Molecular Order and Dynamics of Tris(2-ethylhexyl)phosphate Confined in Uni-Directional Nanopores

Abstract

Infrared Transition Moment Orientational Analysis (IR–TMOA) and Broadband Dielectric Spectroscopy (BDS) are combined to study molecular order and dynamics of the glass-forming liquid Tris(2-ethylhexy)phosphate (TEHP) confined in uni-directional nanopores with diameters of 4, 8, and 10.4 nm. The former method enables one to determine the molecular order parameter of specific IR transition moments. It is observed that the central P=O moiety of TEHP has a weak orientational effect (molecular order parameter S z = −0.1 ± 0.04) due the nanoporous confinement, in contrast to the terminal C–H groups. BDS traces the dynamic glass transition of the guest molecules in a broad spectral range and at widely varying temperature. An enhancement of the mobility takes place when approaching the glass transition temperature and becomes more pronounced with decreasing pore diameter. This is attributed to a slight reduction of the density of the confined liquid caused by the 2-dimensional geometrical constraint.

Glassy dynamics of two poly(ethylene glycol) derivatives in the bulk and in nanometric confinement as reflected in its inter- and intra-molecular interactions

“…To obtain the effective dielectric strength for confined molecules, a model of two impedances in parallel was employed as described in detail elsewhere. 31 Fourier transform infrared (FTIR) absorption measurements were carried out using a Bio-Rad FTS 6000 spectrometer from 700 cm −1 to 5000 cm −1 with a resolution of 2 cm −1 . The temperature was controlled with an uncertainty of less than 0.5 K by means of a Linkam THMS 600 cell equipped with ZnSe windows.…”

“…The significance of the contribution of intramolecular interaction to dynamic glass transition has been recently proven by a combination of Broadband Dielectric Spectroscopy (BDS) and Fourier-Transform Infrared (FTIR) spectroscopy. [29][30][31] This approach has been employed to study liquid crystals under confinement, 32 glass transition of low molecular weight, 29,30,33 and polymeric systems 30,34 in bulk. It has been reported that various 0021-9606/2018/149(6)/064501/9/$30.00…”

Unexpected Crossover in the kinetics of mutarotation in the supercooled region: the role of H-bonds

“…Recent reports by the group of Kremer 16 – 18 also demonstrated that the splitting of the structural and secondary relaxation processes at T c is very often accompanied by the change in intramolecular dynamics. Therefore, to address this issue additional temperature-dependent FTIR measurements above and below T c were carried out to follow intramolecular dynamics in L-sorbose.…”

“…Similar observations, but without special explanation, have been also reported by Kaminski et al . 35 and the group of Kremer 17 , 18 . Such correspondence between intra- and intermolecular dynamics was found much above the glass transition temperature ( T ≈ 1.2 T g ).…”

“…In this context, one can recall papers by Kremer et al . who investigated the dynamics of simple glass formers by means of FTIR and BDS spectroscopies 16 – 18 . They demonstrated that in the temperature range ( T ≈ 1.2 T g ), where the structural and local processes merge, a clear change in intramolecular mobility can be detected.…”