Engineered deposition of coatings from nano- and micro-particles: A brief review of convective assembly at high volume fraction

Prevo, Brian G.; Kuncicky, Daniel M.; Velev, Orlin D.

doi:10.1016/j.colsurfa.2007.08.030

Cited by 150 publications

(131 citation statements)

References 69 publications

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“…86 The final mask fabricated in this way always includes a number of crystal defects; however, colloidal masks can be assembled using other similar techniques, such as dip-coating, that reduce defect concentrations, but these alternate strategies are rarely as fast or simple as the process described here. 94,95 Once the mask is ready, a material, usually a metal, is deposited onto the substrate through the mask. Thermal evaporation is the most common method for this deposition step.…”

Section: Nanosphere Lithographymentioning

confidence: 99%

Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy

Kent

Vikesland

2012

Environ. Sci. Technol.

127

129

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Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, and the height increased by 6-12 nm. Subsequently, particle height and inplane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution.iii Acknowledgements I thank my advisor, Dr. Peter Vikesland, for his insight, guidance, and innovative ideas throughout my time at Virginia Tech, and for giving me the opportunity to work on this research project. He was ready and available to help whenever I needed his input. I also thank the other members of my committee,

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Section: Nanosphere Lithographymentioning

confidence: 99%

Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy

Kent

Vikesland

2012

Environ. Sci. Technol.

127

129

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“…Pickering emulsions). Particle stabilized foams and emulsions are also used for the fabrication of colloid-based solid foams, gels, and bijels, and crystalline monolayers find applications as superhydrophobic or antireflection coatings, and templates for micro and nanostructured materials [2]. Central to these applications is the surface organization of the colloids, which is a balance between interparticle attractive and repulsive forces, external forces applied parallel to the interface, and the viscous resistance or surface drag due to the hydrodynamic motion of the colloids along the fluid surface.…”

mentioning

confidence: 99%

“…For example, for a spherical colloid of radius R at a vapor/liquid interface of interfacial tension γ (Fig. 1a), the minimum free energy relative to the vapor phase is [1] ∆F = −πγR 2 (1 + cos θ) 2 where the contact angle θ is measured through the liquid. For particles of large enough size, ∆F can overwhelm the typical thermal energy k B T and the particle becomes trapped, as thermal fluctuations cannot dislodge the particle from the interface.…”

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confidence: 99%

Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

Koplik

Maldarelli

2017

Phys. Rev. Fluids

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Measurements of the surface diffusivity of colloidal spheres translating along a vapor/liquid interface show an unexpected decrease in diffusivity, or increase in surface drag (from the Stokes-Einstein relation) when the particles situate further into the vapor phase. However, direct measurements of the surface drag from the colloid velocity due to an external force find the expected decrease with deeper immersion into the vapor. The paradoxical drag increase observed in diffusion experiments has been attributed to the attachment of the fluid interface to heterogeneities on the colloid surface, which causes the interface, in response to thermal fluctuations, to either jump or remain pinned, creating added drag. We have performed molecular dynamics simulations of the diffusivity and force experiments for a nanoparticle with a rough surface at a vapor/liquid interface to examine the effect of contact line fluctuations. The drag calculated from both experiments agree and decrease as the particle positions further into the vapor. The surface drag is smaller than the bulk liquid drag due to the partial submersion into the liquid, and the finite thickness of the interfacial zone relative to the nanoparticle size. Contact line fluctuations do not give rise to an anomalous increase in drag.When a colloid particle breaches the interfacial zone between two adjoining immiscible fluid phases the interfacial energy of the particle changes, because the area of the fluid interface decreases and the contact areas of the particle with the bounding fluid phases are altered. For a particle which only partially wets both adjoining fluids, the change in interfacial energy is at a minimum when the colloid partially straddles both adjoining phases. For example, for a spherical colloid of radius R at a vapor/liquid interface of interfacial tension γ (Fig. 1a), the minimum free energy relative to the vapor phase is [1] ∆F = −πγR 2 (1 + cos θ) 2 where the contact angle θ is measured through the liquid. For particles of large enough size, ∆F can overwhelm the typical thermal energy k B T and the particle becomes trapped, as thermal fluctuations cannot dislodge the particle from the interface. Monolayers of strongly adsorbed colloids at the fluid interfaces of foams and emulsions provide steric barriers to coalescence of the dispersed phase, and find applications as foam and emulsion stabilizers (e.g. Pickering emulsions). Particle stabilized foams and emulsions are also used for the fabrication of colloid-based solid foams, gels, and bijels, and crystalline monolayers find applications as superhydrophobic or antireflection coatings, and templates for micro and nanostructured materials [2]. Central to these applications is the surface organization of the colloids, which is a balance between interparticle attractive and repulsive forces, external forces applied parallel to the interface, and the viscous resistance or surface drag due to the hydrodynamic motion of the colloids along the fluid surface. As we explain, the surface drag is not w...

