Grafted Silica Nanoparticles Research Articles

Hydrophilic and anti-fouling polyethersulfone ultrafiltration membranes with poly(2-hydroxyethyl methacrylate) grafted silica nanoparticles as additive

Here we report the preparation and properties of polyethersulfone (PES) ultrafiltration (UF) membranes with poly(2-hydroxyethyl methacrylate) (PHEMA) grafted silica (SiO2) nanoparticles (PHEMA@SiO2 NPs) as the blending additive. The PHEMA@SiO2 NPs were first prepared by grafting PHEMA brushes onto SiO2 NPs via a surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization. The organic–inorganic hybrid membranes of PES with PHEMA@SiO2 NPs were fabricated via the traditional non-solvent induced phase separation (NIPS) process. During membrane formation, the hydrophilic PHEMA@SiO2 NPs tended to migrate toward the membrane top surfaces. The membrane surface porosities were increased and the surface hydrophilicity was enhanced after introducing PHEMA@SiO2 NPs. More importantly, the water permeability, solute rejection and anti-fouling ability of PES membranes were improved significantly. This phenomenon indicated that the trade-off between permeability and selectivity of PES UF membranes was broken by the incorporation of PHEMA@SiO2 NPs. Different from traditional neat inorganic NPs additive, the PHEMA@SiO2 organic–inorganic NPs could be held in/on PES membrane for a long period of time due to the intertwisting of polymer chains. The present work provides a simple approach for stable and nearly permanent hydrophilization of PES UF membranes, which can also be extended to more membrane materials prepared by NIPS process.

New fluorinated hybrid organic/inorganic water soluble polymeric network

This work presents the elaboration of nanoparticle networks from HASE (hydrophobically alkali-soluble emulsion) thickeners grafted with silica nanoparticles. Three HASE were realized by copolymerization in emulsion of methacrylic acid and ethyl acrylate or trifluoroethyl methacrylate and a hydrocarbon or fluorocarbon macromonomer. The macromonomer contains a hydrophobic pendant group separated from the backbone by a polyethylene glycol spacer chain. The free acid functions of the copolymer were coupled with amine functionalized silica nanoparticles. In basic aqueous solutions, the suspensions containing 1 wt.% of this polymer/SiO2 nanocomposite characterized by DLS (size analysis) and Cryo-SEM are stable, translucent, and gel-like at pH = 7.5. Rheological measurements demonstrated that the grafting of silica nanoparticles did not affect the thickening effect of precursor co-polymers. Coating of glass plates was realized with these hybrid networks and characterized by AFM, indicating that the silica nanoparticles were more homogeneously dispersed when a fluorocarbon co-polymer was used.

Synthesis of core-shell poly (N-isopropylacrylamide) grafted silica nanoparticles by distillation precipitation polymerization

Poly(N-isopropylacrylamide) PNIPAAm is among the smart hydrogels widely used in novel drug delivery systems. In this work, silica/poly(N-isopropylacrylamide) (SiO2/PNIPAAm) core-shell hybrid nanoparticles were prepared by a two-step reaction, starting with acrylate modified silica nanoparticles (ASNPs) prepared by one-pot synthesis/modification method. The PNIPAAm was grafted onto ASNPs by distillation precipitation polymerization of N-isopropylacrylamide (NIPAAm) in acetonitrile and, in the presence of 2,2´-azobisisobutyronitrile (AIBN) as the initiator without using any stabilizer or surfactant. The core-shell particles were obtained with average diameter of about 90 nm still having the possibility to increase the thickness of PNIPAAm shell by successive polymerization reactions. The infrastructure, property and chemistry of the core-shell nanoparticles were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), thermal gravimetric analysis (TGA) in addition to surface characterization by water contact angle measurement.

Polymeric nanocapsules with controllable crosslinking degree via combination of surface‐initiated atom transfer radical polymerisation and photocrosslinking techniques

The crosslinked polystyrene nanocapsules with controllable crosslinking degree have been prepared by the ultraviolet (UV)-induced photocrosslinking of the polystyrene grafted silica nanoparticles (SN-PS), which was obtained by the surface-initiated atom transfer radical polymerisation of styrene from the modified silica nanoparticle templates, after the silica templates were etched with hydrofluoric acid. The effect of the UV-irradiating time on the inner diameter of the nanocapsules, and the degree of crosslinking and the thickness of the shells was investigated. The dynamic light scattering results showed that the degree of crosslinking of the obtained nanocapsules increased with the prolongation of the UV-irradiation time, therefore the inner diameter of the nanocapsules increased. However, the percentage of grafting of the crosslinked polymer shells decreased with increasing the UV-irradiation time because of the photodecomposition of the polystyrene grafted during the UV-irradiated crosslinking process, according to the thermogravimetric analysis.

