Free volume polymer

Loutfy RO (1986) Fluorescence probes for polymer free-volume. Pure Appl Chem 58 (9) 1239-1248... 

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

This apparent anomaly may be due to increased dipolar contributions as well as to possible decrease in the free volume of polymer. Free volumes of the resin... 

Loutey R. O. (1986) Fluorescence Probes for Polymer Free Volume, Pure e[ Appl. Chem. 58, 1239-1248. 

R. O. Loutfy, Fluoresence probes for polymer free-volume, Pure AppL Chem. 58, 1239 (1986). 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

Even when using LDPE and PP, the diffusive losses of most nonpolar solvents may be unacceptably large for A designs that exceeded 1 cm . This is especially true at higher exposure temperatures because both solute diffusion and polymer free volume increase with temperature (Comyn, 1985). Even when solvent losses were not excessive, uptake of HOCs by membrane-enclosed solvents appeared to become curvilinear well before thermodynamic equilibrium was approached. This phenomenon is likely due to the outward flux of sampler solvent with elevated HOC levels (relative to water), which appears to facilitate residue... 

This differential equation states that the creep rate during irradiation is directly related not only to the deflection of the unstressed sample which has occurred up to that time (D2, which may be related to the increase in polymer free volume) but also to the rate of increase of D2 with time. The reason for the dependence of the creep rate on dDo/dt is not apparent but may be related to the fact that gas is being generated at an increasing rate as time progresses (as in the case of PVC). This relationship emphasizes the strong dependence of the ac-... 

Previous studies on paraffins, rhodamine dyes, and l,3-bis(N-carbozoyl) propane excimers have concluded that there is a relationship between km and polymer viscosity and free volume [103-105], Indeed, this dependence has been investigated in the context of decreasing free volume during methyl methacrylate polymerization [83,84], It has been shown that the nonradiative decay processes follow an exponential relationship with polymer free volume (vf), in which kra reduces as free volume is decreased [see Eq. (5)]. Here, k. represents the intrinsic rate of molecular nonradiative relaxation, v0 is the van der Waals volume of the probe molecule, and b is a constant that is particular to the probe species. Clearly, the experimentally observed changes in both emission intensity and lifetime for/ac-ClRe(CO)3(4,7-Ph2-phen) in the TMPTA/PMMA thin film are entirely consistent with this rationale. 

The concept of polymer free volume is illustrated in Figure 2.22, which shows polymer specific volume (cm3/g) as a function of temperature. At high temperatures the polymer is in the rubbery state. Because the polymer chains do not pack perfectly, some unoccupied space—free volume—exists between the polymer chains. This free volume is over and above the space normally present between molecules in a crystal lattice free volume in a rubbery polymer results from its amorphous structure. Although this free volume is only a few percent of the total volume, it is sufficient to allow some rotation of segments of the polymer backbone at high temperatures. In this sense a rubbery polymer, although solid at the macroscopic level, has some of the characteristics of a liquid. As the temperature of the polymer decreases, the free volume also decreases. At the glass transition temperature, the free volume is reduced to a point at which the... 

S. The diffusion coefficients of gases in glassy polymer membranes are strong functions of the penetrant gas concentration in the membranes (or of the gas pressure), and depend also on polymer morphology (crystallinity, orientation), crosslinking, and chain mobility. The chain mobility depends, in turn, on the polymer free volume, the... 

Kobayashi, Y., Haraya, K., Hattori, S. (1994) Evaluation of polymer free volume by positron annihilation and gas diflusivity measurements . Polymer 35(5), 925. 

From this significant body of work, one can surmise that although incorporating fluorine into a compound may enhance its solubility in CO2, it is also necessary for the compound to be somewhat polar if high solubility in CO2 is to be obtained. Partial fluorination of a compound can lead to creation of dipoles, which enhance the solubility in CO2 owing to specific interactions with CO2. In addition, increases to polymer-free volume, based on choice of materials with substantial backbone flexibility, increases solubility in CO2. 

The water-polymer interaction depend on the polymer free volume, crystallinity, porosity, chemical structure, etc... It is known that strong interactions between water and polymer can produce important modifications of the solid polymer like swelling or crystallisation. If these interactions are not homogeneous inside the polymer matrix it may result in some "clustering" of the water molecules with formation of holes inside the polymer. 

It now appears that the dissolution dynamics of glassy polymers is at the very least a complicated process and its kinetics depends on many parameters of the solvent, the polymer and the processing condition. We have also found that one of the dynamical processes that strongly affect the dissolution kinetics of polymers with high Tg is the diffusion rate of the solvent into the polymer matrix which primarily depend on at least 4 factors polymer free volume and segmental mobility, solvent size and the osmotic pressure (chemical potential difference between the polymer solution and pure solvent). We believe that the above finding has important implication in resist technology. Positive... 

The diffusion coefficient of small penetrants in glassy polymers can also be correlated with the polymer free volume. In view of the fact that experimental techniques for the determination of the free volume are inherently difficult, Shah, Stern, and Ludovice (Shah, V.M. Stern, S.A. Ludovice, P.J., submitted for publication in Macromolecules) have utilized the detailed atomistic modeling of relaxed polymer glasses developed by Theodorou and Suter ( 2, 3) to estimate the free volume available in polymer glasses for the diffusion of small molecules. 

As with all photochromic polymers, the polymer matrix effect is very important in fulgides and fulgimides as the polymer free volume affects rate of photocoloration and photobleaching. For example, Bahajaj and Asiri recently reported that the rate of photochemical reactions of fulgide doped in a variety of polymer matrices decreased in the order polystyrene > poly(methyl methacrylate) > epoxy resin [37]. Polystyrene possesses a larger free volume than poly(methyl methacrylate) and epoxy resin... 

Positron annihilation lifetime spectroscopy (PALS) allows the quantitative investigation of the polymer free volume [1, 2]. Additionally, the PALS beam technique makes a direct depth resolution possible, by implanting the probe - the positron - within a definite sample depth interval depending on the positron kinetic energy [3]. It is one of the very few nondestructive techniques for investi-... 

Positron Annihilation Lifetime Spectroscopy. The details of PALS will not be discussed here since several other chapters in this book are specifically concerned wifii this experimental technique and provide more than adequate description. Suffice it to say here that or//ioPositronium (oPs), which is formed when a positron binds to an electron of parallel spin, tends to locate in free volume sites within a polymer, and the time required for it to annihilate via pickoff with an electron of anti-parallel spin residing in the surrounding material is related to the size of the free volume site. There are two parameters that are sensitive to polymer free volume the oPs pickoff component lifetime, xa, which is related to the mean radius of the free volume cavities, and the oPs pickoff component intensity, I3, which is related to the concentration or number of fr volume cavities. 

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