Electrostatic assembly of core-corona silica nanoparticles onto cotton fibers

In this investigation core-corona silica nanoparticles were employed to decorate cotton fibers using electrostatic forces. The resultant composites of silica and cellulose were characterized by FESEM and TEM techniques revealed that layers of the core-corona silica deposited on cotton fibers were more uniform and smoother than those of colloidal silica nanoparticles. This improvement was mostly due to the enhanced dispersion and stabilization capabilities of the covalently bonded corona of silica nanoparticles. Experimental results also unveiled that the adsorption amount of nano core-corona silica materials was strongly governed by the surface charge density and charge strength of the cellulosic substrates. The incorporation of core-corona nanoparticles on cotton will provide a wide range of applications for this natural substrate as the surface properties can be fine tuned by a judicious choice of core, corona materials or by attaching complementary organic or inorganic shells (nano particles or polymers) to the charged corona.     

Effect of PEG crystallization on the self-assembly of PEG/peptide copolymers containing amyloid peptide fragments

The effect of poly(ethylene glycol) PEG crystallization on beta-sheet fibril formation is studied for a series of three peptide/PEG conjugates containing fragments modified from the amyloid beta peptide, specifically KLVFF, FFKLVFF, and AAKLVFF. These are conjugated to PEG with M n = 3300 g mol (-1). It is found, via small-angle X-ray scattering, X-ray diffraction, atomic force microscopy, and polarized optical microscopy, that PEG crystallinity in dried samples can disturb fibrillization, in particular cross-beta amyloid structure formation, for the conjugate containing the weak fibrillizer KLVFF, whereas this is retained for the conjugates containing the stronger fibrillizers AAKLVFF and FFKLVFF. For these two samples, the alignment of peptide fibrils also drives the orientation of the attached PEG chains. Our results highlight the importance of the antagonistic effects of PEG crystallization and peptide fibril formation in PEG/peptide conjugates.     

Adsorption of charged diblock copolymers on porous silica

Block copolymers of styrene and 2-vinylpyridine of different molecular weights were synthesized and chemically modified to poly(vinyl pyridine)/poly(styrene sulfonate) or polystyrene/poly(2-vinyl pyridinium) salts. Adsorption on “Spherosil” silica with a high specific surface area was performed from aqueous solutions of polyelectrolyte copolymers or from noncharged copolymer in an organic medium and subsequent sulfonation or quaternization in the adsorbed state. The adsorption mechanism was studied under various solvent conditions to give silica maximal ion-exchange properties. Modification of silica resulted in a highly stable coated material which combines the mechanical properties of the porous beads and the ion-exchange properties of the “supported” and “pellicular” ion-exchangers and should have potential use in chromatography.     

Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.     

Amplified fluorescence response of chemosensors grafted onto silica nanoparticles

In conventional fluorescent chemosensors, the recognition of the target by the receptor unit affects the fluorescence properties of a single covalently coupled fluorescent moiety. Here we show for the first time that when a suitable TSQ derivative is densely grafted onto the surface of preformed silica nanoparticles electronic interactions between the individual chemosensor units enable the free units to recognize the state of the surrounding complexed ones. As a result, the fluorescence transduction is not limited to the local site where binding occurs, but it involves a wider region of the fluorophore network that is able to transfer its excitation energy to the complexed units. Such behavior leads to an amplification of the fluorescence signal. What we report here is the first example of amplification in the case an off-on chemosensor due to its organization onto the surface of silica nanoparticles. We also describe a simple general model to approach amplification in multifluorophoric systems based on the localization of the excited states, which is valid for assemblies such as the supramolecular ones where molecular interactions are weak and do not significantly perturb the individual electronic states. The introduction of an amplification factor f in particular allows for a simple quantitative estimation of the amplification effects.     

