Hydrophobic Association Effect Research Articles

Study on the rheological properties and salt resistance mechanism of an amphiphilic polymer with twin-tailed group

Partially hydrolyzed polyacrylamide (HPAM) is the most widely used polymer for oil recovery. Its thickening ability has been severely compromised in high salinity reservoirs. To improve polymer viscosity in high salinity reservoirs, a twin-tailed amphiphilic polymer P(AM/AMPS/DtC18) was developed by radical copolymerization method using AM, AMPS and DtC18 monomers, abbreviated as PAAD18. The contrast polymer P(AM-AMPS) was prepared by the same method and reaction conditions. The structure of PAAD18 was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and H Nuclear Magnetic Resonance Spectra (1H NMR). The relationship between its rheological properties and microstructure was studied using rheological analysis and Scanning Electron Microscope (SEM). The mechanism of salt resistance was revealed. The results show that under the condition of XJ reservoir with 98558mg/L and 40℃, the viscosity of PAAD18 with concentration of 2200mg/L is 25 mPa·s. PAAD18 has better temperature and salt resistance than HPAM and P(AM-AMPS). P(AM-AMPS) has better temperature resistance and salt resistance than HPAM. The salinity ranges from 0 to 5 × 104mg/L, the viscosity of PAAD18 is reduced due to the action of electrostatic shielding. At a salinity of 5 × 104mg/L, the electrostatic shielding effect and the hydrophobic association effect reach a balanced point, and the solution viscosity is the lowest. The salinity increases from 5 × 104mg/L to 15 × 104mg/L, then the hydrophobic association is enhanced due to the increased polarity of the solution. It was found that the polymer network structure of PAAD18 was more complex, the viscosity of the solution increased instead. The salt thickening properties were demonstrated in the rheology measurement. This work provides a new material for polymer flooding technology in high salinity reservoirs, with good application potential and guiding significance.

Inter-/intra-molecular synergism improve self-assembly behavior of hydroxamate-modified amino acid surfactant for flocculation of micro-fine particles

Flotation recovery of micro-fine minerals has been constrained by low flotation efficiency due to the large surface area and small quality of fines, causing a huge waste of valuable resources. Herein, we developed a novel hydroxamate-modified N-acyl amino acid surfactant, 2-decanoylamino-4-hydroxycarbamoyl-butyric acid (DHBA), which can self-assemble via synergism among amide, carboxyl, and hydroxamate functional groups for achieving the efficient flocculation and recovery of fine rhodochrosite. The theoretical calculations and interface analyses revealed from microscopic perspective that the intramolecular synergistic chelation effect between carboxyl and hydroxamate groups conferred strong adsorption affinity of DHBA on rhodochrosite. On the other hand, the intermolecular H-bonds not only promote the tight arrangement of collectors on particle surface to enhance hydrophobic association effect, but also induce the agglomeration of collectors into net-like “macromolecules” clusters to produce adsorption bridging for fines. Eventually, the flocculation and flotation tests confirmed that DHBA exhibits a superior flocculation and collecting performance for fine rhodochrosite than very common collector octanoylhydroxamate acid (OHA) (the recovery reached 95.2% for 1 × 10−4 mol·L−1 DHBA while 66.8% for OHA). This research provides a feasible surfactant development strategy for flocculation-flotation.

A Thermal-Responsive Zwitterionic Polymer Gel as a Filtrate Reducer for Water-Based Drilling Fluids.

It is crucial to address the performance deterioration of water-based drilling fluids (WDFs) in situations of excessive salinity and high temperature while extracting deep oil and gas deposits. The focus of research in the area of drilling fluid has always been on filter reducers that are temperature and salt resistant. In this study, a copolymer gel (PAND) was synthesized using acrylamide, N-isopropyl acrylamide, and 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate through free-radical polymerization. The copolymer gel was then studied using FTIR, NMR, TGA, and element analysis. The PAND solution demonstrated temperature and salt stimulus response characteristics on rheology because of the hydrophobic association effect of temperature-sensitive monomers and the anti-polyelectrolyte action of zwitterionic monomers. Even in conditions with high temperatures (180 °C) and high salinities (30 wt% NaCl solution), the water-based drilling fluid with 1 wt% PAND displayed exceptional rheological and filtration properties. Zeta potential and scanning electron microscopy (SEM) were used to investigate the mechanism of filtration reduction. The results indicated that PAND could enhance bentonite particle colloidal stability, prevent bentonite particle aggregation, and form a compact mud cake, all of which are crucial for reducing the filtration volume of water-based drilling fluid. The PAND exhibit excellent potential for application in deep and ultra-deep drilling engineering, and this research may offer new thoughts on the use of zwitterionic polymer gel in the development of smart water-based drilling fluid.

