An improved protocol is proposed for preparation of a humiditysensitive soft actuator through the layer-by-layer assembling of weight-ratio-variable composites of sodium alginate (SA) and poly(vinyl alcohol) (PVA) into laminated structures. The design induces nonuniform hygroscopicity in the thickness direction and gives rise to strong interfacial interaction between layers, making the actuator have directional motility. A mathematical model reveals that the directional motion is driven by the chemical potential of humidity, and its energy conversion efficiency from humidity to mechanical work reaches 81.2% at 25 °C. By coating with CoCl 2 , the composite film of SA@PVA/CoCl 2 can act as a warning sign that provides reminder information to prevent people from slipping or falling by a conspicuous red sign during a high-humidity environment. When the film is involved in a bidirectional switch, it is capable of turning on/off light-emitting diodes by humidity, showing promising potential in control over humidity-dependent devices.
Hollow
hydrogel tubes that are capable of maintaining their flexibility and
structural stability in extreme temperature conditions have potential
for use in biomedical scaffolds, carriers, and soft robotics over
a wide temperature range. However, the preparation of hollow hydrogel
tubes still remains challenging because it normally requires templates
or complex devices and it is hard to endow the hollow tubes with antifreezing
heat-resistant capabilities. We report a protocol that does not require
a template or complex devices, in which sodium alginate film strips
are immersed in an aqueous mixture of CaCO3, CaCl2, NaHCO3, and HCl, which results in the manufacture of
hollow tubes in 30 min. These hollow tubes are functionalized by glycerol
and poly(ethylene glycol), which provides the tubes with antifreezing
heat-resistant performances and enables them to keep their flexibility
and hollow structures from −70 to 120 °C. This is the
first report on antifreezing heat-resistant hollow hydrogel tubes,
to the best of our knowledge. Such hollow tubes as carriers can control
the sublimation of a mothball at a rate of 1.1 mg/h, which is one-tenth
of the sublimating rate of an unloaded mothball. This sublimating
rate reduces the hazard to environments along with maintaining the
repellent effects. As the tube is a honey carrier, it enables the
sustainable release of the honey over 800 min with a high efficacy
for tricking and capturing ants. The simple applications demonstrate
that the antifreezing heat-resistant hollow tubes might be feasible
as carriers for the controlled release in extremely cold/hot environments.
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