Charged Silica Research Articles

Bioinspired silicification of chloroplast for extended light-harvesting ability

We report a hybrid bioactive system inspired by the biosilicification of diatoms. Monodisperse chloroplast/silica hybrid microspheres with core–shell structure were designed and prepared. Natural fresh chloroplasts, the photosynthetic plant organelle, were surfacely covered with silica shell by mild sol–gel process. The charge of chloroplast surface attracts negatively charged silica particles in the sol generated from subsequent hydrolysis and condensation of the tetraethyl orthosilicate (TEOS), which benefits single-chloroplast encapsulation. SEM images confirm the closed topologies, sizes, and dispersions of hybrid microspheres comparable to those of parent chloroplasts. The elemental analysis using EDX, the particle size distribution analyses using DLS, the thermochemical analyses using TGA measurements and structural characterization using XRD provide evidence for the formation of silica coating. Monitoring declines in the visible light absorption production yields information regarding the declines in the light-harvesting ability of chlorophyll, which confirmed that the silica shell in the present work extends the photochemical vitality of chloroplasts. Results from oxygen production measurements also demonstrate the existence of silica shell confers real protection on the bioactivity of chloroplasts. We envisage that the stand-alone chloroplast encapsulation enables preparation of living-cell-templated microspheres exhibiting capacity for photosynthetic bioreactors, sensors, green coatings, catalysts, more generally opening a window for construction of stable, environment friendly, functional hybrid materials.

PH-Responsive Pickering Emulsions Stabilized by Silica Nanoparticles in Combination with a Conventional Zwitterionic Surfactant.

pH-responsive oil-in-water Pickering emulsions were prepared simply by using negatively charged silica nanoparticles in combination with a trace amount of a zwitterionic carboxyl betaine surfactant as stabilizer. Emulsions are stable to coalescence at pH ≤ 5 but phase separate completely at pH > 8.5. In acidic solution, the carboxyl betaine molecules become cationic, allowing them to adsorb on silica nanoparticles via electrostatic interactions, thus hydrophobizing and flocculating them and enhancing their surface activity. Upon increasing the pH, surfactant molecules are converted to zwitterionic form and significantly desorb from particles' surfaces, triggering dehydrophobization and coalescence of oil droplets within the emulsion. The pH-responsive emulsion can be cycled between stable and unstable many times upon alternating the pH of the aqueous phase. The average droplet size in restabilized emulsions at low pH, however, increases gradually after four cycles due to the accumulation of NaCl. Experimental evidence including adsorption isotherms, zeta potentials, microscopy, and three-phase contact angles is given to support the postulated mechanisms.

Foaming in aqueous solutions of hexadecyltrimethylammonium bromide and silica nanoparticles: Measurement and analysis of rheological and interfacial properties

ABSTRACTThe properties of aqueous foams stabilized by a mixture of negatively charged silica nanoparticles and hexadecyltrimethylammonium bromide were studied in this work. Rheological properties of the foams were studied. The interaction between nanoparticles and surfactant molecules in the bulk phase was studied by zeta potential and size measurements of the particles. The interaction at the interface was studied by means of interfacial shear rheology, surface pressure measurement, and atomic force microscopy. It was found that foams were more stable at low surfactant concentrations, though the foamability was low. This was due to the formation of a strong viscoelastic film of surfactant-laden particles at the air–water interface. A suitable mechanism has been proposed to explain the stability of foams in the presence of nanoparticles at different surfactant concentrations.

Catechol-cation adhesion on silica surfaces: molecular dynamics simulations.

