Sheath-core fibers for superelastic electronics, sensors, and muscles
Superelastic conductive fibers, and more particularly, sheath-core fibers for superelastic electronics, sensors, and muscles, and a process for fabricating of highly stretchable sheath-core conducting fibers by wrapping fiber-direction-oriented conductive nanofiber sheets on stretched rubber fiber cores.
1. A superelastic conductive fiber comprising
(a) a reversibly stretchable fiber core; and
(b) one or more layers of nanofiber sheets wrapped on the stretchable fiber core, wherein
(i) the one or more layers of nanofiber sheets were wrapped on the stretchable fiber core while the reversibly stretchable fiber core was in a stretched position,
and
(ii) the orientation of the nanofibers in at least one of the one or more layers of nanofiber sheets is parallel to the length direction of the stretchable fiber core.
2. The superelastic conductive fiber of claim 1 , wherein the superelastic conductive fiber is operable as a fiber selected from the group consisting of fiber capacitors, tensile strain sensors, and artificial muscles that provide torsional actuation, tensile actuation, or a combination thereof.
3. The superelastic conductive fiber of claim 2 , wherein
(a) the superelastic conductive fiber is operable as a fiber capacitor in which 950% stretch of superelastic conductive fiber provides at least 800% increase in capacitance, and
(b) the increase in capacitance change is substantially non-hysteretic and reversible.
4. The superelastic conductive fiber of claim 1 , wherein the orientation of the nanofibers in each of the one or more layers of nanofiber sheets is parallel to the length direction of the stretchable fiber core.
5. The superelastic conductive fiber of claim 2 , wherein the superelastic conductive fiber is operable as an artificial muscle based on electrostatic attraction between electrodes of dielectric rubber capacitors.
6. The superelastic conductive fiber of claim 5 , wherein the artificial muscle is a high stroke torsional fiber muscle made by inserting twist into the superelastic conductive fiber.
7. An elastomeric electrically conducting fiber that is operable for being periodically buckled in a first dimension and a second dimension, wherein the elastomeric electrically conducting fiber comprises:
(a) an elastomeric fiber core; and
(b) a nanofiber sheath having nanofibers that are predominately oriented parallel to the length direction of the elastomeric fiber core, wherein
(i) the first dimension is provided by length direction of the elastomeric electrically conducting fiber;
(ii) the second dimension is provided by belt direction of the elastomeric electrically conducting fiber; and
(iii) the periodic buckling in the first dimension and the second dimension provides out-of-plane buckling.
8. The elastomeric electrically conducting fiber of claim 7 , wherein the periodic buckling in the first dimension and the second dimension is operable to occur out-of-phase in the length direction and the belt direction as length of the elastomeric electrically conducting fiber is varied by either mechanical stretch or release of mechanical stretch.
9. The elastomeric electrically conducting fiber of claim 8 , wherein the buckling in the first direction and the second direction is hierarchical in that, in each of the first direction and the second direction, both long period and short period buckling is operable to occur.