Positron annihilation spectroscopy as a probe of microscopic structure and physical aging in polymer

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7181044

Yu, M

Positron annihilation is studied as a characterization method for the properties of polymers. Previous studies indicate that the orthopositronium lifetime [tau][sub 3] and intensity I[sub 3] is correlated to the free volume [open quotes]hole[close quotes] size and number density of holes in a polymer. Positron annihilation lifetime (PAL) studies in polymers measure the change in free volume, and they are sensitive to different physical environments. PAL studies of the temperature dependence of a disphenol-A polycarbonate shows that the free volume increases with increasing temperature, and it also obtains the transition temperatures T[sub g] and T[sub [beta]][prime], from the [tau][sub 3] curve and the I[sub 3] curve, respectively. The isothermal aging in polycarbonate shows that: I[sub 3] decreases while [tau][sub 3] remains constant during a long-time annealing at a temperature far below T[sub g]; and I[sub 3] remains constant while [tau][sub 3] goes through a [open quotes]over shooting[close quotes] in the first hours after quenching and annealing at a temperature just below T[sub g]. The free volume in polycarbonate increases with applied tensile strain up to 4%, then levels off. Similarly, the free volume in polymethyl metacrylate (PMMA) decreases with applied tensile compressional strain also up to [minus]4% then levels off. A negative change in both [tau][sub 3] and I[sub 3] has been observed when polycarbonate is under 3% tensile strain and after release of strain. A more advance technique of positron annihilation, PAL-momentum correlation which can give more detailed information about free volume structure in polymers, has also been studied and improved. Two 5-cm-diameter, 5-cm-long CsF scintillation detectors for lifetime measurement, and a 30-cm-diameter Anger camera whose y-analog pulse gives one-dimensional ACAR information, comprise a new experimental arrangement of PAL-momentum correlation system.

• Research Organization: Case Western Reserve Univ., Cleveland, OH (United States)
• OSTI ID: 7181044
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
PMMA
AGING
MICROSTRUCTURE
POSITRON REACTIONS
POLYCARBONATES
ANNIHILATION
SPECTROSCOPY
STRAIN AGING
TEMPERATURE DEPENDENCE
BASIC INTERACTIONS
CARBON COMPOUNDS
CARBONATES
ELECTROMAGNETIC INTERACTIONS
ESTERS
INTERACTIONS
LEPTON REACTIONS
NUCLEAR REACTIONS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
OXYGEN COMPOUNDS
PARTICLE INTERACTIONS
POLYACRYLATES
POLYMERS
POLYVINYLS
360602* - Other Materials- Structure & Phase Studies
360603 - Materials- Properties