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Abstract We report an innovative and facile approach to fabricating an ultrasensitive plasmonic paper substrate for surface-enhanced Raman spectroscopy (SERS). The approach exploits the self-assembling capability of poly(styrene-b-2-vinyl pyridine) block copolymers to form a thin film at the air-liquid interface within the single microdroplet scale for the first time and the subsequent in situ growth of silver nanoparticles (AgNPs). The concentration of the block copolymer was found to play an essential role in stabilizing the droplets during the mass transfer phase and formation of silver nanoparticles, thus influencing the SERS signals. SEM analysis of the morphology of the plasmonic paper substrates revealed the formation of spherical AgNPs evenly distributed across the surface of the formed copolymer film with a size distribution of 47.5 nm. The resultant enhancement factor was calculated to be 1.2 × 107, and the detection limit of rhodamine 6G was as low as 48.9 pM. The nanohybridized plasmonic paper was successfully applied to detect two emerging pollutants—sildenafil and flibanserin—with LODs as low as 1.48 nM and 3.45 nM, respectively. Thus, this study offers new prospects for designing an affordable and readily available, yet highly sensitive, paper-based SERS substrate with the potential for development as a lab-on-a-chip device.

We report an innovative and facile approach to fabricating an ultrasensitive plasmonic paper substrate for surface-enhanced Raman spectroscopy (SERS). The approach exploits the self-assembling capability of poly(styrene-b-2-vinyl pyridine) block copolymers to form a thin film at the air-liquid interface within the single microdroplet scale for the first time and the subsequent in situ growth of silver nanoparticles (AgNPs). The concentration of the block copolymer was found to play an essential role in stabilizing the droplets during the mass transfer phase and formation of silver nanoparticles, thus influencing the SERS signals. SEM analysis of the morphology of the plasmonic paper substrates revealed the formation of spherical AgNPs evenly distributed across the surface of the formed copolymer film with a size distribution of 47.5 nm. The resultant enhancement factor was calculated to be 1.2 × 107, and the detection limit of rhodamine 6G was as low as 48.9 pM. The nanohybridized plasmonic paper was successfully applied to detect two emerging pollutants—sildenafil and flibanserin—with LODs as low as 1.48 nM and 3.45 nM, respectively. Thus, this study offers new prospects for designing an affordable and readily available, yet highly sensitive, paper-based SERS substrate with the potential for development as a lab-on-a-chip device. [ABSTRACT FROM AUTHOR]

Silver-nanoparticle-doped poly(9-vinylcarbazole) (PVK) nanocomposites were prepared via the reduction of Ag+ ions and the self-assembly of PVK on AgNO3 aqueous solution surfaces. The formed composite nanostructures depended strongly on the experimental temperature. Thick round disks of PVK surrounded by discrete Ag nanoparticles and/or with irregular holes formed at room temperature; nanotubes and micronetworks doped with Ag nanoparticles formed at about 30-40°C, and networks formed at higher temperature. Further investigation revealed that the nanotubes were transformed from thin round disks. The length of the PVK/Ag composite nanotubes were longer than 10 μm, and the average size of the embedded Ag nanoparticles was found to be about 3.5 nm. The composite networks were composed of round pores with diameters of several hundred nanometers and fine silver nanoparticles embedded in the thin polymer films that covered the pores. The formation of the nanotubes was a very interesting self-assembly phenomenon of the polymer at the air-water interface that has not been reported before. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [ABSTRACT FROM AUTHOR]

Abstract: Thin solid films containing luminescent europium complex were fabricated on glass and sol–gel formed TiO2 surfaces modified by phosphate groups and characterized by electron probe microscopy (EPM), fluorescence microscopy (FM) and UV–vis and photoluminescent (PL) spectroscopy. It was found that the two kinds of luminescent films show different morphologies, the film fabricated on TiO2 layer is more homogeneous, and the energy absorbed by TiO2 can be transferred to Eu(III) ions. The thermal and mechanical stability of this inorganic–organic composite material is improved greatly and has important application in electrical and optical devices. [Copyright &y& Elsevier]