Understanding the interaction mechanism between catechol-cation and inorganic surfaces is vital for controlling the interfacial adhesion behavior. In this work, molecular dynamics simulations are employed to study the adhesion of siderophore analogues (Tren-Lys-Cam, Tren-Arg-Cam and Tren-His-Cam) on silica surfaces with different degrees of ionization and the effects of cationic amino acids and ionic strength on adhesion are discussed. Simulation results indicate that adhesion of catechol-cation onto the ionized silica surface is dominated by electrostatic interactions. At different degrees of ionization, the rank of the adhesions of three siderophore analogues on silica is different. Further analysis shows that the amino acid terminus has a large influence on the adhesion process, especially histidine adhesion on negatively charged surfaces. Tren-Lys-Cam (TLC) has a larger adhesion free energy than Tren-Arg-Cam (TAC) at a higher degree of ionization (18%); both the bulkier structure and delocalized charge of Arg decreased the cation's electrostatic interaction with the charged silica. In addition, the adhesion free energy on ionized silica surfaces decreased with increasing ionic strength of aqueous solutions. A linear correlation between the potential of mean force obtained from umbrella sampling and the rupture force via steered molecular dynamics simulations for siderophore analogue adhesion on silica surfaces is also found. This work may provide some guidance for developing the next generation underwater adhesives.

Adsorption of perfluorocarboxylic acids at the silica surface.

Water molecules may force the hydrophobic perfluoroalkyl chain of perfluorocarboxylic acids (PFCAs) to aggregate at hydrophobic siloxane patches ([triple bond, length as m-dash]Si-O-Si[triple bond, length as m-dash]) of the silica surface despite electrostatic repulsion between surface silanol ([triple bond, length as m-dash]SiO-) and the carboxylate (-COO-) headgroup of PFCA. Acidic pH and background cations promote the adsorption further by reducing the anion-anion Coulomb repulsion.

Tuning of surface protein adsorption by spherical mixed charged silica brushes (MCB) with zwitterionic carboxybetaine component.

Controlled protein adsorption and release without deformation and loss of activity under mild conditions is an essential issue for biological carriers. A spherical mixed charged silica brush (MCB), which could tune protein adsorption, has been prepared by introducing zwitterionic carboxybetaine copolymer onto the surface of silica nanoparticles for the first time. The simple surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) was applied to synthesize the MCB precursor - poly(2-(dimethylamino)ethyl methacrylate) modified silica nanoparticles (SiO2@PDMAEMA). Then, the end group in PDMAEMA was quaternized with propiolactone to obtain poly(DMAEMA-co-carboxybetaine methacrylate) modified silica nanoparticles (SiO2@poly(DMAEMA-co-CBMA)), which was denoted as MCB. In comparison, fully quaternized MCB (SiO2@PCBMA) was also prepared by a one-step strategy. Physicochemical behaviours of MCB in solution were systematically studied. The zwitterionic CBMA component endows the MCB with tunable adsorption towards both acidic and basic proteins through simple adjustment of the DMAEMA to CBMA ratio under mild conditions. This study may have great potential applications in the biomedical field, including tunable drug loading and releasing, and immobilized enzymes, etc.

Interactions between silica particles in the presence of multivalent coions.

Forces between charged silica particles in solutions of multivalent coions are measured with colloidal probe technique based on atomic force microscopy. The concentration of 1 : z electrolytes is systematically varied to understand the behavior of electrostatic interactions and double-layer properties in these systems. Although the coions are multivalent the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory perfectly describes the measured force profiles. The diffuse-layer potentials and regulation properties are extracted from the forces profiles by using the DLVO theory. The dependencies of the diffuse-layer potential and regulation parameter shift to lower concentration with increasing coion valence when plotted as a function of concentration of 1 : z salt. Interestingly, these profiles collapse to a master curve if plotted as a function of monovalent counterion concentration.

