Yin-Ning Zhou

Smart Fiber Membrane for pH-Induced Oil/Water Separation

Wastewater contaminated with oil or organic compounds poses threats to the environment and humans. Efficient separation of oil and water are highly desired yet still challenging. This paper reports the fabrication of a smart fiber membrane by depositing pH-responsive copolymer fibers on a stainless steel mesh through electrospinning. The cost-effective precursor material poly(methyl methacrylate)-block-poly(4-vinylpyridine) (PMMA-b-P4VP) was synthesized using copper(0)-mediated reversible-deactivation radical polymerization. The pH-responsive P4VP and the underwater oleophilic/hydrophilic PMMA confer the as-prepared membrane with switchable surface wettability toward water and oil. The three-dimensional network structure of the fibers considerably strengthens the oil/water wetting property of the membrane, which is highly desirable in the separation of oil and water mixtures. The as-prepared fiber membrane accomplishes gravity-driven pH-controllable oil/water separations. Oil selectively passes through the membrane, whereas water remains at the initial state; after the membrane is wetted with acidic water (pH 3), a reverse separation is realized. Both separations are highly efficient, and the membrane also exhibits switchable wettability after numerous cycles of the separation process. This cost-effective and easily mass-produced smart fiber membrane with excellent oil-fouling repellency has significant potential in practical applications, such as water purification and oil recovery.

Poly(ionic liquid)s-based nanocomposite polyelectrolytes with tunable ionic conductivity prepared via SI-ATRP

In this study, a novel kind of organic–inorganic core–shell SiO2-poly(p-vinylbenzyl) trimethylammonium tetrafluoroborate (SiO2–P[VBTMA][BF4]) nanoparticle was well designed and successfully synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used to confirm the formation of the core–shell nanoparticles and the surface modification. In order to overcome the challenge of the characterization of the number average molecular weight of poly(ionic liquid)s, “sacrificial initiator” method was used here employing a trimethylsilyl (TMS)-labeled initiator as the NMR marker for integration. In addition, good thermal stability of the new hybrid polyelectrolyte was proved by thermogravimetric analysis. The electrochemical impedance measurements revealed that the room temperature conductivity reached 10−4 S cm−1, which is much higher than that of the pure poly(ionic liquid)s and varies with the amount of the grafted polymer and the test temperature. The X-ray diffraction (XRD) tests further investigated the crystal structure of the nanocomposite and pure P[VBTMA][BF4]. The temperature dependence of ionic conductivity conforms to Arrhenius behavior for both of the nanocomposites and the pure polymer. The results indicated that the SI-ATRP approach provided a simple and versatile route to tune the ionic conductivity of the hybrid nanoparticles by changing the chain length of the grafted polymer, which can be potentially used in a variety of electrochemical devices.

Facile synthesis of gradient copolymers via semi-batch copper(0)-mediated living radical copolymerization at ambient temperature

In this work, we report an example of the facile synthesis of methyl methacrylate/tert-butyl acrylate (MMA/tBA) gradient copolymers (poly(MMA-grad-tBA) using the Cu(0) and conventional ATRP ligands as catalysts in DMF solvent at 25 °C. Semi-batch copper(0)-mediated living radical copolymerization technique (Cu(0)-mediated LRP) was used for achieving the chain gradient microstructure of the resulting copolymers. We also compared copolymerizations with two different ATRP ligands at ambient temperature allowing control over the molecular weight and polydispersity with a quarter of catalyst concentration versus a conventional ATRP in dipolar protic solvent (i.e. DMF), while the reaction temperature up to 80 °C in a non-polar medium (i.e. toluene) in order to reach the above polymerization efficiency. The addition of a small amount of reducing agent (i.e. hydrazine hydrate) into the reaction system allows the reaction proceeding in the oxygen tolerant system without losing control and decreasing total conversion such as using the reagents without deoxygenating.

