Phase state and rheology of polyisobutylene mixtures with decyl surface modified silica nanoparticles

The miscibility of linear polyisobutylene and silica nanoparticles with surfaces modified by decyl groups is studied. The phase state of these systems corresponds to the amorphous equilibrium and may be described by a binodal with the UCST. As the radius of the inorganic core of nanoparticles and the molecular mass of polyisobutylene increase, the insolubility region on the phase diagram becomes wider. The addition of nanoparticles to the polymer leads to decreases in the viscoelastic characteristics of homogeneous media and provides the non-Newtonian behavior of the composition in the two-phase region. Shear deformation causes shifts of the phase equilibrium lines in the direction depended on the sizes of the nanoparticles.     

Elaboration of corona functionalized regular unimolecular hyperbranched polystyrene nanoparticles

Functional arborescent graft polystyrenes prepared by the “graft-on-graft” technique, involving the iterative grafting of end functional polymer chains onto reactive polymer backbones were synthesized. The zero-generation comb polymers and then the first generation hyperbranched structures were obtained by the coupling reaction of living α-acetal polystyryllithium onto linear or comb chains of poly(chloroethyl vinyl ether) (PCEVE) of controlled D̄P̄_n and structure. Both the PS grafts and the PCEVE reactive backbones were synthesized individually by living polymerization techniques. Initiation of styrene polymerization from acetal functionalized lithium derivatives yield the ω-functionalization of all external polystyrene branches. Derivatization of these acetal branch termini allowed the generation of aldehyde, hydroxyl and carboxyl groups as well as the introduction of functional organic molecules at the periphery of the nanoparticles.     

Formation of silver nanoparticles at the air-water interface mediated by a monolayer of functionalized hyperbranched molecules

Nanofibrillar micellar structures formed by the amphiphilic hyperbranched molecules within a Langmuir monolayer were utilized as matter for silver nanoparticle formation from the ion-containing water subphase. We observed that silver nanoparticles were formed within the multifunctional amphiphilic hyperbranched molecules. The diameter of nanoparticles varied from 2-4 nm and was controlled by the core dimensions and the interfibrillar free surface area. Furthermore, upon addition of potassium nitrate to the subphase, the Langmuir monolayer templated the nanoparticles' formation along the nanofibrillar structures. The suggested mechanism of nanoparticle formation involves the oxidation of primary amino groups by silver catalysis facilitated by "caging" of silver ions within surface areas dominated by multibranched cores. This system provides an example of a one-step process in which hyperbranched molecules with outer alkyl tails and compressed amine-hydroxyl cores mediated the formation of stable nanoparticles placed along/among/beneath the nanofibrillar micelles.     

Chemo‐selective reduction of nitro and nitrile compounds using Ni nanoparticles immobilized on hyperbranched polymer‐functionalized magnetic nanoparticles

The nitro and nitrile groups in aromatic and aliphatic compounds containing various reducible substituents such as carboxylic acid, ketone, aldehyde and halogen are selectively reduced to the corresponding amines in water as a green solvent with excellent yields by employing NaBH₄ in the presence of Fe₃O₄@PAMAM/Ni(0)‐b‐PEG nanocatalyst. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The designed catalyst system because of it being covered with hydrophilic polymers is soluble in a wide range of solvents (e.g. water and ethanol) and suitable for immobilizing and stabilizing Ni nanoparticles in aqueous mediums. In addition, the catalyst can be easily recovered from a reaction mixture by applying an external magnetic field and can be reused up to six runs without significant loss of activity.     

Synthesis of an organosilicon hyperbranched oligomer containing alkenyl and silyl hydride groups

A new organosilicon hyperbranched oligomer has been prepared that contains both double bonds and silyl hydride groups. The monomer is prepared via the hydrosilylation of propargyl chloride with methyldichlorosilane in the presence of a platinum catalyst. The product is a mixture resulting from both α- and β-addition. Treatment of the monomer mixture with magnesium results in the formation of a hyperbranched oligomer, which is then treated with LiAlH₄. Control of monomer addition speed to the magnesium is critical in order to keep head-head coupling low. The resulting oligomer is air- and water-stable, and has an average degree of polymerization of 8. This material gives a char yield of 24% but after crosslinking with platinum catalyst, the char yield increases to 69%. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3778–3784, 1999     

Gold nanoparticles functionalized with supramolecular macrocycles

Cold nanoparticles(AuNPs) functionalized with supiamolecular macrocycles are versatile and diverse hybrid nanoinaterials,which combine and enhance the characteristics of the two components.In this mini-review,we summarize the recent research progress on the synthesis and assembly of AuNPs functionalized with different supramoleciilar macrocyclic compounds,i.e.,crown ethers,cyclophanes, cyclodextrins(CDs),cucurbit[n]urils(CB[n]),calix[n]arenes,and pillar[n]arenes(P[n]A).Meanwhile, applications of these supramoleciilar hybrid nanomaterials in the fields of sensors,biomedicine and plasmonic devices are also presented.     

