Effect of nanoparticle dispersion on glass transition in thin films of polymer nanocomposites

We present spectroscopic ellipsometry measurements on thin films of polymer nanocomposites consisting of gold nanoparticles embedded in poly(styrene). The temperature dependence of thickness variation is used to estimate the glass transition temperature, T _g . In these thin films we find a significant dependence of T _g on the nature of dispersion of the embedded nanoparticles. Our work thus highlights the crucial role played by the particle polymer interface morphology in determining the glass transition in particular and thermo-mechanical properties of such nanocomposite films.     

Determination of the melting temperature of palladium nanoparticles by X-ray absorption spectroscopy

The anharmonicity parameters of the interatomic potential in ~4-nm palladium nanoparticles deposited on poly(tetra)fluoroethylene microgranules 0.2–0.5 μm in average size were studied by X-ray absorption spectroscopy from an analysis of temperature-dependent EXAFS Pd K edges. The parameters of the interatomic potential obtained were used to calculate melting temperature T_melt = 1591 K and Debye temperature Θ_D = 257 K of palladium nanoparticles; these temperatures are significantly lower than those in metallic palladium: 277 K and 1825 K, respectively.     

Photo-decomposition of thin palladium acetate films with 126 nm radiation

2 O₃, AlN and Si substrates produced by vacuum ultraviolet induced decomposition of palladium acetate is described. The palladium films formed and the palladium acetate layers used were characterised by using ultraviolet spectrophotometry and Fourier transform infrared (FTIR) spectroscopy. The optical transmission of the films after irradiation with pseudo-continuous 126 nm radiation generated by an excimer lamp provided information about the decomposition rate at different pressures and exposure times. The FTIR spectra recorded the chemical changes of the C=O, COO^- and CH₃ groups at different exposure times. The decomposition mechanism of the palladium acetate under these conditions appears to be quite different to that induced by pulsed laser irradiation. Received: 25 November 1996/Accepted: 1 July 1997     

Nanocomposites of magnetic cobalt nanoparticles and cellulose

Polymeric matrices with stabilized metallic nanoparticles constitute an important class of nanostructured materials, because polymer technology allows fabrication of components with various electronic, magnetic and mechanical properties. The porous cellulose matrix has been shown to be a useful support material for platinum, palladium, silver, copper and nickel nanoparticles. In the present study, nanosized cobalt particles with enhanced magnetic properties were made by chemical reduction within a microcrystalline cellulose (MCC) matrix. Two different chemical reducers, NaBH₄ and NaH₂PO₂, were used, and the so-formed nanoparticles were characterized with X-ray absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These experimental techniques were used to gain insight into the effect of different synthesis routes on structural properties of the nanoparticles. Magnetic properties of the nanoparticles were studied using a vibrating sample magnetometer. Particles made via the NaBH₄ reduction were amorphous Co-B or Co oxide composites with diminished ferromagnetic behaviour and particles made via the NaH₂PO₂ reduction were well-ordered ferromagnetic hcp cobalt nanocrystals.     

Microflow reactor synthesis of palladium nanoparticles stabilized with poly(benzyl ether) dendron ligands

A simple glass capillary microflow reactor system has been applied for the synthesis of palladium nanoparticles by thermal decomposition of palladium acetate (Pd(OAc)₂) in diphenyl ether in the presence of poly(benzyl ether) dendron ligands (PBED Gn-NH₂, n = 1–3) as a stabilizer. Effect of hydrodynamic parameters (capillary diameter, linear flow rate, volume flow rate, and reaction temperature) and concentrations (precursor and stabilizer) on the particle size was investigated. The particle size can be controlled by varying linear flow rate and temperature as well as ligand/precursor concentration ratio. Volume flow rate does not affect the particle size when the linear flow rate is held constant for different capillary diameters (150–320 μm). Unlike batch systems, in this microreactor system, smaller particles are produced at low ligand concentrations when the molar ratio of the ligand to metal precursor ranged from 1 to 5. As another characteristic of the microreactor synthesis, the concentration of the Pd precursor can be increased (up to 27 mM) with maintaining a constant particle size (3.1 ± 0.2 nm) and a good monodispersity, while in the batch system a significant increase and broadening in the particle size are observed with increasing precursor concentration.     

