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Controlling surface wettability of titanium with phosphonic acid self-assembled monolayers and laser patterning Cheuk Ying Tam (21648791) Self assembled monolayers (SAM) Laser heating Wettability alteration mechanism Chemically well-defined surface regions to control cell response are beneficial in understanding cell behaviour on a substrate and can increase the biocompatibility of implant materials such as titanium. Applying self-assembled monolayers (SAMs) is an effective way of chemically modifying surface properties. For a number of substrate materials, cell adhesion has been shown in the literature to be controlled by tailoring SAM molecules with specific terminal groups, and the area of cell attachment can be controlled by the location of the SAM species. A range of different SAM patterning methods have been developed to provide different levels of resolution, but mostly applied over small areas and flat surfaces. It is beneficial to develop a protocol for substrates with rougher surface finish and more irregular shape.The aim of this research was to develop a protocol to create a pattern of distinct functionalised regions on a rough surface. To achieve this, phosphonic acids were first selected as suitable candidates that can form a stable SAM on metal oxides, including titanium. Two SAM forming molecules: a long chain, methyl terminated hexadecylphosphonic acid (HDPA) and a short chain, carboxylic acid terminated 6-phosphono hexanoic acid (6PA) were selected for this study. The deposition of these SAMs on rough and polished commercially pure titanium surfaces was investigated to identify suitable parameters to form a strong bond between the molecules and the substrate with surface sensitive characterisation methods including X-ray photoelectron (XPS) spectroscopy and water contact angle. XPS identified phosphorus (P) peaks and change in carbon (C) peak shape after SAM deposition. Wettability increased from hydrophilic to hydrophobic after HDPA coating and the water contact angle decreased after 6PA coated. The SAMs altered the chemical and physical properties of the titanium surface.Direct laser patterning (DLP) of SAMs was selected as a rapid and flexible patterning method; however, only a limited number of previous studies have been conducted with titanium as the substrate. This work investigated the patterning of the HDPA SAMs on titanium by exposure to a relatively low cost CO2 laser (10.6 μm wavelength, continuous wave, Gaussian distribution with 300 μm diameter) at power levels of 10 to 100 W with traverse speeds of 100 to 1000 mm/s. It was found that a threshold power level was required to achieve patterning by the laser heating of the material. XPS line scans across the samples showed a reduction in the C1s peaks in the laser-irradiated regions implying thermal decomposition of the HDPA molecules, but the P level remained similar. The molecules were partially thermal decomposed by the laser induced heat. An increase in the wettability of the irradiated areas could also be observed, that was similar to changes in HDPA SAMs that underwent thermal stability tests with conventional furnace heating methods. After creating regions of laser damaged HDPA, the shorter chain 6PA molecule with a hydrophilic-COOH terminal group was substituted into the laser irradiated area by liquid immersion deposition. The non-irradiated area remained coated with HDPA and was not substituted by the 6PA molecules. This created an area of 6PA SAM within a HDPA matrix. A contrast in chemical environment, hence wettability, was achieved. The 6PA SAM region confined a large droplet of water into shapes be- cause of the contrast of hydrophobicity between the hydrophillic 6PA molecules and the surrounding hydrophobic HDPA molecules. The rate of moisture condensation and the condensed droplet shape between the two regions were also different. Moisture was less likely to settle on the HDPA SAM and droplets formation was slower than on the 6PA SAM, where larger condensed droplets formed. 2025-07-04T13:36:35Z Text Thesis 10.26174/thesis.lboro.29464763.v1 https://figshare.com/articles/thesis/Controlling_surface_wettability_of_titanium_with_phosphonic_acid_self-assembled_monolayers_and_laser_patterning/29464763 CC BY-NC-ND 4.0