Fabrication of metallized nanoporous films from the self-assembly of a block copolymer and homopolymer mixture

Inorganic compound HAuCl4, which can form a complex with pyridine, is introduced into a poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) block copolymer/poly(methyl methacrylate) (PMMA) homopolymer mixture. The orientation of the cylindrical microdomains formed by the P2VP block, PMMA, and HAuCl4 normal to the substrate surface can be generated via cooperative self-assembly of the mixture. Selective removal of the homopolymer can lead to porous nanostructures containing metal components in P2VP domains, which have a novel photoluminescence property.     

Adsorption of poly(N-isopropylacrylamide-co-4-vinylpyridine) onto core-shell poly(styrene-co-methylacrylic acid) microspheres

Adsorption of the thermoresponsive copolymer of poly(N-isopropylacrylamide-co-4-vinylpyridine) (PNIPAM-co-P4VP) onto the core-shell microspheres of poly(styrene-co-methylacrylic acid) (PS-co-PMAA) is studied. The core-shell PS-co-PMAA microspheres are synthesized by one-stage soap-free polymerization in water. The copolymer of PNIPAM-co-P4VP is synthesized by free radical polymerization of N-isopropylacrylamide and 4-vinylpyridine in the mixture of DMF and water using K₂S₂O₈ as initiator. Adsorption of PNIPAM-co-P4VP onto the core-shell PS-co-PMAA microspheres results in formation of the composite microspheres of PS/PMAA-P4VP/PNIPAM. The driven force to adsorb the copolymer of P4VP-co-PNIPAM onto the core-shell PS-co-PMAA microspheres is ascribed to hydrogen-bonding and electrostatic affinity between the P4VP and PMAA segments. The resultant composite microspheres of PS/PMAA-P4VP/PNIPAM with surface chains of PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 33 °C.     

Dynamic Supramolecular Ruthenium-Based Gels Responsive to Visible/NIR Light and Heat

A simple supramolecular crosslinked gel is reported with a photosensitive ruthenium bipyridine complex functioning as a crosslinker and poly(4-vinylpyridine) (P4VP) as a macromolecular ligand. Irradiation of the organogels in H₂O/MeOH with visible and NIR light (in a multiphoton process) leads to cleavage of pyridine moieties from the ruthenium complex breaking the cross-links and causing degelation and hence solubilization of the P4VP chains. Real-time (RT) photorheology experiments of thin films showed a rapid degelation in several seconds, whereas larger bulk samples could also be photocleaved. Furthermore, the gels could be reformed or healed by simple heating of the system and restoration of the metal–ligand crosslinks. The relatively simple dynamic system with a high sensitivity towards light in the visible and NIR region make them interesting positive photoresists for nano/micropatterning applications, as was demonstrated by writing, erasing, and rewriting of the gels by single- and multiphoton lithography.     

Water-soluble surface-anchored gold and palladium nanoparticles stabilized by exchange of low molecular weight ligands with biamphiphilic triblock copolymers

A study is presented of the stabilization of gold and palladium nanoparticles (NPs) via a place-exchange reaction. Au and Pd NPs of approximately 3.5 nm were prepared by a conventional method using tetraoctylammonium bromide (TOAB) as the stabilizing agent. The resulting nanoparticles, referred to as Au-TOAB or Pd-TOAB, were later used as templates for the replacement of TOAB ligand with poly(ethylene oxide)- b-polystyrene- b-poly(4-vinylpyridine) (PEO- b-PS- b-P4VP) triblock copolymer. This biamphiphilic triblock copolymer was synthesized by atom transfer radical polymerization (ATRP) with control over the molecular weight and polydispersity. The place-exchange reaction was mediated through strong coordination forces between the 4-vinylpyridine copolymer and the metal species located on the surface of the nanoparticles. In addition, the displacement of the outgoing low molecular weight TOAB ligands by high molecular weight polymers is an entropy-assisted process and is believed to contribute to stabilization. The prepared complex, polymer-NP, exhibits greatly improved stability over the metal-NP complex in common organic solvents for the triblock copolymer. Self-assembly in water after ligand exchange resulted in micellar structures of about approximately 20 nm (electron microscopy) with the metal NP found located on the surface of the micelles. The stability of the nanoparticles in water was shown to depend greatly on the grafting density of the copolymer, with high stability (more than 6 months) at high grafting density and low stability, accompanied with irreversible agglomeration, at relatively low grafting densities. The surprising location of the metal NP (for both Au and Pd) on the surface of the micelles in water is explained by the fact that, upon self-assembly in THF/water system, the most hydrophobic chains (i.e., PS) undergo self-assembly first at low water content forming the core, followed by the P4VP (whether or not associated with the metal) forming a shell, and finally the PEO forming the corona. In lower metal content assemblies, the P4VP chains located in the shell undergo swelling in an acidic medium causing a substantial increase in micellar corona size, as confirmed by dynamic light scattering measurements. The present study offers a simple approach for the stabilization of various metal nanoparticles of catalytic interest, using a unique polymeric support that can be dispersed in organic solvents as well as aqueous solutions.     