A Universal and Simple Method to Obtain Hydrogels with Combined Extreme Mechanical Properties and Their Application as Tendon Substitutes.

With the development of biomedical engineering, the preparation of hydrogels with combined extreme mechanical properties similar to those of some biological hydrogels becomes an important research topic for scientists. In this work, a single-network hydrogel with combined extreme mechanical properties is prepared through a simple and universal method, wherein the strength, elongation at break, toughness, and fracture energy of the hydrogel WPU-3PAAm-6PAN are achieved at 24.7 MPa, 544.0%, 68.9 MJ m-3, and 37.2 kJ m-2, respectively. Herein, a series of photosensitive resins in emulsion form are synthesized, and due to the water-oil diphasic characteristic, hydrophobic monomers and high-efficient hydrophobic photo-initiators are adopted into the resins, which can significantly improve the mechanical properties of the hydrogels due to the hydrophobic association effect and solve the biggest barrier of low curing rate in digital light processing (DLP) fabrication of hydrogels, respectively. Moreover, the simple and facile method to obtain robust and tough hydrogels can be universally applied to other polymer systems. Combined with the excellent mechanical properties and printing ability, the hydrogels with optimized structures are fabricated through DLP printing technology and applied as tendon substitutes. The tendon substitutes exhibit superior performance for mechanical connection and regeneration of collagen fibers. Although further clinical research is required, the hydrogels have great potential applications in various biological areas.

A novel treatment for amelioration of sludge dewaterability using green starch-grafted flocculant and realized mechanism

To clarify the effect of extracellular polymeric substances (EPS), protein and hydrophilic substances on the dewatering efficiency during starch-grafted flocculant (SBF) conditioning, a green and cost-saving SBF was synthesized. Dewatering performance of sludge, secondary structure of protein, change of hydrophobic substances and removal of bound water were investigated. Results showed that after SBF conditioning, filter cake moisture content and specific resistance to filtration decreased from 75.63 % and 2.31 × 1012 m/kg to 66.76 % and 5.68 × 1011 m/kg, respectively. SBF neutralized the negative charges from the sludge system, promoting the increase of sludge flocs size and EPS decomposition, decreasing the compressibility of sludge and constructing a channel for water release. Moreover, the secondary structures of protein were changed through the interaction between SBF and the oxygen-containing functional groups in EPS, resulting in the reduction of hydrophilic substances and the increase of hydrophobic substances, which increased the hydrophobicity of molecules and thus improved the dewatering capacity of sludge. Meanwhile, the construction of sludge skeleton channels, charge neutralization, hydrophobic association effect were the primary mechanisms of SBF conditioning sludge dewatering. Additionally, SBF has an excellent economy as a sludge conditioner. This paper provided a new ideal for starch-based flocculants for improving the dewatering capacity of sludge treatment.

Improving the mechanical performance of P(N‐hydroxymethyl acrylamide/acrylic acid/2‐acrylamido‐2‐methylpropanesulfonic acid) hydrogel via hydrophobic modified nanosilica

AbstractHydrogels with high mechanical strength are essential for its most industrial applications. In this work, the hydrophobic SiO2nanoparticles (M‐SiO2NPs) modified with octadecyltrimethoxysilane were used as physical crosslinker to toughen the mechanical properties of hydrogels. The solution of monomers containing M‐SiO2NPs, N‐hydroxymethyl acrylamide (NHAM), acrylic acid (AA), 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), was polymerized to prepare a P(NHAM/AA/AMPS)‐based composite hydrogel without any chemical cross‐linker. The composition and microstructure of the hydrogel were carefully studied with Fourier transform infrared spectroscopy and scanning electron microscopy. The mechanical properties of the hydrogel were investigated through compressive and tensile tests. Dynamic swelling tests were carried out at different pH values (1.0–12.0) and salinity (2000–20,000 mg/L) to study the acid resistance, alkali resistance, and salt resistance of the hydrogel. The obtained results showed that the hydrogel exhibited excellent mechanical performance, which was attributed to the unique 3D network formed by the hydrogen bond between M‐SiO2NPs and polymer as well as the hydrophobic association effect between the hydrophobic chains of M‐SiO2NPs. Furthermore, the hydrophobic association effect was enhanced when contacting with salt, acid, and alkali solutions, thus endowing the hydrogel with intensified salt resistance and wider acid–base adaptability range.

