Lily Nari Kim

Biomimetic Microfingerprints for Anti‐Counterfeiting Strategies

An unclonable, fingerprint-mimicking anti-counterfeiting strategy is presented that encrypts polymeric particles with randomly generated silica film wrinkles. The generated wrinkle codes are as highly unique as human fingerprints and are technically irreproducible. Superior to previous physical unclonable functions, codes are tunable on demand and generable on various geometries. Reliable authentication of real-world products that have these microfingerprints is demonstrated using optical decoding methods.

In Situ Fabrication and Actuation of Polymer Magnetic Microstructures

We demonstrate a single-exposure in situ magnetic actuator fabrication technique using magnetic nanoparticles (MNs) containing UV curable polymer in a Polydimethylsiloxane (PDMS) channel. Microstructures with a 3-D anchored cantilever as well as free-floating components are fabricated in a single step at a single site without the use of a sacrificial layer. By controlling the location of high oxygen concentration area through PDMS substrate patterning, we can create partially bound and free-floating movement-restricted structures. This allows us to create complex magnetic actuators, such as a 3-D anchored cantilever, motor type, and rail-guided magnetic actuators. The actuating performance of UV photopatterned magnetic microstructures depends on the MN concentration in photopolymer resin and magnetic field intensity. The measured translational velocity of magnetic microactuators with a 1 : 10 MN concentration is 140 μm/s under 1400 G of magnetic field in poly(ethylene glycol) diacrylate resin. Also, we demonstrate selective magnetic actuation of heterogeneous structures composed of magnetic and nonmagnetic parts self-assembled in railed microfluidic channels. Only magnetic parts from the assembly selectively actuated due to the magnetic field without response to the flow. Therefore, we have developed a versatile magnetic microstructure fabrication method that is very simple and fast, enabling rapid in situ fabrication and actuation.

Controllable fabrication of tube-in-tubes using anodic aluminum oxide templates

We have developed a method to fabricate tube-in-tubes that are relatively long and made in all the pores of porous anodic aluminum oxide (AAO) nano-templates. Relatively a very small amount of Co was deposited in the pores of AAO templates prepared without doing a voltage drop at the end of anodization, and then etched in NaOH solution. This caused the carbon nanotubes (CNTs) to grow out from all the pores, and larger diameter carbon nanotubes were also made on the inner surface of all the pores, by forming tube-in-tubes. We were able to control the gap between the inner surface of the larger tubes and the outer surface of the smaller ones of tube-in-tubes in some range by changing the etching time in NaOH solution. Tube-in-tubes that are relatively long and controlled the gap could be used as a storage, particularly for hydrogen gas.

Wrinkiled microparticles for unclonable microtaggants

This paper presents wrinkled microparticles as unreplicable, unique, yet configurable microtaggants for anti-counterfeiting purposes. We mimicked the shape of the human fingerprint in microscale structures using three-dimensional wrinkle patterning. We utilized irreproducible distributions of ridges on wrinkled microparticles as unique codes, similar to human fingerprints, for identification. These wrinkled microparticles can provide reliable authentication by attaching to authentic products because they can be analyzed by general fingerprint-identification methods, exhibit high individuality, and allow mass production by combining lithography-free patterning with a particle-based substrate.

Photonic bandgap fusion by magnetically aligned 3D photonic bandgap structures

We demonstrate the photonic bandgap fusion by the sequential self-assembly of superparamagnetic nanoparticle and ultra-violet(UV) exposure.