¹H nuclear magnetic resonance, differential scanning calorimetry, and electrical conductivity studies on the phase transitions of pentylammonium chloride and the cationic self-diffusion in its rotator phase

Abstract

This paper is dedicated to Professor Charles A. McDowell on the occasion of his seventieth birthdaySHIGEHIKO IWAI, RYUICHI IKEDA, and DAIYU NAKAMURA. Can. J. Chem. 66, 1961Chem. 66, (1988. Measurements of 'H nrnr, differential thermal analysis, and differential scanning calorimetry have revealed that solid pentylarnmonium chloride, cooled rapidly from room temperature, forms a mixture of the stable and metastable low-temperature phases below the phase transition temperature, T,, (238 K). The sample annealed just below T,, for 3 h was shown to consist of a single stable phase down to about 100 K, indicating the existence of a time-consuming phase transition taking place successively just below the normal transition. In the rotator phase obtainable above T,, (257 K), ' H nrnr studies proved the presence of axial rotation of the whole cation about the long axis, similar to n-paraffins in their rotator phase. Above room temperature, the onset of the translational self-diffusion of the cations within 2D planes in the layer structure of the rotator phase was detected by measuring the temperature dependence of electrical conductivity as well as 'H T I and TI,. 2D self-diffusion constants and diffusional correlation times evaluated from the electrical conductivity observed between room and the melting temperatures indicate that the 2D cationic diffusion near the melting point is as fast as 3D self-diffusion in usual plastic crystals. Cationic motions in the two different rotator phases a and a' are compared.SHIGEHIKO IWAI, RYUICHI IKEDA, et DAIYU NAKAMURA. Can. J. Chem. 66, 1961Chem. 66, (1988. Des mesures de rmn du ' H , d'analyse thermique diffirentielle et de calorimCtrie a balayage differentielle ont rCvClt que le chlorure de pentylammonium solide, refroidi rapidement de la tempkrature ambiante a des tempCratures inferieures a la tempirature de transition, T, (238 K), forme un mClange de phases stables et mCtastables a basse tempkrature. On a montre qu'un Cchantillon recuit juste endessous de la T, pour trois heures consiste en une seule phase stable jusqu'i environ 100 K; ces resultats sugg2rent qu'il se produit une transition de phase lente juste endessous de la transition normale. Dans la phase rotatrice qu'on peut obtenir au-dessus de la T,, (257 K), les Ctudes par rmn du 'H ont mis en evidence la presence d'une rotation axiale de I'ensemble du cation autour de I'axe allongC, comme on en observe avec le n-paraffines dans leur phase rotatrice. Au-dessus de la temperature ambiante, faisant appel 9 des mesures de dipendance de la conductivitC electrique en fonction de la temptrature ainsi que des T I et T I , on a dCtectC le dCbut d'une auto-diffusion de translation a I'intCrieur des plans bidimensionnels de la structure de lacouche rotatrice. Les constantes d'auto-diffusion bidimensionnelles et les temps de corrClation de diffusion, qui ont Cte CvaluCs a partir de la conductivite Clectrique observCe entre les tempkratures ambiante et de fusion, indiquent que la diffusion bidimensionnelle des cations prks du po...

Dielectric relaxation of alkyl chains in graphite oxide and n-alkylammonium halides

“…Together, Tables I, II, and III reveal that dielectric relaxations in all the alkylammonium halides and all their nanocomposites share almost identical value of actual activation energy E a = 110 meV ± 5%, which value, furthermore, agrees with the internal rotation barrier in alkyl macromolecule. 3 Additionally, the motional correlation times for Table I. restricted small-angle wobbling of this macromolecule around its long molecular axis below room temperature fall within the range of 10 −3 − 10 −4 s, 25,26 consistent with the measurement frequencies of 10 4 − 10 6 Hz in our experiments. Thus the observed relaxation can definitely be attributed to the intrinsic wobbling motions of alkyl chains.…”

“…They undergo uniaxial rotation of the long rod-like cations and 2D self-diffusion, 1 as well as a C 3 reorientation of the CH 3 and NH + 3 groups. 2,3 As the alkylammonium halides find diverse use in surface modification through interaction between the cation of headgroup and an anion of host material, their dynamic in different environments is a key factor in designing novel materials. [5][6][7] Like graphene, Graphite oxide (GO) consists of 2D sheets, 8 retaining the layered structure of graphite, but on each layer carbon atoms randomly bond with epoxide and hydroxyl radicals on both sides.…”

“…[5][6][7] Like graphene, Graphite oxide (GO) consists of 2D sheets, 8 retaining the layered structure of graphite, but on each layer carbon atoms randomly bond with epoxide and hydroxyl radicals on both sides. Nanocomposites can form when various n-alkylammonium cations C n H 2n+1 N(CH 3 the work reported here aims to elucidate whether and how these intercalated alkylammonium cations modify their dynamical behaviours from the halide case. Being ionic, they can be probed with dielectric spectroscopy, but with a possible complication that, having alkyl chains in close proximity, they may not respond to external field as independent dipoles with a single relaxation time, such that the Debye model for their relaxation may need correlated-stated correction.…”

Influence of the head group on dynamics in surfactant intercalated graphite oxide

“…n-alkylammonium halides form tetragonal crystals around room temperature belonging to space group P4/nmm. [7][8][9] They have a two-dimensional (2D) lamellar-type structure with rod-like cations and halides anions stacked alternately along the crystallographic C 4 axis. The cations are dynamically disordered and packed between the layers of anions keeping their long axis perpendicular to the layers.…”

“…Ikeda's group have proved that the rotator phase of n-alkylammnonium chlorides (C 6 -C 10 ) has uniaxial rotation of the long rod-like cations, 7 and also C 3 reorientation of the CH 3 and NH 3 + was observed by nuclear magnetic resonance (NMR). 8,9 The dynamical behaviors of alkylammonium cations conned in layered materials have been investigated by computational and experimental techniques, for example molecular simulation, 11 solid state NMR, 12,13 Fourier-transform infrared spectroscopy (FTIR), 14 and so on. There have been some common conclusions that the conned alkylammonium cations assume an all-trans conformation at low temperatures and change to the gauche conformation upon heating, then leading to a phase transition at relatively elevated temperatures.…”