Hydrophobic Nanosilica Research Articles

Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development

The use of hydrophobic nano-silica particles in concrete for improved corrosion resistance and durability has been explored in recent years, and its potential impact on sustainable urban development and green building practices has been studied. The impact of substituting hydrophobic nano-silica particles for 2% of the cement weight in high-strength concrete mixes was investigated in this research. The study focuses on evaluating the physical-mechanical properties, including compressive strength, tensile strength, modulus of elasticity, and Poisson’s ratio. Additionally, the influence of these mixes on corrosion resistance is examined. The concrete designs feature a high strength of 42 MPa, and the hydrophilic nano-silica particles undergo functionalization processes to obtain hydrophobic properties. Contact angle measurements and water absorption tests confirm the hydrophobicity of the material. Physical, electrochemical, and electrical tests were conducted to determine the corrosion resistance contribution of the nano-silica particles when substituted at 2% of the cement weight. The research findings reveal that concrete containing nano-silica particles demonstrates improved physical-mechanical properties compared to other mixes. Incorporating nano-silica enhances concrete by accelerating hydration, increasing early-age strength, and providing hydrophobicity, resulting in improved physical-mechanical properties over other mixes. However, it was observed that the addition of hydrophobic and non-hydrophobic nano-silica tends to reduce corrosion resistance compared to concrete without these particles, despite exhibiting greater compactness. This suggests a direct influence of nano-silica on the corrosion phenomenon.

Nanostructured systems based on polymethylsiloxane and nanosilicas with hydrophobic and hydrophilic functionalities

Nanostructured adsorbents composed of nanoparticles with hydrophobic and hydrophilic surface functionalities are of interest for practical applications due to the dual nature of their surfaces. To prepare nanostructured hydrogels including a hydrophobic component, its hydrophobicity should be low, e.g., due to the shortest hydrophobic functionalities (–CH3). Therefore, hydrophobic nanosilica (AM1) and polymethylsiloxane (PMS) both with methylsilyl functionalities and residual silanols were selected as components of composites with hydrophilic nanosilica A–300. These hydrophobics were well wetted–stirred with A–300 to control the blend hydrophilicity. To analyze interfacial phenomena in PMS(AM1)/A–300, the temperature behavior of bound water alone or with different co-sorbates and solutes was studied in various dispersion media using low-temperature 1H NMR spectroscopy of static samples. The adsorbents were studied using microscopy, spectroscopy, thermogravimetry, adsorption, and quantum chemistry methods. Obtained results allow us to elucidate several general regularities, caused by the nano-morphology, texture, and structure of components and blends located in different dispersion media, related to the interfacial and temperature behaviors of bound compounds depending on pretreatments changing the organization of ‘soft’ nanostructured systems. This study allows one a deeper insight into the interfacial phenomena in nanostructured hydrophobic/hydrophilic PMS(AM1)/A–300 blends, which could be of interest from a practical point of view for applications as, e.g., drug delivery systems characterized by prolonged release varied for hydrophilic and hydrophobic drugs due to changes in the blend components and their pretreatments.

Hydrophobic aerogel-modified hemostatic gauze with thermal management performance.

Current hemostatic agents or dressings are not efficient under extremely hot and cold environments due to deterioration of active ingredients, water evaporation and ice crystal growth. To address these challenges, we engineered a biocompatible hemostatic system with thermoregulatory properties for harsh conditions by combining the asymmetric wetting nano-silica aerogel coated-gauze (AWNSA@G) with a layer-by-layer (LBL) structure. Our AWNSA@G was a dressing with a tunable wettability prepared by spraying the hydrophobic nano-silica aerogel onto the gauze from different distances. The hemostatic time and blood loss of the AWNSA@G were 5.1 and 6.9 times lower than normal gauze in rat's injured femoral artery model. Moreover, the modified gauze was torn off after hemostasis without rebleeding, approximately 23.8 times of peak peeling force lower than normal gauze. For the LBL structure, consisting of the nano-silica aerogel layer and a n-octadecane phase change material layer, in both hot (70°C) and cold (-27°C) environments, exhibited dual-functional thermal management and maintained a stable internal temperature. We further verified our composite presented superior blood coagulation effect in extreme environments due to the LBL structure, the pro-coagulant properties of nano-silica aerogel and unidirectional fluid pumping of AWNSA@G. Our work, therefore, shows great hemostasis potential under normal and extreme temperature environments.

