KEY PUBLICATIONS
A MEAN DENSITY MODEL OF IONIC SURFACTANTS FOR DISPERSION OF CARBON NANOTUBES IN AQUEOUS SOLUTIONS
Young Soo Joung
Applied Surface Science, Volume 439, 2018, Pages 1133-1142
In this work, we present a mean-density model of surfactants to illuminate the mechanism of carbon nanotube (CNT) dispersion in aqueous solutions of ionic surfactants. Ionic surfactants have been widely used to make well dispersed CNT suspensions in aqueous solutions. However, the mechanism of the dispersion is not clear. To understand the mechanism, molecular dynamic (MD) simulations were recently employed but it needs high computing performance and time cost to obtain final results. With the mean-density model, we can effectively estimate the potential of mean force between CNTs stabilized with surfactants. Notably, we found that the osmotic pressure between CNTs plays important role to determine the stability of dispersion. The mean-density model can effectively help to determine appropriate surfactants and their concentrations for stable dispersion of CNTs.
Conductive hydrogel films produced by freestanding electrophoretic deposition and polymerization at the interface of immiscible liquids
Young Soo Joung, Eric Bailey, Robert B. Ramirez, and Cullen R. Buie,
Composites Science and Technology, Volume 153, 2017, Pages 128-135
Conductive hydrogels are promising materials for energy and biomedical applications due to their bio-compatibility, high porosity, and outstanding swelling-capability. In this work we present a unique method to fabricate nanomaterial-hydrogel composite films using Electrophoretic Deposition (EPD) at the interface of two immiscible liquids. During interfacial EPD, nanoparticles such as carbon nanotubes (CNTs) electro-migrate to an oil/water interface, where polymer cross-linking is induced to form composite hydrogel films. The key aspect of this method is that polymerization occurs away from a solid substrate while surrounded by both water and oil, allowing for the integration of CNTs into the hydrogel. Properties of the composite hydrogel films are controlled by EPD parameters and polymerization conditions, facilitating the potential for mass production without complex machinery. This fabrication method is cost-effective and scalable for composite hydrogels with tunable electrical, mechanical, and biological properties. Potential applications include fabrication of doped hydrogels for drug delivery and biological sensors.
BIOAEROSOL GENERATION BY RAINDROPS ON SOIL
Young Soo Joung, Zhifei Ge, and Cullen R. Buie
Nature Communications, Article number: 14668 (2017)
doi:10.1038/ncomms14668
Aerosolized microorganisms may play an important role in climate change, disease transmission, water and soil contaminants, and geographic migration of microbes. While it is known that bioaerosols are generated when bubbles break on the surface of water containing microbes, it is largely unclear how viable soil-based microbes are transferred to the atmosphere. Here we report a previously unknown mechanism by which rain disperses soil bacteria into the air. Bubbles, tens of micrometres in size, formed inside the raindrops disperse micro-droplets containing soil bacteria during raindrop impingement. A single raindrop can transfer 0.01% of bacteria on the soil surface and the bacteria can survive more than one hour after the aerosol generation process. This work further reveals that bacteria transfer by rain is highly dependent on the regional soil profile and climate conditions.
ANTIMICROBIAL BEHAVIOR OF NOVEL SURFACES GENERATED BY ELECTROPHORETIC DEPOSITION AND BREAKDOWN ANODIZATION
Jessamine A. Quijano, Young Soo Joung, Nichola Kinsinger, Xinglin Lu, Cullen R. Buie, Sharon L. Walker,
Colloids and Surfaces B: Biointerfaces, Vol.134, pp. 204–212, 2015.
Biofilms have devastating impacts on many industries such as increased fuel consumption and damage to surfaces in maritime industries. Ideal biofouling management is inhibition of initial bacterial attachment. The attachment of a model marine bacterium (Halomonas pacfica g) was investigated to evaluate the potential of these new novel surfaces to resist initial bacterial adhesion. Novel engineered surfaces were generated via breakdown anodization or electrophoretic deposition, to modify three parameters: hydrophobicity, surface chemistry, and roughness. Mass transfer rates were determined using a parallel plate flow chamber under relevant solution chemistries. The greatest deposition was observed on the superhydrophilic surface, which had micro- and nano-scale hierarchical structures composed of titanium oxide deposited on a titanium plate. Conversely, one of the hydrophobic surfaces with micro-porous films overlaid with polydimethylsiloxane appeared to be most resistant to cell attachment.
