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Since the influence of carbon dioxide (CO2) on the dynamic interfacial tension of crude oil and aqueous solutions at the elevated temperatures and pressures is an important issue, this investigation is aimed to measure the IFT of crude oil/water, CO2, and carbonated water. The measured values reveal that the IFTs of crude oil/CO2 are decreased through the first interval, while a gradual and continuous reduction in IFT is obtained at the second interval. Although both intercepts and slopes of the first interval lines are more than the second interval for all the studied temperatures, they show a similar trend as a function of temperature. The used vanishing IFT method measurement reveals that the minimum miscibility pressure (MMP), first contact miscibility pressure, and intersection point (where the slopes of the linear curves change) of two linear equations have a linear increasing trend as temperature changes. However, this trend was not observed for the aqueous solution saturated with CO2 (i.e., carbonated water) which can be related to the difference between liquid- and gas-phase behavior as well as the formation of carbonic acid in the carbonated water process. IFT values reduced from 18.6 mN/m (@ pH = 8) to 0.3 mN/m (@ pH = 14) with an increase in pH of the aqueous solution, while miscibility conditions can be obtained for CO2 cases at pressures higher than the MMP points. Considerably higher IFT values were measured in the presence of water and carbonated water in the range of 9.1–17.5 mN/m and 12.2–17.4 mN/m, respectively. The most important feature of the CW process can be the swelling factor of crude oil due to the fact that the oil swelling of up to 40% was achieved at elevated temperature (75 °C) and pressure (4500 psi) after only1600 s.

Since knowing the effect of salt type is a vital parameter during smart-water injection for enhanced oil recovery (EOR) purposes, surface-free energies on the carbonate surface contacted by crude o...

We reported the solubility values for an active pharmaceutical ingredient (API) at different operational conditions. Tenoxicam was considered as the API model in this work, and the values of API so...

Understanding the roles of asphaltene and resin as natural surfactants existed in crude oil can enlighten contradicting reported results regarding interfacial tension (IFT) of crude oil/aqueous solution as a function of salinity and ion type. In this way, this study is aimed to investigate the effect of these natural surface active agents on IFT of with special focus on SO42− anion and Mg2+ cation. Two different synthetic oil solutions of 8 wt% of the extracted asphaltene and resin dissolved in toluene are prepared, and then IFT values are measured. After that, the obtained results are compared with the IFT of intact crude oil in contact with the same saline solutions examined in the previous stage. The obtained results showed a synergistic effect of Na2SO4 + MgCl2 solution unlike the MgSO4 + MgCl2 and CaSO4 + MgCl2 solutions on IFT reduction of resin at MgCl2 concentration of 15000 mg·kg−1. In summary, it is found that the affinity of asphaltene molecules towards the interface of oleic phase/ionic solution leads to higher IFT variation.

Pebax®1657 and [Omim][PF6] ionic liquid (IL) were used to fabricate a blend membrane and applied for CO2 separation. The changes upon adding ionic liquid into the polymer matrix as well as the membrane characteristics were studied through SEM, FTIR, DSC and TGA analysis. The obtained gas permeation results indicated that the CO2 permeability in all membranes was much higher than the other studied gases. CO2 permeability of Pebax containing 8 wt% IL increased from 82.3 Barrer up to 125.6 Barrer at a pressure of 2 bar, which showed a 53% increment compared to the neat Pebax membrane. Furthermore, as the [Omim][PF6] loading within the polymer matrix was increased, the CO2/CH4 and CO2/N2 selectivities improved. In addition, the permeability and selectivity of gases was enhanced as the feed pressure increased. Upon increasing feed pressure to 10 bar, the CO2 permeability of Pebax containing 8 wt% IL reached 185.3 Barrer, which was approximately 48% higher than the permeability at a pressure of 2 bar. Moreover, the selectivity of CO2/CH4 and CO2/N2 for the Pebax/8wt% IL membrane at pressure of 2 bar was 15.3 and 46.5, respectively, which improved to 19.7 and 59.8 as the pressure increased to 10 bar.

Sulfate anion is well-known for being one of the most active agents to be injected into the oil reservoirs and being capable of not only altering the interfacial properties of crude oil but...

