Nanoparticles In Polymer Matrices Research Articles

Crosslinking Metal Nanoparticles into the Polymer Backbone of Hydrogels Enables Preparation of Soft, Magnetic Field‐Driven Actuators with Muscle‐Like Flexibility

The combination of force and flexibility is at the core of biomechanics and enables virtually all body movements in living organisms. In sharp contrast, presently used machines are based on rigid, linear (cylinders) or circular (rotator in an electrical engine) geometries. As a potential bioinspired alternative, magnetic elastomers can be realized through dispersion of micro- or nanoparticles in polymer matrices and have attracted significant interest as soft actuators in artificial organs, implants, and devices for controlled drug delivery. At present, magnetic particle loss and limited actuator strength have restricted the use of such materials to niche applications. We describe the direct incorporation of metal nanoparticles into the backbone of a hydrogel and application as an ultra-flexible, yet strong magnetic actuator. Covalent bonding of the particles prevents metal loss or leaching. Since metals have a far higher saturation magnetization and higher density than oxides, the resulting increased force/volume ratio afforded significantly stronger magnetic actuators with high mechanical stability, elasticity, and shape memory effect.

Dispersion of functionalized silver nanoparticles in polymer matrices: Stability, characterization, and physical properties

AbstractThree types of silver/polymer nanocomposite films were prepared: (1) silver/polymethyl methacrylate, (2) silver/polystyrene, and (3) silver/polyt‐butyl methacrylate by mixing colloidal solution of functionalized Ag nanoparticles with solution of pre‐made polymers. The nanoparticles are randomly dispersed into the matrices. The desired surface functionality of Ag nanoparticle was achieved by using specific amphiphilic block copolymer (specific hydrophobic block part) as stabilizer. The stability of nanoparticles in these host hydrophobic polymer matrices was determined after annealing the nanocomposite films at high temperature. The nanoparticles remained stable and no agglomeration occurred upon annealing up to 120°C. Up to 20 wt% of block copolymer stabilized Ag nanoparticles (11% Ag) was successfully loaded in the polymer matrix. Such a dispersion of Ag nanoparticles into a hydrophobic polymer matrix significantly enhances the mechanical properties of the nanocomposite films. The storage and loss modulus increase with increasing Ag nanoparticles content. Compared with a polymer matrix, the polymer/Ag nanocomposites film (containing 0.65% of Ag) prepared by this method displayed storage modulus that are up to 130% higher. This is attributed to the high surface area of the polymer coated Ag nanoparticles in the polymer matrix and van der Waal's attraction force between surface of Ag nanoparticles (polymer brush) and host polymer matrix. Comparison of thermal properties of polymer and polymer/Ag nanocomposite films showed that the thermal stability of nanocomposites increases by about 20°C. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Model for reversible nanoparticle assembly in a polymer matrix

The clustering of nanoparticles (NPs) in solutions and polymer melts depends sensitively on the strength and directionality of the NP interactions involved, as well as the molecular geometry and interactions of the dispersing fluids. Since clustering can strongly influence the properties of polymer-NP materials, we aim to better elucidate the mechanism of reversible self-assembly of highly symmetric NPs into clusters under equilibrium conditions. Our results are based on molecular dynamics simulations of icosahedral NP with a long-ranged interaction intended to mimic the polymer-mediated interactions of a polymer-melt matrix. To distinguish effects of polymer-mediated interactions from bare NP interactions, we compare the NP assembly in our coarse-grained model to the case where the NP interactions are purely short ranged. For the "control" case of NPs with short-ranged interactions and no polymer matrix, we find that the particles exhibit ordinary phase separation. By incorporating physically plausible long-ranged interactions, we suppress phase separation and qualitatively reproduce the thermally reversible cluster formation found previously in computations for NPs with short-ranged interactions in an explicit polymer-melt matrix. We further characterize the assembly process by evaluating the cluster properties and the location of the self-assembly transition. Our findings are consistent with a theoretical model for equilibrium clustering when the particle association is subject to a constraint. In particular, the density dependence of the average cluster mass exhibits a linear concentration dependence, in contrast to the square root dependence found in freely associating systems. The coarse-grained model we use to simulate NP in a polymer matrix shares many features of potentials used to model colloidal systems. The model should be practically valuable for exploring factors that control the dispersion of NP in polymer matrices where explicit simulation of the polymer matrix is too time consuming.

