Grafting of poly(acrylic acid) onto an aluminum surface

Chain-Extendable Crosslinked Hydrogels Using Branching RAFT Modification

Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition–fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA–EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Ammonia Gas Detection under Various Humidity Conditions Using Waveguide Surface Plasmon Resonance Spectroscopy

Analysis of NH₃ gas under various humidity conditions was conducted using a waveguide surface plasmon resonance (SPR) sensor with dual sensing parts. Two pairs of Ag films/sensing polymer films were prepared separately on a waveguide core of BK-7 slide glass. Poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) were used as sensing materials. A white light was guided through the core by illuminating the substrate edge, and the SPR property was investigated by observing the output light spectrum. The thicknesses of PAA and PVA films were adjusted to induce SPR at different wavelengths. PAA exhibited remarkable response against NH₃ gas, but it also exhibited a strong dependence on humidity. In contrast, PVA responded to humidity but hardly responded to NH₃ gas below 20 ppm. The dual sensing would allow us to conduct precise NH₃ measurements under various humidity conditions.

Liquid/Liquid interfacial fabrication of thermosensitive and catalytically active Ag nanoparticle-doped block copolymer composite foam films

An aqueous solution of AgNO3 (upper phase) and a DMF/CHCl3 solution of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) or PS-b-PAA-b-PS/1,6-diaminohexane (DAH) (lower phase) constituted a planar liquid/liquid interface. The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the "ouzo effect". Polymer molecules, DAH molecules, and Ag(+) ions assembled into microcapsules around emulsion droplets that adsorbed at the planar liquid/liquid interface, resulting in formation of a foam film. DAH acted as a cross-linker during this process. Transmission electron microscopic observations indicated that Ag nanoclusters that were generated through reduction of Ag(+) ions by DMF were homogeneously dispersed in the walls of the foam structure. X-ray photoelectron spectroscopic investigations revealed that Ag(I) and Ag(0) coexisted in the film, and Ag(I) transformed to Ag(0) after further treatment. The film formed without DAH was not stable, while the film formed with DAH was very stable due to intermolecular attraction between PAA and DAH and formation of amides, as revealed by FTIR spectra. The film formed with DAH exhibited high and durable catalytic activity for hydrogenation of nitro compounds and, very interestingly, exhibited thermoresponsive catalytic behavior.

Fabrication of composite polymer foam films at the liquid/liquid interface through emulsion-directed assembly and adsorption processes

The foam films of polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-b-PAA-b-PS) doped with Cd(II) or Pb(II) species were fabricated at the planar liquid/liquid interfaces between a DMF/chloroform (v/v: 1/1) solution of the polymer and aqueous solutions containing cadmium acetate or lead acetate at ambient temperature. Optical microscopic observation shows the thin film is uniform on a larger length scale. Transmission electron microscopic (TEM) investigations reveal that the foam films are made up of microcapsules with the size of several hundreds of nanometers to micrometers. The walls of the microcapsules have a layered structure decorating with nanofibers and hollow nanospheres, where numerous inorganic fine nanoparticles are dispersed homogeneously. The film formation is a result of emulsion droplet-templated assembly and adsorption of the formed microcapsules at the planar liquid/liquid interface. Because of the miscibility of DMF with chloroform and water, DMF migrates to the aqueous phase while water migrates to the organic phase across the interface, resulting in the formation of a W/O emulsion, as revealed by optical microscopic observation, freeze fracture transmission electron microscopic (FF-TEM) observation, and dynamic laser scattering (DLS) investigation. The triblock copolymer molecules and the inorganic species adsorb and self-assemble around the emulsion drops, leading to the formation of the composite microcapsules. X-ray photoelectron spectroscopic (XPS) and FTIR spectroscopic results indicate that two kinds of Cd(II) or Pb(II) species, metal oxide or hydroxide, resulting from the hydrolysis of the metal ions and the coordinated metal ions to the carboxyl groups coexist in the formed thin films, which transform to metal sulfide completely after treating with hydrogen sulfide to get metal sulfide nanoparticle-doped polymer thin films.

CVD of polymeric thin films: applications in sensors, biotechnology, microelectronics/organic electronics, microfluidics, MEMS, composites and membranes

Polymers with their tunable functionalities offer the ability to rationally design micro- and nano-engineered materials. Their synthesis as thin films have significant advantages due to the reduced amounts of materials used, faster processing times and the ability to modify the surface while preserving the structural properties of the bulk. Furthermore, their low cost, ease of fabrication and the ability to be easily integrated into processing lines, make them attractive alternatives to their inorganic thin film counterparts. Chemical vapor deposition (CVD) as a polymer thin-film deposition technique offers a versatile platform for fabrication of a wide range of polymer thin films preserving all the functionalities. Solventless, vapor-phase deposition enable the integration of polymer thin films or nanostructures into micro- and nanodevices for improved performance. In this review, CVD of functional polymer thin films and the polymerization mechanisms are introduced. The properties of the polymer thin films that determine their behavior are discussed and their technological advances and applications are reviewed.