COLL 209 |
| Cesar Marquez-Beltran and Dominique Langevin. Laboratoire de Physique des Solides, Université Paris Sud, Batiment 510, Orsay, 91405, France |
| We have studied free horizontal thin liquid films made with semi-dilute solutions of an anionic polysaccharide, Carboxymethylcellulose, and stabilized by ionic surfactants. We have focused on the influence of surface viscoelasticity and bulk viscosity on the thinning kinetics. We have found stratification phenomena whatever the nature of the surfactant charge. The stepsize of the stratification domains varies as the inverse square root of the polymer concentration, and is closed to the mesh size of the polymer network. During stratification, dark spots form and expand, the outer ultrathin polymer layers dewetting the remaining thinner film. When the films are stabilized with cationic (alkyltrimethylammonium bromides) surfactants a slow-stratification is obtained, and the expansion of dark spots is diffusive-like (size increasing as square root of time). Here, strong polymer-surfactant interactions create an enhanced co-adsorption of both components at the air-water interface; the resulting surface viscoelasticity increases with surfactant concentration, whereas the dark spot expansion slows down. When an anionic surfactant (AOT) is used, a rapid-stratification is observed. Below a critical radius rc, the stratification kinetics is again diffusive-like, but above rc, the radius r(t) of dark spots grows linearly with time. Simultaneously, the rim surrounding the spots breaks into droplets (Rayleigh type instability). In this case, the dark spot expansion becomes faster when the film thickness decreases, suggesting an increase of the chain mobility for the confined polymers. These findings are similar to the behavior of polymer melts confined between adsorbing or non-adsorbing surfaces, respectively |
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Posters: Fundamental Research in Surface and Colloid Chemistry
6:00 PM-8:00 PM, Monday, March 29, 2004 Disneyland -- North Exhibit Hall, Poster
Division of Colloid and Surface Chemistry |