Sol-gel nanocomposites for optical applications

In this paper the results obtained in the last ten years by the authors in the field of sol-gel nanocomposites for optical applications are reviewed. Two type of applications are, in particular, discussed: (a) nanocomposite materials containing semiconductor quantum dots for photonic and optoelectronic applications; (b) nanocomposite materials for optical gas sensing. Nanocomposite multifunctional materials, based on the incorporation of QDs in inorganic or hybrid organic-inorganic matrices, characterized by stable optical properties, good chemical stability, and easy processability, can be obtained using the sol-gel method in combination with colloidal methods. Optical gas sensors based on surface plasmon resonance (SPR) demonstrate great potential both for better understating the chemical interactions at the nanoscale and the development of real devices. A careful control of the film structure allows to achieve very selective gas sensors with tailored microstructure. In both type of applications, the general aspects related to the synthesis and characterization of the materials, and the results obtained in the specific cases, are described with the aim to give an overview of the development of these materials.

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Sol-gel optical nanocomposites: Design and applications

The history and method of producing gel-polymer composites is presented. Tailoring properties, such as density, refractive index, hardness, elastic modulus, compressive strength, abrasion resistance, and modulus of rupture is achieved through controlling the ratio of gel-derived silica to polymer phases. Several different applications of composite technology are presented. Solid-state lasing in dye-doped silica gel-PMMA composites has been recently achieved. The difficulties in generating stable photochromism in gels and gel-derived composites are discussed. Microlens arrays for data reading, employing large gel-polymer spheres, have been developed. In addition, a new flat-screen color display technology, based upon the periodic arrangement of dye-doped microsphere pixels, emitting blue, green and red light, is disclosed for the first time.     

Chitosan-based nanocomposites for medical applications

Chitosan as a biobased polymer is gaining increasing attention due to its extraordinary physico-chemical characteristics and properties. While a primary use of chitosan has been in horticultural and agricultural applications for plant defense and to increase crop yield, recent research reports display various new utilizations in the field of advanced biomedical devices, targeted drug delivery, and as bioimaging sensors. Chitosan possesses multiple characteristics such as antimicrobial properties, stimuli-responsiveness, tunable mechanical strength, biocompatibility, biodegradability, and water-solubility. Further, chitosan can be processed into nanoparticles, nano-vehicles, nanocapsules, scaffolds, fiber meshes, and 3D printed scaffolds for a variety of applications. In recent times, nanoparticles incorporated in chitosan matrices have been identified to show superior biological activity, as cells tend to proliferate/differentiate faster when they interact with nanocomposites rather than bulk or micron size substrates/scaffolds. The present article intents to cover chitosan-based nanocomposites used for regenerative medicine, wound dressings, drug delivery, and biosensing applications.     

Hybrid materials covalently incorporated with isophorone-based dyes through sol-gel process for nonlinear optical applications

Two new push-pull type second-order nonlinear optical (NLO) active isophorone-based alkoxysilane dyes with the same acceptor were synthesized and characterized. One silane (ICTES-HEMA) bears a chromophore with a hydroxyethyl methylamino donor and the other silane (ICTES-HMPP) is a bulkier analogue with a hydroxymethyl diphenylamino donor. Transparent, homogeneous films were prepared via the copolymerization of tetraalkoxysilane (TEOS) and different NLO silanes with the ratio of 5:1. The d(33) values obtained for the HEMA and HMPP films are 46.3 and 20.6 pm/V, respectively. Normalized UV-vis spectra reveal that the introduction of a diaryl group would help to prevent unfavorable organization of the chromophores. The reorientation dynamic stabilities of the samples were studied by second-harmonic generation (SHG) measurements, demonstrating that bulkier chromophores incorporated in sol-gel materials would not necessarily lead to higher stabilities over time.     

Ceramic films for optical applications

Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories.     

Graphene‐polymer nanocomposites for biomedical applications

Despite the significant efforts in the synthesis of new polymers, the mechanical properties of polymer matrices can be considered modest in most cases, which limits their application in demanding areas. The isolation of graphene and evaluation of its outstanding properties, such as high thermal conductivity, superior mechanical properties, and high electronic transport, have attracted academic and industrial interest, and opened good perspectives for the integration of graphene as a filler in polymer matrices to form advanced multifunctional composites. Graphene‐based nanomaterials have prompted the development of flexible nanocomposites for emerging applications that require superior mechanical, thermal, electrical, optical, and chemical performance. These multifunctional nanocomposites may be tailored to synergistically combine the characteristics of both components if proper structural and interfacial organization is achieved. The investigations carried out in this aim have combined graphene with different polymers, leading to a variety of graphene‐based nanocomposites. The extensive research on graphene and its functionalization, as well as polymer graphene composites, aiming at applications in the biomedical field, are reviewed in this paper. An overview of the polymer matrices adequate for the biomedical area and the production techniques of graphene composites is presented. Finally, the applications of such nanocomposites in the biomedical field, particularly in drug delivery, wound healing, and biosensing, are discussed.     

