Hydroxylation of organic polymer surface: method and application

UV-Induced Thiol-Ene "Click" Surface Grafting Polymerization on BOPP Substrate and Its Postmodifying for Hydrophilic and Antibacterial Applications

This paper proposed a novel and versatile surface modification route by integrating UV light-mediated thiol-ene "click" surface grafting polymerization and postmodification via the reactions of the surface thiol groups. At first, poly(thiol ether) layers with tunable thiol group density, up to 8.2 × 102 ea/nm3 for cross-linked grafting layers, were grafted from biaxially oriented polypropylene (BOPP) film. Then, the surface -SH groups reacted with epoxy compounds to introduce quaternary ammonium salt. With the immobilized quaternary ammonium salt and coordinated Zn2+ ions, the modified film demonstrated 99.98% antibacterial rate against Staphylococcus aureusafter soaking in DI water for 21 days and in a highly alkaline environment (0.1 M NaOH aqueous solution) for 3 days, and the surface water contact angle decreased to 39°. At last, the polymethacrylate chains were also successfully grafted from the surface thiol groups of the cross-linked poly(thiol ether) under visible light irradiation. With 2-(dimethyldodecylammonium) ethyl methacrylate as the grafting monomer, the modified BOPP film had shown a 99.99% antibacterial rate against both Escherichia coliand S. aureus. Meanwhile, with 2-methacryloxyethyl phosphoryl choline as grafting monomer, the modified surface showed an excellent antibioadhesion of living S. aureus, and the surface water contact angle was as low as 48°.

Mechanism of Reduced Glutathione Induced Lysozyme Defolding and Molecular Self-Assembly

The distinctive assembly behaviors of lysozyme (Lys) feature prominently in food, materials, biomedicine, and other fields and have intrigued many scholars. Although our previous work suggested that reduced glutathione (GSH) could induce lysozyme to form interfacial films at the air/water interface, the underlying mechanism is still obscure. In the present study, the effects of GSH on the disulfide bond and protein conformation of lysozyme were investigated by fluorescence spectroscopy, circular dichroism spectroscopy, and infrared spectroscopy. The findings demonstrated that GSH was able to break the disulfide bond in lysozyme molecules through the sulfhydryl/disulfide bond exchange reaction, thereby unraveling the lysozyme. The β-sheet structure of lysozyme expanded significantly, while the contents of α-helix and β-turn decreased. Furthermore, the interfacial tension and morphology analysis supported that the unfolded lysozyme tended to arrange macroscopic interfacial films at the air/water interface. It was found that pH and GSH concentrations had an impact on the aforementioned processes, with higher pH or GSH levels having a positive effect. This paper on the exploration of the mechanism of GSH-induced lysozyme interface assembly and the development of lysozyme-based green coatings has better instructive significance.

Conventional and emerging strategies for the fabrication and functionalization of PDMS-based microfluidic devices

Microfluidics is an emerging and multidisciplinary field that is of great interest to manufacturers in medicine, biotechnology, and chemistry, as it provides unique tools for the development of point-of-care diagnostics, organs-on-chip systems, and biosensors. Polymeric microfluidics, unlike glass and silicon, offer several advantages such as low-cost mass manufacturing and a wide range of beneficial material properties, which make them the material of choice for commercial applications and high-throughput systems. Among polymers used for the fabrication of microfluidic devices, polydimethylsiloxane (PDMS) still remains the most widely used material in academia due to its advantageous properties, such as excellent transparency and biocompatibility. However, commercialization of PDMS has been a challenge mostly due to the high cost of the current fabrication strategies. Moreover, specific surface modification and functionalization steps are required to tailor the surface chemistry of PDMS channels (e.g. biomolecule immobilization, surface hydrophobicity and antifouling properties) with respect to the desired application. While significant research has been reported in the field of PDMS microfluidics, functionalization of PDMS surfaces remains a critical step in the fabrication process that is difficult to navigate. This review first offers a thorough illustration of existing fabrication methods for PDMS-based microfluidic devices, providing several recent advancements in this field with the aim of reducing the cost and time for mass production of these devices. Next, various conventional and emerging approaches for engineering the surface chemistry of PDMS are discussed in detail. We provide a wide range of functionalization techniques rendering PDMS microchannels highly biocompatible for physical or covalent immobilization of various biological entities while preventing non-specific interactions.

