Emulsions Stabilized by Chitosan-Modified Silica Nanoparticles: pH Control of Structure-Property Relations

Smart Emulsions Stabilized by a Multi-headgroup Surfactant Tolerant to High Concentrations of Acids and Salts

Retaining emulsions stable at high acidity and salinity is still a great challenge. Here, we report a novel multi-headgroup surfactant (C3 H7 -NH+ (C10 COOH)2 , di-UAPAc) which can be reversibly transformed among cationic, anionic and zwitterionic forms upon pH variation. Stable oil-in-dispersion (OID) emulsions in strong acidity (pH=2) can be co-stabilized by low concentrations of di-UAPAc and silica nanoparticles. High salinity at pH=2 improves the adsorption of di-UAPAc on silica particles through hydrogen bonding, resulting in the transformation of OID emulsions into Pickering emulsions. Moreover, emulsification/demulsification and interconversion between OID and Pickering emulsions together with control of the viscosity and droplet size can be triggered by pH. The present work provides a new protocol for designing surfactants for various applications in harsh aqueous media, such as strong acidity and high salinity, involved in oil recovery and sewerage treatments.

Wettability-tuned silica particles for emulsion-templated microcapsules

Pickering emulsions play a significant role in generating advanced materials and have widespread application in personal care products, consumer goods, crude oil refining, energy management, etc. Herein, we report a class of wettability tuned silica-based Pickering emulsifiers which stabilize a diverse range of fluid-fluid interfaces: oil/water, ionic liquid/oil, and oil/oil, and their use to prepare microcapsules via interfacial polymerization. To alter particle wettability, colloidal suspensions of SiO2 particles (22 nm) were modified via silanization with reagents of varied hydrophilicity/hydrophobicity, giving particles that could be dispersed in solvents that became the continuous phase of the emulsions. To test the viability of this system as templates for the fabrication of composite materials, the different particle-stabilized emulsions were coupled with interfacial polymerization, leading to microcapsules with polyurea/silica shells. These results demonstrate that a single particle feedstock can be coupled with fundamental chemical transformation to access a versatile toolkit for the stabilization of diverse fluid interfaces and serve as a template for the preparation of hybrid architectures.

Dispersion Homogeneity of Silicon Anode Slurries with Various Binders for Li-Ion Battery Anode Coating

We aimed to determine the relationship between surface chemistry and the rheological properties of silicon anode slurries in lithium-ion batteries. To accomplish this, we investigated the use of various binders such as PAA, CMC/SBR, and chitosan as a means to control particle aggregation and improve the flowability and homogeneity of the slurry. Additionally, we utilized zeta potential analysis to examine the electrostatic stability of the silicon particles in the presence of different binders, and the results indicated that the conformations of the binders on the silicon particles can be influenced by both neutralization and the pH conditions. Furthermore, we found that the zeta potential values served as a useful metric for evaluating binder adsorption and particle dispersion in the solution. We also conducted three-interval thixotropic tests (3ITTs) to examine the structural deformation and recovery characteristics of the slurry, and the results demonstrated that these properties vary depending on the strain intervals, pH conditions, and chosen binder. Overall, this study emphasized the importance of taking into account surface chemistry, neutralization, and pH conditions when assessing the rheological properties of the slurry and coating quality for lithium-ion batteries.

Investigation of the Contact Angle and Packing Density of Silica Nanoparticles at a Pickering Emulsion Interface Fixed by UV Polymerization

The contact angle of colloidal particles at an oil-water interface plays a crucial role in determining Pickering emulsion stability and emulsion type, but the contact angle cannot be directly determined using conventional methods. In this work, a Pickering emulsion was prepared with photocurable resin as the internal phase containing silica nanoparticle stabilizers. Particles adsorbed at the oil-water interface were then fixed through UV curing, allowing for the investigation of various parameters that influence the contact angle of colloidal particles at the interface. After curing, the contact angle can then be observed using scanning electron microscopy and subsequently measured. The contact angle of interfacial adsorbed silica nanoparticles gradually decreases as the size increases due to the line tension at the three-phase contact line, but, more importantly, we found that the surface chemistry of the silica nanoparticles plays the most important role in determining the contact angle. The fast fixation of solid nanoparticles at emulsion interfaces facilitates accurate measurements of the partition of particles between oil and water, providing a new method for studying the factors that affect Pickering emulsion stability.