Two-dimensional (2D) Janus nanostructures have attracted much interest due to their unique structure and properties, and researchers are making great efforts continuously to explore new preparation methods. Herein, we reported a facile method to fabricate Janus nanosheets with lamellar structures at the air/liquid interface of a water-miscible organic solution of fatty acids and an aqueous solution of metal ions. The organic solution spread on the subphase surface and diffuse into the subphase simultaneously, and the aqueous solution diffused into the organic solution at the same time. Thus, the fatty acid molecules and metal ions self-assembled into layered nanosheets with the aid of hydrophobic interaction of alkyl chains and coordination between carboxylic groups and metal ions in the mixed solution. The sides facing to air and the subphase are composed of alkyl chains and carboxylates, respectively, indicating that the nanosheets are Janus ones. Various organic solvents, metal ions and fatty acid molecules have been tried to fabricate such layered Janus nanosheets. This method is expected to be a useful way to assemble Janus nanostructures. [ABSTRACT FROM AUTHOR]

Two-dimensional helical nanowire and nanosphere superstructures of PS- b -P2VP/S-mandelic acid with homochirality have been fabricated at the liquid/liquid and air/liquid interfaces via two kinds of approaches, respectively. [Display omitted] • PS-b-P2VP co-assembled with S-mandelic acid in the liquid/liquid interfacial phase. • Helical nanowires and nanospheres with homochirality formed. • These nanowires and nanospheres further assembled into 2D superstructures. • This is a one-step method to fabricate 2D superstructures of helical nanostructures. Chiral supramolecules have attracted great research interest due to their unique properties and functions. How to assemble them into the ordered superstructures, however, remains a challenge. In this paper, two methods have been developed to fabricate such superstructures. In method I, polystyrene- b -poly (2-vinylpyridine) (PS- b -P2VP) and S-mandelic acid (S-MA) diffused from the oil and aqueous phases respectively to the oil/water interface, combined and self-assembled into helical nanowires and nanospheres with monochirality, and formed parallel-aligned nanowire arrays and close-packed arrays at the liquid/liquid interface. In method II, PS- b -P2VP in DMF droplets was introduced into the aqueous solution of S-MA through a liquid/liquid interfacial phase transfer process. Then the polymer molecules self-assembled into helical nanowires and nanospheres with monochirality in the aqueous phase, which adsorbed at the air/liquid interface and organized into superstructures. The formation of chiral aggregates should be attributed to the induction of S-MA, while the superstructures at the interfaces were considered to result from the modulation by the interfacial pressures. This study has developed one-step techniques to assemble the chiral aggregates and superstructures, which is expected to become universal for fabrication of functional superstructures. [ABSTRACT FROM AUTHOR]

Large area layered ultrathin films have attracted much attention in recent years, as they have ordered structure, unique properties and potential applications in various areas, such as transportation, separation and catalysis. Herein, we reported the successful preparation of large area layered ultrathin films of a bola-type amphiphilic molecule, perfluorodecanedioic acid (PFDDA) at the liquid/liquid interface in the absence or presence of metal ions. It was found that the ultrathin thin film of PFDDA/Zn(II) has a hexagonal closed packed crystal structure with the crystal parameters of a = 0.302 and c = 1.9 nm. The formation of the film was attributed to the weaker intermolecular interactions, the restriction of the interfacial phase, and the epitaxial growth. However, dodecanedioic acid (DDDA) and docosanedioic acid (DCDA) formed ultrathin nanosheets instead of large area films through this approach, reflecting different self-assembly behavior of the perfluorocarbon chains and the hydrocarbon chains. Large area layered ultrathin films of a bola-amphiphilic perfluorodecanedioic acid were fabricated at the liquid/liquid interface. [Display omitted] • Large area layered ultrathin films of bola-amphiphilic molecules were fabricated. • The amphiphilic molecule is perfluorodecanedioic acid. • The films were fabricated at the planar liquid/liquid interface. • The fabrication process includes nucleation and 2D epitaxial growth. • Amphiphobic effects, coordination or H-bonds are responsible for the film formation. [ABSTRACT FROM AUTHOR]

