Share this“Dry” cleaning does not mean cleaning your suit with perchloroethylene or CO2. “Dry” cleaning means that the cleaning work is not done with the parts immersed in liquid.
Table 1 shows some of the more significant technologies currently used or being developed to remove smaller particles (residues), listed in descending order of my estimate of particle size limitation. Space does not permit listing of all technologies.
Pulsed Laser
A laser pulse strikes a substrate. Some of the absorbed pulse energy heats what it strikes. That produces a rapid thermal expansion of the irradiated substrate. Elastic waves accelerate along the substrate. Naturally, the particles attached to the surface are accelerated. The particles are detached when the net force resulting from the acceleration exceeds the adhesion force binding the particle to the substrate. This action is repeated via the pulsed laser contact1,2,3,4
Argon Aerosol
You are probably familiar with CO2 snow cleaning. Solid CO2 flakes are “shot” at surfaces and knock off particles by momentum transfer. Argon aerosol is similar. Only, solid Argon (Ar) “flakes” are used. Obviously, this approach requires cryogenic conditions.
Laser Induced Plasma
Here, a laser is focused to a point on the substrate. This causes rapid local temperature elevation. Consequently, a hot ionized gas (a plasma) is produced. The effect of the expanding plasma, and resultant wavefront, creates a localized flow that detaches and transports the particles away from the point on the surface.5
Vaporization via Laser Heating
This is not similar to pulsed laser cleaning or laser-induced plasma. Particles are not removed via surface movement or local fluid movement. Particles are removed by vaporization of the material of which the particle is composed. Obviously, biological debris are more easily vaporized than are metal oxides.
Energetic Focused Cluster Beam
High-energy clusters are beams of micro-droplets (less than 1000 nm in diameter). They are formed by pneumatically feeding a conductive fluid to the tip of a capillary emitter. A high voltage electric field is applied to the capillary tip, charging the micro droplets (clusters). These relatively large clusters expend their energy over an extended area of the surface lifting off micron and submicron particles, organic film, and metallic contaminants. A commonly used fluid is a high purity glycerol solvent doped with an electrolytic additive such as ammonium acetate.
“Laser Tweezer”
The technology is based on the principle that dielectric particles (those that do not conduct electric current) experience forces that draw them to where the light is brightest. Optical tweezers are constructed using optical gradient forces from a single beam of light. Individual particles can be manipulated, and thus removed.
Microscopic Gripping Mechanism
This approach is purely mechanical. A nano-sized gripping mechanism and a complementary “handle” are created. The gripper can grasp any nano-sized mechanism, including a particle.
Summary
The latter two technologies are surface manipulation techniques. In the final part of this series we’ll see how they can transition to become particle removal techniques.
1 Cetinkaya, Cunli Wu, and Chen Li. “Laser-Based Transient Surface Acceleration for Thermoelastic Layers,” Journal of Sound and Vibration, Vol. 231, No. 1, pp. 195-217, 2000.
2 Cetinkaya , T. Hooper. “Efficiency Studies of Particle Removal with Pulsed-Laser Induced Plasma,” In Press (M1417) in Journal of Adhesion Science and Technology, 2002.
3 Cetinkaya, and R. Vanderwood. “Nanoparticle Removal from Trenches and Pinholes with Pulsed-Laser Induced Plasma and Shock Waves,” Journal of Adhesion Science and Technology, Volume 17, No. 1, pp. 129-147, 2003.
4 Cetinkaya and J. Lin. “Potential Laser Induced Damage in Nanoparticle Removal With Pulsed Lasers,” Journal of Adhesion Science and Technology, Volume 17, No. 1, pp. 1148, 2003.
5 Cetinkaya, R. Vanderwood, and M. Rowell, “Nanoparticle Removal From Substrates With Pulsed-Laser Generated Plasma and Shock Waves,” Journal of Adhesion Science and Technology, Vol. 16, No. 9, pp. 1201-1214, 2002.