Commercial Surfactants Research Articles

Development of Polyoxyethylene Zwitterionic Surfactants for High‐Salinity High‐Temperature Reservoirs

AbstractSubstantial efforts are underway to improve the recovery factor from existing oil reserves to meet the ever‐growing global oil demand. Surfactants are known to increase oil recovery through reducing interfacial tension (IFT) and/or altering the rock wettability. The selection of surfactants for high‐salinity high‐temperature oil fields is a challenging task owing to poor thermal stability, precipitation, and adsorption of surfactants on reservoir rocks. Sulfobetaine‐based polyoxyethylene zwitterionic surfactants have shown excellent thermal and surface properties. However, their solubility in high‐salinity brines becomes poor particularly with a long hydrophobic tail (>C17). Recently, we synthesized such types of surfactants by incorporating ethylene oxide (EO) units into the hydrophobic tail, which improved the solubility in formation water (213,734 ppm) and seawater (SW) (57,643 ppm). In this work, we investigated the IFT, thermal stability, rheological behavior, and foaming properties of two polyoxyethylene zwitterionic surfactants having different degrees of ethoxylation. Aging experiments exhibited excellent thermal stability and no change in the chemical structure was detected. The surfactant with lesser EO units (EASB‐1a) showed a lower IFT compared to the surfactant with higher EO units (EASB‐1b). Rheological studies revealed that the addition of both surfactants reduced the viscosity of the acrylamide copolymer. However, the effect of EASB‐1a was more prominent compared to that of EASB‐1b. The surfactant with a higher degree of ethoxylation showed lower adsorption compared to the surfactant with a lesser degree of ethoxylation. Both surfactants showed excellent foamability and foam stability compared to the commercial surfactants. Excellent thermal stability, water solubility under harsh reservoir conditions, foaming properties, and lower adsorption make them a suitable choice for high‐temperature, high‐salinity reservoirs.

Hydrodynamics and energy analysis of heavy crude oil transportation through horizontal pipelines using novel surfactant

Improvement of flow properties of crude oil through pipelines, the effect of temperature, diameter, water cut, and novel extracted surfactant on pressure drop, shear viscosity was studied along with energy analysis. The impact of diameter, temperature, and the addition of novel surfactant extracted from Madhuca longifolia (Mahua) on pressure drop, shear viscosity, pumping power saving and flow increment were investigated during heavy crude oil flow in horizontal pipelines. Minimum pressure drop was observed in 0.0508 m ID pipeline owing to the collective effect of temperature and 2000 ppm Mahua during the flow of 85% heavy crude oil+15% water. Shear viscosity reduced appreciably in 0.0381 m and 0.0508 m ID pipelines after addition of 2000 ppm Mahua at a temperature of 50 °C. Maximum power saving (130.8%) was achieved and maximum flow increment of 121.8% was accomplished after addition of 2000 ppm Mahua to 85% heavy oil and 15% water mixture during its transportation in 0.0508 m ID pipeline at a 50 °C and at the rate of 7.2 m3/hr. The natural surfactant is substantially efficient to decrease the pumping power consumption for heavy crude oil transportation. It was concluded that the extracted novel natural surfactant is very beneficial for being used as an emulsifier, viscosity reducer, flow improver and also an alternative for the commercial surfactant.

Modification of a Poly(tetrafluoroethylene) Porous Membrane to Superhydrophilicity with Improved Durability

AbstractThe commercial fluorocarbon surfactant (FCS) DuPont™ Zonyl 321 fluorinated cationic surfactants, was employed to modify both flat‐sheet and hollow‐fiber poly(tetrafluoroethylene) (PTFE) porous membranes. The variation of morphology, wettability, and hydrophilicity durability to acid and alkali as well as the filtration performance of both membranes were investigated. Such superhydrophilic membranes showed better wetting stability and higher resistance to acid and alkali solutions. Moreover, both membranes exhibited good filtration performance.