Ellipsoidal and spherical superstructures, network structure and hierarchical structure of noble metal spherical or rod-like nanoparticles were fabricated through a liquid/liquid interface mass transfer-assisted self-assembly process in aqueous solutions. • A general approach has been developed to fabricate superstructures of nanoparticles. • A liquid/liquid interface mass transfer process was used to introduce amines into hydrosols. • The fatty amines combined with colloidal particles and organized into superstructures. • Ellipsoidal and spherical superlattices of spherical nanoparticles were obtained. • Network and hierarchical structures of nanospheres and nanorods were obtained. Organized assemblies of noble metal nanoparticles (NPs) exhibit unique optical, electronic and catalytic properties and potential applications in various areas. Many kinds of methods have been developed to fabricate such functional systems. In this work, we report a facile and novel method to fabricate the organized aggregates of Au and Ag NPs. Their freshly prepared hydrosols were used as upper phase, and the DMF/chloroform solutions of different fatty amines were used as bottom phases to form a planar liquid/liquid interface. The mass transfer across the interface occurred immediately, where the DMF droplets containing fatty amines entered into the hydrosols, leading to the formation of organized aggregates of NPs through a self-assembly process of amine molecules. It was found that several kinds of assemblies were generated, including ellipsoidal and spherical superstructures of spherical NPs, networks of spherical NPs and nanorods, and hierarchical structure of nanorods. In addition, networks composed of Au NPs/Ag skeleton satellite-core type nanorods were further constructed, which exhibited good catalytic performance and SERS property. [ABSTRACT FROM AUTHOR]

Amphiphilic block copolymers can self-assemble into various aggregates in which functional inorganic nanoparticles and organic chromophores can be incorporated. A variety of fabrication methods have been developed. In this work, the liquid/liquid interface mass transfer-assisted self-assembly method was extended to fabricate composite organized structure of polystyrene-b-polyacrylic acid (PS-b-PAA) with small organic molecules, such as diamines, dopamine and dyes. It was found that long uniform nanowires, hollow spheres and foams were generated when using these organic molecules under different conditions, which correspond to worm-like micelles, vesicles and aggregates of microcapsules, respectively. The length of the nanowires reaches to several tens of micrometers. The influence of the molecular structure of the organic molecules, especially the diamines was investigated and discussed, and the formation mechanism of these aggregates was analyzed. This method may be developed to a facile and useful approach to fabricate functional composite structure of block copolymers and small molecules. [ABSTRACT FROM AUTHOR]

The nanostructures based on polymers have attracted much research interest because of their rich morphologies, unique properties and potential applications in various fields. In particular, helical nanostructures have been research hotspots in recent years. In this work, composite non-helical and helical nanowire arrays of atactic poly(2-vinylpyridine) (P2VP), and block copolymers polystyrene- block -poly(2-vinylpyridine) (PS- b -P2VP) were fabricated successfully with inorganic species such as HAuCl 4 through a liquid/liquid interfacial adsorption and self-assembly approach without addition of any chiral inducers. The formation process of the helical nanowires of P2VP includes the following steps, i.e. adsorption of the polymer molecules and HAuCl 4 at the interface, the following protonation of pyridine groups, straightening of the P2VP chains by mutual repulsion between the protonated pyridine groups, aggregation of the P2VP chains due to the hydrophobic interactions between the backbones, and ordered organization of the pyridine groups through π-π interactions. The helical nanowires of PS- b -P2VP are worm-like micelles with a PS core and a P2VP shell, which are formed through the self-assembly of the block copolymer molecules with HAuCl 4 within the interfacial phase with the help of hydrophobic interaction between the PS blocks and orderly stacking of the P2VP blocks. The different formation mechanisms reflected the effects of molecular structure on the self-assembly of polymers. In addition, the formed nanowires further self-organize into ordered arrays due to the increasing interfacial pressure during the generation of the nanowires. The results of this study expand the scope of research on polymer self-assembly and the application of liquid/liquid interfacial self-assembly techniques to acquire highly ordered supramolecular nanostructures. [Display omitted] • PS and PS-b-P2VP self-assembled into helical nanowires with chloroauric acid. • The nanowires formed in the liquid/liquid interfacial phase. • These nanowires further organized into parallel arrays. • The PS nanowires result from chain straightening, aggregation and ordered packing. • The PS-b-P2VP nanowires are actually worm-like micelles. [ABSTRACT FROM AUTHOR]

