Tailoring the Hydrophilicity for Delayed Condensation Frosting in Antifogging Coatings.

In the last few decades, numerous studies have focused on designing suitable hydrophilic materials to inhibit surface-induced fog or frost under extreme conditions. As fogging and condensation frosting on a film involves molecular interaction with water prior to forming discrete droplets on the surface, it is essential to control the extent of a film to strongly bind with water molecules for antifogging coatings. While the water contact angle measurement is commonly used to probe the hydrophilicity of a film, it oftentimes fails to predict the antifogging and antifrosting performance as this value only reflects the wettability of a given surface to water droplet. In this work, a polysaccharide-based film composed of chitosan (CHI) and carboxymethyl cellulose (CMC) is used as the model system and oligo(ethylene glycol) (OEG) moieties are additionally introduced to study the effect of OEG moieties on antifogging and condensation frosting. We show that the film containing OEG-grafted CHI exhibits excellent frost-resistant capability due to the OEG moieties in the film that serve as active sites for water molecules to strongly interact in a nonfreezable state.

Biocompatible Wax-Based Microcapsules with Hermetic Sealing for Thermally Triggered Release of Actives.

We present a microfluidic approach that utilizes temperature-responsive and biocompatible palm oil as the shell material in microcapsules to simultaneously achieve hermetic sealing as well as on-demand temperature-triggered release of the encapsulated actives. Unlike common paraffin waxes (e.g., eicosane), microcapsule shells comprising palm oil do not form pores or cracks during freezing and provide a hermetic seal, a nearly perfect seal that separates the core containing the actives from the surrounding environment over a prolonged period of time. This allows effective isolation and protection of complex cargoes such as small molecules with high diffusivity, strong acids, and cosmetic actives including niacinamide. Moreover, the palm oil shell melts above the defined melting temperature, allowing the on-demand release of the encapsulated actives. Furthermore, palm oil is biocompatible, is edible, and leaves a minimal footprint when used in personal care and cosmetic products, offering new perspectives in the design of microcapsules for cosmetic applications.

Wet-Style Superhydrophobic Antifogging Coatings for Optical Sensors.

Transparent substrates are widely used for optical applications from lenses for personal and sports eyewear to transparent displays and sensors. While these substrates require excellent optical properties, they often suffer from a variety of environmental challenges such as excessive fogging and surface contamination. In this work, it is demonstrated that a wet-style superhydrophobic coating, which simultaneously exhibits antifogging, antireflective, and self-cleaning properties, can be prepared by pattern transferring low-surface-energy microstructures onto a heterostructured nanoscale thin film comprising polymers and silica nanoparticles. The polymer-silica nanocomposite base layer serves as a hydrophilic reservoir, guiding the water molecules to preferentially condense into this underlying region and suppress reflection, while the low-surface-energy microstructure enables contaminants adsorbed on the surface to be easily removed by rinsing with water.

Spontaneous Generation of a Molecular Thin Hydrophobic Skin Layer on a Sub-20 nm, High-k Polymer Dielectric for Extremely Stable Organic Thin-Film Transistor Operation.

Polymer dielectric materials with hydroxyl functionalities such as poly(4-vinylphenol) and poly(vinyl alcohol) have been utilized widely in organic thin-film transistors (OTFTs) because of their excellent insulating performance gained by hydroxyl-mediated cross-linking. However, the polar hydroxyl functionality also deleteriously affects the performance of OTFTs and significantly impairs the device stability. In this study, a sub-20 nm, high-k copolymer dielectric with hydroxyl functionality, poly(2-hydroxyethyl acrylate-co-di(ethylene glycol) divinyl ether), was synthesized in the vapor phase via initiated chemical vapor deposition. The inherently dry environment offered by the vapor-phase polymer synthesis prompted the snuggling of polar hydroxyl functionalities into the bulk polymer film to form a molecular thin hydrophobic skin layer at its surface, verified by near-edge X-ray absorption fine structure analysis. The chemical composition of the copolymer dielectric was optimized systematically to achieve high dielectric constant (k ≈ 6.2) as well as extremely low leakage current densities (less than 3 × 10-8 A/cm2 in the range of ±2 MV/cm) even with sub-20 nm thickness, leading to one of the highest capacitance (higher than 300 nF/cm2) achieved by a single polymer dielectric to date. Exploiting the structural advantage of the cross-linked high-k polymer dielectric, high-performance OTFTs were obtained. Notably, the spontaneously formed molecular thin, hydrophobic skin layer in the copolymer film substantially suppressed the hysteresis in the transistor operation. The trap analysis also suggested the formation of bulk trap with a high energy barrier and sufficiently low trap densities at the semiconductor/dielectric interface, owing to the surface skin layer. Furthermore, the OTFTs with the -OH-containing copolymer dielectric showed an unprecedentedly excellent operational stability. No apparent OTFT degradation was observed up to 50 000 s of high constant voltage stress (corresponding to the applied electric field of 1.4 MV/cm) because of the markedly suppressed interfacial trap density by the hydrophobic skin layer, together with the current compensation by the bulk hydroxyl functionalities. We believe that the surface modification-free, one-step polymer dielectric synthetic strategy will provide a new insight into the design of polymer dielectric materials for high-performance, low-power soft electronic devices with high operational stability.

Water and Oil Insoluble PEGDA-Based Microcapsule: Biocompatible and Multicomponent Encapsulation.

Despite the recent development in various materials capable of encapsulating biomolecules, there exist limited reports on multicomponent encapsulation in biocompatible microcapsules. In this letter, we utilize the molecular weight dependent solubility of poly(ethylene glycol) diacrylate (PEGDA) and droplet microfluidics to achieve direct encapsulation of both hydrophilic and hydrophobic cargoes in PEG microcapsules. By using PEGDA 250 as the middle phase, we demonstrate that these PEGDA-based microcapsules allow simultaneous encapsulation of both hydrophilic and hydrophobic cargoes. We further confirm the validity of this approach by demonstrating that complex biomolecule such as protein can be effectively encapsulated within these PEGDA-based microcapsules.