Phase-Change Thermoplastic Elastomer Blends for Tunable Shape Memory by Physical Design

Abstract

Intelligent polymeric materials are of increasing interest in contemporary technologies due to their low cost, light weight, facile processability, and inherent ability to change properties, shape, and/or size upon exposure to an external stimulus. In this study, we consider thermally programmable shape-memory polymers (SMPs), which typically rely on chemistry-specific macromolecules composed of two functional species. An elastic, network-forming component permits stretched polymer chains to return to their relaxed state, and a switching component affords at least one thermal transition to regulate fixation of a desired strain state and return to a previous strain state. Here, we produce designer shape-memory materials by combining thermoplastic elastomeric triblock copolymers with a midblock-selective phase-change additive, thereby yielding shape-memory polymer blends (SMPBs). These materials not only exhibit tunable switch points but also controllable recovery kinetics. We further highlight the versatility of SMPBs through laminate welding for intermediate multishape fabrication and liquid metal inclusion for shape-memory electronics.

4D Printing of Shape‐Memory Hydrogels for Soft‐Robotic Functions

“…[5] Smart or stimuliresponsive materials have the unique ability to return from a temporary deformed state, induced by heat, light, pH, ultrasound, chemical substances, [6][7][8][9][10][11][12][13] etc., to their permanent, i.e., original, shape, thus exhibiting advantages for applications in numerous sectors, such as sensors and actuators, [14] tissue engineering, [15] bio-separation devices, and controlled drug delivery. [5] Smart or stimuliresponsive materials have the unique ability to return from a temporary deformed state, induced by heat, light, pH, ultrasound, chemical substances, [6][7][8][9][10][11][12][13] etc., to their permanent, i.e., original, shape, thus exhibiting advantages for applications in numerous sectors, such as sensors and actuators, [14] tissue engineering, [15] bio-separation devices, and controlled drug delivery.…”

Dielectric and Resistive Heating of Polymeric Media: Toward Remote Thermal Activation of Stimuli‐Responsive Soft Materials

“…A polyimide (Kapton HN, DuPont), a glassy polymer with a T g between 360 and 410 °C, ρ = 1.42 g/cm 3 and ε ′ ≈ 3.5 at 1 kHz according to the manufacturer, was used to discern if the model could capture sensible heat changes. The second material investigated here was a shape‐memory polymer blend and dielectric elastomer composed of a poly[styrene‐ b ‐(ethylene‐ co ‐butylene)‐ b ‐styrene] triblock copolymer (G1651, Kraton Polymers) with an upper T g near 100 °C, a linear C 20 H 42 hydrocarbon ( n ‐eicosane, Fisher Scientific) with T m = 38 °C, and a cycloaliphatic tackifying resin (5380, ExxonMobil) with T g = 30 °C. The copolymer number‐average molecular weight and polydispersity were ≈270 kDa and <1.10, respectively, according to size‐exclusion chromatography, and the copolymer composition was 33 wt% styrene from H NMR.…”

“…The copolymer number‐average molecular weight and polydispersity were ≈270 kDa and <1.10, respectively, according to size‐exclusion chromatography, and the copolymer composition was 33 wt% styrene from H NMR. On the basis of a previous study, a single blend composition was selected for investigation: 30/50/20 w/w/w copolymer/hydrocarbon/tackifier. Polyimide film measuring 170 µm thick was obtained directly from the manufacturer and used as‐received.…”

“…First, it is important to recognize how this stimuli‐responsive system functions. In the presence of the hydrocarbon and tackifying resin at temperatures below its order‐disorder transition, the copolymer self‐organizes into a spherical morphology wherein glassy (styrenic) micelles serve as physical crosslinks and stabilize a highly swollen polyolefin network . At T > T m , the blend behaves as a thermoplastic elastomer gel (TPEG) that can exhibit remarkable mechanical properties .…”

“…If the blend is deformed under these conditions and then the temperature is dropped below T m , the new strain state will remain intact with a high level of strain fixity (typically >95%). The purpose of the added tackifier is to hasten recovery when the specimen is re‐heated above T m . Important benefits of this blend design over bifunctional macromolecules include i) the trigger temperature can be precisely chosen from the length of the hydrocarbon, ii) the extent to which the TPEG can be deformed depends on copolymer content, and iii) shape recovery can approach purely elastic with little viscoelastic contributions and negligibly low cyclic hysteresis.…”