An official website of the United States government
Pore wetting is a major constraint to the performance of membrane distillation (MD) for hypersaline brine treatment. Despite the existence of surfactants with diverse properties, an explicit relationship between the properties of surfactants and their capabilities of inducing pore wetting has yet to be established. In this study, we perform a comparative analysis of the wetting behaviors of various surfactants with different charges and molecular weights in MD desalination. The induction time of surfactants to initiate pore wetting was correlated to the apparent contact angle and surface tension of the feedwater. Our results show that different surfactants resulting in similar feedwater surface tensions can lead to drastically different wetting potential, suggesting that both charge of the head group and molecular weight of surfactants have a significant influence on membrane pore wetting. Further, we demonstrate that parameters that have been commonly used to indicate wetting potential, including apparent contact angle and solution surface tension, are not reliable in predicting the wetting behavior of MD membranes, which is intricately linked with surfactant properties such as charge and molecular size. We envision that our results not only improve our fundamental understanding of surfactant-induced wetting but also provide valuable insights that necessitate thorough consideration of surfactant properties in evaluating wetting potential and membrane wetting resistance for MD desalination.
more »
« less
Physical Properties of Plasma-Activated Water
Recent observations of plasma-activated water (PAW)’s surfactant behavior suggest that the activation of water with non-equilibrium plasma can decrease the surface tension of the water. This suggested change to the surface tension also indicates that the addition of plasma can lead to changes in the physical properties of the water, knowledge of which can expand existing PAW applications and open new ones. While the chemical behavior of PAW has been extensively analyzed, to the best of our knowledge the physical properties of PAW have not been investigated. This study focuses on the need for experimental determination of PAW’s physical properties—namely, surface tension, viscosity, and contact angle. The experimental results of this study show that the addition of plasma lowers the surface tension of water at room temperature, increases the viscosity of water at high temperatures, and lowers the contact angle of droplets on glass surfaces at room temperatures. Potential factors influencing these changes include plasma alteration of the mesoscopic structure of water at low temperatures and plasma additives acting as foreign particles in water at higher temperatures. Ultimately, this investigation demonstrates that the physical properties of water change due to plasma activation, which could lead to potential industrial applications of PAW as a surfactant or as a washing-out and cleaning agent.
more »
« less
- Award ID(s):
- 1747671
- PAR ID:
- 10397295
- Date Published:
- Journal Name:
- Plasma
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2571-6182
- Page Range / eLocation ID:
- 45 to 57
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Material relationships at low temperatures were determined for concentrated surfactant solutions using a combination of rheological experiments, cross-polarized microscopy, calorimetry, and small angle X-ray scattering. A lamellar structured 70 wt% solution of sodium laureth sulfate in water was used as a model system. At cold temperatures (5 °C and 10 °C), the formation of surfactant crystals resulted in extremely high viscosity. The bulk flow behavior of multi-lamellar vesicles (20 °C) and focal conic defects (90 °C) in the lamellar phase was similar. Shear-induced crystallization at temperatures higher than the equilibrium crystallization temperature range resulted in an unusual complex viscosity peak. The effects of processing-relevant parameters including temperature, cooling time, and applied shear were investigated. Knowledge of key low-temperature structure–property-processing relationships for concentrated feedstocks is essential for the sustainable design and manufacturing of surfactant-based consumer products for applications such as cold-water laundry.more » « less
-
Activation of liquids with atmospheric pressure plasmas is being investigated for envi-ronmental and biomedical applications. When activating the liquid using gas plasma produced species (as opposed to plasmas sustained in the liquid), a rate limiting step is transport of these species into the liquid. To first order, the efficiency of activating the liquid is improved by in-creasing the ratio of the surface area of the water in contact with the plasma compared to its vol-ume – often called the surface-to-volume ratio (SVR). Maximizing the SVR then motivates the plasma treatment of thin films of liquids. In this paper, results are discussed from a computa-tional investigation using a global model of atmospheric pressure plasma treatment of thin water films by a dielectric barrier discharge (DBD) sustained in different gases (Ar, He, air, N2, O2). The densities of reactive species in the plasma activated water (PAW) are evaluated. The resi-dence time of the water in contact with the plasma is increased by recirculating the PAW in plasma reactor. Longer lived species such as H2O2aq and NO3−aq accumulate over time (aq de-notes an aqueous species). DBDs sustained in Ar and He are the most efficient at producing H2O2aq, DBDs sustained in argon produces the largest density of NO3−aq with the lowest pH, and discharges sustained in O2 and air produce the highest densities of O3aq. Comparisons to experi-ments by others show agreement in the trends in densities in PAW including O3aq, OHaq, H2O2aq and NO3−aq, and highlight the importance of controlling desolvation of species from the activated water.more » « less
-
The effects of surfactants on a mechanically generated plunging breaker are studied experimentally in a laboratory wave tank. Waves are generated using a dispersively focused wave packet with a characteristic wavelength of$$\lambda _0 = 1.18$$m. Experiments are performed with two sets of surfactant solutions. In the first set, increasing amounts of the soluble surfactant Triton X-100 are mixed into the tank water, while in the second set filtered tap water is left undisturbed in the tank for wait times ranging from 15 min to 21 h. Increasing Triton X-100 concentrations and longer wait times lead to surfactant-induced changes in the dynamic properties of the free surface in the tank. It is found that low surface concentrations of surfactants can dramatically change the wave breaking process by changing the shape of the jet and breaking up the entrained air cavity at the time of jet impact. Direct numerical simulations (DNS) of plunging breakers with constant surface tension are used to show that there is significant compression of the free surface near the plunging jet tip and dilatation elsewhere. To explore the effect of this compression/dilatation, the surface tension isotherm is measured in all experimental cases. The effects of surfactants on the plunging jet are shown to be primarily controlled by the surface tension gradient ($$\Delta \mathcal {E}$$) while the ambient surface tension of the undisturbed wave tank ($$\sigma _0$$) plays a secondary role.more » « less
-
null (Ed.)Key engineering properties of unsaturated soils such as volume change and shear strength can be defined using the effective stress principle. Several problems like prolonged drought, high-level radioactive waste, buried high voltage cables can subject surface and near-surface unsaturated soils to elevated temperatures. Such elevated temperatures can affect the hydraulic and mechanical behavior of unsaturated soils. It is very important to develop a closed-form model that can reasonably estimate the effective stresses under different elevated temperatures. For this purpose, the current study incorporates the temperature effect into a suction stress-based representation of Bishop’s effective stress. The proposed model accounts for the effect of temperature on matric suction and degree of saturation. A temperature-dependent soil water retention curve is used to account for thermal effects on surface tension, contact angle, and enthalpy of immersion per unit area. The proposed effective stress model is then used to calculate the effective stress for two soils, Pachapa loam, and Seochang sandy clay, at various temperatures ranging from 25°C to 100°C. The validity of the model is examined by comparing the predicted effective degree of saturation and suction stress values against the experimental data reported in the literature for GMZ01 bentonite. At a constant net normal stress, the results for both soils show that the impact of temperature on effective stress can be significant. The proposed model can be used for studying geotechnical and geoenvironmental engineering applications that involve elevated temperatures.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/plasma6010005
