Polyelectrolyte multilayer films under mechanical stretch†
Polyelectrolyte multilayers can be used to design films which respond to mechanical stimuli. The behaviors of three different polyelectrolyte multilayers deposited onto silicone sheets were investigated: PAH/PSS, PDADMA/PSS and PLL/HA films [PAH: poly(allylamine); PSS: poly(styrene sulfonate); PDADMA: poly(diallyldimethylammonium); PLL: poly(L-lysine); HA: hyaluronic acid]. While (PLL/HA) and (PDADMA/PSS) multilayers remain undamaged under stretch, (PAH/PSS) films are very brittle and cracks are formed for low elongation degrees. PAH/PSS films behave more like glasses whereas (PLL/HA) and (PDADMA/PSS) multilayers behave rather as gels. (PSS/PAH) and (PSS/PDADMA) multilayers were also deposited as a capping and impermeable layer on top of a (PLL/HA)30 multilayer acting as a compartment. Whereas (PSS/PAH) barriers exhibit large micrometric cracks under stretch, (PSS/PDADMA) barriers open through nanopore formation for a given stretching degree. When these films are brought back to the non-stretched state, the nanopores close and the barrier becomes tight again. In the case of (PSS/PAH) barriers, only a partial tightening is achieved.