Unfunctionalized Silica Research Articles

Nanoparticle-assisted tubulin assembly is environment dependent

Nanomaterials acquire a biomolecular corona upon introduction to biological media, leading to biological transformations such as changes in protein function, unmasking of epitopes, and protein fibrilization. Ex vivo studies to investigate the effect of nanoparticles on protein-protein interactions are typically performed in buffer and are rarely measured quantitatively in live cells. Here, we measure the differential effect of silica nanoparticles on protein association in vitro vs. in mammalian cells. BtubA and BtubB are a pair of bacterial tubulin proteins identified in Prosthecobacter strains that self-assemble like eukaryotic tubulin, first into dimers and then into microtubules in vitro or in vivo. Förster resonance energy transfer labeling of each of the Btub monomers with a donor (mEGFP) and acceptor (mRuby3) fluorescent protein provides a quantitative tool to measure their binding interactions in the presence of unfunctionalized silica nanoparticles in buffer and in cells using fluorescence spectroscopy and microscopy. We show that silica nanoparticles enhance BtubAB dimerization in buffer due to protein corona formation. However, these nanoparticles have little effect on bacterial tubulin self-assembly in the complex mammalian cellular environment. Thus, the effect of nanomaterials on protein-protein interactions may not be readily translated from the test tube to the cell in the absence of particle surface functionalization that can enable targeted protein-nanoparticle interactions to withstand competitive binding in the nanoparticle corona from other biomolecules.

PDMS‐silica composite gas separation membranes by direct ink writing

AbstractPolydimethylsiloxane (PDMS)‐based membranes containing amine‐functionalized and unfunctionalized silica particles were fabricated via direct ink writing for CO2/N2 gas separation. The printability of the inks was evaluated by rheological measurements, while spectroscopy, microscopy, thermal measurements, and mechanical testing were employed to characterize the printed membranes. The surface morphology of the membranes revealed the absence of voids, demonstrating their suitability for gas separation. The printed membranes also exhibited desirable thermal and mechanical properties (i.e., thermal degradation temperature of 518 °C and tensile strength as high as 1.178 MPa with 529% elongation). The PDMS‐based membranes generally displayed high permeability for CO2 but slightly low selectivity for the CO2/N2 gas pair. The best‐combined permeability‐selectivity performance of 8794 barrer and selectivity of 11.64 was demonstrated by the printed PDMS membrane containing no SiO2 fillers. The inclusion of unfunctionalized SiO2 particles generally increased the membrane's gas permeability but compromised the selectivity. In contrast, membranes with amine‐functionalized silica showed improved selectivity compared to membranes containing unfunctionalized silica. Overall, the performance and characteristics offered by the PDMS/silica composite membranes demonstrated the potential of 3D printing as an economical and sustainable fabrication approach to developing materials for carbon capture applications.

Cover Image, Volume 138, Issue 47

The cover image by Bishnupada Mandal's team shows an FETEM image representing (3-Aminopropyl) trimethoxysilane (APTMS)-modified silica nanoparticles (AFSNP). The nanoparticle exhibited uniform spherical structure with a narrow particle size distribution. The particle morphology showed no significant change with functionalization of the silica nanoparticles. However, the APTMS modified silica nanoparticles (AFSNP) exhibited slightly rough-edged spherical structures compared to the unfunctionalized silica nanoparticles. This could be attributed to the polymerization of the organic layer on the particle surface. The interconnectivity formed due to the silanol-amine interaction, in this case, ensured efficient enhancement of CO2 separation. DOI: 10.1002/app.51438

Surface molecularly imprinted core-shell nanoparticles and reflectance spectroscopy for direct determination of tartrazine in soft drinks

