Hydrophilic Silica Nanoparticles Research Articles

Synergistic effect of hydrophilic nanoparticles and anionic surfactant on the stability and viscoelastic properties of oil in water (o/w) emulations; application for enhanced oil recovery (EOR)

With the rapidly increased global energy demand, great attention has been focused on utilizing nanotechnology and particularly nanofluids in enhanced oil recovery (EOR) to produce more oil from low-productivity oil reservoirs. Nanofluid flooding has introduced as one of the promising methods for enhanced oil recovery using environment-friendly nanoparticles (NPs) to be as an innovative-alternative for chemical methods of EOR. This work investigates the synergistic effects of anionic surfactant and hydrophilic silica nanoparticles on the stability and the mechanical behavior of oil in water (O/W) emulsions for their application in EOR.
 To achieve this, an extensive series of experiments were conducted at a wide range of temperatures (23 – 70 °C) and ambient pressure to systematically evaluate the stability and the viscoelastic properties of the oil in water (O/W) emulsion with the presence of hydrophilic silica nanoparticles and an anionic surfactant. In this context, the initial oil to water volume ratio was 25:75. Sodium dodecylsulfate (SDS) was used as the anionic surfactant and n-decane was used as model oil. A wide concentration ranges of NPs (0.01 – 0.2 wt%) and surfactant (0.1 – 0.3 wt%) were used to formulate different emulsions. For stability measurements, a dynamic light scattering and zetasizer were used to measure the particle size distribution and zeta potential respectively. Creaming and phase behaviors were also investigated. The viscoelastic measurements were conducted using Discovery Hybrid Rheometer. 
 Results show that in the presence of surfactant, and NPs mitigates the coalescence of dispersed oil droplets giving high promises in EOR applications. Further, over the tested range of temperatures, the viscosity of O/W emulsion remains stable which indicates thermal stability.
 Despite studies examining the use of nanoparticle-surfactant combination in sub-surface applications, no reported data is currently available, to the best of our knowledge, about the potential synergistic effect of this combination on the stability and viscoelastic properties of O/W emulsion. This study gives the first insight on nanoparticle-surfactant synergistic effect on oil in water (O/W) emulsion for EOR applications.

Aggregation behavior and foam properties of the mixture of hydrocarbon and fluorocarbon surfactants with addition of nanoparticles

Aqueous foam is widely used in many industrial fields. Study on foam properties is the key to reducing additive amount of foaming agents and stabilizers as well as the economic cost, and improving utilization efficiency of foam products. The molecular aggregation behavior, foaming ability, foam drainage, and foam coarsening of the mixtures of hydrophilic silica nanoparticle (NP), anionic hydrocarbon surfactant (SDS), and amphoteric fluorocarbon surfactant (FS-50) were studied systematically. Results indicated that the addition of NP slightly affected the molecular aggregation behavior of the mixed solutions of SDS/FS-50. The surface activity, dynamic viscosity, and foaming ability of the foam dispersions increased slightly with increasing NP concentration. The conductivity of the dispersions decreased slightly with increasing NP concentration. Foam stability was significantly affected by NP concentration. When the NP concentration is lower than 1%, the addition of NPs accelerated foam drainage and coarsening. When the NP concentration is higher than 1%, the addition of NPs decelerated foam drainage and foam coarsening and thus reduced foam stability. The foam stability of SDS/FS-50 solutions was further enhanced with increasing NP concentration. This study provides a basis for the application of foams stabilized by NPs in fire extinguishing agents.

Membrane Biofouling Control by Surface Modification of Quaternary Ammonium Compound Using Atom-Transfer Radical-Polymerization Method with Silica Nanoparticle as Interlayer.

A facile approach to fabricate antibiofouling membrane was developed by grafting quaternary ammonium compounds (QACs) onto polyvinylidene fluoride (PVDF) membrane via surface-initiated activators regenerated by electron transfer atom-transfer radical-polymerization (ARGET ATRP) method. During the modification process, a hydrophilic silica nanoparticle layer was also immobilized onto the membrane surface as an interlayer through silicification reaction for QAC grafting, which imparted the membrane with favorable surface properties (e.g., hydrophilic and negatively charged surface). The QAC-modified membrane (MQ) showed significantly improved hydrophilicity and permeability mainly due to the introduction of silica nanoparticles and exposure of hydrophilic quaternary ammonium groups instead of long alkyl chains. Furthermore, the coverage of QAC onto membrane surface enabled MQ membrane to have clear antibacterial effect, with an inhibition rate ~99.9% of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), respectively. According to the batch filtration test, MQ had better antibiofouling performance compared to the control membrane, which was ascribed to enhanced hydrophilicity and antibacterial activity. Furthermore, the MQ membrane also exhibited impressive stability of QAC upon suffering repeated fouling–cleaning tests. The modification protocols provide a new robust way to fabricate high-performance antibiofouling QAC-based membranes for wastewater treatment.

