Showing papers by "Sung Hoon Kang published in 2018"
TL;DR: By infusing a ferrofluid into a microstructured matrix and applying a magnetic field, dynamic, multiscale topographical reconfigurations emerge, enabling functions such as colloidal self-assembly, switchable adhesion and friction, and biofilm removal.
Abstract: Developing adaptive materials with geometries that change in response to external stimuli provides fundamental insights into the links between the physical forces involved and the resultant morphologies and creates a foundation for technologically relevant dynamic systems1,2. In particular, reconfigurable surface topography as a means to control interfacial properties3 has recently been explored using responsive gels4, shape-memory polymers5, liquid crystals6-8 and hybrid composites9-14, including magnetically active slippery surfaces12-14. However, these designs exhibit a limited range of topographical changes and thus a restricted scope of function. Here we introduce a hierarchical magneto-responsive composite surface, made by infiltrating a ferrofluid into a microstructured matrix (termed ferrofluid-containing liquid-infused porous surfaces, or FLIPS). We demonstrate various topographical reconfigurations at multiple length scales and a broad range of associated emergent behaviours. An applied magnetic-field gradient induces the movement of magnetic nanoparticles suspended in the ferrofluid, which leads to microscale flow of the ferrofluid first above and then within the microstructured surface. This redistribution changes the initially smooth surface of the ferrofluid (which is immobilized by the porous matrix through capillary forces) into various multiscale hierarchical topographies shaped by the size, arrangement and orientation of the confining microstructures in the magnetic field. We analyse the spatial and temporal dynamics of these reconfigurations theoretically and experimentally as a function of the balance between capillary and magnetic pressures15-19 and of the geometric anisotropy of the FLIPS system. Several interesting functions at three different length scales are demonstrated: self-assembly of colloidal particles at the micrometre scale; regulated flow of liquid droplets at the millimetre scale; and switchable adhesion and friction, liquid pumping and removal of biofilms at the centimetre scale. We envision that FLIPS could be used as part of integrated control systems for the manipulation and transport of matter, thermal management, microfluidics and fouling-release materials.
210 citations
TL;DR: In this article, the authors investigated the effects of architected cuts on functional materials like piezoelectric materials and found that they can provide desired mechanical features like enhanced compliance, stretchability, and controllable Poisson's ratio and resonance frequency.
Abstract: Introducing architected cuts is an attractive and simple approach to tune mechanical behaviors of planar materials like thin films for desirable or enhanced mechanical performance. However, little has been studied on the effects of architected cuts on functional materials like piezoelectric materials. We investigated how architected cut patterns affect mechanical and piezoelectric properties of polyvinylidene fluoride thin films by numerical, experimental, and analytical studies. Our results show that thin films with architected cuts can provide desired mechanical features like enhanced compliance, stretchability, and controllable Poisson’s ratio and resonance frequency, while maintaining piezoelectric performance under static loadings. Moreover, we could observe maximum ∼30% improvement in piezoelectric conversion efficiency under dynamic loadings and harvest energy from low frequency (<100 Hz) mechanical signals or low velocity (<5 m/s) winds, which are commonly existing in ambient environment. Using architected cuts doesn’t require changing the material or overall dimensions, making it attractive for applications in self-powered devices with design constraints.
12 citations
Patent•
25 Jan 2018TL;DR: In this article, a strategy to create self-healing, slippery liquid-infused porous surfaces is described, which outperforms other conventional surfaces in its capability to repel various simple and complex liquids (water, hydrocarbons, crude oil and blood).
Abstract: The present disclosure describes a strategy to create self-healing, slippery liquid-infused porous surfaces. Roughened (e.g., porous) surfaces can be utilized to lock in place a lubricating fluid, referred to herein as Liquid B to repel a wide range of materials, referred to herein as Object A (Solid A or Liquid A). Slippery liquid-infused porous surfaces outperforms other conventional surfaces in its capability to repel various simple and complex liquids (water, hydrocarbons, crude oil and blood), maintain low-contact-angle hysteresis (<2.5°), quickly restore liquid-repellency after physical damage (within 0.1-1 s), resist ice, microorganisms and insects adhesion, and function at high pressures (up to at least 690 atm). Some exemplary application where slippery liquid-infused porous surfaces will be useful include energy-efficient fluid handling and transportation, optical sensing, medicine, and as self-cleaning, and anti-fouling materials operating in extreme environments.
2 citations
TL;DR: Feng et al. as discussed by the authors used the incorrect reference number for the fractal cut in the final paragraph on page 331 in Fang et al.'s paper, where the reference number was 18 instead of 38.
Abstract: doi: 10.1557/jmr.2018.6, Published by Materials Research Society with Cambridge University Press, 14 February 2018. In the final paragraph on page 331 in Fang et al.,1 sentence reading “Recently, the fractal cut has been developed to introduce even higher stretchability compared to other cut patterns,” lists the incorrect reference number. The reference cited should be 18 instead of 38. The authors apologize for this error.
1 citations