Fabrication and properties of ultrafiltration membranes composed of polysulfone and poly(1-vinylpyrrolidone) grafted silica nanoparticles

Membranes for ultrafiltration were prepared from polysulfone (PSf) composites with poly(1-vinylpyrrolidone) grafted silica nanoparticles (PVP-g-silica). For the synthesis of PVP-g-silica, hydroxyl terminated silica nanoparticles were reacted with (3-methacryloxypropyl)trimethoxysilane (γ-MPS) to form γ-MPS terminated silica nanoparticles (silica-MPS), which were further reacted with VP monomer. Formation of PVP-g-silica was confirmed by FT-IR, XPS, TGA, FE-SEM, and HR-TEM. PSf/PVP-g-silica membranes exhibited higher water flux than PSf membranes without any loss in solute rejection for membranes containing less than or equal to 5wt% of PVP-g-silica. The water flux of a membrane containing 1wt% PVP-g-silica was 2.3 times higher than that of PSf membrane. The hydrophilicity of the PSf/PVP-g-silica membrane also increased with increasing PVP-g-silica content. The hydrophilicity of the PSf/PVP membrane decreased with increasing retention time in a water bath, while the hydrophilicity of the PSf/PVP-g-silica membrane did not change with retention time. PSf/PVP-g-silica membranes exhibited enhanced fouling resistance in fouling experiments using nonionic surfactants.

Polydicyclopentadiene Reinforced with Grafted Silica Nanoparticles

Polydicyclopentadiene (PDCPD) nanocomposites reinforced with nanoscale silica were prepared by an in-situ polymerization technique in simulating reaction injection molding system. The nanoscale silica particles were treated with toluene diisocynate (TDI) and 5-norbornene-2-carboxylic acid (NCA). The analysis of IR, TGA and dispersion test on the modified nanoscale silica showed the success of surface modification. The incorporation of nanoscale silica of low content had an positive effect on hardness and bending strength of the PDCPD matrix. The wear resistance of PDCPD/ silica nanocomposite is significantly improved in comparison with neat PDCPD, and the SEM micrographs of the worn surface revealed their wear mechanisms.

Synthesis and characterization of polystyrene chains on the surface of silica nanoparticles: comparison of SANS, SAXS, and DLS results

An extensive characterization of well-defined polystyrene (PS)-grafted silica nanoparticles is reported. Bare SiO2 particles (diameter 50 nm) were functionalized with a suitable initiator for the surface-initiated anionic polymerization of styrene. Both grafted and free PS chains were characterized and compared by size-exclusion chromatography (SEC). PS-grafted particles were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS), and dynamic light scattering (DLS). The thickness of the grafted PS chains was obtained by SANS and DLS and scaled with \(M_{\mathrm {w}}^{0.6}\) displaying similar behavior with free PS chains in the same solvent used, tetrahydrofuran (THF). Grafting densities obtained from SANS data and TGA were found to be small, and the thickness of the grafted PS chains determined by SANS was found to be similar to \(2R_{\mathrm {g}}\) of free PS chains in THF. Both results are consistent with a “coil-like” conformation of the grafted PS chains.

Synthesis and Characterization of Dye-Labeled Poly(methacrylic acid) Grafted Silica Nanoparticles

The synthesis of dye-labeled poly(methacrylic acid) (PMAA) grafted silica nanoparticles was studied. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of tert-butylmethacrylate (tBuMA) was conducted on dye-labeled CPDB coated silica nanoparticles followed by sequential removal of the thiocarbonylthio end groups and the tert-butyl moieties. Additionally, as a more straightforward strategy, direct polymerization of methacrylic acid on silica nanoparticles with a diameter size as small as 15 nm was conducted via the RAFT polymerization technique. A variety of PMAA brushes with different lengths and densities were prepared on nanoparticle surfaces via surface-initiated RAFT polymerization with excellent control and surface grafting densities as high as 0.65 chains/nm2. The grafted PMAA was methylated by trimethylsilyldiazomethane to conduct organic phase GPC characterization. The dye-labeled PMAA grafted nanoparticles provide a platform to bind biomolecules and to track the movement of the nanoparticles in biological systems.