Structure and properties of chitosan/sodium dodecyl sulfate composite films

In this study, we investigated the effect of sodium dodecyl sulfate (SDS) content on the structure and properties of chitosan films. It is found that the binding of SDS to chitosan was realized through the interactions between –SO₄⁻ and –NH₃⁺, forming an ionically cross-linked film. Structural analysis revealed that the crystallization was greatly hindered by introducing SDS. With an increase of SDS content, the glass transition temperatures (T_g) of chitosan films increased due to the formation of crosslinks. Compared to pure chitosan film, the composite films had lower content of moisture and possessed better thermal stability. In addition, the mechanical properties of the as-obtained composite films were closely related to the content of SDS, and were significantly improved in the biopolymer films with moderate SDS content. These results indicate that the microstructure as well as properties of the chitosan films can be regulated by adding SDS.

SDS binds strongly to chitosan through electrostatic interactions, and it has a remarkable effect on the structure and properties of chitosan films.

Supersmall Dendritic Mesoporous Silica Nanospheres as Antioxidant Nanocarriers for Pickering Emulsifiers

Encapsulation of flavor and aromatic compounds in emulsions holds great potential for development of novel formulations in food applications. In this paper, supersmall dendritic mesoporous silica nanospheres (DMSNs) were fabricated by the one-pot strategy. The morphologies of DMSNs were directly tuned in terms of diameter from 35 ± 2 to 85 ± 4 nm. The obtained DMSNs are nanocarriers for hydrophilic or hydrophobic antioxidants with superior loading performance. Both DMSNs and antioxidant-loaded ones can emulsify the flavor and aromatic compounds yielding stable Pickering emulsions with droplets of approximately 2 μm in diameter. The emulsions possess excellent physical stability for at least half a year. More importantly, gas chromatography-mass spectrometry-olfactometry (GC-MS-O) analysis shows that antioxidant-loaded DMSNs provide outstanding protective functionalities to the encapsulated flavoring oil. A universality study reveals that DMSNs are an ideal platform for stable Pickering emulsions for aromatic compounds. Our design could provide a new path for flavor and sensitive bioactives for codelivery with excellent stability in food, medicine, cosmetics, etc.

Assessment and Application of Modified Cationic Polyvinyl Alcohol Emulsifiers in Bitumen Emulsions

In this work, a series of emulsifiers were prepared by changing the molar ratio of polyvinyl alcohol (PVA) to the long chain quaternary ammonium salt (A0). The emulsifiers were characterised by FTIR and 1HNMR. The stability of the emulsions was checked and evaluated by determining the phase separation and by UV-Vis spectrophotometry. The emulsion stability increased with increasing emulsifier concentration, which was mainly due to the reduced droplet size and increased viscosity of the emulsions. Stability was also dependent on pH. At pH values between 5 to 3, stability was increased, but at further decreasing pH values, the emulsion became unstable or the emulsion separated. This could be mainly because the excess of positive ions compresses the double electron layer. The experimental results showed that PVA as a macromolecular matrix material has a great application potential for the emulsification process.