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“…It can also be used for energy storage [2] or in membrane technology [3]. As a principle, the deposition of micro-and nanoparticles on a substrate is relevant for manufacturing different kinds of coatings [4], but also to prepare micro-and nanowires [5] and to deposit complicated organized biological structures, such as DNA [6,7]. There are several ways to achieve particle deposition, such as dip coating, sedimentation and electrostatic assembly.…”

Section: Introductionmentioning

confidence: 99%

Self-assembly by multi-drop evaporation of carbon-nanotube droplets on a polycarbonate substrate

Machrafi

Minetti

Dauby

et al. 2017

Physica E: Low-dimensional Systems and Nanostructures

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Carbon nanotubes are allowed to self-assemble by depositing a droplet of a water dispersion thereof and letting it evaporate on a polycarbonate substrate. The effect of the number of droplets, evaporated on the same deposition spot, on the self-assembly density is assessed to be more than proportional for the first five depositions. The obtained nanoporous nanostructures are further tested for their electrical resistance and wettability. Two concentrations are used. It is found that a higher concentration and more importantly a higher number of droplet depositions causes the electrical resistance to decrease up to four orders of magnitude and the static contact angle to decrease more than three times. The contact angle hysteresis also increases due to an increasing advancing contact angle and a decreasing receding one. This is explained by the degree of coverage of the substrate by the carbon nanotubes as is also shown by scanning electron microscope images. A better coverage is suggested to cause more pinning for an advancing droplet and a higher capillary force for a receding droplet.Keywords: Multi-drop evaporation, Carbon nanotube droplets, Self-assembled nanostructure, Electrical resistance, Contact angle, Wettability, Contact angle hysteresis IntroductionSelf-assembly has many applications. It is applied in the medical sector [1]. It can also be used for energy storage [2] or in membrane technology [3]. As a principle, the deposition of micro-and nanoparticles on a substrate is relevant for manufacturing different kinds of coatings [4], but also to prepare micro-and nanowires [5] and to deposit complicated organized biological structures, such as DNA [6,7]. There are several ways to achieve particle deposition, such as dip coating, sedimentation and electrostatic assembly. Convective deposition and more particularly drop evaporation are convenient ways to deposit micro-and nanoparticles [8]. The amount of fluid used is minimized, possibly inducing economic advantages, and the outcome can easily be controlled, by choosing initial parameters [9].The interest lies in creating patterned structures out of evaporating drops, which can be of use for energetic and medical applications. The deposited patterns that are left by the evaporated colloidal drops can present a multiplicity of structures, such as the ring structure [10], a central bump [11], a uniform deposit [12], or more complex structures such as multiple rings [13] and hexagonal arrays [5]. This variety of patterns reflects the multiscale attractive forces and transport phenomena taking place during the droplet evaporation. As for the fluid dynamics, several mechanisms play an important role, depending on whether a droplet is deposited directly on the substrate or dropped from a certain height. If droplet impact is associated, the fluid dynamics are determined by the Reynolds and Weber number of the droplet impact [9], as well as the impact angle, interfacial deformation or break-up. Marangoni forces, wetting characteristics and evaporation at ...

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Engineered deposition of coatings from nano- and micro-particles: A brief review of convective assembly at high volume fraction

Cited by 150 publications

References 69 publications

Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy

Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy

Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

Self-assembly by multi-drop evaporation of carbon-nanotube droplets on a polycarbonate substrate

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