Multifunctional elastomer nanocomposites with functionalized graphene single sheets

We demonstrate the use of functionalized graphene sheets (FGSs) as multifunctional nanofillers to improve mechanical properties, lower gas permeability, and impart electrical conductivity for several distinct elastomers. FGS consists mainly of single sheets of crumbled graphene containing oxygen functional groups and is produced by the thermal exfoliation of oxidized graphite (GO). The present investigation includes composites of FGS and three elastomers: natural rubber (NR), styrene–butadiene rubber, and polydimethylsiloxane (PDMS). All of these elastomers show similar and significant improvements in mechanical properties with FGS, indicating that the mechanism of property improvement is inherent to the FGS and not simply a function of chemical crosslinking. The decrease in gas permeability is attributed to the high aspect ratio of the FGS sheets. This creates a tortuous path mechanism of gas diffusion; fitting the permeability data to the Nielsen model yields an aspect ratio of ～1000 for the FGS. Electrical conductivity is demonstrated at FGS loadings as low as 0.08% in PDMS and reaches 0.3 S/m at 4 wt % loading in NR. This combination of functionalities imparted by FGS is shown to result from its high aspect ratio and carbon‐based structure. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Melt rheology of polylactide/montmorillonite nanocomposites

In this article, the linear and nonlinear shear rheological behaviors of polylactide (PLA)/clay (organophilic‐montmorillonite) nanocomposites (PLACNs) were investigated by an Advanced Rheology Expanded System rheometer. The nanocomposites were prepared by master batch method using a twin‐screw extruder with poly(ε‐caprolactone) (PCL) as a compatibilizer. The presence of org‐MMT leads to obvious pseudo‐solid‐like behaviors of nanocomposite melts. The behaviors caused by the formation of a “percolating network” derived from the reciprocity among the strong related sheet particles. Therefore, the storage moduli, loss moduli, and dynamic viscosities of PLACNs show a monotonic increase with MMT content. Nonterminal behaviors exists in PLACNs nanocomposites. Besides the PLACNs melts show a greater shear thinning tendency than pure PLA melt because of the preferential orientation of the MMT layers. Therefore, PLACNs have higher moduli but better processibility compared with pure PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3189–3196, 2007     

Formation of copper nanoparticles with hyperbranched polyesterpolyols as template

New composite copper nanoparticles stabilized by hyperbranched polyesterpolyols of the second, third, and forth generations have been prepared via chemical reduction at different molar ratios of the precursors. The prepared stabilized copper nanoparticles have exhibited fungicide activity against Penicillium funiculosum, Penicillium ochro chloron, Paecilomyces variotii, Aspergillus niger, Aspergillus oryzae, and Aspergillus terreus strains. Copper nanoparticles stabilized by hyperbranched polyesterpolyols of the second and forth generations are hemocompatible.     

Polymer nanocomposites with iron oxide nanoparticles

Novel polymer nanocomposites with iron oxide nanoparticles in a poly(1-vinyl-1,2,4-triazole) matrix are promising for the development of new biomedical materials of long-term effect.     

Palladium nanoparticles immobilized on amphiphilic and hyperbranched polymer‐functionalized magnetic nanoparticles: An efficient semi‐heterogeneous catalyst for Heck reaction

To address the obstacles facing the use of palladium‐based homogeneous and heterogeneous catalysts in C─C cross‐coupling reactions, a novel semi‐heterogeneous support was developed based on hyperbranched poly(ethylene glycol)‐block ‐poly(citric acid)‐functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@PCA‐b ‐PEG). Because of the surface modification of the Fe₃O₄ nanoparticles with amphiphilic and hyperbranched polymers (PCA‐b ‐PEG), these hybrid materials are not only soluble in a wide range of solvents (e.g. water, ethanol and dimethylformamide) but also are able to trap Pd²⁺ ions via complex formation of free carboxyl groups of the PCA dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of Fe₃O₄@PCA‐b ‐PEG leads to immobilized palladium nanoparticles. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The catalyst was effectively used in the palladium‐catalysed Mizoroki–Heck coupling reaction in water as a green solvent. In addition, the catalyst can be easily recovered from the reaction mixture by applying an external magnetic field and reused for more than ten consecutive cycles without much loss in activity, exhibiting an example of a sustainable and green methodology.     

