This review article exemplifies the importance of self-cleaning materials and coatings. Selfcleaning coatings are becoming an integral part of our daily life because of their utility in various applications such as windows, solar panels, cements, paints, etc. In this review, various categories of materials for the fabrication of hydrophilic, hydrophobic, oleophobic, amphiphobic and multifunctional coatings and their synthesis routes have been discussed. Furthermore, different natural organisms exhibiting superhydrophobic behaviour have been analysed. This review also covers the fundamentals of self-cleaning attributes such as water contact angle, surface energy, contact angle hysteresis, etc. Fig. 1 Pictures of water droplets on Lotus (left) and Ramee (right) leaf indicating the self-cleaning property inherent in nature. 1 Inset of a: pictures of water droplet on Lotus (left) and Ramee leaf (right) indicating their inherent selfcleaning nature.

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Cellulose Nanocrystals (CNC) are explored to stabilize oil/water emulsions for their ability to adsorb at the oil/water interface. In this work, the role of electrostatic forces in the CNC ability to stabilize oil/water emulsions is explored using canola oil/water and hexadecane/water as model systems. Canola oil/water and Hexadecane/ water (20/80, v/v) emulsions were stabilized with the addition of CNCs using ultrasonication. Emulsion droplet sizes range from 1 to 4 μm as measured by optical microscopy. It is found that CNC can stabilize oil/water emulsions regardless of their charge density. However, reducing the surface charge density, by adding salts and varying pH, can reduce the amount of CNC's required to form a stable emulsion. Just by adding 3 mM Na+ or 1 mM or less Ca+2 to a CNC suspension, the amount of CNC reduced by 30% to stabilized 2 mL of Canola oil. On the other hand, adding salt increases the emulsion volume. The addition of 100 mM Na+ or the reduction of pH below 2 leads to the aggregation of CNC; emulsions formed under these conditions showed gel-like behavior. This work shows the potential of nanocellulose crystal in stabilizing food and industrial emulsions. This is of interest for applications where biodegradability, biocompatibility, and food grade requirements are needed.

Cellulose nanocrystals (CNCs) are a particularly appealing format of the natural biopolymer due to their exceptional strength, nanoscale dimensions, and needle-like shape anisotropy. However, CNCs are hydrophilic and hence their wettability makes them impractical for many coating applications, with various approaches using chemical functionalization to overcome this. Here we show that CNC-coated surfaces can be rendered hydrophobic by alignment of the native CNCs using a wrinkled template-mediated printing process. We present a novel and simple method allowing full release of the CNCs from the template and their permanent adsorption into fine patterns onto the surface, thus preventing CNC repositioning during wetting. The aligned CNCs induce strong pinning effects that capture and retain water droplets with high contact angle and large roll-off angles, without becoming susceptible to oil contamination. The fabrication process for these coatings could be achieved by large-scale printing, making them a practical and cost-effective solution to hydrophobic coatings from raw cellulosic materials.

Cellulose nanocrystal (CNC) research has addressed increased attention in the bioprocessing community, especially the utility of these materials in different fields, including biomedical and materials applications. In this review, the different preparation methods and properties of CNC materials will be initially briefly discussed. The latter focuses special attention on the alignment of CNCs and its applications. Different methods to induce CNC alignment, including self-assembly, shear-based alignment, magnetic and electric field alignment, spin-coating, dip-coating, etc., are reviewed in detail, followed by the different characterization techniques to quantify the alignments of CNCs. The current and potential applications of aligned CNCs, such as fillers to enhance the mechanical and thermal properties of biocomposites, photonic materials to deal with structural colors and enhancement in optical properties of iridescent films, and reduced wettability for high-resolution printing, are further discussed to provide more insights into this promising research direction. We hope that this review will shine light on CNC alignment and also open the door to different types of applications.

In this study, we report a photoanode consisting of a polymeric/inorganic nanojunction between novel nanostructured 3D C N nano-networks and BiVO substrate. This nanojunction is formed such that 3D C N nano-networks with a positively charged surface are efficiently anchored on the BiVO photoanode with a negatively charged surface. This electrostatic self-assembly can initiate and contribute to an intimate contact at the interfaces, leading to an enhanced photoelectrochemical activity and stability compared with that fabricated by non-electrostatic assembly. The C N nano-network/BiVO photoanode achieved a remarkable photocurrent density of 4.87 mA cm for water oxidation at 1.23 V (vs. reversible hydrogen electrode) after depositing FeOOH/NiOOH as oxygen-evolution co-catalyst, which is among the highest photocurrent densities reported so far for BiVO -based photoanodes.

High-resolution inkjet printing of a hydrophobic polymer surface (polystyrene, PS) was accomplished using a patterned coating of cellulose nanocrystals (CNCs) that prevents the ink from bleeding. A periodically crack-free, wrinkled (wavelength of around 850 nm) stamp was prepared by surface oxidation of an uniaxially stretched poly­(dimethylsiloxane) elastomeric substrate and was used as a template to transfer aligned patterns of cellulose nanocrystals (CNCs) onto PS surfaces by wet stamping. The morphology of the aligned CNC coatings on PS was then compared with randomly deposited CNCs on PS using atomic force microscopy. The wettability of the CNCs and polymer surfaces with water and ink was measured and analyzed in the context of inkjet printing. This biomaterial coating technique enables high-resolution printing of modern water-based inks onto hydrophobic surfaces for applications in renewable packaging and printing of biomolecules for high throughput diagnostics. Further, with suitable modifications, the technology is scalable to roll-to-roll manufacturing for industrial flexo printing.

The concept of blood typing diagnostics using blood drops dried onto transparent cellulose nanocrystal thin film (∼35 nm) coatings has been demonstrated. The substrate onto which the blood drops are dried plays an important role in such tests, depending on surface composition, roughness, and wettability. The drying profile of three different fluid dispersions: model latex particles, reagent blood cells, and whole human blood was studied on a range of different surfaces, including cellulose nanocrystals (CNCs), regenerated cellulose, and several hydrophobic polymers, in order to understand the role of surface chemistry, roughness, and fluid dispersion properties. The morphology of these surfaces was investigated using atomic force microscopy, roughness was calculated, and wettability was explored via contact angle measurement. The morphology of dried drops of human blood on different cellulosic surfaces was compared in order to understand the importance of cellulose crystallinity. Well-defined dried blood drops were observed on random and aligned CNC surfaces, facilitating visualization of individual cells. A simple antibody–antigen test was used to demonstrate the effectiveness of the CNC substrate for blood testing, showing high and reproducible selectivity.