Silver nanoparticles blended PEG/PVA nanocomposites synthesis and characterization for food packaging

In this research investigation Silver nanoparticles were synthesised using rapid biological methods using leaf broth of Capparis zeylanica that provides an environmentally friendly, simple and efficient route for synthesis. Anti-microbial study was investigated against different pathogenic bacteria. Synthesized AgNPs were blended with PVA/PEG biopolymer blend and it has been confirmed by FTIR, DSC, Moisture absorption and Anti-microbial analysis that the AgNPs enhances the stability of the polymer PVA/PEG. This thin film composite shows an excellent characteristic in all aspect that able it for food packaging and bio medical applications.     

Enzymatic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate catalyzed by PPL immobilized on silica nanoparticles

Silica nanoparticles were first used as the carrier for the porcine pancreas lipase (PPL) immobilization. The result of transmission electron microscopy (TEM) showed that the immobilized lipase was still in nanosize after enzyme immobilization. The ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) catalyzed by this immobilized PPL (IMPPL) was explored. ¹H NMR spectra suggested no evidence of decarboxylation during propagation. Influences of IMPPL concentration and reaction temperature on the molecular weight and yield of poly(DTC) were studied. The recovery and reuse of IMPPL for the ring-opening polymerization of DTC was also investigated. The recycling IMPPL showed even higher catalytic activity and a higher molecular weight of polycarbonate could be achieved.     

Preparation of polystyrene/montmorillonite nanocomposites using a new radical initiator-montmorillonite hybrid via in situ intercalative polymerization

Polystyrene/montmorillonite (PS/MMT) nanocomposites were prepared by in situ free radical intercalative polymerization, using 1, 3 and 5 wt% of a new cationic radical initiator-MMT hybrid. The corresponding nanocomposites were designated as PS/MMT-1, PS/MMT-3 and PS/MMT-5, respectively. The silicate layers were well exfoliated and randomly dispersed in the PS/MMT-1 and PS/MMT-3, but were less exfoliated in the PS/MMT-5, due to the predominant extra-gallery polymerization over the intra-gallery polymerization. The unique properties of nanocomposites resulted from the strong interactions between the nano-sized silicate layer surfaces and the polymer chains. The onset temperature of thermal degradation, and the glass transition temperature, increased with increasing hybrid content, up to 3 wt%. The molecular weights of the PS in the PS/MMT-1 and PS/MMT-3 were less than those calculated theoretically, due to the predominant intra-gallery polymerization.     

Green synthesis and characterization of polymer-stabilized silver nanoparticles

Silver nanoparticles (Ag-NPs) were synthesized using a facile green chemistry synthetic route. The reaction occurred at ambient temperature with four reducing agents introduced to obtain nanoscale Ag-NPs. The variables of the green synthetic route, such as acidity, concentration of starting materials, and molar ratio of reactants were optimized. Dispersing agents were employed to prevent Ag-NPs from aggregating. Advanced instrumentation techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis), and phase analysis light scattering technique (ZetaPALS) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetic behavior of the Ag-NPs. UV–vis spectra detected the characteristic plasmon at approximately 395–410 nm; and XRD results were indicative of face-centered cubic phase structure of Ag. These particles were found to be monodispersed and highly crystalline, displaying near-spherical appearance, with average particle size of 10.2 nm using citrate or 13.7 nm using ascorbic acid as reductants from particle size analysis by ZetaPALS, respectively. The rapid electrokinetic behavior of the Ag was evaluated using zetapotential (from −40 to −42 mV), which was highly dependant on nanoparticle acidity and particle size. The current research opens a new avenue for the green fabrication of nanomaterials (including variables optimization and aggregation prevention), and functionalization in the field of nanocatalysis, disinfection, and electronics.     

Facile synthesis of palladium nanoparticles supported on urea-based porous organic polymers and its catalytic properties in Suzuki-Miyaura coupling

By using urea linked porous organic polymers as template, a new nano palladium catalyst with low Pd loading can be easily prepared (1.0 wt% Pd only). Although such less amount of Pd was contained in this new catalyst, it is still an effective catalyst for the Suzuki-Miyaura coupling of aryl iodines and aryl boric acids, affording biphenyl products in excellent yields with outstandingly enhanced turnover numbers (up to 10,536) under green solvent (water).     