Magnetic polymer nanocomposites for environmental and biomedical applications

Hybrid nanomaterials have received voluminous interest due to the combination of unique properties of organic and inorganic component in one material. In this class, magnetic polymer nanocomposites are of particular interest because of the combination of excellent magnetic properties, stability, and good biocompatibility. Organic–inorganic magnetic nanocomposites can be prepared by in situ, ex situ, microwave reflux, co-precipitation, melt blending, and ceramic–glass processing and plasma polymerization techniques. These nanocomposites have been exploited for in vivo imaging, as superparamagnetic or negative contrast agents, drug carriers, heavy metal adsorbents, and magnetically recoverable photocatalysts for degradation of organic pollutants. This review article is mainly focused on fabrication of magnetic polymer nanocomposites and their applications. Different types of magnetic nanoparticles, methods of their synthesis, properties, and applications have also been reviewed briefly. The review also provides detailed insight into various types of magnetic nanocomposites and their synthesis. Diverse applications of magnetic nanocomposites including environmental and biomedical uses have been discussed.     

Hybrid materials for solid-state dye laser applications

The quest for a solid-state tunable dye laser can be satisfied by sol-gel prepared organic-inorganic hybrids. A photostability study of porous silica-Rhodamine 6G hybrids prepared via a sol-gel method is presented. The dye molecules can be incorporated into the silica matrix by forming weak or covalent bonds (hybrids of classes I and II, respectively). New class II samples and traditional class I materials prepared by the pre-doping method were synthesized. Samples were characterized by photoluminescence measurements to compare the emission properties and the photostability of the samples. The decay of the fluorescence signal as the cumulative excitation energy increases is reported and interpreted by hypothesizing that the dye molecules can be hosted in different surroundings within the porous glass matrix. The reported photoluminescence and photobleaching features indicate the class II samples as good candidates for solid-state dye lasers.     

Nematic nanocomposites with enhanced optical birefringence

The proper performance of electro-optical devices utilising liquid crystals (LCs) requires materials with high diffraction efficiency, i.e. with high optical/dielectric anisotropy, low threshold voltage and fast switching. One can achieve increase of dielectric anisotropy by using chemical synthesis or mixing LC materials. However, in most cases, this causes an increase in the threshold voltage and switching times. Therefore obtaining materials with high dielectric anisotropy and keeping threshold voltage and switching times low is a challenging task. We achieved promising results by making binary mixtures of a polar nematic LC 4'-hexyl-4-biphenylcarbonitrile (HBPCN) with low percentage (1–10% by weight) gold nanoparticles. We report that for the mixtures with 1% and 2% gold the dielectric anisotropy increases by 100% and the birefringence by about 50% of their values for pure nematic. We also report that the increase of the dielectric anisotropy in the mixtures only slightly affects threshold voltage and switching times. We propose that this increase is caused by cluster formation in the mixtures.     

Characterization of polypropylene (PP) nanocomposites for industrial applications

This study aims in the examination of a new class of materials named polymer layered silicate nanocomposites. In our case, composites are usually combinations of polypropylene matrix with solid mineral reinforcements named silicates (e,g. montmorillonite, a natural clay). In this study, two complementary techniques used to characterize nanocomposites. Fourier transform infrared spectroscopy (FT-IR) both in transmission and attenuated total reflectance (ATR) modes combined with X-ray photoelectron spectroscopy (XPS).     

Facile synthesis of ZnS/MnS nanocomposites for supercapacitor applications

Journal of Solid State Electrochemistry - In this study, we have reported a facile fabrication of pristine zinc sulfide (ZnS), manganese sulfide (MnS), and ZnS/MnS nanocomposites (NCs) via...     

