Humidity- and Sunlight-Driven Motion of a Chemically Bonded Polymer Bilayer with Programmable Surface Patterns

Abstract

We report a bilayer of sodium alginate/polyvinylidene fluoride (SA/PVDF) that is chemically bonded through a series of interfacial coupling reactions. The SA layer is hydrophilic in structure and is capable of strong interaction with water molecules, thus presenting high sensitivity to humidity, whereas the PVDF layer is hydrophobic, inert to humidity. This structural feature results in the bilayer having asymmetric humidity-responsive performances that can thus make its shape change with directionality, which cannot be achieved in an SA single layer. The responsive process to humidity can be adjusted by exposure of the bilayer to sunlight by means of a photothermal effect that accelerates dehydration of the bilayer to cause more rapid shape deformations. When the sunlight is removed, the bilayer adsorbs humidity again and returns to its original shape, indicating good reversibility. To exactly regulate the shape deformations of the bilayer with external stimuli, we employ Ca-treated filter paper to customize crosslinking reactions in the SA layer as desired patterns which are capable of causing different mechanical tensors and swellabilities in the bilayer so as to regulate and control the actuations for self-folding, curling, twisting, and coiling in response to sunlight and humidity.On the other hand, the chemically bonded bilayer has stronger interfacial toughness and is capable of reaching 300 J m, which is around 12 times the interfacial toughness of the physically combined bilayer; as a result, the chemically bonded bilayer is capable of sustaining continuous shape deformations without interfacial failure. The directionally mechanical actuations can be utilized in designing an indicator to roughly indicate the range of intensity of sunlight by coupling the chemically bonded bilayer into a typical electric circuit, in which the range of intensity of sunlight can be easily estimated by visual observation of the light-emitting diodes.

Robust Jumping Actuator with a Shrimp‐Shell Architecture

“…Since the PIQA/CNS actuators could achieve a very large bending angle in a short time, a combination of the response rate (° s −1 ) and response time (s), as well as that of the response rate and bending angle were compared with literature results (Figure 3d,e; Table S2, Supporting Information). [9,10,[18][19][20]22,23,27,28,[48][49][50][51][52][53] It is evident that the actuation speed of the vapor-induced PIQA/CNS actuators (314.1−6000° s −1 ), which also exhibited a large bending angle (188-288° mm −1 ), was among the best vapor-driven actuators (Figure 3d,e). Particularly, the actuation speed (7875° s −1 ) and response time (0.04 s) obtained by blowing the CH 2 Cl 2 vapor through a tube were higher than those of state-of-the-art vapor-driven bimorph actuators (Figure 3d).…”

3D and 4D printable dual cross-linked polymers with high strength and humidity-triggered reversible actuation

“…See DOI: 10.1039/d1ma00223f bending, 6,16,17 twisting, 5,9,18 spiraling 19 and locomotion. 2,20 These programmable 3D shapes could be realized through selective chemical modification of specific areas on the polymer films' surface using photochemistry patterning, 21 TiO 2 patterning, 22 ion patterning 23 and local base and acid treatment. 5,10 Moreover, controlling molecular alignment of liquid crystalline polymers, 6 hierarchical self-assembly structures 3 as well as orientation of incorporated inorganic nanofillers 3,9 have also been reported to program sophisticated motions.…”

Smart Devices Based on the Soft Actuator with Nafion-Polypropylene-PDMS/Graphite Multilayer Structure

“…In recent years, the demand for smart actuators based on flexible intelligent driving materials has increased [1][2][3][4]. The role of flexible intelligent driving materials is to convert external stimuli (such as light, heat, humidity, magnetic field/electric field) into executable actions or signals needed by processors through rapid, reversible and controllable structural/morphological changes [5][6][7][8][9][10][11][12][13][14][15][16]. Flexible smart actuators driven by these stimuli have significant advantages in the soft robot, electronic skin, bionic technology and other fields [17][18][19][20].…”