Axisymmetric Drop Shape Analysis Research Articles

Minimum miscibility pressure and interfacial tension measurements for N2 and CO2 gases in contact with W/O emulsions for different temperatures and pressures

In this research, the IFT behavior of two different specimens of W/O emulsion with distinctive soluble ingredients of water in contact with CO2 and N2 was examined. The Minimum Miscibility Pressure (MMP) of the mentioned gases with emulsion specimens were measured and compared with the case of the original crude oil with no water content. This study focuses on the quantity of water in the W/O emulsion specimens and its effects on IFT and MMP values. The IFT behavior of W/O emulsions was surveyed for two different cases of distinctive water soluble ingredients, i.e. sea water and reservoir brine. The tests were performed under high pressure-high temperature (HPHT) conditions utilizing Axisymmetric Drop Shape Analysis (ADSA) procedure. The equilibrium IFT values between the two distinctive specimens of W/O emulsions with different amounts and compositions of dispersed water and two types of gases, i.e. CO2 and N2, were measured. The outcomes were compared with the behavior of original crude oil, i.e. crude oil with no water content. The temperature was set in two distinctive values of 313.15 K and 333.15 K, and the pressure changes in the scope of 1 MPa–20.68 MPa. The outcomes manifested that the IFT behavior of the emulsion could be correlated directly with pressure for two distinctive variation rates, categorized in two different regions. Comparing to the original crude oil, in the case of W/O emulsion the equilibrium IFT increases, and this incremental behavior is much significant in the case of N2-emuslion system. Additionally, the outcomes of IFT versus pressure, in the case of N2-emulsion system, manifested that the slope of the first part of the curve decreases with increment in dispersed water content in the crude oil. However, the IFT values versus pressure in the second region were not affected by the water content of the emulsion. Also, Vanishing Interfacial Tension (VIT) technique was used to estimate the MMP of N2-emulsion systems. According to the outcomes, MMP was increased in the existence of water, and the incremental behavior becomes significant when the water content is increased. It is worthy to note that the outcomes of the CO2-emulsion systems manifested that both IFT behavior and MMP values were not changed significantly by water content. Finally, in light of the test information gathered in this research, various relationships were proposed to express the IFT and MMP correlations as dependants of pressure at distinctive temperatures.

An Investigation of Oil Spreading Coefficient in Carbonated Water+ Gas + Oil System: an Experimental Study in an Iranian Asphaltenic Oil Reservoir

To provide supplementary oil recovery after the primary and secondary processes, enhanced oil recovery (EOR) techniques are introduced. Carbonated water injection (CWI) as an EOR method can improve sweep efficiency and the risk of gas leakage. On the other hand, the interfacial tension (IFT) is one of the key factors which can affect fluid displacement during the process of CWI greatly. Therefore, the analysis of the IFT on an oil-carbonated water-CO2 system is vital. In this paper, the interfacial interactions of binary systems of asphaltenic crude oil (ACO), carbon dioxide (CO2), and carbonated water (CW) at different pressures and at two temperatures of 40 °C and 50 °C and their effects on the oil spreading in the water phase in the presence of gas are experimentally investigated. The IFT measurements were performed by axisymmetric drop shape analysis (ADSA) technique for the pendant/rising oil drop case. It is found out that the equilibrium interfacial tension (EIFT) of the two systems of crude oil-CO2 and water-CO2 is reduced almost linearly with pressure but increased with temperature. Moreover, the pressure has an increasing and decreasing effect on the water-oil and CW-oil IFT’s respectively. However, temperature has a reverse effect for the both systems. Spreading coefficient (SC) concept would help better understand the oil recovery mechanisms and potential. The results show that SC curve has a minimum point value as a specific pressure, which increases with temperature. The presence of CO2 in the water phase could strongly affect the oil spreading phenomenon through which oil recovery could be significantly enhanced.

Melting of the Dipalmitoylphosphatidylcholine Monolayer.

