Dynamic security device
A security device that elicits at least one dynamic response upon acceleration, or upon change of orientation with respect to gravity, wherein the dynamic response continues after cessation of the acceleration or the change of orientation. In addition, the dynamic response can be optical, such that it is visually observable by an unaided human eye. Alternatively, the response can be machine readable. In some cases, the dynamic response has duration of from about 0.01 s to about 100 s, or from about Is to about 10 s.
1. A security device that exhibits at least one dynamic response upon change of orientation of the security device with respect to gravity, wherein:
the security device comprises one or more microfluidic chambers filled with a liquid and one or more microscopic elements; and
the dynamic response:
a) continues after cessation of the change of orientation with respect to gravity; and
b) comprises a transition of the one or more microscopic elements:
i) from substantial mechanical equilibrium to non-equilibrium upon action of the change of orientation with respect to gravity; and
ii) back to substantial mechanical equilibrium after cessation of the change of orientation with respect to gravity, and
wherein the one or more microscopic elements undergo at least one of a rotational motion and a translational motion relative to the liquid during the transition, and the volumetric space collectively occupied by the liquid and the one or more microscopic elements is unchanging relative to the rest of the security device throughout the dynamic response.
2. The security device of claim 1 , wherein the transition leads to the generation of one or more macroscopic effects.
3. The security device of claim 2 , wherein at least one of the macroscopic effects is optical.
4. The security device of claim 3 , wherein the optical macroscopic effect is visually observable by an unaided human eye.
5. The security device of claim 2 , wherein at least one macroscopic effect is machine readable.
6. The security device of claim 1 , wherein the one or more microscopic elements transitions from substantial mechanical equilibrium to non-equilibrium and back to substantial mechanical equilibrium in a time interval of from about 0.01 s to about 100 s, preferably from about 0.01 s to about 10 s, more preferably from about 1 s to about 10 s.
7. The security device of claim 1 , wherein the one or more microscopic elements have a size between 0.01 and 100 μm, preferably between 0.01 and 10 μm.
8. The security device of claim 1 , wherein the one or more microscopic elements are integrated into a plurality of independent microchambers.
9. The security device of claim 1 , wherein:
at least a portion of each of the one or more microscopic elements has an average density that is unequal with the liquid's density; and
the one or more microscopic elements transition by way of sedimentation or flotation.
10. The security device of claim 1 , wherein the one or more microscopic elements are dispersed in a liquid matrix that is solidified; and the solidified matrix provides a plurality of microfluidic chambers that are subsequently exposed to a swelling agent that provides the liquid as a shell around the one or more microscopic elements.
11. The security device of claim 10 , wherein the liquid matrix is solidified by curing or solvent evaporation.
12. The security device of claim 9 , wherein the one or more microscopic elements comprises: a first set of microscopic elements each with an average density greater than the liquid density that transition by way of sedimentation; and a second set of microscopic elements each with an average density less than the liquid density that transition by way of flotation.
13. The security device of claim 9 , wherein the liquid comprises a dye that contrasts with the one or more microscopic elements as they transition by way of sedimentation or flotation.
14. The security device of claim 1 , wherein the one or more microscopic elements are configured to transition from substantial alignment to non-alignment with the gravitational field upon action of the change of orientation of the device, and back to substantial alignment with the gravitational field after cessation of the change of orientation.
15. The security device of claim 14 , wherein the one or more microscopic elements are dispersed in the liquid; a portion or all of the microscopic elements each have a centre of mass that is distinct from a centre of volume thereof; and the microscopic elements transition by way of rotation.
16. The security device of claim 14 , wherein the one or more microscopic element is a Janus microparticle comprising: i) an inner core; and ii) a coating on a surface portion of the Janus particle, and the inner core has a density distinct from a density of the coating.
17. The security device of claim 16 , wherein the inner core has a diameter of from 0.1 to 100 μm, the coating has a thickness of from 10 nm to 500 nm and the coating thickness is less than 20% of the diameter.
18. The security device of claim 1 , wherein the dynamic response is generated with no external equipment required.