Carbonated brine (CB) injection, known as one of the effective enhanced oil recovery processes, is highly dependent on the reservoir conditions (i.e. temperature and pressure) as well as the type of dissolved salt in aqueous solution. This study is aimed to investigate the influential parameters on the swelling of crude oil as the most important mechanism during CB injection. The swelling of crude oil in the presence of different CB solutions consisted of different salts such as KCl, NaCl, CaCl2 and MgCl2 with constant concentration of 15,000 ppm is studied using a high-pressure, high-temperature visual cell which measures the volume of drop using image processing software based on Young-Laplace method. Also, the Δ Bond number of crude oil is examined to more reliably find out the mechanisms. According to the results, it can be concluded that the solubility of CO2 in aqueous phase is not the only parameter affecting the swelling behavior, and that the crude oil and ion type as well as temperature have remarkable effect on the mobility of CO2 molecules and their partitioning from aqueous phase toward oil phase.

Ionic liquids (ILs) can be tailored as chemical surfactants and surface active agents to reduce the interfacial tension (IFT) of crude oil/aqueous solutions for enhanced oil recovery processes. The current investigation was aimed to explore the nature of ingenious active agents in crude oil, including asphaltene and resin, and their possible interactions with two families of ILs, namely pyridinium and imidazolium, on the IFT of crude oil/aqueous solutions, both in the presence and absence of MgCl2. To the best of our knowledge, the effect of crude oil type on the IFT of crude oil/aqueous solution containing salts and IL has not been ever investigated. Accordingly, IFTs of light, medium and heavy crude oils (labeled as LCO, MCO and HCO, respectively) and two ILs, i.e. [C8mim] [Cl] and [C8Py] [Cl] were measured. In addition, the effects of the total acid number of crude oils, the amount of ingenious active agents in the crude oils as well as their major structural, molecular parameters such as hydrogen/carbon ratio and type and amount of heteroatoms (i.e. nitrogen, sulfur and oxygen) were investigated. The obtained results indicated that the performance of ILs was influenced by the crude oil and IL types. In details, the aromatic section of cationic part and their interactions with heteroatoms of crude oil showed the most influential role on the IFT variation.

Concerns about climate change have persuaded the researchers to examine CO2 injection in the form of carbonated water (CW) into oil reservoir as a safe and effective CO2 storage and enhanced oil recovery process. Although interfacial tension (IFT) between crude oil and injected fluid has a vital role on the displacement of fluids in porous media, the effect of CO2 and crude oil type on the dynamic IFT of crude oil under different operational conditions is not well understood. Accordingly, this study was carried out to assess the effects of temperature, pressure, crude oil type and CO2 on the dynamic IFT of crude oil/CW. To achieve this goal, two types of crude oil were provided from southern Iranian oil reservoirs and dynamic IFTs with CW were measured in a wide range of temperatures and pressures (i.e. temperature range of 30–80 °C and pressure range of 500–4000 psi); the obtained results were compared with the system without CO2. In addition, the adsorption time of carbonated aqueous phase/crude oil, obtained based on the mono exponential decay model, was also compared with unadulterated water/crude oil system. The outcome of this study showed that crude oil type has the most significant effect on the IFT of crude oil/CW compared to pressure, temperature and CO2 content. In more details, the IFT of crude oil/CW can be affected by the amount and type of acidic/basic components in the crude oil as well as pH of the aqueous solution. Besides, the obtained results revealed that the effect of temperature was more considerable on the IFT of the heavy crude oil compared with the light crude oil in both studied aqueous solutions (i.e. unadulterated water and CW). Although the inversion phase temperature was obtained for unadulterated water/studied crude oils at all studied pressures, this phenomenon was not observed for crude oil/CW at elevated pressure, due to the high amount of CO2 at this condition.

Improving oil recovery and decreasing greenhouse gas emissions are two important attractive features of CO2-enriched water injection into oil reservoirs. Regarding these unique features, the main objective of this study was concentrated to evaluate the swelling behavior of crude oil as a fundamental mechanism of carbonated water (CW) flooding. To achieve these goals, the swelling and Bond number of light and heavy crude oils (namely LCO and HCO, respectively) are measured and compared to each other. The results obtained from the measured swelling factors of crude oil/CW show some complicated behaviors. That is, as temperature increases the swelling factor decreases at low pressure conditions, while at high pressure a reverse trend was observed. In addition, the crossover pressure, which can be contributed to the different swelling behaviors of crude oil for different CO2 contents of water, was shifted to higher pressure for the LCO compared to that for the HCO.

