Thermosensitive polymer (N-isopropylacrylamide) coated nanomagnetic particles: preparation and characterization

Thermosensitive polymer coated nanomagnetic adsorbents were synthesized by seed polymerization using surface modified nanomagnetic particles as the seeds. The Fe3O4 nanomagnetic particles were prepared by chemical precipitation of Fe2+ and Fe3+ salts in the ratio of 1:2 under alkaline and inert condition. The surface of these particles was modified by surfactants to achieve stability against agglomeration. These stable particles were then polymerized using N-isopropylacrylamide (NIPAM) as the main monomer, methylene-bis-acrylamide as the crosslinker and potassium per sulfate as the initiator. The thermosensitive adsorbents were characterized by using transmission electron micrography (TEM) and vibrating sample magnetometer (VSM). TEM showed that the particle remained discrete with a mean diameter of 12 nm. Magnetic measurements revealed that the particles are superparamagnetic only with a decrease of magnetism after binding with the polymer due to the increase in surface spin disorientation. Pure Fe3O4 spinel structure of these nanoparticles was indicated by the X-ray diffraction (XRD) patterns. The polymerization of NIPAM with the surface modified nanomagnetic particles was confirmed by Fourier transform spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). In addition, the adsorption/desorption of BSA molecule on these thermosensitive nanoparticles was investigated as a function of temperature. More than 60% desorption efficiency was achieved under appropriate condition.     

Poly(methyl methacrylate) composites with size‐selected silver nanoparticles fabricated using cluster beam technique

An embedment of metal nanoparticles of well‐defined sizes in thin polymer films is of significant interest for a number of practical applications, in particular, for preparing materials with tunable plasmonic properties. In this article, we present a fabrication route for metal–polymer composites based on cluster beam technique allowing the formation of monocrystalline size‐selected silver nanoparticles with a ±5–7% precision of diameter and controllable embedment into poly (methyl methacrylate). It is shown that the soft‐landed silver clusters preserve almost spherical shape with a slight tendency to flattening upon impact. By controlling the polymer hardness (from viscous to soft state) prior the cluster deposition and annealing conditions after the deposition the degree of immersion of the nanoparticles into polymer can be tuned, thus, making it possible to create composites with either particles partly or fully embedded into the film. Good size selection and rather homogeneous dispersion of nanoparticles in the thin polymer film lead to excellent plasmonic properties characterized by the narrow band and high quality factor of localized surface plasmon resonance. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1152–1159     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Studies on Morphology and Conductivity of Poly (N-methyl aniline) Nanoparticles Prepared in Nonstirred Reaction Medium

Summary: Polyaniline has elicited the most interest due to its wide range of applications in many fields. However insolubility and infusibility are the main factors that affect the application of polyaniline. We have studied and worked on the synthesis of dispersible polyaniline and the results are described here. Poly (N-methyl aniline) PNMANI nanoparticles with controllable morphology and sizes were prepared by removing a routine operation stirring from the conventional method of synthesis and using acrylic acid as a soft template. It is found that polymer formed in the non-stirring experiment predominantly produces highly dispersible, smooth nanoparticles with controllable morphology and sizes. These nanoparticles have large surface area and thereby high conductivity. Mechanism for generation of well dispersed and smooth nanoparticles is supported by homogeneous nucleation of polymer nanoparticles in non stirred experiments and the use of acrylic acid as a soft template. In the case of the experiment where the reaction mixture was stirred at 1000 RPM comparatively coral-like, granular and uncontrolled polymer particles were formed. These coral like granular particles were having comparatively small surface area and less conductivity. Conductivity measurements, UV- visible, XRD, FTIR spectroscopy and SEM were performed to characterize the product. This method can be used to synthesize highly conductive polymers in minimum time and bulk quantity.     

Epoxy polymer coating to prevent the corrosion of aluminum nanoparticles

Aluminum nanoparticles were coated by epoxy polymer in order to prevent the corrosion reaction. The coverage of the epoxy polymer film was controlled from 0% to 100%, which changed the corrosion rate of nanoparticles quantitatively. The surface of the polymer coating was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM), and the corrosion resistance of these nanoparticles was estimated by the wet/dry corrosion test on platinum (Pt) plate with a NaCl solution. From a TEM analysis, 10 mass% polymer‐coated Al particles in the synthesis were almost 100% covered on the surface by a polymer film of 10 nm thick. On the other hand, 3 mass% polymer‐coated Al was partially covered by a film. In the AFM–Kelvin force microscopy, the potential around the Al particles had a relatively low value by the polymer coating, which indicated that the conductivity of the Al was isolated from Pt plate by the polymer. Both the corrosion and H₂ evolution reaction rates were quantitatively reduced by the mass% of polymer coating. In the case of 10 mass% coated sample, there was very little corrosion of Al nanoparticles. This fact suggested that the electrochemical reaction was suppressed by the polymer coating. Thus, it was found that the corrosion reaction rate of Al nanoparticles could be quantitatively suppressed by the mass% of epoxy coating. Copyright © 2015 John Wiley & Sons, Ltd.     