Surfactants with aromatic headgroups for optimizing properties of graphene/natural rubber latex composites (NRL): Surfactants with aromatic amine polar heads

HypothesisThe compatibility of surfactants and graphene surfaces can be improved by increasing the number of aromatic groups in the surfactants. Including aniline in the structure may improve the compatibility between surfactant and graphene further still. Surfactants can be modified by incorporating aromatic groups in the hydrophobic chains or hydrophilic headgroups. Therefore, it is of interest to investigate the effects of employing anilinium based surfactants to disperse graphene nanoplatelets (GNPs) in natural rubber latex (NRL) for the fabrication of electrically conductive nanocomposites. ExperimentsNew graphene-philic surfactants carrying aromatic moieties in the hydrophilic headgroups and hydrophobic tails were synthesized by swapping the traditional sodium counterion with anilinium. 1H NMR spectroscopy was used to characterize the surfactants. These custom-made surfactants were used to assist the dispersion of GNPs in natural rubber latex matrices for the preparation of conductive nanocomposites. The properties of nanocomposites with the new anilinium surfactants were compared with commercial sodium surfactant sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and the previously synthesized aromatic tri-chain sodium surfactant TC3Ph3 (sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate). Structural properties of the nanocomposites were studied using Raman spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Electrical conductivity measurements and Zeta potential measurements were used to assess the relationships between total number of aromatic groups in the surfactant molecular structure and nanocomposite properties. The self-assembly structure of surfactants in aqueous systems and GNP dispersions was assessed using small-angle neutron scattering (SANS). FindingsAmong these different surfactants, the anilinium version of TC3Ph3 namely TC3Ph3-AN (anilinium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate) was shown to be highly efficient for dispersing GNPs in the NRL matrices, increasing electrical conductivity eleven orders of magnitude higher than the neat rubber latex. Comparisons between the sodium and anilinium surfactants show significant differences in the final properties of the nanocomposites. In general, the strategy of increasing the number of surfactant-borne aromatic groups by incorporating anilinium ions in surfactant headgroups appears to be effective.

Organosilane surfactant-directed synthesis of nanosheet-assembled SAPO-34 zeolites with improved MTO catalytic performance

Hierarchical SAPO-34 zeolites with a special nanosheet-assembled morphology were hydrothermally synthesized under dynamic condition by using the commercial quaternary ammonium-type organosilane surfactant [3-(trimethoxysilyl) propyl] octadecyldimethyl-ammonium chloride (TPOAC) for the mesoscopic aggregation and tetraethylammonium hydroxide as the micropore structure-directing agent. The growth evolution during the crystallization process and governing factors including TPOAC content and dynamic hydrothermal condition in the synthesis were discussed in detail, and the possible nucleation and growth process were proposed as well. With a systematic structure characterization by XRD, FTIR, N2 adsorption–desorption, ICP, SEM, TEM, NH3-TPD and pyridine-adsorbed IR measurements, the nanosheet-assembled SAPO-34 (NA-SP34) prepared under the optimized synthesis condition presented the pure phase of CHA framework, high degree of crystallinity, interconnected hierarchical meso-/microporosity and relatively weak acidity comparing with the conventional microporous SAPO-34 (CM-SP34) with micron size and the nanosheet-like SAPO-34 (NL-SP34) synthesized in the absence of TPOAC. Moreover, the catalytic performances evaluated by the methanol-to-olefin reaction indicated that the optimal NA-SP34 catalyst presented remarkable improvements of not only much longer catalytic lifetime (300 min) and slower coke formation rate (0.24 mg g−1 min−1) but also higher ethylene and propylene selectivity (81.93%) comparing with those (95 min, 0.55 mg g−1 min−1 and 80.75%, respectively) of CM-SP34, which can be attributed to the integrated balance of well-remained microporosity, considerable mesoporosity and suitable weak acidity.