Thermal gradient effect on the dynamical behavior of nanoparticles observed using X-ray photon correlation spectroscopy

The effects of a thermal gradient on the dynamical behavior of nanoparticles dispersed in a polymer matrix were studied using X-ray photon correlation spectroscopy. Polystyrene (PS)-grafted silica nanoparticles (SiNPs-PS), which are nanoparticles dispersed in a PS matrix controlled at temperatures above the glass transition temperature, were used in this study. Anisotropic motions of the SiNPs-PS were observed when the sample was kept in a conventional capillary tube, whereas isotropic motion was observed when the sample was kept in a newly designed cell with a low thermal flow, demonstrating the importance of the thermal gradient on the dynamical behavior of the SiNPs-PS.

Preparation, characterization and properties of proton exchange nanocomposite membranes based on poly(vinyl alcohol) and poly(sulfonic acid)-grafted silica nanoparticles

Nanocomposite membranes based on the poly(vinyl alcohol) (PVA)/poly(sulfonic acid)-grafted silica nanoparticles (PSA-g-SN) were prepared via solvent casting of PVA cross linked by glutardialdehyde in the presence of various amounts (0–20 wt%) of silica nanoparticles (SN), poly(styrene sulfonic acid)- (PSSA-g-SN) and poly (2-acrylamido-2-methyl-1-propane sulfonic acid)-grafted silica nanoparticles (PAMPS-g-SN) as hydrophilic inorganic modifiers. PSA-g-SN nanoparticles were synthesized by surface-initiated redox grafting of SSA and AMPS monomers from the surface of the aminopropylated silica nanoparticles. Membranes were then characterized by FTIR, impedance spectroscopy, thermogravimetric analysis (TGA), water uptake, tensile strength test and SEM. The best proton conductivity was observed for membranes containing 5 wt% of nanoparticles. Among three nanoparticles used, the highest proton conductivity (10.4 mS/cm) was observed for PVA membrane prepared in the presence of 5 wt% PAMPS-g-SN nanoparticles. Results showed that grafting of sulfonated monomer onto the silica nanoparticles enhances various properties, for example proton conductivity, of the polymer electrolyte membranes (PEMs).

Silica-Polymer Core-Shell Particles for Fabrication of Poly(methyl methacrylate) Composite Materials

Poly(n-butyl acrylate) grafted silica nanoparticles were compounded with poly(methyl methacrylate) to yield silica/polymer composites with the improved dispersion of silica and interfacial adhesion with the matrix, thus showing increases in storage modulus and glass transition temperature.

A Phase Diagram for Polymer-Grafted Nanoparticles in Homopolymer Matrices

We quantified the stability of polystyrene- (PS-) grafted silica nanoparticles (NPs) in PS matrices with ultrasmall angle X-ray scattering (USAXS) and transmission electron microscopy (TEM) and developed a phase diagram to predict NP dispersion based on the graft polymer density, σ, and the graft and free polymer molecular weights, or N and P, respectively. Using controlled/living polymerizations, polymer nanocomposites were formulated with silica NPs of radius, R = 9 nm where σ = 0.10–0.70 chains/nm2 at an essentially constant N = 61–68 kg/mol. The matrix molecular weight was varied from P = 37–465 kg/mol permitting us to vary the swelling ratio, P/N = 0.6–7.7. Using USAXS and TEM, we determined whether the PS-grafted NPs were stable and dispersed uniformly, or were unstable and aggregated within the matrix. From these measurements we developed a phase diagram for NP miscibility with respect to σ, P, and N to determine the allophobic and autophobic transitions that correspond to the wetting the drying of...

Synthesis and characterisation of highly fluorescent core–shell nanoparticles based on Alexa dyes

Current and future developments in the emerging field of nanobiotechnology are closely linked to the rational design of novel fluorescent nanomaterials, e.g. for biosensing and imaging applications. Here, the synthesis of bright near infrared (NIR)-emissive nanoparticles based on the grafting of silica nanoparticles (SNPs) with 3-aminopropyl triethoxysilane (APTES) followed by covalent attachment of Alexa dyes and their subsequent shielding by an additional silica shell are presented. These nanoparticles were investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence spectroscopy. TEM studies revealed the monodispersity of the initially prepared and fluorophore-labelled silica particles and the subsequent formation of raspberry-like structures after addition of a silica precursor. Measurements of absolute fluorescence quantum yields of these scattering particle suspensions with an integrating sphere setup demonstrated the influence of dye labelling density-dependent fluorophore aggregation on the signaling behaviour of such nanoparticles.

