Interfacial Basicity-Guided Formation of Polydopamine Hollow Capsules in Pristine O/W Emulsions – Toward Understanding of Emulsion Template Roles

In this article, alkane-in-water emulsions have been utilized as templates for polymerization of 3,4-dihydroxyphenylethylamine (dopamine) and l-3,4-dihydroxyphenylalanine (l-dopa). The resulting polymer structures are clearly dependent on the concentration of OH ions, i.e., pH, on the surfaces of the oil droplets, while show little dependence on the electrostatic or hydrophobic interactions between the resulting polymers and the surfaces of the oil droplets. Pristine alkane droplets, stabilized solely by OH ions, have templated formation of hollow capsules due to selective oxidation and self-polymerization of the monomers on the OH ion-rich surfaces of the pristine oil droplets. In contrast, macroporous structures have been obtained when either cationic or anionic surfactants were used to stabilize alkane droplets to lower the concentration of OH ions on the droplet surfaces

Strengthening and Toughening Dynamic Covalent Thermosets via Hydrogen-Bonded Cross-Links

Dynamic covalent thermosets have emerged as a next-generation sustainable plastic that combines the advantages of traditional thermosets and thermoplastics. However, dynamic covalent thermosets generally suffer from the trade-off between strength/stiffness and ductility/toughness. Herein, a strategy to simultaneously strengthen and toughen dynamic covalent thermosets, incorporation of hydrogen-bonded (H-bonded) cross-links into the dynamic covalent networks, is reported. We designed a polyimine network cross-linked by both the dynamic imine bonds and H-bonds, resulting in a remalleable and recyclable polyimine thermoset with high yield strength (ca. 55.2 MPa) and Young’s modulus (ca. 1.7 GPa) as well as high ductility (ca. 72%) and toughness (ca. 32.7 MJ m–3). When the H-bonded cross-links are removed from the polyimine network or replaced by the imine bonds, the mechanical strength or toughness of the polyimines is significantly declined, respectively. Therefore, this work provides an effective design principle for strong and tough dynamic covalent thermosets with modularity and recyclability

Layer-by-Layer-Assembled Multilayer Films of Polyelectrolyte-Stabilized Surfactant Micelles for the Incorporation of Noncharged Organic Dyes

Noncharged pyrene molecules were incorporated into multilayer films by first loading pyrene into poly(acrylic acid) (PAA)-stabilized cetyltrimethylammonium bromide (CTAB) micelles (noted as PAA&(Py@CTAB)) and then layer-by-layer (LbL) assembled with poly(diallyldimethylammonium chloride) (PDDA). The stable incorporation of pyrene into multilayer films was confirmed by quartz crystal microbalance (QCM) measurements and UV−vis absorption spectroscopy. The resultant PAA&(Py@CTAB)/PDDA multilayer films show an exponential growth behavior because of the increased surface roughness with increasing number of film deposition cycles. The present study will open a general and cost-effective avenue for the incorporation of noncharged species, such as organic molecules, nanoparticles, and so forth, into LbL-assembled multilayer films by using polyelectrolyte-stabilized surfactant micelles as carriers

Substrate-Independent, Transparent Oil-Repellent Coatings with Self-Healing and Persistent Easy-Sliding Oil Repellency

Herein we report a simple and substrate-independent approach to fabricate transparent oil-repellent coatings, which involves alternate deposition of poly­(diallyl­dimethyl­ammonium) (PDDA) and poly­(styrene­sulfonate) (PSS) onto substrates, followed by incubation of the coated objects into perfluoro­octanoate (PFO) aqueous solutions for 2 min. Various low-surface-tension liquids can easily slide down the coating surfaces on flat substrates at a sliding angle lower than 12° for 10 μL droplets. The coatings are applicable to different substrates including Si, glass, plastic, steel, and wood, and those with complex shapes and large surface areas. They are also applicable to rough substrates with roughness at both micro/nanoscale and macroscopic scales to realize the easy-sliding oil repellency. Incubation of the PDDA/PSS polyelectrolyte multilayers (PEMs) into PFO solutions induces an effective but nondestructive substitution of PFO anions for PSS in the PEMs, which results in a composite coating with PFO anions homogeneously interspersed in both the coating surface and the bulk. Thanks to the as-described “repeating-layer” composition/structure of the coatings, their easy-sliding oil repellency can be self-healed after surface decomposition or well maintained after physical damages, due to the replenishing surface. Therefore, the advantageous characteristics of the as-developed oil-repellent coatings and the simplicity of the preparation protocol make the coatings highly practical for real-world applications. It is believed that the coatings can perform as antismudge coatings that shield against oil-borne contaminants, chemical-shield coatings that protect coated plastics from dissolution by organic solvents, and nonstick coatings (of oil tankers or pipelines) that enable loss-free oil transportation