Redox and Doubly pH-Switchable Pickering Emulsion.

In this work, a novel Pickering emulsion is stabilized by silica nanoparticles functioned with a redox and pH-responsive surfactant FA-DMDA-Ox that is prepared simply by direct neutralization of ferrocenecarboxylic acid (FA) and N,N-dimethyldodecylamine (DMDA) and exhibits redox and doubly pH-switchable behavior. Here, the Pickering emulsion can be stabilized easily by combining hydrophilic silica nanoparticles with less than 0.1 wt % FA-DMDA-Ox. After adding Na2SO3 and H2O2 alternately, the demulsification and emulsification of this Pickering emulsion are controlled reversibly. Moreover, the emulsion is switched "off" upon the addition of HCl and switched "on" upon the addition of NaOH and is also switched off upon the addition of NaOH and switched on upon the addition of HCl, which demonstrate the doubly pH-switchable behavior. Based on the analysis of ζ-potential, contact angle, and adsorbed amount of silica nanoparticles, the pH and redox-switchable mechanism of the Pickering emulsion are analyzed. Here, the redox-switchable behavior is induced by the reversible adsorption and desorption of FA-DMDA-Ox on the surface of silica nanoparticles. The pH-switchable behavior is driven by the controllable dispersion systems of silica nanoparticles and FA-DMDA-Ox because of the doubly pH switchability of FA-DMDA-Ox. More importantly, upon adding fresh oil after removing the original oil, the Pickering emulsion is recycled three times. Hence, the multiswitchable Pickering emulsion can be expected to be treated as a multifunctional material in practical applications, such as oil or wax removal in the petroleum industry.

Enhancing Oil Recovery with Hydrophilic Polymer-Coated Silica Nanoparticles

Nanoparticles (NPs) have been proposed for enhanced oil recovery (EOR). The research has demonstrated marvelous effort to realize the mechanisms of nanoparticles EOR. Nevertheless, gaps still exist in terms of understanding the nanoparticles-driven interactions occurring at fluids and fluid–rock interfaces. Surface-active polymers or other surface additive materials (e.g., surfactants) have shown to be effective in aiding the dispersion stability of NPs, stabilizing emulsions, and reducing the trapping or retention of NPs in porous media. These pre-requisites, together with the interfacial chemistry between the NPs and the reservoir and its constituents, can result in an improved sweep efficiency. This paper investigates four types of polymer-coated silica NPs for the recovery of oil from water-wet Berea sandstones. A series of flooding experiments was carried out with NPs dispersed at 0.1 wt.% in seawater in secondary and tertiary oil recovery modes at ambient conditions. The dynamic interactions of fluids, fluid–rock, and the transport behavior of injected fluid in the presence of NPs were, respectively, studied by interfacial tension (IFT), spontaneous imbibition tests, and a differential pressure analysis. Core flooding results showed an increase in oil recovery up to 14.8% with secondary nanofluid injection compared to 39.7% of the original oil in place (OOIP) from the conventional waterflood. In tertiary mode, nanofluids increased oil recovery up to 9.2% of the OOIP. It was found that no single mechanism could account for the EOR effect with the application of nanoparticles. Instead, the mobilization of oil seemed to occur through a combination of reduced oil/water IFT, change in the rock surface roughness and wettability, and microscopic flow diversion due to clogging of the pores.

Preparation of Hydrophilic UHMWPE Hollow Fiber Membranes by Chemically Bounding Silica Nanoparticles

In this work, ultra-high molecular weight polyethylene (UHMWPE) microfiltration hollow fiber membranes prepared via the thermally induced phase separation (TIPS) method were modified by chemically bounding hydrophilic silica (SiO2) nanoparticles onto the surface to improve anti-fouling performance. A range of testing techniques including attenuated total reflection Flourier transformed infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), water contact angle, mechanical test, filtration and anti-fouling performance were carried out to discuss the influence of different modification conditions on the properties of the membranes. The prepared hollow fiber membranes display the significantly excellent performance when the vinyl trimethoxy silane (VTMS) concentration was 13%, the pH value of the hydrolyzate was 4 and the hydrolysis reaction time was 6 h. In particular, the hydrophilicity of modified membranes was improved effectively, resulting in the enhancement of membrane anti-fouling properties. The results of this work can be consulted for improving the anti-fouling performance of the UHMWPE microfiltration hollow fiber membrane applied in the field of water purification.