UV-Assisted Li+-Catalyzed Radical Grafting Polymerization of Vinyl Ethers: A New Strategy for Creating Hydrolysis-Resistant and Long-Lived Polymer Brushes as a "Smart" Surface Coating

A facile synthetic route was developed to prepare a surface-grafted brush layer of poly(vinyl ethers) (PVEs) directly by a radical mechanism, with the "naked" Li⁺ acting as a catalyst. Density functional theory calculations suggested that complexation of naked Li⁺ to VEs significantly reduced the highest unoccupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap from 5.08 to 0.68 eV, providing a better prospect for electron transfer. The structure, morphology, and surface properties of grafted polymer layers were characterized using attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and dynamic water contact angle (DCA). Moreover, ellipsometry data indicated that the thickness of the polymer brushes was in the range of 20-60 nm, which corresponds to the grafting densities of 0.65-1.15 chain/nm², and DCA decreased from 84.4 to 45.3°. Most importantly, no hydrolysis was observed for the modified surface after 30 days of exposure to phosphate-buffered saline solution, 0.1 mol/L NaOH(eq) and 0.1 mol/L HCl(eq), demonstrating excellent hydrolysis resistance with long service life. In addition, as a proof of concept, the side hydroxyl groups of grafted PVEs provide active sites for efficient fixation of bioactive molecules, e.g., glycosaminoglycan and serum protein.

Photochemical [2 + 2] polymerization of metal-organic gels of a rigid and angular diene with silver-salts of diverse anions: selective dye-sorption and luminescence by xerogels

Two similar types of dienes, one rigid and the other flexible, were explored for their gel formation abilities with Ag(i) salts. The rigid and angular dienes have shown an exceptional ability for gel formation with silver salts of nitrate, triflate, tetrafluoro borate and hexafluorophosphate. These metal-organic gels (MOGs) and their xerogels are found to have an excellent ability to undergo the photochemical [2 + 2] polymerization reaction upon irradiation. The reactions were monitored, and the products were characterized via1H NMR and MALDI-TOF analyses. Further, the solid-state luminescence behaviour and the selective dye-sorption of the gels have been explored before and after the photo-polymerization reaction.

A Different Silica Surface: Radical Oxidation of Poly(methylsilsesquioxane) Thin Films and Particles (Tospearl)

Surfaces that exhibit the reactivity of silica toward surface modification (silanol condensation) were prepared by treating thin films and particles of poly(methylsilsesquioxane) with aqueous potassium persulfate at elevated temperature. Parallel experiments were carried out using a highly cross-linked poly(dimethylsiloxane). Advancing (θ_A) and receding (θ_R) water contact angles for all of these oxidized surfaces were θ_A/θ_R = ∼10/∼0°, and these low values remain unchanged for months. Reactions of these silica-like surfaces with a range of functional silane reagents indicate that the surface silanol concentration is sufficient to prepare covalently attached monolayers of similar surface density to those prepared using silicon wafers as substrates.

