Ultrastable glasses are generated by vapor deposition on substrates heated near the glass transition temperature (Tg), but it is unclear if the remarkable properties of such glasses are present in ultrathin (g = 0.94. This maximum in modulus is the same modulus obtained for very thin (g = 0.80). However, the modulus of films deposited at this lower temperature abruptly decreases to approximately 1.5 GPa for thicker films; the modulus from deposition at T/Tg = 0.94 is thickness independent. In addition to the thin film modulus, the substrate temperature significantly impacts the water uptake in NPD films. From QCM, the volume fraction of water at equilibrium with nearly saturated water vapor decreases from nearly 4% to less than 1% as the substrate temperature increases from T/Tg = 0.82 to T/Tg = 0.93. The substrate temperature provides a simple route to control mechanical properties and water uptake into vapor-deposited NPD, and these concepts are likely extendable to other organic electronic materials; the increased moduli and decreased water uptake could enable improved performance and lifetime of small molecule glasses for a variety of organic electronic applications.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Materials Chemistry
- Surfaces, Coatings and Films