Effects of Cooling Rate and Physical Aging on the Gas Transport Properties in Polycarbonate

Abstract

The gas transport properties of bisphenol A polycarbonate films were examined as a function of the cooling rate during film processing and subsequent physical aging. Interpretation of the permeation properties using results from dynamic mechanical analysis and density measurements indicated that the diffusion coefficient of small gas molecules in glassy polycarbonate is influenced more by the local chain dynamics rather than by the overall free volume content. A one-dimensional lattice model was developed to help probe the effects of the distribution of energy barriers associated with polymer motion on the transport properties. Fast cooling rates generated highly restricted conformations, which hindered local motions leading to increases in the measured activation energy of diffusion. These results correlated well with a lattice model having a broad distribution of energy barriers. Annealing reduced the measured diffusion coefficients, which was shown to be consistent with narrowing of the energy barrier distribution, as well as an increase in the mean barrier energy. Interestingly, the decrease in the diffusion coefficient with aging was found to occur much more slowly in fast-cooled samples, despite the higher initial free volume content. By contrast, properties such as density or isothermal dynamic mechanical properties were more consistent with the free volume model.

Multiscale modeling of polymer materials using a statistics-based micromechanics approach

“…Many combinations of the conformations of multiple polymer chains are possible for a particular RVE in an equilibrated or non-equilibrated state because of the finite entropy of the material for any temperature above 0 K owing to the dynamics of the constituent chains [2,[14][15][16]. As a result, the molecular structure, and thus density, of a polymer material varies substantially on the nanometer length-scale [16][17][18][19][20][21][22][23].…”

Effects of Thermal Treatment and Physical Aging on the Gas Transport Properties in Matrimid®

“…Therefore, the physical and chemical properties of glassy polymers are particularly influenced by thermal history [16][17][18][19][20][21][22][23][24][25] and physical aging [26][27][28][29][30][31][32], which can substantially change the material response to the external stresses and, what is of particular importance in the present discussion, can definitely affect its permeation properties.…”

“…Depending on the condensability of the penetrant, the solubility decrease can be more or less pronounced, but still monotonic with reducing the available free volume inside the polymer matrix. However, also the opposite behavior has been observed, when the decrease of free volume was associated to a more complex relaxation phenomena: Laot et al [18] for example, presented a decrease of diffusion coefficient and a simultaneous increase of the solubility coefficient in polycarbonate samples subject to different cooling rates, attributing the behavior to a change of the molecular chains mobility. On the other hand, Vaughn et al [23], studying the annealing effect on a polyamideimide membrane, suggested the occurrence of a thermally activated planarization process of polymer chains.…”

Experimental testing of the sorption-mechanical coupled behaviour of polyethylene into pressurized hydrogen

“…Gas transport properties (permeability, diffusivity, solubility) of polymers has been widely investigated in systems made of several gases (among which hydrogen (H2) [1,2], oxygen (O2) [3][4][5], and carbon dioxide (CO2) [4][5][6]) into several amorphous or semi-crystalline polymers (among which polyethylene (PE) [5][6][7], polypropylene (PP) [3] or polyimide [2]). Only a few works considered relationships between gas sorption and mechanical behavior in thermoplastics [7][8][9]. Even less works have been reported on explicit coupling between diffusion and mechanical behavior into a unique constitutive law, like proposed by Valançon et al for water diffusion and viscoelasticity [10].…”