Johari–Goldstein relaxation in orientationally disordered phase of hexa-substituted benzenes

Double Primary Relaxation in a Highly Anisotropic Orientational Glass-Former with Low-Dimensional Disorder

“…In all spectra, a clear relaxation peak is observed (hereafter α relaxation), which displays continuous temperature- and pressure-induced shifts characteristic of the quenching of the molecular dynamics. The frequency position and temperature dependence of this main peak are in agreement with earlier normal-pressure dielectric studies on PCNB. ,− The α relaxation peak is accompanied in all instances by an excess wing (hereafter called α′ process). The α′ relaxation is visible as a shoulder to the main peak, which indicates that its dielectric strength is lower than that of the α relaxation (see Supporting Infomations).…”

“…Panels (a) and (b) of Figure highlight the need of two dipolar processes (displayed as dotted lines) for modeling the dielectric spectra. It should be noticed that the existence of a separate relaxation close to the α relaxation was already pointed out in ref .…”

“…However, few years later, the same authors reported the possible existence of an excess wing in a hexasubstituted benzene derivative (pentachloronitrobenzene, C 6 Cl 5 NO 2 , hereafter PCNB). A recent study has shown that the excess wing in PCNB is actually a separate relaxation process, which we will refer to as α′ relaxation. The phase behavior of this quasi-planar molecule, which forms a layered structure of rhombohedral planes, has been extensively studied. ,− A glass transition was observed by adiabatic calorimetry at 185 K ± 15 K (corresponding to enthalpy relaxation times in the range 1–10 ks), which was assigned to the freezing of the orientational disorder within the hexagonal planes .…”

Direct Evidence of Relaxation Anisotropy Resolved by High Pressure in a Rigid and Planar Glass Former

“…The fundamental importance of the secondary relaxation also has been recognized from the strong connections to the thermal stability, the elastic and deformation behaviors − in glasses, and to the structural α-relaxation. − Suggested by the Coupling Model (CM) and established empirically, τ β is found to be quantitatively related to τ α ,− in the Kohlrausch correlation function, of the α-relaxation, where β KWW is a fractional exponent. So far, all rigid molecules studied experimentally including chlorobenzene, 2-picoline, quinaldine, benzonitrile, , orth o -terphenyl, , toluene, adamantanone, , 1-fluoro-adamantane, hexa-substituted benzenes, and simulations of rigid diatomic toy molecule all show a single secondary relaxation, which verifies the connections of the α and β- relaxations. The α and β- relaxation connections are also verified in some metallic glasses, such as Pd 40 Ni 10 Cu 30 P 20 and La 60 Ni 15 Al 25 , as well as in ionic liquid conductors .…”

“…] KWW of the α-relaxation, where β KWW is a fractional exponent. So far, all rigid molecules studied experimentally including chlorobenzene, 6 2-picoline, 12 quinaldine, 13 benzonitrile, 14,15 ortho-terphenyl, 6,16 toluene, 17 adamantanone, 18,19 1-fluoro-adamantane, 20 hexa-substituted benzenes, 21 and simulations of rigid diatomic toy molecule 22 all show a single secondary relaxation, which verifies the connections of the α and βrelaxations. The α and βrelaxation connections are also verified in some metallic glasses, such as Pd 40 Ni 10 Cu 30 P 20 23 and La 60 Ni 15 Al 25 , 24 as well as in ionic liquid conductors.…”