The aim of the research presented in this paper was to determine the effect of dihydroxy alcohols on the rheological properties of sodium carboxymethylcellulose (Na-CMC) solutions with different degrees of substitution and different average molecular masses. Rheological measurements were carried out with a rotational rheometer in continuous and oscillatory flows. Two dihydroxy alcohols were used in the study: butane-1,3-diol and propane-1,2-diol. The concentration of Na-CMC in the solutions was 1.6% and 2.2%, while the concentration of the dihydroxy alcohols ranged from 10% to 60%. The measurements show that the viscoelastic properties of Na-CMC solutions are strongly linked to the type of solvent used. The application of low-substituted high-molecular-mass Na-CMC makes it possible to obtain fluids with the properties of weak physical gels. On the other hand, the dissolution of Na-CMC with a high degree of substitution (>1) and low molecular mass in dihydroxy alcohol/water mixtures yields a viscoelastic fluid. Based on oscillatory measurements, increasing concentrations of polyhydroxy alcohols in Na-CMC solutions were found to induce an increase in the strength of the network structure. At the same concentrations of polyhydroxy alcohols in solutions containing butane-1,3-diol, a stronger network structure is formed compared to solutions containing propane-1,2-diol. The rheological measurement results presented in this paper may be useful in the formulation of drug carriers and cosmetics in which rheological properties are a significant factor.

Despite extensive research on the use of salts to enhance micellar growth, numerous questions remain regarding the impact of ionic exchange and molecular structure on charge neutralization. This study looks into how certain cations (Na⁺, Ca²⁺, and Mg²⁺) affect the structure of a cocamidopropyl betaine CAPB and sodium dodecylbenzenesulfonate SDBS surfactant mixture, aiming toward applications in targeted delivery systems. The mixture consists of a zwitterionic surfactant, cocamidopropyl betaine (CAPB), and an anionic surfactant, sodium dodecylbenzenesulfonate (SDBS), combined in varying molar ratios at a total concentration of 200 mM. We characterized the macroscale properties through rheological measurements and obtained detailed structural insights using small-angle X-ray scattering (SAXS) and cryogenic electron microscopy (cryo-EM). The findings reveal that increasing the concentration of cations in the CAPB/SDBS mixture induces the formation of peaks in the zero-shear viscosity as a function of salt concentration (salt curve). Analysis through cryo-EM and SAXS showed that these viscosity peaks are related to the change of micellar assemblies from entangled worm-like micelles to branched worm-like micelles and then to bilayer structures (vesicles). The specific cation concentration at which the zero-shear viscosity peak occurs, as well as the maximum viscosity, is strongly influenced by the type of cation present in the CAPB/SDBS solutions, a phenomenon explained by the Hofmeister series. Notably, the differing affinities of cations for the carboxylate COO^- and sulfite SO^3- groups and the partial dehydration of micelles contribute to the lower concentration of magnesium cations required to reach the viscosity peak compared to calcium cations.

The impact of pH, temperature, and metal ions on the rheological and interfacial properties of aqueous mixed surfactant solutions composed of anionic NaC (sodium cholate) and nonionic BrijL4 [polyoxyethylene (4) lauryl ether] surfactants has been investigated. The various compound systems were analyzed, considering variations in each selected factor. The results highlight the unique characteristics of the BrijL4/NaC mixture, suggesting its potential as a viable alternative to other existing surfactants. The synergistic effect between BrijL4 and NaC significantly reduces the critical micelle concentration (CMC) and improves the wetting properties on hydrophobic surfaces, surpassing those of single-component solutions. Additionally, sodium, calcium, and magnesium ions enhance surface wetting and decrease the CMC. Besides, the BrijL4/NaC solutions exhibit viscoelastic fluid behavior at higher surfactant concentrations. These viscoelastic BrijL4/NaC solutions demonstrate stability over various pH and temperature variations, exhibiting lower flow activation and scission energy values than those of other viscoelastic surfactant solutions. Notably, the BrijL4/NaC mixture has potential applications in gel-based foliar fertilizers and drug delivery systems. Furthermore, the rheological studies examine the impact of humic acid on the rheological properties of BrijL4/NaC mixture solutions, revealing that incorporating additional humic acids can achieve stable rheological properties.

The paper presents the results of research on the rheological properties and stability of oil-in-water emulsions containing cellulose derivatives: methylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose. The continuous phase of the emulsion was a 70% ethanol (EtOH) solution by volume. The dispersed phase consisted of mineral, linseed, and canola oils (20% by volume). Rheological measurements were performed in both steady and oscillatory flow. Emulsion stability was assessed on visual observation and changes in droplet diameter over a period of 5 months after preparation. Relatively stable emulsions were obtained without the addition of low-molecular-weight surfactants, exhibiting viscoelastic properties. The presence of ethanol in the continuous phase significantly slowed down the processes of emulsion sedimentation or creaming, as well as droplet coalescence. The reasons for the slow phase separation were linked to changes in density and zero-shear viscosity of the continuous phase caused by the addition of EtOH. All emulsions were highly polydisperse, and the addition of methylcellulose and hydroxypropylmethylcellulose further led to the formation of strongly flocculated emulsions. Droplet flocculation resulted in highly viscoelastic fluids. In particular, for emulsions containing hydroxypropylmethylcellulose, the ratio of the storage modulus to the loss modulus approached a value close to 0.1, which is characteristic of gels.