The present work shows the synergistic application of reflectance spectroscopy and core-shell molecularly imprinted polymer (MIP) for rapid quantification of tartrazine in soft drinks. Studies evaluated the performance of the MIPs synthesized in the presence of silica nanoparticles unfunctionalized and functionalized with [3-(methacryloyloxy)propyl]trimethoxysilane. Although the use of functionalized silica nanoparticles promoted the highest adsorption capability of tartrazine, the material was found to be less selective when it was applied in real samples. Interestingly, the most accurate results were obtained via the application of the MIP synthesized in the presence of unfunctionalized silica nanoparticles (SiO2@MIP). The optimized core-shell MIP was also characterized by Raman spectroscopy and scanning electron microscopy. The use of direct reflectance spectroscopy in the analyte detection strategy after the template extraction from the MIPs resulted in faster and more accurate results than conventional UV–Visible spectroscopy. With regard to the analysis of the soft drink samples, no significant differences were found between the results obtained from the proposed reflectance spectroscopy-based technique and those obtained from the comparative high-performance liquid chromatography technique. Under optimized conditions, this method displayed a linear range of 1.0–12.5 μmol L−1 with LOD and LOQ values of 0.303 and 1.0 μmol L−1, respectively. The selectivity factor (β) ranged between 1.4 up to 264 showed better recognition of tartrazine in front of other dyes. Based on the results obtained, the proposed method is found to be suitable for rapid determination of tartrazine in food samples with complex matrices without the need of applying tedious sample preparation and cost-demanding instruments.

Functionalized mesoporous silica as matrix for shape-stabilized phase change materials

Shape-stabilized phase change materials (ssPCM) are used to reversibly store thermal energy while keeping their macroscopic solid shape. A porous matrix, such as mesoporous silica, can be used to obtain ssPCM through impregnation. However, a non-melting interface layer is formed between the matrix and heat storage component, which severely reduces the available pore volume and the energy storage capacity of the composite. We studied functionalization of mesoporous silica as a strategy for engineering the non-melting layer and improving the heat storage of the resulting composites. Stearic acid was used as the active heat storage phase and mesocellular foam silica as the porous matrix. Phenyl and methyl groups were found to increase the nanoconfined phase enthalpy. The non-melting layer volume is similar to unfunctionalized silica, suggesting that methyl and phenyl groups are present inside the non-melting layer. Carboxylic acid functionalization decreases the layer volume, yielding the highest enthalpy of the nanoconfined phase, of 34.5 J/g. This value is 15% higher than the nanoconfined enthalpy of materials containing unfunctionalized silica. Total heat storage values of 130 J/g were obtained for PCM samples containing phenyl or carboxylic acid functionalized matrices. The functionalized materials show high stearic acid loading (72–79 wt%), shape-stability and constant thermal response over 200 heating-cooling cycles. A facile method for assessing the non-melting layer volume is provided. The study shows that suitable surface functionalization can suppress the non-melting layer formation, providing a path for enhancing the heat storage potential of shape-stabilized PCM containing mesoporous silica matrices.

Fabrication of nanocomposites with silica nanoparticles

Functionalization of silica nanoparticles is needed as to improve the mechanical performance of epoxy nanocomposites. Previous experience showed that direct dispersion of commercially available silica nanofillers does not improve significantly the mechanical properties of resulting nanocomposites. Different methods of fabrication are presented along with comments on the possibilities to improve the quality of obtained specimens. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%. The obtained nanocomposites were subjected to monotonic uniaxial loading at room temperature. The static mechanical properties were not significantly changed regardless the filler type or percentage and type of epoxy resin.

Behaviour of Epoxy Silica Nanocomposites Under Static and Creep Loading

Abstract Specific manufacturing technologies were applied for the fabrication of epoxy-based nanocomposites with silica nanoparticles. For dispersing the fillers in the epoxy resin special equipment such as a shear mixer and a high energy sonicator with temperature control were used. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%.. The obtained nanocomposites were subjected to monotonic uniaxial and creep loading at room temperature. The static mechanical properties were not significantly improved regardless the filler percentage and type of epoxy resin. Under creep loading, by increasing the stress level, the nanocomposite with 0.1 wt% silica creeps less than all other materials. Also the creep rate is reduced by adding silica nanofillers.

Supported Ionic Liquid Silica as Curing Agent for Epoxy Composites with Improved Mechanical and Thermal Properties.