Thermal Gelation for Synthesis of Surface-Modified Silica Aerogel Powders

A spherical silica aerogel powder with hydrophobic surfaces displaying a water contact angle of 147° was synthesized from a water glass-in-hexane emulsion through ambient pressure drying. Water glass droplets containing acetic acid and ethyl alcohol were stabilized in n-hexane with a surfactant. Gelation was performed by heating the droplets, followed by solvent exchange and surface modification using a hexamethyldisilazane (HMDS)/n-hexane solution. The pH of the silicic acid solution was crucial in obtaining a highly porous silica aerogel powder with a spherical morphology. The thermal conductivity, tapped density, pore volume, and BET surface area of the silica aerogel powder were 22.4 mW·m⁻¹K⁻¹, 0.07 g·cm⁻³, 4.64 cm³·g⁻¹, and 989 m²·g⁻¹, respectively. Fourier transform infrared (FT–IR) spectroscopy analysis showed that the silica granule surface was modified by Si-CH₃ groups, producing a hydrophobic aerogel.

Synthesis of a chitosan nanoparticle suspension and its protective effects against enamel demineralization after an in vitro cariogenic challenge

Objective

Our study aims to synthesize, characterize, and determine the effects of a ChNPs suspension on human enamel after cariogenic challenge via pH-cycling.

Methodology

ChNPs were synthesized by ion gelation and characterized by Transmission Electron Microscopy (TEM) and Dynamic Light Scattering. Forty enamel blocks were divided into four groups (n=10/group): (i) ChNPs suspension; (ii) chitosan solution; (iii) 0.05% sodium fluoride (NaF) solution; and (iv) distilled water. Specimens were exposed to cariogenic challenge by cycling in demineralization solution (3 h) and then remineralized (21h) for 7 days. Before each demineralization cycle, the corresponding solutions were passively applied for 90 s. After 7 days, specimens were examined for surface roughness (Ra) and Knoop hardness (KHN) before and after the cariogenic challenge; % KHN change (variation between initial and final hardness), and surface topography by an optical profilometer. The data were analyzed by repeated-measures ANOVA, One-way ANOVA, and Tukey tests (α=0.05).

Results

TEM images showed small spherical particles with diameter and zeta potential values of 79.3 nm and +47.9 mV, respectively. After the challenge, all groups showed an increase in Ra and a decrease in KHN values. Optical profilometry indicated that ChNPs- and NaF-treated specimens showed uneven roughness interspersed with smooth areas and the lowest %KHN values.

Conclusion

The ChNPs suspension was successfully synthesized and minimized human enamel demineralization after a cariogenic challenge, showing an interesting potential for use as an oral formulation for caries prevention.

Influence of molecular interactions on structure, controlled release and cytotoxicity of curcumin encapsulated chitosan - Silica nanostructured microspheres

Curcumin possesses numerous medicinal benefits including anti-cancer and anti-viral properties. However, its wide scale use as a drug is often hindered owing to the dearth of suitable drug-delivery systems which can solubilise it for long-term sustained-release and safeguard its beneficial properties. In this work, a fast, one-step method, employing evaporation induced assembly of colloids, has been employed for the synthesis of curcumin encapsulated organic-inorganic hybrid micron-sized spheres. Detailed physical properties of the microspheres, with scaffolds of silica nanoparticles (∼8.5 nm) cross linked by chitosan, are studied to trace the underlying mechanism of structural assembly in such systems, by tuning the polymer matrix with solubilizing agents, DMSO and Tween 20. A systematic modification in the hydrogen bonding network, conformations and interactions between macromolecules is revealed upon tuning the organic matrix. This in turn is found to control the assembly vis-à-vis the granular morphology, drug entrapment and packing fraction of nanoparticles in the microspheres, which have direct influence on the biological properties. Consequently, the microspheres are found to follow a first order drug release kinetics with a tunable rate constant which follows the ordering of packing fraction of silica nanoparticles in the micro-granules. A sustained curcumin release for a period extending up to 24 h has been achieved. Further studies using human lung and cervical cancer cell lines assert good anti-cancer properties of these nanostructured microspheres in cancer cells, while showing no toxicity towards normal cells. Thus, such hybrid organic-inorganic formulations achieved using multi-component colloidal assembly approach, with enhanced stability against degradation, are promising candidates for future clinical applications of water-insoluble drugs.

