“Click” synthesis of thermally stable au nanoparticles with highly grafted polymer shell and control of their behavior in polymer matrix

Fluorescent Gold Nanoparticles in Suspension as an Efficient Theranostic Agent for Highly Radio-Resistant Cancer Cells

Gold nanoparticles are a promising candidate for developing new strategies of therapy against cancer. Due to their high atomic number and relative biocompatibility, they are commonly investigated as radiosensitizers to locally increase the dose of radiotherapy. In order to optimize this radiosensitizing effect, it is necessary to control the positioning of the nanoparticles in the cells. The purpose of this study is to investigate, by means of fluorescent gold nanoparticles in suspension, the dose enhancement on highly radio-resistant cancer cells. These nanoparticles were successfully produced using modern click-chemistry methods, first by attaching a chelating agent Diethylenetriamine pentaacetate benzylamine to L-cysteine, bonding the resulting ligand to a gold core, grafting propargylamine and then utilizing copper-catalyzed azide-alkyne cycloaddition (CuAAC) to fuse AlexaFluor 647 to the ligands. The results of this study prove the success of the reactions to produce a minimally cytotoxic and highly stable nanoparticle suspension that increases the radiosensitivity of gliosarcoma 9L tumor cells, with a 35% increase in cell death using 5 Gy kilovoltage radiation. Their fluorescent functionalization allowed for their simple localization within living cells and detection in vivo post-mortem.

ON/OFF Switchable Nanocomposite Membranes for Separations

Although water, air, and other resources are abundant on earth, they have been subjected to strict environmental regulations. This is because of their limitation of availability for human consumption. In the separation industry, the membrane system was introduced to increase the amount of resources available to mankind. Experts used an easy-to-use polymeric material to design several membranes with porous structures for wastewater treatment, gas separation, and chemical removal; consequently, they succeeded in obtaining positive results. However, past polymeric membranes exhibited a chronic drawback such that it was difficult to simultaneously augment the permeate flux and improve its selectivity toward certain substances. Because of the trade-off relationship that existed between permeability and selectivity, the membrane efficiency was not very good; consequently, the cost-effectiveness was significantly hindered because there was no other alternative than to replace the membrane in order to maintain its initial characteristics steadily. This review begins with the introduction of a polymer nanocomposite (PNC) membrane that has been designed to solve the chronic problem of polymeric membranes; subsequently, the stimuli-responsive PNC membrane is elucidated, which has established itself as a popular topic among researchers in the separation industry for several decades. Furthermore, we have listed the different types and examples of stimuli-responsive PNC membranes, which can be switched by external stimuli, while discussing the future direction of the membrane separation industry.

Controlled Assembly of Block Copolymer Coated Nanoparticles in 2D Arrays

The defined assembly of nanoparticles (NPs) in polymer matrices is an important prerequisite for next-generation functional materials. A promising approach to control NP positions in polymer matrices at the nanometer scale is the use of block copolymers. It allows the selective deposition of NPs in nanodomains, but the final defined and ordered positioning of the NPs within the domains has not been possible. This can now be achieved by coating NPs with block copolymers. The self-assembly of block copolymer-coated NPs directly leads to ordered microdomains containing ordered NP arrays with exactly one NP per unit cell. By variation of the grafting density, the inter-nanoparticle distance can be controlled from direct NP surface contact to surface separations of several nanometers, determined by the thickness of the polymer shell. The method can be applied to a wide variety of block copolymers and NPs and is thus suitable for a broad range of applications.

Architectural Effects on Solution Self-Assembly of Poly(3-hexylthiophene)-Based Graft Copolymers

While solution assembly of conjugated block copolymers has been widely used to produce long 1-D nanowires (NWs), it remains a great challenge to provide a higher level of control over structure and function of the NWs. Herein, for the first time, we report the solution assembly of graft copolymers containing a conjugated polymer backbone in a selective solvent and demonstrate that their self-assembly behaviors can be manipulated by the molecular structures of the graft copolymers. A series of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) copolymers was designed with two different architectural parameters: grafting fraction (f_g) and molecular weight of P2VP chains (M_n,P2VP) on the P3HT backbone. Interestingly, crystallization of the P3HT-g-P2VP copolymers was systematically modulated by changes in f_g and M_n,P2VP, thus allowing for control of the growth kinetics and curvatures of solution-assembled NWs. When M_n,P2VP (4.4 to 15.1 kg/mol) or f_g (2.8 to 9.2%) of the P3HT-g-P2VP polymers was increased, the crystallinity of the copolymers was reduced significantly. Steric hindrance from the grafted P2VP chains apparently modified the growth of NWs, leading to shorter NWs with a greater degree of curvature for graft copolymers with more hindrance. Therefore, we envision that such conjugated chain-based graft copolymers can be versatile building blocks for producing NWs with controlled length and shape, which can be important for tailoring the optical and electrical properties of NW-based devices.

