Dilational rheology of Langmuir polymer monolayers: Poor-solvent conditions

The viscoelastic moduli (elasticity and dilational viscosity) of monolayers of P4HS have been studied over a broad frequency range (0.1 mHz-200 kHz) u sing a combination of relaxation and capillary waves techniques. The analys is of the surface pressure, the elasticity and the viscosity in the semidil ute regime show that the air-water interface is a poor (near-Theta) solvent for the monolayer. The results of viscoelastic moduli show that there is a broad relaxation process in the low-frequency range (omega <1 Hz), and ano ther very intense relaxation process centered in the kHz region. This behav ior contrasts with the one previously found for PVAc, a polymer for which t he interface is a good solvent. For PVAc the relaxation found at low freque ncies is much narrower, and two processes are clearly distinguished at high er frequencies: one centered at 500 Hz and another one at 40 kHz. (C) 2001 American Institute of Physics.