Fluorinated Metal-Organic Coatings with Selective Wettability

Metal-phenolic network composites: from fundamentals to applications

Composites with tailored compositions and functions have attracted widespread scientific and industrial interest. Metal-phenolic networks (MPNs), which are composed of phenolic ligands and metal ions, are amorphous adhesive coordination polymers that have been combined with various functional components to create composites with potential in chemistry, biology, and materials science. This review aims to provide a comprehensive summary of both fundamental knowledge and advancements in the field of MPN composites. The advantages of amorphous MPNs, over crystalline metal-organic frameworks, for fabricating composites are highlighted, including their mild synthesis, diverse interactions, and numerous intrinsic functionalities. The formation mechanisms and state-of-the-art synthesis strategies of MPN composites are summarized to guide their rational design. Subsequently, a detailed overview of the chemical interactions and structure-property relationships of composites based on different functional components (e.g., small molecules, polymers, biomacromolecules) is provided. Finally, perspectives are offered on the current challenges and future directions of MPN composites. This tutorial review is expected to serve as a fundamental guide for researchers in the field of metal-organic materials and to provide insights and avenues to enhance the performance of existing functional materials in applications across diverse fields.

Evaluation of fluorous affinity using fluoroalkyl-modified silica gel and selective separation of poly-fluoroalkyl substances in organic solvents

In this study, we focused on the fluorous affinity acting among fluorine compounds, and then developed a new separation medium and evaluated their performance. We prepared the stationary phases for a column using silica gel-modified alkyl fluoride and investigated the characteristics of fluorous affinity by comparing them with a typical stationary phase, which does not contain fluorine, using high-performance liquid chromatography (HPLC). In HPLC measurements, we confirmed that while all non-fluorine compounds were not retained, retention of fluorine compounds increased as the number of fluorine increased with the stationary phase. It also revealed that the strength of fluorous affinity changes depending on the types of the organic solvent; the more polar the solvent, the stronger the effect. Additionally, the stationary phase was employed to compare the efficiency of our column with that of a commercially available column, Fluofix-II. The retention selectivity was almost the same, but the absolute retention strength was slightly higher on our column, indicating that the column is available for practical use.

How to Make Plastic Surfaces Simultaneously Hydrophilic/Oleophobic?

Hydrophilic/oleophobic surfaces are desirable in many applications including self-cleaning, antifogging, oil-water separation, etc. However, making plastic surfaces hydrophilic/oleophobic is challenging due to the intrinsic hydrophobicity/oleophilicity of plastics. Here, we report a simple and effective method of making plastics hydrophilic/oleophobic. Plastics, including poly (methyl methacrylate) (PMMA), polystyrene (PS), and polycarbonate (PC), have been coated with a perfluoropolyether (PFPE) (i.e., commercially known as Zdol) via dip coating and then irradiated with UV/Ozone. The contact angle measurements indicate that the treated plastics have a lower water contact angle (WCA) and higher hexadecane contact angle (HCA), i.e., they are simultaneously hydrophilic/oleophobic. The Fourier transform infrared (FTIR) results suggest that UV/Ozone treatment introduces oxygen-containing polar groups on the plastic surfaces, which renders the plastic surfaces hydrophilic. Meanwhile, more orderly packed PFPE Zdol molecules, which is due to the UV-induced bonding between PFPE Zdol and the plastic surface, result in the oleophobicity. Moreover, the simultaneous hydrophilicity/oleophobicity of functionalized plastics does not degrade in aging tests, and they have superior antifogging performance and detergent-free cleaning capability. This simple method developed here potentially can be applied to other plastics and has important implications in the functionalization of plastic surfaces.

Engineering Metal-Phenolic Networks for Solar Desalination with Directional Salt Crystallization

Solar desalination is one of the most promising strategies to address the global freshwater shortage crisis. However, the residual salt accumulated on the top surface of solar evaporators severely reduces light absorption and steam evaporation efficiency, thus impeding the further industrialization of this technology. Herein, a metal-phenolic network (MPN)-engineered 3D evaporator composed of photothermal superhydrophilic/superhydrophobic sponges and side-twining hydrophilic threads for efficient desalination with directional salt crystallization and zero liquid discharge is reported. The MPN coatings afford the engineering of alternating photothermal superhydrophilic/superhydrophobic sponges with high heating efficiency and defined vapor escape channels, while the side-twining threads induce site-selective salt crystallization. The 3D evaporator exhibits a high and stable indoor desalination rate (≈2.3 kg m^-2  h^-1 ) of concentrated seawater (20 wt%) under simulated sun irradiation for over 21 days without the need for salt crystallization inhibitors. This direct desalination is also achieved in outdoor field operations with a production rate of clean water up to ≈1.82 kg m^-2  h^-1 from concentrated seawater (10 wt%). Together with the high affinity and multiple functions of MPNs, this work is expected to facilitate the rational design of solar desalination devices and boost the research translation of MPN materials in broader applications.