Selection of Silica Type and Amount for Flowability Enhancements via Dry Coating: Contact Mechanics Based Predictive Approach.

To investigate the effect of dry coating the amount and type of silica on powder flowability enhancement using a comprehensive set of 19 pharmaceutical powders having different sizes, surface roughness, morphology, and aspect ratios, as well as assess flow predictability via Bond number estimated using a mechanistic multi-asperity particle contact model. Particle size, shape, density, surface energy and area, SEM-based morphology, and FFC were assessed for all powders. Hydrophobic (R972P) or hydrophilic (A200) nano-silica were dry coated for each powder at 25%, 50%, and 100% surface area coverage (SAC). Flow predictability was assessed via particle size and Bond number. Nearly maximal flow enhancement, one or more flow category, was observed for all powders at 50% SAC of either type of silica, equivalent to 1wt% or less for both the hydrophobic R972P or hydrophilic A200, while R972P generally performed slightly better. Silica amount as SAC better helped understand the relative performance. The power-law relation between FFC and Bond number was observed. Significant flow enhancements were achieved at 50% SAC, validating previous models. Most uncoated very cohesive powders improved by two flow categories, attaining easy flow. Flowability could not be predicted for both the uncoated and dry coated powders via particle size alone. Prediction was significantly better using Bond number computed via the mechanistic multi-asperity particle contact model accounting for the particle size, surface energy, roughness, and the amount and type of silica. The widely accepted 200nm surface roughness was not valid for most pharmaceutical powders.

Controllable Construction and Corrosion Resistance Mechanism of Durable Superhydrophobic Micro-Nano Structure on Aluminum Alloy Surface

Aluminum alloy corrosion resistance could be improved by micro-nanostructures on superhydrophobic surfaces, but inadequate mechanical stability remains a bottleneck concern in the sector. Herein, femtosecond laser processing and spray modification techniques are employed to fabricate “armor-style” micro-nanostructures on aluminum alloy surfaces. The construction of durable superhydrophobic surfaces was controllably constructed using this strategy. Applying a spray of hydrophobic nano silica onto the surface of aluminum alloys is an effective method for creating a low surface energy coating, while the femtosecond laser-processed “armor-style” micro-nano structure offers additional adhesion sites for the hydrophobic nano-silica. The findings indicated that the treated surface’s contact angle (CA) reached 152.5° while the slide angle (SA) was only 2.3°, exhibiting favorable superhydrophobic performance. Being worn 100 times with 400# sandpaper, the superhydrophobic surface retained a contact angle above 150°. Electrochemical tests demonstrated significant reductions in the self-corrosion current of superhydrophobic surfaces. Meanwhile, the impedance increased significantly, showing good thermal, mechanical, and chemical stability, enabling better sustainable use of aluminum alloys. These results will serve as a theoretical foundation for the surface protection of aluminum alloys.

Design and fabrication of silicone-silica nanocomposites airway stent

Introduction: Due to the COVID-19 pandemic in recent years, many patients after extubation had stenosis in all tracheal areas because of long-term intubation. Therefore, tracheal stenosis in these patients is benign and can be treated using silicone stents, and many patients need silicone stents during recovery. A silicone stent is an artificial support that plays a significant role in managing airway obstruction.Methods: This research aims to fabricate an optimal silicone stent reinforced with Nanosilica by vacuumed injection molding. Materials-based nanocomposites are made of rtv2 silicone with 1wt%, 3wt%, and 5wt% of hydrophilic and hydrophobic Nanosilica particles. Hardness, tensile, and hydrophobicity properties have been performed for the experimental characterization of the nanocomposites.Results and Discussion: The uniform distribution of nanoparticles in the silicone matrix has been confirmed using SEM images. Adding Nano-silica increases hardness and tensile strength and improves the silicone matrix’s mechanical properties. Also, the addition of nanoparticles changes the surface hydrophobicity properties and roughness. Although the presence of nanoparticles improves the mechanical properties, it also reduces the transparency and increases the viscosity. Our results show that adding 1wt%. Hydrophobic Nano-silica improves nanocomposites’ mechanical properties and preserves transparency and viscosity (mold-ability) for stent construction. Adding 3wt%. Hydrophilic Nano-silica improves mechanical and hydrophobic properties, but moldability is not easy. Finally, the fabricated nanocomposite airway stents were successfully placed on the sheep trachea in the pilot animal study.

