Methods for the calculation of occupied volumes in glassy polymers: The lattice integration and the monte carlo methods

Brumă

2011

Struct Chem

Several polyimides were studied with regard to the influence of their conformational rigidity on the packing in glassy state, and consequently on their physical properties such as glass transition temperature and selectivity of gas separation membranes made from these polymers. The values of their physical properties were taken from literature, while the conformational rigidity parameters such as Kuhn segment, characteristic ratio, and occupied, free, and accessible volumes were calculated here and were correlated with physical properties. It was shown that there are correlations between selectivity of gas separation membranes made from these polyimides on one hand, and characteristic ratio, on another hand.

Section: Methods Of Calculationmentioning

confidence: 99%

Influence of conformational rigidity on membrane properties of polyimides

Brumă

2011

Struct Chem

“…It can be seen that an increase in molecular size of diffusant results in increases in the B 16 and B 17 parameters, that is, in more greater dependences of diffusivity and permeability on fractional accessible volume in various polyimides. The only exception is hydrogen.…”

mentioning

confidence: 96%

Occupied and Accessible Volumes in Glassy Polymers and Their Relationship with Gas Permeation Parameters

Macro Theory & Simulations

Rozhkov

Alentiev

et al. 2003

In order to relate the microstructure of polymer chains to the gas permeation properties, a novel method is proposed for the calculation of the van der Waals (Vw), occupied (Vocc), and accessible (Vacc) volumes of polymers, using polyimides as examples. In this approach, Vocc and Vacc values are obtained as characteristics of polymer–gas systems. Correlations between Vocc and the gas permeability (P) and diffusion (D) coefficients are demonstrated. Accessible volume, Vacc, determined experimental densities, and Vocc calculated using a Monte Carlo technique, as well as the fractional accessible volume (FAV) (Vacc/Vsp), where Vsp is the specific volume of polymers, also correlate well with the P and D values. The slopes of these correlations increase with increasing molecular size of the diffusing molecules. In addition, the parameters of the equations for D(FAV) and P(FAV) strongly depend on conformation rigidity (Kuhn segment) of the polyimides. An interpretation of the results obtained is presented.Definition of occupied volume.imageDefinition of occupied volume.

“…In order to correlate the geometry of the repeating units of polymers with transport properties, the following parameters were calculated: van der Waals volume ( V w ), free volume ( V f ), occupied volume ( V occ ), accessible volume ( V acc ), and fractional accessible volume (FAV) …”

Section: Calculation Methodsmentioning

confidence: 99%

Microstructure relaxation process of polyhexafluoropropylene after swelling in supercritical carbon dioxide

Белов

Alentiev

J of Applied Polymer Sci

et al. 2015

This paper studies the process of relaxation of a polymer after swelling in supercritical carbon dioxide. Polyhexafluoropropylene (PHFP) was chosen as the object for investigation. The relaxation process was monitored by a change of the permeability coefficients for a number of gases. Thin polymeric films of PHFP were modified by different treatments: drying to a constant weight, annealing at a temperature slightly higher than the glass-transition temperature, and swelling in supercritical carbon dioxide. The permeability coefficients of six gases, He, H 2 , O 2 N 2, CO 2 , and CH 4 , were measured after each stage of the treatment. It was shown that the permeability coefficients in the films were increased by 2.4 times for He, 3.6 for H 2 , 5.9 for O 2 , 8.1 for N 2 , 6.7 for CO 2 , and 10.9 for methane. The permeability coefficients of the same gases were measured 50 days later after swelling in supercritical carbon dioxide. A decrease in the permeability coefficient demonstrated that the relaxation process had taken place. Nevertheless, the values exceeded the initial ones for annealed samples by 2.0 times for He, 2.4 for H 2 , 1.8 for O 2 , 1.7 for N 2 , 1.7 for CO 2 , and 1.3 for methane.