Multicomponent shape-memory microfibers electrospun with precisely tunable thermal triggers

Abstract

Shape-memory polymers (SMPs) are of tremendous fundamental and practical interest as stimuli-responsive soft materials since they can spontaneously transform from one strain state to another upon environmental stimulation. Most SMPs are dense films possessing a single thermal trigger that responds to a change in temperature. In this work, we examine novel shape-memory nonwovens (SMNs) comprised of electrospun microfibers randomly arranged into mats and possessing a trigger that can be precisely varied. These SMNs derive from physically-crosslinked triblock copolymers blended with one or more midblock-selective crystallizable hydrocarbons (HCs) with 18–40 carbon units (HC18-HC40). The dependence of the trigger (melting) temperature on blend composition is ascertained by calorimetry for systems composed of a single copolymer and one or more hydrocarbons. Judicious selection of the blends produced here yields designer materials that can be triggered near/at body temperature. Examples of blends satisfying this requirement include a styrenic thermoplastic elastomer (TPE) modified with ∼40–95 wt% HC20 or 80–95 wt% HC18/HC20 (equimass). While the trigger temperature of the latter ternary blend is independent of TPE molecular weight, SMNs composed of a high-molecular-weight TPE possess remarkable mechanical properties, such as elongations exceeding 3000 % strain. We envisage use of these SMNs in applications such as self-fitting personal protection equipment.