Shell-crosslinked nanoparticles through self-assembly of thermoresponsive block copolymers by RAFT polymerization

A reversible addition-fragmentation chain transfer (RAFT) agent, the methyl-2-(n-butyltrithiocarbonyl)propanoate (MBTTCP) has shown to be efficient in controlling the polymerization of N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM) and N-acryloyloxysuccinimide (NAS). Two different strategies have been studied to synthesize block copolymers based on one PNIPAN block and the other a random copolymer of DMA and NAS. When a PNIPAM trithiocarbonate-terminated is used as macromolecular chain transfer agent for the polymerization of a mixture of NAS and DMA, well-defined P(NIPAM-b-(NAS-co-DMA)) block copolymers were obtained with a low polydispersity index. These thermoresponsive block copolymers dissolved in aqueous solution at 25 °C and self-assembled into micelles when the temperature was raised above the LCST of the PNIPAM block. The micelle shell containing NAS units was further crosslinked using a primary diamine in order to get shell-crosslinked nanoparticles. Upon cooling below the LCST of PNIPAM this structure may easily reorganize to form nanoparticles with a water filled hydrophilic core.     

Dispersion of silica nanoparticles bearing perfluorohexyl units into fluorinated copolymers

This study aims at determining the compatibility behavior of nanoparticles surface with fluorinated matrices to obtain a homogenous dispersion and better composites properties. First, modified silica nanoparticles by C₆F₁₃I and C₆F₁₃‐C₂H₄‐SH led to various fluorinated silica of different massic concentrations and grafting rates. The dispersion of these nanoparticles (in 5 wt %) into molten poly(VDF‐co‐HFP) and poly(TFE‐co‐HFP) matrices were studied as well as the hydrophobic, mechanical, and thermal properties of both fluorinated copolymers and resulting composites. In both series, the storage modulus of nanocomposites increased while the melting (T_m) and decomposition (T_10%) temperatures varied with the polymer matrix. They increased for poly(VDF‐co‐HFP) composites (T_m= 134 to 144 °C and T_10%= 441 to 464 °C) but decreased for poly(TFE‐co‐HFP) nanocomposites (T_m= 276 to 268 °C and T_10%= 488 to 477 °C). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1512–1522     

Immobilization of oligonucleotides onto silica nanoparticles for DNA hybridization studies

This paper describes the development of oligonucleotide-functionalized nanoparticles. We used disulfide-coupling chemistry for the immobilization of oligonucleotides onto silica nanoparticles and subsequently demonstrated the properties of the resulting DNA nanoparticles. Factors influencing the immobilization and hybridization processes were examined and optimized. The oligonucleotide-modified silica nanoparticles provide an efficient substrate for hybridization and can be used in the development of DNA biosensors and biochips.     

Effect of anionic surfactants on synthesis and self-assembly of silica colloidal nanoparticles

Effects of the anionic surfactants, sodium dodecyl sulfate and sodium oleate, on the formation and properties of silica colloidal nanoparticles were investigated. At a concentration of approximately 1 x 10(-3) M, adsorption of anionic surfactants increased particle size, monodispersity, and negative surface charge density of synthesized silica particles. As uniformity of particle size and particle-particle interactions increase, colloidal photonic crystals readily self-assemble without extensive washing of the synthesized silica nanoparticles. The photonic crystals diffract light in the visible region according to Bragg's law. The assembled colloidal particle arrays exhibit a face-centered cubic structure in dried thin films. This study offers a new approach for producing ordered colloidal silica thin films.     

Electrostatic assembly of Ag nanoparticles onto nanofibrillated cellulose for antibacterial paper products

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.     

一种新型介孔空腔二氧化硅纳米微球的制备与缓释行为

本文用十六烷基三甲基溴化铵(CTAB)作为试剂,通过软模板法合成介孔二氧化硅,利用在合成过程中,由伪莫尔转动所引起的微粒内部的大量缺陷,通过溶剂抽提,形成了具有空腔结构的介孔二氧化硅纳米微球.采用透射电子显微镜(TEM)、X射线粉末衍射仪(XRD)、N2吸附-脱附等手段对产物的形貌和结构进行了详细的表征.并以溴甲酚绿作为目标物,通过改变压强和温度,调节溴甲酚绿进入空心SiO2微球中的不同部位,对所制备的空腔介孔二氧化硅微球进行染料的装载和释放试验.结果显示该微球腔壁具有可渗透性和缓释性,而且在负压蒸发溶剂的情况下可以得到较高的药物负载量和极大地提高缓释性能.     

