Final Report Summary - SCM4SCF (Surface Characterisation and Modelling for Self-Cleaning Function) Human beings have long tried to learn from and mimic nature by means of nanotechnology to obtain the functional surfaces in many engineering and daily life applications. This research is aimed at establishing functionally useful correlations between surface micro-geometry and mechanical and tribological properties. It specifically focuses to elucidate the effect of surface features on the local adhesion, friction, hardness and elastic modulus in terms of anti-adhesion and anti-contamination performances. The proposal brings the joined expertise in both surface measurement and characterisation by Warwick Group and surface modelling by Dr Tian to achieve above ultimate objectives. We first studied the functional surfaces exhibited by engineered and natural systems for their anti-adhesion performances using the unique TPM and some commercial measurement instruments. Numerical simulation and modelling was investigated out to generate such surfaces with controlled surface parameters, in order to study the effect of surface topography on the contact angle, friction and nano-hardness. The micro/nano fabrication methodologies for generating durable and cost-effective functional surfaces have been explored. This paves a way for scientists and engineers to design and fabricate surface structure or topography for a specific function.We conducted the surface metrology and characterisation of a number of plant and animal surfaces, as well as the machined engineering surfaces obtained by laser ablation, surface coating, wire electro discharge machining, and sand blasting methods with the aid of optical microscopy, drop shape analyser, and scanning tunnel microscopy. We established the contact models based on the DMT and JKR models between the stylus tip and sample surfaces. The transformation between these two models has also been investigated for the different measurement conditions. Further the contact area model between the water drop and the flat surface has been provided based on the Hertzian contact model. The effects of surface topography on the wettability have been extensively investigated using experimental method. In order to obtain the long-term durability superhydrophobic surface, the WEDM and laser ablation methodologies have been utilized in the fabrication and preparation of stainless steel samples. These methods can provide efficient and durable superhydrophobic surfaces without further treatments and coatings.The wettability transition of the machined surface was founded and the reasons for this phenomenon have been explored using surface metrology and chemical analysis methodologies. It is noted that the surface topography can be modified by the laser ablation, and the contact angle can be improved or reduced due to the increase of the contact area between the water droplet and the ablated surfaces. The wettability change is dependent on the laser fluence on the surfaces. Gentle laser ablation can improve the contact angle to some extent, and the strong one will make the surface superhydrophilic at the beginning. However, the superhydrophilic surfaces can change into superhydrophobic surfaces after several days. Through the surface metrology and characterisation, it is noted that the reason for this wettability transition is not due to surface topography change but the chemistry alternation of the top layer. The developed fabrication and characterisation methodologies put one step forward for practical application of the metallic superhydrophobic surfaces in the industrial and academic sectors.Dr. Tian has conducted the training in the usages of drop shape analyser, SEM, optical microscopy and obtained the skills and techniques for surface metrology and analysis. He visited seven UK universities (Birmingham University, University of Bedfordshire, Salford University, Bath University, Nottingham University, Oxford University, and Queens University of Belfast) and a number of companies, and presented his achievements in the functional surfaces. With the help of Dr. Tian, we established new relationships between Warwick University and other EU Universities including Oldenburg University, Tampere University of Technology, University of Kiel, University of Nice, Ecol University of Lyon, and many more. He helped co-supervise 2-PhD students at the School of Engineering, University of Warwick as part of his knowledge transfer. He also acted as the special session chairs of international conferences 3M-NANO 2014 and 2015.The capability of the micro/nano surface measurement, characterisation and fabrication for functional surfaces is of high benefit to both UK and European engineers and scientists. This could result in a new generation of self-cleaning surfaces to address the challenging and timely problems of energy-saving and environmental protection.
