SiO2–poly(amidoamine) dendrimer inorganic/organic hybrids

SiO₂–poly(amidoamine) (PAMAM) dendrimer hybrids were synthesized via (1) a Michael addition reaction between the dendrimer and 3‐(trimethoxysilyl) propyl acrylate, (2) the dissolution of the formed compound in methanol, and (3) the mixing of the latter solution with a methanol solution of partly hydrolyzed tetraethylorthosilicate (TEOS) and its casting on a glass substrate. ¹H NMR indicated that in the first step, 77% of the secondary amines were converted into tertiary amines when the fourth‐generation dendrimer was employed and 46% were converted when the second‐generation dendrimer was used. The final SiO₂–PAMAM dendrimer hybrids were obtained via the hydrolysis and condensation of the compound obtained via the Michael addition and the methanol solution of partly hydrolyzed TEOS. The compartmentalized structure of the hybrids due to the compartments of the dendrimers could be controlled by changing the dendrimer and the amount of TEOS. Scanning electron microscopy and transmission electron microscopy micrographs provided information about the structure of the hybrids. Like the PAMAM dendrimer, the SiO₂–PAMAM dendrimer hybrids exhibited a high metal ion complexing capacity because of the presence of the compartments of the dendrimer; they can be, however, much more easily handled, and, as demonstrated by thermogravimetric experiments, have much higher thermal resistance. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1443–1449, 2000     

Nanostructured Crosslinkable Micropatterns by Amphiphilic Dendrimer Stamping

Summary: Microcontact printing was used to deposit stable, nanostructured, amphiphilic and crosslinkable patterns of poly(amidoamine organosilicon) (PAMAMOS)‐dimethoxymethylsilyl (DMOMS) dendrimer multilayers onto silicon wafers, glass, and polyelectrolyte multilayers. The effects of dendrimer ink concentration, contact time, and inking method, on the thickness, uniformity, and stability of the resulting patterns were studied using optical microscopy, fluorescence microscopy, atomic force microscopy (AFM), and contact‐angle analysis. Microarrayed dendrimer film thickness was found to be controllable by conditions used during spin self‐assembly.

Optical micrograph of the circular patterns, obtained from a 0.5% PAMAMOS dendrimer solution, on a glass substrate.     

Effective functionalization of multiwalled carbon nanotube with amphiphilic poly(propyleneimine) dendrimer carrying silver nanoparticles for better dispersability and antimicrobial activity

Two multiwalled carbon nanotube hybrids have been prepared: (a) multiwalled carbon nanotubes (MWCNTs) functionalized with amphiphilic poly(propyleneimine) dendrimer (APPI), viz. MWCNTs-APPI, and (b) silver nanoparticles (AgNPs)-deposited multiwalled carbon nanotubes functionalized with an amphiphilic poly(propyleneimine) dendrimer (MWCNTs-APPI-AgNPs). The degree of covalent functionalization of APPI in MWCNTs and deposition of AgNPs in MWCNTs-APPI were examined by Fourier transform infrared spectroscopy, zeta potential, scanning and high-resolution transmission electron microscopy, energy-dispersive spectroscopy, thermogravimetric analysis, and Raman spectroscopy. The amount of APPI functionalized on MWCNTs determined by thermal gravimetric analysis was about 67% which enables an effective dispersability in aqueous and organic solvents without sonication and these solutions were stable for 6 months without undergoing aggregation of MWCNTs. The electronic properties of the hybrid materials were not altered drastically as verified by the Raman studies. The antimicrobial activities of MWCNTs-APPI and MWCNTs-APPI-AgNPs against three different bacteria, viz. Bacillus subtilis, Staphylococcus aureus, and Escheriachia coli illustrated excellent activity.     