Fabrication and sustained release properties of porous hollow silica nanoparticles

MCM-41-type mesoporous silica nanospheres(MSN) have been prepared using n-cetyltrimethylammonium bromide(CTAB) as a soft template.The pseudo-moire' rotational pattern inside the MSN results in many interior defects.Hollow mesoporous silica(HMS) spheres were synthesized by solvent extraction of the template from MSN.The morphology and structure of MSN and HMS were studied by TEM,XRD and nitrogen sorption techniques.A model drug,bromocresol green dye,was packed inside different regions of HMS through impregna...     

A novel route for immobilization of oligonucleotides onto modified silica nanoparticles

A novel approach for immobilization of probe oligonucleotides that uses zirconium phosphate modified silica nanoparticles is proposed. The surface modification of nanoparticles was carried out in two stages. Initially binding of Zr4+ to the surface of silica nanoparticles and later treated with phosphoric acid for terminal phosphate groups. Oligonucleotide probes modified with amine group at 5'-end were strongly binds to the phosphate terminated silica nanoparticles with imidazole in presence of 0.1 mol L(-1) EDC [N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide], as phosphate groups are more reactive towards amine group. Various studies, i.e., synthesis of silica nanoparticles, their surface modification, probe immobilization, measurement of hybridization and effect of bovine serum albumin (BSA) were carried out during optimization of reaction conditions. The significant reduction in the background signal was observed by treating the probe modified silica nanoparticles with bovine serum albumin prior to hybridization. The probe modified silica nanoparticles were retained their properties and the hybridization was induced by exposure of single-stranded DNA (ssDNA) containing silica nanoparticles to the complementary DNA in solution. The decrease in the fluorescence signal for one mismatch and three mismatch was observed upon hybridization of probe with target DNAs, while there was no response for the random target ssDNA under the same experimental conditions. The intensity of fluorescence signal was linear to the concentration of target DNA ranging from 3.9 x 10(-9) to 3.0 x 10(-6)mol L(-1). A detection limit of 1.22 x 10(-9) mol L(-1) of oligonucleotides can be estimated. The proposed hybridization assay is simple and possesses good analytical characteristics and it can provide an effective and efficient route in the development of DNA biosensors and biochips.     

Directed self-assembly of functionalized silica nanoparticles on molecular printboards through multivalent supramolecular interactions

Silica nanoparticles functionalized with beta-cyclodextrin (CD) host molecules (5) have been prepared by reacting carboxylic active ester-terminated silica nanoparticles (4) with CD heptamine. Silica nanoparticles functionalized with glucosamine (6), having similar surface properties as 5 but lacking the host-guest recognition motif, were used to perform blank experiments. The CD-functionalized silica nanoparticles 5 were determined by TEM to be 55 +/- 6 nm in size. They exhibited pH-dependent aggregation, which is explained by the presence of free amino and carboxylic acid groups on the particle surface, which was corroborated by zeta potential measurements. The functionalization with CD was further confirmed by host-guest studies in solution and at CD-functionalized silicon substrates. The addition of an adamantyl-terminated dendrimer, capable of multivalent host-guest binding with CD, led to strong aggregation of the CD particles 5, but not of the glucosamine-functionalized 6. Furthermore, 5 gave strong adsorption to CD monolayers on silicon onto which adamantyl-terminated dendrimers were adsorbed, whereas 6 did not. The good discrimination between dendrimer-covered and uncovered areas of the CD monolayer substrates allowed the directed self-assembly of the silica particles 5 onto dendrimer-patterned areas created by microcontact printing.     