The present study aims to improve the mechanical properties of epoxy composite by incorporating supported ionic liquid silica (IL-silica). The IL-silica not only showed improved interfacial interaction and reinforcement, but also served as cure agent of epoxy composites. The differential scanning calorimetry analysis revealed that epoxy composites could be successfully cured with IL-silica without any routine curing agents. IL-silica/epoxy composites presented higher mechanical and thermal properties compared with epoxy composite containing un-functionalized silica (u-silica). The dynamic mechanical analysis showed that the storage modulus of composites significantly increased with the addition of IL-silica in comparison to that with added u-silica, as well as the variation of Tg parameter. The incorporation of IL-silica simultaneously enhanced the tensile strength, toughness, and thermal stability of the epoxy composites. The considerable improvements in mechanical and thermal properties are ascribed to the improved dispersion of IL-silica and the enhanced interfacial interactions between epoxy matrix and IL-silica by strong covalent bonding, which results in an effective load transfer.

Methacrylic Acid Based Polymer Networks with a High Content of Unfunctionalized Nanosilica: Particle Distribution, Swelling, and Rheological Properties

The poor stability and tendency to agglomerate of unfunctionalized nano-SiO2 in the presence of ionic species presents a challenge for preparing poly(methacrylic acid)/nano-SiO2 nanocomposite (NC) hydrogels with desired strength and swelling capability. We proposed a facile and eco-friendly method for the preparation of PMAA/SiO2 NC hydrogels using unfunctionalized silica nanoparticles (NPs) in the form of a suspension. SEM and TEM analyses showed that the NP distribution in the polymer matrix highly depended on the particle concentration. At lower concentrations (up to 13.9 wt %), the NPs were uniformly dispersed as single nanoparticles. With an increase in NP concentration, homogeneously dispersed nanoscale aggregates were formed, while a further increase in the silica concentration led to the formation of homogeneous structures consisting of mutually interacting nanosilica particles coated with PMAA. Swelling experiments confirmed that the silica NPs behaved as adhesive fillers that interacted with PMA...

Friction spot welding of PMMA with PMMA/silica and PMMA/silica-g-PMMA nanocomposites functionalized via ATRP

In the present study, the feasibility of Friction Spot Welding (FSpW) of a commercial-grade poly(methyl methacrylate) (PMMA) (PMMA GS) and PMMA 6N/functionalized silica (SiO2) nanocomposites was investigated. The silica nanoparticles were functionalized via atom transfer radical polymerization (ATRP) with PMMA chains to achieve a uniform dispersion in the polymer matrix. The successful functionalization of silica nanoparticles with PMMA chains via ATRP was evaluated by ATR-FT-IR and TGA measurements. Rheological investigations of the silica nanocomposites showed a plateau of the storage modulus G′ at low frequencies (0.01–0.03 rad/s) as a result of elastic particle–particle interactions. Overlap friction spot welds consisting of PMMA GS and a 2 wt% SiO2-g-PMMA nanocomposite were successfully prepared and compared to spot joints of PMMA GS welded with PMMA 6N and PMMA 6N/silica nanocomposite with 2 wt% unfunctionalized silica nanoparticles. Raman mappings of selected areas of cross-sectional plastographic specimens revealed an increased mixing behavior between the two polymer plates in the case of PMMA GS/2 wt% SiO2-g-PMMA joints. Although the joints welded with PMMA 6N/silica nanocomposites showed a reduction of 22% in lap shear strength and 21% displacement at peak load compared with the neat PMMA spot welds, they can compete with other state-of-the-art PMMA welding techniques such as thermal bonding and ultrasonic welding, which indicates the potential of friction spot welding as an alternative fabrication technology for joining future nanocomposite engineering parts.

Synthesis of a core–shell–shell structured acid–base bifunctional mesoporous silica nanoreactor (MS-SO3H@MS@MS-NH2) and its application in tandem catalysis

An efficient and facile method was designed to produce an acid–base bifunctional mesoporous silica nanoreactor (MS-SO3H@MS@MS-NH2) with acid sites on the inner core, unfunctionalized silica as the neutral zone shell and basic sites on the outer shell. Such acid core–neutral zone–base shell structure design resulted in excellent spatial separation of the hostile functionalities and was better than that of the core–shell structure. The spatial order of acid sites and basic sites in the mesoporous silica nanosphere offered a designated diffusion pathway that was favorable for reaction species, while the mesoporous structure endowed the material with the confinement effect. As a result, the core–shell–shell structured mesoporous silica nanosphere was an excellent bifunctional catalyst for one-pot cascade reaction sequences.

