Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants

Contamination of body surfaces can negatively affect many physiological functions. Insects have evolved different adaptations for removing contamination, including surfaces that allow passive self-cleaning and structures for active cleaning. Here, we study the function of the antenna cleaner in Camponotus rufifemur ants, a clamp-like structure consisting of a notch on the basitarsus facing a spur on the tibia, both bearing cuticular 'combs' and 'brushes'. The ants clamp one antenna tightly between notch and spur, pull it through, and subsequently clean the antenna cleaner itself with the mouthparts. We simulated cleaning strokes by moving notch or spur over antennae contaminated with fluorescent particles. The notch removed particles more efficiently than the spur, but both components eliminated more than 60% of the particles with the first stroke. Ablation of bristles, brush and comb strongly reduced the efficiency, indicating that they are essential for cleaning. To study how comb and brush remove particles of different sizes, we contaminated antennae of living ants, and anaesthetized them immediately after they had performed the first cleaning stroke. Different-sized beads were trapped in distinct zones of the notch, consistent with the gap widths between cuticular outgrowths. This suggests that the antenna cleaner operates like a series of sieves that remove the largest objects first, followed by smaller ones, down to the smallest particles that get caught by adhesion.

A Theoretical Model for Steam Laser Cleaning

A theoretical model for removal of tiny particles from solid surface covered with a thin liquid film by laser cleaning is established by taking adhesion force and cleaning force into account. When pulsed laser irradiates on the solid surface coated with a thin liquid film, a sheet of liquid near the liquid/substrate interface can be superheated through thermal diffusion. The rapid growth of vapor bubbles inside the superheated liquid can generate transient stress wave with high pressure, large enough to expel micron and sub-micron particles from the contaminated surface. By calculating the adhesion force and cleaning force, the cleaning threshold of laser fluence can be predicted from this theoretical model. The difference between cleaning force and adhesion force increases quickly along with the laser fluence and leads to higher cleaning efficiency.

Removal of Poly(Dimethylsiloxane) Contamination from Silicon Surfaces with UV/Ozone Treatment

UV/ozone cleaning is known to be effective for removing thin organic contaminants, but removal of silicon containing contaminants is questionable. Organo-silicon contaminants, e.g., silicones, can result from a variety of integrated circuit chip and electronic packaging fabrication processes. In this investigation, films of poly(dimethylsiloxane) (PDMS) on silicon substrates, with and without a gold coating, have been used to simulate such contamination up to a thickness of 50 nm. Although treatment consistently reduced the advancing DI water contact angle, in some cases from a value greater than 100° to a value less than 5°, the hydrophilic nature of the treated surfaces was not due to complete contaminant removal, i.e., a significant amount of modified contaminant remained on the surface. High resolution x-ray photoelectron spectroscopy (XPS) in the Si 2p region suggest that O-Si-C bonds in the siloxane, observed prior to treatment, are converted to SiOx, where x is between 1.6 and 2. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. Deflection testing was used to evaluate the adhesion of an epoxybased adhesive to intentionally-contaminated silicon chips, before and after UV/ozone treatment. Although PDMS contamination induced loss of adhesion between the chip and the adhesive, complete conversion to silicon oxides by UV/ozone treatment of contaminants having a thickness of 5.0 nm has been demonstrated to restore adhesion to a value equivalent to that of uncontaminated silicon chip surfaces.