Thermoresponsive actuation enabled by permittivity switching in an electrostatically anisotropic hydrogel

The temperature-mediated modulation of anisotropic electrostatics in response to changes of electrostatic permittivity in a hydrogel consisting of cofacially oriented electrolyte nanosheets imparts the hydrogel with actuation properties. Electrostatic repulsion, long used for attenuating surface fri...

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Bibliographic Details
Published in:Nature materials 2015-10, Vol.14 (10), p.1002-1007
Main Authors: Kim, Youn Soo, Liu, Mingjie, Ishida, Yasuhiro, Ebina, Yasuo, Osada, Minoru, Sasaki, Takayoshi, Hikima, Takaaki, Takata, Masaki, Aida, Takuzo
Format: Article
Language:English
Subjects:
140/131
639/301/923/1027
639/638/298/923/1027
Actuators
Anisotropy
Biomaterials
Condensed Matter Physics
Cooling
Deformation resistance
Dielectric constant
Electrostatics
Friction
Heating
Hydrogels
letter
Materials Science
Nanostructure
Nanotechnology
Optical and Electronic Materials
Permittivity
Water uptake
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Summary:The temperature-mediated modulation of anisotropic electrostatics in response to changes of electrostatic permittivity in a hydrogel consisting of cofacially oriented electrolyte nanosheets imparts the hydrogel with actuation properties. Electrostatic repulsion, long used for attenuating surface friction 1 , 2 , is not typically employed for the design of bulk structural materials. We recently developed a hydrogel 3 with a layered structure consisting of cofacially oriented electrolyte nanosheets 4 . Because this unusual geometry imparts a large anisotropic electrostatic repulsion 5 to the hydrogel interior, the hydrogel resisted compression orthogonal to the sheets but readily deformed along parallel shear. Building on this concept, here we show a hydrogel actuator 6 , 7 , 8 , 9 , 10 , 11 that operates by modulating its anisotropic electrostatics 12 in response to changes of electrostatic permittivity associated with a lower critical solution temperature transition 13 , 14 . In the absence of substantial water uptake and release, the distance between the nanosheets rapidly expands and contracts on heating and cooling, respectively, so that the hydrogel lengthens and shortens significantly, even in air. An L-shaped hydrogel with an oblique nanosheet configuration can thus act as a unidirectionally proceeding actuator that operates without the need for external physical biases 15 , 16 , 17 , 18 .
ISSN:1476-1122
1476-4660
DOI:10.1038/nmat4363