Beyond the Spherical Approximation: Elongated Free Volume Holes in Rubbers: A Positron Annihilation Study

Consolati, G.; Nichetti, Dario; Briatico‐Vangosa, Francesco; Quasso, F.

doi:10.5254/rct.19.80452

Cited by 2 publications

(6 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similar findings were found in various elastomers [ 124 , 132 , 133 ]: in these cases, too, holes are well represented by flattened cylinders. Therefore, it seems that flattened holes are more common than spherical holes, in our investigated polymers.…”

Section: Discussion Of Some Pals Results In Polymeric Systemssupporting

confidence: 86%

“…In particular, in polybutadiene-polyisoprene blends we found that p decreases almost linearly with the content of polyisoprene volume fraction (Figure 13), while the presence of acrylonitrile in acrylonitrile-butadiene blends does not change, within the errors, the value of p found for pure butadiene. Similar findings were found in various elastomers [124,132,133]: in these cases, too, holes are well represented by flattened cylinders. Therefore, it seems that flattened holes are more common than spherical holes, in our investigated polymers.…”

Section: Coupling Pals and Dilatometry: An Alternative Route To The F...supporting

confidence: 85%

“…Since the Simha-Somcynsky theory is valid for amorphous polymers at equilibrium, we restricted our investigations to temperatures above the glass transition, although it is possible to also extend the theory in the glassy state [ 125 ]. We explored polystyrene with different molecular weight [ 126 ], perfluoropolyethers and polypropylene glycols with low molecular weights [ 127 , 128 ], atactic polypropylene [ 129 ], polyvinyl acetate [ 130 ], a thermoplastic polyurethane [ 131 ], and different rubber blends [ 124 , 132 , 133 ]. Our goal was to explore a possible influence of the investigated structure on the free volume.…”

Section: Discussion Of Some Pals Results In Polymeric Systemsmentioning

confidence: 99%

See 2 more Smart Citations

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Nichetti²,

Quasso

2023

Polymers

Self Cite

View full text Add to dashboard Cite

Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10−7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

show abstract

Section: Discussion Of Some Pals Results In Polymeric Systemssupporting

confidence: 86%

Section: Coupling Pals and Dilatometry: An Alternative Route To The F...supporting

confidence: 85%

Section: Discussion Of Some Pals Results In Polymeric Systemsmentioning

confidence: 99%

See 1 more Smart Citation

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Consolati

Nichetti²,

Quasso

2023

Polymers

Self Cite

View full text Add to dashboard Cite

show abstract

“…Similar results were also obtained for a fluoroelastomer and for a cis-polyisoprene rubber. 20 It is remarkable that a typical size of holes at the glass transition for different elastomers matches quite well to l, a parameter related to reptation motions and largely independent of the macromolecular structure.…”

Section: Discussionmentioning

confidence: 89%

“…The results well fitted the theoretical free volume fractions, but at the price of introducing a fictitious occupied volume, that is, not corresponding to the one provided by the theory. In a previous paper concerning cis-polyisoprene, 20 we used an occupied volume in agreement with the theory and showed that it is possible to solve this contrast by assuming cylindrical holes forming the free volume in cis-polyisoprene. This stimulated us to investigate the shape of the free volume holes in other rubbers and we turned to blends containing isoprene.…”

Section: Introductionmentioning

confidence: 99%

Free volume expansion in some polybutadiene–acrylonitrile rubbers: comparison between theory and experiments

Consolati

Nichetti²,

Quasso

2022

Polymer International

Self Cite

View full text Add to dashboard Cite

The dependence of free volume on temperature was investigated in three butadiene–acrylonitrile copolymers and in a butadiene–acrylonitrile–isoprene terpolymer, above the glass transition in order to apply the lattice‐hole model. Macroscopic behaviour was highlighted by dilatometry; positron annihilation lifetime spectroscopy was used to shed light on the free volume microstructure. Coupling of the two techniques allowed us to obtain the number density of holes under specific geometrical assumptions about cavities. Comparison with the theoretical free volume fraction suggests hole shapes more similar to discs than to spheres, but with aspect ratio decreasing at increasing temperature. Such preferential growth in the radial direction is not influenced by the presence of acrylonitrile, contrarily to that recently found in butadiene–isoprene blends, where an increasing amount of isoprene makes such expansion less anisotropic. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

show abstract

Beyond the Spherical Approximation: Elongated Free Volume Holes in Rubbers: A Positron Annihilation Study

Cited by 2 publications

References 30 publications

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy

Free volume expansion in some polybutadiene–acrylonitrile rubbers: comparison between theory and experiments

Contact Info

Product

Resources

About