Hydrophobic Fumed Silica Nanoparticles Research Articles

Drycells: Cell-suspension micro liquid marbles for single-cell picking.

Cell-picking technology is essential for cell culturing. Although the recently developed tools enable single-cell-level with a >95% aqueous culture medium, thereby acting as a powerful cell-picking tool, is reported. The proposed "drycells" are formed by spraying a cell suspension onto a powder bed of hydrophobic fumed silica nanoparticles. The particles adsorb to the droplet surface and form a superhydrophobic shell, which prevents the drycells from coalescence. The number of encapsulated cells per drycell can be controlled by adjusting the drycell size and cell-suspension concentration. Moreover, it is possible to encapsulate a pair of normal or cancerous cells and create several cell colonies within a single drycell. A sieving process can be used to sort the drycells according to size. The size of the droplet can range from one to hundreds of micrometers. The drycells are sufficiently stiff to be collected using a tweezer; however, centrifugation separates them into nanoparticles and cell-suspension layers, with the separated particles being recyclable. Various handling techniques, such as splitting coalescence and inner liquid replacement, can be used. We believe that the application of the proposed drycells will greatly improve the accessibility and productivity of single-cell analysis. This article is protected by copyright. All rights reserved.

Anticorrosive self-stratified PDMS-epoxy coating for marine structures

Four self-stratified coatings were prepared by dispersion of titanium dioxide (TiO2) and hydrophobic fumed silica (SiO2) nanoparticles in polydimethylsiloxane (PDMS)-Epoxy mix separately and in combination. Incorporating a definite ratio of nanofillers in PDMS-Epoxy incompa ible polymer blend to form a single coat paint system with anticorrosive and improved hydrophobic properties by the self-stratifying process is the chief highlight of this research work. The appropriate characterization techniques like Fourier Transform Infrared (FTIR) spectroscopy in Attenuated Total Reflection (ATR) mode of the coatings top and bottom layers emphasized the intended stratification. The Field Emission Scanning Electron Microscopy (FESEM) displayed the morphology of the coated samples top and bottom layers and the existence of the intended stratification in the coatings cross-section. The PDMS-Epoxy coating inclusive of both the nanofillers exhibited improved hydrophobic nature, appreciable surface free energy, augmented adherence to the substrate and lesser shear force in pseudo barnacle strength test in terms of shear. This innovative formulation pertains to the application on underwater substrates with improved anti-biofouling properties.

Hydrophobic AEROSIL®R972 Fumed Silica Nanoparticles Incorporated Monolithic Nano-Columns for Small Molecule and Protein Separation by Nano-Liquid Chromatography.

A new feature of hydrophobic fumed silica nanoparticles (HFSNPs) when they apply to the preparation of monolithic nano-columns using narrow monolithic fused silica capillary columns (e.g., 50-µm inner diameter) was presented. The monolithic nano-columns were synthesized by an in-situ polymerization using butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) at various concentrations of AEROSIL®R972, called HFSNPs. Dimethyl formamide (DMF) and water were used as the porogenic solvents. These columns (referred to as HFSNP monoliths) were successfully characterized by using scanning electron microscopy (SEM) and reversed-phase nano-LC using alkylbenzenes and polyaromatic hydrocarbons as solute probes. The reproducibility values based on run-to-run, column-to-column and batch-to-batch were found as 2.3%, 2.48% and 2.99% (n = 3), respectively. The optimized column also indicated promising hydrophobic interactions under reversed-phase conditions, while the feasibility of the column allowed high efficiency and high throughput nano-LC separations. The potential of the final HFSNP monolith in relation to intact protein separation was successfully demonstrated using six intact proteins, including ribonuclease A, cytochrome C, carbonic anhydrase isozyme II, lysozyme, myoglobin, and α-chymotrypsinogen A in nano-LC. The results showed that HFSNP-based monolithic nanocolumns are promising materials and are powerful tools for sensitive separations.