Architectural engineering of rod-coil compatibilizers for producing mechanically and thermally stable polymer solar cells

While most high-efficiency polymer solar cells (PSCs) are made of bulk heterojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they have a significant morphological instability issue against mechanical and thermal stress. Herein, we developed an architecturally engineered compatibilizer, poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP), that effectively modifies the sharp interface of a BHJ layer composed of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs was successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-g-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-g-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-b-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as supported by molecular dynamics simulations.

In Situ Formation of Polymer-Gold Composite Nanoparticles with Tunable Morphologies

A simple and efficient route to gold-polymer nanoparticle composites is described. Our versatile synthetic route exerts facile control over polymer nanoparticle morphology, including micelles, rod-like structures, and vesicles, all easily attainable from a single polymerization taken to different monomer conversions. Specifically, poly[oligo(ethylene glycol) methacrylate]-b-poly(dimethylaminoethyl methacrylate)-b-poly(styrene) (POEGMA-b-PDMAEMA-b-PST) triblock copolymers were synthesized using a polymerization induced self-assembly (PISA) approach. Subsequently, spherical gold nanoparticles (10 nm AuNPs) were formed at the hydrophilic-hydrophobic nexus of the assembled triblock copolymer nanoaggregates by the addition of chloroauric acid (HAuCl₄) followed by in situ reduction using NaBH₄. After reduction, the cloudy white nanoparticle dispersions turned to a red-purple color. The gold nanoparticles that formed were stabilized by the enveloping polymeric nanostructures, neither precipitation nor agglomeration occurred. We demonstrated that we were able to tune the gold nanoparticle composition in these polymer-gold composites by varying the concentration of chloroauric acid. Morphology, particle size, molecular weight, AuNP content, and chemical structure of the polymer structures were characterized by transmittance electron microscopy (TEM), dynamic light scattering (DLS), size exclusion chromatography (SEC), thermal gravimetric analysis (TGA), and ¹H NMR. Finally, the formation of the AuNPs occurred without affecting the polymer nanoparticle morphology.

Aspect-Ratio Effect of Nanorod Compatibilizers in Conducting Polymer Blends

Nanoparticles (NPs) at the interface between two different polymer blends or fluid mixtures can function as compatibilizers, thereby dramatically improving the interfacial properties of the blends or the fluid mixtures. Their compatibilizing ability is strongly dependent on their size, shape, and aspect ratios (ARs), which determines their adsorption energy to the interface as well as their entropic penalty when they are being strongly segregated at the interface. Herein, we investigated the effect of the ARs of nanorod surfactants on the conducting polymer blend of poly(triphenylamine) (PTPA) templated by polystyrene (PS) colloids. The lengths of the polymer-coated CuPt nanorods (CuPt NRs) were 5, 15, and 32 nm with a fixed width of 5 nm, thus producing three different AR values of 1, 3, and 6, respectively. For quantitative analysis, the morphological and electrical behaviors of the polymer blends were investigated in terms of the volume fraction and AR of the NRs. The dramatic change in the morphological and electrical properties of the blend film was observed for all three NR surfactants at the NR volume fraction of approximately 1 vol %. Therefore, NR surfactants with larger ARs had better compatibilizing power for a given number of NRs in the blends. Also, they exhibited a stronger tendency to be aligned parallel to the PS/PTPA interface. Also, we demonstrated the successful use of the NR surfactants in the fabrication of conducting polymer blend film that requires only minimal concentrations of conducting polymers. To the best of our knowledge, this is the first report of an experiment on the AR effect of NR compatibilizers in polymer blends.

Efficient colorimetric pH sensor based on responsive polymer-quantum dot integrated graphene oxide

In this paper, we report the development of a versatile platform for a highly efficient and stable graphene oxide (GO)-based optical sensor that exhibits distinctive ratiometric color responses. To demonstrate the applicability of the platform, we fabricated a colorimetric, GO-based pH sensor that responds to a wide range of pH changes. Our sensing system is based on responsive polymer and quantum dot (QD) hybrids integrated on a single GO sheet (MQD-GO), with the GO providing an excellent signal-to-noise ratio and high dispersion stability in water. The photoluminescence emissions of the blue and orange color-emitting QDs (BQDs and OQDs) in MQD-GO can be controlled independently by different pH-responsive linkers of poly(acrylic acid) (PAA) (pKa=4.5) and poly(2-vinylpyridine) (P2VP) (pKa=3.0) that can tune the efficiencies of Förster resonance energy transfer from the BQDs to the GO and from the OQDs to the GO, respectively. As a result, the color of MQD-GO changes from orange to near-white to blue over a wide range of pH values. The detailed mechanism of the pH-dependent response of the MQD-GO sensor was elucidated by measurements of time-resolved fluorescence and dynamic light scattering. Furthermore, the MQD-GO sensor showed excellent reversibility and high dispersion stability in pure water, indicating that our system is an ideal platform for biological and environmental applications. Our colorimetric GO-based optical sensor can be expanded easily to various other multifunctional, GO-based sensors by using alternate stimuli-responsive polymers.