Accurate knowledge and prediction of the liquid–liquid transition phase consisting of ionic liquids and organic solvents are key points in different industrial processes. In this way, the effects o...

In the light of artificial neural network (ANN) model advantages, a predictive ANN model is proposed to correlate the surface tension of common hydrocarbons including normal alkanes (i.e. n-C4–n-C40), linear alkenes (i.e. 1-C4–1-C40), and cycloalkanes (C4–C20) in a wide range of temperatures. The most important advantage of the current proposed network is its low number of input variables which are only temperature of the system as well as carbon number and critical temperature of components utilized to differentiate among the different components. The obtained results revealed that a model trained by the Levenberg–Marquardt algorithm with hyperbolic tangent and linear transfer functions for the hidden and output layers, respectively, comprised of 27 hidden neurons is the optimum structure. In sum up, the obtained results demonstrated that the proposed ANN model is capable to satisfactorily predict and correlate the 5461 surface tension data points of normal alkanes, linear alkenes, and cycloalkanes as a function of temperature with maximum deviation of 0.47, 0.40 and 0.43 mN/m, respectively, just using three inputs parameters considering testing data subset.

In recent years, the behavior of crude oil interfacial tension (IFT) as a function of salt concentration have been investigated. The results found in literature are highly controversial, thus the current experimental study aimed to clarify the reasons behind this by developing a methodology based on extracting asphaltene and resin from three different crude oils and performing elemental analysis on them. In addition, the effect of salinity on the IFT of three studied crude oil was compared with the synthetic crude oil consisted of different weight percent (wt%) of asphaltene and resin in toluene. The obtained results revealed that the IFT of crude oil as a function of salinity depended not only on the wt% of asphaltene and resin fractions but also on the aromaticity of asphaltene and resin. In fact, as the aromaticity of asphaltene increased, the performance of asphaltene decreased as a function of salinity while the aromaticity of resin led to a revers trend on IFT variation.

In the current study, a novel approach which takes into account the effectiveness of both convectional surfactants and biosurfactants was investigated. The biosurfactant produced by Enterobacter cloacae strain was utilized concomitant with conventional surfactant (sodium dodecyl benzene sulfonate (SDBS)) to evaluate its capability to reduce the SDBS adsorption on rock surface (biosurfactant acts as sacrificial agent) or synergistically enhance the effectiveness of the SDBS. In this regard, the wettability alteration and interfacial tension (IFT) measurements and calculation of spreading coefficient were performed considering two different scenarios. In the first scenario, SDBS was added to the incubated bacterial solution medium while in the second case, SDBS was added to the bacterial solution before the incubation stage. Based on the obtained results, it was revealed that the wettability altered from original oil wet towards water wet state using bacterial solution, while the addition of SDBS deteriorated this trend for both scenarios. According to IFT measurements, the first scenario was more effective than the individual solution of bacteria and SDBS as well as the second scenario. In conclusion, the measured spreading coefficient demonstrated that the bacterial solution was a more effective EOR agent in comparison to other studied cases.

A basic understanding of the activities of indigenous surfactants of crude oil at the water/oil interface as a function of aqueous phase pH can give us a better insight into the alkaline enhanced oil recovery processes. The present study aimed to elucidate the effect of salinity and crude oil type, specifically the influence of resin and asphaltene molecules during alkaline flooding through interfacial tension (IFT) measurements via pendant drop and spinning techniques. Several model oils containing asphaltene and resin fractions were prepared and their IFTs were compared with those of the original crude oils. Moreover, the elemental analyses of asphaltene and resin fractions were performed, and the total acid numbers of all oils were measured as well. The IFT results of three studied crude oils and the asphaltenic and resinous model oils with sea water and deionized water underlined the importance of the degree of salinity, and qualitative and quantitative nature of resin and asphaltene fractions. It was also revealed that the amount of asphaltene and resin fractions as well as their structural nitrogen and oxygen contents were the most influential parameters on the IFT of crude oil as a function of pH values. In addition, the variations of IFT crude oils/the ionic solution and deionized water were more noticeable in the basic aqueous solutions.

