Polymer-surfactant Interactions Research Articles

Relationship between polymer-surfactant interaction and micellar solubilization revealed by NMR spectroscopy

Micellar solubilization is considered as a key factor affecting the recovery efficiency in chemically enhanced oil recovery (cEOR). However, it is poorly understood how polymers in surfactant-polymer (SP) flooding influences the micellar solubilization. Guar gum (GG) and hydroxyethyl cellulose (HEC) are two important and widely used polysaccharide polymers. In this work, the effect of GG and HEC on the solubilization of a crude oil model compound methyl benzoate (MB) in anionic sodium dodecyl sulfate (SDS) micelles and the underlying mechanism were explored at the molecular scale by NMR spectroscopy. GG and HEC slightly increased the MB solubility in SDS micelles but did not change the solubilization capacity. No correlation peak was observed to demonstrate the attractive interaction between polymer and SDS. After examination, there is weak electrostatic repulsion between HEC/GG and SDS, which made the polymer independent from SDS micelles and was unable to participate in the formation of micelles to alter micellar structure and solubilization behavior. Although the solubility of MB was slightly increased, this increase should originate from weak molecular interactions between polymers, surfactants and hydrophobic molecules, including hydrogen bonding, van der Waals forces and hydrophobic interactions, etc. In summary, without strong electrostatic attraction between polymer and surfactant, the solubilization of polymers and the solubilization of micelles proceed independently, resulting in that the solubilization capacity of SDS micelles was not improved.

Effects of polymer-surfactant interactions on drag reduction performance and mechanisms: Molecular dynamics simulations and experimentation

This work provides a more favorable implementation of synergistic drag reduction strategies based on molecular simulations of the strength of polymer-surfactant interactions. The simulated preferred system identifies polyethylene oxide (PEO) and guar gum (GG) as polymers, and dodecyl dimethyl benzyl ammonium chloride (DDBAC) and dodecyl hydroxy sulfobetaine (DHSB). To forecast the drag reduction capability and identify the drag reduction process, important elements such as aggregation phenomena, charge distribution, shear deformation, and interfacial behavior were examined. Experimental measurements of viscosity, surface tension, and drag reduction validate the interactions. It was found that the compound system demonstrates enhanced viscosity, surface tension, and drag reduction efficiency compared to individual systems. The PEO-DHSB system achieves a drag reduction rate of 63.68% during initial flow, while the GG-DHSB system maintains a rate of 47.26% even after prolonged water circulation. This work visualizes the poly-surface aggregation phenomenon using the density distribution of surfactant hydrophobic tail chains, dynamically demonstrating the deformation of polymer and surfactant molecules during the shear process and interfacial behavior, and providing molecular-scale intuitive insights for understanding the drag reduction mechanism of poly-surface systems. Meanwhile, by comparing the effects of molecular type and structure on poly-surface interactions and drag reduction performance, it provides a theoretical foundation for the development and application of subsequent poly-surface drag reduction schemes, thereby broadening the application of drag reduction technology in the field of energy conservation and emission reduction.

