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Positron Annilation Lifetime and Glass Transition Temperatures in CO_2 Sorption Polystyrene

100%

Jean Y., Chen H., Lee L., Yang J.

Acta Physica Polonica A

2008

vol. 113

issue 5

1385-1395

Positron annihilation lifetime spectroscopy was used to measure the free-volume size and distributions as a function of temperature in polystyrene with and without 400 psi CO_2 sorption. The transition temperatures in the polystyrene with CO_2 sorption obtained from ortho-positronium lifetimes were found to depend on the thermal cycles and a meta-stable state showing a negative thermal expansion coefficient was observed between 53°C and 82°C during the first heating up experiment. The observed T_g in polystyrene with, and without CO_2 sorption after annealing from ortho-positronium lifetimes were found to be 86°C and 91°C, which are 5°C higher, and 10°C lower than from the differential scanning calorimetry data, respectively. The observed free-volume variations are discussed in terms of hole expansion, creation, free-volume relaxation, plasticization, and hole filling in amorphous polymers.

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

88%

Eren B., Wu F., Eren E., Jean Y., Van Horn J.

Acta Physica Polonica A

2017

vol. 132

issue 5

1456-1460

Studies of the interaction of polarized light or particles (including electrons, e¯, or positrons, e⁺) with asymmetric forms of matter has been of interest to scientists since the discovery of chirality and the subsequent development of particle physics. Researchers have been interested in e⁺ interactions with chiral molecules for decades, but with mixed and indecisive results. After reviewing the field, we speculated that the e⁺ or positronium (Ps) might interact differently with chiral pairs of large single crystals, i.e., the left-handed or right-handed asymmetric forms of the crystals - and subsequently observed significant differences in "free positron" annihilation and intensities in the evaluation of left-handed or right-handed quartz single crystals. This result may be understood to be a "particle stereorecognition" phenomenon. To extend this line of inquiry we crystallized mm scale L- or D-alanine crystals and performed positron annihilation lifetime spectroscopy measurements using a ²²Na positron source. Alanine crystals were obtained via slow evaporation of water in a Dewar, or from water/acetone solvent in a temperature-controlled environment. These methods resulted in small ( ≈0.5 cm/side) or large ( ≥1.0 cm/side) crystals, respectively. While some intensity (I₂) results from left-handed and right-handed crystals varied in positron annihilation lifetime spectroscopy analysis, the errors associated with the measurements do not indicate a stereorecognition of alanine via positron interactions.

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2 Acta Physica Polonica A

1 2017

1 2008

2 Jean Y.

1 Chen H.

1 Eren B.

1 Eren E.

1 Lee L.

1 Van Horn J.

1 Wu F.

1 Yang J.

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Positron Annilation Lifetime and Glass Transition Temperatures in CO_2 Sorption Polystyrene

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals