Point of zero potential of single-crystal electrode/inert electrolyte interface

In this work, a method to prepare a thermally stable QDs/clay powder is reported. First, several water soluble CdTe QDs characterised by different size-dependent emission wavelengths were synthesised through wet chemistry. Montmorillonite-Na(+) clay in water was dispersed into a muddy suspension by sonication. Then, the clay-water suspension was used as the host media for CdTe QDs to prepare the QDs/clay powder by freeze drying. The experiments showed that QDs/clay powder could be re-dispersed in water without changing the luminescent property of the QDs; this process was reversible. EDX showed that Cd and Te elements existed in the QDs/clay powder and the XRD tests showed that the clay [001] reflection peaks for raw clay, QDs (λ(em)=514 nm)/clay and QDs (λ(em)=560 nm)/clay were the same, namely 2θ=7.4°. Finally, QDs/clay powder was applied to the HDPE polymer extrusion process at 200 °C to produce thin films; the resultant QDs-polymer nanocomposite film exhibited strong fluorescence.     

基于聚合物多齿配体的高性能CdTe量子点的微波水相合成

针对当前水相合成的量子点(QDs)光性能与稳定性等方面存在的不足,发展了基于聚合物多齿配体的水相制备策略.利用巯基修饰的聚丙烯酸(PAA-SH)作为多齿配体代替常用的巯基丙酸等单齿配体,结合微波辅助加热制备了CdTe量子点,研究了多齿配体对量子点的生长机制与荧光性能的影响.以PAA-SH为配体制备的CdTe量子点荧光性能优异(荧光量子效率(PLQY)可达75%),流体力学直径较小(~10 nm),稳定性也有明显提高.基于聚合物多齿配体的量子点制备技术有助于实现生物医学研究中急需的兼具高亮度、高稳定性、小尺寸等特征的高性能量子点生物探针的制备.     

Polymer alloys of Nodax copolymers and poly(lactic acid)

Properties of polymer alloys comprising poly(lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3-hydroxybutyrate (3HB) and other 3-hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium-chain-length (mcl) side groups effectively lowers the crystallinity and the melt temperature, Tm, of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower Tm makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.     

A Simple Protocol to Stabilize Gold Nanoparticles using Amphiphilic Block Copolymers: Stability Studies and Viable Cellular Uptake

Di‐ and triblock non‐ionic copolymers based on poly(ethylene oxide) and poly(propylene oxide) were studied for the stabilization of nanoparticles in water at high ionic strength. The effect of the molecular architecture (di‐ vs. triblock) of these amphiphilic copolymers was investigated by using gold nanoparticles (AuNPs) as probes for colloidal stability. The results demonstrate that both di‐ and triblock copolymers can provide long term stability, and that in both cases AuNPs are individually embedded within globules of polymers. However, in the case of diblock copolymers, the colloidal stability was related to the formation of micelles, in contrast with the case of triblock copolymers, which were previously shown to provide good stability even at concentrations at which micelles do not form. Quartz crystal microbalance (QCM) experiments showed that the presence of the hydrophobic block in the structure of the polymer is important to ensure quantitative adsorption upon a gold surface and to limit desorption. We demonstrate that with an appropriate choice of polymer, the polymer/AuNP hybrids can also undergo filtration and freeze‐drying without noticeable aggregation, which can be very convenient for further applications. Finally, preliminary studies of the cytotoxicity effect on fibroblast cells show that the polymer/AuNP hybrids were not cytotoxic. TEM micrographs on ultrathin sections of cells after incubation with the colloidal solutions show that the nanoparticles were internalized into the cells, conserving their initial size and shape.     

Poly(trialkylsilyl methacrylate)s: A family of hydrolysable polymers with tuneable erosion profiles

Polymers containing hydrolytically labile trialkylsilyl ester side groups were synthesised via a conventional and a controlled radical polymerization. The trialkylsilyl methacrylate monomer unit was chosen for its capacity to hydrolyse into basic, acid or sea water varying the hydrophilic character of the resulting polymer backbone with time. The hydrolysis or saponification reaction of the ester bond of the trialkylsilyl methacrylate was monitored through a ¹H NMR study showing the formation of siloxane side-products. Several copolymers and polymer blends were prepared as matrixes for controlled erodible systems. Their capacity to hydrolyse was demonstrated through SEM investigations with selective dissolution of free films containing hydrolysable copolymers and PMMA blends. Well-defined random and diblock copolymers with methyl methacrylate were investigated to show the effect of the microstructure on the erosion properties of the corresponding coatings. Poly(methyl methacrylate-b-tert-butyldimethylsilyl methacrylate) diblock copolymers synthesised through the RAFT process showed a better control of the erosion with a constant erosion rate over a long-time service in sea water at pH = 8.2. In addition, experiments showed that the erosion rate could be modulated by varying the molar proportion of hydrolysable side groups onto the copolymer backbone and the weight amount of copolymers mixed with PMMA in toluene solution.     

两亲性壳聚糖衍生物的制备及其包覆量子点

以天然壳聚糖为功能性高分子的骨架,通过西弗碱还原法,以正辛醛和端醛基聚乙二醇单甲基醚(mPEG aldehyde,mPEG-ald)修饰壳聚糖,制备了具有亲疏水性质的N-辛基化-N-mPEG化壳聚糖衍生物(N-octyl-N-mPEG-chitosan,OPEGC),并且以此两亲性壳聚糖衍生物包覆量子点制备了水溶性聚合物量子点纳米粒子.用FTIR、1H-NMR对壳聚糖衍生物进行了结构表征.制备的水溶性胶束,用动态光散射(DLS)测试其流体力学直径与分布,研究了烷基链接枝比率对粒径大小的影响,研究结果表明:烷基链接枝率越高,聚合物胶束粒径越小.以芘为分子探针,通过荧光光谱法测定了壳聚糖衍生物的临界胶束浓度(CMC)为2.032×10-2mg/mL,并对水溶性聚合物量子点纳米粒子进行了紫外、荧光及形貌表征,结果表明得到了荧光发射产率高的聚合物量子点纳米粒子,且尺寸均一、水溶性好.     

Free Radical–Induced Graft Copolymerization onto Natural Fibers

Surface modification of a natural cellulosic polymer system is required to improve the physicochemical properties of the fibers to be used as reinforcement for green composite applications. Surface modification through graft copolymerization improves the existing properties of the cellulosic fibers for a number of applications. Therefore, in the present study, an attempt was made to synthesize butyl acrylate (BA)-g-Saccaharum cilliare fibers using a redox initiator. Graft copolymers were characterized through FT-IR/SEM/TGA/DTA/DTG techniques, and the effect of grafting percentage on the water absorption properties of raw as well as grafted fibers was also investigated.     

Incorporation into paper of cellulose triacetate films containing semiconductor nanoparticles

CdSe/ZnS quantum dots (QDs) were embedded in films of cellulose triacetate (CTA) to give clear films with the broad absorbance and well-defined, size-tunable fluorescence characteristic of QDs. The relative quantum yields of the QDs in polymer were compared to that of the initial QDs dispersed in toluene. Alkaline hydrolysis of the film surfaces to regenerated cellulose rendered the previously hydrophobic CTA film surfaces hydrophilic and compatible with aqueous papermaking. Films containing combinations of different sized QDs gave more complex emission patterns. Small pieces of fluorescent films were added to pulp slurries and incorporated into laboratory paper sheets through hydrogen bonding between the regenerated cellulose film surfaces and cellulosic pulp fibers. The film system (cellulose ester bulk/cellulose surface) can be used to incorporate hydrophobic particles or molecules compatible with solutions of cellulosic polymers into paper products at both high and low loadings. QDs in paper may prove useful for security applications, such as sheets with unique optical signatures.     

Remote Control of One-Handed Helicity in Polyacetylenes through Flexible Spacers in Water: Impact of the Spacer Length

We report the unprecedented sergeants and soldiers (S&S)-type remote control of one-handed helicity in copolymers of chiral/achiral biphenylylacetylenes bearing amphiphilic oligo(ethylene glycol) (OEG) side chains. A small amount of chiral binaphthyl residues (≤10 mol %) introduced at the terminal of the achiral OEG spacers as many as 80 bonds away from the polymer backbones induced a complete one-handed helix in water through preferential intramolecular encapsulation of the binaphthyl groups within a cavity of the copolymers. A fully one-handed helix can be induced virtually independent of the OEG spacer length and concentrations. At a specific spacer length, however, its helix-sense was inverted. The copolymers also form an excess one-handed helix in organic solvents in an OEG spacer-length dependent manner, yet far from the polymer backbones. We show the superiority of the present covalent-bond driven S&S-type remote helicity control over the corresponding noncovalent helicity induction approach.     

Preparation of nanocomposites by reversible addition‐fragmentation chain transfer polymerization from the surface of quantum dots in miniemulsion

Herein, we report the synthesis of quantum dots (QDs)/polymer nanocomposites by reversible addition‐fragmentation chain transfer (RAFT) polymerization in miniemulsions using a grafting from approach. First, the surfaces of CdS and CdSe QDs were functionalized using a chain transfer agent, a trisalkylphosphine oxide incorporating 4‐cyano‐4‐(thiobenzoylsulfanyl)pentanoic acid moieties. Using a free radical initiator (AIBN) to activate the RAFT process, a polystyrene (PS) block was grafted from the surface of the QDs. Quantum confinement effects were identified for the nanocomposite obtained, so attesting to the integrity of the QDs after the polymerization. Free PS chains were also present in the final nanocomposite, indicating that the RAFT polymerization from the surface of the QDs was accompanied by conventional free radical polymerization. After isolating the nanocomposite particles, a second poly(n‐butyl acrylate) block was tentatively grown from the initial PS block. The first results indicated a successful polymerization of the second polymer and show the potential of the current strategy to prepare block copolymers from the surface of the RAFT‐modified QDs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5367–5377, 2009     

Fluorescent quantum dots for microbial imaging

QDs (Semiconductor QDs, CDs, SiQDs, and Pdots) are used in imaging microorganisms including viruses, bacteria, and fungi.     

Grafted semiconducting polymer amphiphiles for multimodal optical imaging and combination phototherapy

Semiconducting polymer nanoparticles (SPNs) have gained growing attention in biomedical applications. However, the preparation of SPNs is usually limited to nanoprecipitation in the presence of amphiphilic copolymers, which encounters the issue of dissociation. As an alternative to SPNs, grafted semiconducting polymer amphiphiles (SPAs) composed of a semiconducting polymer (SP) backbone and hydrophilic side chains show increased physiological stability and improved optical properties. This review summarizes recent advances in SPAs for cancer imaging and combination phototherapy. The applications of SPAs in optical imaging including fluorescence, photoacoustic, multimodal and activatable imaging are first described, followed by the discussion of applications in imaging-guided phototherapy and combination therapy, light-triggered drug delivery and gene regulation. At last, the conclusion and future prospects in this field are discussed.

This review summarizes the applications of grafted semiconducting polymer amphiphiles (SPAs) as multimodal optical nanoagents for cancer imaging and combination phototherapy.     

Pyrolysis of polyphenylenes with PCL or/and PSt side chains

Thermal degradation characteristic of polyphenylenes is an important issue for developing a rational technology of polymer processing and applications. In this study, we discussed thermal degradation of polyphenylenes (PP) with poly(ɛ-caprolactone) (PCL) and/or PCL/polystyrene copolymers (PSt) prepared by combined controlled polymerization and cross-coupling processes via direct pyrolysis mass spectrometry. When PP-graft-PCL/PSt copolymers were considered, thermally less stabile PCL side chains decomposed in the first step. In the second stage of pyrolysis, the decomposition of the polystyrene chains has taken place. A slight increase in thermal stability of PCL chains for PP-graft-PCL/PSt copolymers was noted compared to copolymer PP-graft-PCL due to the interaction between PSt and PCL chains. This interaction was stronger when PSt chains were linked to the 2-position of the 1,4-phenylene ring.     

Optical sensing quantum dot-labeled polyacrolein particles prepared by layer-by-layer deposition technique

Optical sensing polymer particles with tailored semiconductor nanocrystal (QD) loading are prepared by layer-by-layer deposition technique (LbL). Polyacrolein particles of 1.2 μm diameter are used as solid support for deposition of hydrophilic CdSe/ZnS nanocrystal/polyelectrolyte multilayers formed by electrostatic interactions. The pH-dependent fluorescence of QDs and pH-dependent conformations of polyelectrolytes, which likely passivate the surface state of nanocrystals, allow a creation of both mono- and multiplex coded polymer particles with pH-dependent fluorescence intensity. Bovine serum albumin (BSA) as outermost layer makes it possible to design the optical sensing polymer particles with reversibly responded fluorescence at pH variations. The fluorescence of such polymer particles with BSA outer layer is sensitive to copper(II) ion while the fluorescence of these particles is practically insensitive to the other divalent cations (Zn(2+), Ca(2+), Ba(2+), Co(2+), Mg(2+)). The detection limit of Cu(2+) is about 15 nM. Adaptation of LbL method to prepare QD-labeled polymer particles with enhanced complexity (e.g. several types of QDs, multiple biofunctionality) is expected to open new opportunities in biotechnological applications.     

开环易位聚合合成瓶刷聚合物

瓶刷聚合物是一类具有独特侧链结构的梳形聚合物。功能性瓶刷聚合物在光子晶体、表面活性剂、医药载体、防污涂层以及智能材料等领域具有良好的应用价值。通过开环易位聚合合成瓶刷聚合物的方法具有合成步骤简单、聚合物接枝密度高和侧链组成均一等优点,在控制聚合物组成、分子量和分散性等方面具有显著优势。本文基于开环易位聚合,简述了合成瓶刷均聚物以及嵌段型、混合型和核-壳型三种类型的瓶刷共聚物的方法,并介绍了合成精确结构的瓶刷聚合物的新进展。     

Surface modification of quantum dots and magnetic nanoparticles with PEG-conjugated chitosan derivatives for biological applications

In this paper, amphiphilic chitosan derivatives (N-octyl-N-mPEG-chitosan, mPEG = poly(ethylene glycol) monomethyl ether; OPEGC) were successfully synthesised via the Schiff base reduction reaction of chitosan and mPEG-aldehyde, or octanal, with chitosan acting as the backbone of the grafted copolymers, and mPEG-aldehyde providing the hydrophilic chain or octanal providing the hydrophobic alkyl chain. The synthesis was confirmed by characterisation employing Fourier transform infrared spectroscopy (FTIR) and ¹H NMR. In the subsequent procedure, water-soluble quantum dots (QDs) and iron(II,III) oxide (IO) nanoparticles, widely used as nanoprobes in medical applications, were produced by the incorporation of QDs or IO inside the polymeric micelle core. Finally, the optical properties of QDs incorporated into OPEGC (OPEGC@QDs) were characterised by UV-VIS spectroscopy, fluorescence spectroscopy, cell viability was obtained through MTT, and the morphology of their assembly formed in water were observed by atomic force microscope (AFM) and transmission electron microscope (TEM) and the QDs content of OPEGC@QDs was calculated following thermo gravimetric analysis (TGA). In addition, the properties of IO incorporated into OPEGC (OPEGC@IO) were characterised by vibrating sample magnetometry (VSM), FT-IR, MTT, TGA, AFM, and TEM. The results indicated that the OPEGC composite nanoparticles with size narrowly distributed, good water solubility, and low cytotoxicity were prepared here, which represented a high quantum yield or good super-paramagnetism.     