The synthesis of polyacrylamide nanoparticles in supercritical carbon dioxide

Polyacrylamide nanoparticles, 50 to 200 nm, were created by inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. The cross-linked polyacrylamide was produced by intermolecular imidization.     

Improved self-healing performance of polymeric nanocomposites reinforced with talc nanoparticles (TNPs) and urea-formaldehyde microcapsules (UFMCs)

The present work reports the self-healing performance of the epoxy based polymeric nanocomposite coatings containing different concentrations (1 and 3 wt%) of talc nanoparticles (TNPs) modified with sodium nitrate (NaNO₃), and a fixed amount (5 wt%) of urea-formaldehyde microcapsules (UFMCs) encapsulated with linseed oil (LO). The polymeric nanocomposites were developed, coated on polished steel substrates, and their structural, thermal, and self-healing characteristics were investigated using various techniques. The successful loading (~wt 10%) of NaNO₃ into TNPs, which can be ascribed to the involvement of physio-chemical adsorption mechanism, is validated and proceeds without altering the TNPs parent lamellae structure. The performed tests elucidated that the self-release of the corrosion inhibitor (NaNO₃) from TNPs is sensitive to the pH of the solution and immersion time. In addition, the release of the linseed oil (self-healing agent) from UFMCs in response to the external damage was found to be a time-dependent process. The superior self-healing and corrosion inhibition performance of the protective polymeric nanocomposites coatings containing 3 wt% TNPs and UFMCs/LO are proven using the electrochemical impedance spectroscopy (EIS) studies. A careful selection of smart carriers, inhibitor, and self-healing agent compatible with polymeric matrix has enabled to attain decent self-healing and convincing corrosion inhibition efficiency of 99.9% and 99.5%, respectively, for polymeric nanocomposites coatings containing 3 and 1 wt% TNPs, making them attractive for many industrial applications.     

Effects of production parameters on the structure of resol type phenolic resin/layered silicate nanocomposites

Polymer/layered silicate nanocomposites belong to one of the most promising group of materials of the past few decades and most probably for the near future. Following the pioneering works of Toyota Research Group in the 1980s, the interest on these materials increased rapidly and research is now being carried out world wide, using all kinds of polymers as base material.In this present study, the aim was to investigate the effects of several different production parameters; on the morphology of resol type phenol formaldehyde based layered silicate nanocomposites produced by mixing and casting. For this purpose; two different liquid resol type phenolic resins (PF76 and PF76TD), two different curing methods (heat cure route and acid cure route), two different montmorillonite clays (unmodified Cloisite Na+ and modified Rheospan), two different clay sources (Wyoming-USA and Tokat-Turkey), and five different clay amounts (0.5%, 1%, 1.5%, 3%, 10%) were used.XRD, SEM, TEM analyses and mechanical tests indicated that resol type phenolic resins lead to better structures when they were modified with ethylene glycol and cured by the use of an acidic curing agent. It was also observed that use of modified clay with no more than 1.5 wt% in the phenolic matrix lead to certain degree of exfoliation consequently better structure and higher mechanical performance.     

One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85×10^–8 to 6.15×10^–7 M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.     

Size-controllable synthesis of monodispersed colloidal silica nanoparticles via hydrolysis of elemental silicon

A new method is presented for preparing monodisperse and uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions including solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the silica particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10–100 nm were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media.     

The formation of hydrophobic inorganic nanoparticles in the presence of amphiphilic copolymers

The presented paper describes a novel procedure for the preparation of inorganic nanoparticles and their surface functionalization in situ dedicated to an application in technical polymers. Using an inverse emulsion technique and amphiphilic block or statistical copolymers as stabilizers, a broad variety of nanoparticles such as ZnO, CdS, MgCO₃, Ni, or Cu can be prepared. The amphiphilic polymers serve not only as surface active compounds in the emulsion but also to hydrophobize the inorganic particles as they remain adsorbed on the surface after the precipitation. As a consequence of the high degree of surface coverage by polymer chains, organic solvents are able to redisperse these particles in the aggregate free manner. The utilization of the block copolymers instead of statistical copolymers resulted in the formation of the particles, which were larger in size and possessed a much broader size distribution. The chemical nature of the adsorbed polymer layer on the particle surface is crucial to the preparation of polymer nanocomposites. The primary goal of this contribution is to demonstrate the universality of such a one-pot synthetic procedure, which was found to be relevant for industrial use.     

Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.     

Synthesis of a novel benzoxazine monomer‐intercalated montmorillonite and the curing kinetics of polybenzoxazine/clay hybrid nanocomposites

Polybenzoxazine (PBZ), which has a structure similar to that of phenolic resin, is formed through the thermal self‐curing of benzoxazine, that is through a heterocyclic ring opening reaction that requires no catalyst and releases no condensation byproducts. We have used the solvent blending method to prepare PBZ/clay nanocomposites possessing various clay contents. We synthesized a monofunctional benzoxazine monomer (MBM) and then treated the clay with this intercalation agent. The results of X‐ray diffraction (XRD) analysis indicated that MBM intercalated into the galleries of the clay; the nanocomposite possessed an exfoliated structure at 3% clay content. To better understand the curing kinetics of the PBZ/clay nanocomposites, we performed dynamic and isothermal differential scanning calorimetry (DSC) measurements. We describe the thermodynamics of the curing process, using all three of the Kissinger, Ozawa, and Kamal models. The Kissinger and Ozawa methods gave fairly close results for the calculated activation energies, which decreased upon increasing the clay content. The Kamal method, based on an autocatalytic model, suggested a total reaction order of between 2.4 and 2.8. The glass transition temperature (T_g) decreased upon increasing the clay content. Thermogravimetric analysis (TGA) indicated that the nanocomposites have higher decomposition temperatures than does the pristine PBZ; this finding suggests an enhancement in their thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 347–358, 2006     

Synthesis of miktoarm star (block) polymers based on a heterofunctional initiator via combination of ROP, ATRP and functional group transformation

Versatile miktoarm three-arm star polymers, (polystyrene)(polyε-caprolactone)₂ ((PS)(PCL)₂), (PS-b-poly(n-butyl acrylate))(PCL-b-PS-b-poly(n-butyl acrylate))₂ ((PS-b-PnBA)(PCL-b-PS-b-PnBA)₂) and (PtBA-b-PS)(PCL-b-PtBA-b-PS)₂ were synthesized via combination of atom-transfer radical polymerization (ATRP), functional group transformation technique and ring opening polymerization (ROP) using 1,1-dihydroxymethyl-1-(2-bromoisobutyryloxy)methyl ethane (DHB) as a heterofunctional initiator. In the synthesis of (PS)(PCL)₂ by combination of ROP of ε-caprolactone (ε-CL) and ATRP, the implementation sequence, ROP followed by ATRP, was proved to be effective to get a well-defined miktoarm star polymer than the reverse one. The two miktoarm star block polymers, (PS-b-PnBA)(PCL-b-PS-b-PnBA)₂ and (PtBA-b-PS)(PCL-b-PtBA-b-PS)₂, were prepared by one ROP step, one group transformation and ATRP steps using the same initiator. All the polymers have defined structures and their molecular weights are adjustable with good controllability.     

Conductive elastomeric nanocomposites based on oxidation of aniline with silver nitrate via inverse emulsion polymerization

The present investigation describes a facile and rapid approach of conductive nanocomposites production and assesses the opportunity of their use as electro‐mechanical sensors. Hybrid materials containing silver and polyaniline nanoparticles reinforcing a thermoplastic elastomeric matrix were studied. The approach developed includes ultrasonically assisted in situ inverse emulsion polymerization of aniline oxidized by a weak oxidant and silver nitrate, and supported with a strong oxidant, ammonia peroxydisulfate. Aniline was doped with dodecylbenzene sulfonic acid in the presence of dissolved styrene–isoprene–styrene thermoplastic elastomer. While conventional polymerization of aniline with silver nitrate takes 2 weeks, by utilization of inverse emulsion polymerization, the reaction time reduces to 5 days. The assistance of a strong oxidant dramatically shortens the reaction time to 30 min. The technique developed results in uniform distribution of polyaniline/silver (PANI/Ag) conductive nanoparticles in the elastomeric matrix. The morphological studies of the films reveal spherically shaped 45 nm Ag particles. The presence of PANI/Ag in the styrene–isoprene–styrene elastomeric matrix enhances the electrical, thermal, and mechanical properties of the nanocomposites. The approach described provides an opportunity of the development of tunable structures and a remarkably distinctive architecture. A rapid electrical resistance response to an applied strain makes the nanocomposites developed useful as sensitive strain sensors. Copyright © 2014 John Wiley & Sons, Ltd.     

