김석 교수

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a

Being inspired by gecko foot hairs, microfibers with flat spatulate tips are proposed as repeatable adhesives. They are fabricated by molding a master template fabricated using deep reactive ion etching and the notching effect. Fabricated polyurethane fiber arrays with 4.5μm fiber and 9μm tip diameter demonstrated macroscale adhesion pressures up to 18N∕cm2 and overall work of adhesion up to 11J∕m2 on a 6mm diameter glass hemisphere for a preload pressure of 12N∕cm2. These results show around fo

We calculate the superconformal index for N=6 Chern–Simons-matter theory with gauge group U(N)k×U(N)−k at arbitrary allowed value of the Chern–Simons level k. The calculation is based on localization of the path integral for the index. Our index counts supersymmetric gauge invariant operators containing inclusions of magnetic monopole operators, where latter operators create magnetic fluxes on 2-sphere. Through analytic and numerical calculations in various sectors, we show that our result perfe

Instanton partition functions of 5d $$ \mathcal{N}=1 $$ gauge theories are Witten indices for the ADHM gauged quantum mechanics with (0, 4) SUSY. We derive the integral contour prescriptions for these indices using the Jeffrey-Kirwan method, for gauge theories with hypermultiplets in various representations. The results can be used to study various 4d/5d/6d QFTs. In this paper, we study 5d SCFTs which are at the UV fixed points of 5d SYM theories. In particular, we focus on the Sp(N ) theories w

We present a shape memory polymer (SMP) surface with repeatable, very strong (>18 atm), and extremely reversible (strong to weak adhesion ratio of >1 × 10(4)) dry adhesion to a glass substrate. This was achieved by exploiting bulk material properties of SMP and surface microstructuring. Its exceptional dry adhesive performance is attributed to the SMP's rigidity change in response to temperature and its capabilities of temporary shape locking and permanent shape recovery, which when combined wit

This work reports thin-film terminated micro-fibrillar adhesives made of adhesive polymers and shape memory polymers as reversible dry adhesives with thermally controllable adhesion. Structurally different adhesives were fabricated by coating a continuous thin layer of an elastomeric adhesive polymer onto either a flat or a fibrillar shape memory polymer surface. Experimental results exhibited that pull-off forces of the adhesives can be up to four times different depending on thermal conditions

We report that hydrophilic polyurethane mushroom shaped microfiber arrays possess wet self-cleaning ability using the lotus effect as biologically inspired synthetic fibrillar adhesives. In comparison with a flat surface made of the same polyurethane, the fiber array exhibited almost 100% wet self-cleaning without any degradation of adhesive strength. We attribute this cleaning ability to the mushroom shaped tip ending geometry of the fiber array, which causes the fiber array to be apparently hy

Previous studies have demonstrated that gecko foot-hair inspired elastomer microfibers with spatulate tips have significant adhesion enhancement compared to the flat elastomer surface. In this study, we report the friction enhancement of these highly adhesive fibers and analyze the relation between adhesion and friction of elastomer microfiber arrays with spatulate tips. Fabricated polyurethane fiber arrays with spatulate tips demonstrate macroscale static friction pressures up to 41N∕cm2 for a

We study a family of 2d $$ \mathcal{N}=\left(0,\ 4\right) $$ gauge theories which describes at low energy the dynamics of E-strings, the M2-branes suspended between a pair of M5 and M9 branes. The gauge theory is engineered using a duality with type IIA theory, leading to the D2-branes suspended between an NS5-brane and 8 D8-branes on an O8-plane. We compute the elliptic genus of this family of theories, and find agreement with the known results for single and two E-strings. The partition functi