Two-way Shape Memory Polymers Research Articles

High performance and tunable artificial muscle based on two-way shape memory polymer

Polymeric artificial muscle by twist insertion in precursor fiber is a recent discovery. This study shows that chemically cross-linked two-way shape memory polymer muscles have remarkable and tunable axial actuation with lower actuation temperature.

Artificial muscles made of chiral two-way shape memory polymer fibers

In this work, we demonstrate the unusual improvement of the tensile actuation of hierarchically chiral structured artificial muscle made of two-way shape memory polymer (2W-SMP) fiber. Experimental results show that the chemically cross-linked poly(ethylene-co-vinyl acetate) 2W-SMP fibers possess an average negative coefficient of thermal expansion (NCTE) that is at least one order higher than that of the polyethylene fiber used previously. As expected, the increase in axial thermal contraction of the precursor fiber leads to an increase in the recovered torque (4.4 Nmm) of the chiral fiber and eventually in the tensile actuation of the twisted-then-coiled artificial muscle (67.81±1.82%). A mechanical model based on Castigliano's second theorem is proposed, and the calculated result is consistent with the experimental result (64.17% tensile stroke). The model proves the significance of the NCTE and the recovered torque on tensile actuation of the artificial muscle and can be used as a guidance for the future design.

Thermally driven microfluidic pumping via reversible shape memory polymers

The need exists for autonomous microfluidic pumping systems that utilize environmental cues to transport fluid within a network of channels for such purposes as heat distribution, self-healing, or optical reconfiguration. Here, we report on reversible thermally driven microfluidic pumping enabled by two-way shape memory polymers. After developing a suitable shape memory polymer (SMP) through variation in the crosslink density, thin and flexible microfluidic devices were constructed by lamination of plastic films with channels defined by laser-cutting of double-sided adhesive film. SMP blisters integrated into the devices provide thermally driven pumping, while opposing elastic blisters are used to generate backpressure for reversible operation. Thermal cycling of the device was found to drive reversible fluid flow: upon heating to 60 °C, the SMP rapidly contracted to fill the surface channels with a transparent fluid, and upon cooling to 8 °C the flow reversed and the channel re-filled with black ink. Combined with a metallized backing layer, this device results in refection of incident light at high temperatures and absorption of light (at the portions covered with channels) at low temperatures. We discuss power-free, autonomous applications ranging from thermal regulation of structures to thermal indication via color change.

Two-way shape memory polymer with “switch–spring” composition by interpenetrating polymer network

In the present work, a novel molecular strategy was employed to fabricate a two-way shape memory polymer (2WSMP), which is an interpenetrating network (IPN) with elastomeric and crystalline components leading to a “switch–spring” composition. In this 2WSMP the switch, a PCL crystalline network, is responsible for the reversible shape shrinkage. While the spring, the compressed PTMEG elastomeric network, provides the push force for shape expansion. This IPN polymer has the desired two-way shape effect (2WSME) as proved by DMA.

Combined One-Way and Two-Way Shape Memory in a Glass-Forming Nematic Network

Past research in the field of shape memory polymers has led to significant advancements in the areas of so-called one-way and two-way (reversible) shape memory. While one-way shape memory polymers allow indefinite fixing of a temporary shape until triggered thermally to recover to an equilibrium shape, two-way shape memory polymers feature muscle-like contraction on heating and expansion on cooling under tensile load, the latter anomalous elongation occurring due to an ordering transition. Previously, reversible actuation has been reported for liquid crystalline elastomers featuring a monodomain (uniformly aligned) structure, suggesting that such alignment is required for actuation. In this work, we have prepared a glass-forming polydomain nematic network that combines reversible actuation associated with a polydomain−monodomain transition with lower temperature one-way shape memory centered at Tg. To test separability of these phenomena, distinct deformations were achieved and temporarily fixed by (1) co...