Facile Surface Functionalization of Cyclic Olefin Copolymer Film with Anhydride Groups for Protein Microarray Fabrication

Immobilization of protein at high efficiency is a challenge for fabricating polymer-based protein chips. Here, a simple but effective approach was developed to fabricate a cyclic olefin copolymer (COC)-based protein microarray with a high immobilization density. In this strategy, poly(maleic anhydride-co-vinyl acetate) (poly(MAH-co-VAc)) brushes were facilely attached on the COC surface via UV-induced graft copolymerization. The introduction of poly(MAH-co-VAc) brushes resulted in an obvious increase in the surface roughness of COC. The functionalized COC showed little reduction in transparency compared with pristine COC, indicating that the photografting treatment did not alter its optical property. The graft density of the anhydride groups on the modified COC could be tuned from 0.46 to 3.2 μmol/cm². The immobilization efficiency of immunoglobulin G (IgG) on functionalized COC reached 88% due to the high reactivity between anhydride groups and amine groups of IgGs. An immunoassay experiment demonstrated that the microarray showed high sensitivity to the target analyte.

An effective hydroxylation route for a highly sensitive glucose sensor using APTES/GOx functionalized AlGaN/GaN high electron mobility transistor

A highly sensitive glucose sensor based on AlGaN/GaN high electron mobility transistor (HEMT) has been fabricated. The hydroxyl groups on the GaN surface were achieved by the decomposition of hydrogen peroxide solution (H₂O₂) under UV irradiation for the production of hydroxyl radicals. The self-assembled monolayers (SAMs) of 3-aminopropyltriethoxysilane (APTES) with terminal amino groups formed on the hydroxylation surface were used as substrates for glucose oxidase (GOx) immobilization. The chemical groups on the GaN surface after hydroxylation were confirmed by X-ray photoelectron spectroscopy. From the analysis of current signals, the biosensor constructed with APTES/GOx exhibited good current response to glucose over a linear range from 10 to 100 µM with a sensitivity of 3.15 × 10⁴ µA mM⁻¹ cm⁻² and a detection limit of 10 nM. Meanwhile, the anticipated idea about the hydroxylation of GaN surface, can be an efficient approach for the design of AlGaN/GaN HEMT based biosensors in the future.

A highly sensitive glucose sensor based on AlGaN/GaN high electron mobility transistor (HEMT) has been fabricated.

Photochemical C-H oxygenation of side-chain methyl groups in polypropylene with chlorine dioxide

The chlorine dioxide radical (ClO2˙) was found to act as an efficient oxidizing agent for the aerobic C-H oxygenation of the side-chain methyl groups in polypropylene under photoirradiation and ambient conditions (298 K and 1 atm). The oxygenated side-chain methyl groups were selectively converted to carboxylic acid and hydroxy groups.

Construction of Soft Base Tongs on Separator to Grasp Polysulfides from Shuttling in Lithium-Sulfur Batteries

Rechargeable lithium-sulfur batteries, which use sulfur as the cathode material, promise great potentials to be the next-generation high-energy system. However, higher-order lithium polysulfides, Li₂ S_x (x = 4, 6, and 8), regardless of in charge or in discharge, always form first, dissolve subsequently in the electrolyte, and shuttle to the cathode and the anode, which is called "shuttle effect." The polysulfides shuttle effect leads to heavy loss of the active-sulfur materials. Literature works mostly "cover or fill" the pores to block polysulfides from shuttling, which also hinder the lithium ion transfer. Here a protocol is invented to grasp polysulfides based on the "soft and hard acid-base" theory. Tertiary amine layer (TAL) polymerized on a polypropylene separator selectively coordinates with the dissolved high-order Li₂ S_x in the cathode. Meanwhile, the transportation of lithium cations is not interrupted because of enough pores left for their transportation. After 400 cycles of charge/discharge at 0.5C, the TAL modified separator battery still possesses a capacity of 865 mAh g^-1 , which is among the best of the state-of-the-art performances of lithium-sulfur batteries. The flexible "polysulfides tongs" construction method paves a new way for Li-S batteries to reach desired performances with less worry about polysulfides shuttle.

