Nanoscale Casting Using Supercritical Fluid

Fukushima, Yoshiaki; Wakayama, Hiroaki

doi:10.1021/jp984649q

Cited by 67 publications

(45 citation statements)

References 8 publications

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“…Increasing pressure facilitate the particle removal in the CO 2 + H 2 O solution because the net adhesion force decrease and equilibrium separation distance increase with increased pressure in this cleaning system. Addition of surfactant (PFPE COO − NH 4 + or DiF 8 -PO 4 − Na + ) into the CO 2 + H 2 O cleaning system can result in the net adhesion force decrease significantly, yet the equilibrium separation distance decrease also with an increase in surfactant concentration. This model is helpful to design and analysis of high pressure CO 2 -based precision cleaning systems.…”

Section: Discussionmentioning

confidence: 99%

“…From Fig. 4, we could see that addition of surfactant could significantly reduce the surface tension, the NAF of H 2 O-CO 2 system with surfactant (PFPE COO − NH 4 + or DiF 8 -PO 4 − Na + ) was much less, and the value of NAF decreased with the increase of surfactant. The surfactants can also provide steric stabilization for particles suspended in CO 2 , as the hydrophobic tails extend outwards into CO 2 .…”

Section: Co 2 + H 2 O System Without and With Surfactantmentioning

confidence: 94%

“…The first step was to solve Eqs. (1)(2)(3)(4)(5) to work out the parameters, such as Hamaker constant A 132 , dielectric constant of fluid mixture ε, and refractive index of the fluid mixture n. This optimizing process utilized the trial and error method, so as to reach an appropriate ESD, where the capillary pressure effect force offsets the total adsorption force completely. Eqs.…”

Section: Capillary Pressure Effect Forcementioning

confidence: 99%

“…Meanwhile, we could see that the ESD also decreased with increasing surfactant concentration, suggesting that adding surfactant into cleaning system facilitated the particles removal, but it was still a challenge to lift these particles out of the trench with large aspect ratio. In this work, we calculated the NAF and ESD in the case of H 2 O-CO 2 system with anionic surfactant (PFPE COO − NH 4 + or DiF 8 -PO 4 − Na + ). Studies on more kinds of surfactants are now in progress.…”

Section: Co 2 + H 2 O System Without and With Surfactantmentioning

confidence: 99%

“…The surface tension of liquid carbon dioxide is 1.5 mN/m at 25 • C and reaches zero at the critical point [3], where liquid droplets are no longer formed. These beneficial transport and interfacial properties accelerate the rates of mass transfer and promote the penetration of small features [4], and provide a sig-nificant advantage over liquid and aqueous-based cleaning agents particularly with respect to cleaning high aspect ratio features [5,6].…”

Section: Introductionmentioning

confidence: 99%

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Microscopic model of nano-scale particles removal in high pressure CO2-based solvents

Chai

Zhang

Huang

et al. 2009

The Journal of Supercritical Fluids

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a b s t r a c tA physical model is presented to describe the kinds of static forces responsible for adhesion of nano-scale copper metal particles to silicon surface with a fluid layer. To demonstrate the extent of particle cleaning, equilibrium separation distance (ESD) and net adhesion force (NAF) of a regulated metal particle with different radii (10-300 nm) on the silicon surface in CO 2 -based cleaning systems under different pressures were simulated. Generally, increasing the pressure of the cleaning system decreased the net adhesion force between spherical copper particle and silicon surface entrapped with medium. For CO 2 + isopropanol cleaning system, the equilibrium separation distance exhibited a maximum at temperature 313.15 K in the regions of pressure space (1.84-8.02 MPa). When the dimension of copper particle was given, for example, 50 nm radius particles, the net adhesion force decreased and equilibrium separation distance increased with increased pressure in the CO 2 + H 2 O cleaning system at temperature 348.15 K under 2.50-12.67 MPa pressure range. However, the net adhesion force and equilibrium separation distance both decreased with an increase in surfactant concentration at given pressure (27.6 or 27.5 MPa) and temperature (318 or 298 K) for CO 2 + H 2 O with surfactant PFPE COO − NH 4 + or DiF 8 -PO 4 − Na + .

