Design and fabrication of superhydrophobic cellulose nanocrystal films by combination of self-assembly and organocatalysis

Recent developments in the fabrication, performance, and application of transparent superhydrophobic coatings

Conventional superhydrophobic coatings frequently rely excessively on micron-sized protrusions on the surface, which leads to light scattering effects and significantly reduces the light transmission of the materials, thus limiting the range of coating applications. Transparent superhydrophobic coatings further expand the applications of coatings in areas such as solar photovoltaic panels, electronic components, architectural glass, automotive, cultural heritage preservation, and biomedical applications by combining the common properties of superhydrophobic coatings with optical transparency. This review summarizes the basic principles of transparent superhydrophobic coatings from the perspectives of superhydrophobicity and transparency theories. Advancements and characteristics of various fabrication processes are summarized. In addition, this review summarizes the strategies for synchronizing the superhydrophobicity with the transparency of the coatings and the mechanisms for enhancing the durability of the coatings. Finally, the progress in the applications is summarized and prospects of transparent superhydrophobic coating research are proposed. In all, transparent superhydrophobic coatings should be developed in the direction of balancing environmental friendliness, durability, optical transparency, and intelligence. This review is expected to effectively supplement existing works of literature on transparent superhydrophobic coatings and provide more insights for the large-scale applications of transparent superhydrophobic coatings in the future.

Cellulose/TiO2 Humidity Sensor

Resistivity-type humidity sensors, which detect changes in electrical resistance in response to variations in environmental humidity, have garnered significant interest due to their widespread application in industry, agriculture, and daily life. These sensors rely on diverse materials for fabrication, but their increasing variety has contributed to the accumulation of electronic waste. As a biodegradable polymer, cellulose offers unique advantages, including a naturally hydrophilic structure and a large specific surface area. These properties enable cellulose to reduce e-waste generation while facilitating the efficient adsorption of water molecules. However, despite these benefits, humidity sensors based solely on cellulose often suffer from poor sensitivity due to its limited hydrophilicity and non-adjustable structure. To overcome these limitations, the development of composite materials emerges as a promising solution for enhancing the performance of cellulose-based humidity sensors. Combining the complementary properties of cellulose and TiO2, this work presents the development of a cellulose/TiO2 composite humidity sensor through a sustainable approach. The resulting composite material exhibits significantly improved sensitivity compared with a sensor fabricated purely from cellulose. To achieve this, TiO2 nanoparticles were incorporated into cellulose extracted from potato peels, and the composite film was fabricated using the casting method. The sensor's performance was evaluated by analyzing the dependence of its complex impedance, measured over a frequency range between 2 kHz and 10 MHz, while varying relative humidity (RH).

Biomimetic Superhydrophobic Surfaces by Nanoarchitectonics with Natural Sunflower Pollen

Superhydrophobic surfaces, known for their water-repellent, and self-cleaning properties, are widely used in various applications. These advanced functional surfaces exhibit high contact angles (>150°), achieved through low surface energy chemistries and hierarchical roughness. Natural sunflower pollen is micron-sized spherical particles with nano-sized spikes on the surface. This study engineered superhydrophobic coatings using the unique hierarchical structure of sunflower pollen and low surface energy additives like polydimethylsiloxane (PDMS) and silane additives such as 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FTS), octadecyltrichlorosilane (OTS) and dichlorodimethylsilane (DCDMS). The pollen content significantly modulates surface structure, roughness, and water contact angle. Higher pollen content enhances roughness and water repellency by creating micro-nano hierarchical structures. Pollen-PDMS-FTS and Pollen-PDMS coatings demonstrated the highest water contact angles (165 ± 2° and 163 ± 3°, respectively) and lowest sliding angles (4.5 ± 1° and 7.6 ± 2.6°, respectively), achieving a "lotus effect." Conversely, Pollen-PDMS-OTS or Pollen-PDMS-DCDMS coatings resulted in high sliding angles and water adhesion, producing a "rose petal effect." These "lotus effect" coatings are effectively applied in self-cleaning and water displacement in oil pipelines on hilly terrain. This study provides insights into the interplay between hierarchical structure and surface-free energy for designing superhydrophobic surfaces tailored for specific applications.

Birch-Bark-Inspired Synergistic Fabrication of High-Performance Cellulosic Materials

There is a growing demand for the utilization of sustainable materials, such as cellulose-based alternatives, over fossil-based materials. However, the inherent drawbacks of cellulosic materials, such as extremely low wet strength and resistance to moisture, need significant improvements. Moreover, several of the commercially available wet-strength chemicals and hydrophobic agents for cellulosic material treatment are toxic or fossil-based (e.g., epichlorohydrin and fluorocarbons). Herein, we present an eco-friendly, high-yield, industrially relevant, and scalable method inspired by birch bark for fabricating hydrophobic and strong cellulosic materials. This was accomplished by combining simple surface modification of cellulosic fibers in water using colloidal particles of betulin, an abundant triterpene extracted from birch bark, with sustainable chemical engineering (e.g., lignin modification and hot-pressing). This led to a transformative process that not only altered the morphology of the cellulosic materials into a more dense and compact structure but also made them hydrophobic (contact angles of up to >130°) with the betulin particles undergoing polymorphic transformations from prismatic crystals (betulin III) to orthorhombic whiskers (betulin I). Significant synergistic effects are observed, resulting in a remarkable increase in wet strength (>1400%) of the produced hydrophobic cellulosic materials.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.