Targeting of Leukemic Stem Cells By Antibody Functionalized Mesoporous Silica Nanoparticles in a Mouse Model of CALM-AF10 Positive Acute Myeloid Leukemia

Acute myeloid leukemia has still a dismal prognosis with up to 8 of 10 patients relapsing despite dose intense chemotherapies. AML is propagated by so called leukemic stem cells (LSCs), which are considered to be the cell population responsible for relapse. Based on this it is one major goal to develop treatments which are able to eradicate LSCs, but spare normal hematopoietic stem cells (HSCs) in this disease. We now demonstrate that antibody functionalized mesoporous silica nanoparticles (MSN) are able to target LSCs in a mouse model of CALM-AF10 (CA10) positive AML. We previously showed that in this model AML is initiated and maintained by LSCs being negative for stem cell and myeloid markers, but positive for the lymphoid associated antigen B220 (Deshpande et al., Cancer Cell, 2006). To specifically target B220+ LSCs in this model we generated a multifunctional particle system based on differently charged mesoporous silica nanoparticles (MSN) functionalized with the anti- mouse B220 antibody. To achieve this first amine functionalized and pure silica particles were synthesized and functionalized with a carboxysilane and treated with different amounts of succinic anhydride. In a next step the MSN were loaded with the anthracyline drug daunorubicin. Finally, the particles were further modified with the anti-mouse B220 antibody to obtain specific targeting to murine B220 positive LSCs. MSN coated with the anti-human CD9 antibody served as control. To follow cellular uptake by flow cytometry the antibody tagged MSNs were labelled with the fluorescent dye Atto594. To track the intracellular release of the anthracyline drug daunorubicin, the lipophilic dye DiR was used. First, we tested 7 zwitter-ionic MSNs, with varying surface charge tagged with anti-B220 antibody (conc. 10 µg/mL) for cellular uptake at 4 and 24 hrs in CA10 positive cells. The cellular uptake of the B220 antibody tagged MSN by the CA10 cells was 20.7% and 24.7% higher than in B220-negative AML control cells at 4 hrs and 24 hrs, respectively. The ratio of particle uptake in CA10 cells was 1.3 and 1.9-fold at 4 hrs and at 24 hrs, respectively, compared to the control. This correlated to a 4.6-fold higher mean fluorescence intensity (MFI) of the fluorescent dye Atto594 in the CA10 cells at 4 hrs compared to the control. To demonstrate selectivity, cellular uptake of the anti-B220 MSN was compared to the anti-human CD9 antibody tagged MSN control with a difference in uptake up to 30.8% (particle concentration 100 µg/ml) and a MFI difference and DiR difference of 35.7% and a 34%, respectively after 24 hrs. Loading of the anti-B220 MSN particle with 1.6 µg of daunorubicin per 100 µg of particles induced 100% cell death of CA10 cells at a concentration of 100ug/ml. To confirm that induced cell death was mediated by interaction of the B220 antigen with the anti-B220 antibody-labeled MSN, we blocked the B220 antigen on CA10 cells with unlabeled anti-mouse B220 antibody (81.6% blocking efficiency after 24 hrs). Blocked and unblocked CA10 cells were treated with the anti-B220 MSN loaded with 1.6 µg of daunorubicin/100 µg particles (corresponding to a final concentration of 300ng daunorubicin per ml medium) or free daunorubicin (300 ng/ml). At a particle concentration of 100 µg/ml, 96.5% of the unblocked CA10 cells were eradicated by the anti-B220 MSN compared to 46.5% of the B220 antigen blocked CA10 cells. Anti-B220 MSNs were also more effective than free drug which killed 67% of the cells. Importantly, treatment of CA10 cells with anti-B220 MSN in vitro was able to significantly delay leukemia development after transplantation into lethally irradiated mice with a median onset of disease of 160 days (n=6) compared to a median of 22 days after treatment with the anti-CD9 MSN (n=3)(p<0.0001). Collectively, these data demonstrate the potential of antibody functionalized targeted MSN to selectively kill AML stem cells. This system allows rapid exchange of the antibody coated to MSN, thereby opening the door to target a wide range of LSC associated surface antigens. DisclosuresBuske:Celltrion, Inc.: Consultancy, Honoraria.

