Purpose Additive manufacturing (AM) is readily capable of producing models and prototypes of complex geometry and is advancing in creating functional parts. However, AM processes typically underperform traditional manufacturing methods in mechanical properties, surface roughness and hermeticity. Solvent vapor treatments (vapor polishing) are commonly used to improve surface quality in thermoplastic parts, but the results are poorly characterized. Design/methodology/approach This work quantifies the surface roughness change and also evaluates the effect on hermeticity and mechanical property impacts for “as-printed” and acetone vapor-polished ABS tensile specimens of 1-, 2- and 4-mm thicknesses produced by material extrusion (FDM). Findings Vapor polishing proves to decrease the power spectral density for surface roughness features larger than 20 µm by a factor of 10× and shows significant improvement in hermeticity based on both perfluorocarbon gross leak and pressure leak tests. However, there is minimal impact on mechanical properties with the thin specimens showing a slight increase in elongation at break but decreased elastic modulus. A bi-exponential diffusion decay model for solvent evaporation suggest a thickness-independent and thickness-dependent time constant with the latter supporting a plasticizing effect on mechanical properties. Originality/value The contributions of this work show vapor polishing can have a substantial impact on the performance for end-use application of ABS FDM components.

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Many processes rely on wetting of liquids on surfaces. The way a liquid wets a solid depends on chemistry, geometry, and local energy inputs. Low-frequency surface vibrations can effect wetting changes prompted by droplet oscillations. High-frequency (ultrasonic) surface vibration can also cause a liquid to wet or spread out on a solid, but governing mechanisms are relatively uncharacterized. To investigate, droplets are imaged as they vibrate on a hydrophobic surface over different high frequencies (> 10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with surface resonance modes. The wetting change is proportional to droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle. Wetting control has various industry applications, and understanding these basic phenomena will help develop a deeper understanding of how ultrasonic vibration can be utilized to tune the behavior of liquids on any surface.

Many industrial processes depend on the wetting of liquids on various surfaces. Understanding the wetting effects due to ultrasonic vibration could provide a means for changing the behavior of liquids on any surface. In previous studies, low-frequency surface vibrations have been used to alter wetting states of droplets by exciting droplet volume modes. While high-frequency (>20 kHz) surface vibration can also cause droplets to wet or spread on a surface, this effect is relatively uncharacterized. In this study, droplets of various liquids with volumes ranging from 2 to 70 µL were vibrated on hydrophobic-coated (FluoroSyl) glass substrates fixed to a piezoelectric transducer at varying amplitudes and at a range of frequencies between 21 and 42 kHz. The conditions for contact line motion were evaluated, and the change in droplet diameter under vibration was measured. Droplets of all tested liquids initially begin to spread out at a similar surface acceleration level. The results show that the increase in diameter is proportional to the maximum acceleration of the surface. Finally, liquid properties and surface roughness may also produce some secondary effects, but droplet volume and excitation frequency do not significantly change the droplet spreading behavior within the parameter range studied.

Adhesives, medical devices, and many cleaning products depend on the wetting of liquids on solid surfaces. The liquid/solid interaction depends on chemistry, surface topology, and external energy input. For instance, surfactants are commonly used in cleaning solutions to improve their effectiveness, and electrical fields are frequently used to control the contact angle of liquid droplets. Low frequency vibration has been used to spread, move, and manipulate droplets using the mode shape oscillations of the droplet to displace the contact line. Ultrasonic vibration (above 20 kHz) can also cause a liquid droplet to wet or spread out on a solid surface under the right circumstances. We have previously demonstrated that ultrasonic vibration can be used to control the wetting/spreading of liquid droplets on smooth hydrophobic surfaces and that the response is relatively insensitive to excitation frequency or fluid properties [1]. This paper reports on the use of ultrasonic vibration to initiate spreading on surfaces with etched pillars. Ultrasonic vibration successfully initiated a transition from Cassie to Wenzel states in all geometries with no apparent need to tune excitation frequencies to the geometry. However, the magnitude of the acceleration required to initiate the transition decreased with increased pillar spacing. For small pillar spacing, some smooth spreading in the Cassie wetting mode was observed before transition.