Thermal degradation of poly(vinylpyridine)s

The thermal stability and the temperature at which maximum degradation yields are detected were quite similar for both poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP). However, considerable differences among the thermal degradation products of both polymers were detected indicating a correlation between the polymer structure and the degradation mechanism. Direct pyrolysis mass spectrometry analyses revealed that P2VP degrades via a complex degradation mechanism, yielding mainly pyridine, monomer, and protonated oligomers, whereas depolymerization of P4VP takes place in accordance with the general thermal behaviour of vinyl polymers. The complex thermal degradation behaviour for P2VP is associated with the position of the nitrogen atom in the pyridine ring, with σ-effect.     

Immobilization of Tris-(8-hydroxyquinoline) aluminum onto P4VP polymer thin films by UV irradiation cross-linking

We report a novel method for the immobilization of Tris-(8-hydroxyquinoline) aluminum (Alq₃) onto poly(4-vinylpyridine) (P4VP) thin polymer films by UV irradiation cross-linking. The polymer films were prepared by spin-coating of P4VP onto cleaned silicon wafer surface followed by UV irradiation. The thicknesses of the polymer thin films were measured by ellipsometry with different irradiation times. The immobilization of Alq₃, orientation and the surface activity were followed using photoluminescence and UV-visible spectroscopy. The surface morphology was investigated by using field emission scanning electron microscopy and atomic force microscopy. Patterning of Alq₃ on P4VP film was obtained using photolithography technique. Our experimental results show that the cross-linked P4VP thin film is a universal surface modifier.     

An approach for the surface functionalized gold nanoparticles with pH-responsive polymer by combination of RAFT and click chemistry

In this report, we demonstrated a novel efficient post-modification route for preparation of smart hybrid gold nanoparticles with poly(4-vinylpyridine) (P4VP) based on RAFT and click chemistry. A new azide terminated ligand was first synthesized to modify gold nanoparticles by ligand exchange reaction, and then click reaction was used to graft alkyne terminated P4VP which was prepared by RAFT onto the surface of gold nanoparticles. The functionalized hybrid gold nanoparticles were characterized by TEM, FTIR, and XPS etc. The results indicated that the P4VP was successfully grafted onto the surface of gold nanoparticles by click reaction. The surface grafting density was calculated to be about 6 chains/nm²_. In addition, the hybrid gold nanoparticles showed a pH responsive phenomenon as the pH value changed around 5.     

聚(丙烯酸钠-4-乙烯基吡啶)的生物降解性和功能性研究

用自由基共聚法制备了一系列可生物降解的功能聚合物聚(丙烯酸钠-4-乙烯基吡啶)[P(SA-co-4VP)],研究了其组成和分子量与生物降解性、资合性及分散性间的关系.结果表明:聚合物中小乙烯基吡啶含量越大,P(SA-co-4VP)的生物降解越显著.分子是一定时,少量的个乙烯基吡啶引入聚丙烯酸钠主链是增强聚合物生物降解性和保持原有功能特性的有效途径.     

Responsive polymer/gold nanoparticle composite thin films fabricated by solvent-induced self-assembly and spin-coating

Self-assembled poly(4-vinylpyridine)-grafted gold (Au) nanoparticles (NPs) and polystyrene-b-poly(4-vinylpyridine) block copolymers were fabricated by the introduction of a selective solvent to a common solution. The assembled mixtures were spin-coated onto solid substrates to fabricate composite gold/polymer thin films composed of copolymer-hybridized Au NPs and independent copolymer micelles. The obtained composite Au thin films had variable localized surface plasmon resonance (LSPR) bands and microscopic morphologies upon vapor annealing with selective solvents because the adsorption and dissolving of solvent molecules into the films could rearrange the copolymer block. The hybrid nanostructured Au thin films may have potential in vapor sensing and organic assays.     

PEO-b-P4VP/Yttrium Hydroxide Hybrid Nanotubes as Supporter for Catalyst Gold Nanoparticles

The adsorption of poly (ethylene oxide)-b-poly(4-vinylpyridine)(PEO-b-P4VP) micelles onto the surface of yttrium hydroxide nanotubes (YNTs) resulted in the hybrid nanotubes with a dense P4VP inner layer and a stretched PEO outer layer surrounding YNTs. The dense P4VP layer was further stabilized by the crosslinking using 1,4-dibromobutane as the crosslinker. Then, the crosslinked hybrid nanotubes (CHNTs) were used as a novel nano supporter for loading the catalyst gold nanoparticles (GNPs) within the crosslinked P4VP layer. The resultant GNPs/CHNTs (GNTs loaded on CHNTs) were applied to catalyze the reduction reaction of p-nitrophenol. The results indicate that this novel nano supporter has advantages such as good dispersity in the suspension, high capacity in loading GNPs (0.87 mmol/g), high catalytic activity of the loaded GNPs (12.9 μmol^-1min^-1), and good reusability of GNTs/CHNTs.     

Self-assembly behavior of A-B diblock and C-D random copolymer mixtures in the solution state through mediated hydrogen bonding

We have synthesized poly(methyl methacrylate- b-4-vinylpyridine) (PMMA- b-P4VP) and poly(styrene- r-vinylphenol) (PS- r-PVPh) copolymers by using anionic and free radical polymerizations, respectively. Well-defined micelles through hydrogen bonding have been prepared by mixing PMMA- b-P4VP diblock copolymer and PS- r-PVPh random copolymer in a single solvent. Block copolymers were mixed with random copolymers, with various [N]/[OH] ratios (4/1, 2/1, 1/1, and 1/4) in which "[N]/[OH]" represents the molar ratio of pyridine groups on P4VP to hydroxyl groups on PVPh. The presence distribution of PVPh/P4VP and PVPh/PMMA hydrogen bonding depends on the feeding ratio of PVPh to P4VP. When the PVPh content is lower than that of P4VP, hydrogen bonding occurs only between PVPh and P4VP; with excess PVPh, additional hydrogen bonding between PVPh and PMMA would occur. Furthermore, the effect of the solvent quality on the self-assembly behavior of PMMA- b-P4VP/PS- r-PVPh blends is investigated by considering tetrahydrofuran (THF) and dimethylformamide (DMF) as common solvents. We can mediate the strength of hydrogen bonding in blend systems by adopting different solvents and inducing different morphology transitions.     

Transport of organic and inorganic solutes through charged mosaic composite membranes

A template pattern with alternating poly(4-vinylpyridine) (P4VP)/poly(vinyl alcohol) (PVA) lamellae was fabricated upon a microporous poly(vinyl chloride) (PVC) membrane by casting of poly[4-vinylpyridine(4VP)-g-vinyl alcohol (VA)] graft copolymer. After a treatment of both binding of microporous membrane with graft copolymer and domain fixing of the PVA matrix, a dilute solution of poly[acrylic acid (AA)-benzyl N,N-dimethyldithiocarbamate (DMTC)]/P4VP or poly[sodium p-styrenesulfonate (SSS)-DMTC]/P4VP binary blend was cast on this template surface. Two types of weak acid/strong base or strong acid/strong base microdomains formed by phase growth were oriented perpendicularly to the membrane surface. After the chemical treatments: introduction of the charge and domain fixing of ion exchange regions, two types of such mosaic microdomains could be constructed on a microporous membrane. We studied the transport behaviors of organic and inorganic solutes through charged mosaic composite membranes. The permeability of inorganic electrolyte, such as KCl was about 20-fold compared to those of organic nonelectrolytes, such as glucose and sucrose. l-Phenylalanine exhibits a low value of permeability at the pH of its isoelectric point.     