Scalable parallel self-assembly of nanoparticle anti-reflection coatings

Here we report a simple, inherently parallel, and scalable bottom-up approach for fabricating nanoparticle anti-reflection coatings on large glass substrates. Negatively charged silica nanoparticles are electrostatically adsorbed onto a surface-functionalized glass substrate with positive surface charges to form a disordered monolayer nanoparticle coating. Systematic experiments have been conducted to optimize the critical process parameters, including the dispersing dielectric media, nanoparticle concentration of the colloidal suspensions, and the coating time, that significantly affect the uniformity and the anti-reflection properties of the final coatings. Specular reflection and transmission measurements demonstrate that good anti-reflection performance (with <1% two-sided reflection) and high optical transmission (>99%) can be achieved by the self-assembled nanoparticle coatings. This innovative technology also enables the simultaneous coating of multiple 5-in.-sized glass substrates with high and reproducible qualities. Importantly, we combine experiments with theoretical calculations to address a fundamental question faced by the fabrication of monolayer nanoparticle-based anti-reflection coatings — what is the optimal nanoparticle surface area coverage for best anti-reflection performance? Our optical simulations based on a rigorous coupled-wave analysis model indicate that the optimal nanoparticle coverage is ~60% which is readily achievable by this electrostatics-assisted bottom-up technology.

Pore Structure of Macroporous Polymers Using Polystyrene/Silica Composite Particles as Pickering Stabilizers.

A novel approach for the preparation of interconnected macroporous polymers with a controllable pore structure was reported. The method was based on the polymerization of water-in-oil Pickering high internal phase emulsion (HIPE) stabilized by polystyrene (PS)/silica composite particles. The composite Pickering stabilizers were facilely obtained by mixing positively charged PS microspheres and negatively charged silica nanoparticles, and their amphiphilicity could be delicately tailored by varying the ratio of PS and silica. The droplet size of Pickering HIPEs was characterized using an optical microscope. The pore structure of polymer foams was observed using a scanning electron microscope. The interconnectivity of macroporous polymers was evaluated upon their gas permeability, which was greatly improved after etching PS microspheres included in the Pickering stabilizers with tetrahydrofuran. As a result, fine tailoring of the pore structure of polymer foams could be realized by simply tuning the ratio of PS to silica particles in the composite stabilizer.

Gated Molecular Transport in Highly Ordered Heterogeneous Nanochannel Array Electrode.

In biology, all protein channels share a common feature of containing narrow pore regions with hydrophobic functional groups and selectivity filter regions abundant with charged residues, which work together to account for fast and selective mass transport in and out of cells. In this work, an ultrathin layer of polydimethylsiloxane (PDMS) was evaporated on the top orifices of charged silica nanochannels (2-3 nm in diameter and 60 nm in length) vertically attached to the electrode surface, and the resulting structure is designated as heterogeneous silica nanochannels (HSNs). As evidenced by voltammetric studies, the transport of ionic species in these HSNs was controlled by both hydrophobic rejection and electrostatic force arising from the top PDMS layer and from the bottom silica nanochannels, respectively. Anionic species encountered both hydrophobic rejection and electrostatic repulsion forces, and thus, their transport was strongly prohibited, while the transport of cationic species was permitted once the electrostatic attraction exceeded the hydrophobic rejection. Moreover, the magnitude of hydrophobic force could be regulated by the PDMS layer thickness, and that of the electrostatic force can be modulated by the salt concentration, solution pH, or applied voltage. It was demonstrated that the HSNs could be activated from an OFF state (no ion can transport) to an ON state (only cation transport occurs) by decreasing the salt concentration, increasing the solution pH, or applying negative voltages.

