Adhesion of viscous liquids on packaging surfaces could lead to wastage, an increase of recycling costs, and even customers' dissatisfaction in applications related to food, cosmetics and agrochemical industries. Lubricant-impregnated surfaces (LIS) gained much attention recently over other surface functionalisation technologies due to their non-sticking response to highly viscous liquids. This work reports an investigation into anti-adhesive properties of LIS, with an emphasis on their durability. It provides an insight into the rationale design of LIS topographies in order to maximise their lubricant retention in potential food packaging applications. Femtosecond laser processing and hot embossing were employed to produce two types of topographies for LIS on stainless steel, polypropylene and polystyrene surfaces. The first type was single-scale sub-micron laser induced periodic surface structures (LIPSS), while the second one was multi-scale (MS) structures with both micron and sub-micron features.Droplet shedding characteristics of such LIPSS-LIS and MS-LIS substrates with water, milk and honey were examined under vibration and shear. The critical sliding angles at which liquid droplets attained motion on LIS were observed to be less than 32 o for all investigated liquids. However, the LIPSS-LIS substrates retained their functionality even after subjecting them to severe vibration, while the MS-LIS substrates partially lost their anti-adhesive characteristics.At the same time, the MS-LIS substrates exhibited premature pinning of droplets as compared to LIPSS-LIS substrates, under shear forces. Both vibration-and shear-induced loss of lubricant impacted the MS-LIS functionality.
The average power of ultrashort laser source has been increasing continuously and, therefore, solutions are required to employ fully these technology advances for improving the ablation efficiency in laser micro-processing. The use of burst mode processing is one of the solutions that has attracted a significant research and industrial interest in the past decade. A novel empirical methodology is proposed and implemented in this research to assess the MHz burst mode impact on the specific removal rate (SRR) and processing efficiency in ultrashort laser micro-machining. Especially, the capability of the MHz burst mode processing is investigated to scale up SRRs achievable on copper and stainless steel while utilising fully the available maximum pulse energy and average laser power. The results showed that the MHz burst mode offer a significant SRR scalability potential that can be attributed to beneficial near optimum fluence level and other side effects such as heat accumulation. Also, it is evidenced from the obtained results that the surface quality attained with the burst mode processing was comparable to that achieved with the single-pulse processing and even better at some specific process settings. Thus, the obtained SRR improvements were not in expense of the surface quality and the MHz bust mode processing represents a promising solution to employ fully the constantly increasing average power in ultrashort laser processing operations.
Endoscopes are ubiquitous in minimally invasive or keyhole
surgeries
globally. However, frequent removal of endoscopes from the patient’s
body due to the lens contaminations results in undesirable consequences.
Therefore, a cost-effective process chain to fabricate thermoplastic-based
endoscope lenses with superior antifouling and optical properties
is proposed in this research. Such multifunctional surface response
was achieved by lubricant impregnation of nanostructures. Two types
of topographies were produced by femtosecond laser processing of metallic
molds, especially to produce single-tier laser-induced periodic surface
structures (LIPSS) and two-tier multiscale structures (MS). Then,
these two LIPSS and MS masters were used to replicate them onto two
thermoplastic substrates, namely polycarbonate and cyclic olefin copolymer,
by using hot embossing. Finally, the LIPSS and MS surfaces of the
replicas were infiltrated by silicone oils to prepare lubricant-impregnated
surfaces (LIS). Droplet sliding tests revealed that the durability
of the as-prepared LIS improved with the increase of the lubricant
viscosity. Moreover, the single-tier LIPSS replicas exhibited longer-lasting
lubricant conservation properties than the MS ones. Also, LIPSS-LIS
replicas demonstrated an excellent optical transparency, better than
the MS-LIS ones, and almost match the performance of the reference
polished ones. Furthermore, the LIPSS-LIS treatment led to superior
antifouling characteristics, i.e., regarding fogging, blood adhesion,
protein adsorption, and microalgae attachment, and thus demonstrated
its high suitability for treating endoscopic lenses. Finally, a proof-of-concept
LIPSS-LIS treatment of endoscope lenses was conducted that confirmed
their superior multifunctional response.
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