Dry Water as a Promoter for Gas Hydrate Formation: A Review.

Applications of clathrate hydrate require fast formation kinetics of it, which is the long-standing technological bottleneck due to mass transfer and heat transfer limitations. Although several methods, such as surfactants and mechanical stirring, have been employed to accelerate gas hydrate formation, the problems they bring are not negligible. Recently, a new water-in-air dispersion stabilized by hydrophobic nanosilica, dry water, has been used as an effective promoter for hydrate formation. In this review, we summarize the preparation procedure of dry water and factors affecting the physical properties of dry water dispersion. The effect of dry water dispersion on gas hydrate formation is discussed from the thermodynamic and kinetic points of view. Dry water dispersion shifts the gas hydrate phase boundary to milder conditions. Dry water increases the gas hydrate formation rate and improves gas storage capacity by enhancing water-guest gas contact. The performance comparison and synergy of dry water with other common hydrate promoters are also summarized. The self-preservation effect of dry water hydrate was investigated. Despite the prominent effect of dry water in promoting gas hydrate formation, its reusability problem still remains to be solved. We present and compare several methods to improve its reusability. Finally, we propose knowledge gaps in dry water hydrate research and future research directions.

Thermodynamically-equilibrium LCST phase diagram of PCL/SAN mixtures determined by thermal analysis: Opposing effects of hydrophilic and hydrophobic silica nanoparticles

In this work, the isothermal crystallization kinetics of PCL in PCL/SAN blend and PCL/SAN/nanosilica nanocomposite systems has been applied as a useful and sensitive variable for determining the LCST phase diagram. By eliminating the impacts of kinetic variables, the variations in the equilibrium LCST phase boundary of PCL/SAN mixtures were evaluated. The presence of hydrophobic nanoparticles shifted the equilibrium LCST phase diagram to higher temperatures as expected owing to the compatibilization effect of nanoparticles, while the hydrophilic nanoparticles shifted it to lower temperature. The preferential migration of hydrophilic nanosilica into SAN-rich phase with slower molecular dynamics caused larger viscoelastic asymmetry of polymeric phases and consequently, lower area of phase miscibility window. In contrast, the addition of hydrophobic nanosilica with better dispersion state and no preferential localization in PCL/SAN blend resulted in a shift of LCST phase diagram to higher temperatures.

Nanosilica incorporated coarse wool-epoxy hybrid biocomposites with improved physico-mechanical properties

In the reported work, the wool fabric was coated with epoxy resin by hand layup method to fabricate the wool-epoxy composites. Hydrophobic nanosilica was used as a filler to improve their mechanical characteristics. The physico-mechanical properties of the composites were analyzed using various analytical techniques. The surface morphology was examined with the aid of Scanning Electron Microscope. The biodegradability of the developed composites was determined by soil burial test. The presence of nanosilica in the composite was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). According to the findings, up to 0.5% nanosilica content significantly increases the tensile and impact strength of the wool-epoxy composites. The contact angle measurement showed a slight enhancement in the hydrophobic properties of the composites due to the dispersion of hydrophobic nanosilica particles. The presence of nanosilica slightly reduced the water diffusivity in wool-epoxy-nanosilica composites when compared to wool-epoxy composites. The SEM images detected nanosilica inside the composites. After soil burial test, all the composites showed a weight reduction below 1.0%.

