Interaction Of Silica Nanoparticles Research Articles

Promotion of protein assembly by nanoparticles: From in vitro to in-cell.

Engineered nanomaterials are increasingly being studied for biomedical applications such as in diagnosis and therapeutics, due to their similarity in size to subcellular scales, and their tunable physico-chemical properties. Nanomaterials acquire a biomolecular corona upon introduction to biological media, which can influence their biological identity and subsequently, their interactions within the cell. Nanoparticle-protein interactions at the nano-bio interface also affect proteins in the corona, leading to biological transformations such as a change in protein function, unmasking new epitopes, and fibrilization. Silica nanoparticles - one of the most widely studied nanomaterials in biomedical applications - were reported to show a dose-dependent or surface ligand-dependent effect on the kinetics and morphology of protein self-assembly in systems like amyloid-β fibrils, α-synuclein and lysozyme. The interaction of silica nanoparticles with polymerizing cytoskeletal proteins, specifically tubulin proteins, has not been investigated quantitatively. BtubA and BtubB are a pair of bacterial tubulin proteins identified in Prosthecobacter strains, acquired by bacteria from eukaryotic cells via horizontal gene transfer. BtubAB dimers are known to self-assemble like eukaryotic tubulin, forming four-stranded microtubules in vitro as well as five-stranded microtubules in vivo. FRET-labeling of each of the Btub monomers with a donor (mEGFP) and acceptor (mRuby3) fluorescent protein provides a quantitative tool to measure the binding interactions of BtubAB dimers in the presence of silica nanoparticles in vitro and in cell using fluorescence spectroscopy and microscopy. We show that silica nanoparticles enhance BtubAB dimerization in vitro, whereas they appear to have little effect on bacterial tubulin self-assembly in the complex mammalian cellular environment.

Interaction of Silica Nanoparticles with Microalgal Extracellular Polymers

The properties of engineered nanoparticles (NPs) in the marine environment are influenced not only by the high ionic strength of seawater but also by the interaction of NPs with naturally occurring components of seawater, especially natural organic matter. The aim of this study was to investigate the interaction of engineered silica nanoparticles (SiO2 NPs, diameter of 12 nm) with microalgal extracellular polymers (EPS) released by the marine diatom Cylindrotheca closterium. Dissolved organic carbon (DOC) content of the prepared EPS suspension (200 μg mL−1) used throughout the study was 3.44 mg C L−1. The incorporation of individual SiO2 NPs (height range 10–15 nm) and their nanoscale aggregates (height up to 25 nm, length up to 600 nm) into the EPS network was visualized by atomic force microscopy (AFM), whereas their molecular-level interaction was unraveled by the change in the signal of the Si-O group in their FTIR spectra. AFM imaging of C. closterium cells taken directly from the culture spiked with SiO2 NPs (10 μg mL−1) revealed that the latter are bound to the EPS released around the cells, predominantly as single NPs (height range 10–15 nm). Since AFM and dynamic and electrophoretic light scattering results demonstrated that SiO2 NPs dispersed in seawater without EPS showed enhanced aggregation (aggregate diameter of 990 ± 170 nm) and a 2.7-fold lower absolute zeta potential value compared to that measured in ultrapure water, our findings suggest that the presence of EPS biopolymers alters the aggregation affinity of SiO2 NPs in the marine environment. This might be of outmost importance during microalgal blooms when increased EPS production is expected because EPS, by scavenging and stabilizing SiO2 NPs, could prolong the presence of NPs in the water column and pose a threat to marine biota.

Serum apolipoprotein A-I depletion is causative to silica nanoparticles–induced cardiovascular damage

The rapid development of nanotechnology has greatly benefited modern science and engineering and also led to an increased environmental exposure to nanoparticles (NPs). While recent research has established a correlation between the exposure of NPs and cardiovascular diseases, the intrinsic mechanisms of such a connection remain unclear. Inhaled NPs can penetrate the air-blood barrier from the lung to systemic circulation, thereby intruding the cardiovascular system and generating cardiotoxic effects. In this study, on-site cardiovascular damage was observed in mice upon respiratory exposure of silica nanoparticles (SiNPs), and the corresponding mechanism was investigated by focusing on the interaction of SiNPs and their encountered biomacromolecules en route. SiNPs were found to collect a significant amount of apolipoprotein A-I (Apo A-I) from the blood, in particular when the SiNPs were preadsorbed with pulmonary surfactants. While the adsorbed Apo A-I ameliorated the cytotoxic and proinflammatory effects of SiNPs, the protein was eliminated from the blood upon clearance of the NPs. However, supplementation of Apo A-I mimic peptide mitigated the atherosclerotic lesion induced by SiNPs. In addition, we found a further declined plasma Apo A-I level in clinical silicosis patients than coronary heart disease patients, suggesting clearance of SiNPs sequestered Apo A-I to compromise the coronal protein's regular biological functions. Together, this study has provided evidence that the protein corona of SiNPs acquired in the blood depletes Apo A-I, a biomarker for prediction of cardiovascular diseases, which gives rise to unexpected toxic effects of the nanoparticles.