Spotting Local Environments in Self-Assembled Monolayer-Protected Gold Nanoparticles

Organic-inorganic (O-I) nanomaterials are versatile platforms for an incredible high number of applications, ranging from heterogeneous catalysis to molecular sensing, cell targeting, imaging, and cancer diagnosis and therapy, just to name a few. Much of their potential stems from the unique control of organic environments around inorganic sites within a single O-I nanomaterial, which allows for new properties that were inaccessible using purely organic or inorganic materials. Structural and mechanistic characterization plays a key role in understanding and rationally designing such hybrid nanoconstructs. Here, we introduce a general methodology to identify and classify local (supra)molecular environments in an archetypal class of O-I nanomaterials, i.e., self-assembled monolayer-protected gold nanoparticles (SAM-AuNPs). By using an atomistic machine-learning guided workflow based on the Smooth Overlap of Atomic Positions (SOAP) descriptor, we analyze a collection of chemically different SAM-AuNPs and detect and compare local environments in a way that is agnostic and automated, i.e., with no need of a priori information and minimal user intervention. In addition, the computational results coupled with experimental electron spin resonance measurements prove that is possible to have more than one local environment inside SAMs, being the thickness of the organic shell and solvation primary factors in the determining number and nature of multiple coexisting environments. These indications are extended to complex mixed hydrophilic-hydrophobic SAMs. This work demonstrates that it is possible to spot and compare local molecular environments in SAM-AuNPs exploiting atomistic machine-learning approaches, establishes ground rules to control them, and holds the potential for the rational design of O-I nanomaterials instructed from data.

Antibacterial Inorganic Coating of Calcium Silicate Hydrate Substrates by Copper Incorporation

Under environmental conditions, biofilms can oftentimes be found on different surfaces, accompanied by the structural degradation of the substrate. Since high-copper-content paints were banned in the EU, a solution for the protection of these surfaces has to be found. In addition to hydrophobation, making the surfaces inherently biofilm-repellent is a valid strategy. We want to accomplish this via the metal exchange in calcium silicate hydrate (CSH) substrates with transition metals. As has been shown with Europium, even small amounts of metal can have a great influence on the material properties. To effectively model CSH surfaces, ultrathin CSH films were grown on silicon wafers using Ca(OH)2 solutions. Subsequently, copper was incorporated as an active component via ion exchange. Biofilm development is quantified using a multiple-resistant Pseudomonas aeruginosa strain described as a strong biofilm former cultivated in the culture medium for 24 h. Comprehensive structural and chemical analyses of the substrates are done by environmental scanning electron microscopy (ESEM), transmission Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results do not show any structural deformation of the substrates by the incorporation of the Cu combined with three-dimensional (3D) homogeneous distribution. While the copper-free CSH phase shows a completely random distribution of the bacteria in biofilms, the samples with copper incorporation reveal lower bacterial colonization of the modified surfaces with an enhanced cluster formation.

Droplet Bouncing: Fundamentals, Regulations, and Applications

Droplet impact is a ubiquitous phenomenon in nature, daily life, and industrial processes. It is thus crucial to tune the impact outcomes for various applications. As a special outcome of droplet impact, the bouncing of droplets keeps the form of the droplets after the impact and minimizes the energy loss during the impact, being beneficial in many applications. A unified understanding of droplet bouncing is in high demand for effective development of new techniques to serve applications. This review shows the fundamentals, regulations, and applications of millimeter-sized droplet bouncing on solid surfaces and same/miscible liquids (liquid pool and another droplet). Regulation methods and current applications are summarized, and potential directions are proposed.