PS-b-PAA/copper composite two-dimensional nanoflowers with highly heterogeneous catalytic activity and good stability was fabricated at the liquid/liquid interface. To design and prepare heterogeneous catalysts with both high catalytic activity and good stability is still a challenge. Herein, we fabricated a composite Cu/PS-b-PAA film consisting of unique nanoflowers for the heterogeneous catalytic reactions such as hydrogenation of nitroarenes in aqueous solutions at the planar liquid/liquid interface through the interfacial adsorption and self-assembly process. The nanoflowers are comprised of nanoplates with a thickness of about 10 nm. The nanoplates have layered structure composed of an inner layer of hydrophobic PS and two surface layers of hydrophilic PAA where the copper species are dispersed. The composite film exhibited high catalytic activity for the reduction of p -nitroaniline (p -NA) in aqueous solutions and the rate constant reached to 396.45 s−1 g−1. Inaddition, the composite film also showed good stability and high recyclability without any changes in the rate constant and conversion efficiency in 15 successive cycles. These should be attributed to the special structure of the composite nanoflowers. We developed an excellent heterogeneous catalyst system possessed of both high activity and good stability through delicate design and fabrication. [ABSTRACT FROM AUTHOR]

It is of great importance to explore the self-assembly behavior of amphiphilic block copolymers at the liquid/liquid interface for the construction of hierarchical nanostructures and evaluation of emulsifiers. In this work, the adsorption and self-assembly of PS- b -PEO, a typical amphiphilic and temperature-sensitive block copolymer with abundant coordination sites were investigated by using a liquid/liquid interfacial assembly method in which pure water covered a chloroform solution of PS- b -PEO to form a planar liquid/liquid interface first, and then the aqueous solution of copper acetate was added dropwise into the water. It was found that spontaneous interfacial emulsification occurred when Cu2+ aqueous solution was added into the water at 28 °C. The PS- b -PEOs with shorter PEO chains self-assembled into hollow spheres, hierarchical hollow spheres, and hollow spheres with layered walls, depending on the relative length of the PEO blocks; while the PS- b -PEO with a longer PEO chain formed Janus sheets. While, PS- b -PEOs self-assembled into Janus sheets with monolayer or stepped multilayer structures at 18 and 8 °C through interfacial adsorption and assembly, regulated by the molecular structures. In addition, the concentrations of PS- b -PEO and Cu2+ ions also affect the self-assembly behavior and the aggregate morphologies. [Display omitted] • The liquid/liquid interfacial self-assembly of PS- b -PEOs was investigated. • They self-assembled into various hollow spheres at higher temperature. • The formation of hollow spheres was attributed to spontaneous emulsification. • They self-assembled into monolayer or multilayer Janus sheets at lower temperature. • The self-assembly behavior also depends on molecular structure and metal ions. [ABSTRACT FROM AUTHOR]

Hierarchical composite microstructures of block copolymers, polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)/Ag have been fabricated successfully at the air/liquid interface through a self-assembly and adsorption process. The films with various morphologies including foam, nanorod and nanowire array, hollow sphere, and nanosphere were obtained. These morphologies are closely related to the aggregates formed in the aqueous phase, such as microcapsules, cylindrical micelles, vesicles and spherical micelles, which can be controlled by tuning the critical packing parameters of the amphiphilic block copolymer molecules through changing the concentration of Ag + ions in the aqueous solution. The length of the P2VP blocks in the PS-b-P2VPs exerts great influences on the self-assembly behavior of the polymers and the final microstructures, which provides a deep insight into the formation mechanism of the microstructures. Additionally, these hybrid films doped with silver nanoparticles provide potential application in surface enhanced Raman scattering (SERS) and catalysis. [ABSTRACT FROM AUTHOR]