Exceptionally high energy storage density for seasonal thermochemical energy storage by encapsulation of calcium chloride into hydrophobic nanosilica capsules

Exceptionally high energy storage density for seasonal thermochemical energy storage by encapsulation of calcium chloride into hydrophobic nanosilica capsules

Effect of composition of geopolymer composites containing fly ash and waste glass powder on their durability and resistivity demonstrated in presence of a nanocarbon additive in a form of graphene

The objective of this study was to obtain a geopolymer composite with semi-conductive or conductive properties for self-control of abnormal symptoms caused by damages to its microstructure. For that purpose effects of different content of fly ash, waste glass powder, as well as two types of graphene and hydrophilic and hydrophobic nanosilica on electrical, physical and mechanical properties were tested. Measurements of resistivity showed the capacity for electrical charge flow in composites, which depended on their composition and products of the geopolymer hardening process. Based on results of the electrical charge flow intensity and observations of geopolymer composite microstructure by means of XRD and scanning microscopy, a possible course of the electrical conductivity mechanism in geopolymer materials was indicated. It was found that geopolymer composites containing fly ash, as well as addition of graphene and hydrophobic nanosilica, showed the most favourable electrical charge conductivity parameters and the highest strength gain.

Surroundings effects on the interfacial and temperature behaviors of NaOH/water bound to hydrophilic and hydrophobic nanosilicas

HypothesisIt has been assumed that the temperature and interfacial behaviors of concentrated alkali solutions under confined space effects may depend on adsorbent surface structure, hydrophilicity/hydrophobicity, porosity of solids, and dispersion media properties causing kosmotropic or chaotropic effects onto hydrogen bond network (HBN) in bound water and NaOH solution. ExperimentsTo analyze these effects, systems with NaOH/water (0.1 g/g/0.1 g/g) deposited onto compacted hydrophilic (A-300) and hydrophobic (AM1) nanosilicas were studied using 1H NMR spectroscopy (215–287 K). The materials were characterized using several experimental and theoretical methods. FindingsIt has been shown that bound water and water/NaOH represent various clusters and domains whose characteristics depend strongly on nanosilica hydrophilicity/hydrophobicity, dispersion media (air, CDCl3, DMSO, CDCl3/DMSO), subsequent or simultaneous deposition of NaOH and water, and temperature. Water amount (0.1 g/g) was selected too small to completely dissolve NaOH (0.1 g/g) under confined space effects and low temperatures. Chaotropic hydrophobic AM1 and CDCl3 enhance water clusterization and HBN disorder (weakly associated water, WAW appears) in contrast to kosmotropic hydrophilic A-300, NaOH, and DMSO reducing the clusterization and HBN disorder in bound water (WAW disappears). Several aspects related to the interfacial and temperature behaviors of water and co-adsorbates bound to the nanosilicas were elucidated.

Fabrication of a superhydrophobic micron-nanoscale hierarchical structured surface for delayed icing and reduced frosting

Multifunctional superhydrophobic surfaces with dual-scale hierarchical structures have drawn considerable interest in real-world applications. The complicated fabricating process, higher costs, and poor durability limit the widespread utilization of bio-inspired superhydrophobic surfaces. Herein, we use an effective method to create a micron-nanoscale (dual-scale) hierarchical structure, which is composed of a micron-scaled rough structure constructed by a chemical-etching process and a secondary nanostructure obtained by hydrophobic nano silica (SiO2) modification. The micron-nanoscale hierarchical structured surface has superhydrophobicity with a water contact angle of 161.5°±1.9°. Compared with the micron-scaled rough structure surface, the manufactured micron-nanoscale hierarchical structured surface presented excellent anti-icing properties with a freezing delay time of 5013.6 s at -15 °C. The frost layer on the micron-nanoscale hierarchical structured surface can be rapidly melted to transform into some isolated water droplets in about 7 s due to its ultra-low water adhesion force. Additionally, the prepared superhydrophobic micron-nanoscale hierarchical structured surface has chemical stability and mechanical durability except for the delayed icing and reduced frosting performance. The construction of a micron-nanoscale hierarchical structure is expected to expand superhydrophobic surface applications in anti-icing, anti-frosting, and self-cleaning.