One-Pot Preparation of Skin-Inspired Multifunctional Hybrid Hydrogel with Robust Wound Healing Capacity

Bioinspired hydrogels have demonstrated multiple superiorities over traditional wound dressings for wound healing applications. However, the fabrication of bioinspired hydrogel-based wound dressings with desired functionalities always requires multiple successive steps, time-consuming processes, and/or sophisticated protocols, plaguing their clinical applications. Here, a facile one-pot strategy is developed to prepare a skin-inspired multifunctional hydrogel within 30 min by incorporating elastin (an essential functional component of the dermal extracellular matrix), tannic acid, and chitosan into the covalently cross-linked poly­(acrylamide) network through noncovalent interactions. The resulting hydrogel exhibits a Young’s modulus (ca. 36 kPa) comparable to that of human skin, a high elongation-at-break (ca. 1550%), a satisfactory tensile strength (ca. 61 kPa), and excellent elastic self-restorability, enabling the hydrogel to synchronously and conformally deform with human skin when used as wound dressings. Importantly, the hydrogel displays a self-adhesive property to skin tissues with an appropriate bonding strength (ca. 55 kPa measured on intact porcine skin), endowing the hydrogel with the ability to rapidly self-adhere to intact human skin, sealing the wound surface and also easily being removed without residue left or trauma caused to the skin. The hydrogel also possesses remarkable antibacterial activity, antioxidant capability, and hemocompatibility. All of these collective beneficial properties enable the hydrogel to significantly accelerate the wound healing process, outperforming the commercial wound dressings

Simply Formulated Dry Pressure-Sensitive Adhesives for Substrate-Independent Underwater Adhesion

Due to the long-standing challenge to realize underwater adhesion, there are a few commercially available underwater pressure-sensitive adhesives (PSAs), which are, however, ubiquitously used for dry adhesion. Herein, a dry underwater PSA is developed on the basis of a simple, low-cost, and easily commercial formulation, which only involves the copolymerization of butyl acrylate (BA) and acrylic acid (AA). By tuning the ratios between the hydrophobic BA unit and H-bonding AA unit, we optimize the viscoelastic properties of the PSA to maximize the underwater adhesion performance. The PSA exhibits high underwater bonding strength (e.g., >115 kPa) for diverse substrates (e.g., glass, metals, plastics), at the preload (e.g., 250 kPa) easily accessed by finger pressing. Moreover, the PSA exhibits dry adhesion capability, rendering it conveniently adhered to a backing material to form an underwater adhesive tape. The dry PSA can well-maintain its underwater adhesion performance even after long-term storage in air or incubation in water

Rapid Seeded Growth of Monodisperse, Quasi-Spherical, Citrate-Stabilized Gold Nanoparticles via H₂O₂ Reduction

In this report, we demonstrate a rapid and simple seeded growth method for synthesizing monodisperse, quasi-spherical, citrate-stabilized Au nanoparticles (Au NPs) via H₂O₂ reduction of HAuCl₄. Au NPs with diameter ranging from 30 to 230 nm can be synthesized by simply adding 12 nm citrate stabilized Au NP seeds to an aqueous solution of H₂O₂ and HAuCl₄ under ambient conditions. The diameter of the resulting Au NPs can be quantitatively controlled by the molar ratio of HAuCl₄ to the Au seeds. The standard deviation of the Au NP sizes is less than 10%, and the ellipticity (ratio of major to minor axes) of the NPs is less than 1.1. Compared to existing ones, the present seeded growth approach is implemented within 1 min under ambient condition, and no unfavorable additives are involved because H₂O₂ can readily decompose into H₂O during storage or via boiling

Substrate-Independent, Transparent Oil-Repellent Coatings with Self-Healing and Persistent Easy-Sliding Oil Repellency