Langmuir monolayer self-assembled at the air-water interface represents an excellent model for studying phase transition and lipid polymorphism in two dimensions. Compared with numerous studies of phospholipid phase transitions induced by isothermal compression, there are very scarce reports on two-dimensional phase transitions induced by isobaric heating. This is mainly due to technical difficulties of continuously regulating temperature variations while maintaining a constant surface pressure in a classical Langmuir-type film balance. Here, with technological advances in constrained drop surfactometry and closed-loop axisymmetric drop shape analysis, we studied the isobaric heating process of the dipalmitoylphosphatidylcholine (DPPC) monolayer. It is found that temperature and surface pressure are two equally important intensive properties that jointly determine the phase behavior of the phospholipid monolayer. We have determined a critical point of the DPPC monolayer at a temperature of 44 °C and a surface pressure of 57 mN/m. Beyond this critical point, no phase transition can exist in the DPPC monolayer, either by isothermal compression or by isobaric heating. The melting process of the DPPC monolayer studied here provides novel insights into the understanding of a wide range of physicochemical and biophysical phenomena, such as surface thermodynamics, critical phenomena, and biophysical study of pulmonary surfactants.

Dynamic interfacial tension measurement method using axisymmetric drop shape analysis

The current method describes a simple modification to the dynamic and equilibrium interfacial tension (IFT) measurement in a multiphase system (gas-liquid/liquid-liquid) by the Axisymmetric Drop Shape Analysis (ADSA) pendant drop technique. The primary difficulty associated with dynamic IFT measurement by ADSA is providing the appropriate phase densities, especially in a system consisting of gas (CO2, methane, and propane) and liquids (water and hydrocarbon). The density of the phases is calculated using a, considering the solubility og gases in liquids, as a function of time. The calculated densities of the phases are then used as inputs in the experiment to measure the IFT at high pressure and temperature PVT-cell.The method offers benefit such as:•Straightforward and cost effective as it does not require additional experimental setup (like density meter) or a complicated equation of state.•The composition of the binary mixtures (mole and mass) and the density changes of the binary mixture due to mass transfer may be obtained as a function of time at fixed pressure and temperature.•IFT as a function of time is measured by taking into consideration of correct phase density.

A precise goniometer/tensiometer using a low cost single-board computer

Measuring the surface tension and the Young contact angle of a droplet is extremely important for many industrial applications. Here, considering the booming interest for small and cheap but precise experimental instruments, we have constructed a low-cost contact angle goniometer/tensiometer, based on a single-board computer (Raspberry Pi). The device runs an axisymmetric drop shape analysis (ADSA) algorithm written in Python. The code, here named DropToolKit, was developed in-house. We initially present the mathematical framework of our algorithm and then we validate our software tool against other well-established ADSA packages, including the commercial ramé-hart DROPimage Advanced as well as the DropAnalysis plugin in ImageJ. After successfully testing for various combinations of liquids and solid surfaces, we concluded that our prototype device would be highly beneficial for industrial applications as well as for scientific research in wetting phenomena compared to the commercial solutions.

Characterization of highly hydrophobic textiles by means of X-ray microtomography, wettability analysis and drop impact

Highly hydrophobic surfaces have been intensively investigated in the last years because their properties may lead to very promising technological spillovers encompassing both everyday use and high-tech fields. Focusing on textiles, hydrophobic fabrics are of major interest for applications ranging from clothes to architecture to environment protection and energy conversion. Gas diffusion media – made by a gas diffusion layer (GDL) and a microporous layer (MPL) – for fuel cells are a good benchmark to develop techniques aimed at characterizing the wetting performances of engineered textiles. An experimental investigation was carried out about carbon-based, PTFE-treated GDLs with and without MPLs. Two samples (woven and woven-non-woven) were analysed before and after coating with a MPL. Their three-dimensional structure was reconstructed and analysed by computer-aided X-ray microtomography (µCT). Static and dynamic wettability analyses were then carried out using a modified axisymmetric drop shape analysis technique. All the surfaces exhibited very high hydrophobicity, three of them near to a super-hydrophobic behavior. Water drop impacts were performed, evidencing different bouncing, sticking and fragmentation outcomes for which critical values of the Weber number were identified. Finally, a µCT scan of a drop on a GDL was performed, confirming the Cassie-Baxter wetting state on such surface.