Morphology and rheology of polystyrene nanocomposites based upon organoclay

A correlation between morphology development and rheology of polystyrene nanocomposites based upon organophilic layered silicates (organoclay) such as fluoromicas was found as a function of the silicate modification. Organoclay was obtained by means of ion exchange of clay with protonated amine‐terminated polystyrenes with molar mass of M_n = 121 and 5 800 g/mol. Only when applying shear forces during melt compounding of organoclay modified with high molar mass polystyrene (PS), individual silicate platelets of 1 nm diameter and 600 nm length were obtained. Dispersions of such in‐situ formed nanoparticles with aspect ratio of 600 accounted for unique elastic properties observed in the low frequency range of the dynamic modulus, whereas organoclay modified with low molecular PS did not exfoliate and exhibited rheological behavior very similar to that of conventional fillers.     

Multiscale modeling of proteins interaction with functionalized nanoparticles

Understanding protein interactions with inorganic nanoparticle is central to the rational design of new tools in biomaterial sciences, nanobiotechnology, and nanomedicine. Theoretical modeling and simulations provide complementary approaches for experimental studies and are applied for exploring protein–particle surface-binding mechanisms, the determinants of binding specificity toward different surfaces, and the thermodynamics and kinetics of adsorption. The use of multiscale approaches is inevitable because the adsorption events extend over a wide range of time and length scales, which require the system to be addressed at different resolution levels. Here, we review the latest advances in coarse-grained treatment of these systems, usually addressed using residue-level resolution for proteins and mesoscale for the nanoparticle. We illustrate the parameterization strategies, focusing on those combining experimental and atomistic simulation data, within the theoretical framework of multiscale approaches.     

Phase transitions and rheology of aramid solutions

Clearing temperatures of solutions of poly(4-4′-benzanilidylene-terephthalamide) in concentrated sulphuric acid are presented as a function of polymer concentration and average molecular weight. The orientational order parameter <P ₂> is obtained from birefringence measurements. The experimental results are explained by a mean-field type theory similar to the Maier-Saupe model for thermotropic liquid crystals. Molecular flexibility, concentration and molecular weight are taken into account by using simple scaling factors. The birefringence induced by shear flow in an isotropic solution of poly(para-phenylene-terephthalamide) shows a strong pretransitional behaviour. This indicates the occurrence of a flow-induced phase transition.     

Synthesis and properties of transparent luminescent nanocomposites with surface functionalized semiconductor nanocrystals

5-Amino-1,10-phenanthroline (Aphen) was used as an organic ligand to functionalize CdS nanocrystals (NCs) by a ligand-exchange process. The functional Aphen-CdS NCs have strong luminescent emission at 552 nm and good dispersibility in the polar organic monomers. The Aphen-CdS NCs were dispersed in polymeric monomers to prepare a series of transparent luminescent nanocomposites with excellent thermal stability via in-situ bulk polymerization. The fluorescent properties of the Aphen-CdS NCs were well retained in the polymer matrix. It was found that when the methacrylic acid (MAA) and glycidyl methacrylate (GMA) as the comonomers were introduced into the polymer matrix, the emission peaks of the resultant nanocomposites had a blue shift and the fluorescent intensities also increased due to the interaction between NCs and the polymer matrices. The transparent NCs/polymer nanocomposites with tunable fluorescent emission can be potentially used for the fabrication of optoelectronic devices.     