Synthesis of novel chitosan-based flocculants with amphiphilic structure and its application in sludge dewatering: Role of hydrophobic groups

Natural polymeric flocculants as sludge conditioners have received great attention due to their non-toxic and biodegradable advantages. However, the application of amphiphilic natural flocculants as sludge conditioners is rarely reported. In this work, the novel chitosan-based flocculants (CS-g-PAO) with amphiphilic structure were synthesized by ultraviolet light initiated method for the enhancement of sludge dewatering performance. The solubility of CS-g-PAO was significantly improved in a wide pH range (2.0–10.0). Various characterization methods were used to investigate the structure, thermal stability and surface morphology of copolymers, suggesting the successful synthesis of CS-g-PAO. In dewatering experiments, CS-g-PAO showed superior dewatering performance, and filter cake moisture content could be decreased to 77.98% from 95.14%. Moreover, the results of extracellular polymeric substances (EPS) components indicated that hydrophobic effect of CS-g-PAO was beneficial to remove the protein in S-EPS and TB-EPS, which had the crucial influence on dewatering performance. Furthermore, the dewatering mechanism was discussed based on the effects of zeta potential, apparent viscosity, surface tension and flocs structure on dewaterability. Results revealed that CS-g-PAO had strong hydrophobic association effect and surface activity. In addition, enhanced charge neutralization and hydrophobic interaction played a synergetic role in improving the dewaterability of CS-g-PAO.

Preparation and property evaluation of a hydrophobically modified xanthan gum XG-C16

Hydrophobic long carbon chains (C16) were grafted onto the main chains of Xanthan Gum by etherification under the ordered conformation of Xanthan. Rheology and pyrene fluorescence spectroscopy experiments discovered that the critical association concentration (CAC) of modified Xanthan solution was 0.16%, and ANS fluorescence probe test indicated modified Xanthan had better hydrophobic association effect than before. Additionally, macroscopic and microscopic properties of modified Xanthan solutions, as well as the effects of temperature and salt on its association behavior were explored by rheology and scanning electron microscopy (SEM), revealed the reason of the improvement of modified Xanthan properties in micro levels. The results show that the modified Xanthan had better high-temperature resistance, which retained 421 mPa·s at 140 °C, about four times the apparent viscosity of Xanthan before modification (125 mPa·s). Adding NaCl up to the salt concentration of 4.0%, modified Xanthan still maintained well spatial network structure and a high apparent viscosity (728 mPa·s), while the apparent viscosity of Xanthan before modification was much lower than 728 mPa·s. Since the hydrophobically modification didn’t change the structure of Xanthan, the improvement of the above properties all came from the contribution of hydrophobic chain graft.

Ultrasound-initiated synthesis of cationic polyacrylamide for oily wastewater treatment: Enhanced interaction between the flocculant and contaminants

Weak interaction between flocculants and oil is a main bottleneck in the treatment of oil-containing wastewater. To solve this problem, a novel flocculant PAB with cationic micro-block structure and hydrophobic groups of benzene rings was synthesized by ultrasound initiated polymerization technique and applied to remove turbidity and oil from water. To avoid unnecessary addition of reagents in traditional template and micellar copolymerization, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) with self-assembly ability in aqueous solution was employed to synthesize flocculants. The critical association concentration of BMDAC measured by conductivity and surface tension methods was 0.014 mol·L−1. The results of reactivity ratio, statistical analysis of sequence-length distribution and 1H NMR provided evidence for the synthesis of copolymer with cationic micro-block. In addition, the apparent viscosity measurement indicated that PAB had an obvious hydrophobic association property. Finally, flocculation tests demonstrated that flocculation performance was greatly improved by adding PAB and the removal rate of oil and turbidity both reached the maximum (87.5% and 92%) at dosage of 40 mg·L−1 and pH of 7.0. Flocculation mechanism investigation demonstrated that the cooperation of charge neutralization, adsorption bridging, and hydrophobic association effect played an important role. The formed flocs by PAB was large, compact, difficult to break, and easy to regrow because of the enhanced interaction between flocculants and oil. In summary, this study can provide important reference in the design of organic flocculants in oily wastewater treatment applications.