Interactions of O(2) with Pd nanoparticles on alpha-Al(2)O(3)(0001) at low and high O(2) pressures

The interaction of O(2) with small Pd particles (2-10 nm) supported on an alpha-Al(2)O(3)(0001) single crystal under both ultrahigh vacuum (UHV) and high-pressure conditions has been studied by temperature-programmed desorption (TPD), temperature-programmed low-energy ion scattering (TP-LEIS), and X-ray photoelectron spectroscopy (XPS). A low O(2) exposure (30 L) at 500 K leads to surface oxygen adatoms on the Pd nanoparticles, which desorb in TPD as O(2) in a peak at approximately 880 K. Surface O adatoms on the smallest Pd particles move to subsurface sites starting at 400 K, and they almost all move subsurface by approximately 750 K, desorbing mainly at considerably higher temperature. The dominant oxygen species above 700 K is subsurface, implying that it is more stable than oxygen adatoms on Pd. Exposures of the Pd nanoparticles to 25 Torr O(2) at 373-473 K readily convert the Pd to a species whose Pd XPS peak shifts by the same amount as the binding energy difference between bulk Pd and bulk PdO. We attribute this to PdO nanoparticles (or a thin film of PdO on or under the Pd for the larger particles). The decomposition of the PdO on these nanoparticles to Pd in an equilibrium O(2) pressure of 10-7 Torr does not occur until approximately 750 K, or approximately 200 K higher than the equilibrium decomposition of bulk PdO. This is attributed to the higher energy of Pd nanoparticles compared to bulk Pd and, for the larger particles, to the adhesion energy of the PdO film to the Pd, both of which stabilize the PdO on these Pd nanoparticles relative to bulk PdO. This PdO-like film on the larger particles may be similar to the ordered oxide thin film previously reported to form on Pd(111) but may also reside at the alpha-Al(2)O(3) interface and be partially stabilized by adhesion to this interface.     

Co-Pt alloy nanoparticles produced using a template of nanoparticle array

A monolayer of Co-Pt alloy nanoparticles in the nanometer-size regime was fabricated using a nanotemplate approach. 1.7-nm-thick Co46Pt54 film was deposited onto a preexisting array of Ni seed particles embedded in a polyimide film. During subsequent annealing, the deposited Co46Pt54 film coalesced onto the seed particles to produce a monolayer of Co-Pt alloy particles. Deposition and annealing were repeated to increase both average particle size and volume fraction of the alloy particles. It was also shown that the annealing temperature was critical in controlling the particle size distribution and the final composition of the nanoparticles. This method of forming a single layer of vertically aligned nanoparticles can be easily extended to a large area as well as to produce a different combination of alloy particles on a polymer film.     

Green Synthesis of Fe and Fe/Pd Bimetallic Nanoparticles in Membranes for Reductive Degradation of Chlorinated Organics

Membranes containing reactive nanoparticles (Fe and Fe/Pd) immobilized in a polymer film (polyacrylic acid, PAA-coated polyvinylidene fluoride, PVDF membrane) are prepared by a new method. In the present work a biodegradable, non-toxic -"green" reducing agent, green tea extract was used for nanoparticle (NP) synthesis, instead of the well-known sodium borohydride. Green tea extract contains a number of polyphenols that can act as both chelating/reducing and capping agents for the nanoparticles. Therefore, the particles are protected from oxidation and aggregation, which increases their stability and longevity. The membrane supported NPs were successfully used for the degradation of a common and highly important pollutant, trichloroethylene (TCE). The rate of TCE degradation was found to increase linearly with the amount of Fe immobilized on the membrane, the surface normalized rate constant (k(SA)) being 0.005 L/m(2)h. The addition of a second catalytic metal, Pd, to form bimetallic Fe/Pd increased the k(SA) value to 0.008 L/m(2)h. For comparison purposes, Fe and Fe/Pd nanoparticles were synthesized in membranes using sodium borohydride as a reducing agent. Although the initial k(SA) values for this case (for Fe) are one order of magnitude higher than the tea extract synthesized NPs, the rapid oxidation reduced their reactivity to less than 20 % within 4 cycles. For the green tea extract NPs, the initial reactivity in the membrane domain was preserved even after 3 months of repeated use. The reactivity of TCE was verified with "real" water system.     