Large area of nanodot arrays of polystyrene- block -poly(2-vinylpyridine) (PS- b -P2VP) with inorganic species, including phosphotungstic acid, phosphomolybdic acid or transition metal ions have been fabricated at the planar liquid/liquid interface between pure water and chloroform solution of the block copolymers by adding the aqueous solution of the inorganic species dropwise into the water phase. The nanodots arrange into a quasi-hexagonal pattern, the area reaches to several hundreds of square microns, and the size of the nanodots and the distance between the nanodots can be tuned. The formation of the nanodot arrays is attributed to the interaction between the pyridine groups in the P2VP blocks and the inorganic species through electrostatic interaction or coordination that enhances the hydrophilicity of the block copolymers and leads to aggregation of the P2VP blocks during the adsorption and self-assembly process. This is a novel way to fabricate large area of ordered nanostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Composite films with different structures were formed at the liquid/liquid interface. [•] These films are composed of diblock or triblock copolymers and inorganic species. [•] PS-b-P4VP/Au and PS-b-P4VP/Ag have honeycomb and foam structure, respectively. [•] P4VP-b-PS-b-P4VP/Au forms a free-standing film with a nanosphere array structure. [•] Co-adsorption and self-assembly of polymer and the ions lead to the film formation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Composite network and microporous P2VP/Cu(II) structures were fabricated. [•] Composite nano-shuttle and microbelt of P2VP/Cu(OH)2 were obtained. [•] These nanostructures were fabricated at the liquid/liquid interface. [•] Adsorption, hydrolysis and self-assembly processes were involved in the fabrication. [•] The two kinds of nanostructures exhibited different catalytic properties. [Copyright &y& Elsevier]

Abstract: Free-standing films of poly(2-vinylpyridine) doped with Ag+ ions were fabricated at the planar liquid/liquid interface of an aqueous solution of AgNO3 and a chloroform solution of the polymer through adsorption of the polymer molecules, combination with Ag+ ions, and self-assembly of the composite species. Transmission electron microscopic (TEM) investigations indicated that the films were composed of planar thin layers decorated with separated microcapsules and foam structures of conglutinated microcapsules, and no Ag nanoparticles formed in the pristine films. After UV-light irradiation and KBH4 aqueous solution treatment, Ag nanoparticles with the average size of 3.2nm appeared and incorporated in the polymer matrices. X-ray photoelectron spectra (XPS) and UV–vis spectra are consistent with the TEM observations. Thermogravimetric analysis (TGA) showed good thermal stability of the composite films. The silver content was estimated to be 24.0% from the TG curve, closing to the calculated value. The catalytic performance of the composite films was evaluated by using the reduction of nitro-compounds, including nitrobenzene, 4-nitrophenol, and 4-nitrobenzoic acid by KBH4 in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity. The apparent reaction constants are related to the size of the nitro-compounds, suggesting that the Ag nanoparticles were incorporated in the matrices, and the diffusion of the reactant molecules has a great influence on the catalytic reaction. [Copyright &y& Elsevier]

Abstract: Free-standing thin films of poly(2-vinylpyridine) (P2VP) doped with platinum complex ions were fabricated at the planar aqueous solution of H2PtCl6/chloroform solution of P2VP interface. The formation of the free-standing thin films was attributed to the adsorption and combination of the polymer molecules and the complex ions at the interface, and self-assembly of the composites. The films were composed of thin layers decorated with separated and conglutinated microcapsules. After treatment with KBH4 aqueous solution, the platinum complex ions incorporated in the polymer matrices transformed to platinum nanoparticles with the mean size of 2.2nm, which was confirmed by transmission electron microscopic investigations and X-ray photoelectron spectroscopic (XPS) analysis of the samples. Both the contents of the platinum element in the untreated and treated composite films estimated based on the thermagravimetric analysis (TGA) were close to each other, indicating no loss of platinum during the treatment process. The catalytic activity of the composite films was evaluated by using the reduction of 4-nitrophenol by KBH4 in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity. [Copyright &y& Elsevier]