Fabrication of large-scale, flexible, and robust superhydrophobic composite films using hydrophobic fumed silica nanoparticles and polydimethylsiloxane

We propose a simple and cost-effective method to fabricate superhydrophobic films comprising a composite layer of polydimethylsiloxane (PDMS) and hydrophobic fumed silica nanoparticles on the top and a PDMS bonding layer at the base. The PDMS layer was coated onto a substrate by spray-coating while the composite layer was formed by compressing the silica nanoparticles into the PDMS layer via low vacuum conditions. The prepared film exhibited excellent superhydrophobicity with an apparent contact angle greater than 177° and a sliding angle of less than 2°. The robustness of the superhydrophobic film was evaluated through a mechanical durability test, chemical stability test, and long-term storage in the air. The test results showed good mechanical durability and stability due to a thick composite layer and good bonding among the materials. Additionally, the superhydrophobic films were coated with different shapes and were separated successfully from flat shapes and three-dimensional curved shapes with a release agent as the flexible films. These results demonstrated a facile fabrication process to generate robust superhydrophobic films with a large area and complex shapes for industrial applications such as drag reduction, anti-icing, anti-corrosion, and others.

Environment‐tolerant conductive and superhydrophobic poly(m‐phenylene isophthalamide) fabric prepared via γ‐ray activation and reduced graphene oxide/nanoSiO2modification

AbstractAs one of the high‐performance polymer fibers, poly(m‐phenylene isophthalamide) (PMIA) is widely used in the area of military and aerospace applications. Whereas, its insulation and hydrophilic nature may lead to electric charge accumulation and dust adherence. This work aims to fabricate a PMIA fabric with integrated conductive and superhydrophobic abilities via a simple method including γ‐ray irradiation and dip‐coating. Results show that after γ‐ray irradiation, the surface roughness of PMIA was enhanced and the content of the oxygen element was increased. In the dip‐coating step, the micro‐pits and grooves on the surface of PMIA were covered totally by a layer of graphene oxide (GO). After reduction to reduced GO (rGO), a conductive network was built. The conductivity of the fabric was decreased to a minimum value of 0.5 Ω m. Meanwhile, the quite low volume resistivity was retained as 1H, 1H, 2H, 2H‐perfluorooctyltriethoxysilane (PFTS)/hydrophobic fumed silica nanoparticles (SiO2) was decorated on rGO. Due to the microscale aggregation constituted by nano‐SiO2, the fabric presented a superhydrophobic property and self‐cleaning ability against simulated Lunar dust. Furthermore, the durability performance proves that an excellent environment‐tolerant ability has been endowed to the PMIA fabric by the modification.

Thermal and Rheological Properties of Hydrophobic Nanosilica in Sunflower Oil Suspensions at High Pressures.

Nowadays, the reduction of the environmental impact associated with the operation of the oil industry is a primary concern. A growing trend is to develop low-toxicity formulations based on biodegradable components. In this sense, vegetable oils structured with nanomaterials could be an alternative to mineral or synthetic oils for sustainable fluid formulations. Hydrophobic fumed silica nanoparticles have the capability to change the rheological behavior of oil in suspensions, providing a large variety of non-Newtonian behaviors over a wide range of temperatures, from shear-thinning to gel-like, depending on the concentration and the nanosilica’s hydrophobicity, that permits the design of fluids with selected characteristic and applications. This work explores the microstructure and the rheological behavior of hydrophobic fumed silica dispersed in a sunflower oil as a function of temperature and pressure. The results suggest that the suspensions of hydrophobic silica in sunflower oil reveals appropriate rheological and thermal properties over a wide range of temperatures and pressures to serve as components of sustainable drilling fluids.

