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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]

A new and facile strategy to fabricate composite thin films with tunable morphologies via self-assembly of block copolymer molecules at the air/liquid interface is first reported. The morphologies (parallel nanowires and foams) of these freestanding thin films can be tuned by varying the molecular structure or other experimental conditions. [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]

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]

Hypothesis Our previous studies have shown that the metal nanoparticle/polymer composite structures fabricated at the liquid/liquid interface have good reusability but lower catalytic activity for heterogeneous reactions in aqueous solutions. This should be attributed to the poor water wettability and more compact structure of the polymer matrices. Therefore, it should be possible to improve the catalytic activity through designing and fabricating a porous composite structure with good water wettability. Experiments A modified liquid/liquid interface adsorption and fabrication method was used. An aqueous solution of copper acetate and a chloroform/DMF mixed solution of PS- b -PAA acted as the two phases. Through spontaneous emulsification, self-assembly of the polymer molecules with Cu 2+ ions in the droplets, and adsorption of the formed spherical micelles and nanofibers to the planar liquid/liquid interface, a porous composite microstructure was formed. Findings This structure consisted of nanofiber-connected nanospheres which have a PS core and a PAA corona. Tiny and well-dispersed Cu nanoparticles were embedded in the hydrophilic corona and were adsorbed on the nanofibers surface as well. After physical cross-linking with 1,6-diaminohexane, the composite material exhibited high catalytic activity and good reusability for the reactions in aqueous solutions. For example, the rate constant for the reduction of p -nitroaniline reached 1965 s −1  g −1 . [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]

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]

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]

An emulsion-directed assembly and adsorption approach has been used to fabricate composite films of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) and Eu 3+ and La 3+ ions at the planar liquid/liquid interface of the polymer DMF/chloroform (1:1, v/v) mixed solution (lower phase) and aqueous solutions of the corresponding salts (upper phase). The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the “ouzo effect”. Polymer molecules and the metal ions assembled around emulsion droplets that adsorbed at the planar liquid/liquid interface at last, resulting in formation of composite films. The film morphologies and structures depend on Ln 3+ ions: polymer/Eu 3+ composite films were foam films composed of microcapsules ranging in size from several hundreds of nanometers to micrometers, while polymer/La 3+ composite films were composed of hollow spheres several tens of nanometers in size. Fourier transform infrared (FTIR) spectra revealed that the coordination modes of carboxyl groups to Eu 3+ and La 3+ were bridging bidentate and ionic, respectively, in the two types of composites. These results indicate that stable microcapsules can be fabricated around droplets for polymer/Eu 3+ systems, while microcapsules of polymer/La 3+ are unstable. This leads to different film morphologies and structures. Compositions of these films were characterized using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, foam films of polymer/Eu 3+ /2,2′-bipyridine (bpy) were fabricated using this approach, and their photoluminescence properties were investigated. [ABSTRACT FROM AUTHOR]

Abstract: Gold nanoparticle-doped poly(2-vinylpyridine)-block-polystyrene-block-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP) thin films were prepared at the planar liquid/liquid interface between the chloroform solution of the polymer and aqueous solution of HAuCl4. Transmission electron microscopic (TEM) investigations revealed that foam films composed of microcapsules as well as one-dimensional belts were formed, and numerous Au nanoparticles were incorporated in the walls of the microcapsules and the nanobelts. The walls and the belts have layered structure. The formation mechanism of the foams and the belts was attributed to adsorption of the polymer molecules, combination of the polymer molecules with AuCl4 − ions, microphase separation and self-assembly of the composite molecules at the interface. This microstructure is different apparently from those formed in solutions, in casting or spin-coating thin films and at the air/water interface of this triblock copolymer, reflecting unique self-assembly behavior at the liquid/liquid interface. This microstructure is also different from those formed by homo-P2VP and P4VP-b-PS-b-P4VP at the liquid/liquid interface, indicating the effects of molecular structures on the self-assembly behaviors of the polymers. After further treatment by UV-light irradiation and KBH4 aqueous solution, the gold species were reduced completely, as indicated by UV–vis spectra and X-ray photoelectron spectra (XPS). Thermogravimetric analysis indicated that the composite films have high thermal stability, and the content of gold was estimated to be about 9.1%. These composite films exhibited high catalytic activity for the reduction of 4-nitrophenol by KBH4 in aqueous solutions. [Copyright &y& Elsevier]

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]

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]