Optimization of surfactant-polymer flooding for enhanced oil recovery

Chemical enhanced oil recovery applications continue to face a variety of obstacles, particularly in high saline and high-temperature reservoirs, in addition to high chemical prices. This issue creates difficulty in developing optimal recipes that can withstand these extreme circumstances and so achieve maximal hydrocarbon recovery at the lowest feasible cost. The usefulness of surfactant polymer (SP) in mobilizing oil and increasing sweep efficiency in carbonate rocks is assessed in this article. A thermo-viscosifying polymer and an acrylamido tertiary butyl sulfonate (ATBS)/acrylamide (AM) copolymer were employed. Surfactants of various grades of amphoteric carboxybetain are used. These potential chemicals were chosen after a thorough study of previous research, which included long-term thermal stability, fluid rheology, interfacial tension, adsorption, and microfluidic tests. The contact angles were measured using a captive drop analyzer at high pressure and high temperature. The core-flooding experiments for slug size and injection sequence optimization were carried out using 12-inch long and 1.5-inch diameter limestone cores. For two weeks, the samples were aged. The trials were carried out at 90 °C. The seawater (SW) salinity utilized in the injection was 57,000 ppm. The findings highlighted the importance of surfactant-polymer interactions in wettability and fluid rheology. The best chemical combination was carboxybetaine (0.05 wt%) and ATBS/AM (0.25 wt%) which recovered 31.29% of the residual oil saturation (ROS), or 11.63% of the original oil in place (OIIP). The optimal slug size was 3.5 PV, which recovered 34.21% of the ROS and 17.05% of the OIIP. The optimum injection sequence was the co-injection of surfactant and polymer SW-S1P1-SW, which extracted 31.29% of the ROS and 11.63% of the OIIP. The recoveries were discovered to be related to the slug’s size. The chemical injection sequence was critical to the eventual oil recovery. Among the other sequences, SW-SP-SW had the highest recovery (SW-P-S-SW, SW-S-SW-P-SW, and SW-P-SW-S-SW). This is thought to be owing to the compounds' synergistic impact. We found that there is no systematic optimization process that combines the effect of chemicals, slug size, and sequence in one study, which gave us the motivation to cover the research gap.

Colloidal Deposition by Polymer-Surfactant Complexes with Dilution and Shear.

Deposition of silica microparticles on glass substrates was measured as a function of cationic polymer-anionic surfactant composition and shear rate. Particles were initially deposited in quiescent conditions in different polymer-surfactant compositions, which were chosen based on prior measurements of composition-dependent polymer-surfactant interactions and deposition behavior (up to 0.5 wt % polymer and 12 wt % surfactant). Programmed shear and dilution profiles in a flow cell together with optical microscopy observation were used to continuously track particle deposition, detachment, and redeposition. Knowledge of the shear-dependent torque on each particle provides information on adhesive torque mediated by polymer-surfactant complexes. Detachment of colloids initially deposited by depletion interactions occurs at low shear rates (∼100 s-1) due to lack of tangential forces or an adhesive torque. Further dilution produced redeposition of particles that resisted detachment (up to ∼2000 s-1) as the result of strong cationic polymer bridge formation, presumably due to preferential surfactant removal. Dilution from different initial compositions indicates a pathway dependence of polymer-surfactant de-complexation into shear-resistant cationic bridges. These findings demonstrate the ability to program deposition behavior via the informed design of initial polymer-surfactant compositions and shear profiles. The particle trajectory analysis developed in this work provides an assay to screen composition-dependent colloidal deposition in diverse materials and applications.

Chitosan derivatives as surfactant carriers for enhanced oil recovery – Experimental and molecular dynamic evaluations of polymer-surfactant interactions

Surfactant injections in enhanced oil recovery (EOR) are very efficient, lowering the oil-water interfacial tension (IFT) and altering rocks wettability. Although efficient, surfactant injection during EOR process is economically unfeasible due to the high-cost caused by surfactant losses due to adsorption or precipitation on the rock surface. One strategy to reduce these losses during the flooding process is using surfactant carriers such as nanoparticles, emulsions, and polymers. Polymers are good candidates because they can act in transportation, alter rock wettability, and improve sweeping efficiency. Recently, the potential of chitosan derivatives as wettability modifiers of carbonate rocks was demonstrated. This way, using chitosan derivatives as surfactant carriers is an interesting strategy due to its high storage capacity and environment-friendly product. In this study, cationized (TMC) and hydrophobized (TMC-C14) chitosan derivatives were synthesized, characterized, and evaluated as OADA (oleic acid diethanolamide) surfactant carriers for EOR. Interfacial tension tests evaluated the potential of OADA in low and high salinity medium. Particle size measurements, done by dynamic light scattering, and molecular dynamics simulations (MD), allowed the understanding of the interaction between TMC or TMC-C14 and the surfactant. The controlled surfactant release at the water/oil interface by chitosan derivatives was evaluated by IFT measurements and MD simulations. The results showed that OADA is an excellent surfactant whose IFT reaches 10−2 mN/m, and chitosan derivatives were able to carry the surfactant to the site containing the oil. Thus, chitosan derivatives are an efficient supramolecular surfactant carrier system that can minimize surfactant losses by adsorption on the rock surface, being an interesting alternative for EOR application.

