A theory for the surface tensions and contact angles of hydrogen-bonding liquids

Study on the imbibition production mechanism and main controlling factors of low-permeability reservoir

With high water cuts and high permeability reservoirs entering the middle and late stage, many old oil fields in China are facing the dilemma of oil and gas resource exhaustion, while low-permeability reservoir resources remain very rich. As an oil recovery technology, imbibition displacement plays an important role in the exploitation of low-permeability reservoirs and prolongs the production cycle of old oil fields. Based on the imbibition kinetic equation, the mechanism and process of oil displacement in imbibition recovery are explained in this paper. Based on the characteristics of small particle size and high activity, the influence of temperature, viscosity, permeability, and salinity on the degree of imbibition recovery was studied. The results show that the imbibition production of low-permeability reservoirs mainly depends on capillary force, which firstly drains oil from small pores to large pores, and then drains it by buoyancy. Using nanofluids for imbibition oil recovery, a higher recovery effect of up to 45.59% can be achieved. The change in different external conditions will affect the imbibition recovery effect. The imbibition recovery efficiency increases with the increase in temperature, decreases with the increase in oil viscosity, and increases with the increase in core permeability. The increase in salinity has an inhibiting effect on the imbibition recovery efficiency. Based on the multivariate analysis of variance, the change in permeability has the greatest influence on the degree of imbibition recovery, and the change in viscosity has the least influence on the degree of imbibition recovery.

Mechanism of the Decrease in Surface Tension by Bulk Nanobubbles (Ultrafine Bubbles)

The mechanism of the decrease in the surface tension of water containing bulk nanobubbles (ultrafine bubbles) is studied theoretically by numerical simulations of the adsorption of bulk nanobubbles at the liquid's surface based on the dynamic equilibrium model for the stability of a bulk nanobubble under the conditions of the Tuziuti experiment (Tuziuti, T., et al., Langmuir, 2023, 39, 5771-5778). It is predicted that the concentration of bulk nanobubbles in the bulk liquid decreases considerably with time, as many bulk nanobubbles are gradually adsorbed at the liquid's surface. A part of the decrease in surface tension is due to the Janus-like structure of a bulk nanobubble that could partly break the hydrogen bond network of water molecules at the liquid's surface because more than 50% of the bubble's surface is covered with hydrophobic impurities, according to the dynamic equilibrium model. The theoretically estimated decrease in surface tension due to the Janus-like structure of a bulk nanobubble agrees with the experimental data of the decrease in surface tension solely by bulk nanobubbles obtained by the comparison of before and after the elimination of bulk nanobubbles by the freeze-thaw process. This effect cannot be explained by the electric charge stabilization model widely discussed for the stability of a bulk nanobubble, although the present model is only applicable to the solution containing hydrophobic impurities. Another part of the decrease in surface tension should be due to impurities produced from a nanobubble generator, such as a mechanical seal, which was partly confirmed by the TOC measurements.

Selectively Permeable FeOOH Amorphous Layer Coating CdS for Enhancing Photocatalytic Conversion of Benzyl Alcohol and Selectivity to Benzaldehyde

The development of new strategies to improve reaction efficiency and light utilization is one of the biggest challenges in photosynthetic chemistry. Dynamics control, particularly tuning the adsorption/desorption of reactants and products, is an ideal way to improve the conversion and selectivity in catalytic reactions, but it is rarely studied for photocatalytic organic synthesis. This study concerns the design of an amorphous FeOOH coating to decorate CdS photocatalyst to control the adsorption and desorption of reactants and products to improve reaction efficiency for the photocatalytic conversion of benzyl alcohol (BA) into benzaldehyde (BAD). The best conversion of the core-shell photocatalyst is 74.1 % in 2 h, together with >99.9 % selectivity to BAD, and the photocatalyst exhibits response above 600 nm, which is the longest active wavelength reported for the reaction. Further data illustrate that the amorphous FeOOH coating enables selective sorption of BA/BAD molecules by H-bonding interactions, which may result in the excellent performance. Construction of amorphous coating layers and understanding the selective permeability may provide a new strategy for the design of more efficient photocatalytic systems for organic synthesis.

