Jihoon Shin

Polyurethane microcapsules for self-healing paint coatings

Polyurethane microcapsules containing water-borne polyurethane (PU) paint as a core material for self-repairing protection coatings were successfully manufactured via interfacial polymerization of diol–diisocyanate prepolymer and 1,4-butanediol as a chain extender in an emulsion solution. The chemical structure of the resultant microcapsules was characterized by Fourier Transform Infrared Spectroscopy. Spherical capsules were observed with an average diameter of 39–72 μm and average shell thickness of 3.8–5.5 μm, while controlling agitation rates (2000–8000 rpm). The PU shell wall thickness was linearly proportional to the measured capsule diameter, thus, showing that the ratio of capsule wall thickness to diameter was constant (∼0.08). The typical core content and synthetic yield of the filled capsules were approximately 44–59 wt% and 31–67%, respectively. Thermal gravimetric analysis and scanning electron microscopy results support the determined thermal stability and morphology of the samples. Scratch tests, used to evaluate self-healing protection coating systems, showed that these materials had significant ability to recover from damage on the substrate, depending on the diameter and the concentration of the PU capsules in the paint layer, which could control the efficiency.

Microencapsulation of the triazole derivative for self-healing anticorrosion coatings

Polyurethane microcapsules containing the triazole derivative and the oleate derivative as core materials were successfully prepared via interfacial polymerization in an oil-in-water emulsion of the diol-diisocyanate prepolymer and 1,4-butanediol as a chain extender under agitation or ultrasound sonication. The diameters of the resultant capsules which possess the triazole derivative core agent are 25–276 μm and shell thickness is 1.9–18.0 μm at controlled agitation rates (1000–6000 rpm). Typical core content of the microcapsule and yield of the capsule polymerization were 45–67% and 38–75%, respectively, with varied reaction conditions. The ratio of shell wall thickness to the capsule diameter was relatively constant, with an average value of 0.07. A steel substrate was coated with the synthesized PU capsules for use in self-healing anticorrosion protection. The results as determined by salt spray tests indicated noteworthy rust retardancy in self-repairing corrosion protection systems, slightly depending on kinds of corrosion inhibitors.

Intrinsic DNA curvature of double-crossover tiles

A theoretical model which takes into account the structural distortion of double-crossover DNA tiles has been studied to investigate its effect on lattice formation sizes. It has been found that a single vector appropriately describes the curvature of the tiles, of which a higher magnitude hinders lattice growth. In conjunction with these calculations, normal mode analysis reveals that tiles with relative higher frequencies have an analogous effect. All the theoretical results are shown to be in good agreement with experimental data.

Nanoscale topographical replication of graphene architecture by artificial DNA nanostructures

Despite many studies on how geometry can be used to control the electronic properties of graphene, certain limitations to fabrication of designed graphene nanostructures exist. Here, we demonstrate controlled topographical replication of graphene by artificial deoxyribonucleic acid (DNA) nanostructures. Owing to the high degree of geometrical freedom of DNA nanostructures, we controlled the nanoscale topography of graphene. The topography of graphene replicated from DNA nanostructures showed enhanced thermal stability and revealed an interesting negative temperature coefficient of sheet resistivity when underlying DNA nanostructures were denatured at high temperatures.

Artificial DNA lattice fabrication by noncomplementarity and geometrical incompatibility.

Fabrication of DNA nanostructures primarily follows two fundamental rules. First, DNA oligonucleotides mutually combine by Watson-Crick base-pairing rules between complementary base sequences. Second, the geometrical compatibility of the DNA oligonucleotide must match for lattices to form. Here we present a fabrication scheme of DNA nanostructures with noncomplementary and/or geometrically incompatible DNA oligonucleotides, which contradicts conventional DNA structure creation rules. Quantitative analyses of DNA lattice sizes were carried out to verify the unfavorable binding occurrences, which correspond to errors in algorithmic self-assembly. Further studies of these types of bindings may shed more light on the exact mechanisms at work in the self-assembly of DNA nanostructures.

Hairpin embedded DNA lattices grown on a mica substrate

We constructed hairpin-embedded double crossover (DX) tile-based DNA lattices using a substrate-assisted growth method. The in situ growth of protruding hairpin tiles on a substrate during annealing demonstrates the feasibility of substrate-assisted self-assembly even with geometrical hindrances.

Kinetic Trans-Assembly of DNA Nanostructures

The central dogma of molecular biology is the principal framework for understanding how nucleic acid information is propagated and used by living systems to create complex biomolecules. Here, by integrating the structural and dynamic paradigms of DNA nanotechnology, we present a rationally designed synthetic platform that functions in an analogous manner to create complex DNA nanostructures. Starting from one type of DNA nanostructure, DNA strand displacement circuits were designed to interact and pass along the information encoded in the initial structure to mediate the self-assembly of a different type of structure, the final output structure depending on the type of circuit triggered. Using this concept of a DNA structure trans-assembling a different DNA structure through nonlocal strand displacement circuitry, four different schemes were implemented. Specifically, 1D ladder and 2D double-crossover (DX) lattices were designed to kinetically trigger DNA circuits to activate polymerization of either ring structures or another type of DX lattice under enzyme-free, isothermal conditions. In each scheme, the desired multilayer reaction pathway was activated, among multiple possible pathways, ultimately leading to the downstream self-assembly of the correct output structure.