Flow improvement of fine oxidizer using nano-additives

Ammonium perchlorate (AP) is an oxidizer and major component for any solid composite propellant. The handling and processing of AP powder plays an important role in the performance of rocket fuel. AP being hygroscopic in nature; especially particle size<50 μm is highly cohesive in nature, which results in extensive agglomeration and poor flowability. This causes inherent handling problems in the propellant processing plant. In this work, the flowability of 8 μm and 50 μm AP particles was improved through the dry coating method using nano-additives such as TiO2 and Fe2O3. In addition, the influence of hydrophobic nano-silica (R972 type) coating on AP particles under high humidity was investigated. The results showed that coating of AP with nano-additive reduced the inter-particle forces hence cohesivity and improves the packing and flowability of fine AP powder. Hydrophobic coating was found to have added advantage at higher humidity. Moreover, coating with these nano-additives also improved the exothermicity of AP.

Using modified nano-silica to prevent bubble Ostwald ripening under low atmospheric pressure: From liquid foam to air-entrained cement mortar

Air bubble instability leads to the deterioration of air-void structure and threatens the frost resistance of air-entrained concrete, especially in plateau low atmospheric pressure environment. In this study, modified partially hydrophobic nano-silica (NS) particles are used to stabilize entrained air bubbles in cement mortar under low atmospheric pressure. The experimental results indicate that low atmospheric pressure has a limited effect on the bubble size distribution during the bubble generation process. However, the accelerated Ostwald ripening of the bubble system under low atmospheric pressure leads to a significant increase in the mean bubble size and air content loss. Furthermore, the modified NS shows a noticeable bubble stabilization effect. When adding 3% modified nano-silica (NS/MPS), the air-void structure of cement mortar does not show deterioration under 60 kPa. The analysis of bubble shells in foam, fresh and hardened paste system revealed that the NS/MPS with suitable wettability could strongly adsorb at the air-water interface and form adsorption layers around bubbles, thus reduce the gas permeability across the bubble films and prevent the Ostwald ripening of bubbles. This work finally provides a viable method to stabilize air bubbles and improve the air-void structure of concrete in some extreme environments.

Improvements on multiple direct compaction properties of three powders prepared from Puerariae Lobatae Radix using surface and texture modification: Comparison of microcrystalline cellulose and two nano-silicas

It has been reported that hydrophilic nano-silica (N) markedly improved direct compaction (DC) properties of Zingiberis Rhizoma alcoholic extract. This study aims to examine the broader scope and generality of the previous work by investigating (i) three powders, i.e., the directly pulverized product, ethanol extract, and water extract prepared from the same medicinal herb-Puerariae Lobatae Radix (named DP, EE, and WE) and (ii) the effects on their DC properties of co-processing with N, hydrophobic nano-silica (BN), or microcrystalline cellulose (C). Unexpectedly, C provided the best improvement on tabletability for WE, while N for both DP and EE. More importantly, only N could move all parent powders to a regime suitable for DC, and BN rather than C enabled parent WE to be directly compressed. Typically, 6/9 N-modified powders simultaneously met the requirements of DC on bulk density, flowability, and tablet tensile strength (σt). Principal component analysis indicated that DC properties were mainly governed by flowability and texture properties. The partial least-squares regression model revealed that flowability, texture parameters, and deformation behavior of powders were dominating factors impacting tablet σt and solid fraction. Overall, the findings are promising for the manufacture of high drug loading tablets of herbs by DC.

Distribution pattern and surface nature-mediated differential effects of hydrophilic and hydrophobic nano-silica on key direct compaction properties of Citri Reticulatae Pericarpium powder by co-processing

This work aims to improve direct compaction properties of Citri Reticulatae Pericarpium powder (CB) by liquid dispersion co-processing with hydrophilic or hydrophobic nano-silica (INS or ONS). Such wet co-processing was applied to evenly distribute NS to CB. Typically, INS achieved up to 13.8-fold improvement in CB tabletability by affecting both bonding area and bonding strength. In comparison, ONS did better in improving flowability (angle of repose from 35.6° to 27.8°) and achieved up to 4.2-fold improvement in tabletability. Moreover, the bulk density of CB-NS was increased to ~0.65 g/mL at the ratio of 10:1. There was generally a bell-shaped relationship between improvements and CB/NS ratios, especially for ONS. The different distribution pattern and surface nature of INS and ONS caused by polarity difference were the key reasons for their different effects. Compared to the traditional MCC-based formulation strategy, qualified tablets with 3-fold higher CB loading (91.0%) were achieved.