Study on preparation and fluorescence characteristic of coordinated Eu2O3/polymer hybrid films

The cyclohexane solution of TTA (trifluorothenoyl-acetone), phen (8-hydroxylquinoline) and PS (polystyrene), the ethyl acetate solution of TTA, phen and PMMA (polymethyl methacrylate) were used as flowing liquid, the coordinated Eu₂O₃/polymer hybrid colloids were successively produced by focused pulsed laser ablation of Eu₂O₃ target in interface of solid and flowing liquid. As solvent in the hybrid colloids has volatilized, the coordinated Eu₂O₃/polymer hybrid films were obtained. The hybrid colloids and films were characterized by TEM, UV-vis spectrum, fluorescence spectrum, TG-FTIR and X-ray photoelectron spectrum. The results show the coordinated Eu₂O₃ nanoparticles with average size of less than 20 nm are surrounded by the three-dimensional network and are properly incorporated into the PMMA and PS matrix, the hybrid films can emit intense red light under ultraviolet radiation, and their emission fluorescence spectra display same characteristic emission peaks of Eu³⁺ ions. The Eu₂O₃ hybrid films have better thermo stability than the related pure polymers because of strong interaction between surface europium ions of the nanoparticles and polymer. Because the coordinated Eu₂O₃ nanoparticles were wrapped by polymer, they have higher chemical stability than the related europium complex.     

Investigation of PdZn nanoparticle formation upon the thermal decomposition of acetate precursors by in situ XRD and XAFS

The formation of metal or metal-oxide nanoparticles from four different precursor systems, including palladium(II) acetate, zinc(II) acetate, their 1: 1 mechanical mixture and the palladium-zinc bimetallic acetate complex PdZn(OCOMe)₄(H₂O), upon heating in a He + 5% H₂ atmosphere is studied using the X-ray diffraction and EXAFS (Extended X-ray absorption fine structure) techniques in the in situ mode. X-ray diffraction is primarily used to monitor changes in the phase composition of the samples. At specific moments when qualitative changes in the composition occur, EXAFS spectra at the K-edges of Pd and Zn are also measured. Using a combination of these two techniques, a detailed sequence of the phase transformations in each of the four precursor systems is revealed. It is found that the bimetallic acetate complex and the mixture of two monometallic acetates undergo chemical reduction to form zerovalent palladium under milder conditions than zinc acetate. However, the formation of a PdZn alloy from the mixture of metal acetates proceeds with a significant diffusion barrier.     

Synthesis and characterization of noscapine loaded magnetic polymeric nanoparticles

The delivery of noscapine therapies directly to the site of the tumor would ultimately allow higher concentrations of the drug to be delivered, and prolong circulation time in vivo to enhance the therapeutic outcome of this drug. Therefore, we sought to design magnetic based polymeric nanoparticles for the site directed delivery of noscapine to invasive tumors. We synthesized Fe₃O₄ nanoparticles with an average size of 10±2.5 nm. These Fe₃O₄ NPs were used to prepare noscapine loaded magnetic polymeric nanoparticles (NMNP) with an average size of 252±6.3 nm. Fourier transform infrared (FT-IR) spectroscopy showed the encapsulation of noscapine on the surface of the polymer matrix. The encapsulation of the Fe₃O₄ NPs on the surface of the polymer was confirmed by elemental analysis. We studied the drug loading efficiency of polylactide acid (PLLA) and poly (l-lactide acid-co-gylocolide) (PLGA) polymeric systems of various molecular weights. Our findings revealed that the molecular weight of the polymer plays a crucial role in the capacity of the drug loading on the polymer surface. Using a constant amount of polymer and Fe₃O₄ NPs, both PLLA and PLGA at lower molecule weights showed higher loading efficiencies for the drug on their surfaces.     

Isothermal decomposition of γ-irradiated palladium acetate

The isothermal decomposition of un-irradiated (pristine) and pre-γ-irradiated palladium acetate was studied in the temperature range (498–508 K) and in air using the isothermal thermogravimetric technique. The data were analysed using various solid state reaction models. The results showed that the kinetics of isothermal decomposition of palladium acetate was governed by random nucleation reaction (Erofe'ev equation A ₃). The activation energies of the main decomposition process for un-irradiated and pre-γ-irradiated samples were calculated. The change in texture and crystal structure of the investigated palladium acetate by γ-irradiation was studied using electron microscopy and X-ray diffraction techniques.     

Nucleation of electroactive β-phase poly(vinilidene fluoride) with CoFe2O4 and NiFe2O4 nanofillers: a new method for the preparation of multiferroic nanocomposites

Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive β-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe₂O₄ and NiFe₂O₄ nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,. The dispersed ferrite nanofiller particles strongly enhance the nucleation of the β-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual α- to β-phase transformation by stretching of the polymer matrix.     