Chitosan oligosaccharide/silica nanoparticles hybrid porous gel for mercury adsorption and detection

Hybrid porous gel has successfully been prepared in situ by interaction of silica nanoparticles with chitosan oligosaccharide lactate. The concentration of silica nanoparticle is crucial for the formation of the gel. Water remediation using this material was explored where the hybrid gel was used as adsorbent for mercury ions from aqueous media and the metal ion removal was investigated under different conditions. Moreover, the detection of mercury ions was performed using emission fluorescence spectroscopy in the presence of a specific fluorophore molecule, such as curcumin. Adding mercury ions was followed by the penetration of curcumin into the hydrophobic pocket of chitosan oligosaccharide lactate, boosting thereby the emission intensity. In addition, the selectivity towards mercury was studied. The elaborated technique was found to be selective, simple and fast with low limit of detection value.

Water-based nanofluid-alternating-CO2 injection for enhancing heavy oil recovery: Considering oil-nanofluid emulsification

The efficiency of CO2 water-alternating-gas (WAG) flooding is highly limited in low-permeability heavy oil reservoirs due to the viscosifying action of W/O emulsification and high mobility contrast between W/O emulsion and CO2. Here we examine an enhanced oil recovery (EOR) process which involves water-based nanofluid-alternating-CO2 (NWAG) injection, and investigate its underlying mechanisms governing the flooding efficiency. Firstly, the bulk rheology and interfacial properties of the oil-nanofluid and oil-water emulsions were tested. Then, the interaction of silica nanoparticles (NPs) and heavy oil was analyzed by scanning electron micrograph (SEM) after the carbonization of emulsions. Finally, core flooding tests were conducted to examine the NWAG flooding efficiency and its underlying mechanisms. Results showed that the bulk viscosity of oil-nanofluid emulsion was decreased by 84.39% compared to oil-water emulsion, and part of the emulsion was changed from W/O to O/W. Meanwhile, the addition of silica NPs enhanced the interfacial adsorption of crude oil heavy components with interfacial activity (e.g., resin and asphaltene). However, the self-assembly structure of the oil-nanofluid interfaces was destroyed due to the interaction of silica NPs and heavy components, which was confirmed by the reduction of the interfacial viscosity and the broken layer of heavy components after carbonization. During the core flooding experiments, NWAG injection could reduce the displacement pressure by 57.14% and increase oil recovery by 23.31% compared to WAG injection. Meanwhile, the mass content of middle components (C10~C16) in produced oil by CO2 flooding process of NWAG injection was 9.55%, which was much lower than that by WAG injection (15.21%) and that in crude oil (22.69%), indicating that more of middle components were extracted by CO2 and the interaction between crude oil and CO2 was improved after oil-nanofluid emulsification. This work could provide a new insight into the high-efficiency exploitation of low-permeability heavy oil reservoirs.

Hofmeister effects in the gelling of silica nanoparticles in mixed salt solutions