Lamellar bridged silsesquioxanes: self-assembly through a combination of hydrogen bonding and hydrophobic interactions

The synthesis of four bis(trialkoxysilylated) organic molecules capable of self-assembly--(EtO)3Si(CH2)3NHCONH-(CH2)n-NHCONH(CH2)3Si(OEt)3 (n = 9-12)--associating urea functional groups and alkylidene chains of variable length is described. These compounds behave as organogelators, forming supramolecular assemblies thanks to the intermolecular hydrogen bonding of urea groups. Whereas fluoride ion-catalysed hydrolysis in ethanol in the presence of a stoichiometric amount of water produced amorphous hybrids, acid-catalysed hydrolysis in an excess of water gave rise to the formation of crystalline lamellar hybrid materials through a self-organisation process. The structural features of these nanostructured organic/inorganic hybrids were analysed by several techniques: attenuated Fourier transformed infrared (ATR-FTIR), solid-state NMR spectroscopy (13C and 29Si), scanning and transmission electron microscopy (SEM and TEM) and powder X-ray diffraction (PXRD). The reaction conditions, the hydrophobic properties of the long alkylidene chains and the hydrogen-bonding properties of the urea groups are determining factors in the formation of these self-assembled nanostructured hybrid silicas.     

Electrochemical synthesis of nanostructured tellurium films

Direct templating of materials via lyotropic liquid crystalline mesophases of non-ionic surfactants provides an elegant and highly versatile route to the production of a wide range of nanostructured materials with well-defined mesoporous architectures of extended spatial periodicities. This technique has now been applied in the electrochemical synthesis of adherent nanostructured tellurium films. This represents an important step towards the synthesis of II–IV semiconductor compounds such as cadmium telluride. Low angle X-ray scattering and transmission electron microscopy (TEM) studies of the resulting tellurium films indicate the presence of a system of uniform cylindrical pores organized in an hexagonal array.     

聚酰胺-胺基两亲树枝状大分子与十二烷基硫酸钠混合体系的分子聚集行为

以浊度分析、动态激光光散射(DLS)、透射电子显微镜(TEM)以及原子力显微镜(AFM)等方法研究了以1.0代(G1)聚酰胺-胺(PAMAM)为核心、以聚环氧丙烷-聚环氧乙烷(PPO-PEO)为辐射臂的树枝状大分子与十二烷基硫酸钠(SDS)之间的相互作用.值得注意的是,当树枝状大分子溶液的浓度为1%(质量分数),SDS的浓度远低于临界胶束浓度(cmc)时,体系的浊度值开始明显升高,DLS、TEM以及AFM的研究结果显示出此时聚集体的尺寸逐渐增加,意味着SDS与树枝状大分子有着很强的分子间相互作用,形成了树枝状大分子与SDS构成的复合物.当SDS浓度增高至0.1mmol·L-1(约为cmc的1%)左右时,体系的浊度值随着SDS浓度的增加变化不大,DLS、TEM、AFM的实验结果显示,聚集体尺寸趋于稳定状态.当SDS的浓度继续升高至0.25和0.5mol·L-1时,体系中形成了SDS分子间的自聚集或者存在多个SDS分子与单个树枝状大分子的分子间聚集.     

Investigation of thermal behaviour of hybrid nanostructures based on Fe2O3 and PAMAM dendrimers

Dendrimers or biofunctionalized dendrimers can be assembled onto magnetic iron oxide nanoparticles to stabilize or functionalize inorganic nanoparticles. Carboxylated poly(amidoamine) PAMAM dendrimers (generation 4.5) have been used for the synthesis of iron oxide nanoparticles, resulting nanocomposites with potential biomedical applications. The present paper aims to systematically investigate the thermal behaviour of nanostructured hybrids based on ferric oxide and PAMAM dendrimers, by differential scanning calorimetry (DSC) technique. The novelty consists both in synthesis procedure of hybrid nanostructures as well as in DSC approach of these nanocomposites. For the first time, we propose a new method to prepare Fe₂O₃??dendrimer nanocomposite, using soft chemical process at high pressure. Commercial PAMAM dendrimers with carboxylic groups on its surface were used. When high pressure is applied, polymeric structures suffer morphological changes leading to hybrid nanostructures' formation. In the same time, crystallinity of inorganic nanoparticles is provided. DSC results showed an increase in thermal stability of composites as compared to commercial dendrimers. This could be due to the formation of strong interactions between ferric oxide and carboxyl groups, as confirmed by Fourier transform infrared spectroscopy. Electron microscopy analysis (SEM/EDX) and size measurements were performed to demonstrate the existence of nanosized particles.     