Characterizations of a nanocomposite biochemical-sensing membrane of γ-APTES incorporated with silica nanoparticles prepared by ultrasonic liquid atomizer spray

Large-area and uniformly distributed 3-aminopropyltriethoxysilane (γ-APTES) incorporated with poly-dimethylsiloxane-treated hydrophobic fumed silica nanoparticles (NPs) sensing membranes with different mixed ratios were deposited by using ultrasonic liquid atomizer (ULA) spray. Nanoscale current–voltage (I–V) characteristics of the deposited membranes were then characterized by using conductive atomic force microscopy. It is found that the ULA-sprayed γ-APTES plus NPs (γ-APTES + NPs) membrane has smaller leakage current and higher breakdown voltage than does the ULA-sprayed pure γ-APTES membrane. Excellent glucose sensing performances are found when using the deposited ULA-sprayed γ-APTES + NPs as sensing membrane on polysilicon wire sensor. Further sensing performance enhancement was obtained as the γ-APTES + NPs membrane was subjected to UV illumination. Our experiment’s results confirmed that the ULA spray is a promising method for large area deposition of γ-APTES + NPs membrane and that it can be utilized for biomedical sensor applications.

표면처리 실리카 나노입자를 포함하는 폴리우레탄 폼의 안락 특성

자동차 산업에서 폴리우레탄 폼은 주로 쿠션재, 흡음재로 사용된다. 본 연구에서는 연질 폴리우레탄 폼에 표면 특성이 다른 두 종류(hydrophilic, hydrophobic)의 실리카 나노입자를 첨가하여, 안락 특성에 미치는 영향을 조사하였다. 소수성 실리카 입자(Aerosil-R972)는 우레탄 사슬과의 우수한 접착으로 인해 내부 형태학과 안락 특성의 변화가 거의 없었다. 반면, 친수성 실리카 입자(Aerosil-300)는 우레탄 사슬과의 불안정한 접착성으로, 폼의 강성이 저하되는 결과를 보였다. 이로 인해, 공동과 미세구멍의 크기가 증가했고 친수성 실리카 표면이 미세구멍의 생성을 유도하는 역할을 하게 되어 공동 당 평균 미세구멍의 수가 증가하였다. 이러한 형태학적 특성에 따라 친수성 입자의 함량이 증가함에 따라 이력손실과 꺼짐인자는 증가하는 경향을 보였다. 결과적으로, 친수성 입자를 1.5 wt% 첨가할때, 이력손실 10% 증가와 꺼짐인자 38% 증가의 결과를 나타내었다.

Influence of particle concentration on multiple droplet formation in Pickering emulsions

HypothesisMultiphase droplets form when oil and water are mixed together at the ambivalent conditions that occur close to phase inversion. In this paper we propose a mechanism for the stabilisation of multiphase droplets by a single population of particles. ExperimentsWe investigated the microstructure of emulsions formed when dodecane and water are mixed in the presence of hydrophobic fumed silica nanoparticles. We identified the range of compositions, mixing times and rates where water-in-oil-in-water emulsions are stabilised in a single mixing step. To explore how the particle availability and mixing conditions lead to multiple emulsion formation we used light scattering and microscopy techniques to probe the size and morphology of the drops, and the particle coverage of the interfaces. FindingsOur key finding is that to stabilise multiphase drops there should be sufficient particles available to coat water drops that are entrained within coalescing oil droplets. The size of an entrained drop is determined by the volume of the rupturing film that forms between the oil drops. The particle coating prevents the entrained drop from escaping into the external aqueous phase. These results suggest a simple route for controlling the formation and stability of multiple emulsions for encapsulation applications.

Preparation of partially neutralized poly(acrylic acid) microspheres via inverse pickering suspension polymerization

Partially neutralized poly(acrylic acid) (PAA) microspheres have been prepared by Inverse Pickering Suspension Polymerization (IPSP) using 1,2‐dichlorobenzene (DCB) and hydrophobic fumed silica nanoparticles (HFSi‐NPs) as organic dispersing media and dispersing agent respectively. As crosslinker N,N'‐methylene bisacrylamide (MBAc), as initiator potassium persulfate (KPS) and sodium metabisulfite (SMBS) redox couple were used. Neutralization degrees were adjusted using 8N NaOH solution and polymerizations were initiated at 34°C. Water/oil phase ratio was set to 1/7 for all polymerizations. Morphology of prepared dry poly(acrylic acid) beads was examined by two microscopic methods, scanning electron microscopy (SEM) and optical microscopy. Prepared microsized polymer beads were observed as smooth and spherical in shape. Effect of neutralization degree (α) varied from 70% to 90% on absorptions in both distilled water and saline solutions, absorption under load (AUL) and crosslink density (CD) results were also investigated. POLYM. ENG. SCI., 59:162–169, 2019. © 2018 Society of Plastics Engineers

Rheology of Hydrate-Forming Emulsions Stabilized by Surfactant and Hydrophobic Silica Nanoparticles

Observed effects of hydrophobic fumed silica nanoparticles (of average primary particle size 7 nm) on the rheological behavior of hydrate-forming emulsions are presented. Liquid cyclopentane (CP) is the hydrate former. The hydrate slurry is prepared in a Couette geometry at atmospheric pressure from a water-in-oil emulsion with the phases density matched to avoid segregation. Hydrates are formed upon quenching to a low temperature at a fixed shear rate. Dispersed water droplets convert to hydrate particles, leading to an effective viscosity increase by orders of magnitude. The hydrate inhibition by silica nanoparticles at the water–oil interface, forming a Pickering type of emulsion, is characterized using the onset time of steep viscosity rise after seeding with small hydrate particles; this is termed the critical time. Seeding eliminates stochasticity associated with nucleation of the hydrate. The critical time is increased when the interface is covered with silica nanoparticles. For a particle concentr...

Laser Printing of Superhydrophobic Patterns from Mixtures of Hydrophobic Silica Nanoparticles and Toner Powder

In this work, a new and facile dry printing method was developed for the direct fabrication of superhydrophobic patterns based on silica nanoparticles. Mixtures of hydrophobic fumed silica nanoparticles and toner powder were printed on paper and polymer sheets using a commercial laser printer to produce the superhydrophobic patterns. The mixing ratio of the toner powder (for the laser printer) to hydrophobic silica was also investigated to optimize both the printing quality and the superhydrophobicity of the printed areas. The proper mixing ratio was then used to print various superhydrophobic patterns, including triangular, square, circular, and complex arrangements, to demonstrate that superhydrophobic surfaces with different patterns can be fabricated in a few seconds without any post-processing. The superhydrophobicity of each sample was evaluated by contact angle measurements, and all printed areas showed contact angles greater than 150°. The research described here opens the possibility of rapid production of superhydrophobic surfaces with various patterns. Ultimately, the obtained findings may have a significant impact on applications related to self-cleaning, control of water geometry and position, fluid mixing and fluid transport.

Robust, self-healing, superhydrophobic coatings highlighted by a novel branched thiol-ene fluorinated siloxane nanocomposites

In this work, we present one-step dip-coating strategy for fabricating robust, self-healing and superhydrophobic coatings using a coating solution that contains a novel branched thiol-ene fluorinated siloxane (T-FAS), polydimethylsiloxane (PDMS) elastomer and hydrophobic fumed silica nanoparticles (SiO2 NPs). The novel branched T-FAS, with low fluorinated surface energy and high sol-gel reactivity, was prepared by introducing (N-methyl-perfluorohexane-1-sulfonamide) ethyl acrylate (FSA) and γ-methacryloxypropyltrimethoxysilane (MPS) into pentaerythritol tetra (3-mercaptopropionate) (PETMP) via thiol-ene click reaction. The superhydrophobic coating, being high stable to strong acid, UV, thermal and smudge treatment, has a water contact angle of 165 ± 2° and shedding angle of 4 ± 1°. It can withstand at least 100 cycles of abrasion with 1500 grit sandpaper under 45 KPa due to the interpenetrating polymer networks (IPN) constructed by T-FAS/PDMS. The IPN is also self-healing to chemically etching using long perfluoro-terminated chains of T-FAS which can spontaneously reorient to new air interfaces. The robust self-healing IPN may lead to the development of new efficient strategies for durable protective coatings in various applications.

HIERARCHICAL MICRO–NANO COATINGS BY PAINTING

In this paper, the wettability properties of coatings with hierarchical surface structures and low surface energy were studied. Hierarchically structured coatings were produced by using hydrophobic fumed silica nanoparticles and polytetrafluoroethylene (PTFE) microparticles as additives in polyester (PES) and polyvinyldifluoride (PVDF). These particles created hierarchical micro–nano structures on the paint surfaces and lowered or supported the already low surface energy of the paint. Two standard application techniques for paint application were employed and the presented coatings are suitable for mass production and use in large surface areas. By regulating the particle concentrations, it was possible to modify wettability properties gradually. Highly hydrophobic surfaces were achieved with the highest contact angle of 165[Formula: see text]. Dynamic contact angle measurements were carried out for a set of selected samples and low hysteresis was obtained. Produced coatings possessed long lasting durability in the air and in underwater conditions.

Hydrophobic silica nanoparticles as reinforcing filler for poly (lactic acid) polymer matrix

Properties of poly (lactic acid) (PLA) and its nanocomposites, with silica nanoparticles (SiO2), as filler were investigated. Neat PLA films and PLA films with different percentage of hydrophobic fumed silica nanoparticles (0.2, 0.5, 1, 2, 3 and 5 wt. %) were prepared by solution casting method. Several tools were used to characterize the influence of different silica content on crystalline behavior, and thermal, mechanical and barrier properties of PLA/SiO2 nanocomposites. Results from scanning electron microscope (SEM) showed that the nanocomposite preparation and selection of specific hydrophobic spherical nano filler provide a good dispersion of the silica nanoparticles in the PLA matrix. Addition of silica nanoparticles improved mechanical properties, the most significant improvement being observed for lowest silica content (0.2wt.%). Barrier properties were improved for all measured gases at all loadings of silica nanoparticles. The degree of crystallinity for PLA slightly increased by adding 0.2 and 0.5 wt. % of nano filler.

Direct Evidence for Percolation of Immobilized Polymer Layer around Nanoparticles Accounting for Sol-Gel Transition in Fumed Silica Dispersions.

Immobilized polymer fractions have been claimed to be of vital importance for sol-gel transitions generally observed in nanoparticle dispersions but remain a matter of debate regarding mechanism and difficulty for prediction. Here we investigate the immobilized layer structures of trifunctionality polyether polyol (PPG) near the surfaces of hydrophilic and hydrophobic fumed silica (FS) nanoparticles to reveal the role of surface chemistry on the molecular dynamics and sol-gel transitions of the dispersions. Using modulated differential scanning calorimetry, we measure the specific heat capacity during glass transition and the enthalpy during cold-crystallization. Comparing with hydrophobic FS that forms a fully immobilized (glassy) layer, we find that hydrophilic FS immobilizes more PPG, forming a partially immobilized outer layer being unable to crystallize next to the inner glassy layer. By correlating the thickness of the glassy layer with half of the minimum spacing between nanoparticles, we directly evidence the percolation of this layer along the nearest neighbor nanoparticles responsible for the sol-gel transition. Using effective volume fraction including the glassy layer, we successfully construct master curves of relative viscosity of both hydrophilic and hydrophobic FS dispersions, pointing to a common sol-gel transition mechanism mediated by the surface chemistry.

Interfacial Properties of Mixed DPPC–Hydrophobic Fumed Silica Nanoparticle Layers

The combination of interfacial thermodynamic, dilational rheology, and Brewster angle microscopy (BAM) has allowed the evaluation of the effect of hydrophobic fumed silica nanoparticles on the interfacial properties of Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC). Fumed silica particles modify the surface pressure–area (Π–A) isotherm of DPPC, modifying both the phase behavior and the collapse conditions. These modifications are strongly dependent on the relative quantity of DPPC and Nanoparticles initially spread at the air–water interface. The incorporation of nanoparticles at the fluid interface alters the balance of interactions within the monolayer, thus leading to the disruption of the interfacial structure and consequently of the lipid packing. Measurements of dilational viscoelastic modulus against the frequency have been carried out by the mean of the oscillatory barrier method at different degrees of compression of the monolayer. The dynamic response is also modified...

