Synergistic Role of Temperature and Salinity in Aggregation of Nonionic Surfactant-Coated Silica Nanoparticles

Abstract

The adsorption of nonionic surfactants onto hydrophilic nanoparticles (NPs) is anticipated to increase their stability in aqueous medium. While nonionic surfactants show salinity- and temperature-dependent bulk phase behavior in water, the effects of these two solvent parameters on surfactant adsorption and self-assembly onto NPs are poorly understood. In this study, we combine adsorption isotherms, dispersion transmittance, and small-angle neutron scattering (SANS) to investigate the effects of salinity and temperature on the adsorption of pentaethylene glycol monododecyl ether (C12E5) surfactant on silica NPs. We find an increase in the amount of surfactant adsorbed onto the NPs with increasing temperature and salinity. Based on SANS measurements and corresponding analysis using computational reverse-engineering analysis of scattering experiments (CREASE), we show that the increase in salinity and temperature results in the aggregation of silica NPs. We further demonstrate the non-monotonic changes in viscosity for the C12E5–silica NP mixture with increasing temperature and salinity and correlate the observations to the aggregated state of NPs. The study provides a fundamental understanding of the configuration and phase transition of the surfactant-coated NPs and presents a strategy to manipulate the viscosity of such dispersion using temperature as a stimulus.

Uptake and release of perfluoroalkyl carboxylic acids (PFCAs) from macro and microplastics

“…Here the use of buffer solutions was intentionally avoided as increasing the ionic strength (due to the presence of buffers) will not only alter the interactions of the PFCA with MPs but also influence the hydrophobic interactions between the tails of the PFCA molecules and impact corresponding adsorption behavior. 36 Further work is needed to delineate the roles of pH, ionic strength, and ionization state of the headgroup on the adsorption of PFCAs onto solid–liquid interfaces.…”

“…The concentration of the model PFCAs in DI water was determined using pendant drop tensiometry performed on an optical tensiometer (Biolin Scientic) and corresponding pendant droplet shape analysis. [33][34][35][36] Optical tensiometry and pendant drop analysis is a traditional method to determine surfactant concentrations in water. Pendant drop analysis involves suspending a drop of the liquid phase from the tip of a needle or capillary tube.…”

“…fell outside the linear range of the calibration curve, the solution was diluted by a known factor, which was later applied to estimate PFCA concentration in the bulk solution. 36 Additionally, the contact angle of water on PE was obtained using the sessile droplet mode of the same optical tensiometer/goniometer. The measurements were performed using a 5 mL sessile droplet of DI water placed on 1 cm 2 PE pellet.…”

Parabolic Viscosity Behavior of NaCl-Thickened Surfactant Systems upon Temperature Change

“…Although parabola-type formulas have been reported in some cases, gemini or cationic surfactants have to be used in these formulas, and the vertex of the parabola is located in the high-temperature region, higher than room temperature. ,– In the meantime, most of the rheological studies have focused on dilute system solution, and only a few reports have studied the concentrated surfactant solution, which is close to the real applications. – It has been reported that, in a concentrated solution, a giant micelle including wormlike micelle will be formed, which is an important hotspot in surfactant studies due to its unique polymer-like behavior. ,– In dilute surfactant systems, the shape transition of micelles can be studied by static and dynamic light scattering, while it is not feasible in a concentrated solution. Thus, the giant micelle for the latter has been studied by rheology, NMR, SANS, and visually FF-TEM or cryo-TEM. – …”

Effect of shape anisotropy on the precipitation of dimeric nanoparticles

“…Ma et al recently observed that the aggregation of silica nanoparticles in the presence of non-ionic surfactants depends on the salinity of the dispersing medium and temperature. 53 Physical adsorption is also related to the behavior of nanoparticles in biological systems. For example, Bharti et al observed that the aggregation of silica nanoparticles is affected by the binding of lysozymes and results in a pH-dependence of the size of aggregates and their internal structure.…”