Two- and three-dimensional micro/nanostructure patterning of CdS–polymer nanocompositeswith a laser interference technique and in situ synthesis

Two- and three-dimensional (2D and 3D) micro/nanostructures of CdS–polymernanocomposites have been successfully patterned, combining photopolymerization via alaser four-beam interference technique with in situ synthesis of CdS nanoparticles in thepatterned polymer matrix. The morphology and optical properties of CdS nanoparticles inpolymer matrices have been confirmed using TEM, XRD, FTIR, UV–vis absorption andfluorescence spectroscopy. Laser irradiation time and film thickness are certified to be thekey factors for the control of the micro/nanostructures. With thickening film, the fabricatedmicrostructures of CdS–polymer nanocomposites were dramatically changed from 2D rodsto 3D networks which were composed of nanofibres, nanometre-scale walls andmicrometre-scale rods. These kinds of 2D and 3D micro/nanostructures could be expectedas potential applications in the development of nanotechnology, such as nanomedicalsystems, micro-fluidic chips, nanoreactors and micro/nanopurification or separationsystems.

Thermally Driven Assembly of Nanoparticles in Polymer Matrices

Thermally responsive bulk polymer films utilizing reversible Diels−Alder chemistry have been developed. Gold nanoparticles (AuNPs) were passivated with thiol-terminated poly(styrene)-b-poly(ethylene glycol) (PS-b-PEG) copolymer ligand, where the PS and PEG blocks are joined via a Diels−Alder (DA) linkage. The ligand-functionalized nanoparticles were dispersed within a microphase-separated PS-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer. Nanoparticle location was dictated by the compatibility of the external shell with the block copolymer matrix. As cast, the PEG shell compatibilized the nanoparticles with the PMMA domains. Subsequent thermal treatment caused the Diels−Alder linkages between the polymer blocks to dissociate, leaving the AuNPs functionalized by PS ligands. Immiscibility within the PMMA matrix caused AuNP migration to the PS domains. Migration of the Au nanoparticles was determined using morphological characterization via small-angle X-ray scattering (SAXS) and cross-sectional transmission electron microscopy (TEM).

Strategies for Dispersing Nanoparticles in Polymers

AbstractControlling the dispersion of nanoparticles in polymeric matrices is the most significant impediment in the development of high-perform ance polymer nanocomposite ma te rials and results primarily from the strong interpar ticle interactions between the nanopar ticles. This review examines the theoretical and experimental strategies employed in developing appropriate chemical and physical methods to achieve controlled dispersion of nanopar ticles. Methods to characterize the state of dispersion, including force and electron micros copy, and scattering, electrical, and mechanical spectroscopy, are considered with special emphasis on achieving quantitative meas ures of the dispersion. Some of the outstanding issues, such as long-term aging and the implication for the dispersion of nanopar ticles, development of high-throughput methods for rapid screening, and methods for in-line monitoring, are also discussed.

Improved properties of epoxy nanocomposites for specific applications in the field of MEMS/NEMS

Increasing interest in specific applications in the field of micro- and nano-electromechanical systems (MEMS and NEMS) has raised the request for new functional polymeric materials. Hybrid materials consisting of inorganic nanoparticles in polymer matrices represent a novel class of materials for lithographic patterning with unique properties, which arise from the synergism between the properties of both components [N. Damean, B.A. Parviz, J.N Lee, T. Odom, G.M Whitesides, J. Micromech. Microeng. 15 (29) (2005)]. We demonstrate the miscibility of epoxy resin surface-modified SiO 2 nanoparticles into epoxy photomaterial to create a patternable material with new properties, such as reduced refractive index for waveguiding applications. The lithographic, optical and mechanical properties of the silica-doped epoxy materials were investigated depending on the silica content in the photomaterial. Up to 60 μm thick layers were processed using UV lithography.