Pickering emulsion stabilized by organoclay and intermediately hydrophobic nanosilica for high-temperature conditions

Pickering emulsions show great promise for many applications in the oil and gas industry. However, the thermal stability of Pickering emulsions reported thus far has been unfavorable for safe operation in the always high-temperature deep underground condition. Here we report a Pickering water-in-oil (W/O) emulsion that exhibits high temperature tolerance in the absence of any surfactant due to the synergistic effect between organoclay and silica nanoparticles (NPs) with intermediate hydrophobicity. The interaction between silica NPs and organoclay was characterized by X-ray diffraction, thermogravimetric analysis, zeta potentials, scanning electron microscopy and transmission electron microscopy. The results of gel volume and water contact angle measurement confirmed the hydrophobicity of the organoclay. The effects of varying the hydrophobicity and concentration of the silica NPs, the clay concentration of the organoclay, and the thermal-rolling temperature on the emulsion stability, droplet size, morphology, and rheology were investigated in detail. The optimal synergy for stabilizing the W/O emulsion was found to occur with 1 wt% silica NPs exhibiting intermediate hydrophobicity and 1 wt% organoclay. As expected, neither hydrophobic nor hydrophilic silica NPs could improve the emulsion stability due to inefficient adsorption at the water-oil interface. Organoclay was found to have a significant influence on the stability and rheological properties of the W/O Pickering emulsion since it dominates the formation of networks in the continuous phase due to its excellent swelling and exfoliation. The adsorption of silica NPs further enhanced the interactions between the particles and the medium, making it possible for the retainment of rheology even after thermal rolling at 220 ℃. The increase in temperature tolerance achieved through a simple and environmentally friendly method makes this Pickering emulsion applicable in potential drilling fluids for the oil and gas field.

Rheological characteristics and flow dynamics of polymer nanohybrids in enhancing oil recovery from low permeable carbonate oil reservoirs

As the chemical flooding has proved to be one of the most efficient methods to unlock the trapped oil in porous media, studies on any further improvements in the rheological, phase, and flow behaviors of the common Chemical Enhanced Oil Recovery (CEOR) agents through the use of nanostructured-based materials have gathered significant importance in the field of petroleum engineering. Despite the extensive research in this area, the role of physical properties of polymers including molecular weight (MW) in the improvement of the flow characteristics of the resultant hybrid in a low-permeable carbonate rock has been scrutinized neither experimentally nor numerically so far. The purpose of this study was to clarify the effect of dispersed Hydrophilic Silica-Nanoparticles (HSNPs) in the polymer solution on the improvement of oil recovery during polymer flooding. Thus, rheological studies were performed to scrutinize the impacts of salinity, polymer content, and polymer MW on the viscoelastic behavior of the hybrid. An understanding of how the hybrid behaves when flowing through a relatively low-permeable carbonate rock was acquired by conducting core flood experiments. To monitor the mechanisms of the fluid flow and determine the influencing factors in the fluid distribution through complex pore systems, microfluidic models were utilized. The viscoelastic behavior of the hybrid shows that dispersing HSNPs in a polymer solution consisting of a polymer with lower MW can improve the viscosifying ability and non-Newtonian behavior of the solution. This trend becomes more noticeable by increasing polymer content. However, the employed Nanoparticles (NPs) have a distinct impact on the non-Newtonian behavior of the polymers with higher MW. The results from core flooding experiments reveal that the oil recovery factor is nearly 60% of Original Oil In-Place (OOIP) for the hybrid flooding, which displays pronounced enhancement in ultimate oil recovery, due to the proper mobility ratio of the displacement process. Pore-scale observations and the outputs of numerical simulations exhibit that wettability reversal and polymer adsorption reduction are also responsible for the improvement of oil recovery. The findings of this study not only present the underlying mechanisms of oil recovery during the hybrid flooding of low-permeable carbonate rocks but also provide a new reference for formulating a novel CEOR agent.

Rewritable superhydrophobic coatings fabricated using water-soluble polyvinyl alcohol

Superhydrophobic surface has potential applications in various fields due to its excellent water repellency. In particular, fluorine-free superhydrophobic film has attracted extensive attentions. In this study, an eco-friendly and rewritable superhydrophobic coating is successfully prepared by a simple spray-coating method. Hydrophilic silica nanoparticles are immobilized on a substrate by water-soluble polyvinyl alcohol (PVA), and then the surface is further modified by polydimethylsiloxane (PDMS) to obtain a superhydrophobic coating. The prepared coating has a water contact angle of 160o, and exhibits good stability. Most importantly, when the superhydrophobic coating is no longer needed, it can be removed and the substrate can be reused. The eco-friendly and rewritable superhydrophobic coating should have promising potentials in daily life.

Highly toughened poly(lactic acid) (PLA) prepared through melt blending with ethylene-co-vinyl acetate (EVA) copolymer and simultaneous addition of hydrophilic silica nanoparticles and block copolymer compatibilizer

In this study, a highly toughened PLA was prepared through physical melt-blending with EVA at the presence of hydrophilic nanosilica and SEBS-g-MA block copolymer compatibilizer. The effect of nanosilica and compatibilizer on the morphology, mechanical properties, and linear rheology of the PLA/EVA blends was also investigated. According to TEM images, nanosilica was selectively located in the PLA matrix while some were placed on the interface between the two polymers as was also predicted by thermodynamic and kinetic analysis. Upon the addition of nanoparticles, the interfacial adhesion between the phases was enhanced and the average droplet size decreased. Interestingly, incorporation of SEBS-g-MA induced morphological changes as the spherical EVA droplets turned into a cylindrical shape. DSC results indicated that blending with EVA copolymer resulted in the reduction of crystallization of PLA matrix; however, the crystallinity increased at the presence of nanoparticles up to 5 wt%. The addition of compatibilizer considerably hindered the crystallization of the PLA phase. PLA/EVA blend containing optimum levels of nanosilica exhibited considerably enhanced tensile toughness, elongation at break, and impact strength. On the other hand, the simultaneous addition of nanoparticles and SEBS-g-MA led to synergistic toughening effects and the compatibilized blend containing nanosilica exhibited excellent impact toughness. For instance, the elongation at break of the compatibilized PLA/EVA blend containing the optimal content of nanosilica was increased from 7% to 121% (compared to neat sample). The notched Izod impact strength was also increased from 5.1 to 65 kJ/m2. Finally, the microstructure of the blends was assessed by rheological measurements.

Role of nanoparticles in the performance of foam stabilized by a mixture of hydrocarbon and fluorocarbon surfactants

The molecular interaction, foaming ability, and foam stability of the mixtures of hydrophilic silica nanoparticles, a cationic hydrocarbon surfactant, and a nonionic short-chain fluorocarbon surfactant were studied systematically. The results indicate that nanoparticle concentration has a considerable impact on surface activity, dynamic viscosity, conductivity, foaming ability, and foam stability. The surface activity and dynamic viscosity of the foam dispersions increased rapidly with increasing nanoparticle concentration. The conductivity and foaming ability of the dispersions decreased with the addition of nanoparticles and further decreased with increasing nanoparticle concentration. At a nanoparticle concentration below 0.1%, the addition of nanoparticles accelerated foam drainage and coarsening. At a nanoparticle concentration above 0.1%, the addition of nanoparticles enhanced foam stability by decelerating foam drainage and foam coarsening. The foam stability was further enhanced as the nanoparticle concentration increased. This study provides a basis for the application of foams stabilized by nanoparticles in fire extinguishing agents.

Effect of Interlayer Interactions on the Dynamic Self‐Stiffening Behaviors of Graphene Oxide‐Based Films

AbstractThe responsive behaviors of graphene oxide (GO)‐based films under external straining make it possible to develop man‐made adaptive materials. Some researches have suggested that GO nanosheet alignment plays important roles in dynamic stiffening behaviors; however, the effects of inter‐sheet interactions have not been thoroughly investigated. In this study, the GO interlayer interactions are tuned by third components, including hydrophilic nanofumed silica (SiO2) nanoparticles, chemically modified SiO2 nanoparticles, and waterborne polyurethane particles, and their stiffening behaviors and structural changes during periodic external straining are systematically characterized. During external dynamic straining, the storage modules (E′) of GO‐based composite films increases up to 55.5% after 12 h. It is observed that the interlayer adhesion is important for the self‐stiffening behaviors of GO‐based films. The interaction types, including reversible H‐bonding and non‐reversible chemical bonding, play different roles on the structural‐responsive behaviors. During external dynamic straining, the interlayer contact between GO nanosheets is improved, and the higher interlayer adhesion leads to improved mechanical properties, instead of the improvement of GO sheet orientation. These findings are helpful to better understand the responsive behaviors of nanomaterials as well as to develop new types of man‐made adaptive materials.

Compatibilization of immiscible blends of polypropylene and isosorbide containing copolyester with silica nanoparticles

AbstractIn the present study, compatibilization of immiscible blends of polymers was investigated based on the Pickering emulsion concept with various mixing procedures. Silica nanoparticles were incorporated into poly (1,4‐cyclohexanedimethylene isosorbide terephthalate) (PEICT)/isotactic polypropylene (iPP) blends. Localization of nanoparticles was effectively modified by varying mixing procedures. Relocation of hydrophilic silica occurred in a secondary mixing procedure with the PEICT, which has relatively high affinity when primarily mixed with iPP. The final location of the silica nanoparticles was confirmed by SEM images. SEM and an optical microscope were used to follow morphological change. By simply changing the mixing procedure, the hydrophilic silica nanoparticles were able to perform the role of a morphology modifier successfully without modifying the surface characteristics. The mechanical properties and crystallization behavior were also compared depending on the surface characteristics of the silica nanoparticles and their final localization.

Colloidal stability and dynamic adsorption behavior of nanofluids containing alkyl-modified silica nanoparticles and anionic surfactant

Abstract Nanofluids containing slightly hydrophobic silica nanoparticles have been shown to reduce surfactant adsorption on rocks in enhanced oil recovery methods. In this work, we chemically modified the surface of silica nanoparticles with two different alkyl groups (octyl and hexadecyl) to study in detail the mechanisms of interaction with anionic surfactants in nanofluids. The alkyl-modified nanoparticles showed higher colloidal stability compared to hydrophilic silica nanoparticles when dispersed in micellar solutions of sodium dodecyl sulfate, forming small, highly-charged nanoclusters. The presence of the hydrocarbon chains on the silica surface was able to significantly improve the anionic surfactant retention in solution (up to 90%), due to additional hydrophobic interactions with the surfactant tails. Results from dynamic adsorption tests using an unconsolidated porous medium showed an increase in the surfactant recovery after nanofluid injection, suggesting a fast adsorption/desorption mechanism. Therefore, the nanofluids containing alkyl-modified nanoparticles were more effective in reducing the adsorption loss, retaining the anionic surfactant in bulk and limiting the amount of free surfactant available for adsorption on the porous medium.

Bovine hemoglobin adsorption onto modified silica nanoparticles: Multi-spectroscopic measurements based on kinetics and protein conformation

Herein, the effects of bovine hemoglobin (BHb) binding to hydrophilic silica nanoparticles (SN1) and hydrophobic silica nanoparticles (SN2) were explored under physiological conditions. SEM and XRD were used to characterize silica nanoparticles (SNs). Zeta potential and DLS confirmed the formation of protein corona (PC), and SN2 showed more increase in their size after PC formation comparing with SN1. The adsorption isotherms were fitted well by the Freundlich model, and the kinetics tended to follow pseudo-second-order kinetics. Then, the second structure of BHb has been analyzed by UV–vis and FT-IR spectroscopy, which implied the impact of SN2 on the secondary structure of BHb was greater than that of SN1 on BHb. Moreover, fluorescence spectroscopy and Raman spectroscopy showed that SNs may induce heme degradation to form fluorescent heme product, resulting in increased fluorescence intensity. This investigation will be significant in exploring the toxicity profile of SNs for their in vivo.

Evaluation of mechanical properties of nanoparticles using a constant-volume shear tester

Nanoparticles have advantageous small-size and surface effects that impart them with unique mechanical properties. To evaluate these properties, a constant-volume shear tester that can precisely measure stresses on the shear plane was used. Six samples, namely, hydrophilic and hydrophobic silica, alumina, and titania nanoparticles, were prepared for the shear tests. For each sample, a single shear test provided the void fraction, stress relaxation ratio, stress transmission ratio, powder yield locus, consolidation yield locus, critical state line, shear cohesion, and flow function. All the tests were conducted under ambient conditions using powder beds, in which the void fractions were in the range of 0.89–0.96. A series of analyses demonstrated that the hydrophilic nanoparticles have lower flowability than the hydrophobic nanoparticles, indicating that moisture on the surface increases the cohesion and inhibits the flow.