Understanding the nature of specific interaction of ions with the charged silica nanoparticles is vital not only to produce gels for applications such as grouting but also for determining their long term stability. Interaction of silica nanoparticles in single salt solutions has been thoroughly investigated but in mixed salt solutions is rarely investigated. In this work we have investigated the gelling of silica nanoparticles in the mixtures of monovalent ions as well as in the mixtures of divalent and monovalent ions. To gain an understanding of the interaction of ions with the charged silica surface at molecular level we have performed molecular dynamics (MD) simulations. Our overall goal was to find out if in salt mixtures ions silica interactions follow the Hofmeister series or not and how ion specific interactions may change when chaotropic ions are successively replaced by kosmotropic or vice versa. The gelling results show that generally monvalent ions in salt mixtures follow the Hofmeister series, e.g., the gel times in the mixtures of lithium and sodium chlorides are much longer than in the mixtures of lithium and potassium chlorides. On the other hand, gel times in the salt mixtures containing divalent ions do not follow the expected Hofmeister series e.g. mixtures of magnesium and sodium chlorides show shorter gel times than that of calcium and sodium chlorides. However, pH dependent gelling revealed that at pH values less than 9 gelling in these mixtures follow the normal Hofmeister series i.e., longer gelling time in magnesium and sodium chlorides than in calcium and sodium chlorides. This reversal of Hofmeister series for divalent and monovalent salt mixtures at pH > 9 and normal Hofmeister series at pH < 9 is reported for the first time in literature. Such a revesal at pH> 9 is explained due to enhanced surface charge, ordring of surface water layer which leads to enhanced ion specificity of strongly hydrated ions such as Mg2+. Moreover, in mixtures having the same divalent salt but different monovalent salts such as magnesium chlorides mixtures with lithium, sodium and potassium chlorides a normal Hofmeister series prevails. MD simulations results revealed that Mg2+ ions retain their strong hydration shell while interacting with the oppositely charged silica surface which means that the shorter gelling times obtained in magnesium salts mixtures are not due to inner sphere complexation of magnesium with the silica surface. Instead magnesium interacts with the silica surface through its hydrating water molecules.

Characterization of Key Bio-Nano Interactions between Organosilica Nanoparticles and Candida albicans.

Nanoparticle-cell interactions between silica nanomaterials and mammalian cells have been investigated extensively in the context of drug delivery, diagnostics, and imaging. While there are also opportunities for applications in infectious disease, the interactions of silica nanoparticles with pathogenic microbes are relatively underexplored. To bridge this knowledge gap, here, we investigate the effects of organosilica nanoparticles of different sizes, concentrations, and surface coatings on surface association and viability of the major human fungal pathogen Candida albicans. We show that uncoated and PEGylated organosilica nanoparticles associate with C. albicans in a size and concentration-dependent manner, but on their own, do not elicit antifungal activity. The particles are also shown to associate with human white blood cells, in a similar trend as observed with C. albicans, and remain noncytotoxic toward neutrophils. Smaller particles are shown to have low association with C. albicans in comparison to other sized particles and their association with blood cells was also observed to be minimal. We further demonstrate that by chemically immobilizing the clinically important echinocandin class antifungal drug, caspofungin, to PEGylated nanoparticles, the cell-material interaction changes from benign to antifungal, inhibiting C. albicans growth when provided in high local concentration on a surface. Our study provides the foundation for defining how organosilica particles could be tailored for clinical applications against C. albicans. Possible future developments include designing biomaterials that could detect, prevent, or treat bloodstream C. albicans infections, which at present have very high patient mortality.

The interaction of silica nanoparticles with catalase and human mesenchymal stem cells: biophysical, theoretical and cellular studies.

AimNanoparticles (NPs) have been receiving potential interests in protein delivery and cell therapy. As a matter of fact, NPs may be used as great candidates in promoting cell therapy by catalase (CAT) delivery into high oxidative stress tissues. However, for using NPs like SiO2 as carriers, the interaction of NPs with proteins and mesenchymal stem cells (MSCs) should be explored in advance.MethodsIn the present study, the interaction of SiO2 NPs with CAT and human MSCs (hMSCs) was explored by various spectroscopic methods (fluorescence, circular dichroism (CD), UV-visible), molecular docking and dynamics studies, and cellular (MTT, cellular morphology, cellular uptake, lactate dehydrogenase, ROS, caspase-3, flow cytometry) assays.ResultsFluorescence study displayed that both dynamic and static quenching mechanisms and hydrophobic interactions are involved in the spontaneous interaction of SiO2 NPs with CAT. CD spectra indicated that native structure of CAT remains stable after interaction with SiO2 NPs. UV-visible study also revealed that the kinetic parameters of CAT such as Km, Vmax, Kcat, and enzyme efficiency were not changed after the addition of SiO2 NPs. Molecular docking and dynamics studies showed that Si and SiO2 clusters interact with hydrophobic residues of CAT and SiO2 cluster causes minor changes in the CAT structure at a total simulation time of 200 ps. Cellular assays depicted that SiO2 NPs induce significant cell mortality, change in cellular morphology, cellular internalization, ROS elevation, and apoptosis in hMSCs at higher concentration than 100 µg/mL (170 µM).ConclusionThe current results suggest that low concentrations of SiO2 NPs induce no substantial change or mortality against CAT and hMSCs, and potentially useful carriers in CAT delivery to hMSC.

