title: Rheology of poly(methyl methacrylate) Langmuir monolayers: percolation transition to a soft glasslike system.
abstract: An experimental study of the equilibrium properties and of the surface rheology of Langmuir monolayers of poly(methyl methacrylate) (PMMA) at the air/water interface has been carried out as a function of polymer concentration (Γ) and molecular weight (M(w)). Dilational and shear complex elasticity moduli covering a frequency range from 10(-3) to 0.2 Hz have been discussed. It was found that the air∕water interface behaves as a poor solvent for PMMA monolayers, thus suggesting that the polymer coils take collapsed soft-disks (pancakes) shape at the interface. The equilibrium and dynamic results suggest a fluid-to-soft-glass transition as the polymer concentration increases above a critical packing fraction at constant temperature. This two-dimensional transition is in agreement with results previously discussed for the dilational rheology of poly(4-hydroxystyrene) [F. Monroy, F. Ortega, R. G. Rubio, H. Ritacco, and D. Langevin, J. Chem. Phys. 95, 056103 (2005)]. Furthermore, the Γ-dependence of the relaxation dynamics of the monolayers suggests that the gel state may be considered as a fragile soft glass.
authors.affiliation: Departamento de Química Física I, Facultad de Química, Universidad Complutense, Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Maestro
authors.forename: F
authors.initials: F
authors.lastname: Ortega
authors.forename: R G
authors.initials: RG
authors.lastname: Rubio
authors.forename: M A
authors.initials: MA
authors.lastname: Rubio
authors.forename: J
authors.initials: J
authors.lastname: Krägel
authors.forename: R
authors.initials: R
authors.lastname: Miller