Super-tough double-network hydrogels reinforced by covalently compositing with silica-nanoparticles

We have successfully developed hydrogels with high compressive toughness by reinforcing the double-network structure (PAMPS/PAAm) with grafted silica nanoparticles. Silica nanoparticles grafted with vinyl end groups were used as macro-crosslinkers to copolymerize with AMPS, yielding a nanocomposite first network. Subsequent introduction of a secondary PAAm network resulted in super-tough double-network (DN) composite hydrogels, which do not fracture upon loading up to 73 MPa and a strain above 0.98. The compressive strength, swelling behavior, and morphology of the silica-grafted DN hydrogels were investigated as functions of nanoparticle content and particle size, in comparison with silica nanoparticle-filled DN gels without covalent bonding to the polymer network. Maximal reinforcement of the DN gels was achieved at around 1 wt% (weight percent) of grafted silica nanoparticles with respect to AMPS. Unique embedded micro-network structures were observed in the silica-grafted DN gels and accounted for the substantial improvement in compressive toughness. The fracture mechanism is discussed in detail based on the yielding behavior of these covalently composited hydrogels.

Interface and Interphase Dynamics of Polystyrene Chains near Grafted and Ungrafted Silica Nanoparticles

The chain and segmental dynamics of free and grafted 20-monomer atactic polystyrene chains surrounding a silica nanoparticle have been investigated employing atomistic molecular dynamics simulations. The effect of the nanoparticle curvature and grafting density on the mean square displacement of free polystyrene chains and also on the mean relaxation time of various intramolecular vectors was investigated as a function of separation from the surface. Confinement, reduced surface curvature, and densification resulted in a reduction of the mean square displacement and an increase in the mean relaxation time of the Cα–H bond vector and chain end-to-end vector in the vicinity of the surface. Depending on the property investigated, the thickness of the interphase, i.e., the distance beyond which the polymer has bulk behavior, varies between 1 and 3 nm, corresponding to 1–3 radii of gyration of the bulk polymer. Therefore, the presence of a surface has a significant influence on the dynamics of the surrounding polymer chains especially the ones in the interfacial region.

Phase Behavior of Poly(sulfobetaine methacrylate)-Grafted Silica Nanoparticles and Their Stability in Protein Solutions

Biocompatible and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was grafted onto the surface of initiator-modified silica nanoparticles via surface-initiated atom transfer radical polymerization. The resultant samples were characterized via nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined via gel permeation chromatography after the removal of silica by etching. Moreover, the phase behavior of these polyzwitterionic-grafted silica nanoparticles in aqueous solutions and stability in protein/PBS solutions were systematically investigated. Dynamic light scattering and UV-visible spectroscopy results indicate that the silica-g-PSBMA nanoparticles exhibit an upper critical solution temperature (UCST) in aqueous solutions, which can be controlled by varying the PSBMA molecular weight, ionic strength, silica-g-PSBMA nanoparticle concentration, and solvent polarity. The UCSTs shift toward high temperatures with increasing PSBMA molecular weight and silica-g-PSBMA nanoparticle concentration. However, increasing the ionic strength and solvent polarity leads to a lowering of the UCSTs. The silica-g-PSBMA nanoparticles are stable for at least 72 h in both negative and positive protein/PBS solutions at 37 °C. The current study is crucial for the translation of polyzwitterionic solution behavior to surfaces to exploit their diverse properties in the development of new, smart, and responsive coatings.

Preparation and dispersibility of poly(L‐lactide)‐grafted silica nanoparticle

AbstractTo improve dispersibility of silica nanoparticle in organic solvents, the grafting of poly(L‐lactide) (PLLA) onto silica nanoparticle surface by ring‐opening polymerization of L‐lactide (LA) was investigated in the presence of an amidine base catalyst. The ring‐opening polymerization of LA successfully initiated in the presence of silica having amino groups (silica‐NH2) and an amidine base catalyst to give PLLA‐grafted silica, but not in the presence of untreated silica (silica‐OH). In the absence of the amidine base catalyst no ring‐opening polymerization of LA even in the presence of silica‐NH2 and no grafting of PLLA onto silica were observed. It became apparent that the amidine base catalyst acts as an effective catalyst for the ring‐opening graft polymerization of LA from the surface of silica‐NH2. In addition, it was found that the percentage of PLLA grafting onto silica could be controlled according to the reaction conditions. The average particle size of PLLA‐grafted silica was smaller than that of silica‐NH2. Therefore, it was considered that the aggregation structure of silica nanoparticles was considerably destroyed by grafting of PLLA onto the surface. The PLLA‐grafted silica gave a stable dispersion in polar solvents, which are good solvents for PLLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Lanthanide-DTPA grafted silica nanoparticles as bimodal-imaging contrast agents