Efficient temperature sensing platform based on fluorescent block copolymer-functionalized graphene oxide

Efficient temperature-sensing platform was demonstrated using temperature-responsive, fluorescent P7AC-b-PNIPAM-b-PSN3 block copolymer-anchored graphene oxide sheets (FGO). FGO exhibited extraordinary stability in water and showed fast optical on-off switching behavior in response to temperature change.

Nanoporous bicontinuous structures via addition of thermally-stable amphiphilic nanoparticles within block copolymer templates

Herein, we fabricated the bicontinuous structures from nanocomposites of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer and the shell-cross-linked, thermally stable gold nanoparticles (Au NPs). The surface property of Au NPs was controlled with ligands containing various compositions of PS and PMMA so that the resulting Au NPs were selective to PS or PMMA block or nonselective (i.e., neutral) to both blocks. The amphiphilic Au NPs were also prepared by coating the surface of Au NPs with equimolar mixtures of PS and PMMA selective ligands. Consequently, it was found that the morphological behaviors of thermally annealed nanocomposites containing amphiphilic Au NPs and PS-b-PMMA were dramatically different from the case of neutral Au NPs that were coated with nonselective ligands. With increasing the amount of amphiphilic Au NPs, a transition from lamellar to bicontinuous structures was observed, whereas the neutral Au NPs were aggregated within the PS-b-PMMA lamellae. Furthermore, the nanoporous bicontinuous thin films were fabricated on the silicon substrates and the morphological behaviors were quantitatively investigated by grazing-incidence small-angle X-ray scattering (GISAXS) analysis.

Mesostructured Block Copolymer Nanoparticles: Versatile Templates for Hybrid Inorganic/Organic Nanostructures

We present a versatile strategy to prepare a range of nanostructured poly(styrene)-block-poly(2-vinyl pyridine) copolymer particles with tunable interior morphology and controlled size by a simple solvent exchange procedure. A key feature of this strategy is the use of functional block copolymers incorporating reactive pyridyl moieties which allow the absorption of metal salts and other inorganic precursors to be directed. Upon reduction of the metal salts, well-defined hybrid metal nanoparticle arrays could be prepared, while the use of oxide precursors followed by calcination permits the synthesis of silica and titania particles. In both cases, ordered morphologies templated by the original block copolymer domains were obtained.

'Click' preparation of CuPt nanorod-anchored graphene oxide as a catalyst in water

In this paper, a simple and powerful method of producing nanoparticle-anchored graphene oxide (GO) composites using a 'click' reaction is demonstrated. This method affords a facile means of anchoring of nanoparticles with various shapes and sizes on the GO. CuPt nanorods with controlled size, aspect ratio (from 1 to 11), and uniformity are synthesized. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy measurements are made to monitor the formation and characterize the properties of the CuPt nanorod-grafted GO composites. Their catalytic properties in the water phase are investigated using an o-phenylenediamine oxidation reaction. The results of this study clearly demonstrate that nonpolar CuPt nanorods immobilized on GO can function as a catalyst in an aqueous solution and that GO can be used as a catalytic nanorod support.

Gold-decorated block copolymer microspheres with controlled surface nanostructures

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures.

Living Radical Polymerization by the RAFT Process – A Third Update

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.

Creating opal-templated continuous conducting polymer films with ultralow percolation thresholds using thermally stable nanoparticles

We propose a novel and robust strategy for creating continuous conducting polymer films with ultralow percolation thresholds using polymer-coated gold nanoparticles (Au NPs) as surfactant. Continuous poly(triphenylamine) (PTPA) films of high internal phase polymeric emulsions were fabricated using an assembly of cross-linked polystyrene (PS) colloidal particles as template. Polymer-coated Au NPs were designed to be thermally stable even above 200 °C and neutral to both the PS and PTPA phases. Therefore, the Au NPs localize at the PS/PTPA interface and function as surfactant to efficiently produce a continuous conducting PTPA polymer film with very low percolation thresholds. The volume fraction threshold for percolation of the PTPA phase with insulating PS colloids (as measured by electron microscopy and conductivity measurements) was found to be 0.20. In contrast, with the addition of an extremely low volume fraction (φ(p) = 0.35 vol %) of surfactant Au NPs, the volume fraction threshold for percolation of the PTPA phase was dramatically reduced to 0.05. The SEM and TEM measurements clearly demonstrated the formation of a continuous PTPA phase within the polyhedral phase of PS colloids. To elucidate the influence of the nanoparticle surfactant on the blend films, the morphology and conductivity of the blends at different PS colloid/PTPA volume ratios were carefully characterized as a function of the Au NP concentration. Our approach provides a methodology for a variety of applications that require a continuous phase for the transport of molecular species, ions, or electrons at low concentrations and a second phase for mechanical support or the conduction of a separate species.