Impedance change induced by varying polymerization temperature of conducting polymer thin films

In this study, we use a conducting polymer precursor to build layer-by-layer (LbL) films. Thermal conversion of the polymer precursor to conducting polymer makes the LbL films intractable, so the LbL films can be used as protective layers in salt solution. The conducting polymer LbL film shows stabilizing effect on top of another LbL thin film that contains nanoparticles. The LbL film prepared in this study shows a 35-fold increase of conductivity than the literature values obtained from non-conducting polymer films. The stabilization of the films is the result of the polymerization of the conducting polymer, so other anionic polymers or nanoparticles may be used to afford additional functionalities.     

化学修饰电极的研究ⅩⅢ. 聚乙烯二茂铁(PVFc)薄膜电极和电催化效应

本文研究了影响PVFc薄膜电极伏安性质的各种因素, 讨论了聚合物薄膜电极的电荷传递过程。溶液平衡离子的水合半径大小、离子强度、溶剂对薄膜的溶胀性质以及聚合物薄膜的厚度是影响聚合物薄膜电极伏安性质的主要因素。研究了PVFc薄膜电极对亚铁氰化钾、左旋多巴和儿茶酚的电催化作用, 用旋转园盘电极研究了催化过程动力学。抗坏血酸和儿茶酚的混合物在PVFc薄膜电极上呈现分开的氧化还原峰, 有应用于生物化学分析的意义。     

Fe, Co, Ni-聚合物-C复合催化剂的制备及对乙醇电催化氧化性能研究

采用模板聚合物与金属离子配位-碳粉负载-还原方法得到的纳米复合材料P-M-C (P为聚合物, M为Fe, Co, Ni金属纳米颗粒, C为碳粉XC72). 利用红外光谱(IR)对中间产物进行了表征, 结果表明所制物质为目标产物P; 透射电镜(TEM)结果表明Fe, Co, Ni纳米粒子粒径多数为20～30 nm, 部分在10 nm左右, 纳米粒子均匀地分散在聚合物P上; 扫描电镜的能谱(SEM-EDS)分析结果证实了Fe, Co, Ni三种元素的存在. 通过循环伏安和计时电流法研究表明, 碱性介质中P-M-C复合催化剂对乙醇电化学氧化具有高催化活性和稳定性; 反向高效液相色谱(HPLC)结果表明乙醇氧化后的产物部分为乙醛和乙酸的混合物.     

Encapsulation and sustained release of a model drug, indomethacin, using CO(2)-based microencapsulation

A carbon dioxide (CO(2))-based microencapsulation technique was used to impregnate indomethacin, a model drug, into biodegradable polymer nanoparticles. Compressed CO(2) was emulsified into aqueous suspensions of biodegradable particles. The CO(2) plasticizes the biodegradable polymers, increasing the drug diffusion rate in the particles so that drug loading is enhanced. Four types of biodegradable polymers were investigated, including poly(d,l-lactic acid) (PLA), poly(d,l-lactic acid-co-glycolic acid) (PLGA) with two different molar ratios of LA to GA, and a poly(d,l-lactic acid-b-ethylene glycol) (PLA-PEG) block copolymer. Biodegradable nanoparticles were prepared from polymer solutions through nonsolvent-induced precipitation in the presence of surfactants. Indomethacin was incorporated into biodegradable nanoparticles with no change of the particle size and morphology. The effects of a variety of experimental variables on the drug loadings were investigated. It was found that the drug loading was the highest for PLA homopolymer and decreased in PLGA copolymers as the fraction of glycolic acid increased. Indomethacin was predicted to have higher solubility in PLA than in PLGA based on the calculated solubility parameters. The drug loading in PLA increased markedly as the temperature for impregnation was increased from 35 to 45 degrees C. Drug release from the particles is a diffusion-controlled process, and sustained release can be maintained over 10 h. A simple Fickian diffusion model was used to estimate the diffusion coefficients of indomethacin in the biodegradable polymers. The diffusion coefficients are consistent with previous studies, suggesting that the polymer properties are unchanged by supercritical fluid processing. Supercritical CO(2) is nontoxic, easily separated from the polymers, can extract residual organic solvent, and can sterilize biodegradable polymers. The CO(2)-based microencapsulation technique is promising for the production of drug delivery devices without the use of harmful solvents.     