The fabrication of photosensitive self-assembly Au nanoparticles embedded in silica nanofibers by electrospinning

In this study, we demonstrated a simple, efficient, and low-cost method to fabricate large-area self-assembly Au nanoparticles (AuNPs) encapsulated within silica nanofibers (Au/SiO₂). The method is based on electrospinning and thermal decomposition of hybrid nanofibers prepared from the solution of tetraethylorthosilicate (TEOS), polyvinylpyrrolidone (PVP) and AuNPs. This study employed the electrospinning technique for the first time as a successful method for preparing a self-organized AuNP peapod chain in a silica nanofiber matrix, under mild conditions. It has the advantage of easily controlling the diameters of the silica nanofibers as well as the concentration of the AuNPs in the spinning solution. The Au/SiO₂ hybrid nanofibers fabricated by this method exhibited an obvious photoelectric response under the illumination wavelength around the Au/SiO₂ nanofibers surface plasmon resonance (SPR) absorption band, whereas no photoelectric response was observed for the pure silica fibers. The excellent characteristics of photoelectric response suggest that the electrospinning technique has a great potential for large-scale fabrication of functional nanofiber devices. The ability of coupling light responses into the nanosystems dependent on metallic nanoparticle SPR opens up new prospects for the construction of nanoscale waveguiding devices, sensors and optoelectronics.     

Photocatalytic air-cleaning using TiO2 nanoparticles in porous silica substrate

For air-cleaning, TiO₂ photocatalysis represents one of the very efficient advanced oxidation processes (AOPs) that can decompose chemically and microbiologically stable volatile organic compounds (VOCs). However, the photocatalytic activity of nanocrystalline TiO₂ powders can be significantly suppressed due to TiO₂’s poor adsorption characteristics for organic compounds and its relatively low surface area. The present study sought to solve this problem by immobilising nanocrystalline TiO₂ in the porous silicate substrate. Two titania sources were used in an aqueous solution form: a suspension from a TiO₂ producer in Slovenia, Cinkarna Celje (CC-40) and a TiO₂ sol, prepared by a low-temperature synthesis developed at the University of Nova Gorica (TiO₂-UNG). Two different types of mesoporous silica were used: SBA-15 with an ordered hexagonal pore arrangement and KIL-2 with disordered inter-particle mesoporosity. The structural characteristics, adsorption properties and photocatalytic activity of catalysts deposited on aluminium plates as thin films were investigated. CC-40 exhibited higher adsorption and photocatalytic activity than TiO₂-UNG due to the greater quantity of Ti-OH groups on its surface. The addition of mesoporous silica led to higher adsorption and catalytic activity for both TiO₂ sources. SBA-15 was more efficient than KIL-2.     

Modification of silica nanoparticles by grafting of copolymers containing organosilane and fluorine moities

The free‐radical cotelomerization of 3‐(trimethoxysilyl)propyl methacrylate (TMSPMA) with 1,1,2,2‐tetrahydroperfluorodecyl acrylate (PFDA) in the presence of 2‐mercaptoethanol was performed at 80 °C in acetonitrile. Hydroxy end‐groups of the cotelomers were reacted with 2‐isocyanatoethyl methacrylate to give macromonomers. The P(TMSPMA‐stat‐PFDA) cotelomers, containing fluoro and silane groups, were then grafted onto silica nanoparticles. Optimal grafting conditions were found with TMSPMA monomer alone in toluene at 110 °C. The structure of the modified silica was analyzed by FTIR and ²⁹Si solid‐state NMR. The amount of grafted TMSPMA or P(TMSPMA‐stat‐PFDA) was calculated by thermogravimetric and elemental analyzes. The grafting yield increased with the copolymer/silica weight ratio until a maximum value of 2.26 μmol/m². © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4617–4628, 2009     

Self-assembly of Nafion molecules onto silica nanoparticles formed in situ through sol-gel process

Self-assembly of Nafion onto in situ formed silica nanoparticles in ethylene glycol–water mixture solvent has been investigated in this study. It was found that the formation of silica nanoparticles depends on the concentration of Nafion in dispersions. At relatively low concentration, 0.8% in weight in this case, the existing Nafion is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the concentration of Nafion increased to 2% in weight, self-assembled Nafion layer on the surface stabilizes the initial formed silica nanoparticles and silica particles with average diameters of 4.2±0.5 nm were found to be uniformly distributed in the dispersion. With further increasing the concentration of Nafion, the number of Nafion aggregates increases and silica nanoparticles were mainly formed inside the entangled Nafion chains, resulting in an observation of clusters of silica nanoparticles.