Preparation and catalytic activity of P4VP–Cu(II) complex supported on silica gel

Micron-sized silica gel particles were chemically modified on their surfaces with the coupling agent, γ-methacryloxypropyl trimethoxysilane (MPS), double bond was introduced onto the surfaces of silica gel particles, and the modified particles MPS–SiO₂ were obtained. Then, poly(4-vinylpyridine) (P4VP) was grafted from the silica gel surfaces, and grafting particles P4VP/SiO₂ was prepared. Finally, the coordination between grafted P4VP and cupric ions Cu²⁺ was performed, and the supported complex Cu(II)–P4VP/SiO₂ was obtained. The grafting particles P4VP/SiO₂ and the supported complex Cu(II)–P4VP/SiO₂ were characterized with infrared spectra (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Cu(II)–P4VP/SiO₂ was used as a catalyst for the oxidation of ethyl benzene into acetophenone with molecular oxygen under ordinary pressure. The experimental results show that the supported complex Cu(II)–P4VP/SiO₂ can be successfully prepared via grafting polymerization of 4VP and coordination between the grafted P4VP and cupric ions Cu²⁺. In oxidation of ethyl benzene into acetophenone by molecular oxygen under ordinary pressure, the supported complex Cu(II)–P4VP/SiO₂ displayed high catalytic activity and excellent catalytic selectivity up to more than 98% for the transformation of ethyl benzene to acetophenone.     

Balance of hydrophobic and electrostatic forces in the pH response of weak polyelectrolyte capsules

A detailed study of the role of solution pH and ionic strength on the swelling behavior of capsules composed of the weak polyelectrolytes poly(4-vinylpyridine) (P4VP) and poly(methacrylic acid) (PMA) with different numbers of layers was carried out. The polyelectrolyte layers were assembled onto silicon oxide particles and multilayer formation was followed by zeta-potential measurements. Hollow capsules were investigated by scanning electron microscopy and atomic force microscopy. The pH-dependent behavior of P4VP/PMA capsules was probed in aqueous media using confocal laser scanning microscopy. All systems exhibited a pronounced swelling at the edges of stability, at pHs of 2 and 8.1. The swelling degree increased when more polymer material was adsorbed. The swollen state can be attributed to uncompensated positive and negative charges within the multilayers, and it is stabilized by counteracting hydrophobic interactions. The swelling was related to the electrostatic interactions by infrared spectroscopy and zeta-potential measurements. The stability of the capsules as well as the swelling degree at a given pH could be tuned, when the ionic strength of the medium was altered.     

Electroless deposition of nickel on fluoropolymers modified by surface graft copolymerization

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) films via UV-induced graft copolymerization with 4-vinylpyridine (4VP), 2-vinylpyridine (2VP) or 1-vinylimidazole (VIDz) was carried out. Electroless deposition of nickel could be carried out on these graft-modified fluoropolymer surfaces after PdCl₂ activation. The surface compositions of the graft-modified films were studied by X-ray photoelectron spectroscopy. The adhesion strength between the surface graft-copolymerized fluoropolymer film and the electrolessly deposited nickel was affected by the type of monomers used for graft copolymerization and the graft concentration. The optimum T-peel adhesion strengths of the electrolessly deposited Ni on the 4VP graft-copolymerized PTFE and PVDF surfaces were about 7 and 13 N/cm, respectively. The metal/fluoropolymer assemblies delaminated by cohesive failure inside the fluoropolymer substrates. The enhanced adhesion between the electrolessly deposited Ni and the surface-modified fluoropolymers is attributable to the interfacial charge transfer interactions between the grafted polymer chains and the deposited metals (Pd and Ni), the spatial distribution of the graft chains into the metal matrix and the covalent tethering of the graft chains on the fluoropolymer surface.     