A couple new ways of surface tension determination

Axisymmetric liquid-fluid interface (ALFI) and axisymmetric drop shape analysis (ADSA) are the methods used in surface phenomena investigations. A photographed contour of a drop or a bubble is detected and fitted to numerically integrated Young-Laplace equation. However, ALFI fails in the stationery points, while ADSA gives the wrong surface tension value at the apex. An analytical expression for an interface shape overcome the weaknesses of the numerical models. It shows that pressure inside a drop is higher than outside, while a bubble encloses gas with negative gauge pressure. Since, the close-formed solutions origin from a force balance which preserves constant volume as well as temperature, entropy, and masses of ingredients are invariable the new formulas can be considered in the surface tension measurements. Hence, surface tension can be determined in the new ways. Each new method needs the measurements of two dimensions only and a solution of quite simple set of the equations. Moreover, the spare equations verify the solution. Then achieved surface tension is an input to obtain bubble shapes which are compared with experiment successfully.

Surface tension measurement with a smartphone using a pendant drop

In this study, a novel powerful mobile surface tension instrument based on a smartphone (mobile-phone or handy) is developed. Axisymmetric drop shape analysis method was implemented on a smart-phone (mobile-phone) for surface or interfacial tension measurements. The novelty of this work is that we have been able to implement all the needed calculations on a smartphone, and used the smartphone hardware for image acquisition and display purposes. As such we have been able to create an instrument that is significantly more economical compared to current systems; also it is compact, and can be mobile for field work. It is shown that the accuracy of our method can be 0.001% with ideal synthetic drop profiles (750 synthetic droplets representing a wide range of surface tension values were used). The performance of this instrument was also compared with a high-end commercial surface tension measurement instrument. We used various liquids (from high to low surface tension), and show that our instrument and the developed methodology can provide surface tension measurements as precise and accurate as current commercial instruments.

Accuracy of Axisymmetric Drop Shape Analysis in Determining Surface and Interfacial Tensions.

Axisymmetric drop shape analysis (ADSA) has been used in a broad range of applications for determining surface tensions of air-liquid surfaces and interfacial tensions of liquid-liquid interfaces. However, it is well-known that the accuracy of ADSA deteriorates upon the reduction of drop volume. Here, we systematically compared different criteria and parameters in evaluating the accuracy of ADSA upon reducing drop volume. By scrutinizing the dependence of ADSA accuracy on various parameters, including the capillary constant (c), the Bond number (Bo), the Worthington number (Wo), and the shape parameter (Ps), we concluded that the classical Bond number failed to predict the accuracy of drop shape analysis at very small drop volumes. Thus, we proposed a replacement of the classical Bond number, called the Neumann number Ne ≡ (ΔρgR0H)/γ. The design rationale of this new dimensionless number lies in the use of the geometric mean of the radius of curvature at the drop apex (R0) and the drop height (H) as the new characteristic length (L) to represent the drop size, that is, L = (R0H)1/2. It is found that the Neumann number is capable of evaluating the accuracy of ADSA. Moreover, we have demonstrated the usefulness of the local Neumann number, Nez ≡ (ΔρgR0/γ)z, in evaluating the contribution of the local drop profile to the accuracy of ADSA.

Tuning of properties of alkyl phenol formaldehyde resins in petroleum demulsifiers. 2. Interfacial dilatational properties

ABSTRACTIn the context of the study of crude oil dehydration, two hydrophilic ethoxylated phenol formaldehyde polymeric resins with different degrees of ethoxylation 10 (PR_A) and 20 (PR_B) were studied at the oil/water interface. Viscoelastic properties of model monolayers were obtained by frequency sweep tests, using a drop tensiometer and axisymmetric drop shape analysis. Overall, a significant gap was measured between the values of elastic modulus of PR_A and PR_B monolayers, and the experimental data showed a good correlation with the Lucassen and Van den Tempel model. These results indicate that interfacial intramolecular interaction appear stronger for resin PR_B likely related to its hydrophobic structure favoring surface active properties. On the other hand, PR_B has shown a better ability than PR_A to destabilize crude oil monolayers and better demulsifying properties, counteracting the effect of asphaltenes as stabilizers. This study allows a better understanding of the demulsifying properties of such resins.