Investigations on Natural Surfactant obtained from Soap-Nuts through Spectrophotometric Interactions with Congo Red and Comparison with Commercial Surfactants

A natural surfactant (NS) of plant-base was obtained from the fruit pericarp of soapnuts by using a simple and economical method. The interaction of this natural surfactant with direct dye, anionic dye, Congo red (CR) was studied spectrophotometrically in sub-micellar and micelle concentration range in aqueous solution. These interactions (CR-NS) were compared with that of CR-CTAB (cationic surfactant-cetyl trimethylammonium bromide, CTAB), CR-SDS (anionic surfactant-sodium dodecyl sulphate, SDS) and CR-TX 100 (neutral surfactant - Triton X-100, TX 100) and were useful to understand the nature of natural surfactant. The mechanism of formation of complex due to interactions between Congo red and natural surfactant was suggested. This spectrophotometric method was used for the determination of critical micelle concentration (CMC), at which the formation of micelles was started. The CMC values obtained spectrophotometrically for the natural surfactant was coincided with the experimental value available in the literature. A definite change in the absorbance maxima of Congo red in the presence of natural surfactant (micelles of natural surfactant) was also observed. The change in maxima was also interpreted in terms of pH and CMC. The equilibrium constant of interaction between Congo red and natural surfactant was calculated on the theoretical model. The stability of the complexes of Congo red with different surfactants like CTAB, SDS, TX 100 and natural surfactant may be written in increasing order as: CR-TX 100 > CR-CTAB > CR-NS > CR-SDS. The biodegradable, non-toxic, inexpensive, environmental friendly, renewable natural surfactant was suggested in place of synthetic surfactants.

Bio-based surfactant for enhanced oil recovery: Interfacial properties, emulsification and rock-fluid interactions

Anionic surfactants are very effective for application in enhanced oil recovery (EOR) in sandstone reservoirs because of their promising surface-active properties. Considering the non-biodegradability of some of the commercial surfactants, the present study deals with an anionic surfactant synthesized from naturally occurring soap-nut oil with excellent interfacial properties for application in EOR. The soap-nut surfactant showed the promising properties of interfacial tension (IFT) reduction, emulsification, rock wettability alteration, which are desirable for its application in EOR. An ultra-low IFT value of 2.123 × 10−2 mN/m between crude oil and surfactant solution was obtained at critical micelle concentration (CMC), which was further reduced to 2.037 × 10−3 mN/m at optimum salinity. Phase behaviour studies showed the formation of Winsor III emulsion phase which is beneficial for recovery of the trapped oil from the fine pores of the reservoir by miscibility mechanism. The surfactant exhibited favourable rock-wetting ability from oil-wet rock to water-wet condition. The loss of surfactant by adsorption on the rock surface was studied, and the adsorption data were analysed by Langmuir and Freundlich models. Injection of a small pore volume of surfactant-slug augmented with polymer slug as mobility buffer recovered more than 30% of original oil in place (OOIP) after the conventional water-flooding.

Micellization and interactions for ternary mixtures of amino sulfonate surfactant and nonionic octylphenol polyoxyethylene ethers in aqueous solution: 1 Blending with nonionic surfactants with smaller numbers of hydrophilic unit

The micellization and the molecular interactions for the ternary mixture of an amphoteric surfactant, sodium 3-(N-dodeyl ethylenediamino)-2-hydropropyl sulfonate (C12AS), with two nonionic surfactants, octylphenol polyoxyethylene ethers with different number (n) of oxyethylene glycol ethers (OP-n), e.g., OP-10 and OP-7, or OP-10 and OP-4, in aqueous solution were investigated by the tensiometry. Specifically, the effect of the addition of OP-7 or OP-4 on the micellization of binary mixture of C12AS/OP-10 was probed. The addition can decrease the value of mixed critical micellar concentration (cmc) and change the composition of mixed micelle. Thermodynamic data indicate that though the addition decreases the contribution of entropy to the process of micellization, its overwhelming effect is not changed, or in other words, the effect of the addition is relatively limited in this investigation. These findings may help with understanding the molecular interaction for the ternary surfactant mixture constituted by commercial surfactants, which are usually not single but the mixture of homologues.