Interaction of silica nanoparticles with tau proteins and PC12 cells: Colloidal stability, thermodynamic, docking, and cellular studies

Study on the side effects of the nanoparticles (NPs) can provide useful information regarding their biological and medical applications. Herein, the colloidal stability of the silicon dioxide NPs (SiO2 NPs) in the absence and presence of tau was investigated by TEM and DLS techniques. Afterwards, the thermodynamic parameters of interaction between SiO2 NPs and tau were determined by fluorescence spectroscopy and docking studies. Finally, the cytotoxic effects of SiO2 NPs on the viability of PC12 cells were investigated by MTT, AO/EB staining and flow cytometry assays. TEM, DLS, and zeta potential investigations revealed that tau can reduce the colloidal stability of SiO2 NPs. Fluorescence spectroscopy study indicated that SiO2 NPs bound to the tau with high affinity through hydrogen bonds and van der Waals interactions. Docking study also determined that Ser, Thr and Tyr residues provide a polar microenvironment for SiO2 NPs/tau interaction. Cellular studies demonstrated that SiO2 NPs can induce cell mortality through both apoptosis and necrosis mechanisms. Therefore, it may be concluded that the biological systems such as nervous system proteins can affect the colloidal stability of NPs and vice versa NPs in the biological systems can bind to proteins and cell membranes non-specifically and may induce toxicity.

Interactions between silica nanoparticles and phospholipid membranes

Silica nanoparticles (SNPs) are widely used for biomedical applications. However, their parenteral administration may induce hemolysis. Molecular mechanisms leading to this effect are still controversially discussed. We therefore used a combination of biophysical techniques to investigate the interaction of hemolytic and non-hemolytic SNPs with model phospholipid membranes. MethodsInteraction of SNPs with membranes was studied using a dye-leakage assay, dynamic light scattering (DLS), isothermal titration calorimetry, and solid state nuclear magnetic resonance. Results and discussionThe dye leakage assay revealed that only hemolytic, negatively charged SNPs, but not non-hemolytic positively charged SNPs, destabilized POPC based phospholipid bilayers. Interaction of SNPs with lipid vesicles leading to particle agglomeration was demonstrated by DLS. Isothermal titration calorimetry confirmed the interaction between negatively charged SNPs and phospholipids, which is characterized by an exothermic reaction enthalpy ΔH0SNP of −0.04cal/g at 25°C. Calorimetric titrations at different temperatures revealed a molar heat capacity change of zero. This finding excluded a contribution of electrostatic interactions. Mechanistic insight was provided by solid state phosphorus-31 NMR and deuterium NMR measurements. ConclusionsOur results demonstrate that electrostatic interaction between hemolytic SNPs and model phospholipid membranes is negligible. SNPs induce membrane destabilization and adsorptive processes induced by agglomeration of phospholipid vesicles. The interaction is driven by van der Waals forces at the level of the hydration layer on the vesicles surface.

Factors Ruling the Uptake of Silica Nanoparticles by Mesenchymal Stem Cells: Agglomeration Versus Dispersions, Absence Versus Presence of Serum Proteins.

The results of a systematic investigation of the role of serum proteins on the interaction of silica nanoparticles (NP) doped in their bulk with fluorescent molecules (IRIS Dots, 50 nm in size), with human mesenchymal stem cells (hMSCs) are reported. The suspension of IRIS Dots in bare Dulbecco-modified Eagle's medium results in the formation of large agglomerates (≈1.5 μm, by dynamic light scattering), which become progressively smaller, down to ≈300 nm in size, by progressively increasing the fetal bovine serum (FBS) content of the solutions along the series 1.0%, 2.5%, 6.0%, and 10.0% v/v. Such difference in NP dispersion is maintained in the external cellular microenvironment, as observed by confocal microscopy and transmission electron microscopy. As a consequence of the limited diffusion of proteins in the inter-NP spaces, the surface of NP agglomerates is coated by a protein corona independently of the agglomerate size/FBS concentration conditions (ζ-potential and UV circular dichroism measurements). The protein corona appears not to be particularly relevant for the uptake of IRIS Dots by hMSCs, whereas the main role in determining the internalization rate is played by the absence/presence of serum proteins in the extracellular media.

