Durable superhydrophobic coatings

Superhydrophobic coatings exhibiting contact angle greater than 150° and sliding angle smaller than 10° have raised great interest during the last few years. Their unique surface structure together with "right" chemistry allow their use in variety of applications such as self-cleaning, anti-biofouling, anti-corrosion, anti-icing and more. The main limitation today using superhydrophobic coatings in commercial applications is their low mechanical integrity. Therefore, improving their durability is necessary and urgent.;In this thesis, extensive work was done to establish superhydrophobic coating with enhanced durability. Chapter 1 is a general introduction to literature. Chapter 2 and 3 cover the synthesis of photoreactive hybrid silica NPs that can covalently bond to a polymer matrix upon UV radiation and stabilize NPs localization on the polymer surface. Chapter 4 introduces three different binders and silica NPs that when appropriately combined create superhydrophobic coatings with enhance durability. Chapter 5 covers different durability tests to ensure high durability of the coatings.;Chapter 1 reviewed three basic wetting states; Young state for flat surface, Wenzel state for rough homogenous surface, and Cassie-Baxter state for rough heterogeneous surface due to air trapped between the bumps. One example for Cassie-Baxter state in nature discussed here is the lotus leaf. It was revealed that the leaf comprises cellular micro bumps and super structuring waxy nano crystals, which gives its unique superhydrophobic and self-cleaning properties. Lastly, abrasion resistance of superhydrophobic coatings is presented with few examples from literature.;Chapter 2 covered the study of synthesis photoreactive hybrid silica NPs with benzophenone groups that upon UV radiation opens to form ketyl radical. With the presence of a polymer, the ketyl radical can react through abstraction and termination reactions to covalently bond with the polymer matrix. Two different polymers were studied, urethane acrylate radiation curing and epoxy photoresist. Nano-manipulation technique was used to evaluate the bonding of the NPs to the polymer surface.;Chapter 3 covered the synthesis of three different particles size (65, 156 and 294 nm) of photoreactive hybrid silica NPs and their influence on superhydrophobicity and durability. Additional layers of fumed silica NPs (roughness contribution) and fluoroalkylsilane top layer (chemistry contribution) exhibited in superhydrophobicity for the three different particles size. Air flow and accelerated aging tests were performed to evaluate the different coatings' durability with increasing photoreactive hybrid silica NPs particles size.;Chapter 4 presents novel materials based on silica nanoparticles and three different polymer binders (ethyl cyanoacrylate, epoxy and urethane acrylate) that, when appropriately combined and applied to a surface, create superhydrophobic coatings. A fundamental understanding of the effect of composition and substrate interactions that drive the creation of such superhydrophobic surfaces. Thermodynamic analysis of the system was used to understand and predict the localization of the NPs on the surface. The thermodynamic investigation was in good agreement with the SEM analysis with respect to the localization of the NPs as function of the binder concentrations and substrate type. Tape test was used to evaluate the coatings' durability.;Chapter 5 covers different durability tests that were performed to evaluate durability. 10 wt% epoxy based superhydrophobic coating that showed high durability under Tape test was also tested under subsonic and supersonic wind tunnel test. In subsonic wind tunnel different air velocities up to 156 mph were tested. Measurement ofthe dynamic pressure, the static pressure, and temperature rise in the airflow were taken as well. In supersonic wind tunnel March 2, 2.3 and 3 were tested. High pressure chamber was used to store high-pressure air which was then accelerated through a nozzle to provide supersonic flow. 10 wt% epoxy based superhydrophobic coating showed highly durability when its superhydrophobicity retained after all the above tests.