Enhancing the Stability of Asphalt Emulsion Using Environmentally Friendly Cationically Modified Hydroxyethyl Cellulose (CMHEC) at Different Concentrations and pH Values

The cationically modified hydroxyethyl cellulose (CMHEC) was synthesized successfully and applied for preparing the cationic asphalt emulsion. The apparent viscosity and phase separation of the emulsion were studied at different CMHEC concentrations and pH values. The results indicated that the apparent viscosity of the emulsion was increased with increasing CMHEC concentration, and the phase separation was significantly reduced correspondingly. In addition, the effect of pH value on the emulsion quality was involved. The apparent viscosity of the emulsion showed the tendency to decrease firstly and then increase to the minimum value at pH 2. All results indicated that CMHEC has excellent potential in the manufacture of asphalt emulsion and the research of the pH effect on the formulation of asphalt emulsion has essential significance.

Pickering Emulsions Based on the pH-Responsive Assembly of Food-Grade Chitosan

Few natural, biocompatible, and inexpensive emulsifiers are available because such emulsifiers must satisfy severe requirements, be produced synthetically rather than naturally, be nontoxic, and require minimal effort to produce. Therefore, the synthesis of food-grade and biocompatible nanoparticles as an alternative to surfactants has recently received attention in the industry. However, many previous efforts involved chemical modification of materials or the introduction of secondary cocomponents for emulsion formation. To achieve the goal of simple preparation, we consider here chitosan nanoparticles to prepare Pickering emulsions of food-grade oil through the control of pH, without further chemical modification or extra additives. A mild process can prepare nanoparticles from chitosan by simply increasing the pH from 3.0 to 6.0. The results showed that the average radius of chitosan at pH 6.0 was 170 nm, while large aggregates were formed at pH 6.5. These nanoparticles were utilized to prepare the Pickering emulsion. The average size of emulsion droplets decreased upon increasing the pH from 3.0 to 6.0. Moreover, Pickering emulsions at different oil fractions and nanoparticle concentrations were stable and showed a low creaming index for 45 days. The emulsions were stable against coalescence and flocculation and behaved rheologically as gel-like, shear-thinning fluids (G' > G″). Pickering emulsion prevents the growth of the microorganism (Staphylococcus aureus) at different pH values and chitosan concentrations. These results demonstrate that chitosan nanoparticles could be a cost-effective and biocompatible emulsifier for the food or pharmaceutical industry for encapsulation and bioactive compounds, and Pickering emulsions have promising antibacterial effects for further applications.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Functionalization of Chitosan Oligomers: From Aliphatic Epoxide to Cardanol-Grafted Oligomers for Oil-in-Water Emulsions

Hydrophobically modified chitooligosaccharides (COSs) were tested for suitability as an emulsifier in cationic bituminous emulsions. COSs with polymerization degrees (DPs) of 5, 10, 15, and 20 were obtained by nitrous acid deamination. A complete study on depolymerization and precise product and side product characterization was undergone. Chemical modification of COSs was performed to achieve amphiphilic structures using three fatty epoxides with a growing chain length butyl (C4), octadecyl (C9), and hexadecyl glycidyl ether (C16)). The grafting efficiency according to reaction conditions was established. Different substitution degrees (DSs) were obtained by modulating the ratio of fatty epoxy to NH₂. It was shown that after a certain DS, the oligomers thus formed were not water-soluble anymore. At the end, cardanol glycidyl ether was grafted on DP 5, 10, and 15 COSs, cardanol being a biobased compound extracted from cashew nut shell; this reaction led to a potentially fully biobased structure. Water-soluble candidates with a higher DS were used as surfactants to emulsify motor oil as a simulation of bitumen. Cardanol-chitosan-based surfactants led to direct oil-in-water emulsion (60/40 w/w) composed of particles of 15 μm average size that were stable at least for 24 h.