The design and synthesis of a combined MRI-optical probe for bio-imaging are reported. The materials studied join the properties of lanthanide (Ln 3+) complexes and nanoparticles (NPs), offering an excellent solution for bimodal imaging. The hybrid SiO 2@APS/DTPA:Gd:Ln (Ln = Eu 3+ or Tb 3+) (APS: 3-aminopropyltriethoxysilane, DTPA: diethylenetriamine pentaacetic acid) system increases the payload of the active magnetic centre (Gd 3+) and introduces a Ln 3+ long-life excited state (Eu 3+: 0.35 ± 0.02 ms, Tb 3+: 1.87 ± 0.02 ms), with resistance to photobleaching and sharp emission bands. The Eu 3+ ions reside in a single low-symmetry site. Although the photoluminescence emission is not influenced by the simultaneous presence of Gd 3+ and Eu 3+, a moderate r 1 increase and a larger enhancement of r 2 are observed, particularly at high fields, due to susceptibility effects on r 2. The presence of Tb 3+ instead of Eu 3+ further raises r 1 but decreases r 2. These values are constant over a wide (5–13) pH range, indicating the paramagnetic NPs stability and absence of leaching. The uptake of NPs by living cells is fast and results in an intensity increase in the T 1-weighted MRI images. The optical properties of the NPs in cellular pellets are also studied, confirming their potential as bimodal imaging agents.

Synthesis of Poly-l-glutamic Acid Grafted Silica Nanoparticles and Their Assembly into Macroporous Structures

Polypeptide-coated silica nanoparticles represent an interesting class of organic-inorganic hybrids since the ordered secondary structure of the polypeptide grafts imparts functional properties to these nanoparticles. The synthesis of a poly-l-glutamic acid (PLGA) silica nanoparticle hybrid by employing N-carboxyanhydride (NCA) polymerization to synthesize the polypeptide chains and Cu catalyzed azide alkyne cycloaddition reaction to graft these chains onto the silica surface is reported. This methodology enables the synthesis of well-defined polypeptide chains that are attached onto the silica surface at high surface densities. The PLGA-silica conjugate particles are well dispersed in water, and have been thoroughly characterized using multinuclear ((13)C, (29)Si) solid state NMR, thermogravimetric analysis, Fourier transform infrared, dynamic light scattering, and transmission electron microscopy. The pH-dependent reversible aggregation of the PLGA-silica particles, driven by the change in PLGA structure, has also been studied. Preliminary results on the use of aqueous dispersions of silica-PLGA for the preparation of three-dimensional macroporous structures with oriented pores by ice templating methodology are also demonstrated. These macroporous materials, comprising a biocompatible polymer shell covalently attached to rigid inorganic cores, adopts an interesting lamellar structure with fishbone-type architecture.

PEGylated polyethyleneimine grafted silica nanoparticles: enhanced cellular uptake and efficient siRNA delivery

The present paper reports the utilization of hybrid nanocomposite particles consisting of PEI25k-PEG5k copolymer grafted silica nanoparticles (SiO(2)NPs) for enhanced cellular uptake and siRNA delivery. High-resolution transmission electron microscopy and dynamic light scattering measurements ensured the average particle size of the final hybrid component as 45nm (core SiO(2), 28-30nm and shell PEI25k-PEG5k, 12-15nm). Surface morphology from atomic force microscopy analysis showed the significant relationship between the particle size and shape. (29)Si and (13)C cross-polarization-magic angle spinning solid state nuclear magnetic resonance (NMR), (1)H-NMR, and Fourier transform infrared spectroscopy were used to obtain the relevant structural information (such as Q3, silanol; Q4, siloxane functional groups of SiO(2)NPs; resonance shifts and bending vibrations of PEI25k, -CH(2)-CH(2)-NH-; and PEG5k, -CH(2)-CH(2)-O-) from copolymer nanoparticle. Stable complexation of siRNA and nanocomposite particle (wt.%:wt.%) was achieved from 1:5 to 1:15 ratio. Nanocomposite particle (N/P) ratio and siRNA concentration determine the stability and knockdown efficiency of the PEI25k-PEG5k-graft-SiO(2)NPs-siRNA complexes. It was shown that highly positively charged (zeta potential, +66mV) PEI25k-PEG5k-graft-SiO(2)NPs result in strong affinity with negatively charged siRNA. Confocal microscopy showed intensified cellular uptake of siRNA into cytoplasm of A549 cancer cell utilized for in vitro study. In conclusion, the coherence, graft density of copolymer-SiO(2)NPs, and siRNA concentration were found to strongly influence the stability, and hence determine the knockdown efficiency, of PEI25k-PEG5k-graft-SiO(2)NPs-siRNA complexes.