ANTIWETTING FABRIC PRODUCED BY A COMBINATION OF LAYER-BY-LAYER ASSEMBLY AND ELECTROPHORETIC DEPOSITION OF HYDROPHOBIC NANOPARTICLES
Young Soo Joung and Cullen R. Buie,
ACS Applied Materials & Interfaces, 2015, 7 (36), pp 20100–20110
This work describes a nanoparticle coating method to produce durable antiwetting polyester fabric. Electrophoretic deposition is used for fast modification of polyester fabric with silica nanoparticles embedded in polymeric networks for high durability coatings. Typically, electrophoretic deposition (EPD) is utilized on electrically conductive substrates due to its dependence on an applied electrical field. EPD on nonconductive materials has been attempted but are limited by weak adhesion, cracks, and other irregularities. To resolve these issues, we coat polyester fabric with thin polymer layers using electrostatic self-assembly (layer-by-layer self-assembly). Next, silica nanoparticles are uniformly dispersed on the polymer layers. Finally, polymerically stabilized silica nanoparticles are deposited by EPD on the fabric, followed by heat treatment. The modified fabric shows high static contact angle and low contact angle hysteresis, while keeping its original color, flexibility, and air permeability. During a skin fiction resistance test, the hydrophobicity of the coating layer was maintained over 500 h. Furthermore, we also show that this approach facilitates patterned regions of wettability by modifying the electric field in EPD.
AEROSOL GENERATION BY RAINDROP IMPACT ON SOIL
Young Soo Joung and Cullen R. Buie,
Nature Communications 6, 6083, 2015
Aerosols are investigated because of their significant impact on the environment and human health. To date, windblown dust and sea salt from sea spray through bursting bubbles have been considered the chief mechanisms of environmental aerosol dispersion. Here we investigate aerosol generation from droplets hitting wettable porous surfaces including various classifications of soil. We demonstrate that droplets can release aerosols when they influence porous surfaces, and these aerosols can deliver elements of the porous medium to the environment. Experiments on various porous media including soil and engineering materials reveal that knowledge of the surface properties and impact conditions can be used to predict when frenzied aerosol generation will occur. This study highlights new phenomena associated with droplets on porous media that could have implications for the investigation of aerosol generation in the environment.
DESIGN OF CAPILLARY FLOWS WITH FUNCTIONALLY GRADED POROUS TITANIUM OXIDE FILMS CONTROLLED BY ANODIZATION INSTABILITY
Young Soo Joung, Bruno Michel Figliuzzi, Cullen R. Buie,
Journal of Colloid and Interface Science, Vol. 423, pp. 143–150, 2014
We have developed an electrochemical fabrication method utilizing breakdown anodization (BDA) to yield capillary flows that can be expressed as functions of capillary height. This method uses anodization instability with high electric potentials and mildly acidic electrolytes that are maintained at low temperature. BDA produces highly porous micro- and nano-structured surfaces composed of amorphous titanium oxide on titanium substrates, resulting in high capillary pressure and capillary diffusivity. With this fabrication technique the capillary flow properties can be controlled by varying the applied electric field and electrolyte temperature. Furthermore, they can be expressed as functions of capillary height when customized electric fields are used in BDA. To predict capillary flows on BDA surfaces, we developed a conceptual model of highly wettable porous films, which are modeled as multiple layers of capillary tubes oriented in the flow direction. From the model, we derived a general capillary flow equation of motion in terms of capillary pressure and capillary diffusivity, both of which can be expressed as functions of capillary height. The theoretical model was verified by comparisons with experimental capillary flows, showing good agreement. From investigation of the surface morphology we found that the surface structures were also functionally graded with respect to the capillary height (i.e. applied electric field). The suggested fabrication method and the theoretical model offer novel design methodologies for microscale liquid transport devices requiring control over propagation speed.
SCALING LAWS FOR DROP IMPINGEMENT ON POROUS FILMS AND PAPERS
Young Soo Joung and Cullen R. Buie,
Physical Review E, 89, 013015 (2014)
This study investigates drop impingement on highly wetting porous films and papers. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a nondimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops.
HIERARCHICAL SURFACES FOR CRITICAL HEAT FLUX ENHANCEMENT
Kuang-Han Chu, Young Soo Joung, Ryan Enright, Cullen R. Buie and Evelyn N. Wang,
Applied Physics Letters, 102, 151602 (2013)
We report large enhancements in critical heat flux (CHF) on hierarchically structured surfaces, fabricated using electrophoretic deposition of silica nanoparticles on microstructured silicon and electroplated copper microstructures covered with copper oxide (CuO) nanostructures. A critical heat flux of ≈250 W/cm2 was achieved on a CuO hierarchical surface with a roughness factor of 13.3, and good agreement between the model proposed in our recent study and the current data was found. These results highlight the important role of roughness using structures at multiple length scales for CHF enhancement. This high heat removal capability promises an opportunity for high flux thermal management.