Transparent and luminescent YVO4 : Eu/polymer nanocomposites prepared by in situpolymerization

We report the synthesis and characterization of transparent nanocomposites consisting of YVO4 : Eu nanoparticles in polymer matrices. The composite materials are made by in situ polymerization of particle dispersions in methyl methacrylate (MMA) and lauryl acrylate (LA). Two different pathways for the preparation of these dispersions and their polymerization are presented. The first method, based on reverse microemulsions, yields a dispersion of YVO4 : Eu nanoparticles in MMA. The microemulsion droplets function as space-confined containers for the precipitation reaction of YVO4 : Eu and their hydrodynamic diameter can be controlled in the range of 6–90 nm as measured by dynamic light scattering (DLS). When a microemulsion with a droplet size of 7 nm is used, nanoparticles with a crystallite size of 5.8 nm are obtained as determined from X-ray diffraction patterns. Crystalline particles are identified by transmission electron microscopy (TEM) in samples taken directly from the microemulsion. A phase transfer of YVO4 : Eu nanoparticles from an aqueous dispersion into nonpolar solvents is the key step for the second preparation method. A crystallite diameter of 5 nm was determined by XRD, while crystalline particles in the size range of 3–18 nm could be identified with TEM. The modified particles were dispersed in LA to give a clear dispersion. No aggregation or particle growth takes place during the steps of phase transfer, isolation and redispersion of the nanoparticles as confirmed by DLS and powder X-ray diffraction. Both particle dispersions in MMA and in LA were polymerized using an in situ polymerization approach resulting in solid nanocomposites with excellent optical properties. The obtained materials are highly transparent (transmission >90% at 600 nm), possess a low haze (0.7–1.4%) and show red photoluminescence upon UV excitation, due to the integration of luminescent YVO4 : Eu nanoparticles.

Synthetic, layered nanoparticles for polymeric nanocomposites (PNCs)

AbstractThis review discusses preparation and use of the synthetic layered nanoparticles in polymer matrices, i.e., in the polymeric nanocomposites (PNCs). Several types of synthetic or semi‐synthetic layered materials are considered, namely the phyllosilicates (clays), silicic acid (magadiite), layered double hydroxides (LDHs), zirconium phosphates (ZrPs), and di‐chalcogenides. The main advantage of synthetic clays is their chemical purity (e.g. absence of amorphous and gritty contaminants, as well as arsenic, iron, and other heavy metals), white to transparent color that assures reproducibly of brightly colored products, as well as a wide range of aspect ratios, p = 20 to ≤6000. Several large scale production facilities have been established. The synthetic clay and LDH industries are oriented toward big volume markets: catalysis, foodstuff, cosmetics, pharmaceuticals, toiletry, etc. The use of these materials in PNCs is limited to synthetic clays and LDHs, mainly for reinforcement, permeability control, reduction of flammability, and stabilization, e.g. during dehydrohalogenation of chlorinated macromolecules. The use of lamellar ZrPs and di‐chalcogenides is at the laboratory stage of functional polymeric systems development, e.g. for electrically conductive materials, catalysts or support for catalysts, in photochemistry, molecular and chiral recognition, or in fuel cell technologies, etc. Copyright © 2007 John Wiley & Sons, Ltd.