The potential of crude oil swelling is dominant mechanism in the development and implementation of carbonated water (CO 2 saturated water) flooding as an environmental friendly enhanced oil recovery method. In this study, the volume of crude oil drop in carbonated water (CW) was measured at temperatures of 30, 50 and 80 °C and pressures of 500, 1000, 2000 and 4000 psi to investigate the swelling behavior of crude oil during CW flooding. In addition, the variations of dynamic and equilibrium Bond number of CW/crude oil due to dissolution of CO 2 in the crude oil are compared to the crude oil/water systems. It is expected that crude oil swelling decreases as temperature increases due to a reduction of the concentration of CO 2 in the CW phase in all the studied pressures. However, interesting and unexpected results was observed. That is, the swelling of crude oil drops significantly different in two distinct regions: in the first region (i.e. pressure lower than crossover), the swelling of crude oil decreases when temperature increases; in the second region (i.e. pressure higher than crossover), the behavior of the crude oil swelling versus temperature is in the opposite of that in the first region.

A systematic series of experiments are designed and performed including interfacial tension (IFT) measurements concomitant with Bond (BN, the ratio of gravity forces to capillary forces) and swelling/extraction measurements. Dynamic IFT, BN and swelling/extraction are measured as a function of pressure at temperatures of 30, 50 and 80 °C. In addition, in the light of measured IFT the minimum miscibility pressure (MMP) of CO 2 and light crude oil is determined based on a method called vanishing interfacial tension (VIT). The obtained results interestingly revealed that equilibrium IFT decreases linearly with pressure in two distinct pressure intervals while equilibrium BN shows an increasing trend as a function of pressure for all of the studied cases while no obvious trend is observed for swelling of crude oil and extraction of light-components regarding time, temperature and pressure.

Low salinity (LS) and smart water (SW) flooding processes which receive a great interest as cost-effective and environmental friendly techniques are relatively new enhanced oil recovery methods. Although shifting carbonate surfaces towards a water-wet state is the main mechanism behind these methods, effects of controlling factors (for instance: ion type or salinity) are already remained unsettled. In this regard, the effects of sulfate ion types (i.e. Na2SO4, MgSO4 and CaSO4) and their concentrations (i.e. 0–45,000 ppm) on wettability alteration are investigated using contact angle (CA) measurement technique. In addition, work of cohesion, work of adhesion and spreading coefficient of all examined salts are calculated based on the experimental interfacial tension (IFT) and CA measurements. The results reveal that reduction of salinity of the aqueous solution and presence of sulfate anion at high salinity conditions (15,000–45000 ppm) are two important parameters for wettability alteration.

The objective of this study is to design and validate a highly accurate approach based on an artificial neural network (ANN) to predict both bubble and dew point pressures of various CO 2 –refrigerant binary systems in the tem­perature range of 263.15–367.30 K and pressure of 0.18–9.09 MPa. 503 Expe­rimental vapour–liquid equilibria (VLE) data of nine different CO 2 ‑refrigerant binary mixtures were used for preparation, validation and testing of ANN model. The developed ANN model correlates bubble and dew point pressure to reduced temperature, critical pressure, acentric factor of refrigerant, and disti­bution of CO 2 between the vapour and liquid phases. Trial and error procedure reveals that a three-layer neural network with fourteen neurons in the hidden layer is able to predict the pressure with mean square error ( MSE ), average absolute relative deviation ( AARD ), root mean square error ( RMSE ), and correl­ation coefficient ( R 2 ) of 0.0133, 2.79 %, 0.1153 and 0.99836, res­pectively. The results confirmed that the ANN model can accurately apply for predicting the VLE data of different binary CO 2 –refrigerant systems.

A wide application of ionic liquids in different separation processes, such as multiple reaction, extraction cycles, and azeotropic or close-boiling-mixture distillation processes, has been reporte...

Although several investigations have studied the low-salinity water injection (LSWI) performance during the past decades, the effect of crude oil type on the interfacial tension (IFT) and wettabili...

Spearmint oil known as aromatic volatile compound of plants are widely used in food industries. In the present study, supercritical carbon dioxide (SC-CO2) extraction is used to extract the essential oil from spearmint leaves. In this way, a series of extraction experiments are designed to investigate the effect of different operating conditions such as extraction pressure (85–120 bar), extraction temperature (38–50 °C), CO2 flow rate (0.059–0.354 g/min), mean particle size (0.177–2 mm) and dynamic extraction time (20–120 min) on efficiency of the extracted essential oils. In the last step, not only a second order polynomial equation is developed to obtain the optimal SC-CO2 extraction parameters, but also the composition of extracted essential oil at optimum operating condition is analyzed using gas chromatography-mass spectrometry (GC–MS).