The Potentiality of Municipal Solid Waste to Produce Volatile Fatty Acids (VFAs)

Volatile fatty acids (VFAs) are proposed platform molecules for the production of basic chemicals and polymers from organic waste streams. A simple bio-reactor was fabricated with locally available materials to conduct this study. A lab-scale anaerobic batch reactor was fed with potato waste and banana waste as substrate to find out the potential organic waste that has maximum VFAs production capacity. Between these two wastes, banana waste was found better for VFAs production. The product spectrum remained similar at the pH range 4.0-4.5 but higher pH reduced the VFAs production. The operation of anaerobic digestion with uncontrolled pH reduced the pH 4.0 to 4.5. Therefore, it is better to run the anaerobic digestion without controlling the pH while aiming to VFAs production. A small amount nutrient (ammonium nitrogen) significantly increases the VFAs production but higher amount nutrient has an inhibition effect. However commercial surfactant has a strong inhibition effect on VFAs producing organism and hence reduced the VFAs production. The efficient production of VFA at uncontrolled pH with a small amount of ammonium nitrogen increases the economic feasibility of organic waste-based VFAs production.

Multivariate study and optimization of biodiesel production using commercial surfactants

Alkaline transesterification of vegetable oils or animal fats (apolar substances) with a short-chain alcohol (polar substance) is the best-known chemical route for biodiesel production. However, because they are substances of different polarities, there is a need to promote contact between the phases. Biodiesel was produced from soybean oil, methanol, potassium hydroxide, and surfactants DBB 7104 and DBB 7107. In this paper we verify whether it is better to use surfactant DBB 7104 or DBB 7107, and if there is an optimum experimental condition for the surfactant. The yield in biodiesel was verified for different production conditions on a bench scale. From a fractional experimental plan (26-2), with a variation of temperature, time, methanol-to-oil mole ratio, weight of surfactant, type of surfactant and weight of catalyst, it was possible to perform a multivariate analysis of the process. The most influential variables in the response were the temperature and the weight of the catalyst. Surfactant DBB 7107 was considered better than the surfactant DBB 7104. The optimal conditions were 0.7% w/w of the surfactant DBB 7107, 1 g of KOH, 30 min, methanol to oil mole ratio of 6:1 and temperature equal to 33.5?C.

Study on Surfactant-Solvent Mixture Formulation and Its Application on Pesticide Emulsion Product

Nettle caterpillars (Setothosea asigna) are one of the common insects found in palm tree plantation which significantly reduce palm oil production by eating palm tree leaves. Surfactant is commonly used as an emulsifier and stabilizer in the pesticide mixture to refrain the mixture from separating. Commercial surfactants that are being used by the farmers holds the emulsion for approximately 2 hours. The performance of Diethanolamide (DEA) as surfactant for the insecticide mixture was investigated in this research. The various concentration of DEA in pesticide mixture showed the increasing mixture stability up to 24 hours before separating. Commercial surfactant used by the farmers is at 7-10% of the mixture. Meanwhile, DEA lowers the percentage of usage to 5%. The reduction of percentage of surfactant usage leads to the reduction of surfactant cost. Sample A5B5 found to be the best among other surfactants. Sample A5B5 has the density of 0.878 g/cm3, viscosity of 19.72 cP, surface tension of 24.311 dyne/cm, and contact angle of 31.7830.

CO2 foam for enhanced oil recovery (EOR) applications using low adsorption surfactant structure

The ability of surfactants to interact with CO2 is essential if the CO2 foam is intended to augment a water flooding process as a method to displace oil from a reservoir. Apart from improved sweep efficiency of foam, CO2 reduces the oil viscosity, causes the oil to swell, lowers the high interfacial tension between oil and rock, dislodges the immobile oil, and hence increases the volumetric sweep efficiency. The surfactant must possess suitable structure to successfully play these roles. In this context, a new surfactant with different functionalities has been synthesized to examine its CO2-philicity. The surfactant was evaluated for the enhanced oil recovery (EOR) suitability by firstly examining the fluid–fluid compatibility in various temperatures, salinity, and hardness conditions. The foaming properties were also assessed. The interfacial tension (IFT) between the surfactant and CO2 gas at 90 °C and up to 2700 psi pressure revealed some interesting findings. The IFT of CO2–brine without surfactant dropped from a value of 70 to 30 mN/m when CO2 critical pressure approached 1070 psi, and it remained at 30 mN/m at higher pressures. The incorporation of surfactant achieved the lowest IFT of 1.76 mN/m at critical pressure conditions at 90 °C. The foam stability of the surfactants was also evaluated. In the core flooding test, the mobility reduction factor (MRF) values reflected the same trend as that of IFT lowering and foam stability. The three-tailed surfactant showed the MRF of 3.4 while alpha olefin sulfonate (AOS) (commercial surfactant) had the MRF value of 1.3. The three-tailed surfactant provided the highest recovery of 96% of residual oil in place (ROOIP). The adsorption of the surfactant was low at less than 0.5 mg/g.