Janus复合材料调控界面

Janus材料集成不同组成/功能于一体,具有明确的空间分区特征,是一类特殊的高分子复合功能材料.有机高分子链提供亲水/亲油及响应特性,无机组成提供丰富的光、电、磁、热等功能性.两亲性的Janus材料在高效稳定界面同时,还能赋予界面功能性并可在外场作用下实现操控.本文重点总结了不同结构和功能的Janus材料在稳定界面和调控界面的近期主要进展,包括聚集行为、固体乳化剂、界面增容、界面催化、功能涂层、细胞诊断与治疗等方面.     

CONDUCTING BLENDS OF POLY (2-VINYL PYRIDINE) AND POLYETHYLENE OXIDE WITH HIGH MOLECULAR WEIGHT

Ionic, electronic and mixed (ionic-electronic) conductivities of blends of poly(2-vinylpyridine) (P2VP) and poly(ethylene oxide) (PEO) with high molecular weight after dopedwith LiClO_4, TCNQ or LiClO_4 and TCNQ were investigated. Effects of LiClO_4 and TCNQconcentrations on the conductivity of PEO/P2VP/LiClO_4 or TCNQ blend were studied.The ionic conductivity of PEO/P2VP/LiClO_4 blend increases with increasing PEO content.At a Li/ethylene oxide molar ratio of 0.10 and a TCNQ/2-vinyl pyridine molar ratio of 0.5,the mixed conductivity of PEO / P2VP / LiClO_4 / TCNQ is higher than the total of ionicconductivity of PEO/P2VP/LiClO_4 and electronic conductivity of PEO/P2VP/TCNQwhen the weight ratio of PEO and P2VP is 6/4 or 5/5. Scanning electron microscopy(SEM) on the broken cross-section of the PEO/P2VP/LiClO_4 blend and differential scan-ning calorimetry (DSC) results show that LiClO_4 could act as a compatibilizer in the blend.     

多嵌段共聚物(P4VP-b-PS-b-P4VP)_n的胶束化行为研究

研究了一系列具有不同链段长度和组成的聚4-乙烯基吡啶-聚苯乙烯-聚4-乙烯基吡啶多嵌段共聚物(P4VP-b-PS-b-P4VP)n在其选择性溶剂甲苯和pH<3的水中的胶束化过程,主要研究了多嵌段共聚物链段长度、溶液浓度和溶剂对其胶束形态的影响.透射电镜和原子力显微镜结果表明随着P4VP段链的相对增长,多嵌段共聚物在甲苯中的胶束形态由蠕虫链状向短棒状到球状胶束变化,而其在pH<3的水溶液中均形成球形胶束.由于特殊的链结构,聚合物的浓度对(P4VP-b-PS-b-P4VP)n多嵌段共聚物的胶束行为和胶束形态有着重要的影响.同时,(P4VP-b-PS-b-P4VP)n多嵌段共聚物分子量分布的多分散性对其在选择性溶剂中的胶束形态也有所影响.     

Organosulfur-functionalized Au, Pd, and Au-Pd nanoparticles on 1D silicon nanowire substrates: preparation and XAFS studies

A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes.     

Changes in thermodynamic interactions at highly immiscible polymer/polymer interfaces due to deuterium labeling

Deuterium labeling has been shown previously to affect thermodynamic interactions at polymer surfaces, polymer/polymer heterogeneous interfaces, and in bulk (away from a surface or interface). However, the changes in polymer-polymer interactions due to deuterium labeling have not been thoroughly investigated for highly immiscible systems. It is shown here that deuterium labeling can influence polymer-polymer interactions at heterogeneous interfaces with highly immiscible systems, namely, polystyrene/poly(2-vinylpyridine) (PS/P2VP), polystyrene/poly(4-vinylpyridine) (PS/P4VP), and polystyrene/poly(methyl methacrylate) (PS/PMMA). Using secondary ion mass spectrometry, segregation of deuterium labeled polystyrene (dPS) in a dPS + unlabeled PS (dPS:hPS) blend layer was observed at the dPS:hPS/hP2VP, dPS:hPS/hP4VP, and dPS:hPS/hPMMA heterogeneous interfaces. However, a reference system involving PS on a PS brush shows no segregation of dPS to the interface.