Industrially produced PET nanocomposites with enhaced properties for food packaging applications

Gas permeation of polymers is one of the important factors to be considered in the selection of materials for many packaging applications, such as modified atmosphere packaging (MAP) for foods. Poly (ethylene therephthalate) (PET) is known to exhibit very low gas permeation compared with most polymers such as polystyrene, polyethylene and polypropylene. However, MAP applications require better barrier performance than that of PET. In the present work PET trays reinforced with organically modified sepiolite, fibrillar nanoclay, have been produced at industrial processes. Permeability to water vapour, oxygen and carbon dioxide has been studied in PET nanocomposites as well as their microstructure through transmission electron and scanning electronic microscopy (TEM and SEM), and their mechanical properties. Results show a better performance in barrier properties as well as an increase in tensile strength, and impact resistance when the sepiolite content is lower than 2.5%.     

Hybrid polysaccharide-silica nanocomposites prepared by the sol-gel technique

New monolithic nanocomposite silica biomaterials were synthesized on the basis of various natural polysaccharides and recently introduced completely water-soluble precursor tetrakis(2-hydroxyethyl) orthosilicate. The sol-gel processes were performed in aqueous solutions without the addition of organic solvents and catalysts. The silica polymerization was promoted by the polysaccharides through acceleration and catalytic effect on the processes. By introducing poly(vinyl alcohol) or poly(ethylene oxide) in the precursor solution, it was shown that the jellification took place in the case of the hydroxyl-containing polymer. Therefore, it was suggested that the catalysis was caused by a formation of hydrogen bonds between hydroxyl groups in macromolecules and products of precursor hydrolysis (silanols). It was also demonstrated that the polysaccharides radically changed the structure of biomaterials. In place of the cross-linked nanoparticles, there was a three-dimensional network from crossed or branched fibers and uncrossed spherical particles that filled the mesh space. The density of network, thickness of fibers, and properties of synthesized biomaterials depended on the polysaccharide type, charged degree of their macromolecule, and concentration. By varying these parameters, it was possible to manipulate the structural organization of hybrid polysaccharide-silica nanocomposites.     

A new procalcitonin optical immunosensor for POCT applications

A new immunosensor for the determination of procalcitonin was developed. A sandwich assay format was implemented on a polymethylmetacrylate optical biochip, opportunely shaped in order to obtain several flow channels and potentially suitable for point of care testing applications. The sandwich format makes use of two new rat monoclonal antibodies. The capture antibody was covalently immobilised on the surface of the plastic chip, and the detection antibody was labelled with DY647 dye. Different combinations of capture and detection antibodies were investigated, and particular attention was devoted in order to avoid the non-specific adsorption. A limit of detection of 0.088 mg L⁻¹ was achieved within the working range of 0.28–50 mg L⁻¹ in buffer samples. The assay was also implemented in human serum, and 0.2 and 0.7–25 mg L⁻¹ were the attained limit of detection and working range, respectively.     

Pickering emulsion-polymerized conducting polymer nanocomposites and their applications

The fabrication of conducting polymer nanocomposites via the Pickering emulsion polymerization process has become a spotlight of the research recently. One of the excellent applications of such conducting polymer nanocomposites is as an electrorheological (ER) fluid, which is a special type of smart suspension with controllable fluidity under an electric field. In this short review, we summarize the range of core–shell-structured conducting polymer nanocomposites synthesized by the Pickering emulsion method and their ER applications.     

Dielectric properties of PANI-PEG nanocomposites filled with silica media for antistatic applications

The dielectric investigations of porous synthetic silica gel modified with polyaniline (PANI) and polyethylene glycol (PEG) polyblend at various concentrations are demonstrated in this paper. By using the chemical oxidative process to embed polyaniline (PANI) and polyethylene glycol (PEG) into a silica matrix, conducting gel nanocomposites were synthesized. For various dopant concentrations, the dielectric permittivity (ε′), D.C. conductivity (σ_dc), loss tangent (tanδ) and dielectric loss (ε″) were investigated. The samples were characterized using differential thermal analysis/thermogravimetric analysis, Fourier transform infrared spectroscopy and high-resolution transmission electron microscopy. Depending on the co-blend content, PANI-PEG modified silica structures produce nanoparticles ranging in size from 9.9 to 48.1 nm. The variation of DC conductivity (σ_dc) with PANI/PEG content shows Maxwell-Wagner Sillars (MWS) effect confirming the role of the conjugation and the structural order.     

Recyclable grease-proof cellulose nanocomposites with enhanced water resistance for food serving applications

Cellulose - Recyclable cellulose nanofibril (CNF) and lignin-containing cellulose nanofibril (LCNF) coated wood flour composites were fabricated using a vacuum-filtration process for food serving...