Preparation and characterization of modified nanosilica/PNIPAm hybrid cryogels

A series of macroporous hybrid cryogels based on poly(N-isopropylacrylamide) (PNIPAm) were synthesized by free radical polymerization in the presence of organically modified nanosilica. To improve the interaction of silica nanoparticles with polymer structure, the silica surface was first treated with 3-methacryloxypropyltrimethoxysilane (MPTMS). Then a series of hybrid cryogels each containing 1 wt.% nanosilica and various amounts of MPTMS (1–4 wt.% to monomer NIPAm) were prepared. The yield of methacrylate modification of the nanosilica surface determined by TGA analysis was 11.2 wt.%. The particle size distribution of modified nanosilica particles was investigated by dynamic light scattering technique (DLS) and the mean particle diameter with respect to number was found as 68 nm. The morphology of cryogels was evaluated by SEM. The improvement in the thermal and mechanical properties using the addition of modified silica nanoparticles was achieved.

Emulsions stabilized by the interaction of silica nanoparticles and palmitic acid at the water–hexane interface

The interaction between palmitic acid (PA) and silica nanoparticles at the water/hexane has been studied in relation to the ability in the stabilization of water in oil emulsions. To this aim, emulsions formed by aqueous silica nanoparticle dispersions and PA solutions in hexane have been investigated. In contrast with other previous studies, where the interaction of nanoparticles and surfactant molecules occurs already in the bulk phases, here PA and silica nanoparticles are dissolved/dispersed in different phases and interact only at the liquid–liquid interface. As for other particle-stabilized emulsions, the investigated system can provide emulsions stable over very long time because of the formation of nanoparticle–surfactant complexes, which accumulate at the droplets interface, providing a steric hindrance of coalescence. However, the present study has pointed out that these enhanced stability conditions are achieved only when the amount of surfactant leads to the formation of single surfactant layers onto the particles surface. Whereas an excess surfactant amount interacts with the particles, the formation of multilayers would be possible, and the formed complexes can be redispersed again in the aqueous bulk phase. This recalls to a scenario where the degree of hydrophobization of the particles is critical for the emulsion stabilization. This can be easily tuned by the control of the surfactant concentration and the volume ratio between the liquid phases. Interfacial tension measurement of the same couple of liquids, has allowed us to explore in more detail such phenomena, revealing a non-monotonic evolution of the dynamic interfacial tension at large PA concentrations. Also these observations can be rationalized assuming the redispersion of the complexes mentioned above, which allows explaining the interfacial tension evolution on the basis of the succession of adsorption and desorption of the different species – nanoparticles, nanoparticle–PA complexes, PA molecules – involved.

Microscopy study on the interaction of silica nanoparticles with lung epithelial cells

The lung is one of the main target organs of nanoparticle exposure and the particles interact with lung cells depending on their physicochemical properties. Knowledge about nanoparticle uptake and intercellular fate is of great interest for the biomedical as well as toxicological field. As both, nanoparticles and cellular structures are in the nanometer size-range, high-resolution microscopy techniques are needed to study particle-cell interactions in vitro.

Interactions of silica nanoparticles with poly(ethylene oxide) and poly(acrylic acid): Effect of the polymer molecular weight and of the surface charge

The properties and the structure of polymer-modified silica nanoparticles were investigated by several characterization methods, with an emphasis on scattering techniques. Both bare and amino functionalized nanoparticles were used. To determine the effect of the charge, the polymer used was either nonionic poly(ethylene oxide) (PEO) or partially deprotonated poly(acrylic acid) (PAA). The particles coated with PEO were investigated by small-angle neutron scattering using the method of external contrast variation to observe the polymer coverage. The quantity adsorbed was found to be increasing with the molecular weight, and the surface type, bare or aminated, did not have a significant influence on the quantity adsorbed. The adsorption of PAA on positively charged aminated particles was investigated by dynamic light scattering and zeta potential measurements. A charge reversal, from positive to negative, was induced by the presence of PAA. Through the derivation of the structure factor, small-angle X-ray scattering provided significant information on the formation of aggregates at low PAA concentrations.

Interaction of Silica Nanoparticles with Phospholipid Membranes

Abstract A fluorescence leakage assay was used in a high-throughput setup to obtain information on the phospholipid vesicle leakage induced by the addition of silica nanoparticles. We showed that this method can be used not only to scan for the conditions under which leakage occurs, but also to obtain quantitative information on the interaction between these nanoparticles and the phospholipid membranes.

