Extrusion printing of liquid crystal elastomers
A method of ink-extrusion printing an object, including providing a mixture including liquid crystal monomers and photo-catalyzing or heating the mixture to produce a liquid crystal ink. The ink is in a nematic phase. The method includes extruding the ink through a print-head orifice moving along a print direction to faun an extruded film of the object. The extruded film exhibits birefringence. Also disclosed are a liquid crystal ink. The ink includes a mixture including liquid crystal monomers. The mixture when at a target printing temperature is in a nematic phase. Also disclosed is ink-extrusion-printed object. The object includes an extrusion-printed film including a nematic liquid crystal elastomer, wherein the film exhibits birefringence along an extrusion axis of the film.
1. A method of ink-extrusion printing an object, comprising:
providing a mixture including liquid crystal monomers;
photo-catalyzing or heating the mixture to produce a liquid crystal ink, wherein the ink is in a nematic phase; and
extruding the ink through a print-head orifice moving along a print direction to form an extruded film of the object, wherein the extruded film exhibits birefringence and an outer surface of the film includes micro-ridges, the micro-ridges having a long axis substantially parallel to the extrusion axis and thereby increased elastic modulus anisotropy of the film in directions parallel versus perpendicular to the extrusion axis as compared to the film without micro-ridges.
2. The method of claim 1 , wherein extruding the ink through the orifice exposes the ink to a shear rate in a range from 1 to 100 s −1 .
3. The method of claim 1 , wherein photo-catalyzing or heating the mixture to produce a liquid crystal ink includes forming liquid crystal oligomers from the liquid crystal monomers, the oligomers in the nematic phase and having a molecular weight in a range from about 2 to 25 kD.
4. The method of claim 1 , wherein the extruding of the ink is carried out at a temperature below the nematic to isotropic transition temperature (T NT ) of the ink.
5. The method of claim 1 , further including applying an external stimulus to accelerate crosslinking of the extruded film to form a cured film, wherein the cured film exhibits birefringence.
6. The method of claim 5 , wherein the cured film includes a liquid crystal polymer network including cross-linked copolymers of liquid crystal diacrylate monomers.
7. An ink-extrusion-printed object, comprising:
an extrusion-printed film including a nematic liquid crystal elastomer, wherein:
the film exhibits birefringence along an extrusion axis of the film, and
an outer surface of the film include micro-ridges, the micro-ridges having a long axis substantially parallel to the extrusion axis and thereby increased elastic modulus anisotropy of the film in directions parallel versus perpendicular to the extrusion axis as compared to the film without micro-ridges.
8. The object of claim 7 , wherein the film has an elastic modulus in a direction parallel to the extrusion axis that is at least 2 times greater than an elastic modulus of the film in a direction perpendicular to the extrusion axis.
9. The object of claim 8 , wherein the elastic modulus in the direction parallel to the extrusion axis is a value in a range from 10 x to 10 y Pa where x=5 and y=9.
10. The object of claim 7 , wherein the film include at least one bend wherein a direction of the extrusion axis in a first segment of the film before the bend and a direction of the extrusion axis in a second segment of the film are non-parallel.
11. The object of claim 7 , wherein the film changes anisotropically in response to an isotropic external stimulus, the isotropic external stimulus being one or more of: visible light, a change in temperature or exposure to a chemical stimulus of liquid water, water vapor, organic liquid or organic vapor.
12. The object of claim 11 , wherein the film changes by reversibly contracting parallel to the extrusion axis when the external stimulus is an increase in temperature and by reversibly expanding parallel to the extrusion axis when the external stimulus is a decrease in temperature.
13. An ink-extrusion-printed object, comprising:
a first extrusion-printed film including a nematic liquid crystal elastomer, wherein the first film exhibits birefringence along an extrusion axis of the film, and
a second extrusion-printed film including a second nematic liquid crystal elastomer, wherein the second film exhibits birefringence along an extrusion axis of the second film and the second nematic liquid crystal elastomer of the second film has a nematic to isotropic transition temperature that is different than the nematic liquid crystal elastomer of the first film.
14. The object of claim 13 , wherein an outer surface of one or both of the first film or second film includes micro-ridges, the micro-ridges having a long axis substantially parallel to the extrusion axes of the films, respectively, and thereby increases an elastic modulus anisotropy of the first film or second film in directions parallel versus perpendicular to the extrusion axes, as compared to the respective film without micro-ridges.