Equilibrium and surface rheology of monolayers of insoluble polycations with side chains.

We have studied monolayers of poly(n-tetradecyl 4-vinylpyridinium-co-4-vinylpyridine) bromide with different degrees of quaternization at the air-water interface. The isotherms (surface pressure vs area) present several phase transitions: at low monolayer coverage, there is a phase transition over a characteristic area that increases on increasing the quaternization degree. This behavior can be rationalized in terms of a mean-field theory of 2D semiflexible polymeric chains and could be an indication of a disorder-order transition from a 2D isotropic liquid (IL) at low surface concentration to a 2D nematic phase (N) at higher concentrations.

Temperature and concentration effects on the equilibrium and dynamic behavior of a Langmuir monolayer: from fluid to gel-like behavior.

The equilibrium isotherms of monolayers of poly(4-hydroxystyrene) on the air/water interface have been studied in the 5-60 degrees C range. The results indicate that the interface is a poor solvent for the monolayers over the whole temperature range. For surface pressures within the semidilute regime, the plot of the area occupied by the polymer coils versus temperature at constant surface pressure shows a sharp change of slope near 30 degrees C.

Equilibrium and dynamics of Langmuir monolayers when the interface is a selective solvent: Polystyrene-b-poly(t-butyl acrylate) block copolymers.

The surface pressure of monolayers of insoluble diblock copolymers has been measured. One of the blocks is made of poly(t-butyl acrylate) (PtBA), and the other one by polystyrene (PS). The interface is a good solvent for PtBA, while it is a poor solvent for PS.

Long-time relaxation dynamics of langmuir films of a glass-forming polymer: evidence of glasslike dynamics in two dimensions.

We have carried out an experimental study on the mechanical relaxation of Langmuir films of a glass-forming polymer, poly-(4-hydroxystyrene), a good example of a two-dimensional system made of condensed polymer coils (at poor-solvent conditions). This study allows us to explore the response functions of the film and the temperature and density dependencies of the relaxation time. The dynamical properties show glasslike features (non-Debye mechanical response and non-Arrhenius relaxation times) reconcilable within the frame of the mode-coupling model.

Relaxation dynamics of langmuir polymer films: a power-law analysis.

We report an experimental study on the mechanical relaxation of Langmuir films of a flexible polymer: polyvinylacetate, a good example of a two-dimensional polymeric system at good-solvent conditions. This study allows us to explore the dependence of the relaxation times and the surface viscosity on the concentration. In the semidilute regime, both dynamical properties follow well-defined power laws, which are in quantitative agreement with 2D reptation.