Krafft phenomenon-based study of the polymer-surfactant interaction

Krafft phenomenon-based study of the polymer-surfactant interaction

Anti-swelling hydrogels based on surfactant–polymer interactions for underwater sensing with excellent mechanical properties

We synthesized an anti-swelling, tough, double-crosslinked, dual-network hydrogel, P(AA-SMA)-CMC-Na, for underwater sensing.

Polymer enhanced foam for improving oil recovery in oil-wet carbonate reservoirs: A proof of concept and insights into the polymer-surfactant interactions

The feasibility of polymer enhanced foam (PEF) for enhanced oil recovery (EOR) in a strongly oil-wet and heterogeneous carbonate reservoir with medium temperature (131 °F) and high salinity was experimentally investigated. An Alkyl Poly-Glycoside (APG) surfactant was firstly selected because of its prominent foam behavior in oil-wet carbonates. The effect of polymer type, flow rate and brine composition on foam strength and stability were systematically investigated, aiming to understand how the interactions between polymer and surfactant could influence the transport behavior and performance of PEF in porous media. It was found that, with either an associative polymer or a nonionic polymer (PAM), the foam strength and foam stability could be largely enhanced, both in the absence and in the presence of oil. A significant improvement in oil recovery efficiency was obtained for PEF with an associative polymer, approximately 5% higher than that achieved for conventional polymer-free foam. The PEF behavior is intimately dependent on the interactions between the polymer and the surfactant. It is hypothesized that the increased foam strength by adding polymer at oil-wet conditions may be resulted from an increase of aqueous phase viscosity, the wettability alteration from oil-wet to less oil-wet, the generation of a highly viscoelastic film and (or) the creation of a more stable pseudo-emulsion film. This study provides a robust approach for PEF mobility control and reservoir conformance in oil-wet and heterogeneous carbonate reservoir under analogous reservoir conditions.

Solubilization of pyrene by mixed polymer-cationic/nonionic surfactant systems: Effect of polymer concentration

Polymers can be used to alter the ability of surfactant micelles to solubilize PAHs depending upon polymer–surfactant interactions. The focus of this study is to investigate the solubilization ability of the mixtures of anionic polymer sodium carboxymethyl cellulose (NaCMC) with nonionic polyoxyethylene [10] cetyl ether (Brij 56) and cationic cetyltrimethylammonium bromide (CTAB) surfactant micelles towards pyrene (PAH). Solubilization efficiency of these mixed systems and their comparison with individual systems has been quantified in terms of the molar solubilization ratio, micelle - water partition coefficient and free energy of solubilization. While the addition of anionic polymer NaCMC accelerates the solubilization capacity of cationic CTAB micelles, that of nonionic Brij56 micelles was retarded. Moreover, enhancement in the solubilization capacity of the above said mixed systems is observed as the polymer concentration changes from below overlap (i.e.; 0.5 %) to overlap (i.e.; %).

Visualization of Polymer-Surfactant Interaction by Dual-Emissive Gold Nanocluster Labeling.