Tannic acid enhanced the physical and oxidative stability of chitin particles stabilized oil in water emulsion

In this work, the stability of CP-TA complex stabilized emulsion was first characterized. It was found that the peak thickness, Turbiscan Stability Index (TSI) and droplet size of CP-TA complex stabilized emulsion gradually decreased with increasing content of TA, indicating the gradually enhanced physical stability of emulsion, which was attributed to the gradually decreased interfacial tension, zeta potential and increased viscosity of CP-TA complex. Moreover, the oxidative stability of CP-TA complex stabilized emulsion gradually enhanced with increasing of TA content due to the antioxidant activity of TA. XRD and FTIR results suggested that the interaction between CP and TA gradually enhanced with increasing content of TA in CP-TA complex, leading to the formation of larger CP-TA clusters shown in AFM results. In conclusion, the presence of tannic acid (TA) enhanced the physical and oxidative stability of chitin particles-tannic acid (CP-TA) complex stabilized oil in water emulsion.

Responsive Colloidosomes with Triple Function for Anticorrosion

Strategies for corrosion protection are required to prolong the life span of metallic structures used by the construction, aerospace, and transport industries. Currently, there are no coatings that can provide at the same time information about the corrosion status of the coated metal and protect the metal against corrosive species and mechanical damage. Herein, triple-functional microcarriers with functions of corrosion sensing, self-healing, and corrosion inhibition are produced and embedded in coatings to prolong the lifetime of metals and enhance the anticorrosion performance of coatings. The microcarriers are prepared by creating Pickering droplets loaded with a corrosion inhibitor and a healing agent and stabilized by silica nanocapsules containing thymol blue as corrosion sensor. The microcarriers are then embedded in a water-based polymer matrix coated on metal substrates. When the coating or metal is mechanically damaged, the healing agent is released from the droplets to hinder further corrosion of the metal. When the local pH value near the metal surface is changing by the generation of hydroxide ion due to the corrosion process, a change of color is detected as well as a release of corrosion inhibitor, leading to a significant decrease of corrosion rate of the coated metal.

Pickering/Non-Pickering Emulsions of Nanostructured Sulfonated Lignin Derivatives

Sulfoethylated lignin (SEKL) polymeric surfactant and sulfoethylated lignin nanoparticles (N-SEKL) with a size of 750±50 nm are produced by using a facile green process involving a solvent-free reaction and acidification-based fractionation. SEKL forms a liquid-like conventional emulsion with low viscosity that has temporary stability (5 h) at pH 7. However, N-SEKL forms a gel-like, motionless, and ultra-stable Pickering emulsion through a network of interactions between N-SEKL particles, which creates steric hindrance among the oil droplets at pH 3. The deposition of SEKL and N-SEKL on the oil surface is monitored by a using a quartz crystal microbalance. Experimentally, the formation of emulsions at pH 7 is found to be reversible owing to the low adsorption energy ΔE of SEKL on the oil droplet (ΔE≈15 k_B T), which is determined with the help of three-phase contact-angle measurements. However, the high desorption energy (ΔE≈6.0×10⁵  k_B T) of N-SEKL makes it irreversibly adsorb on the oil droplets. SEKL is too hydrophilic to attach to the oil interface (ΔE≈0) and thus does not facilitate emulsion formation at pH 11. Therefore, it is feasible to apply SEKL for the formulation of Pickering or non-Pickering emulsions in the form of nanoparticles or polymeric surfactants, depending on the targeted application.

Multistimuli-Responsive Pickering Emulsion Stabilized by Se-Containing Surfactant-Modified Chitosan