In this way, after experimental measurement of interfacial tension, different models including mono-exponential decay, dynamic adsorption models and empirical equation are used to correlate this time-dependent behavior of interfacial tension (IFT). During the modeling approach, the induction, adsorption, equilibrium, and meso-equilibrium times as well as diffusivity of surface active components known as natural surfactant including asphaltene and resin from crude oil to the interface are obtained. In addition, the surface excess concentration of surface active components at the interface and Gibbs adsorption isotherm are utilized to analyze the measured dynamic IFTs. Finally, the mechanisms of crude oil/aqueous solution IFT including (a) the activity of surface-active components and (b) surface excess concentration of them at fluid/fluid interface are proposed and discussed in details.

The interfacial properties of crude oil are highly complex and are not yet well understood. This study aimed to evaluate the effect of temperature (30–80 °C) and pressure (3.44–27.58 MPa) on the dynamic interfacial tension (IFT) of crude oil/aqueous solutions consisting of 15 000 ppm of salt containing different chloride anions, e.g. NaCl, KCl, MgCl2, and CaCl2. To reach this goal, several parameters such as dynamic and equilibrium IFT, adsorption time, diffusivity of resin, and asphaltene as surface-active agents from bulk of crude oil towards fluid/fluid interface and surface excess concentration of them at the interface were compared as a function of temperature, pressure, and ion type. The obtained results clarified the reason why there are contradicting observations in the literature on the influence of temperature on the equilibrium IFT of crude oil/brine solutions. This article is protected by copyright. All rights reserved

Carbonated water has been recently proposed as an enhanced oil recovery method for crude oil reservoirs. Interfacial tension (IFT) plays a crucial rule on the displacement of trapped oil ganglia in the porous media. This investigation is designed to systematically assess the dynamic interfacial tension (DIFT) of two different types of crude oils with carbonated water (CW). In addition, the measured experimental data were applied into specified models. The DIFT behavior of acidic and non-acidic crude oil samples/CW and deionized water (DW) are also compared to find the effect of dissolved carbon dioxide in water on IFT. At the next stage, DIFT of all the results were used through three different models namely diffusion-controlled, mono-exponential models and an empirical equation. In this way, induction, adsorption (i.e. relaxation or rapid fall), equilibrium and meso equilibrium times, diffusivity of surface active materials in the crude oil to the crude oil/aqueous phase interface (D SA ) and surface excess concentration of surface active components (Г SA ) of CW systems are calculated and compared with those of the crude oil-DW systems. While IFT reduction is considered as an effective mechanism of CW injection for more oil recovery, the obtained results in the current investigation show a contradicting trend. In details, the dissolved CO 2 reduces the pH of the aqueous phase, consequently, increases the basic natural surfactant ionization. The obtained results show that domination of Г SA reduction compared to the ionization of basic natural surfactant leads to IFT enhancement.

Recently, carbon dioxide (CO2) flooding into depleted reservoirs regardless of miscible or immiscible displacement is widely investigated not only to improve oil recovery but also to reduce the greenhouse effect of this gas produced by numbers of industries in the globe. In the light of this fact, in the first stage of this investigation, the minimum miscibility pressure (MMP) of CO2 and light crude oil (API° = 35) with low asphaltene content was determined at temperatures of 30, 50 and 80 °C using vanishing interfacial tension (VIT) method. The obtained results demonstrated that the MMP of the studied system is almost linear function of temperature with slope of 0.15 MPa/K. The interesting point is that the results revealed a reduction in slope as the composition of light components of crude oil increases.

A feedforward artificial neural network was used to correlate 956 experimentally measured thermal diffusivity data of hydrocarbons and aromatics. A network consisted of one input, one hidden and on...