Controlled confined space effects on clustered water bound to hydrophobic nanosilica with nonpolar and polar co-adsorbates

It has been assumed that hierarchical nanoparticle/aggregate/agglomerate structure, texture, and surface characteristics of hydrophobic nanosilica AM1 stirred with a small amount of water may lead to different interfacial and temperature behaviors of bound weakly (WAW, δH = 0.5–1.5 ppm) and strongly (SAW, δH = 4–6 ppm) associated waters, depending on the amounts of weakly polar (chloroform), polar (dimethyl sulfoxide, DMSO), and ionic (trifluoroacetic acid, TFAA) co-adsorbates. Initial and hydro-compacted nanosilicas are characterized using adsorption, desorption, microscopic, spectroscopic, XRD, SAXS, and quantum chemistry methods. The 1H NMR spectroscopy (at 210–280 K) and cryoporometry (T < 273 K) results show significant re-organization of the interfacial water forming clusters and domains differently affected by chloroform, TFAA, and DMSO. Changes in the free surface energy (γS) due to interaction of unfrozen (T < 273 K) water with silica nanoparticles depend on the hydration degree and type and amounts of co-adsorbates. The γS value is maximal for SAW affected by chloroform + TFAA, and it is six times greater than that without TFAA, but a similar effect of TFAA is absent for WAW. Chloroform enhances WAW contribution, but DMSO similarly affects SAW. Thus, the use of a small amount of water bound to treated AM1 allows one to perform quantitative analysis of WAW and SAW, as well as weakly (frozen at 265–273 K) and strongly (unfrozen at T < 265 K) bound waters affected by various co-adsorbates. A fraction of water (its volume per gram of AM1 h/ρw >Vp pore volume) added to AM1 without strong stirring remains unbound due to hydrophobic properties of AM1, but another fraction of water (<Vp) is bound.

Fabrication of a Hydrophobic Hierarchical Surface on Shale Using Modified Nano-SiO2 for Strengthening the Wellbore Wall in Drilling Engineering

Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development. This paper introduces a hydrophobic nano-silica (HNS) for use in strengthening the wellbore wall when using a water-based drilling fluid (WBF). The wellbore-strengthening performance was studied using the linear swelling test, hot-rolling recovery test, and compressive strength test. The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential, particle size, contact angle, and surface tension, and with the use of a scanning electron microscope (SEM). The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method. The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion. Compared with the use of water, the use of HNS resulted in a 20% smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines. More importantly, the addition of HNS was effective in preventing a decrease in shale strength. According to the mechanism study, the good wellbore-strengthening performance of HNS can be attributed to three aspects. First, the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption, thus inhibiting osmotic hydration. Second, HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption, which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy, thereby inhibiting surface hydration. Third, the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability. The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.

Effects of hydrophilic and hydrophobic nanosilica on the hydromechanical behaviors of mudstone soil

In this study, the effects of hydrophilic (HPI) and hydrophobic (HPO) nanosilicas (NS) on the hydromechanical properties of mudstone soil were investigated in a laboratory. Mudstone soil samples treated with different contents (0.3%, 0.6%, 0.9%, and 1.2%) of both types of NS were prepared and rigorously examined through standard Proctor compaction, unconfined compression, three-dimensional volumetric shrinkage, and one-dimensional consolidation tests. In addition to the hydromechanical tests, nondestructive tests, including X-ray diffraction, X-ray fluorescence, and Fourier-transform infrared spectroscopy, were employed to inspect the geochemical and mineral composition of treated and untreated samples. Finally, scanning electron microscopy was used to monitor the packing state of the specimens. The experimental results reveal that the shrinkage and compressibility characteristics of mudstone soils can be significantly improved through NS treatment. In particular, the results demonstrate that the mudstone soils treated with 0.3% NS, regardless of type, had the highest compressive strength. Our results provide insight into the contribution of NS to the hydromechanical properties of mudstone soils and suggest that NS-HPI may be a better treatment than NS-HPO due to its improved ability to strengthen mudstone soils.