Interactions of silica nanoparticles with lung epithelial cells and the association to flotillins

Amorphous silica nanoparticles (aSNPs) gain increasing popularity for industrial and therapeutic claims. The lung with its surface area of 100–140 m2 displays an ideal target for therapeutic approaches, but it represents also a serious area of attack for harmful nanomaterials. The exact nature of the cytotoxic effects of NPs is still unknown. Furthermore, cellular pathways and the destiny of internalized NPs are still poorly understood. Therefore, we examined the cytotoxicity (MTS, LDH) and inflammatory responses (IL-8) for different-sized aSNPs (30, 70, 300 nm) on our lung epithelial cells line NCI H441 and endothelial cell line ISO-HAS-1. Additionally, colocalization studies have been conducted via immunofluorescence staining for flotillin-1- and flotillin-2-bearing endocytic vesicles. Subsequently, the relevance of flotillins concerning the viability of aSNP-exposed epithelial cells has been evaluated using flotillin-1/2 depleted cells (siRNA). This study reveals the relevance of the nanoparticle size regarding cytotoxicity (MTS, LDH) and inflammatory responses (IL-8), whereat the smaller the size of the nanoparticle is, the more harmful are the effects. All different aSNP sizes have been incorporated in flotillin-1- and flotillin-2-labelled vesicles in lung epithelial and endothelial cells, which display a marker for late endosomal or lysosomal structures and appear to exhibit a clathrin- or caveolae-independent mode of endocytosis. Flotillin-depleted H441 showed a clearly decreased uptake of aSNPs. Additionally, the viability of aSNP-exposed cells was reduced in these cells. These findings indicate a contribution of flotillins in as yet unknown (clathrin or caveolae-independent) endocytosis mechanisms and (or) endosomal storage.

Interaction of Silica Nanoparticles with a Flat Silica Surface through Neutron Reflectometry

Neutron reflectometry (NR) was employed to study the interaction of nanosized silica particles with a flat silica surface in aqueous solutions. Unlike other experimental tools that are used to study surface interactions, NR can provide information on the particle density profile in the solution near the interface. Two types of silica particles (25 and 100 nm) were suspended in aqueous solutions of varying ionic strength. Theoretical calculations of the surface interaction potential between a particle and a flat silica surface using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were compared to the experimental data. The theory predicts that the potential energy is highly dependent on the ionic strength. In high ionic strength solutions, NR reveals a high concentration of particles near the flat silica surface. Under the same conditions, theoretical calculations show an attractive force between a particle and a flat surface. For low ionic strength solutions, the particle concentration near the surface obtained from NR is the same as the bulk concentration, while depletion of particles near the surface is expected because of the repulsion predicted by the DLVO theory.

Continuous maximum flow segmentation method for nanoparticle interaction analysis

In recent years, tomographic three-dimensional reconstruction approaches using electrons rather than X-rays have become popular. Such images produced with a transmission electron microscope make it possible to image nanometre-scale materials in three-dimensional. However, they are also noisy, limited in contrast and most often have a very poor resolution along the axis of the electron beam. The analysis of images stemming from such modalities, whether fully or semiautomated, is therefore more complicated. In particular, segmentation of objects is difficult. In this paper, we propose to use the continuous maximum flow segmentation method based on a globally optimal minimal surface model. The use of this fully automated segmentation and filtering procedure is illustrated on two different nanoparticle samples and provide comparisons with other classical segmentation methods. The main objectives are the measurement of the attraction rate of polystyrene beads to silica nanoparticle (for the first sample) and interaction of silica nanoparticles with large unilamellar liposomes (for the second sample). We also illustrate how precise measurements such as contact angles can be performed.

Interactions of Silica Nanoparticles and Ionic Liquids Probed by High Pressure Vibrational Spectroscopy

Gel-like ionic liquid/nanosilica mixtures have been prepared with the addition of 10 wt % nanosilica to 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMI+TFSA–), but no changes in C–H spectral features of EMI+TFSA– were observed in the presence of nanosilica under ambient pressure. As the gel-like mixture of EMI+TFSA–/nanosilica was compressed, a new alkyl C–H band at ca. 3017 cm–1 arose. This new spectral feature at ca. 3017 cm–1 may be attributed to the structural reorganization of alkyl C–H groups induced by the interactions between ionic clusters and nanosilica. The imidazolium C–H bands display nonmonotonic shifts as the pressure is elevated. They blue shift slightly initially, but red shifts occur upon further increase of the pressure. The compression also leads to an increase in the relative intensity of the imidazolium C–H band at ca. 3105 cm–1. This observation suggests that some associated species are switched to the isolated form due to the presence of nanosilica under high pre...