Fabrication of solvent transfer-induced phase separation bijels with mixtures of hydrophilic and hydrophobic nanoparticles.

Bicontinuous interfacially jammed emulsion gels (bijels), in which the oil and water phases are co-continuous throughout the structure, have potential for applications in separation, catalysis, tissue engineering and energy devices. Among the possible fabrication paths, the solvent transfer-induced phase separation (STRIPS) method has proven to be a powerful approach to produce bijels in a continuous fashion with a broad selection of liquids and nanoparticles. The successful formation of bicontinuous domains requires the use of neutrally wetting particles which was achieved by in situ modification of silica nanoparticles with an oppositely charged surfactant. This approach, however, is not ideal for applications that are adversely affected by the presence of surfactant. In this work, we use a pair of nanoparticles, one hydrophilic, and the other hydrophobic, to stabilize STRIPS bijels without any surfactants and show that the ratio of the hydrophilic to hydrophobic nanoparticles required to form stable bijels changes with the polarity of the oil phase. Highly non-polar oils require a smaller ratio than moderately polar oils. Furthermore, if a sufficiently polar oil is selected, STRIPS bijels can be stabilized using only the hydrophilic nanoparticle. Our results demonstrate the potential to imbue the interface of biphasic liquid mixtures such as bijels with multifunctionality by using two functional nanoparticles of opposite polarity.

Enhanced Ice Nucleation and Growth by Porous Composite of RGO and Hydrophilic Silica Nanoparticles

A porous composite of 3-dimensional (3D) reduced graphene oxide (rGO) and silica dioxide nanoparticles (PrGO-SN) was synthesized via a single-step hydrothermal process, which can initiate facile ice nucleation and growth starting from temperature as high as −8 °C and 5–8% RH supersaturation and sustain rapid ice crystal growth. The excellent ice nucleation activity of the PrGO-SN composite demonstrates a novel means of ice nucleation relative to known materials, attributed to not only the lattice match between the ice and crystalline structure of the PrGO-SN composite but also higher specific surface area, larger water vapor adsorption capacity, better porosity, and more hydrophilic surface of the composite than rGO. Moreover, environmental scanning electron microscope (E-SEM) in situ observation confirmed detailed growth patterns of ice crystals on the composite, which were affected by the regions with different surface roughness. These findings enabled further understanding of the factors that affected the heterogeneous ice nucleation process and shed light on the design and fabrication of more efficient functional porous ice nucleation materials for many practical applications such as cloud seeding.

Rheological and Ionic Transport Properties of Nanocomposite Electrolytes Based on Protic Ionic Liquids and Silica Nanoparticles.

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO2CF3)2]), [DBU][TfO] ([TfO] = [CF3SO3]), and [DBU][TFA] ([TFA] = [CF3CO2]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH3SO3]) system. A relatively strong interaction between the silanol groups and the ions of [DBU][MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

The effect of silica/polyurethane waterborne dispersion on the perforating features of impregnated polypropylene-based fabric

In an attempt to improve the puncturing behavior of a commercial technical textile, this study investigated the effects of fabric impregnation with waterborne polyurethane dispersions (WPUDs). The infusing solutions were prepared by mixing a commercially available WPUD with other components, such as water, hydrophilic and hydrophobic silica (SiO2) nanoparticles, and a crosslinker. Quasi-static perforation tests were performed on a dynamometer machine equipped with a spherical spike and pointed blade as piercing probes. The results showed that the polyurethane impregnation augmented the puncture performances of the treated textiles. Then, further improvements in the spike and blade strength of the impregnated fabrics were obtained by adding hydrophilic silica nanoparticles and crosslinker into WPUDs, respectively. No effect of silica functionalization (hydrophilic or hydrophobic) has been verified on the mechanical features of the respective treated samples for the tested filler contents of 3% and 5% in wt. The best fabric features (blade strength increase of +63% and puncture strength increase of +71% compared to the neat material) were obtained by combining the two additives, nano SiO2 and crosslinker, into the polyurethane. The performances of these last systems were also superior to those obtained by doubling the amount of polymeric dispersion applied to the neat materials. The discussion of the results was supported by electron scanning microscopy, infrared spectroscopy, and further measurements of the cutting resistance. Finally, the mass per unit area of the substrate for the impregnated samples was measured in order to assess weight gain due to treatment.