Polymer-surfactant interaction decides the performance of corresponding complexes, making its rapid and intuitionistic visualization important for enhancing the performance of products and/or processing in related fields. In this study, the fluorescence visualization of the interaction between cationic hyperbranched polyethyleneimine and anionic sodium dodecyl sulfonate surfactant was realized by dual-emissive gold nanocluster labeling. The sensing mechanism was due to the interaction-induced polymer conformation change, which regulated the molecular structure and subsequent photoradiation process of the gold nanoclusters. All three inflection points of the interactions between the polymers and the surfactants were obtained by the change in fluorescence emission ratio of the designed dual-emissive gold nanoclusters. Moreover, these inflection points are verified by the hydrodynamic diameter and zeta potential measurements.

Influence of surfactants on the electrospinnability of lignin-PVP solutions and subsequent oil structuring properties of nanofiber mats

This work focuses on the improvement of the electrospinnability of low-sulfonate lignin (LSL)/polyvinylpyrrolidone (PVP) solutions by the addition of surfactants (SDS, CTAB and Tween-20) as well as on the ability of resulting nanofibers to structure castor oil. Solutions with two LSL/PVP weight ratios (70:30 and 90:10) in DMF were prepared by adding variable surfactant concentrations (0–1 wt.%), and physicochemically characterized. Electrical conductivity, surface tension and rheological measurements were performed. Variations of these physicochemical properties were explained on the basis of surfactant-polymer interactions. The addition of surfactants to LSL/PVP solutions improves electrospinnability, producing more compact and uniform fiber mats in 70:30 LSL/PVP systems, generally reducing the average diameter of the nanofibers and the number of beads. In contrast, nanofiber mats were not obtained with 90:10 LSL/PVP solutions, but different nanostructures composed of particle clusters. Dispersions of nanofiber mats obtained by electrospinning from 70:30 LSL/PVP solutions in castor oil were able to generate physically stable strong oleogels. In general, linear viscoelastic functions of oleogels increased with surfactant concentration. In addition, these oleogels exhibited excellent lubrication performance in a tribological contact, with extremely low values of the friction coefficient and wear diameters, which may lead to potential applications as lubricants.

Tough, Anti-Swelling Supramolecular Hydrogels Mediated by Surfactant-Polymer Interactions for Underwater Sensors.

It is a great challenge for traditional hydrogel-based sensors to be effective underwater due to unsatisfactory water resistance and insufficient wet adhesion. Herein, a tough supramolecular hydrogel aiming at underwater sensing is prepared by the modification of hydrophilic poly(acrylic acid) (PAA) with a small amount of hydrophobic lauryl methacrylate (LMA) in the presence of high concentrations of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Owing to the synergistic effects of the electrostatic interactions and hydrophobic associations of CTAB with the P(AA-co-LMA) copolymer, the hydrogel with a water content of approximately 58.5 wt % demonstrates outstanding anti-swelling feature, superior tensile strength (≈1.6 MPa), large stretchability (>900%), rapid room-temperature self-recovery (≈3 min at 100% strain), and robust wet adhesion to diverse substrates. Moreover, the strain sensor based on the hydrogel displays keen sensitivity in a sensing range of 0-900% (gauge factor is 0.42, 3.44, 5.44, and 7.39 in the strain range of 0-100, 100-300, 300-500, and 500-900%, respectively) and pronounced stability both in air and underwater. Additionally, the hydrogel can be easily recycled by dissolving in anhydrous ethanol. This work provides a facile strategy to fabricate eco-friendly, tough supramolecular hydrogels for underwater sensing.

Application of a novel amphiphilic polymer for enhanced offshore heavy oil recovery: Mechanistic study and core displacement test