Particle-stabilized emulsions that can respond to external stimuli have attracted significant concerns due to their intelligent-controlled stability, whereas particle-stabilized Pickering emulsions responding to multistimuli but based on biomass have been rarely reported. Here, a multistimuli-responsive Pickering emulsion was developed using the modified chitosan as stabilizer. Due to electrostatic attraction, Se-containing anionic surfactant, sodium 11-(butylselenyl)undecylsulfate (C₄SeC₁₁S), can bind with CS at an acidic pH and form CS-C₄SeC₁₁S complexes which can further self-associate to form micrometer-sized particles with the character of partially hydrophobicity. Therefore, at pH < pK_a, an oil-in-water Pickering emulsion can be formed using CS-C₄SeC₁₁S particles as stabilizers and can spontaneously respond to redox, ion, and pH. First, with the addition of oxidation, the hydrophilicity of C₄SeC₁₁S was enhanced, and thus, hydrophobic association of CS-C₄SeC₁₁S decreased, leading to the disruption of CS-C₄SeC₁₁S particles. Hence, the emulsion destabilized. The demulsification process is closely related with the dosage of oxidant and the oxidation time. Second, introduction of a competitive ion (e.g., CTAB) could break the binding between C₄SeC₁₁S and CS, leading to the disruption of particle emulsifier. Thereby, demulsification occurred. Third, with sequentially increasing/decreasing pH, the emulsion can be switched from stable to unstable and then to stable again accordingly. Such a unique pH-responsive behavior has never been discovered in other pH-responsive Pickering emulsions. All of the stimuli-responsive behaviors were reversible. Upon alternately adding oxidant/reductant, CTAB/C₄SeC₁₁S, or base/acid, the current emulsion can be reversibly switched off (destabilization) and on (stabilization). Such a Pickering emulsion may be a good candidate as a vehicle of functional ingredient.

Synthesis and surface modification of chitosan built nanohydrogel with antiviral and antimicrobial agent for controlled drug delivery

As hydrophobic drug carriers, chitosan (CS) and Starch (SR) were copolymerized as biodegradable nanohydrogel and were functionalized with pthalic-anhydride and hexamethylenetetramine via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide catalyzed coupling, respectively. The structure, morphology, physicochemical and drug loading performance of native and functioned hydrogel were investigated by using several characterization techniques. With the successive functionalization the significant properties like porosity increases and crosslinking density decreases due to the formation of hydrophilic contacts with aqueous solutions. The FESEM analysis revealed the hydrogel matrices with uniform particle size, porosity and deep pores with high internal surface area for extreme swelling and interacting with the drug and biomolecules for efficient drug administration. The effect of induced functionalities on the physicochemical performance and release of hydrophobic- anionic model drug (Bromocresol green) were studied at physiological conditions. The drug release capability of the synthesized nanohydrogel was increased from 65% to 80% and 85% by successive functionalization. The drug administration in selective hydrogel was not significant, presumably due to stronger H-bonding and entanglement within the system which was finely tuned by the induced hydrophilic, flexible and biocompatible functionalities in term of extended interfaces for the drug solutions. The physicochemical and electrokinetic performances suggested the selective hydrogel as promising carriers for the hydrophobic- anionic drugs at physiological conditions.

Synthesis of Mesoporous/Macroporous Microparticles Using Three-Dimensional Assembly of Chitosan-Functionalized Halloysite Nanotubes and Their Performance in the Adsorptive Removal of Oil Droplets from Water

Halloysite nanotubes (HNTs) were assembled into mesoporous/macroporous microparticles (c-g-HNTs MPs) using Pickering template-assisted approach. To unravel the stabilization mechanism in Pickering emulsion form, several emulsions and microparticles were prepared at various conditions and visualized using confocal laser scanning microscopy. The prepared c-g-HNTs MPs were used to treat emulsified oil solutions resulting in a maximum removal efficiency of 94.47%. The kinetics data of oil adsorption onto c-g-HNTs MPs was best fitted by the pseudo-second-order kinetic model ( R² = 0.9983). The maximum monolayer adsorption capacity of oil onto c-g-HNTs MPs as predicted by the multilayer Brunauer-Emmett-Teller model was found to be 788 mg/g. Compared with pristine HNTs, c-g-HNTs MPs exhibited higher self-settleability rates in aqueous solutions as well as in emulsified oil solutions, demonstrating their candidacy for practical water treatment applications. The c-g-HNTs MPs were repeatedly used for five adsorption-desorption cycles with minimal losses noticed in their performance.