Natural halloysite nano-clay electrolyte for advanced all-solid-state lithium-sulfur batteries

Solid polymer electrolytes (SPEs) show increasing potential for application in high energy lithium sulfur batteries due to good flexibility and high safety. However, low room temperature ionic conductivity of SPEs has become the main limitation. Herein, a novel SPE film using natural halloysite nano-clay has been fabricated, which exhibits exceptional ionic conductivity of 1.11×10−4Scm−1 and lithium ion transference number of 0.40 at 25°C. The mechanism of enhanced lithium ion transport is considered. The oppositely charged halloysite nanotube surfaces separate lithium salt into lithium ions that are absorbed on the negatively charged outer silica surface, and anions may be accommodated on the positively charged inner aluminol surface. So, an ordered 3D structure for free lithium ion transport is suggested. This potential application of the natural halloysite nano-clay has been demonstrated by an all-solid-state lithium-sulfur battery over a wide temperature range of 25–100°C. These results reveal the possibility of realizing sustainable high energy storage at a reduced cost.

Omniphobic Polyvinylidene Fluoride (PVDF) Membrane for Desalination of Shale Gas Produced Water by Membrane Distillation.

Microporous membranes fabricated from hydrophobic polymers such as polyvinylidene fluoride (PVDF) have been widely used for membrane distillation (MD). However, hydrophobic MD membranes are prone to wetting by low surface tension substances, thereby limiting their use in treating challenging industrial wastewaters, such as shale gas produced water. In this study, we present a facile and scalable approach for the fabrication of omniphobic polyvinylidene fluoride (PVDF) membranes that repel both water and oil. Positive surface charge was imparted to an alkaline-treated PVDF membrane by aminosilane functionalization, which enabled irreversible binding of negatively charged silica nanoparticles (SiNPs) to the membrane through electrostatic attraction. The membrane with grafted SiNPs was then coated with fluoroalkylsilane (perfluorodecyltrichlorosilane) to lower the membrane surface energy. Results from contact angle measurements with mineral oil and surfactant solution demonstrated that overlaying SiNPs with ultralow surface energy significantly enhanced the wetting resistance of the membrane against low surface tension liquids. We also evaluated desalination performance of the modified membrane in direct contact membrane distillation with a synthetic wastewater containing surfactant (sodium dodecyl sulfate) and mineral oil, as well as with shale gas produced water. The omniphobic membrane exhibited a stable MD performance, demonstrating its potential application for desalination of challenging industrial wastewaters containing diverse low surface tension contaminants.

Tumor stroma-containing 3D spheroid arrays: A tool to study nanoparticle penetration