Accurate estimation of liquid thermal conductivity is highly necessary to appropriately design equipments in different industries. Respect to this necessity, in the current investigation a feed-forward artificial neural network (ANN) model is examined to correlate the liquid thermal conductivity of normal and aromatic hydrocarbons at the temperatures range of 257–338 K and atmospheric pressure. For this purpose, 956 experimental thermal conductivities for normal and aromatic hydrocarbons are collected from different previously published literature. During the modeling stage, to discriminate different substances, critical temperature ( T c ), critical pressure ( P c ) and acentric factor ( ω ) are utilized as the network inputs besides the temperature. During the examination, effects of different transfer functions and number of neurons in hidden layer are investigated to find the optimum network architecture. Besides, statistical error analysis considering the results obtained from available correlations and group contribution methods and proposed neural network is performed to reliably check the feasibility and accuracy of the proposed method. Respect to the obtained results, it can be concluded that the proposed neural network consisted of three layers namely, input, hidden and output layers with 22 neurons in hidden layer was the optimum ANN model. Generally, the proposed model enables to correlate the thermal conductivity of normal and aromatic hydrocarbons with absolute average relative deviation percent (AARD), mean square error (MSE), and correlation coefficient ( R 2 ) of lower than 0.2%, 1.05 × 10 − 7 and 0.9994, respectively.

Although rotating beds show promise for intensified separations, the fundamentals of their hydrodynamics are still poorly understood. In many operating conditions, pressure drop in an irrigated bed can be considerably lower than that across a dry bed. Previously published correlations don’t provide good prediction of these phenomena. In this research, a semi-empirical correlation is developed to predict the pressure drop across the rotating packed beds. The results show the agreement of predicted pressure drop with the experimental data is acceptable. This model can also predict the pressure drop unexpected phenomena of higher pressure drop in dry beds than in wet beds.

The concerns for water availability, affordability and environmental consideration have motivated more research on the development of smart water injection for enhanced oil recovery process. Although wettability alteration has been considered as the dominant mechanism, there is an ample space in this area needs to be explored more. Therefore, a systematic series of experiments is designed and performed to examine the effect of salinity and ion type on the wettability of the carbonate rock surface to find the active mechanisms. For this purpose, the concentrations of different salts including NaCl, KCl, CaCl 2 and MgCl 2 are examined during 10 days of soaking for salts concentrations range of 0–45,000 ppm. Based on the measurements of contact angle (CA), it is concluded that the monovalent cation bonded to the chloride anion showed better performance on the wettability alteration of oil wet carbonate rock surface compared to the divalent cations bonded to the chloride anion. In addition, comparing the results of CA measurements of NaCl and KCl solutions as a function of concentration showed completely different wettability behaviors. The presence of KCl shifted the wettability of the carbonate rock surfaces from strongly oil wet to strongly water wet state for all of studied concentrations while as the concentration of NaCl was decreased, the more wettability alteration was observed.

Changing the wettability of reservoir rock towards strongly water-wet state is effective way to enhance oil recovery from fractured carbonate reservoirs which are typically oil-wet. Regarding this fact, the injection of surfactant and the bacterial solution as EOR agents is proposed in the current work as a potential method to alter the wettability of rock surface reservoir. Nevertheless, there is a definite lack of experimental data regarding this method and the synergistic effect of both chemical and bacterial solutions on this process. In this study, the sole and combined effects of the bacterial solution using an Enterobacter cloacae strain as a biosurfactant-producer are compared with sodium dodecylbenzenesulfonate (SDBS) and dodecyltrimethylammonium bromide (C12TAB) as anionic and cationic surfactants, respectively. For this purpose, static contact angle measurement are utilized to investigate the wettability alteration. The obtained results revealed that bacterial solution can alter the wettability of calcite surfaces to the same extent of C12TAB and more than SDBS. In addition, base on the obtained results it can be concluded that the combination of bacterial solution and chemical surfactant are not proposed for in-situ biosurfactant techniques, since the Enterobacter cloacae uses the chemical surfactant as the carbon source concomitantly a reduction in the biosurfactant production occurs.

The main objectives of this study are to determine the influence of crude oil type, salinity, temperature and pressure on the dynamic interfacial tension (DIFT) of crude oil based on the experiments and modeling approaches. DIFT is also modeled using dynamic adsorption models, mono-exponential decay model as well as empirical equations. The results showed that when temperature increases, unlike deionized water which inversion phase temperature was observed, the equilibrium IFT of crude oils/sea water increases due to reduction of surface excess concentration of natural surfactants at the fluid/fluid interface as a dominant mechanism.