A molecular modified polyacrylamide with Gemini surfactant monomers, named as HA1, was evaluated in this paper as an alternative to enhance the offshore heavy oil recovery. The physical properties of HA1 solution including apparent viscosity, rheological properties, static adsorption, interfacial activities (IFT, interfacial visco-elasticity and contact angle), emulsification ability, as well as oil recovery capacity were comprehensively investigated. Our results indicate that due to the hydrophobic and Gemini surfactant monomers on the acrylamide backbone, this novel amphiphilic polymer possesses more advanced functions than conventional polymers. HA1 demonstrates pronounced aqueous-phase viscosifying ability by forming 3D network in solution when the concentration is above CAC. In addition, the IFT, interfacial visco-elasticity and contact angle response illustrate that HA1 interacts strongly with the oil-phase which gives rise to its significant interfacial activity. Thereby, HA1 is able to reduce the heavy oil viscosity by emulsifying oil into water phase even at relatively low water content (20%) and also avoids dehydration difficulty by reducing the oil-brine interfacial rigidity. Furthermore, the asphaltene morphology change due to HA1 observed by SEM and AFM proves that HA1 can disperse the asphaltene aggregates in the crude oil, leading to a direct reduction of the heavy oil viscosity. At last, the coreflooding in an artificially synthesized triple-layered porous media shows that HA1 gives rise to an additional oil recovery of 27.04%, at the optimum concentration of 1600 ppm, by improving sweep efficiency, microscopic efficiency and dispersion of the asphaltene aggregates. Therefore, the potential of HA1 to enhance heavy oil recovery is comparable to traditional multi-component polymer-surfactant flooding. Since HA1 is single-component, it can also mitigate incompatibility issues like chromatography separation and surfactant-polymer interactions. Overall, this new self-assembly system shows potential for applications in heavy oil recovery.

Synergistic Behavior of Anionic Surfactants and Hydrolyzed Polyacrylamide under an Extensional Field: Effect of Hydrophobicity.

Surfactant-polymer interaction has been studied by many academic and industrial researchers. Associative polymers have attracted attention, especially in enhanced oil recovery due to their ability to generate higher resistance than parental polyacrylamide (HPAM) at a lower concentration. The effect of hydrophobicity on the associative polymer-surfactant interaction has been studied through many means including rheology. Previous rheological studies were restricted to shear-based behavior, and no efforts were undertaken to study the effect of hydrophobicity on the extensional rheological behavior of the surfactant-HPAM system. In this work, the extensional behavior of anionic surfactant-polyacrylamide systems was studied for varying levels of hydrophobicity. The concentration of the surfactant used in the surfactant-polymer formulation ranged from 0 to 0.3%, and the polymer concentration was fixed at 1000 ppm. Extensional rheology was performed using a capillary breakup extensional rheometer. Surface tension studies were also conducted. The results revealed that the parental HPAM-surfactant system shows the maximum extensional viscosity for the concentration range studied here. This is contrary to shear behavior reported in the literature, and it appears that electrostatic repulsive interaction associated with HPAM-surfactant systems becomes dominant in the extensional field. Associative polymer-surfactant systems characterized by higher hydrophobicity showed the least maximum extensional viscosity, as opposed to the literature-reported behavior in the shear field. Hydrophobic interaction associated with associative polymer-surfactant systems appears to become weaker in the extensional field.

Effect of methanol on surfactants and surfactant–PEO mixtures

AbstractMethanol–water system possesses unusual interactions, which may affect surfactant self‐assembly. The main objective of this study was to investigate the interactions and aggregation behavior of ionic surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) and their equimolar catanionic binary mixtures (CAM) and their ternary mixtures with poly(ethylene oxide) (PEO) in aqueous solutions containing different volume percentages of methanol. Conductometry, surface tensiometry, and dynamic light scattering were employed for this purpose. The aggregation in all the systems showed methanol‐dependent patterns. The maximum shifts observed in the critical aggregation concentrations were 5.5, 2.7, 6.3, 4.1, and 4.4 mM, respectively, for SDS, CTAB, CAM, SDS/PEO, and CTAB/PEO systems for variation in MeOH from 5% to 30% v/v. The change in dielectric of the media and chaotropic nature of methanol was responsible for alteration in self‐assembly. The nature of surfactant especially and head group hydrophobicity also played a significant role in the process. The maximum change in area per molecule (i.e., ~4 nm2) occurred for CTAB/PEO system. The aggregation was delayed in surfactant solutions; however, the presence of polymer induced aggregation due to favorable polymer–surfactant interactions involving the surfactant adsorption onto polymer chains and formation of mixed aggregates. The hydrodynamic radii for CTAB/PEO systems, which were nearly 10 times greater than those recorded for SDS/PEO, showed the transition of system to nonspherical aggregated states. In short, the presence of methanol retarded the aggregation in surfactant and surfactant–polymer systems.

