acidthough

Acidthrough is a term used to describe a diffusion-controlled chemical etching process in which an acid is permitted to penetrate a material from one surface to the opposite surface, producing etching or dissolution across the thickness. The concept emphasizes the coupling of mass transport (diffusion) and surface chemistry (acid attack). The term is not universally standardized, but it appears in discussions of through-thickness patterning and thinning of thin films and membranes.

Mechanism and scope: In acidthrough, acid species diffuse through pores, microchannels, or defects within a substrate and react with the material along the diffusion path. The resulting material removal can progress progressively from the exposed side toward the far side, creating through-thickness features. The process is governed by exposure time, acid concentration, temperature, and substrate properties such as porosity, crystallinity, thickness, and surface finish. When lateral diffusion is limited and the reaction is sufficiently fast, the etching can approximate one-dimensional through-thickness progress.

Methods and control: Practical implementations often involve applying a masking layer to define the intended pattern on one face, followed by immersion or spraying with an acid solution. Mask removal, rinsing, and a quenching step may be used to halt the reaction. Control parameters include acid strength, exposure duration, temperature, and substrate preparation. Monitoring methods range from profilometry to cross-sectional microscopy to assess etch depth.

Applications and materials: Potential applications include fabrication of microfluidic channels and through-holes in thin polymer films and glassy substrates, patterning of biodegradable polymers for biomedical devices, and exploratory studies in coating thinning. Common substrates discussed in acidthrough contexts include poly(methyl methacrylate), various glasses, and porous polymers.

Safety and limitations: Acidthrough involves corrosive acids and reactive species, requiring appropriate PPE and ventilation. Limitations include diffusion-limited depth control, potential undercutting, and material-specific compatibility. The approach is most suitable for thin, porous, or otherwise permeable substrates where controlled through-thickness etching is desirable.