Adsorption and Co-Adsorption of Polyaldehyde Dextran Nanoparticles and Nonionic Surfactant at an Air–Water Interface: Potential Implications for Pulmonary Drug Delivery

Abstract Measurements of dynamic surface tension were carried out in aqueous systems (water or 0.1 mM Triton X-100) comprising nanoparticles formed from chemically modified polyaldehyde dextran (PAD). The nanostructures, considered as potential drug carriers in aerosol therapy, were obtained from biocompatible polysaccharides by successive oxidation and reactive coiling in an aqueous solution. The dynamic surface tension of the samples was determined by the maximum bubble pressure (MBP) method and by the axisymmetric drop shape analysis (ADSA). Experiments with harmonic area perturbations were also carried out in order to determine surface dilatational viscoelasticity. PAD showed a remarkable surface activity. Ward-Tordai equation was used to determine the equilibrium surface tension and diffusion coefficient of PAD nanoparticles (D = 2.3×10-6 m2/s). In a mixture with Triton X-100, PAD particles showed co-adsorption and synergic effect in surface tension reduction at short times (below 10 s). Tested nanoparticles had impact on surface rheology in a mixed system with nonionic surfactant, suggesting their possible interactions with the lung surfactant system after inhalation. This preliminary investigation sets the methodological approach for further research related to the influence of inhaled PAD nanoparticles on the lung surfactant and mass transfer processes in the respiratory system.

Measurement of Interfacial Tension of CO2 and NaCl Aqueous Solution over Wide Temperature, Pressure, and Salinity Ranges

Interfacial tension data and models are of great importance to the storage of CO2 in deep saline aquifers. In this study, the pendant-drop method combined with axisymmetric drop shape analysis was used in the interpretation of the interfacial behavior of CO2 and brine. Extensive experimental measurements of the interfacial tension between CO2 and an NaCl solution were acquired for pressures ranging from 3.0 to 12.0 MPa, temperatures from 300 to 353 K, and NaCl molalities from 0 to 1.8 mol·kg–1, for a total of 1,254 valid data points. All experiments were conducted in a pressure cell fitted with a capillary tube to create pendant droplets in a CO2-rich atmosphere. The experimental results indicated that interfacial tension decreased with increasing pressure and increased with temperature and salinity. As pressure increased to a certain point, the interfacial tension reached a plateau. At a given temperature, the CO2–aqueous system reached a plateau for different salinities under nearly the same pressure. However, the plateau pressure increased with temperature. The plateau interfacial tension value slightly increased with temperature and salinity. We also found a linear relationship between the change in interfacial tension and the molality concentration of brine. An empirical model was also proposed based on the Parachor model for the prediction of interfacial tension. Most results of this model deviated by less than ±5% from our experimental results, indicating that the model was a good fit to our experiments.

Selecting a potential smart water for EOR implementation in Asab oil field

The IFT and contact angle are believed to have direct impact on wettability alteration of crude oil/water/rock systems. In this work, extensive laboratory work was conducted to investigate the effect of these two key parameters on wettability alteration at elevated temperature (90 °C) and ambient conditions. Twenty-six brines representing various scenarios of dilution and sulphate spiking were prepared and tested to identify the smart water most effective in the alteration of wettability. Sea water (SW) was used a base brine. Diluted and sulphate-spiked versions of SW were synthetically prepared following the standard brine preparation procedures. Also standard procedures were followed for the measurement of IFT and contact angle measurements using Teclis tracker. Pendant drop method was implemented to measure the IFT at ambient and 90 °C conditions using a special software package that adopts the axisymmetric drop shape analysis and fits the Laplace equation. The same software package was used to take snapshots of oil drops at 90 °C, and contact angle was measured manually. The effects of dilution and/or sulphate spiking on the observed IFT and contact angle measurements were investigated using a proposed brine categories-based plotting technique. Natural SW and its sulphate-spiked versions have shown the least oil/brine IFT at ambient and 90 °C conditions. The sulphate-spiked SW and its dilutions have resulted in the reduction in oil/brine IFT, whereas the diluted SW showed an increase in oil/brine IFT. Further reduction in IFT was observed at the elevated temperature. SW and SW/50 (50 times diluted sea water) were the only two brines that could yield a contact angle of 113° and 114°, respectively, indicating the change in wettability from oil-wet to the border line of intermediate-wettability conditions. The natural SW that contains 3944 mg/L of sulphate ion has been found to be the most effective in promoting wettability change and thus represents the selected smart water for EOR implementation in Asab oil field. The contact angle measurements were made from the drops formed by the natural drainage process. These measurements are believed to duplicate contact angles in the selected reservoir because of the continuous change in fluids saturation.