A HYBRID METHOD EMPLOYING BREAKDOWN ANODIZATION AND ELECTROPHORETIC DEPOSITION FOR SUPERHYDROPHILIC SURFACES
Young Soo Joung, Cullen R. Buie,
Journal of Physical Chemistry B, 2013, 117 (6), pp. 1714-1723
A fabrication method is developed for superhydrophilic surfaces with high capillary pressure and fast spreading speed. The fabrication method consists of electrophoretic deposition (EPD) and breakdown anodization (BDA). Nanopores and micropores were produced on titanium plates by EPD and BDA, respectively. In EPD, TiO2 nanoparticles were used to enhance the surface energy and create nanoporous structures, while BDA was employed to produce microporous structures. Capillary rise measurements (CRM) were utilized to characterize superhydrophilic surfaces in terms of capillary pressure and spreading speed. From CRM, it was revealed that microporous structures play a dominant role in determining transport properties, and nanoporous structures affect local wettability without significantly reducing spreading speed. By combining BDA and EPD into a hybrid method, dual-scale (nano and micro) porous structures were produced on titanium plates. The methods presented offer the potential to vary the transport characteristics of superhydrophilic surfaces by altering the nanoscale and microscale features independently. As an example, surfaces with unconventional capillary flows were produced by the hybrid method. This method provides additional opportunities to investigate wetting phenomena while offering a potentially low cost process for industrial applications.
HYBRID ELECTROPHORETIC DEPOSITION WITH ANODIZATION PROCESS FOR SUPERHYDROPHILIC SURFACES TO ENHANCE CRITICAL HEAT FLUX
Young Soo Joung, Cullen R. Buie,
Key Engineering Materials, Vol. 507 (2012) pp. 9-13
Superhydrophilic surfaces with hydrophobic layers were successfully produced in order to enhance critical heat flux (CHF) and reduce boiling inception temperatures (BIT). The novel surfaces were fabricated by a hybrid electrophoretic deposition (EPD) method coupled with a break down anodization (BDA) process. With the BDA process, microporous superhydrophilic surfaces were created on titanium substrates. Subsequently, nanoporous hydrophobic layers were deposited with EPD on the superhydrophilic surfaces. The hydrophobic layers provide numerous nucleation sites, lowering BIT while the superhydrophilic layers prevent film boiling, resulting in increased CHF. The resulting surfaces exhibit higher CHF with lower BIT than untreated titanium surfaces .
ELECTROPHORETIC DEPOSITION OF UNSTABLE COLLOIDAL SUSPENSIONS FOR SUPERHYDROPHOBIC SURFACES
Young Soo Joung, Cullen R. Buie,
Langmuir, 2011. 27(7): pp. 4156-4163
A novel method to fabricate superhydrophobic surfaces using electrophoretic deposition (EPD) is presented. EPD presents a readily scalable, customizable, and potentially low cost surface manufacturing process. Low surface energy materials with high surface roughness are achieved using EPD of unstable hydrophobic SiO2 particle suspensions. The effect of suspension stability on surface roughness is quantitatively explored with optical absorbance measurements (to determine suspension stability) and atomic force microscopy (to measure surface roughness). Varying suspension pH modulates suspension stability. Contrary to most applications of EPD, we show that superhydrophobic surfaces favor mildly unstable suspensions since they result in high surface roughness. Particle agglomerates formed in unstable suspensions lead to highly irregular films after EPD. After only 1 min of EPD, we obtain surfaces with low contact angle hysteresis and static contact angles exceeding 160°. We also present a technique to enhance the mechanical durability of the superhydrophobic surfaces by adding a polymeric binder to the suspension prior to EPD.
OPTIMAL LAYOUT DESIGN OF THREE-DIMENSIONAL GEOMETRICAL NONLINEAR STRUCTURES USING THE ELEMENT CONNECTIVITY PARAMETERIZATION METHOD
Gil Ho Yoon, Young Soo Joung, Yoon Young Kim,
International Journal for Numerical Methods in Engineering, Vol.69 (10), pp.1278–1304, 2007
The topology design optimization of ‘three-dimensional geometrically-non-linear’ continuum structures is still difficult not only because of the size of the problem but also because of the unstable continuum finite elements that arise during the optimization. To overcome these difficulties, the element connectivity parameterization (ECP) method with two implementation formulations is proposed. In ECP, structural layouts are represented by inter-element connectivity, which is controlled by the stiffness of element-connecting zero-length links. Depending on the link location, ECP may be classified as an external ECP (E-ECP) or an internal ECP (I-ECP). In this paper, I-ECP is newly developed to substantially enhance computational efficiency. The main idea in I-ECP is to reduce system matrix size by eliminating some internal degrees of freedom associated with the links at voxel level. As for ECP implementation with commercial software, E-ECP, developed earlier for two-dimensional problems, is easier to use even for three-dimensional problems because it requires only numerical analysis results for design sensitivity calculation. The characteristics of the I-ECP and E-ECP methods are compared, and these methods are validated with numerical examples.