Effect of fluid-solid interactions on symmetry breaking in closed nanoslits

The possibility of symmetry breaking of the fluid (argon) density distribution across a long closed slit with identical walls composed of solid carbon dioxide was noted in previous papers by the authors. The main conclusion was that there is a range of average densities in which symmetry breaking occurs and that outside that range the fluid density profile is symmetrical. A critical temperature T(sb) was also identified below which symmetry breaking can occur. In this paper, symmetry breaking is examined for walls made of other materials and it is shown that it occurs only when the energy parameter epsilon(fw) of the fluid-wall interaction in the Lennard-Jones potential satisfies the inequalities epsilon(fw1) < or = epsilon(fw) < or = epsilon(fw2), where epsilon(fw1) and epsilon(fw2) are temperature-dependent critical values of epsilon(fw). The value of epsilon(fw1) increases and that of epsilon(fw2) decreases with increasing temperature. The comparison of the theory with Monte Carlo simulations confirms the existence of symmetry breaking across the slit. The possibility of symmetry breaking along the slit is also noted.     

Template Mediated Hybrid from Dendrimer

Novel dendrimer-titania hybrids were prepared in this work from hydroxy and amine terminated polyamidoamine dendrimer (PAMAM generation 4) and titanium alkoxide by an in-situ sol-gel process in presence of a ligand. Dendritic polymers are chosen because of their unique architectural features. Such dendrimer nanocomposite (DNC) can then be used for optical, catalytic, biomedical applications. The hybrid material formed in situ is found to be transparent, brittle and yellow in colour. The hybrids show higher thermal stability than their organic precursors. This is due to enhanced interaction of the inorganic material with the dendrimer through hydrogen bonding as evidenced by PA-FTIR. XPS studies show predominantly the existence of tetravalent titanium due to titania formation.     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

低热固相法制备纳米MnO2/CNT超电容复合电极的循环稳定性

为了改善纳米MnO2超级电容器电极的充放电循环稳定性,以Mn(OAc)2·4H2O、NH4HCO3和碳纳米管(CNT)为原料,采用低热固相反应得到前驱体,再经焙烧和酸处理,制备了一系列CNT含量不同的纳米MnO2/CNT复合电极材料,并用X射线衍射(XRD)、透射电镜(TEM)和Brunauer-Emmett-Teller(BET)比表面积测定方法对其进行了表征.XRD分析结果表明,复合材料中的MnO2为纳米γ-MnO2.研究了复合电极在1 mol·L-1 LiOH电解质中的电化学性能,并与不含CNT的纯纳米MnO2电极进行了比较.结果表明,含CNTs为10%(w,质最分数,下同)和20%的MnO2/CNT复合电极的循环稳定性远优于纯纳米MnO2电极的循环稳定性,其中含10%CNTs的MnO2/CNT复合电极不仪具有良好的循环稳定性,而且在1000 mA·g-1高倍率充放电条件下仍具有200 F·g-1的高比电容.     

Facile preparation and enhanced capacitance of the polyaniline/sodium alginate nanofiber network for supercapacitors

A porous and mat-like polyaniline/sodium alginate (PANI/SA) composite with excellent electrochemical properties was polymerized in an aqueous solution with sodium sulfate as a template. Ultraviolet-visible spectra, X-ray diffraction pattern, and Fourier transform infrared spectra were employed to characterize the PANI/SA composite, indicating that the PANI/SA composite was successfully prepared. The PANI/SA nanofibers with uniform diameters from 50 to 100 nm can be observed on scanning electron microscopy. Cyclic voltammetry and galvanostatic charge/discharge tests were carried out to investigate the electrochemical properties. The PANI/SA nanostructure electrode exhibits an excellent specific capacitance as high as 2093 F g(-1), long cycle life, and fast reflect of oxidation/reduction on high current changes. The remarkable electrochemical characteristic is attributed to the nanostructured electrode materials, which generates a high electrode/electrolyte contact area and short path lengths for electronic transport and electrolyte ion. The approach is simple and can be easily extended to fabricate nanostructural composites for supercapacitor electrode materials.     