EFFECTS OF POLYMER CONCENTRATION AND TEMPERATURE ON MICELLIZATION OF CETYLTRIMETHYLAMMNIUM BROMIDE (CTAB) IN AQUEOUS PVP-CTAB MIXED SYSTEM

Polymeric micelles supply an environment, which can be cautiously regulated for drug delivery. The self-assembly of polymeric micellization is dynamic. Micellization thermodynamic describes how the system defines the formation of micelles. The present study enables the micellization behavior of the surfactants in the presence of polymer to be examined by conductometric and tensiometric methods. The effects of polymer concentration and temperature on the micellization thermodynamics of a neutral soluble polymer and cationic cetyltrimethylammomium bromide (CTAB) surfactant mixture in aqueous medium were investigated. To examine polymer-surfactant interaction, critical micellar concentration (CMC) and thermodynamic parameters such as standard free energy ∆G, enthalpy ∆H and entropy ∆S are calculated by using a pseudo-phase model. Based on CMC, ΔG, ΔH and ΔH, the dependence of the compensation temperature on the polymer effect is discussed. This advanced work to understand micelle stability and compatibility can be comprehensively feasible in polymeric systems.

Interfacial complexation of a neutral amphiphilic ‘tardigrade’ co-polymer with a cationic surfactant: Transition from synergy to competition

HypothesisNeutral amphiphilic PEG-g-PVAc co-polymer (a “tardigrade” polymer consisting of a hydrophilic polyethylene glycol, PEG, backbone with hydrophobic polyvinyl acetate, PVAc, grafts) can form complexes at the air–water interface with cationic dodecyltrimethylammonium bromide (DTAB) via self-assembly. Compared to anionic SDS, cationic DTAB headgroups are expected to interact strongly with the negatively charged OH– groups from the partial dissociation of the PVAc grafts. We anticipate a transition from synergistic to competitive behaviour, which is expected to be dependent on the surfactant structural characteristics and concentration. ExperimentsDTAB/PEG-g-PVAc mixtures were investigated using a combination of dynamic and equilibrium surface tension measurements, neutron reflectivity (NR) at the air–water interface, and foaming tests. We varied the concentrations of both the DTAB (0.05 to 5 critical micelle concentration, cmc) and that of PEG-g-PVAc (0.2 and 2 critical aggregation concentration, cac). FindingsOur results show that the interfacial interactions between DTAB and PEG-g-PVAc were both synergistic and antagonistic, depending sensitively on the surfactant concentration. At DTAB concentrations below its cmc, a pronounced cooperative adsorption behaviour was likely driven by the hydrophobic interactions between the DTAB tail and the PVAc grafts and the attraction between the DTAB headgroups and the partially dissociated –O- groups in the partially hydrolysed PVAc grafts, forming a mixed layer. This synergistic adsorption behaviour transitioned to a competitive adsorption behaviour at DTAB concentrations above its cmc, leading to polymer-surfactant partition, forming a “hanging” polymer layer underlying a surfactant monolayer at the interface. We postulate that DTAB/PEG-g-PVAc complexation in the bulk contributed to partial depletion of the mixture from the interface. We therefore consider this polymer/surfactant system to be a moderately interacting system at the air–water interface. No discernible differences in the foaming behaviour were observed between the DTAB/PEG-g-PVAc systems and the pure surfactant. Our results suggest that surfactant headgroup characteristics (particularly charges) were crucial in determining the structure and composition of polymer-surfactant complexes at the air–water interface, as well as the foamability and foam stability, whilst the coexistence of the synergistic and competitive adsorption behaviour is attributed to the unique architecture of the tardigrade polymer with amphiphilicity and partial charge, facilitating different surfactant-polymer interactions at different DTAB concentrations.