Facile synthesis of polyacrylate directed silver nanoparticles for pH sensing through naked eye

Poly(acrylic acid) (PAA) and its salt poly(acrylate) (PA) have been synthesized through modified free radical polymerization in environmentally begin aqueous medium under ultrasound to make the process robust. The synthesized polymer is well-characterized through conventional techniques. Its salt is employed to produce highly stable and stimuli sensitive colloidal silver (Ag-PA sol) without using any additional reducing chemical reagents like sodium borohydride, ascorbic acid, hydrazine, etc or UV/Gamma radiation. A detailed mechanistic path of the polymerization and reduction of Ag⁺ on polyacrylate chains has been evaluated. Finally Ag-PA sol is used for pH sensing through naked eye to eliminate the need for sophisticated instrument for data collection. The present work focuses mainly the development of a low cost pH sensing system based on colorimetric ‘smart polymer’ having high practical utility. The unique structural and photo-physical features of nano-scaled materials open new opportunities for the applications of colorimetric pH sensor. In the present work, Ag nano-clusters capped by PA^? are employed as an effective colorimetric pH sensor for the first time, requiring no further functionalization.     

An intriguing electrochemical impedance aptasensor based on a porous organic framework supported silver nanoparticles for ultrasensitively detecting theophylline

Porous organic frameworks (POFs) are excellently stable porous materials, which can be employed as host platforms to support metal nanoparticles as functional composites for various applications. Herein, a novel POF is successfully prepared via Friedel-Crafts reaction. Silver nanoparticles (Ag NPs) are embedded in the prepared POF to generate an Ag@POF composite, which not only possesses high surface area, outstanding physicochemical stability and outstretched π-conjugation skeleton, but also exhibits preferable electrochemical stability and conductivity. This composite is able to immobilize a mass of aptamer strands to fabricate an intriguing electrochemical aptasensor. Electrochemical impedance spectroscopy (EIS) is a commonly used technology to analyze the electrochemical signal variation. The Ag@POF-based biosensor shows the excellent electrochemical detection behavior through analyzing EIS. For instance theophylline as a research mode, the Ag@POF based electrochemical aptasensor reveals ultra-sensitiveness, high selectivity, remarkable stability, good repeatability and simple operability even in various real samples. Notably, this aptasensor has the sensitive detection performance with the limit of detection of 0.191 pg/mL (1.06 pmol/L) in a wide concentration range of 5.0 × 10^-4 – 5.0 ng/mL (2.78 × 10^-3 – 27.8 nmol/L).     

Tandem synthesis of silver nanoparticles and nanorods in the presence of poly(oxyethylene)-amidoacid template

Sequential formation of silver nanoparticles (AgNPs) and nanorods from the reduction of AgNO₃ was affected by a poly(oxyethylene)-amidoacid (POE-amidoacid) in aqueous solution. The requisite POE-amidoacid, consisting of –(CH₂CH₂O)_n– segments with amide and carboxyl groups, was simply prepared via amidation with trimellitic anhydride of a poly(oxyethylene)-monoamine (POE-amine) of molecular weight (M_w) ∼2000 g/mol. The POE-amidoacid afforded AgNPs as small as 5 nm in diameter, which gradually (over a period of months) self-assembled into nanorods that were 10–15 nm in width and 30–50 nm in length. The hierarchical formation of Ag species occurred only at ambient temperature, but Ag aggregates formed above 50 °C. The process could be monitored by UV absorption at 420 and 380 nm for AgNPs and nanorods, respectively, and by transmission electron microscopy (TEM) for the nanorods. Fourier transform infrared (FTIR) and tapping-mode atomic force microscopy (TM-AFM) analyses revealed that the structurally tailored POE-amidoacid was indeed multifunctional: it reduced Ag⁺, stabilized the obtained Ag⁰ species, and served as a template for the tandem formation of AgNPs and nanorods.