Role of the Polymer Matrix on the Photoluminescence of Embedded CdSe Quantum Dots

The photoluminescence (PL) of CdSe quantum dots (QDs) that form stable nanocomposites with polymer liquid crystals (LCs) as smectic C hydrogen‐bonded homopolymers from a family of poly[4‐(n‐acryloyloxyalkyloxy)benzoic acids] is reported. The matrix that results from the combination of these units with methoxyphenyl benzoate and cholesterol‐containing units has a cholesteric structure. The exciton PL band of QDs in the smectic matrix is redshifted with respect to QDs in solution, whereas a blueshift is observed with the cholesteric matrix. The PL lifetimes and quantum yield in cholesteric nanocomposites are higher than those in smectic ones. This is interpreted in terms of a higher order of the smectic matrix in comparison to the cholesteric one. CdSe QDs in the ordered smectic matrix demonstrate a splitting of the exciton PL band and an enhancement of the photoinduced differential transmission. These results reveal the effects of the structure of polymer LC matrices on the optical properties of embedded QDs, which offer new possibilities for photonic applications of QD–LC polymer nanocomposites.     

Quantum Dots Arrangement and Energy Transfer Control via Charge‐Transfer Complex Achieved on Poly(Phenylene Ethynylene)/Schizophyllan Nanowires

Assemblies of organic and inorganic compounds in the nanoscale region have contributed to the development of novel functional materials toward future applications, including sensors and opto‐electronics. We succeed in fabricating hybrid nanowires composed of a conjugated polymer and semiconductor quantum dots (QDs) by a supramolecular assembly technique. The 1‐D fashion of the nanowire structure is obtained by the polymer wrapping of cationic poly(phenylene ethynylene) (PPE) with helix‐forming polysaccharide schizophyllan (SPG). The electrostatic interaction between cationic PPE and anionic QDs affords the nanowires decorated with QDs. Upon addition of an acceptor molecule, tetranitrofluorenone (TNF), the charge‐transfer (CT) complex between PPE and TNF is formed, resulting in energy transfer from the QDs to PPE arising from the induced spectral overlap. Furthermore, the employment of the conjugated polymer allows highly sensitive quenching of the QD’s emission by raising the transmission efficiency to the CT complexed electron deficient sites along the polymer backbone.     

Self-selective recovery of photoluminescence in amphiphilic polymer encapsulated PbS quantum dots

Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quantum dots (QDs) was observed in water for the first time and possible mechanisms were proposed based on investigations by means of transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and fluorescence spectroscopy. Water-soluble PbS QDs were synthesized by transferring monodispersed QDs capped with hydrophobic ligands of oleylamine from an organic solvent into water via amphiphilic polymers poly(maleic anhydride-alt-1-octadecene-co-poly(ethylene glycol)). The water transfer process leads to a double size distribution (5.6 ± 0.9 nm and 2.7 ± 0.4 nm), attributed to ligand etching together with Ostwald ripening, as well as the fast decay of PL. The automatic recovery of the PL in PbS QDs stored in water in the dark for 3 months was only observed for the subset of smaller QDs and is largely due to the removal of surface defects with aging, as evidenced by the decreased percentage of unpassivated surface atoms from XPS studies. In contrast, the PL of the subset of larger QDs in the same sample does not self-recover in water and can only be slightly recovered by transferring them into environments with less external quenches. The results strongly suggest that it is the surface defect in the larger QDs themselves, introduced during Ostwald ripening, that is primarily responsible for their non-emitting status or rather low PL intensity under different conditions. The increase of unpassivated Pb atoms in larger PbS QDs after the 3 month aging has been confirmed by XPS, which explains their non-recovery behavior in water. The PL-recovered QD sample in water is very stable and shows comparable photostability to the initial QDs dispersed in an organic phase.     

Some Recent Advances in Pure and Applied Aspects of Graft Copolymers

In recent years more attention has been given to the preparation and characterization of graft copolymers and an examination of their properties than to developing novel methods of synthesis. In particular, these property studies can be used to develop applications of graft copolymers. The methods used to prepare and characterize better defined grafts are briefly reviewed. The structure of most graft copolymers is such that considerable amounts of one polymer can be grafted to another without affecting greatly the main properties of that polymer. In this way, the properties of one polymer such as higher water absorption can be imparted to another without changing the mechanical properties, for example, of the second polymer.

Some other inherent properties of graft copolymers are discussed, including their compatibility with the parent homopolymers, their possible con-formational changes, and other features. Finally, the use of the special nature of graft copolymers for the modification of the barrier properties of film and membranes is discussed as one possible general field of application.