Digitally enabled surface function modification for wide area applications
The aim of this work is to produce a digital manufacturing strategy to tailor surface wettability and control fluid deposition to the modified surfaces. The studies combine surface function modification by digitally enabled additive coatings with wide-area laser processing. Nano and femtosecond laser texturing have been used to modify surface topography and chemical functionality. Additive functional coating techniques included delivering materials by vapour transfer, laser induced reverse transfer and inkjet printing.
Laser texturing can be used to modify the wettability of stainless steel from complete water affinity (superhydrophilicity) to repulsion (superhydrophobicity). A focus of experiments was to explore the knowledge gaps around the chemical mechanism of hydrophobic transition after laser texturing. This allowed the development of a manufacturing approach to improve the acceleration of the timeconsuming transition period and to produce surfaces with application-tailored superhydrophobic functionality. XPS analysis of surface chemistry produced new insight into the role of organic compound adsorption in the hydrophobic transition process.
The capability to produce a high level of control of surface wettability and understanding of the underpinning surface science is vital for inkjet printing to glass surfaces. Preconditioning surface treatments were investigated for inkjet deposition of functional material. An emerging industrial trend is the switch to ‘green’ water-based printing inks. However, the use of these inks poses challenges for functional material printing due to their properties such as high surface tension. Shadow masked corona discharge plasma and ultrafast laser ablation of glass were used for localised patterning of wettability which enabled precise control of fluid spreading on the glass surfaces. Another key industrial concern linked to surface energies is the durability of the printed deposits which was investigated through adhesion and abrasion experiments. Typically, conductive tracks printed to flat glass are rapidly removed by abrasion, by using a laser texturing pretreatment the deposit retained conductive properties after exposure to abrasion cycles.
Finally, a novel process of laser induced reverse transfer deposition of low resistivity material was developed. A recently developed capability of holographic phase contrast imaging at nanosecond temporal resolution was used to report the morphology of the confined ablation plume during material transfer and patterning. This revealed previously unobserved phenomena such as the influence of the rebounding pressure wave and the longer plasma lifetime of a confined plume of 230 µs compared to 125 µs for the unconfined case. This showed the importance of plume shielding and incubation effects for applications. 3 common conductive materials: silver, graphite and copper, were tested to assist with materials selection. Silver and graphite were shown to produce conductive deposits with resistivities of 0.03 µΩ m and 340 µΩm respectively.