Synthesis of palladium nanoshell using a layer-by-layer technique

Complete palladium nanoshells were prepared by reducing palladium ions in a one-step reaction onto preformed silica cores of ca. 90 nm, which had been coated with successive layers of poly(diallyldimethyl ammonium chloride), poly(sodium styrenesulfonate) and finally poly(diallyldimethyl ammonium chloride) to reverse the zeta potential of the silica cores. This constitutes the first reported method for complete palladium nanoshell formation without the use of other metals as nucleation sites. The morphology of the nanoshell is of the rough discrete particle type rather than the smooth continuous type.     

Probing Chemical and Mechanical Nanodomains in Copolymer Nanorods with Correlative Atomic Force Microscopy—Nano‐correscopy

The interplay between size, shape, mechanical properties, and surface chemistry of nanoparticles orchestrates cellular internalization, toxicity, circulation time, and biodistribution. Therefore, the safety of nanoparticles hinges on our ability to quantify nanoscale physicochemical characteristics. Current characterization tools, due to their limited resolution, are unable to map these properties correlatively at nanoscale. An innovative use of atomic force microscopy‐based techniques, namely nano‐correscopy, overcomes this limitation and offers multiprobe capability to map mechanical (viscous and elastic) and chemical domains of nanoparticles correlatively. The strengths of this approach are demonstrated using polymer composite nanorods: m‐PEG‐PLGA ((m‐PEG–methoxy‐poly (ethylene glycol)‐b‐poly (lactic‐co‐glycolic) acid). Precise distribution of PLGA (monomers of lactide and glycolide) and poly(ethylene glycol) (PEG) polymer across nanorods is identified. The hydrophobic lactide component is found predominantly at the apex, while hydrophilic glycolide and PEG assembled at the body of the nanorods and correlate with a gradient of nanomechanical properties. New knowledge of how both nanochemical domains and nanomechanical properties are distributed across the nanorod will allow elucidating the interactions of nanorods with the proteins and biomolecules in the future, which will directly influence the fate of nanorods in vivo and will guide new synthesis methods.     

Preparation of Gold/triblock Copolymer Composite Nanoparticles

A kind of novel gold (Au)/hydroxylated poly (styrene-b-butadiene-b-styrene) triblock copolymer (HO-SBS) composite nanoparticles was synthesized by reduction of tetrachloroaurate ions in HO-SBS micelle. The Au–HO-SBS composite nanoparticles are composed by gold core about 35 nm in diameter and polymer shell about 7 nm in thickness. Formation of the Au/HO-SBS nanoparticles is indentified by infrared (IR) and UV-visible absorption spectroscopies. Transmission electron microscopy (TEM) result shows that the composite nanoparticles tend to aggregate into an ordered hexagonal array on carbon-coated grid.     

Imaging {Au0-PAMAM} Gold-dendrimer Nanocomposites in Cells

Dendrimer nanocomposites (DNC) are hybrid nanoparticles formed by the dispersion and immobilization of guest atoms or small clusters in dendritic polymer matrices. They have a great potential in biomedical applications due to their controlled composition, predetermined size, shape and variable surface functionalities. In this work, d=5–25nm spherical nanoparticles composed of gold and poly(amidoamine) (PAMAM) dendrimers have been selected to demonstrate this nanoparticle based concept. {Au(0)_n-PAMAM} gold dendrimer nanocomposites with a well-defined size were synthesized and imaged by transmission electron microscopy both in vitro and in vivo. DNC have also the potential to be used for imaging and drug delivery vehicles either by utilizing bioactive guests or through the incorporation of radioactive isotopes, such as Au-198.     

Surface-initiated atom transfer radical polymerization from TiO2 nanoparticles

Two kinds of hydrophilic polymers, poly(oxyethylene methacrylate) (POEM) and poly(styrene sulfonic acid) (PSSA), were grafted from TiO₂ nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. Chlorine modified TiO₂ nanoparticles (TiO₂-Cl), the ATRP initiators, were synthesized by the reaction of -OH in TiO₂ with 2-chloropropionyl chloride (CPC). FT-IR, UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the polymer chains were successfully grafted from the surface of TiO₂ nanoparticles. The hydrophilically modified TiO₂ nanoparticles have a better dispersion in alcohol than unmodified nanoparticles, as revealed by transmission electron microscopy (TEM). It was also found that the polymer grafting did not significantly alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction (XRD) patterns. Grafting amounts were 10% of the weight for both TiO₂-POEM and TiO₂-PSSA nanoparticles, as determined by thermogravimetric analysis (TGA).     