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self-assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin- and azobenzene-modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3-aminopropyl trimethoxysilane and afterward reacted with tosyl-β-CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation-induced assembly than the unmodified particles.

Colloidal Supported Metal Nanoparticles (CSMNs) as Effective Nanocatalysts for Liquid-Phase Suzuki Cross-Coupling Reactions

We investigate the catalytic activity obtained for three types of nanocatalysts: colloidal supported metal nanoparticles (CSMNs) prepared with silica colloids in solution that are air-dried, CSMNs prepared with dry silica colloids resuspended in doubly deionized water that are air-dried, and palladium nanoparticles loaded onto bulk silica dispersed in doubly deionized water that are air-dried. The three types of catalysts are prepared with and without the aminopropyltriethoxysilane (APTES) linker for a total of six different catalysts that are tested for the liquid-phase cross-coupling reaction between phenylboronic acid and iodobenzene to form biphenyl. TEM images and EDS spectra were obtained for the six different catalysts to see if the palladium nanoparticles are covalently attached to the functionalized silica colloids and functionalized bulk silica supports and to see if the palladium nanoparticles are adsorbed onto the unfunctionalized silica colloids and unfunctionalized bulk silica supports. The ...

Silica-supported aminoxyls as reactive materials for NOxremoval

The design of new materials for gaseous NOx (NO and NO2) removal at ambient temperature using organic active sites is reported. The materials consist of unfunctionalized silica and silica modified by immobilized aminoxyls and function via sequential processes consisting of (i) NO oxidation to NO2 and (ii) NO2 storage. NOx removal by physical mixtures of immobilized PTIO (2-phenyl-4,4,5,5-tetramethyl-imidazoline-3-oxide-1-oxyl) sites on silica as the NO oxidant and hydrated silica as the NO2 trap occurs with significant degradation of the PTIO oxidant via undesired side reactions with NO2 when NO2 adsorption sites are fewer than required for its complete removal along the packed bed. The use of packed beds with sufficient NO2 adsorption sites requires a large excess of unfunctionalized silica, because of its low surface density of geminal silanols, which are shown to be the relevant sites for NO2 storage on silica at ambient temperature based on density functional theory calculations. This PTIO degradation is circumvented by the design of NOx traps consisting of immobilized PTIO on silica as the NO oxidant and immobilized TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) on silica as an adsorbent with a high density of strong NO2 binding sites. Packed beds consisting of a 2 : 1 molar mixture of PTIO and TEMPO sites consume NOx as predicted by stoichiometry without detectable PTIO degradation and also without a contribution from geminal silanols as NO2 storage sites. This result requires that PTIO and TEMPO sites on silica render geminal silanols as inactive towards NO2 storage presumably because of the titration of these silanols by immobilized aminoxyls.

Improving compatibility in LDPE–silica dispersions by photo-grafting reaction. Preparation and solid state NMR investigation

A TSPM-modified silica has been prepared and employed as a filler in LDPE films, in which a photo-grafting reaction between polymerizable groups present on the functionalized filler and the polymer has been performed with the aim of obtaining stable composites with improved properties. Besides FT-IR, TGA and SEM characterization, both the TSPM-modified silica and the polymer-filler blends have been extensively investigated by means of solid state NMR, through a combined analysis of several high- and low-resolution experiments, performed on 29Si, 1H and 13C nuclei. This allowed us on one hand to obtain detailed and quantitative information on the silica functionalisation reaction and on the other hand, to get an insight into the change of the dynamic properties of LDPE due to the presence of the filler. The NMR results and several macroscopic properties of the blend LDPE–silica–TSPM, such as Young's modulus and oxygen permeability, were compared with those of the corresponding blend prepared with unfunctionalized silica.