Sustaining Robust Cavities with Slippery Liquid-Liquid Interfaces

The formation of a stable gas cavity on the surfaces of solid bodies is essential for many practical applications, such as drag reduction and energy savings, owing to the transformation of the originally sticky solid-liquid interface into a free-slip liquid-vapor interface by the creation of either liquid repellency or a Leidenfrost state on the surfaces. Here, it is shown that the simple infusion of a textured sphere with a smooth, slippery liquid layer can more easily create and sustain a stable gas cavity in a liquid at lower impact velocities compared to a dry solid sphere with the same contact angle. With a key parameter of curvature ratio, the early lamella dynamics during water entry of spheres and drops impact on planes are first unified. With the perspective of wetting transition, the unforeseen phenomenon of prone to cavity formation are successfully explained, which is the preferential lamella detachment from a slippery surface due to the higher viscosity of the lubricant relative to air. It is envisioned that the findings will provide an important and fundamental contribution to the quest for energy-efficient transport.

Exploiting Molecular Dynamics in Composite Coatings to Design Robust Super-Repellent Surfaces

Fluorinated motifs are promising for the engineering of repellent coatings, however, a fundamental understanding of how to effectively bind these motifs to various substrates is required to improve their stability in different use scenarios. Herein, the binding of fluorinated polyhedral oligomeric silsesquioxanes (POSS) using a cyanoacrylate glue (binder) is computationally and experimentally evaluated. The composite POSS-binder coatings display ultralow surface energy (≈10 mJ m-2 ), while still having large surface adhesions to substrates (300-400 nN), highlighting that super-repellent coatings (contact angles >150°) can be readily generated with this composite approach. Importantly, the coatings show super-repellency to both corrosive liquids (e.g., 98 wt% H2 SO4 ) and ultralow surface tension liquids (e.g., alcohols), with ultralow roll-off angles (<5°), and tunable resistance to liquid penetration. Additionally, these coatings demonstrate the potential in effective cargo loading and robust self-cleaning properties, where experimental datasets are correlated with both relevant theoretical predictions and systematic all-atom molecular dynamics simulations of the repellent coatings. This work not only holds promise for chemical shielding, heat transfer, and liquid manipulations but offers a facile yet robust pathway for engineering advanced coatings by effectively combining components for their mutually desired properties.

Robust and durable liquid-repellent surfaces

This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.

Macromolecular Engineering of Thermoresponsive Metal-Phenolic Networks

Dynamic nanostructured materials that can react to physical and chemical stimuli have attracted interest in the biomedical and materials science fields. Metal-phenolic networks (MPNs) represent a modular class of such materials: these networks form via coordination of phenolic molecules with metal ions and can be used for surface and particle engineering. To broaden the range of accessible MPN properties, we report the fabrication of thermoresponsive MPN capsules using Fe^III ions and the thermoresponsive phenolic building block biscatechol-functionalized poly(N-isopropylacrylamide) (biscatechol-PNIPAM). The MPN capsules exhibited reversible changes in capsule size and shell thickness in response to temperature changes. The temperature-induced capsule size changes were influenced by the chain length of biscatechol-PNIPAM and catechol-to-Fe^III ion molar ratio. The metal ion type also influenced the capsule size changes, allowing tuning of the MPN capsule mechanical properties. Al^III-based capsules, having a lower stiffness value (10.7 mN m^-1), showed a larger temperature-induced size contraction (∼63%) than Tb^III-based capsules, which exhibit a higher stiffness value (52.6 mN m^-1) and minimal size reduction (<1%). The permeability of the MPN capsules was controlled by changing the temperature (25-50 °C)─a reduced permeability was obtained as the temperature was increased above the lower critical solution temperature of biscatechol-PNIPAM. This temperature-dependent permeability behavior was exploited to encapsulate and release model cargo (500 kDa fluorescein isothiocyanate-tagged dextran) from the capsules; approximately 70% was released over 90 min at 25 °C. This approach provides a synthetic strategy for developing dynamic and thermoresponsive-tunable MPN systems for potential applications in biological science and biotechnology.

Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion

The colloidal properties of suspended metal-organic frameworks (MOFs) are critical for device fabrication and application. Herein, van der Waals attractive, electric double layer repulsive, and steric repulsive forces of a native and encapsulated MOF are quantified for the first time. The van der Waals attractive forces were investigated by conducting environmental ellipsometric porosimetry (EEP) and spectroscopic ellipsometry (SE) on submicron, optical-quality nanoparticle films. The repulsive forces were determined from colloid and material characterization measurements. These data were used to predict suspension properties via extended Derjaguin, Landau, Verwey, and Overbeek theory. The state of dispersion was quantified for comparison with theoretical predictions for nine solvents. The MOF encapsulated with a surface-selective modification showed superior suspension in hydrophobic solvents. These findings should expedite the formulation of MOF colloidal suspensions for future works.