Natural rubber nanocomposites with SiC nanoparticles and carbon nanotubes

Single-walled carbon nanotubes (SWNTs) and SiC nanoparticles were dispersed in natural rubber (NR) polymer solution and subsequently evaporated the solvent to prepare NR nanocomposites. Using this technique, nanoparticles can be better dispersed in the NR matrix. The influence of nano-fillers on the mechanical properties of the resulting nanocomposites was quantified.Mechanical test results show an increase in the initial modulus with nanoscale reinforcements for up to 50% strain compared to pure NR. The modulus and strength of natural rubber with 1.5% SiC nanoparticles appear to be superior to those of SWNTs with the same filler content. In addition to mechanical testing, these nanocomposites were studied using the SEM and Raman spectroscopy techniques in order to understand the morphology of the resulting system and the load transfer mechanism, respectively. The Raman spectrum of the SWNT/NR system is characterized by a strong band at 1595 cm⁻¹ (G mode—C-C stretching) and other two bands at 1300 cm⁻¹ (D mode-disorder induced) and 2590 cm⁻¹ (D* band). A shift of the 2590 cm⁻¹ Raman band to the lower wavenumber was observed after subjecting SWNT/NR sample to cyclic stress testing. Ageing SWNT/NR specimen in distilled water for 30 days also provided a similar result. The Raman shift in aged samples indicates internal stress transfer from the natural rubber matrix to the SWNTs implying the existence of bonding at the interface.     

Hybrids of silver nanoparticles with amphiphilic hyperbranched macromolecules exhibiting antimicrobial properties

Hybrids of silver particles of 1 to 2 nm in size with highly branched amphiphilically modified polyethyleneimines adhere effectively to polar substrates providing environmentally friendly antimicrobial coatings.     

Bio-based thermostable, biodegradable and biocompatible hyperbranched polyurethane/Ag nanocomposites with antimicrobial activity

The enhanced thermal and antimicrobial activity of silver nanoparticles prompts their uses in many medical devices. Mesua ferrea L. seed oil based antimicrobial biocompatible hyperbranched and linear polyurethane/Ag nanocomposites have been prepared in dimethylformamide without using any extra reducing agent. Formation of the stable and well-dispersed Ag nanoparticles was confirmed by ultra violet, X-ray diffractometeric, transmission electron microscopic and Fourier transform infra-red spectroscopic analyses. The enhancement of properties like thermal stability by (46-53)°C and 42 °C, tensile strength to ∼170% and ∼180% for hyperbranched and linear polyurethanes respectively was observed by the formation of nanocomposites. The cytocompatibility test based on the inhibition of RBC hemolysis showed that the materials lack cytotoxicity. The nanocomposites showed biodegradability as conferred from the bacterial degradation. Dose dependent excellent antibacterial activity of the nanocomposites against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli) bacteria and antifouling activity against Candida albicans was observed.     

Synthesis and second-order nonlinear optical properties of a crosslinkable functionalized hyperbranched polymer

A new implementation of copper-free thermal Huisgen 1,3-dipolar crosslinking reaction into a high T_g hyperbranched polyimide polymer in order to stabilize the electro-optic (EO) activity of second-order non linear materials is reported. Towards this goal, two different synthetic approaches were explored. The first strategy is based on the post-functionalization of the polymer with mixtures of DR1 azido derivative and propargylic alcohol, whereas, the second consists in the preparation of two complementary functionalized hyperbranched polymers that are mixed just before the preparation of films. Materials exhibit good second-order nonlinear optical coefficients (d₃₃) close to 30 pm/V at the fundamental wavelength of 1064 nm. Moreover, the thermal stability of the NLO properties of these materials reaches temperatures as high as 150 °C, and probably higher. This represents the highest thermal stability of crosslinkable EO polymers based on the crosslinking Huisgen reaction.     

Site-selective immobilization of gold nanoparticles functionalized with DNA oligomers

The organization of metal and semiconductor nanoparticles to form micro- and nanostructured assemblies is currently of tremendous interest. This communication reports on the utilization of DNA molecules as positioning elements for generating microstructured surface architecture from gold nanoparticles. Citrate-passivated 40 nm gold colloids were modified by chemisorptive coupling with a 5′-thiol-derivatized DNA oligomer. The nucleic acid was used as a molecular handle for the specific immobilization on solid supports, previously functionalized with capture DNA oligomers, complementary to the nanoparticle-bound DNA. As a consequence of the enormous specificity of nucleic acid hybridization, the DNA-directed immobilization (DDI) allows, to site-specifically target the hybrid nanoparticles to microlocations which contain the complementary oligomers. The site-selectivity of the surface adsorption is demonstrated by immobilizing the gold colloids on a DNA microarray on a glass cover slide. Moreover, scanning force microscopy (SFM) analysis, used to characterize the intermediate steps of the DDI on a gold substrate, provided initial insights into the specificity and efficiency of this technique. The application of the DDI to fabricate complex colloidal micro- and nanostructures is anticipated. Received: 26 July 2000/Accepted: 5 October 2000