Herein we report a simple and substrate-independent approach to fabricate transparent oil-repellent coatings, which involves alternate deposition of poly­(diallyl­dimethyl­ammonium) (PDDA) and poly­(styrene­sulfonate) (PSS) onto substrates, followed by incubation of the coated objects into perfluoro­octanoate (PFO) aqueous solutions for 2 min. Various low-surface-tension liquids can easily slide down the coating surfaces on flat substrates at a sliding angle lower than 12° for 10 μL droplets. The coatings are applicable to different substrates including Si, glass, plastic, steel, and wood, and those with complex shapes and large surface areas. They are also applicable to rough substrates with roughness at both micro/nanoscale and macroscopic scales to realize the easy-sliding oil repellency. Incubation of the PDDA/PSS polyelectrolyte multilayers (PEMs) into PFO solutions induces an effective but nondestructive substitution of PFO anions for PSS in the PEMs, which results in a composite coating with PFO anions homogeneously interspersed in both the coating surface and the bulk. Thanks to the as-described “repeating-layer” composition/structure of the coatings, their easy-sliding oil repellency can be self-healed after surface decomposition or well maintained after physical damages, due to the replenishing surface. Therefore, the advantageous characteristics of the as-developed oil-repellent coatings and the simplicity of the preparation protocol make the coatings highly practical for real-world applications. It is believed that the coatings can perform as antismudge coatings that shield against oil-borne contaminants, chemical-shield coatings that protect coated plastics from dissolution by organic solvents, and nonstick coatings (of oil tankers or pipelines) that enable loss-free oil transportation

Substrate-Independent, Transparent Oil-Repellent Coatings with Self-Healing and Persistent Easy-Sliding Oil Repellency

Herein we report a simple and substrate-independent approach to fabricate transparent oil-repellent coatings, which involves alternate deposition of poly­(diallyl­dimethyl­ammonium) (PDDA) and poly­(styrene­sulfonate) (PSS) onto substrates, followed by incubation of the coated objects into perfluoro­octanoate (PFO) aqueous solutions for 2 min. Various low-surface-tension liquids can easily slide down the coating surfaces on flat substrates at a sliding angle lower than 12° for 10 μL droplets. The coatings are applicable to different substrates including Si, glass, plastic, steel, and wood, and those with complex shapes and large surface areas. They are also applicable to rough substrates with roughness at both micro/nanoscale and macroscopic scales to realize the easy-sliding oil repellency. Incubation of the PDDA/PSS polyelectrolyte multilayers (PEMs) into PFO solutions induces an effective but nondestructive substitution of PFO anions for PSS in the PEMs, which results in a composite coating with PFO anions homogeneously interspersed in both the coating surface and the bulk. Thanks to the as-described “repeating-layer” composition/structure of the coatings, their easy-sliding oil repellency can be self-healed after surface decomposition or well maintained after physical damages, due to the replenishing surface. Therefore, the advantageous characteristics of the as-developed oil-repellent coatings and the simplicity of the preparation protocol make the coatings highly practical for real-world applications. It is believed that the coatings can perform as antismudge coatings that shield against oil-borne contaminants, chemical-shield coatings that protect coated plastics from dissolution by organic solvents, and nonstick coatings (of oil tankers or pipelines) that enable loss-free oil transportation

Highly Tough, Stretchable, Self-Healing, and Recyclable Hydrogels Reinforced by in Situ-Formed Polyelectrolyte Complex Nanoparticles

It remains a challenge to fabricate healable and recyclable polymeric materials with simultaneously enhanced tensile strength, stretchability, and toughness. Herein, we report a simple approach to fabricate high-performance polymer hydrogels that not only integrate high tensile strength, stretchability, and toughness but also possess self-healing and recycling capabilities. The polymer hydrogels are fabricated by mixing a positively charged polyelectrolyte mixture of poly­(diallyldimethylammonium chloride) (PDDA)/branched poly­(ethylenimine) (PEI) with a negatively charged polyelectrolyte mixture of poly­(sodium 4-styrenesulfonate) (PSS)/poly­(acrylic acid) (PAA) in an aqueous solution followed by molding, drying, and rehydration. The (PDDA/PEI)–(PSS/PAA) hydrogels with in situ-formed PDDA–PSS nanoparticles have a tensile strength, strain at break, and toughness of 1.26 ± 0.06 MPa, 2434.2 ± 150.3%, and 19.53 ± 0.48 MJ/m3, respectively. The toughness of the (PDDA/PEI)–(PSS/PAA) hydrogels is ∼5.2 and ∼108 times higher than that of the PEI–PAA and PDDA–PSS hydrogels, respectively. Benefiting from the high reversibility of the hydrogen-bonding and electrostatic interactions, the (PDDA/PEI)–(PSS/PAA) hydrogels can efficiently heal from physical damage to restore their original mechanical properties at room temperature in water. Moreover, the (PDDA/PEI)–(PSS/PAA) hydrogels after being dried and ground can be recycled under a pressure of ∼3 kPa at room temperature in the presence of water to reuse the damaged hydrogels