Light-Responsive Smart Surface with Controllable Wettability and Excellent Stability

Novel fluorinated gradient copolymer was designed for smart surface with light-responsive controllable wettability and excellent stability. The switchable mechanism and physicochemical characteristics of the as-prepared surface decorated by designed polymeric material were investigated by ultraviolet-visible (UV-vis) spectrum, scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). Thanks to the functional film and surface roughening, etched silicon surface fabricated by copolymer involving spiropyran (Sp) moieties possesses a fairly large variation range of WCA (28.1°) and achieves the transformation between hydrophilicity (95.2° < 109.2°) and hydrophobicity (123.3° > 109.2°) relative to blank sample (109.2°). The synthetic strategy and developed smart surface offer a promising application in coating with controllable wettability, which bridge the gap between chemical structure and material properties.

Synthesis and pH-responsive micellization of brush copolymers poly(methyl methacrylate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate-graft-acrylic acid): role of composition profile

A series of brush copolymers (i.e. poly(methyl methacrylate (MMA)-co-2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM)-graft-acrylic acid (AA))) having three backbone composition profiles, i.e. random, gradient and block, were synthesized via the combination of atom transfer radical polymerization (ATRP)/model-based semibatch ATRcoP and the “grafting from” method. These samples allowed us to systematically investigate the effects of the composition profile (including the grafting density corresponding to the composition profile) on the micelle formation and pH responsivity of the brush copolymers in solution. FTIR, 1H NMR and GPC were used to provide evidence for the formation of the well-defined brush copolymers. TEM, light transmittance and DLS were used to investigate the self-assembly and pH responsivity of the resulting copolymers. It was found that the micelles formed by these copolymers underwent a different conformational transition caused by the change from acidic to basic in the solution. These transitions were mainly influenced by pH and composition profile since the composition profile also had a strong effect on the acid-dissociation degree of the brush copolymer.

Photoinduced Fe-mediated atom transfer radical polymerization in aqueous media

Photoinduced atom transfer radical polymerization with an Fe catalyst was successfully performed in aqueous media for the first time. Three water-soluble ligands [i.e., tetrabutylammonium bromide (TBABr), tris[2-(2-methoxyethoxy)ethyl]amine (TDA), and triphenylphosphine-3,3′,3′′-trisulfonic acid trisodium (TPPSA)] were screened for polymerization in aqueous media. Linear semilogarithmic plots, increasing molecular weights (Mn) with conversion, and low dispersity (Đ < 1.40) were achieved by using a new water-soluble phosphine ligand TPPSA, indicating a well-controlled polymerization. Subsequently, the polymerization kinetics of different catalyst concentrations and the targeted degree of polymerizations were investigated. The applicability of this system to the polymerization of different water-soluble monomers was examined. Furthermore, the polymerization can be regulated by switching the light on and off, which further confirmed its controlled and “living” nature. A successful experiment of chain extension suggested the retention of chain-end functionality. A study of the mechanism showed that the activator (FeIIX2/L) and the additional initiator were generated by the photochemical reduction of FeIIIX3/L in the presence of a monomer. This work provides an environmentally benign ATRP to synthesize well-defined water-soluble materials.

Synthesis and characterization of polyfluorene-based photoelectric materials: the effect of coil segment on the spectral stability

The origin of the low-energy emission of fluorene-based rod-coil block copolymers still remains controversial. In this work, a series of polyfluorene-based rod-coil block copolymers having different coil segments, i.e., poly[2,7-(9,9-dihexylfluorene)]-block-poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate, (PF-b-PHFBMA), PF-b-poly(butylmethacrylate) (PF-b-PBMA), PF-b-poly(2-hydroxyethyl methacrylate) (PF-b-PHEMA) and PF-b-poly(acrylic acid) (PF-b-PAA), were synthesized using the ATRP technique. The optical and surface properties and thermal behaviors of these copolymers were systematically investigated. In particular, different thermal treatment conditions, including annealing temperature, annealing time and annealing atmosphere were introduced to study the effect of coil segment on the copolymer spectral stability. The incorporation of PBMA, PHEMA and PAA segments to PF could indeed improve the copolymer spectral stability, while the PHFBMA block brought undesirable low-energy emission. In addition, water contact angle (WCA) measurements of the copolymer films before and after annealing further demonstrated that the low-energy emission of PF-based rod-coil block copolymers was attributed to the molecular aggregation rather than the formation of fluorenone defects.