Structural studies of thin films of semiconducting nanoparticles in polymer matrices

Ordered films of nanoscale materials are issue of wide interest for applications in several fields, such as optics, catalysis, and bioelectronics. In particular, semiconducting nanoparticles incorporation in a processable polymer film is an easy way to manipulate such materials for their application.We deposited thin layers of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles embedded in a thermoplastic cyclo-olephin copolymer (COC) with elevated optical transparency and highly bio-compatible. The nanoparticles were obtained by thiolate precursors previously dispersed in the polymer upon thermal treatment at temperatures ranging between 200 and 300 °C depending on the desired size. The precursor/polymer solutions were spin-coated in order to get thin films. The spinning conditions were changed in order to optimise the layer thickness and uniformity. The samples were mainly characterised by X-ray reflectivity (XRR) and by high-resolution transmission electron microscopy (HRTEM) analyses. The thinnest layer we have deposited is 8 nm thick, as evaluated by XRR. The HRTEM measurements showed that the nanoparticles have quasi-spherical shape without evident microstructural defects. The size of the nanoparticles depends on the annealing temperature, e.g. at 232 °C the size of the CdS nanoparticles is about 4–5 nm.

A Facile Route to ZnS–Polymer Nanocomposite Optical Materials with High Nanophase Content via γ‐Ray Irradiation Initiated Bulk Polymerization

Studying the fabrication and composition of semiconductor nanoparticles in polymer matrices has attracted the interest of many scientists because nanoparticle–polymer composites may find applications in high-refractive-index materials, light-emitting diodes, photocatalysts, photovoltaic solar cells, and nonlinear optical devices. Control of the nanoparticle size and size distribution as well as the dispersion homogeneity in the polymer matrix are critical prerequisites for controlling the properties of the composites. However, nanoparticles are prone to aggregation in the polymer because of their high specific surface energies and inherently hydrophilic character. Therefore, it is still a technological challenge to incorporate inorganic nanoparticles into polymer matrices and thus to prepare transparent bulk nanocomposites with high nanoparticle content. Far fewer studies of nanoparticle–polymer bulk materials have been reported than of nanocomposite films. Semiconductor nanoparticles (PbS, CdSe, CdTe) have been introduced into bulk polymer matrices to prepare bulk nanocomposites, although the content of inorganic particles was low (< 5 wt %). In these studies, two main approaches have been developed: in situ formation of nanoparticles in a presynthesized polymer and bulk polymerization of an organic monomer in the presence of premade nanoparticles. The latter provides full synthetic control over both the nanoparticles and the matrices, and is a more effective and practical route for fabricating bulk polymer nanocomposites on a large scale. We have utilized UV radiation curing to prepare transparent ZnS–polymer nanocomposite films with high ZnS contents from a solution mixture of premade ZnS particles and acrylate macromers. This is an effective method for preparing nanocomposite films with nanoparticles dispersed homogeneously horizontally and vertically throughout the entire polymer matrix, but it is unsuitable for preparing thick bulk nanocomposites. In addition, the ZnS nanoparticles obtained by the usual method cannot be redispersed in monomer or solvent because of their incomplete surface modification with organic molecules. The application of c-ray irradiation in the preparation of bulk polymer nanocomposites has remarkable advantages, such as processing under ambient pressure at room temperature and quick polymerization of monomers. These valuable properties can be put to use in the fabrication of nanocomposites with homogeneously dispersed inorganic nanoparticles. In this communication, we report a novel, facile route for the preparation of transparent bulk nanocomposites with high ZnS content via c-ray irradiation initiated polymerization (Fig. 1). Our strategy involves the design and optimization of the nanoparticle surface and polymeric monomer as well as the selection of a suitable polymerization technology. First, we reasoned that the compatibility between nanoparticles and the polymer matrix is a prerequisite for synthesizing a bulk nanocomposite with high nanophase content. So, it is necessary to tailor the corresponding polymer matrix by the decoration of the nanoparticles with organic molecules. Furthermore, it is highly important that the monomer should act as both the ligand and solvent for the inorganic nanoparticles. It has been reported that polar organic solvent molecules, such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), co-ordinate to the surface of ZnS or CdS nanocrystallites and can effectively stabilize them. Thus, it is expected that a monomer with a similar structure to DMF can be selected as both the solvent and ligand for the nanoparticles. Here, we have selected N,N-dimethylacrylamide (DMAA), which can effectively disperse and stabilize ZnS particles, as the monomer. Finally, the c-ray irradiation technique is another crucial factor in the fabrication of a bulk polymer nanocomposite with high particle content. This polymerization method can induce a mild and rapid gelation process for the bulk polymeric system containing a high content of nanoparticles uniformly dispersed inside. We present a simple approach for the large-scale production of mercaptoethanol (ME)-capped ZnS nanoparticles in DMF from Zn(OAc)2 (Ac: acetate) and thiourea. The MEC O M M U N IC A TI O N S