Poly(ethyleneimine) as reducing and stabilizing agent for the formation of gold nanoparticles in w/o microemulsions

This paper is focused on the use of branched poly(ethyleneimine) (PEI) as reducing as well as stabilizing agent for the formation of gold nanoparticles in different media. The process of nanoparticle formation was investigated, in the absence of any other reducing agents, in microemulsion template phase in comparison to the nucleation process in aqueous polymer solution.

On the one hand, it was shown that the polyelectrolyte can be used for the controlled single-step synthesis and stabilization of gold nanoparticles via a nucleation reaction and particles with an average diameter of 7.1 nm can be produced.

On the other hand, it was demonstrated that the polymer can also act as reducing and stabilizing agent in much more complex systems, i.e. in water-in-oil (w/o) microemulsion droplets. The reverse microemulsion droplets of the quaternary system sodium dodecylsulfate (SDS)/toluene–pentanol (1:1)/water were successfully used for the synthesis of gold nanoparticles. The polymer, incorporated in the droplets, exhibits reducing properties, adsorbs on the surface of the nanoparticles and prevents their aggregation. Consequently, nanoparticles of 8.6 nm can be redispersed after solvent evaporation without a change of their size.

Nevertheless, the polymer acts already as a “template” during the formation of the nanoparticles in water and in microemulsion, so that an additional template effect of the microemulsion is not observed.

The particle formation for both methods is checked by means of UV–vis spectroscopy and the particle size and size distribution are investigated via dynamic light scattering and transmission electron microscopy (TEM).     

Preparation of polymer colloids by chemical reactions in aerosols. I. Poly(p-tertiarybutylstyrene)

A procedure was developed by which polymer colloids can be prepared by polymerizing aerosol droplets of monomers with an initiator in the vapor state. This work describes the formation of poly(p-tertiarybutylstyrene) particles by exposing the corresponding monomer droplets to trifluoromethanesulfonic acid. It was found that the monomer-to-initiator mass ratio is the critical factor in determining the uniformity and morphology of the particles. Under ideal conditions spheres of narrow size distribution are obtained. Otherwise porous particles or soft particles with whiskers may develop. The aerosol was prepared in a falling film generator, but other procedures for producing monomer droplets may be used.     

Photoreactions of a polyamic acid containing 2,2-dinitrodiphenylmethane segments at symmetrical positions in the main chain

A polyamic acid containing 2,2^′-dinitrodiphenylmethane segments in the main chain was synthesized from 4,4^′-diamino-2,2^′-dinitrodiphenylmethane and pyrromellitic dianhydride. Irradiation of the polyamic acid was done in solution (in a protic solvent, isopropanol, in isopropanol in the presence of a triplet exciter, benzophenone and in acidified isopropanol) and as thin film. The irradiations were done in an immersion type photoreactor using a 125 W high-pressure mercury vapour lamp. The average molecular weights of the polymers were determined by gel permeation chromatography. The polydispersity index of the polyamic acid and the photoproduct showed the absence of photodegradation. The photoproducts were identified by comparing the spectra of polymer photoproducts with that of low molecular weight 2,2^′-dinitrodiphenylmethane derivatives under identical conditions. A possible mechanism for the phototransformations is suggested. Evaluation of photoresist behaviour of the polyamic acid was also done.     

Nanoparticle Dispersion and Glass Transition Behavior of Polyimide-grafted Silica Nanocomposites

How to control the spatial distribution of nanoparticles to meet different performance requirements is a constant challenge in the field of polymer nanocomposites.Current studies have been focused on the flexible polymer chain systems.In this study,the rigid polyimide(PI) chain grafted silica particles with different grafting chain lengths and grafting densities were prepared by "grafting to" method,and the influence of polymerization degree of grafted chains(N),matrix chains(P),and grafting density(a) on the spatial distribution of nanoparticles in the PI matrix was explored.The glass transition temperature(Tg) of PI composites was systematically investigated as well.The results show that silica particles are well dispersed in polyamic acid composite systems,while aggregation and small clusters appear in PI nanocomposites after thermal imidization.Besides,the particle size has no impact on the spatial distribution of nanoparticles.When σ·N0.5<<(N/P)2,the grafted and matrix chains interpenetrate,and the frictional resistance of the segment increases,resulting in restricted relaxation kinetics and Tg increase of the PI composite system.In addition,smaller particle size and longer grafted chains are beneficial to improving Tg of composites These results are all propitious to complete the microstructure control theory of nanocomposites and make a theoretical foundation for the high performance and multi-function of PI nanocomposites.     

