Dennis. W. Hess

Wood is a sustainable material, but hygroscopicity can affect dimensional stability and mechanical durability. Recent research has increasingly focused on combining citric acid with various polyols as eco-friendly crosslinking systems to improve wood properties. Herein, a solvent-free and catalyst-free method was used to synthesize bio-based polyesters from citric acid and mannitol. In situ curing was carried out after vacuum-pressure impregnation of fast-growing poplar wood (Populus deltoides Marshall). Morphological characterization showed that the polyester filled the cell lumen and penetrated the cell wall structure. It was confirmed by Fourier Transform Infrared (FTIR) and cross-polarization/magic angle spinning (CP/MAS) ¹³C nuclear magnetic resonance (NMR) analysis that the polyester formed covalent ester bonds with wood hydroxyl groups, which indicated successful chemical grafting. The dimensional stability and mechanical properties of the modified wood were greatly improved. The parallel compressive strength of the grain reached 41.5 MPa, which was 41.7% higher than that of the untreated wood. This research adopted a citric acid–mannitol polyester, providing a sustainable, economical, and scalable approach for the development of high-performance, degradable wood composites for construction/furniture applications.

Wood is a widely used carbon-storing material, but its applications are constrained by vulnerabilities to water, oil and fire. Existing coatings have limited functionalities, failing to meet the intelligent requirements of modern wood products and constructions. Inspired by bionics, a robust superamphiphobic fire sensing EP/F-POS@Fe₃O₄ coating was designed on wood substrate, fabricated from functional ferroferric oxide (Fe₃O₄) particles, tetraethyl orthosilicate (TEOS, hydrolyzed into polysiloxane), 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDTMS), and epoxy resin (EP) adhesive. Optimizing the EP content not only enhances coating stability but also engineers surface micronano reentrant structures, endowing the wood with excellent superamphiphobicity (water/oil contact angles >150°). The EP/F-POS@Fe₃O₄ coating maintains robust hydrophobic and oleophobic properties under sandpaper abrasion, tape peeling, glass bead impact, and knife scratching tests. At the same time, the coating's effectiveness in reducing the wood's liquid absorption further confirms its stable water/oil repellency. Importantly, beyond passive flame retardancy, the EP/F-POS@Fe₃O₄ coating features a breakthrough active fire alarm function: nonconductive under ambient conditions, it acts as a sensor upon flame exposure, exhibiting ultrafast (∼3 s) intelligent visual alarm response and excellent repeatability (>10 cycles), holding potential to mitigate fire risks. Obviously, the EP/F-POS@Fe₃O₄ coating shows great promise for future applications in wooden architecture and smart furniture.

Wood, as a natural biomass material, has long been a research focus. Superhydrophobic modified wood, in particular, has shown great promise in a myriad of engineering applications such as architecture, landscape, and shipbuilding. However, commercial development has encountered significant resistance due to preparation difficulties and sometimes unsatisfactory performance. In this study, hydrophobic/superhydrophobic wood comodified with methyltrimethoxysilane (MTMS) and 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDTMS) was fabricated by a one-step sol-gel method that uses an in situ growth process. Low-molecular-weight MTMS was allowed to permeate the three-dimensional porous wood interior. Then, acid-base catalysts were used to regulate the hydrolytic condensation process of MTMS and PFDTMS composite silanes to generate micro/nano hierarchical structures with low surface energy on the wood surface. The physicochemical characteristics of modified wood were investigated and the reaction mechanism established. The modified wood displayed excellent internal hydrophobicity/surface superhydrophobicity, water-moisture resistance, and dimensional stability at low fluorine concentrations. The resulting superhydrophobic surface provided stain resistance, self-cleaning ability, and loading capacity in water while exhibiting good mechanochemical stability; wood mechanical strength was also enhanced. This methodology created a superhydrophobic surface and bulk hydrophobization of wood in one step. Beyond wood, this approach is expected to provide a promising approach for functional modification of other porous composite materials.

