the case of NPG. Remarkably, the activation energies of the high temperature ~-phases are nearly equivalent, suggestive of similar conduction mechanisms and charge carriers. The charge carrier diffusion coefficients, D(t) are in the range of 1 and 3 • 10 10 cm2/s (45 < T < 56~ for NPG, and between 6.9 and 7.3 X 10 10 cm2/s (85 < T < 92~ for AMPL. The ac conductivity in the a-phase exhibits behavior representative of a double well potential energy profile where the low and high frequency conductivities are constant with a Debye-like transition at intermediate frequencies. The ~-phase ac conductivity is frequency independent as is the case in simple hopping conductivity processes. AC impedance spectroscopic measurements on NPG and AMPL have been made and frequency and temperature effects on the conductivities, relaxation times, and diffusional parameters of NPG and AMPL are presented.

Thermodynamic assessment of binary systems Tris(hydroxymethyl)aminomethane-Pentaglycerine (TRIS-PG) and 2-amino-2-methyl-1,3-propanediol-Pentaglycerine (AMPL-PG) phase diagrams

“…Crystallographic and thermodynamic parameters of the pure polyalcohol and amines are already established in the literature [5][6][7][8][9][10][11][12][13]. The low temperature crystal structure of AMPL is reported by Rose et al [5] as monoclinic with lattice parameters: a=8.62 Å, b=11.00 Å, c=6.10 Å, =93.32, V=580.3 Å 3 at 293K (Z=4).…”

Thermodynamic modeling of binary phase diagram of 2-amino-2-methyl-1, 3-propanediol and TRIS(hydroxymethyl)aminomethane system with experimental verification

“…Rose et al [16] reported the low temperature phase structure of AMPL to be monoclinic with lattice parameters; a ¼8.62 Å, b¼ 11.00 Å, c ¼6.10 Å, β¼93.32°, V¼580.3 Å 3 at 293 K (Z¼ 4). Chandra et al [17,18] reported high temperature phase structure of AMPL as BCC with a ¼6.7 Å above 357 K at which the hydrogen/nitrogen bond configuration changes and an isotropic but orientationally disordered BCC structure forms. It should be noted that polyalcohols, such as, pentaerythritol (C 5 H 12 O 4 ) [11], pentaglycerine (C 5 H 12 O 3 ) and others with tetrahedral C-C configuration and O-H…O bonds have FCC (γ or γ') high temperature structure whereas the amine compounds with O-H…N and O-H…O bonds, such as AMPL or TRIS have BCC obtained unlike most of the other plastic crystals which have FCC structure [5].…”

Ionic Conductivity in Ordered and Disordered Phases of Plastic Crystals

“…There is a disconti- where r = 2 ~v. Following the treatments of Jonscher and Almond ~8' 29 for hopping conductivity in ionic conductors, the ac conductivity may be described in the absence of low frequency dispersion as n l-n ~(o~) = K% + Ko~ % [9] where % is defined as the ion hopping rate or the frequency of the peak in the dielectric loss, and K is a constant of proportionality related to the concentration of mobile ions, the hopping distance, and density of sites per unit volume. Factoring out K% from this expression and assuming the dc conductivity ~(0) = Kr (d n…”