A novel UHV microcalorimeter has been used to study the interaction between
calcium and three polymers: MEH-PPV, MEH-PPP and P3HT. All three polymers
behave differently in their reaction kinetics with calcium. On MEH-PPV we measure
45 μJ/cm² of heat generated in excess of the heat of bulk metal growth, 120 μJ/cm²
for MEH-PPP, and 100 μJ/cm² for P3HT. Comparison of the MEH-PPV and MEHPPP
data indicate that the initial reaction of calcium with MEH-PPV occurs at the
vinylene group. We propose, based on hypothetical models, that calcium reacts with
the vinylene groups of MEH-PPV with a reaction heat of 360 kJ/mol and at a
projected surface density of 1.7 sites/nm², while it reacts with the phenylene groups
of MEH-PPP in a two-step process with reaction heats of 200 and 360 kJ/mol
respectively, at a projected surface density of 3.5 sites/nm².
Optical absorption experiments, using either a 1.85 eV diode laser or a xenon lamp
coupled to a scanning monochromator, have also been performed using the same
calorimeter sensor. In the case of MEH-PPV, using the laser we find an optical
absorption cross-section of 3E-¹⁷ cm² per incident calcium atom at low coverages.
The change in absorptance at higher coverages correlates perfectly with the
population of reacted Ca atoms determined calorimetrically. The size of the
absorbance cross-section, and its position just within the band gap of the polymer, are
consistent with the reaction being one of polaron formation. Calcium does not appear
to dope P3HT, while the photon energy range of 1.5 to 3.75 eV used in these
experiments is likely too small for probing polaronic energy states in MEH-PPP.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/863 |
| Date | 11 1900 |
| Creators | Hon, Sherman Siu-Man |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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