Inorganic-Organic Thiol-ene Coated Mesh for Oil/Water Separation.

A highly efficient mesh for oil/water separation was fabricated by using a superhydrophobic and superoleophilic coating of thiol-ene hybrid, consisting of pentaerythritol tetra(3-mercaptopropionate) (PETMP), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TMTVSi), and hydrophobic fumed silica nanoparticles, via a simple two-step fabrication process. Spray deposition and UV curing photopolymerization were sequentially performed, during which solvent evaporation provides microscale roughness while nanoparticle aggregation forms nanoscale roughness. The hierarchical morphologies were stabilized after UV curing photopolymerization. High contact angle (>150°) and low roll-off angle (<5°) were achieved due to the multiscale roughness structure of the hierarchical morphologies. These coatings also have excellent chemical resistance, as well as temperature and pH stability, after curing.

Influence of the coating method on the formation of superhydrophobic silicone–urea surfaces modified with fumed silica nanoparticles

Abstract Effect of the coating method on the formation of superhydrophobic polydimethylsiloxane–urea copolymer (TPSC) surfaces, modified by the incorporation of hydrophobic fumed silica nanoparticles was investigated. Four different coating methods employed were: (i) layer-by-layer spin-coating of hydrophobic fumed silica dispersed in an organic solvent onto TPSC films, (ii) spin-coating of silica–polymer mixture onto a glass substrate, (iii) spray coating of silica/polymer mixture by an air-brush onto a glass substrate, and (iv) direct coating of silica–polymer mixture by a doctor blade onto a glass substrate. Influence of the coating method, composition of the polymer/silica mixture and the number of silica layers applied on the topography and wetting behavior of the surfaces were determined. Surfaces obtained were characterized by scanning electron microscopy (SEM), white light interferometry (WLI) and advancing and receding water contact angle measurements. It was demonstrated that superhydrophobic surfaces could be obtained by all methods. Surfaces obtained displayed hierarchical micro-nano structures and superhydrophobic behavior with static and advancing water contact angles well above 150° and fairly low contact angle hysteresis values.

Superhydrophobic nanocomposites from biodegradable thermoplastic starch composites (Mater-Bi®), hydrophobic nano-silica and lycopodium spores

Due to increasing environmental concerns related to bio-persistence of petroleum based polymers, research efforts have intensified towards developing biodegradable materials with equivalent performance properties. Among these properties liquid repellence is one of the most challenging to obtain due to the fact that most biopolymers such as polysaccharides or bio-polyesters are hygroscopic or hydrophilic. One possible approach is to formulate biopolymer nanocomposites with water repellent properties. Here, we demonstrate such an approach using a commercial thermoplastic starch composite, Materi-Bi®, hydrophobic fumed silica nanoparticles and lycopodium spores. We found that both hydrophobic fumed silica and Materi-Bi® have excellent colloidal stability and solubility in chloroform and they can be spray coated onto various surfaces like paper, metals and semiconductors. By varying the concentration ratio of biopolymer to hydrophobic fumed silica, the wetting properties of the nanocomposites could be tuned. Superhydrophobic nanocomposites displayed raspberry-like surface roughness with water contact angles exceeding 160° with very low water droplet roll-off angles (∼1°). On the other hand, composites of Materi-Bi® and lycopodium spores displayed sticky superhydrophobicity (rose petal effect). Superhydrophobic nanocomposites were found to withstand thermal aging at 250 °C without loss of properties. Due to the resultant micro-morphology of the nanocomposites, certain coatings were rendered superoleophobic by functionalizing with a dilute fluoroacrylic polymer solution in acetone. Oil droplet contact angles reached 166° with droplet roll-off angles of approximately 15°.