Rf plasmas and electrochemical treatments have been used extensively for thin film deposition and etching in the fabrication of microelectronic and photonic devices. These methods can be applied to non-traditional substrates (e.g., paper and stainless steel) to alter surface and bulk properties to create (i) paper-based analytical devices with application to microfluidic devices, and (ii) antibacterial structures on stainless steel. Two examples will be described. First, the effects of plasma-based oxygen etching of cellulose surfaces followed by plasma-enhanced fluorocarbon film deposition will be described and shown to control wetting and adhesion of water droplets. These process steps can also be used to form fully enclosed hydrophilic channels in bulk paper and thereby allow microfluidic device fabrication on inexpensive and renewable substrates. Electrochemical etching of stainless steel creates micro- and nano-structures on stainless steel surfaces that repel water and bacteria. These surfaces have potential applications in orthopedic implants and consumer metal products prone to bacterial contamination.

The wetting behavior of fiber networks, which are central to many research and industrial applications, can be difficult to predict accurately owing to their complex, heterogeneous structure. The cylindrical pore model, widely used to interpret and predict the forced wetting of hydrophobic porous materials, often does not yield correct results when working with fibrous networks like paper substrates and non-woven fabrics. This is because these materials exhibit variation in pore size, fiber length, and fiber diameter, as well as a reentrant pore geometry. Quantitative prediction of the critical wetting resistance of hydrophobized papers to arbitrary entrant liquids requires a more sophisticated analytical approach that considers this unique fibrous structure and the effect of stochastic variations within the pore matrix. In this work, we directly measure the critical breakthrough pressure for different porous substrates across various wetting entrant liquids. To isolate the effects of the structure and stochastics on critical wetting behavior of fibrous networks, we analyze additional materials strategically chosen for their subsets of structural features. Ultimately, we formulate a method that demonstrates physical reasonableness, numerical accuracy, and the ability to elucidate the effects of pore size, pore size distribution, fiber diameter, fiber diameter distribution, surface wettability, and liquid surface tension on critical breakthrough pressure of liquids through hydrophobic fibrous networks.

Microelectronic device fabrication has traditionally been performed by selective removal or etching of material from deposited films to create patterns. Plasma etching has been the mainstay of this process since the early 1970s. The introduction of copper (Cu) metallization (~1997) by IBM resulted in the development of additive approaches (e.g., damascene process) due to the inability to plasma etch Cu. Despite attempts to plasma etch Cu as early as 1980, the only viable plasma-based methods in this time frame were inert gas sputtering, where selectivity to underlying layers and low etch rate were problematic, or chlorinated vapors that required elevated temperatures (>200 C) or significant ion bombardment energies to volatilize Cu chlorides. Both approaches required a hard mask rather than photoresist layers to ensure mask stability and precise pattern transfer. Due to the inability to form high volatility Cu halides that could be removed readily by plasma processes, other non-plasma or partial plasma approaches to Cu etching at lower temperatures were investigated. Addition of a UV lamp to facilitate excitation and desorption of volatile Cu chlorides in plasma etching was invoked. Formation and volatilization of copper by oxidation followed by complexation with organic ligands at lower (~150 C) temperatures was first reported in the mid-1990s, but this processes generated isotropic etch patterns; more recent approaches have reported anisotropy. Plasma chlorination followed by a liquid etch to remove the chlorinated Cu was also reported; due to the directionality of the plasma chlorination step, anisotropic profiles resulted. Hydrogen-based etching of Cu films was reported in 2010, initially with a two-step process consisting of plasma chlorination followed by a hydrogen plasma step to remove volatile products. This effort subsequently demonstrated that etching by pure hydrogen in a one-step process was possible albeit with low etch rates; etch rate increases were observed with vapor additives. Pure hydrogen plasmas etched photoresist layers, thereby requiring hard masks, but additives allowed employment of photoresist as a mask layer. Anisotropic etch profiles from these hydrogen-based processes were possible, in part due to additives protecting sidewalls and photoresist from etching and to ion bombardment during etching. This presentation will describe the development of Cu etching and patterning methods beginning in the 1970s. Mechanistic considerations of the various processes reported will be discussed and the current needs and limitations of these approaches indicated.