Synthesis of a hybrid assembly composed of titanium dioxide nanoparticles and thin multi-walled carbon nanotubes using "click chemistry"

A hybrid assembly composed of thin multi-walled carbon nanotubes (t-MWCNT) and titanium dioxide (TiO(2)) has been prepared by using "click" chemistry for photocatalytic applications. TiO(2)-decorated t-MWCNT hybrids with anatase phase TiO(2) were obtained from the reaction of an azide moiety-containing TiO(2) with alkyne-functionalized t-MWCNTs. The hybrids were systematically characterized using Fourier transform infrared spectroscopic (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrum (EDX), and X-ray diffraction (XRD) measurements. The nanohybrid has been proved to be highly active and robust for photocatalytic degradation of methyl orange. The click coupling approach is a simple and convenient route to efficiently assemble TiO(2) on the surface of carbon nanotubes, and can be extended to obtain many other nanoparticle hybrids based on carbon nanotubes.     

Hybrid and biohybrid silicate based materials: molecular vs. block-assembling bottom-up processes

This critical review introduces a discussion on the influence of preparative procedures (nanofabrication) of nanostructured hybrids and biohybrids, comparing their structural and textural characteristics that determine the properties of the resulting materials. Selected examples of silicate-based hybrids of analogous compositions prepared by both molecular and blocks-assembly bottom-up strategies are discussed to show advantages and inconveniences of each methodology (341 references).     

Gradient shape-persistent pi-conjugated dendrimers for light-harvesting: synthesis, photophysical properties, and energy funneling

A new class of pi-conjugated dendrimers G0, G1, and G2 was developed through a double-stage divergent/convergent growth approach, in which 5,5,10,10,15,15-hexahexyltruxene was employed as the node and oligo(thienylethynylene)s (OTEs) with different lengths as the branching moieties. The dendrimers were fully characterized by (1)H and (13)C NMR, elemental analysis, gel permeation chromatography, and MALDI-TOF MS. Also, by using atomic force microscopy, it was observed that dendrimer G2 laid nearly flat on the mica surface as a single molecule. Dynamic light scattering results showed that the molecule retained its relatively flat shape in solution. To our best knowledge, dendrimer G2, with a radius approaching 10 nm and a molecular weight of 27 072 Da, was the largest among reported second generation dendrimers. The energy gradient in G2 was constructed by linking OTEs of increasing effective conjugation lengths from the dendritic rim to the core. The intramolecular energy transfer process was studied using steady-state UV-vis absorption and photoluminescent spectroscopies, as well as time-resolved fluorescence spectroscopy. Our structurally extended dendrimers showed an excellent energy funneling ability (their energy transfer efficiencies were all over 95%). All results demonstrate that these dendrimers are promising candidates as light-harvesting materials for optoelectronic devices.     

Resolving self-assembly of bile acids at the molecular length scale

The self-assembly behavior of the naturally occurring steroidal bile compounds cholic, deoxycholic, ursodeoxycholic, and lithocholic acid was studied by combining atomic force microscopy (AFM), polarized optical microscopy (POM), Fourier-transform infrared spectroscopy (FTIR), absorption spectroscopy (UV-vis), circular dichroism (CD), and wide-angle X-ray scattering (WAXS). Molecular solutions of these mono-, di-, and trihydroxyl substituted bile acids spontaneously evolved into supramolecular aggregates upon the incremental addition of H(2)O as a poor solvent. Highly crystalline nanostructured multilayered assemblies were formed, which revealed a very rich polymorphism of micro- and macro-structures depending on the chemical structure of the bile acid and the properties of the cosolvent (EtOH or DMSO) used. In particular, AFM allowed resolving the crystalline structure to an unprecedented level. It was thus possible to establish that bile acids associate into H-bonded chiral dimer building blocks, which organize in 2D layers of nanostructured lamellar surface topologies with unique facial amphiphilicity. The detailed understanding of the hierarchical organization in bile acid assemblies may contribute to develop strategies to design bioinspired materials with tailor-made nanostructured surface topologies.     