Stability and interfacial viscoelasticity of oil-water nanoemulsions stabilized by soy lecithin and Tween 20 for the encapsulation of bioactive carvacrol

The rheology of oil-in-water (O/W) droplet interfaces stabilized by food-grade emulsifiers (soy lecithin or Tween 20) under controlled aqueous conditions was investigated to elucidate its contribution in the kinetic stabilization of nanoemulsion-based delivery systems containing carvacrol, a naturally-derived antimicrobial compound. Dilational rheology of surfactant-laden O/W interfaces was measured using axisymmetric drop shape analysis. The kinetic stability of corresponding nanoemulsions (containing mixtures of carvacrol and medium-chain triglyceride (MCT) oil dispersed in water (pH 7)) was characterized using dynamic light scattering. Zwitterionic lecithin molecules adsorbed to the O/W interface for 24h formed a notably viscoelastic layer, compared to nonionic Tween 20 molecules. The kinetic stability within the first 24h for each nanoemulsion was strongly dependent upon encapsulated carvacrol concentration, with higher carvacrol concentrations leading to lower kinetic stability. Lecithin-stabilized nanoemulsions (pH 7) were highly stable, yielding monodispersed droplet size distributions and high resistance to increases in droplet size over 30days. Contrarily, corresponding Tween 20-stabilized nanoemulsions showed large increases in the droplet size and developed a bimodal droplet size distribution over time. The initial size of oil droplets stabilized by lecithin was slightly dependent on pH, yielding smaller droplets at pH 7 and larger droplets at pH 3; however, the extended kinetic stability was not greatly impacted by pH modulation. Determining a positive association between interfacial viscoelasticity and nanoemulsion stability may potentially be very useful for food manufacturers seeking to optimize the encapsulation and delivery of lipophilic antimicrobial molecules using food-grade emulsifiers.

Solubility and interfacial tension of thermoplastic polyurethane melt in supercritical carbon dioxide and nitrogen

Various industries, such as automotive and leisure, show a great interest in foaming thermoplastic polyurethane (TPU) with physical blowing agents. Hence, this study aims to investigate the effects of absorption of carbon dioxide and nitrogen by melt TPU on solubility and interfacial tension. Using a pressure–volume–temperature apparatus for high pressure and temperature combined with a magnetic suspension balance, the solubility of carbon dioxide and nitrogen in thermoplastic polyurethane melt was measured at temperatures from 190°C to 220°C and at pressures to 25MPa. The solubility of both supercritical fluids (SCF) in the TPU melt was then compared with semiempirical data and theoretical values calculated from the Sanchez–Lacombe equations of state (S-L EOS). The surface tension of the TPU/SCF interface was measured using the axisymmetric drop shape analysis profile. It was observed that the dependency of interfacial tension on temperature at high pressures decreases because of a reduction in SCF solubility at high temperatures. The relationship between the interfacial tension and the density difference of polymer-supercritical fluid was also examined using the generalized Macleod's equation.

Effects of temperature, pressure and fluid composition on hydrocarbon gas - oil interfacial tension (IFT): An experimental study using ADSA image analysis of pendant drop test method

An attempt was done to construct a reliable framework for measurement of hydrocarbon gas-oil interfacial tension (IFT) for live crude oil systems at reservoir conditions. We utilized a state-of-the-art experimental apparatus and robust experimental procedure to measure precisely gas/oil IFT using pendant drop technique and analyze the images based on Axisymmetric Drop Shape Analysis method. Initially, all phases were brought into equilibrium at experimental conditions and the density of each phase was measured. To measure IFT for each pair of fluids, an IFT cell was almost filled with the gas phase, and the live crude oil was then injected to create a pendant drop. The image was captured, using a microscope attached to a digital camera, and analyzed with Drop Analysis System software to determine the interfacial tensions. The densitometer and the IFT measurement apparatuses were all calibrated using reference fluids.We tried to spotlight the effects of pressure, temperature and composition on interfacial tensions. The findings show that effects of pressure are more profound on IFT rather than temperature. As pressure increases, particularly at low pressure conditions, the gas-oil interfacial tension declines with a descending trend. This behavior continues even at higher pressure with smaller rates. Increases in temperature increase the interfacial tensions as well. The effects of pressure and temperature are linked to the changes in density contrast, mutual gas-oil solubility, and miscibility development. The IFT variation can also be affected by the oil composition and therefore the trends and/or IFT values might change from one fluid system to another. The effects of composition are found to have significant effects on IFT, which depend on the phase envelope of the sample.

