Broadband Electric Spectroscopy at High CO₂ Pressure: Dipole Moment of CO₂ and Relaxation Phenomena of the CO₂–Poly(vinyl chloride) System

Abstract

Broadband electric spectroscopy (BES) is a technique that shows promise in studying the interactions of dense or supercritical gases with polymers, particularly with respect to chain mobility. Polymers that are treated with dense gases show a reduction in the viscosity, glass transition, and melting temperature. A high pressure cell for BES has been constructed that can be used from ambient temperature and pressure to 353 K and 15 MPa and over a frequency range from 20 Hz to 1 MHz. In the past, the dielectric constant of CO(2) was determined by measurements at only one or two frequency values. New instrumentation and technology allow this experiment to be expanded to cover a wider frequency range. BES measurements of CO(2) do not show any relaxation peaks in the permittivity from 20 Hz to 1 MHz and 1 to 6 MPa. By these measurements, the CO(2) dielectric constant was evaluated between 0.1 and 6 MPa. Cell testing with poly(vinyl chloride) (PVC) at 323 K and CO(2) pressures from 0.1 to 13 MPa indicate an increase in the chain segmental motion at high pressures resulting from a reduction in the glass transition temperature of the PVC-CO(2) system due to plasticization by CO(2).

A first principles approach to the electronic properties of liquid and supercritical CO2

“…20,[33][34][35][36][37][38][39][40][41][42][43] Although CO 2 is considered a non-polar molecule, its miscibility with polar species can be interpreted as an indication that liquid and scCO 2 may have a non-zero dipole moment. 8 The possible polar attributes of scCO 2 have been recently discussed by Raveendran et al 44 These authors pointed out that the behaviour of scCO 2 as a solvent is not well understood on a molecular level. In addition, they suggest that polarization effects should be taken into account to explain the role played by CO 2 as a solvent.…”

Dielectric relaxations and conduction mechanisms in polyether–clay composite polymer electrolytes under high carbon dioxide pressure

“…[18][19][20] Recently, some researchers reported results on ''in situ'' electric response studies carried out on polymer electrolytes under pressurized CO 2 using the BES tool. [21][22][23] These reports demonstrated the plasticization effect of CO 2 molecules on the dielectric relaxation behavior of polymer backbone chains. Our previous reports also revealed that typical polymer electrolytes such as polyether-metal salt mixtures show a positive pressure dependence of the conductivity under CO 2 , which indicates that under particular conditions CO 2 acts as an activation solvent for the ionic conduction.…”

“…The samples are sandwiched between two Pt-plated stainless steel parallel electrodes using 125 mm thick glass fibers as spacers under an Ar atmosphere and are closed in a home-made Teflon conductivity cell. 23 Measurements of electric spectra in high-pressure CO 2 are carried out using a system described elsewhere. 23 The electrode assembly is protected by a stainless steel cylindrical cell bolted together with two flanges and sealed with a neoprene O-ring.…”

A lipophilic ionic liquid based on formamidinium cations and TFSI: the electric response and the effect of CO2 on the conductivity mechanism

“…The complex impedance (Z*(ω) = Z'(ω) + iZ"(ω)) was converted into complex conductivity (σ*(ω) = σ'(ω) + iσ"(ω)) and complex permittivity (ε*(ω) = ε'(ω) -iε"(ω)) using the equations σ*(ω) = k[Z*(ω)] -1 and σ*(ω) = iωε o ε*ω, respectively, where k was the cell constant and ω = 2πf (f was the frequency in Hz). 8 Broadband electric spectra were measured as a function of CO 2 pressure at 40°C from 0 to 60 bar as previously described 9 and summarized here. The measurements were made in a homemade high CO 2 pressure cell.…”

“…The measurements were made in a homemade high CO 2 pressure cell. 9 The gas was pre-dried over a type-A zeolite bed in order to exclude any traces of water from the CO 2 , which could give rise to proton conductivity in the materials. This measurement setup allowed the measurements to be performed on extremely moisture sensitive materials such as PEO-based polymer electrolytes in totally anhydrous conditions 7 .…”