Polymer Surfactant Interactions in Oil Enhanced Recovery Processes

A soil decontamination or enhanced oil recovery procedure typically requires the injection of a surfactant solution to reduce interfacial tension and promote oil recovery at the pore level, followed by the injection of a polymer solution to avoid the creation of preferential pathways and perform a homogeneous sweep of the reservoir. It is well known that polymers and surfactants interact with each other to form aggregates if they are of opposite charge or due to depletion interactions. To date, it is recommended to use polymers and surfactants that do not interact with each other to avoid clogging the wells. We show here that this precaution is not necessary and that in some cases, the use of interacting polymer and surfactant systems can even be an advantage for oil recovery. Contrary to previous studies, we injected previously mixed and homogeneous formulations into the porous medium and not a sequence of surfactant and polymer plugs. In addition to a total recovery of the oil in place, this strategy allows to limit the adsorption of the surfactant in the pore.

A conductivity and cloud point investigation of interaction of cationic and non-ionic surfactants with sodium carboxymethyl cellulose: effect of polyols and urea

Surfactants and polymers are widely used chemicals in different applied fields like pharmaceutical, textile, food, and cosmetic industries. Therefore, the study of surfactant–polymer interaction can improve their activity in related applied fields. Herein, we studied the interaction of polymer, sodium carboxymethyl cellulose (SCMC) with two surfactants. The interaction of SCMC with cetyltrimethylammonium bromide (CTAB), a cationic surfactant, was assessed through conductivity measurement technique, while the interaction between non-ionic surfactant, Triton X-100 (TX-100) and SCMC was assessed by cloud point (CP) analysis. The effect of different organic additives (glucose, maltose, and urea) on the micellar behavior of the CTAB + SCMC mixture and phase partitioning behavior of TX-100 + SCMC mixture was investigated. The critical micelle concentration (cmc) of the CTAB + SCMC system having 0.3 mmolkg−1 SCMC was augmented linearly as a function of temperature and concentration of organic additives. The cmc values of CTAB + SCMC system increased from 1.28 to 1.44 mmolkg−1 and 1.18 to 1.33 mmolkg−1 with the increase in concentration from 0.1 to 8.0 mmolkg−1 of glucose and maltose, respectively. The extent of counterion binding (β) was obtained to be temperature-dependent. The CP values of TX-100 + SCMC were experienced to be reduced up to a certain concentration of glucose/maltose and then augment with enhancing the concentration of glucose and maltose, while the CP values increased monotonically with the concentration of urea. The Gibbs free energy values indicate the spontaneous micellization of the CTAB + SCMC system and non-spontaneous phase partitioning of the TX-100 + SCMC system. The enthalpy and entropy change as well as their compensation were studied and explained with proper explanation.

Isothermal titration calorimetry (ITC): a standard operating procedure (SOP)

Isothermal titration calorimetry (ITC) is currently widely used in many applied areas of research, spanning protein-ligand binding, metal-ligand interactions, DNA/DNA or protein/DNA interactions, partition to membranes, and polymer surfactant interactions, to mention just a few. This is due to the availability of commercial instruments, and thus the production and spread of an accepted and widely followed SOP is felt by most users,in an effort to produce results that are scientifically correct and comparable. Therefore, within the efforts of Working Group 4 of the ARBRE-MOBIEU COST Action (CA15126), this ITC SOP was generated, alongside SOPs for several other biophysical techniques. Here, we discuss the factors that are fundamental for good experimental design and that need to be carefully considered, as well as machine calibration, in particular chemical calibration, linked to another outcome of Working Group 4 on ITC benchmarking, to be also published in this Special Issue.