Aggregation of colloidal nanoparticles in polymer matrices.

Colloidal nanoparticles may possess many functional properties, whose nature may be electronic, chemical, biological, mechanical, . It is often advantageous to incorporate them into a matrix material, , a polymer solution or melt, or an elastomer, in order to obtain a 'nanomaterial' with additional properties brought in by the filler particles. One of the basic but nonetheless crucial properties is the mechanical strength of such polymer nanocomposites, whose rheological (or mechanical) properties are usually better than those of the pure matrix. The precise origin of this mechanical reinforcement effect, however, remains unclear. In this context, some recent studies of the structure and mechanical properties of a special type of nanocomposites are reviewed here. In silica-latex systems, a latex film with silica inclusions is formed from a colloidal solution of both components. During drying of the solution, the formation of silica domains can be controlled the physico-chemical properties of the solution. Well-defined silica aggregates embedded in a polymer matrix can be generated, and the mechanical properties of the resulting nanocomposite have been shown to be directly correlated to the average structure. We believe that the fine-tuning of the structure of the filler phase opens new perspectives for systematic studies of the reinforcement effect, , by modifying filler-polymer interfacial properties at fixed structure, or by generating original structures.

The synthesis of HgS and CdS nanoparticles in polymer matrices

AbstractThe synthesis of CdS nanoparticles in two different polymer matrices ie. polyacrylamide and polystyrene, is described. In addition, we describe the synthesis of HgS nanoparticles in polyacrylamide. Both the CdS and HgS nanocomposites show blue shifts in the optical spectra in relation to the bulk material. The photoluminescence spectra of both materials show broad emission. The transmission electron microscopy (TEM) images confirm the nanocrystalline nature of the CdS and HgS nanocomposites.

Nanometallization of Ultradispersed Polytetrafluoroethylene

The high reactivity of nanoparticles and their tendency toward spontaneous compaction accompanied by deterioration of basic physical properties make stabilization a major challenge in fabrication of materials based on metal nanoparticles. The best-developed method of stabilization is embedding nanoparticles in polymer matrices. The known “friability” of the structures of most partially crystalline carbon-chain polymers forms the basis for the method of introducing metal-containing nanoparticles into solution melts of polymers in hydrocarbon oils [5]. However, this method is inapplicable to “hard” polymer matrices, such as polytetrafluoroethylene. At the same time, creation of materials that combine opposite properties of the components at the nanolevel is one of the rapidly developing strategies of modern materials science. For example, it is expedient to augment the high thermal and chemical stability of polytetrafluoroethylene with electrical conductivity on a semiconductor scale, magnetization by means of introducing metal nanoparticles, or optoelectronic properties by introducing so-called quantum dots— nanoparticles of some metal sulfides and selenides. vents hinder the introduction of different nanoparticles into this matrix and their uniform distribution over its bulk. In searching for the solution to this problem, we have focused our attention on ultradispersed polytetrafluoroethylene (UPTFE). UPTFE was fabricated by a thermal gas dynamic method suitable for commercial production of UPTFE [6]. The essence of the method is in formation of a finely dispersed UPTFE powder upon the thermodestruction of the block polymer. The method of production and the trademark UPTFE-FORUM are covered by patents [6‐8].

