Author/Authors :
Ata، نويسنده , , S. and Muramatsu، نويسنده , , M. and Takeda، نويسنده , , J. and Ohdaira، نويسنده , , T. Uchikoshi T. S. Suzuki Y. Sakka، نويسنده , , R. and Ito، نويسنده , , K. and Kobayashi، نويسنده , , Y. and Ougizawa، نويسنده , , T.، نويسنده ,
Abstract :
Free volume behavior in polystyrene thin films with thickness ranging from 22 to 1200 nm on silicon substrates was studied by energy variable positron annihilation lifetime spectroscopy (EVPALS). The films were prepared by spincasting from toluene solutions of 0.5–5.0 wt% polystyrene with Mw = 1 090 000 g/mol. Distinct deviations from bulk polystyrene in thermal expansion of the free volume holes and the glass transition temperature associated with free volume behavior were observed for the thinnest film with 22 nm thickness, indicating its exclusively high chain mobility. Comparison of the polystyrene concentration in the precursor solution around the overlap concentration suggests that the high chain mobility is due to less entangled chains caused by rapid removal of the solvent from the diluted solution in order to prepare very thin film.