Measurements and Modeling of Interfacial Tension for CO2/CH4/Brine Systems under Reservoir Conditions

Supercritical CO2 injection is a promising way to hydraulically fracture tight/shale gas formations as well as enhance gas recovery from these formations. Understanding of phase behavior and interfacial tension (IFT) of CO2/CH4/brine (NaCl) systems is important, because they affect the performance of such a process in tight/shale gas formations. In this study, we employ the axisymmetric drop shape analysis (ADSA) method to measure the IFT between CO2/CH4 mixtures and brine over the temperature range from 77.0 to 257.0 °F and the pressure range from 15 to 5027 psia. Test results show that the presence of CO2 decreases the IFT of CH4/H2O or CH4/brine (NaCl) systems, while the degree of reduction depends on the molar fraction of CO2 in the gas mixture. Salinity tends to cause an increase in IFT of CO2/CH4/brine (NaCl) systems; a higher salinity leads to an increased IFT for a given system. On the basis of the Parachor model (Weinaug and Katz J. Ind. Eng. Chem. 1943, 35, 239) and Firoozabadi’s model (Firoozab...

Experimental investigation of miscibility conditions of dead and live asphaltenic crude oil\u2013CO2 systems

Carbon dioxide (CO2) injection is a well-established enhanced oil recovery method. The optimization process of CO2 injection is usually performed through estimation of two physical properties, i.e., minimum miscibility and first-contact miscibility pressures (MMP and FCMP) for the crude oil–CO2 system. In this experimental study, the equilibrium IFT of the crude oil–CO2 system is measured at (313.15 and 323.15 K) for two oil types (i.e., live and dead crude oil) using the axisymmetric pendant drop shape analysis method. Vanishing interfacial tension technique is also applied to estimate the MMP and FCMP. The experimental results demonstrate that IFT decreases with different trends as the equilibrium pressure increases for the systems of live oil/CO2 and dead oil/CO2 systems. The IFT test results demonstrate that the estimated MMP and FCMP values of crude oil–CO2 system increase with temperature. It was also observed that the presence of methane gas in the oil phase increases the MMP value, whereas it decreases the FCMP.

Collagen-surfactant mixtures at fluid/fluid interfaces

The effect of three synthetic surfactants on surface activity and surface dilatational rheology of temperature-denatured type I collagen at water/air interface is described. An anionic (sodium dodecyl sulfate, SDS), a cationic (cetyltrimethylammonium bromide, CTAB) and a nonionic (Triton X-100, TX-100) surfactants were employed at variable concentrations (5×10−6molL−1–1×10−4molL−1). With the protein concentration fixed at 5×10−6molL−1, the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:3, 1:5, 1:10 and 1:20 were obtained. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic and equilibrium surface tension, as well as the surface dilatational moduli of the mixed adsorption layers formed at the water/air interface at pH 4.5. For the collagen-SDS mixtures, analogous studies were also performed at the water/tetradecane and water/olive oil interfaces. These results were complemented with the foam and emulsion formation ability tests, and the oil-in-water emulsions were characterized using Dynamic Light Scattering (DLS) and visual assessment.The most beneficial effect on surface activity, mechanical properties of adsorbed layer and foaming ability was observed for the mixtures of temperature-denatured collagen with SDS. The rheological parameters of the adsorbed layers formed by the same mixtures at the water/olive oil and water/tetradecane interfaces worsened significantly (values of rheological parameters E’ and E” are lower than values of E’ and E” of the adsorbed layers formed at the water/air interface). The corresponding emulsions, despite very low interfacial tension values, phase-separated within hours. We hypothesize that the poor kinetic stability was caused by flocculation due to collagen bridging between the oil droplets, resulting in emulsion creaming.

Effect of surfactants on surface activity and rheological properties of type I collagen at air/water interface

We describe the effect of three synthetic surfactants (anionic – sodium dodecyl sulfate (SDS), cationic – cetyltrimethylammonium bromide (CTAB) and nonionic – Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5×10−6molL−1 and the surfactant concentration was varied in the range 5×10−6molL−1–1×10−4molL−1, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV–vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC).Modification of the collagen structure by SDS at low surfactant/protein ratios has a positive effect on the mixture’s surface activity with only minor deterioration of the rheological properties of the adsorbed layers. The collagen/CTAB mixtures do not show that pronounced improvement in surface activity, while rheological properties are significantly deteriorated. The mixtures with non-ionic TX-100 do not show any synergistic effects in surface activity.