Raman spectroscopy combined with advanced chemometric methods: A new approach for detergent deformulation

Deformulation of a commercial surfactant mixture using Raman spectroscopy and advanced chemometric tools have been investigated. Since the use of surfactants is drastically expanding, their fine identification and quantification are required for quality control and regulation. Dilution of the detergent mixtures combined with Raman spectroscopy for signal extraction tools allowed the extraction of the first information concerning the composition of the mixture. The raw materials identified were thus used in an experimental design to obtain a robust model for the determination of detergent composition. The combination of chemometric tools (independent component analysis and Partial Least Square) and spectroscopic methods provided pertinent information for detergent composition. This methodology can easily be transposed to the industrial world.

Pore-level visual analysis of heavy oil recovery using chemical-assisted waterflooding process – Use of a new chemical agent

Chemical-assisted waterflooding enhances the ultimate recovery of a conventional waterflooding process through several mechanisms such as reducing interfacial tension between water and oil, formation of in-situ emulsions, treatment of adverse mobility ratio, and wettability modification. Application of chemical-assisted waterflooding for recovery of heavy oil is still an active research topic. A new chemical technology (i.e. IPC Technology as referred to in this paper) has been developed. A proprietary mixture of surfactants is used in several techniques associated with surface extraction as well as in-situ recovery of heavy oil and bitumen. This formulation of solvents and surfactants is reusable, low foaming, non-flammable, not acutely toxic, and non-carcinogenic. The efficacy of using IPC as an additive for waterflooding was presented earlier through a systematic coreflooding study, which showed increased ultimate recovery of different types of oils when compared with commercial surfactant and alkali flooding. In order to investigate the mechanisms behind the enhanced macro-scale oil recovery, a series of pore-scale tests were designed and conducted in this study. Glass micromodel type of porous media was used in the presence of brines with different ion compositions. The pore-scale chemical-assisted waterflooding tests were carried out in four consecutive stages: brine flooding, chemical flooding, soaking period, and extended brine flooding. High quality pore-scale images were captured for qualitative and quantitative analysis of the IPC-assisted waterflooding at the pore-level. IPC intensified water wettability of grain particles in the presence of NaCl; however in the presence of MgCl2, use of IPC makes solid surfaces oil-wet. The phenomenon of water-in-oil and oil-in-water emulsification was observed when IPC was used along with different brine compositions. This phenomenon is weakened for lighter oils. When the acid number of the oil was low, extension of soaking period intensified wettability alteration and emulsification mechanisms. Other pore-scale phenomena were also observed during visualization tests such as coalescence of microdroplets during the extended waterflooding stage, snap-off mechanism creating daughter droplets during the extended waterflooding stage, occasional flow of bulk oil films toward the production end, and wettability reversal during various flooding stages. Attempts were also made to conduct statistical analysis of emulsion droplet sizes under different test conditions. Several parameters, including chemical concentration as well as ion concentration in brines, were found to significantly affect the emulsion droplet size distribution.