Nanoparticles fabricated by selective reaction of Fe100-xPtx alloy films during imidization of polyamic acid

Nanoparticles with different morphology and composition were fabricated inside a polyimide (PI) matrix based on selectively oxidizing a layer of Fe(100-x)Pt(x) alloy metal film sandwiched between two PI precursor layers. Gamma-Fe2O3, Pt, and Fe3Pt nanoparticles were formed in a monolayer between two PI layers, depending on the alloy film composition and curing conditions. These particles were well-crystallized and sized between 4 and 10 nm. X-ray photoelectron spectroscopy confirmed that Fe in the film preferentially reacted with the organic matrix whereas Pt remained metallic throughout the curing process, which enabled fabrication of particles different morphology and composition. This process can be easily extended to other alloy films, which provides an opportunity to fabricate nanoparticles relatively easily with desired composition and morphology embedded in an inert organic matrix.     

Synthesis of iron oxide nanoparticles in a polyimide matrix

A monolayer of gamma-Fe(2)O(3) nanoparticles embedded in a polyimide (PI) matrix was fabricated by oxidizing an Fe metal film between two PI precursor layers. There was a critical Fe thickness ( approximately 7 nm) above which a continuous layer of gamma-Fe(2)O(3) film was formed in the PI film. Below the critical Fe thickness, the oxide film broke up into fine particles whose size was approximately 8 nm with narrow size distribution. It was further shown that these nanoparticles could have metallic cores, surrounded by an oxide layer. This method offers a unique way of covering a large surface area with fine magnetic oxide nanoparticles for potential application in high-density data-storage media.     

Synthesis and structure of poly-3,4-ethylenedioxythiophene film with the inclusions of palladium nanoparticles

By chemical deposition of ultrafine particles of metallic palladium on the polymer matrix of poly-3,4-ethylenedioxythiophene (PEDOT) composite PEDOT/Pd films were obtained. The conditions of synthesis of the composite films in dependence on the duration of exposure of the reduced form of PEDOT film in a solution of palladium chloride, its concentration and the film thickness were studied. By the methods of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) it was shown that in the process of the synthesis of the composite films the nanosized palladium particles of predominantly quasispherical shape precipitated on the globular structure of the polymer. The size of the palladium nanoparticles in the composite PEDOT film and the nature of their distribution over the film bulk were revealed. An increase in the duration of deposition of the palladium nanoparticles on the film was shown to lead to an increase in their size and in the density of particles in the film.     

Novel synthesis of polyimide with pendant 1-phenylethyl ester using DBU and its thermal acid-catalyzed deesterification

A model reaction of o-(N-phenylcarbamoyl)benzoic acid (amic acid) with threefold amounts of 1-phenylethyl bromide (PEB) and 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) was carried out in NMP. The reaction gave N-[m-(1-phenylethoxycarbonyl)phenyl]phthalimide in almost quantitative yield at room temperature for 2 h. Polyimide containing pendant 1-phenylethyl ester (P-1a) was also prepared from polyamic acid with PEB using DBU according to the model reaction. The obtained polymer was exactly consistent with P-1a synthesized stepwise from the esterification of the corresponding polyimide containing pendant carboxylic acid with PEB. Therefore, the reaction of polyamic acid bearing pendant carboxylic acid with alkyl bromide proceeded quantitatively to give polyimide containing pendant ester in the presence of DBU. Also, this method was applied to the synthesis of polyimide containing 1-phenylethyl ether. However, the polyimide with quantitative etherification was not synthesized. The acid-catalyzed deesterification of P-1a film was carried out by heating the irradiated polymer film containing 10 wt % of p-nitrobenzyl 9,10-diethoxyanthracene-2-sulfonate, which produced sulfonic acid by irradiation, at various temperatures. Although thermal deesterification of P-1a started at 220°C without any acid catalyst, the deesterification occurred when the irradiated film was heated at the lower temperature. The degree of esterification can be determined from the disappearance of absorption at 700 cm⁻¹. The deesterification obeyed first-order kinetics. © 1996 John Wiley & Sons, Inc.