Microbubble Formation from Plasma Polymers

Abstract

We document the formation of liquid-like particles in a toluene glow discharge that subsequently solidify via a process that releases hydrogen to form a solid microbubble with micrometer-size diameter, nanometer-size shell thickness, and high volume fraction, in excess of 90%. Liquid-like particles are produced in a toluene plasma under conditions that promote low degree of cross-linking (low power, high pressure). When these are transferred for observation in TEM, they are seen to transform under irradiation by the electron beam into solid bubbles with diameter of about 3 μm. This transformation also takes place under laser irradiation of sufficient power and under heating. We present evidence that the formation of these microbubbles is due to solidification of the liquid-like precursor that is accompanied by release of hydrogen. This mechanism is supported by a geometric model that provides a quantitative description of the particle size before and after solidification. These unique stimuli-responsive particles exhibit the potential of using temperature, electron beam, or laser as a source to change their size and structure which may find application in thermal insulators, lightweight materials, and light scattering agents.

Passivation of Aluminum Nanoparticles by Plasma-Enhanced Chemical Vapor Deposition for Energetic Nanomaterials

“…The first weight loss for all samples is observed immediately upon heating and is completed at <350 °C (∼20 min). In this temperature range, the plasma coatings are thermally stable. , The initial weight loss is due to the evaporation of water and other volatile vapors. Notably, particles that were kept in glovebox were not exposed to air and humidity and show the smallest weight loss.…”

“…The power is higher when toluene is used to avoid the formation of particles, which tend to form at lower power. 31 During deposition, a small magnetic plate is placed underneath the reactor and is set at 100 rpm to agitate the nanoparticles. A liquid nitrogen trap with a cool wall is used to condense any organic vapors escaping the reactor before entering the pump.…”

“…The plasma is operated at 30 W when IPA or PFD are the precursors, and at 40 W when toluene is used. The power is higher when toluene is used to avoid the formation of particles, which tend to form at lower power . During deposition, a small magnetic plate is placed underneath the reactor and is set at 100 rpm to agitate the nanoparticles.…”

“…17,29 Plasma deposited solids are chemically inert and thermally stable up to 250 °C. 30,31 They contain elements of their precursor molecules, typically carbon, oxygen, and fluorine. 32−35 These elements oxidize readily under combustion conditions, thereby exposing the aluminum core, and they may also contribute to the overall enthalpy of reaction.…”

“…Plasma-deposited solids have unique properties that are especially advantageous as passivating barriers for nanoenergetic materials. Most notably, plasma polymers produce hydrophobic surfaces. − Hydrophobicity adds a chemical interaction to the physical barrier, which alone cannot provide satisfactory protection against moisture. , Plasma deposited solids are chemically inert and thermally stable up to 250 °C. , They contain elements of their precursor molecules, typically carbon, oxygen, and fluorine. − These elements oxidize readily under combustion conditions, thereby exposing the aluminum core, and they may also contribute to the overall enthalpy of reaction . As a dry gas-phase process, plasma offers a further advantage of a well-controlled environment.…”