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Section: Discussionmentioning

confidence: 99%

Section: Co 2 + H 2 O System Without and With Surfactantmentioning

confidence: 94%

Section: Capillary Pressure Effect Forcementioning

confidence: 99%

Section: Co 2 + H 2 O System Without and With Surfactantmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microscopic model of nano-scale particles removal in high pressure CO2-based solvents

Chai

Zhang

Huang

et al. 2009

The Journal of Supercritical Fluids

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Porous Materials and Supercritical Fluids

Cooper¹

2003

Advanced Materials

381

247

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Porous materials are used in a wide variety of applications, including catalysis, chemical separation, and tissue engineering. The synthesis and processing of these materials is frequently solvent intensive. In addition to reducing organic solvent emissions, supercritical fluids offer a number of specific physical, chemical, and toxicological advantages as alternative solvents for the production of functional porous materials. The figure shows an electron image of a porous polyacrylate produced by the templating of a concentrated CO2‐in‐water emulsion—a process that would otherwise be highly solvent intensive.

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Size‐Controlled Synthesis and Catalytic Performance of Pt Nanoparticles in Micro‐ and Mesoporous Silica Prepared Using Supercritical Solvents

Wakayama¹,

Setoyama

Fukushima

2003

Advanced Materials

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TEM photographs were obtained on a JEOL 2010 microscope operated at 200 kV. XRD patterns were obtained on a Bruker D4 X-ray diffractometer using Cu Ka radiation. Nitrogen adsorption±desorption isotherms were acquired using a Micromeritics Tristar 3000 system at 77 K. Metal or semiconductor nanoparticles are of great interest with respect to their applications as catalysts, [1] as well as in sensors and optical [2] and electronic [2] devices. Their properties depend on the size of the nanoparticles. Thus, the accurate control of the particle size is very important for these applications. Nanoparticles have been synthesized by the oxidation or reduction of precursors.[3] Micelles [4] and stabilizing polymers [5] have also been used to restrict particle aggregation. Porous materials have been used as hosts for the synthesis of nanoparticles.[6±10] The synthesis of nanoparticles using porous materials with uniform pore sizes and high surface area as hosts has attracted interest because the sizes of the nanoparticles can be easily controlled in well-defined matrices. Mesoporous (pore size 2±50 nm) silica, FSM-16, [6] MCM-41, [7] SBA-15 [8] have been used for the synthesis of nanoparticles of Pt, Pd, Rh, Au, and Ag. A microporous (pore size < 2 nm) host, zeolite, can also be used for the synthesis of metal carbonyl clusters, [9] which takes a few days for the synthesis in a liquid-phase solvent, [9] and the reduction process generates larger particles on the external surface. These are due to the limitation of mass transfer in the liquid solvent and difficulty in controlling the growth rate of the nanoparticles from salt-type precursors, even though they are smaller than other types of precursors such as organometallic molecules. A filtration process using the vapor phase, such as chemical vapor deposition (CVD), is a very effective method for preparing particles or thin films on a nanometer scale. However, the precursors are limited in terms of high volatility and thermal stability. Conventional methods of preparing nanoparticles in porous matrices often yield nanoparticles of various sizes in the internal pores and on the external surface of the porous matrices. [8,10] Accurate size control of nanoparticles using porous materials as hosts with a wide range of uniform pore sizes, including micropores, and the investigation of the relationship between particle size and their properties still remain challenging. Supercritical fluids [11] (SCFs) have excellent properties of non-cohesivity, high diffusivity, and controllable solubility. Thus, SCFs are expected to overcome the previously men-

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Nanoscale Casting Using Supercritical Fluid

Cited by 67 publications

References 8 publications

Microscopic model of nano-scale particles removal in high pressure CO2-based solvents

Microscopic model of nano-scale particles removal in high pressure CO2-based solvents

Porous Materials and Supercritical Fluids

Size‐Controlled Synthesis and Catalytic Performance of Pt Nanoparticles in Micro‐ and Mesoporous Silica Prepared Using Supercritical Solvents

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