Nanoparticle penetration through tumor tissue after extravasation is considered as a key issue for tumor distribution and therapeutic effects. Most tumors possess abundant stroma, a fibrotic tissue composed of cancer-associated fibroblasts (CAFs) and extracellular matrix (ECM), which acts as a barrier for nanoparticle penetration. There is however a lack of suitable in vitro systems to study the tumor stroma penetration of nanoparticles. In the present study, we developed and thoroughly characterized a 3D co-culture spheroidal array to mimic tumor stroma and investigated the penetration of silica and PLGA nanoparticles in these spheroids. First, we examined human breast tumor patient biopsies to characterize the content and organization of stroma and found a high expression of alpha-smooth muscle actin (α-SMA; 40% positive area) and collagen-1 (50% positive area). Next, we prepared homospheroids of 4T1 mouse breast cancer cells or 3T3 mouse fibroblasts alone as well as heterospheroids combining 3T3 and 4T1 cells in different ratios (1:1 and 5:1) using a microwell array platform. Confocal live imaging revealed that fibroblasts distributed and reorganized within 48h in heterospheroids. Furthermore, immunohistochemical staining and gene expression analysis showed a proportional increase of α-SMA and collagen in heterospheroids with higher fibroblast ratios attaining 35% and 45% positive area at 5:1 (3T3:4T1) ratio, in a good match with the clinical breast tumor stroma. Subsequently, we studied the penetration of high and low negatively charged fluorescent silica nanoparticles (30nm; red and 100 or 70nm; green; zeta potential: −40mV and −20mV) and as well as Cy5-conjugated pegylated PLGA nanoparticles (200nm, −7mV) in both homo- and heterospheroid models. Fluorescent microscopy on spheroid cryosections after incubation with silica nanoparticles showed that 4T1 homospheroids allowed a high penetration of about 75–80% within 24h, with higher penetration in case of the 30nm nanoparticles. In contrast, spheroids with increasing fibroblast amounts significantly inhibited NP penetration. Silica nanoparticles with a less negative zeta potential exhibited lesser penetration compared to highly negative charged nanoparticles. Subsequently, similar experiments were conducted using Cy5-conjugated pegylated PLGA nanoparticles and confocal laser scanning microscopy; an increased nanoparticle penetration was found in 4T1 homospheroids until 48h, but significantly lower penetration in heterospheroids. Furthermore, we also developed human homospheroids (MDA-MB-231 or Panc-1 tumor cells) and heterospheroids (MDA-MB-231/BJ-hTert and Panc-1/pancreatic stellate cells) and performed silica nanoparticle (30 and 100nm) penetration studies. As a result, heterospheroids had significantly a lesser penetration of the nanoparticles compared to homospheroids. In conclusion, our data demonstrate that tumor stroma acts as a strong barrier for nanoparticle penetration. The 30-nm nanoparticles with low zeta potential favor deeper penetration. Furthermore, the herein proposed 3D co-culture platform that mimics the tumor stroma, is ideally suited to systematically investigate the factors influencing the penetration characteristics of newly developed nanomedicines to allow the design of nanoparticles with optimal penetration characteristics.

A novel hybrid filler of halloysite nanotubes/silica fabricated by electrostatic self-assembly

A novel halloysite nanotubes (HNTs)/silica hybrid filler (HNTs-silica) was successfully fabricated by coassembly between negatively charged HNTs and positively charged silica particles modified with 3-triethoxysilylpropylamine in deionized water. In this unique hybrid architecture, it was found that HNTs was uniformly adsorbed by the silica (about 20wt%) particles, which can suppress the aggregation of HNTs and silica and effectively enlarge the specific surface area of HNTs through the silica nano-protrusions on the surface of the nanotubes, making HNTs-silica ideally suited as a novel hybrid filler and opening up new opportunities for the preparation of high performance polymer nanocomposites.

Amplified Charge Transfer for Anionic Redox Probes through Oriented Mesoporous Silica Thin Films

AbstractDiffusion of anionic species through ordered mesoporous silica films is considerably restricted due to electrostatic repulsion by the negatively charged silica surface and this effect is even worse in low ionic strength media (owing to Donnan exclusion effects). This is at the origin of the poor electrochemical response of anionic redox probes at electrodes modified with such mesoporous thin films. Here, by using indium–tin oxide (ITO) electrodes covered with vertically aligned mesoporous silica films generated by electrochemically assisted self‐assembly (EASA), we show that charge transfer for anionic redox probes [i.e. Fe(CN)63−/4−] can be dramatically amplified by using a neutral [ferrocene dimethanol, Fc(MeOH)2] or cationic [(Ru(NH3)63+] redox mediator. This has been observed by cyclic voltammetry, showing current enhancement in the presence of the mediator, which acts as a mobile electron shuttle between the charge‐excluded Fe(CN)63−/4− species from the mesoporous silica film and the underlying ITO surface owing to the ability of the mediator species to diffuse freely through the oriented mesopore channels. This behavior was significantly affected by the relative contents of Fe(CN)63−/4− probe to Fc(MeOH)2 mediator, the potential scan rate, and the supporting electrolyte concentration. The most effective improvements were reached at low Fe(CN)63−/4− concentration, high mediator content, low potential scan rate, and low ionic strength.

Pickering Emulsions Responsive to CO2/N2 and Light Dual Stimuli at Ambient Temperature.