CO2/N2-switchable high internal phase Pickering emulsion stabilized by silica nanoparticles and low-cost commercial N,N-dimethyl-N-dodecylamine

Herein, we reported a CO2-triggered oil-in-water high internal phase Pickering emulsion based on silica nanoparticles functionalized in situ by a trace amount of low-cost commercial CO2-switchable surfactant, N,N-dimethyl-N-dodecyl amine (C12A). Upon alternately bubbling CO2 and N2 at a moderate conditions (35 °C, 40 mL·min−1), C12A could be reversibly switched between cationic and nonionic forms, and then adsorbed on or desorbed from the surface of particles. As a consequent, interfacial active particles were formed, stabilizing the emulsion (CO2), or disrupted, breaking the emulsion (N2). Above a critical concentration, the Pickering emulsion can be formed over the whole concentration scope without interruption, even as zeta potential equals to zero, because of the unusual adsorption of the protonated C12A. Such a stabilizer composed of silica and the protonated C12A can be used to producing high internal phase Pickering emulsion for different oil, showing significant application value.

Simultaneous Extraction and Emulsification of Food Waste Liquefaction Bio-Oil

Biomass-derived bio-oil is a sustainable and renewable energy resource, and liquefaction is a potential conversion way to produce bio-oil. Emulsification is a physical upgrading technology, which blends immiscible liquids into a homogeneous emulsion through the addition of an emulsifier. Liquefaction bio-oil from food waste is characterized by its high pour point when compared to diesel fuel. In order to partially replace diesel fuel by liquefaction bio-oil, this study aimed to develop a method to simultaneously extract and emulsify the bio-oil using a commercial surfactant (Atlox 4914, CRODA, Snaith, UK). The solubility and stability of the emulsions at various operating conditions such as the bio-oil-to-emulsifier ratio (B/E ratio), storage temperature and duration, and co-surfactant (methanol) addition were analyzed. The results demonstrate that higher amounts of bio-oil (7 g) and emulsifier (7 g) at a B/E ratio = 1 in an emulsion have a higher solubility (66.48 wt %). When the B/E ratio was decreased from 1 to 0.556, the bio-oil solubility was enhanced by 45.79%, even though the storage duration was up to 7 days. Compared to the emulsion stored at room temperature (25 °C), its storage at 100 °C presented a higher solubility, especially at higher B/E ratios. Moreover, when methanol was added as a co-surfactant during emulsification at higher B/E ratios (0.714 to 1), it rendered better solubility (58.83–70.96 wt %). Overall, the emulsified oil showed greater stability after the extraction-emulsification process.

Prospective acid microemulsions development for matrix acidizing petroleum reservoirs

The oil exploration and drilling processes cause damage to the reservoir that result in decreasing production. Well stimulation processes are performed to repair this damage and restore the oil flow. Among them, matrix acidizing aims to unblock the pores by dissolving the rock, organic or inorganic scale through reaction with the injected acid, causing the dilation of the deeper pores to form long wormholes that provide a path for oil to flow from the reservoir to the production well. In this work, acid microemulsions were developed aiming to improve the stimulation process and reduce the problems caused by using acidic solutions, such as fast reaction with the reservoir rocks. The solvents used as the oil phase were kerosene and Solbrax Eco 175/235, while the aqueous phase consisted of hydrochloric acid (32%) and commercial nonionic surfactants based on ethoxylated lauryl alcohol containing different ethylene oxide units in their chains, and the cosurfactants were propanol and butylglycol. Initially, pseudo-ternary phase diagrams were constructed with the described components to determine the best concentrations of surfactant, cosurfactant, oil phase and aqueous phase to obtain microemulsions. The acidic microfluids prepared were characterized in terms of appearance, stability, particle size, density, viscosity, pH and type of emulsion. The most stable systems were selected for performance testing, where the rock-fluid reaction rate was measured. The results showed that a stable acid microemulsion was formed at room temperature, but not all the hydrochloric acid remained in the microemulsion. The best systems to retard the rock-fluid reaction rate were those containing ethoxylated lauryl alcohol with 1 unit of ethylene oxide.