Clustering of Iron Oxide Nanoparticles with Amphiphilic Invertible Polymer Enhances Uptake and Release of Drugs and MRI Properties

A functionalization of iron oxide nanoparticles (NPs) of different diameters by the amphiphilic invertible polymer, (PEG600‐alt‐PTHF650)_k (PEG and PTHF stand for poly(ethylene glycol) and poly(tetrahydrofuran), respectively), leads to different NP/polymer architectures for dye/drug uptake and release, as is reported here for the first time. It is demonstrated that 18.6 ± 1.4 and 11.9 ± 0.6 nm NPs are individually coated by this polymer, while 5.9 ± 0.6 nm NPs form nanoparticle clusters (NPCs) which could be isolated by either ultracentrifugation or magnetic separation. This phenomenon is most likely due to the character of the (PEG600‐alt‐PTHF650)_k macromolecule with alternating hydrophilic and hydrophobic fragments and its dimensions sufficient to cause NP clustering. Utilizing Rhodamine B base (RBB) and doxorubicin (DOX), the data on uptake upon mixing and further release via inversion into octanol (mimicking the penetration of the cell biomembrane) are presented. The magnetic NPCs display enhanced uptake and release of both RBB and DOX most likely due to the higher retained polymer amount. The NPCs also display exceptional magnetic resonance imaging properties. This and the high uptake/release efficiency of the NPCs combined with easy magnetic separation make them promising for theranostic probes for magnetically targeted drug delivery.     

Analysis of plasticizer influence in Poly(vinyl acetate)/Poly(vinylidene fluoride) polymer blend electrolyte

Gel polymer electrolyte based on poly(vinyl acetate) and poly(vinylidene fluoride) was prepared by solvent casting technique, in which the addition of plasticizers improves the conductivity of polymer membranes. The blend polymer electrolyte containing propylene carbonate (PC) exhibits the highest conductivity of 0.922?×?10^?2 S cm^?1 at room temperature because of the higher dielectric constant as compared to other plasticizers used in the present study. Material characterizations were done with the help of SEM and FT-IR techniques. The activation energy values were computed from ‘log σ?1/T’ Arrhenius plots.     

Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements

Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine the effects of decreasing film thickness on glass transition temperature, T _g, the relative strength of the glass transition, and the relative rate of physical aging below T _g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at T _g. Positive deviations from bulk T _g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T _g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of physical aging in films as thin as 10 nm. Received 21 August 2001     

Fabrication of water-soluble magnetic nanoparticles by ligand-exchange with thermo-responsive polymers

We report the use of thermo-responsive polymers in the synthesis of Co and γ-Fe₂O₃ nanoparticles using a two-step method involving thermal decomposition of the organometallic complexes in the presence of oleic acid and then followed by ligand-exchange process with thermo-responsive polymer. Among different thermo-responsive polymers investigated, it was found that the polymer based on poly(N-isopropylacrylamide) with a co-monomer component of acrylic acid and acrylamide can be used in the ligand-exchange to coat Co and γ-Fe₂O₃ nanoparticles, respectively. The nanoparticles are found to be water-soluble at temperatures below coil-to-globule phase transition of the coating polymer.     

Temperature-dependent gas-surface chemical kinetic model for methane ignition catalyzed by in situ generated palladium nanoparticles

A temperature-dependent gas-surface kinetic model for methane oxidation over palladium is proposed. Thermodynamic data for the surface species (O, H, OH, H₂O, and CO) are derived from statistical mechanic analysis using literature heats of desorption and vibrational frequencies. The rate parameters in the model also satisfy thermo-kinetic constraints. The hydrogen oxidation submodel is validated against literature stagnation flow reactor experiments at 1300 K and 13 Pa. The current model is further tested against catalytic methane ignition in a laminar flow reactor at atmospheric pressure, and with time-resolved measurements of the size distribution of palladium nanoparticles generated in situ from an aerosol containing palladium acetate. The improved gas-surface model predicts closely the experimental data. The role of palladium nanoparticles in enhancing methane ignition is attributed to heat release due to catalytic methane oxidation over distributed nanoparticle surfaces, leading to a temperature rise and thus an accelerated gas-phase chain-branching process.