Ultrafast Self-Healable Interfaces in Polyurethane Nanocomposites Designed Using Diels-Alder "Click" as an Efficient Microwave Absorber

In the recent times, multifunctional materials have attracted immense interest. Self-healing polymers are in great demand in almost every coating application. With an increase in electromagnetic (EM) pollution, curbing the same has become an urgent necessity. Lightweight coatings and conducting polymeric materials are being highly researched upon in this regard, and combining these properties with self-healing systems would open new avenues in EM interference (EMI) shielding (specifically in the microwave frequency domain) applications. In the current study, a novel approach toward the development of microwave shielding materials capable of self-healing through microwave heating has been attempted. A covalently cross-linked material was developed using Diels-Alder (DA) chemistry, which shows self-healing properties when stimulated by heating. Herein, reduced graphene oxide grafted with magnetite nanoparticles (rGO/Fe₃O₄) was covalently cross-linked to thermoplastic polyurethane using DA chemistry. The addition of multiwalled carbon nanotubes into these nanocomposites led to exceptional EM wave shielding and self-healing properties through a synergistic effect. The synergism led to exceptional EMI shielding of -36 dB, primarily through absorption in the microwave region of the EM spectrum. When used in the form of thin coatings of about 1 mm in thickness, the shielding value reached -28 dB, manifesting in more than 99% attenuation of EM waves through absorption. The material was also found to be capable of healing scratches or cuts through microwave irradiation.

Ag Nanoparticle/Polydopamine-Coated Inverse Opals as Highly Efficient Catalytic Membranes

Polymeric three-dimensional inverse-opal (IO) structures provide unique structural properties useful for various applications ranging from optics to separation technologies. Despite vast needs for IO functionalization to impart additional chemical properties, this task has been seriously challenged by the intrinsic limitation of polymeric porous materials that do not allow for the easy penetration of waterborne moieties or precursors. To overcome this restriction, we present a robust and straightforward method of employing a dipping-based surface modification with polydopamine (PDA) inside the IO structures, and demonstrate their application to catalytic membranes via synthetic incorporation of Ag nanoparticles. The PDA coating offers simultaneous advantages of achieving the improved hydrophilicity required for the facilitated infiltration of aqueous precursors and successful creation of nucleation sites for a reduction of growth of the Ag nanoparticles. The resulting Ag nanoparticle-incorporated IO structures are utilized as catalytic membranes for the reduction of 4-nitrophenol to its amino derivatives in the presence of NaBH4. Synergistically combined characteristics of high reactivity of Ag nanoparticles along with a greatly enhanced internal surface area of IO structures enable the implementation of remarkably improved catalytic performance, exhibiting a good conversion efficiency greater than 99% while minimizing loss in the membrane permeability.

Surface Decoration on Polymeric Gate Dielectrics for Flexible Organic Field-Effect Transistors via Hydroxylation and Subsequent Monolayer Self-Assembly

A simple photochemical reaction based on confined photocatalytic oxidation (CPO) treatment and hydrolysis was employed to efficiently convert C-H bonds into C-OH groups on polymeric material surfaces, followed by investigation of monolayer self-assembly decoration on polymeric dielectrics via chemical bonding for the organic field-effect transistors (OFETs) applications. This method is a low temperature process and has negligible etching effect on polymeric dielectric layers. Various types of self-assembled monolayers have been tested and successfully attached onto the hydroxylated polymeric dielectric surfaces through chemical bonding, ensuring the stability of decorated functional films during the subsequent device fabrication consisting of solution processing of the polymer active layer. With the surface decoration of functional groups, both n-type and p-type polymers exhibit enhanced carrier mobilities in the unipolar OFETs. In addition, enhanced and balanced mobilities are obtained in the ambipolar OFETs with the blend of polymer semiconductors. The anchored self-assembled monolayers on the dielectric surfaces dramatically preclude the solvent effect, thus enabling an improvement of carrier mobility up to 2 orders of magnitude. Our study opens a way of targeted modifications of polymeric surfaces and related applications in organic electronics.

Construction of DNA microarrays on cyclic olefin copolymer surfaces using confined photocatalytic oxidation

A novel strategy for DNA immobilization on cyclic olefin copolymer surfaces.