Whey Proteins as a Potential Co-Surfactant with Aesculus hippocastanum L. as a Stabilizer in Nanoemulsions Derived from Hempseed Oil

The use of natural surfactants including plant extracts, plant hydrocolloids and proteins in nanoemulsion systems has received commercial interest due to demonstrated safety of use and potential health benefits of plant products. In this study, a whey protein isolate (WPI) from a byproduct of cheese production was used to stabilize a nanoemulsion formulation that contained hempseed oil and the Aesculus hippocastanum L. extract (AHE). A Box-Behnken experimental design was used to set the formulation criteria and the optimal nanoemulsion conditions, used subsequently in follow-up experiments that measured specifically emulsion droplet size distribution, stability tests and visual quality. Regression analysis showed that the concentration of HSO and the interaction between HSO and the WPI were the most significant factors affecting the emulsion polydispersity index and droplet size (nm) (p < 0.05). Rheological tests, Fourier transform infrared spectroscopy (FTIR) analysis and L*a*b* color parameters were also taken to characterize the physicochemical properties of the emulsions. Emulsion systems with a higher concentration of the AHE had a potential metabolic activity up to 84% in a microbiological assay. It can be concluded from our results that the nanoemulsion system described herein is a safe and stable formulation with potential biological activity and health benefits that complement its use in the food industry.

Solid-liquid-liquid wettability and its prediction with surface free energy models

Understanding wettability in solid-liquid-liquid (SLL or immersed) systems is important for numerous applications. However, predicting SLL wetting behavior on smooth surfaces has received little attention. The objective of this work was to explore alternatives to predict SLL wettability. To this end, we first present a review of solid surface free energy (σ_S) data obtained from solid-liquid-air (SLA) contact angle (θ_L^a) data and a summary of available SLL contact angle data for selected materials. Next, the existing surface free energy models for SLA systems are discussed in terms of their applicability to predict wettability of SLL systems. Finally, the SLL wettability of toluene drops on glass, mica, stainless steel and PTFE immersed in equilibrated Toluene-water-isopropyl alcohol (IPA) solutions was determined via contact angle (θ_O) measurements through the oil phase using the inverted sessile drop method over a wide range of interfacial tensions (γ_o-aq). The results were plotted as γ_o-aq·cosθ_O vs. γ_o-aq, showing a smooth wetting transition from water-wetting to oil-wetting with decreasing γ_o-aq for glass and stainless steel. Mica remained water-wetting, while PTFE oil-wetting. The Geometric (GM) and Harmonic (HM) mean approaches, and the Equation-of-State (EQS), originally developed for SLA systems, were extended to SLL systems. The extended GM and HM approaches could fit the SLL behavior after fitting the dispersive and polar contributions of the solid surface free energy (σ_S^d, σ_S^p), which required additional SLA θ_L^a measurements using PTFE as the reference surface. However, attempts at predicting θ_O for systems with high γ_o-aq resulted in significant deviations, a problem linked to the high σ_S^d values required to fit the wettability of low γ_o-aq systems (toluene-water-IPA). The extended EQS (e-EQS) method produced reasonable predictions of γ_o-aq·cosθ_O for all the available experimental and literature data. The e-EQS method required fitting one of the interfacial energy terms (γ_S-L). For low surface energy materials, such as PTFE, the γ_S-o value should be fitted. For high surface energy materials, the γ_S-aq should be fitted instead. The fitted values of γ_S-o for PTFE and γ_S-aq for glass were consistent with the values obtained from Young's equation applied to SLA data.

Further Reflections on the Geometric Mean Combining Rule for Interfacial Tension

Wettability is a widely used method to estimate the surface (free) energies of solids. The measured contact angles are usually processed within the framework of Fowkes and Good that uses a geometric mean combining rule of interfacial interactions. Recently, this method of calculating the interfacial tension has been questioned as it appears to yield somewhat unphysical results of interfacial energetics in certain situations. We would like to demonstrate that these unphysical results are consequences of the neglect of the preferential enrichment or depletion of the most surface-active functionalities of a molecule composed of various chemical groups at the liquid-air, liquid-liquid, and liquid-solid interfaces that the quintessential Fowkes-Good analysis does not account for. When the base state of the surface energy is estimated using Lifshitz theory and the preferential segregation of the functional groups at the interface is taken into account, the difficulty associated with the Fowkes-Good approach seems to disappear. This, however, raises new challenges and opportunities related to the estimation of surface energetics based on wettability.