2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/151940The effect of adding nonadsorbing polymer to a lamellar phase of surfactant bilayers is studied theoretically. We find that the polymer produces coexistence between two lamellar phases of different layer spacings. The coexistence region is a closed loop, as in the experiments of Ficheux et al. [J. de Physique II 5 823 (1995)]. Within our model the coexistence is driven by depletion.7 pages, 2 figuresSoft Condensed MatterStatistical Mechanicstext