Improved antifouling properties of polyethersulfone membranes modified with α-amylase entrapped in Tetronic® micelles

A novel method of polyethersulfone membrane modification with α-amylase entrapped in polymeric micelles is proposed to improve the antifouling properties of membranes. The immobilization of α-amylase is performed by its incorporation into micelles based on commercial polymeric surfactants (Tetronic®-701 and Tetronic®-90R4) with their subsequent adsorption on the membrane surface. The size of micelles loaded with enzyme depends on the nature of the surfactant and is equal to 400 and 100 nm for Tetronic®-701 and Tetronic®-90R4, respectively. Biocatalytic activity and membrane stability in the process of starch ultrafiltration are discussed in the paper. The optimal pH was found to be 6.5–7.5 for Tetronic®-701 and 6.0–6.5 for Tetronic®-90R4 micelles. The activity of enzyme entrapped in the micelles, adsorbed on the membrane surface, increased 1.5–1.8 times. The starch conversion rate of 80–90% was observed for membranes with immobilized α-amylase. The biocatalytic activity of immobilized enzyme was maintained at a high level during five cycles of regeneration. Moreover, the layer of micelles with incorporated α-amylase on the membrane surface reduced the effect of concentration polarization due to starch hydrolysis. The micelle immobilization caused hydrophilization of the surface and an increase in the number of bound water molecules which prevented the formation of a cake in the boundary layer.

Prediction of the cloud point of polyethoxylated surfactants and their mixtures by the thermodynamic model of Flory-Huggins-Rupert

The cloud point curves of polyethoxylated surfactants are established experimentally. These experimental data are preliminary to the development of the cloud point extraction process, which appears as an interesting alternative to the usual solvent extraction unit operation. Starting from the thermodynamic model developed by Flory and Huggins for phase separation of polymer aqueous solutions, this paper aims at the prediction of cloud point curves. In this work, Rupert’s approach is extended to commercial nonionic surfactants, mixtures of homologous species, namely a few alkylphenol and alcohol ethoxylates. The limit of such an approach is clearly demonstrated, provided that a fitting parameter is finally required for a successful model application to pilot-plant manufactured surfactants, like C8ΦEn (n = 7.5, 10, 12), C9ΦEn (n = 8, 10, 12), C12E4, C12E6 and commercial Tergitol 15-S-7 (linear C12-C14 secondary alcohol with an average of 7 ethylene oxide units).GRAPHICAL ABSTRACT

Flexible Peptide Linkers Enhance the Antimicrobial Activity of Surface-Immobilized Bacteriolytic Enzymes.

Chemical linkers are frequently used in enzyme immobilization to improve enzyme flexibility and activity, whereas peptide linkers, although ubiquitous in protein engineering, are much less explored in enzyme immobilization. Here, we report peptide-linker-assisted noncovalent immobilization of the bacteriolytic enzyme lysostaphin (Lst) to generate anti- Staphylococcus aureus surfaces. Lst was immobilized through affinity tags onto a silica surface (glass slides) and nickel nitrilotriacetic acid (NiNTA) agarose beads via silica-binding peptides (SiBPs) or a hexahistidine tag (His-tag) fused at the C-terminus of Lst, respectively. By inserting specific peptide linkers upstream of the SiBP or His-tag, the immobilized enzymes killed >99.5% of S. aureus ATCC 6538 cells (108 CFU/mL) within 3 h in buffer and could be reused multiple times without significant loss of activity. In contrast, immobilized Lst without a peptide linker was less active/stable. Molecular modeling of Lst-linker-affinity tag constructs illustrated that the presence of the peptide linkers enhanced the molecular flexibility of the proximal Lst binding domain, which interacts with the bacterial substrate, and such increased flexibility correlated with increased antimicrobial activity. We further show that Lst immobilized onto NiNTA beads retained the ability to kill ∼99% of a 108 CFU/mL microbial challenge even in the presence of 1% of a commercial anionic surfactant, C12-14 alcohol EO 3:1 sodium sulfate, when the Lst construct contained a decapeptide linker containing glycine, serine, and alanine residues. This linker-assisted immobilization strategy could be extended to an unrelated lytic enzyme, the endolysin PlyPH, to target Bacillus anthracis Sterne cells either in buffer or in the presence of anionic surfactants. Our approach, therefore, provides a facile route to the use of antimicrobial enzymes on surfaces.