A dual stimuli-responsive n-octane-in-water Pickering emulsion with CO2/N2 and light triggers is prepared using negatively charged silica nanoparticles in combination with a trace amount of dual switchable surfactant, 4-butyl-4-(4-N,N-dimethylbutoxyamine) azobenzene bicarbonate (AZO-B4), as stabilizers. On one hand, the emulsion can be transformed between stable and unstable at ambient temperature rapidly via the N2/CO2 trigger, and on the other hand, a change in droplet size of the emulsion can occur upon light irradiation/rehomogenization cycles without changing the particle/surfactant concentration. The dual responsiveness thus allows for a precise control of emulsion properties. Compared with emulsions stabilized by specially synthesized stimuli-responsive particles or by stimuli-responsive surfactants, the method reported here is much easier and requires a relatively low concentration of surfactant (≈1/10 cmc), which is important for potential applications.

Interplay between Depletion and Double-Layer Forces Acting between Charged Particles in Solutions of Like-Charged Polyelectrolytes.

Direct force measurements between negatively charged silica particles in the presence of a like-charged strong polyelectrolyte were carried out with an atomic force microscope. The force profiles can be quantitatively interpreted as a superposition of depletion and double-layer forces. The depletion forces are modeled with a damped oscillatory profile, while the double-layer forces with the mean-field Poisson-Boltzmann theory for a strongly asymmetric electrolyte, whereby an effective valence must be assigned to the polyelectrolyte. This effective valence is substantially smaller than the bare valence due to ion condensation effects. The unusual aspect of the electrical double layer in these systems is the exclusion of the like-charged polyelectrolyte from the vicinity of the surface, leading to a strongly nonexponential diffuse ionic layer that is dominated by counterions and has a well-defined thickness. As the oscillatory depletion force sets in right after this layer, this condition can be used to predict the phase of the oscillatory depletion force.

Self-Assembly of Polystyrene-b-poly(2-vinylpyridine) Micelles: From Solutions to Silica Particles Surfaces

The structural understanding of self-assembled nanomaterial in solutions and immobilized on material surfaces has the potential to unlock some of the key questions in self-assembly processes such as the influence of surface forces on the nanostructure of polymer micelles. Here, we demonstrate the design and characterization of charged polymer micelles and their interaction with oppositely charged silica particle surfaces. Small-angle X-ray scattering, dynamic light scattering, and electron microscopy analysis revealed information on the size, shape, and morphology of the micelles in solution and bound to the surface. Electron density distributions calculated from the scattering data established that the surface-bound micelles strongly interact with the silica surface. The surface-induced dispersion and coulomb forces and the modified conformational entropy of polymer chains led to morphological changes in the polymer aggregates. This has important implications for the design of nanostructured surfaces in biomedical or industrial applications for instance as controlled release or bioresponsive materials.

Effect of Different Surfactants on the Interfacial Behavior of the n-Hexane-Water System in the Presence of Silica Nanoparticles.

This paper presents the effect of negatively charged silica nanoparticles (NPs) on the interfacial tension of the n-hexane-water system at variable concentrations of four different surfactants, viz., an anionic surfactant, sodium dodecyl sulfate (SDS), a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and two nonionic surfactants, Tween 20 and Triton X-100 (TX-100). The presence of negatively charged silica nanoparticles is found to have a different effect depending on the type of surfactant. In the case of ionic surfactants, SDS and CTAB, silica NPs reduce the interfacial tension of the system. On the contrary, for nonionic surfactants, Tween 20 and TX-100, silica NPs increase the interfacial tension. The increasing/decreasing nature of the interfacial tension in the presence of NPs is well supported by the calculated surface excess concentrations. The diffusion kinetic control (DKC) and statistical rate theory (SRT) models are used to understand the behavior of dynamic interfacial tension of the surfactant-NP-oil-water system. The DKC model is found to describe the studied surfactant-NP-oil-water systems more aptly.