Free volume structure

Computing Free Volume, Structural Order, and Entropy of Liquids and Glasses... 

Abstract. Free-volume structure in the lanthanum salt of laurinic acid in crystalline and liquid-crystalline states and an effect of dissolved Cgo molecules on the mean nanovoid radius and concentration were studied by means of the positron annihilation technique. La(Ci2H25COO)3 clathrate compound with dissolved C6o molecules was obtained, which is thermodynamically more stable than a simple mixture of components. Increased mean nanovoid radius (from 0.28 to 0.39 nm) after the inclusion of C6o molecules and concomitant decrease of the positronium annihilation rate by a factor of 2.7 indicate the decrease of the smallest nanovoid concentration. 

Abstract. Free volume structure in the lanthanum salt of laurinic acid in crystalline and liquid-crystalline states and an effect of dissolved C60 molecules on the mean... 

However, the derivation of Equation 16 failed to take into account the free-volume ("structural") contribution to xy"(35), nor is the effect negligible with some polymer phases (36). In addition, there remains considerable doubt even as to what constitutes a "family" set of data e.g., with polymers that are liquid-crystalline. The characterization of polymer stationary phases via family-plot regressions of "inverse" gas-chromatographic retentions therefore invites further and comprehensive study. 

Molecular dynamics (MD) simulation studies were carried out to get deeper insight into the free volume structure and its spatial arrangement in the polymers, and into the correlation between the free volume and the transport properties of the materials. It is of crucial importance that MD simulations provide not only local characteristics of the free volume such as FVE size and FVE size distribution, but also information on its topology, enabling a complete visualization in 3D [1,27,32]. 

Usually not just positronium atoms but also positrons are sensitive to changes in the composition or the structure of materials. If the wave function of positronium is replaced with that of the positron inO Eqs. (27.7) and (27.13), one obtains the theoretical foundation of the above statement. Positrons even participate in spur reactions. Consequently, positrons are sensitive to the changes of free volume, structural changes of materials, and chemical composition. Thus, there are usually several distinct positron states in a material, aU of them being sensitive to any change in electron density. The pieces of information provided by the annihilation characteristics of these states complete each other. 

Jeetain Mittal, William P. Krekelberg, Jeffrey R. Errington, and Thomas M. Truskett, Computing Free Volume, Structured Order, and Entropy of Liquids and Glasses. 

This atypical permeability vs. pressure behavior is directly related to the transformations of the free volume structure (i.e. swelling and relaxation) of the polyphenylene oxide membrane. These aspects will be considered below in more detail. 

The results summarized in Table 9 show that intrinsic porosity of the polymer, i.e. the fraction of its total volume accessible to N2 molecules at 77 K, can exceed 20% for the sample conditioned at high propylene pressure and room temperature, decreasing down to ca. 6% upon annealing in vacuum at 373 K. These results allow assuming that the variations in propylene permeability through a membrane described above apparently stem from the changes in the free volume structure, i.e. accessibility of the intrinsic micropores for the gas molecules. Similar conclusion on the expansion of the free volume hole size and the increase in the number of holes upon sorption of CO2 in polycarbonate has been made in [47] on the basis of positron annihilation lifetime spectroscopy investigations. 

Free Volume Structure and Intrinsic Microporosity of Polyphenylene Oxides... 

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