Metalcontaining nano-particles within polymeric matrices: preparation, structure, and properties

Abstract A universal method of introduction of metal-containing nano-particles in polymeric matrices has been developed, which allows for the fabricating of large amounts (kilogram-scale) of polymeric nanoparticles composites. The encapsulation was done by thermal decomposition of metalcontaining compounds (MR n ; M=Cr, Mo, W, Ti, Zr, Fe, Co, Ni, Pd, Pt, Cu; R=CO, HCOO, CH 3 COO, C 6 H 5 CH 2 ) in solution melt of polymer (polyethylene, polypropylene, polytetrafluoroethylene, polyamide, polyarylate, polycarbonate, polysterene, polyethers, polyphenyleneoxide, siloxane). Particle size measurement (2–10 nm) and magnetic properties showed that the material really contained the nanoparticles, which were retaining their unique properties.

Unconventional magnetic behavior of iron-oxide nanoparticles in polymeric matrices

We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in the temperature range 5–300 K on composites containing iron–oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field.

A Convenient Ultraviolet Irradiation Technique for Fabrication of Silver-polymer Nanocomposites

Abstract Silver-polyacrylamide(Ag/PAM) nanocomposites and silver-polymethylmethacrylate(Ag/PMMA) nanocomposites with well homogeneously dispersed silver nanoparticles in polymer matrices were prepared by a novel ultraviolet irradiation technique at room temperature.

98/02070 New type of binder for coal for gasification

A universal method of introduction of metal-containing nano-particles in polymeric matrices has been developed, which allows for the fabricating of large amounts (kilogram-scale) of polymeric nanoparticles composites. The encapsulation was done by thermal decomposition of metalcontaining compounds (MRn; M=Cr, Mo, W, Ti, Zr, Fe, Co, Ni, Pd, Pt, Cu; R=CO, HCOO, CH3COO, C6H5CH2) in solution melt of polymer (polyethylene, polypropylene, polytetrafluoroethylene, polyamide, polyarylate, polycarbonate, polysterene, polyethers, polyphenyleneoxide, siloxane). Particle size measurement (2–10 nm) and magnetic properties showed that the material really contained the nanoparticles, which were retaining their unique properties.

98/02073 Partial oxidation of methane to synthesis gas on a Rh/TiO2 catalyst in a fast flow porous membrane reactor

A universal method of introduction of metal-containing nano-particles in polymeric matrices has been developed, which allows for the fabricating of large amounts (kilogram-scale) of polymeric nanoparticles composites. The encapsulation was done by thermal decomposition of metalcontaining compounds (MRn; M=Cr, Mo, W, Ti, Zr, Fe, Co, Ni, Pd, Pt, Cu; R=CO, HCOO, CH3COO, C6H5CH2) in solution melt of polymer (polyethylene, polypropylene, polytetrafluoroethylene, polyamide, polyarylate, polycarbonate, polysterene, polyethers, polyphenyleneoxide, siloxane). Particle size measurement (2–10 nm) and magnetic properties showed that the material really contained the nanoparticles, which were retaining their unique properties.

98/02068 Multifunctional heat recovery-type coal gasification systems

A universal method of introduction of metal-containing nano-particles in polymeric matrices has been developed, which allows for the fabricating of large amounts (kilogram-scale) of polymeric nanoparticles composites. The encapsulation was done by thermal decomposition of metalcontaining compounds (MRn; M=Cr, Mo, W, Ti, Zr, Fe, Co, Ni, Pd, Pt, Cu; R=CO, HCOO, CH3COO, C6H5CH2) in solution melt of polymer (polyethylene, polypropylene, polytetrafluoroethylene, polyamide, polyarylate, polycarbonate, polysterene, polyethers, polyphenyleneoxide, siloxane). Particle size measurement (2–10 nm) and magnetic properties showed that the material really contained the nanoparticles, which were retaining their unique properties.