Jin-Jin Li

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.

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.

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.