Photocatalytic applications with CdS•block copolymer/exfoliated graphene nanoensembles: Hydrogen generation and degradation of Rhodamine B

Amphiphilic block copolymer poly (isoprene-b-acrylic acid) (PI-b-PAA) stabilized exfoliated graphene in water and allowed the immobilization of semiconductor CdS nanoparticles forming CdS•PI-b-PAA/graphene. Characterization with HR-TEM and EDX justified the success of preparation and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS•PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS•PI-b-PAA/graphene, in the presence of ammonium formate as quencher for the photogenerated holes, resulted on the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (> 80±4% at 20 min; 100% at 24 min), much faster and efficient as compared when reference CdS•PI-b-PAA was used as photocatalyst (< 30±3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS•PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS•PI-b-PAA/graphene was rationalized in terms of effective separation of holes–electrons, contrary to reference CdS•PI-b-PAA, in which rapid recombination of the hole–electron pair is inevitable due to the absence of exfoliated graphene as suitable electron acceptor

Assessment of block and random copolymer overlayers on polymer optical fibers towards protein detection through electrostatic interaction

A simple fiber optic based scheme for the selective detection of proteins, based on surface electrostatic interactions, is presented. The implementation of this method is conducted by using a modified polymer optical fiber's (POF) surface and thin overlayers of properly designed sensitive copolymer materials with predesigned molecular characteristics. Block poly(styrene-b-2vinylpyridine) (PS-b-P2VP) and random poly(styrene-r-2vinylpyridine) (PS-r-P2VP) copolymers of the same monomers and similar molecular weights, were modified and used as sensing materials. This configuration proved to be efficient concerning the fast detection of charged proteins, and also the efficient discrimination of differently charged proteins such as lysozyme (LYS) and bovine serum albumin (BSA). Results on the sensing performance of block and random copolymers are also discussed drawing conclusion on their efficiency given their considerable different fabrication cost

Protein detection by polymer optical fibers sensitized with overlayers of block or random copolymers

In this study a low cost and low complexity optical detection method of proteins is presented by employing a detection scheme based on electrostatic interactions, and implemented by sensitization of a polymer optical fiber (POF) surface by thin overlayer of properly designed sensitive copolymer materials with predesigned charges. This method enables the fast detection of proteins having opposite charge to the overlayer, and also the effective discrimination of differently charged proteins like lysozyme (LYS) and bovine serum albumin (BSA). More specifically, as sensitive materials here was used the block and the random copolymers of the same monomers, namely the block copolymer poly(styrene-b-2vinylpyridine) (PS-b-P2VP) and the corresponding random polymer poly(styrene-r-2-vinylpyridine) (PS-r-P2VP), of similar composition and roughly similar molecular weight. Moreover, this work focused on the comparison of the aforementioned sensitive materials regarding the way in which they can adapt on sensing optical platforms and constitute functional sensing bio-materials

Nanoparticles of Block Ionomer Complexes from Double Hydrophilic Poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) Triblock Copolymer and Oppositely Charged Surfactant

The novel water-dispersible nanoparticles from the double hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) triblock copolymer and oppositely charged surfactant dodecyltrimethyl ammonium bromide (DTAB) were prepared by mixing the individual aqueous solutions. The structure of the nanoparticles was investigated as a function of the degree of neutralization (DN) by turbidimetry, dynamic light scattering (DSL),ζ-potential measurement, and atomic force microscope (AFM). The neutralization of the anionic PAA blocks with cationic DTAB accompanied with the hydrophobic interaction of alkyl tails of DTAB led to formation of core–shell nanoparticles with the core of the DTAB neutralized PAA blocks and the shell of the looped PEO blocks. The water-dispersible nanoparticles with negative ζ-potential were obtained over the DN range from 0.4 to 2.0 and their sizes depended on the DN. The looped PEO blocks hindered the further neutralization of the PAA blocks with cationic DTAB, resulting in existence of some negative charged PAA-b-PEO-b-PAA backbones even when DN > 1.0. The spherical and ellipsoidal nature of these nanoparticles was observed with AFM

End-Functionalized Block Copolymers of Styrene and Isoprene: Synthesis and Association Behavior in Dilute Solution

The dilute solution properties of di-and triblock copolymers of isoprene and styrene having a highly polar sulfozwitterion group on one or both ends of the chain were studied in the nonpolar solvent carbon tetrachloride (a good solvent for polystyrene and polyisoprene) by low-angle laser light scattering. The copolymers were prepared by anionic polymerization using high-vacuum techniques with [3-(dimethylamino) propyl]lithium as initiator. The dimethylamino end group of the chain was transformed to a zwitterion by reaction with cyclopropanesultone. The monofunctional zwitterion-capped copolymers were found to associate in carbon tetrachloride, whereas the difunctional versions formed gels even below the coil overlap concentration, c*. The aggregation number was found to decrease with increasing base molecular weight due to the excluded volume repulsions of the copolymeric tails. Comparison with the corresponding ω-zwitterionic polyisoprene homopolymers in cyclohexane and in carbon tetrachloride shows that for the same base molecular weight the materials with the homopolymeric tails aggregate more strongly. Aggregation numbers for the copolymers are of the same order of magnitude as the degree of association measured for a zwitterion-capped polystyrene. The presence of the phenyl rings in the copolymer chain seems to reduce the extent of aggregation. The effect of position and number of the functional groups on the strength of the association is also discussed. © 1994, American Chemical Society. All rights reserved

Synthesis and dilute solution properties of styrene-isoprene diblock copolymers with mesogenic-zwitterionic end groups

Diblock copolymers of styrene and isoprene with an ionic-liquid crystalline end group were synthesized by anionic polymerization high-vacuum techniques. Using (3-dimethylamino)propyllithium as initiator, the dimethylamino group was introduced at either chain end. This group was converted to a zwitterionic-liquid crystalline end group by reaction with 2-{6-[4-(4-methoxyphenylazo)phenoxy]-hexyloxy}- 2-oxo-1,3,2λ5-phospholane. The dilute solution properties of the diblock copolymers, containing approximately 30 wt % PS, were studied in CCl4, a nonpolar equally good solvent for both the polymeric blocks, by means of static and dynamic light scattering and viscometry. Static light scattering experiments indicate that dimers are formed in most cases, except for copolymers with Mw≤12 000. The estimated aggregation numbers were found to be lower than in the case of sulfozwitterionic end-capped copolymers. It seems that the lower polarity of the nitrogen-phosphorus zwitterion and the increased steric hindrance of the mesogenic group attached to the zwitterionic group are mainly responsible for this behavior. Because of the presence of a liquid crystalline group and the polymeric tail directly bonded to the zwitterion, the formation of elongated aggregate structures is difficult in the studied systems as was observed in sulfozwitterion end-functionalized diblocks. Excluded-volume effects play also some role in the dependence of aggregation number on the molecular weight of the polymeric tails. The results from dynamic light scattering and viscometry agree well with the static light scattering picture if the star model is used to derive aggregation numbers from data on hydrodynamic radii of the end-functionalized copolymers