Naked Au55 clusters: dramatic effect of a thiol-terminated dendrimer

Reaction of the thiol-terminated fourth-generation dendrimer 2-G4 (96 SH groups) with the gold cluster compound Au55(PPh3)12Cl6 in a 3:1 molar ratio in dichloromethane results in the formation of bare Au55 clusters. The cuboctahedrally shaped Au55 particles coalesce to well-formed microcrystals (Au55) infinity. The role of the dendrimer is not only to remove the phosphine and chlorine ligands but also to act as an ideal matrix for perfect crystal growth. Transmission electron microscopy (TEM), small- and wide-angle X-ray diffraction (SAXRD and WAXRD) measurements indicate a structure where rows of edge-linked Au55 building blocks form a distorted cubic lattice. The X-ray data fit best if a 5% reduction of the Au-Au bond length in the Au55 clusters is assumed, in agreement with previous extended X-ray absorption fine structure (EXAFS) measurements. Energy-dispersive X-ray spectroscopy (EDX) analyses and IR investigations show the absence of PPh3 and Cl in the microcrystals.     

Molecular Dynamic Evaluation of starch-PLA blends nanocomposite with organoclay by proton NMR relaxometry

Starch and PLA were used alone and in blends to prepare nanostructured materials using both hydrophilic and organophilic clays, and PVA. All nanostructured materials were obtained by the solution intercalation method using water and chloroform as solvents. These systems were characterized by using conventional X-ray diffraction (XRD), conventional NMR and the non-conventional fast field cycling (FFC) NMR technique. The spin-lattice relaxation times were measured as a function of the Larmor frequency. The FFC results showed that the starch has only one relaxation time related to the amorphous region. PLA hybrids presented two distinct spin-lattice relaxation times. The blends of the two polymers also showed two relaxation times. The renormalized Rouse formalism was applied to describe the polymer molecular dynamics behavior in the studied systems containing starch. By adding clay or PVA, differences could be observed in relaxation time corresponding to the more amorphous region, indicating that, when adding clay and PVA, the effect that each has on the dynamics of the mixture is cancelled out.     

Arylamide dendrimers with flexible linkers via haloacyl halide method

[reaction: see text] Soluble arylamide dendrons with flexible linkers, peripheral ester or carboxyl groups (R), and focal amino or halogen functionalities (F) were synthesized from aryl glycineamide (AG) building blocks. The AG blocks were prepared in high yields from trivial starting materials by Fischer's haloacyl halide method, which also could be extended to the dendrimer synthesis itself. The G2 AG dendrons were coupled to a Pd porphyrin core, demonstrating outstanding encapsulation efficiency in aqueous solutions.     

Nanostructuring of a polymeric substrate with well-defined nanometer-scale topography and tailored surface wettability

This study demonstrates a simple and highly reproducible method for fabricating well-defined nanostructured polymeric surfaces with aligned nanoembosses or nanofibers of controllable aspect ratios, showing remarkable structural similarity with interesting natural biostructures such as the wing surface of Cicada orni and the leaf surface of Lotus. Our studies on the present biomimetic surfaces revealed that the wetting property of the nanostructured surface of a given chemical composition could be systematically controlled by rendering nanometer-scale roughness. The nanofabricating method we developed can be readily extended to other thermoplastic polymeric materials (e.g., light-emitting polymers, conducting polymers, block copolymers, liquid crystalline polymers), and it could be applied to developing a new generation of optical and electronic devices.