Structuring Nanofibers of SMEC Sheets: A New Approach to Control Self-Folded Shape by Uniaxial Stretching

Shape-memory elastomer composite (SMEC) sheets, made of a honeycomb structured electrospun poly(ε-caprolactone) (PCL) fiber mat embedded in a silicone (PDMS) elastomer, fold on themselves upon uniaxial traction. The self-folding of the composite sheet originates from a bi-layered structure obtained by a simple one-step impregnation process. Indeed, the impregnation of a structured PCL fiber mat by oily PDMS in a flat Teflon mold leads, after curing, to an asymmetric composite sheet made of one PDMS flat thin layer on the mold side and one rough PDMS/PCL composite layer on the other side due to specific affinities between the three polymers involved. The self-folded shape of such structured single sheet obtained upon uniaxial stretching and stress release is controlled by the honeycomb pattern orientation versus stretching direction, by the pattern size and by the applied uniaxial stretching stress. High shape recovery and robust shape memory cycling are also demonstrated by dynamic mechanical analysis. This innovative process based on the mat structuration allows a straightforward one-step fabrication of shape memory sheets, with a wide scope of tunable self-folded curvatures exhibiting efficient temperature shape recovery.