Synthesis and properties of high temperature resistant and salt tolerant filtrate reducer N,N-dimethylacrylamide 2-acrylamido-2-methyl-1-propyl dimethyl diallyl ammonium chloride N-vinylpyrrolidone quadripolymer

Abstract N,N-dimethylacrylamide (DMAA), 2-acrylamido-2-methyl-1-propyl (AMPS), dimethyl diallyl ammonium chloride (DMDAAC) and N-vinylpyrrolidone (NVP) monomers were copolymerized to synthesize a zwitterionic copolymer filtrate reducer. The results of Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) indicated that the molecular structure and chemical compositions of the quadripolymer matched with the design, and the result of the differential scanning calorimetry (DSC)-thermogravimetric analysis (TGA) showed that the polymer had good thermal stability. The effects of the quadripolymer on the properties and salt tolerance of drilling fluids were investigated. The environmental scanning electron microscope (ESEM) was used to observe the microstructure of the DMAA/AMPS/DMDAAC/NVP quadripolymer-bentonite system and filter cake of the drilling fluid added the copolymer. Results showed that a one space grid structure was formed by the molecular film with a hydrophobic association effect and electrostatic interaction between the groups in the positive and negative charges of the quadripolymer. It adsorbed and coated clay particles, and kept the particles distributing multilevels which contributed to forming a compact filter cake to reduce fluid loss. The spatial structure of the quadripolymer in drilling fluid could be destroyed partly by high temperatures, sodium and calcium, but the polymer still had a good effect on reducing fluid filtration.

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G'' proportional to omegan'') was observed for all gelling systems with n' = n'' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel.

Altering Associations in Aqueous Solutions of a Hydrophobically Modified Alginate in the Presence of β-Cyclodextrin Monomers

The formation of associative networks in semidilute aqueous solutions of hydrophobically modified alginate (HM-alginate) is dependent on intermolecular hydrophobic interactions. Addition of beta-cyclodextrin (beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. This results in a dramatic decrease in the viscoelastic response of the system and a more extended local structure of the polymer chains, as shown by small-angle neutron scattering (SANS) measurements. The zero-shear viscosity decreases about an order of magnitude when the beta-CD concentration is increased from 0 to 12 mm. The lifetime of the associative network decreases strongly with increasing levels of beta-CD addition. These findings clearly demonstrate that the hydrophobic association effect is efficiently reduced as the amount of beta-CD is increased. In the framework of drug delivery, this effect may be useful to improve the release of therapeutic molecules that can be entrapped in the polymer matrix.

Interaction between the strong anionic character of strong anions and the hydrophobic association property of hydrophobic blocks in macromolecular chains of a water‐soluble copolymer

AbstractThe copolymerization of acrylamide, sodium 2‐acrylamido‐2‐methyl propane sulfonate, and styrene was carried out in a microemulsion medium, and ternary copolymers based on polyacrylamide, which contained both strong anionic groups (SO3Na) and hydrophobic blocks (polystyrene), were synthesized. The structures and compositions of the copolymer were characterized by various means (Fourier transform infrared, ultraviolet, and elemental analysis). The aqueous solution properties were investigated with a florescence probe technique and apparent viscosity measurements, and the interactions between the strong anionic character of the anionic groups and the hydrophobic association behavior of the hydrophobic blocks was intensively examined. After the simultaneous addition of the strong anionic groups and hydrophobic association blocks to the main chains of polyacrylamide, the synergism of the electroviscosity effect of the strong anionic groups and the hydrophobic association effect of the hydrophobic blocks obviously enhanced the apparent viscosity of aqueous copolymer solutions, and the synergism of greater salt tolerance of the strong anionic groups and the strengthened hydrophobic association of the hydrophobic blocks in brine solutions resulted in increased salt resistance for the copolymer. However, the presence of strong anionic groups (SO) in the macromolecules weakened the intermolecular hydrophobic association effect of the copolymer in aqueous solutions to a certain degree; that is, the strong anionic groups produced a certain negative influence on the hydrophobic association effect of the hydrophobic blocks. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 714–722, 2005

New method for the selective capture of antibodies under physiological conditions.

Hydrophobic charge induction chromatography is a recently developed method for protein separation based on the use of dual-mode ligands. They are designed in such a way so as to combine a molecular interaction supported by a mild hydrophobic association effect in the absence of salts. When environmental pH is changed, the ligand becomes ionically charged resulting into the desorption of the protein. This method is applied to the separation of antibodies from ascite fluids and culture supernatants from hybridomas cultured in the presence of fetal bovine serum or in protein free environment. Typically adsorption from cell culture supernatants is accomplished without any pH or ionic strength adjustment; the column is then washed with a typical buffer to eliminate protein impurities. Antibodies are then desorbed using acetate buffer, pH 4. Antibody binding capacity is in the range of 30 mg per ml of resin at 10% breakthrough. Antibody purity varies according to the initial feed stock and can reach values higher than 90% in a single pass. One example of antibody purification process involving hydrophobic charge induction chromatography as a capture step followed by a polishing phase with DEAE Ceramic HyperD is described. Longevity and ligand leakage are compatible with large-scale applications.