Self-assembly behavior of amphiphilic block copolymers has attracted much attention recently. In this paper, a novel liquid/liquid interface-mediated self-assembly behavior of block copolymer is reported. An aqueous solution of HAuCl 4 and a chloroform solution of poly(2-vinylpyridine)- block -polycaprolactone (P2VP 199 -b-PCL 22) are employed as the upper phase and the bottom phase, respectively. Structural transitions from toroids and plate like structures to vesicles and large compound vesicles are observed in the bottom phase by using transmission electron microscopy (TEM). It is proved that vesicles and large compound vesicles are formed through adsorption and desorption of copolymers at the liquid/liquid interface, molecular aggregation and microphase separation in the bottom phase due to the amphiphilic property of protonated P2VP 199 -b-PCL 22. The well-dispersed Au nanoparticles are formed during the self-assembly process and embedded in the bilayers of the vesicles. The concentrations of HAuCl 4 and P2VP 199 -b-PCL 22 have an effect on the self-assembly behavior. A unique structure, "pearl necklace", is obtained at higher concentrations. In addition, it was found that P2VP 252 -b-PCL 44 also formed vesicles, while P2VP 195 -b-PCL 75 and P2VP 195 -b-PCL 307 formed spherical micelles in the bottom phase through the same approach. The dependence of the aggregate morphology and the molecular structure was discussed based on the critical packing parameter, p. Vesicles and large compound vesicles were generated through a liquid-liquid interface-mediated self-assembly process including adsorption, desorption, aggregation, and microphase separation steps. Unlabelled Image • Composite vesicles, compound vesicles and micelles of block copolymer/Au nanoparticles were generated. • These aggregates were formed through a liquid/liquid interface mediated process. • The block copolymer molecules adsorbed at the interface, combined with inorganic ions and returned to the organic phase. • The composite molecules formed aggregates in the organic phase through self-assembly and microphase separation. • The morphology of the aggregates depends on the critical packing parameters of the composite block copolymers. [ABSTRACT FROM AUTHOR]

Composite nanostructures of PS-b-PAA/Mn+ with various morphologies were fabricated in solutions, emulsions and at interfaces. • A DMF−CHCl 3 solution of PS-b-PAA/aqueous solution of salt interface was constructed. • O/W and W/O emulsions were generated through a spontaneous emulsification process. • PS-b-PAA self-assembled into various organized aggregates in these emulsions. • The molecular structure of PS-b-PAA greatly affects the self-assembly behavior. • The concentration and sort of the metal ions also affect the self-assembly behavior. Composite organized molecular assemblies of amphiphilic block copolymers exhibit various properties and functionalities and have attracted much attention recently. Many research studies have focused on adjusting these properties by varying the fabrication approach and by controlling the morphology of the aggregates. This work involved an investigation of the self-assembly behavior of a series of polystyrene-b-polyacrylic acid (PS-b-PAA) homologues with different block ratios in water-in-oil (W/O) and oil-in-water (O/W) emulsions. These emulsions simultaneously formed via a spontaneous emulsification process across the liquid/liquid interface. A variety of aggregates of the polymers with metal ions were obtained, including microcapsules, spherical micelles, rod-like and disc-like micelles, vesicles, and interior microphase-separated particles. These structures formed either in the emulsion droplets or in the continuous phase, and then proceeded to adsorb at the air/liquid interface or the planar liquid/liquid interface to form thin films. The influence of the molecular structure, the concentration of the metal ions, and the nature of the metal ion on the self-assembly behavior of the polymer molecules and the aggregate morphologies is discussed. In addition, these composite structures are shown to exhibit higher catalytic activity and good stability for the hydrogenation of nitroarenes in aqueous solutions. [ABSTRACT FROM AUTHOR]