Ionic strength effects on the microstructure and shear rheology of cellulose nanocrystal suspensions

The effect of ionic strength on the rheology and microstructure of Cellulose nanocrystals (CNC) aqueous suspensions are studied over a broad range of CNC (3–15 wt%) and NaCl concentrations (0–15 mM), using polarized optical microscopy combined with rheometry. The CNC suspensions are isotropic at low concentration and form chiral nematic liquid crystalline structure above a first critical concentration and gel above a second critical one. It has been shown that for isotropic CNC suspensions, increasing the ionic strength of the system up to 5 mM NaCl concentration weakens the electro-viscous effects and thus reduces the viscosity of these suspensions. For biphasic samples, which contain chiral nematic liquid crystal domains, increasing the ionic strength up to 5 mM NaCl concentration decreases the size of the chiral nematic domains, and leads the viscosity of the samples at low shear rates to increase. On the other hand, at high shear rates, where all the ordered domains are broken, the viscosity decreases with NaCl addition. For gels, the addition of NaCl up to 5 mM weakens the gel structure and decreases the viscosity. Further addition of NaCl (10 and 15 mM NaCl concentrations) results in extensive aggregation and de-stabilizes the CNC suspensions.     

Mono- and Di-valent Salts as Modifiers of PEO-PPO-PEO Block Copolymer Interactions with Silica Nanoparticles in Aqueous Dispersions

Colloidal stabilization of nanoparticle dispersions is central to applications including coatings, mineral extraction, and dispersion of oil spills in oceanic environments, which often involves oil-mineral-aggregates (OMAs). We have an ongoing interest in the modulation of amphiphile micellization and adsorption behavior in aqueous colloidal dispersions in the presence of various additives. Here we evaluate the effect of added salts CaCl₂, MgCl₂, and NaCl on the micellization and adsorption behavior of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer Pluronic P105 (EO₃₇PO₅₆EO₃₇). In 0.10 wt% silica nanoparticle (10.6 nm average diameter) dispersion, adsorbed block copolymer layer formation begins at a critical surface micelle concentration (csmc) of 0.02 wt%, well below the critical micellization concentration of Pluronic P105 in water. Dye solubilization experiments demonstrate an increase in the csmc upon addition of each salt. Each added salt reaches a level of maximum effectiveness in its ability to disfavor Pluronic P105 adsorption at the silica surface. These peak levels occur at concentrations of 0.005, 0.03, and 0.05 M for CaCl₂, MgCl₂, and NaCl, respectively, in the presence of 0.10 wt% silica nanoparticles. We explain these results in the context of an electrostatic displacer mechanism and discuss possible connections to OMA-dispersant formation.     

Original Preparation of PEKK Dispersion for Coating by Transfer from a Chloroform Stable Dispersion to an Aqueous Stable Dispersion,by Emulsion/Solvent Evaporation

In this work, aqueous dispersions of PolyEtherKetoneKetone (PEKK) oligomers were obtained by an emulsion/dispersion solvent evaporation technique. The PEKK oligomers were synthesized by a Friedel–Crafts acylation with a number average degree of polymerization of 4. The synthesized PEKK oligomers had very good thermal stability and spontaneously formed a stable dispersion of swollen micrometric fibers in chloroform. After sonication of the chloroform dispersion in water in the presence of sodium dodecyl sulfate (SDS) and evaporation, we obtained aggregated particles with a mean diameter between 120 and 160 nm, decreasing linearly with the PEKK concentration. The most stable dispersions were obtained with 0.5% wt of surfactant and, at a fixed concentration of SDS, the stability decreased when the PEKK concentration was increased. The different dispersions of PEKK in water were very stable and, after water evaporation, formed homogeneous films for high-performance coating.     

Low degree of substitution cellulosic textile coatings with improved physiological parameters

To further improve the physiological properties of textiles, solutions of low degree of substitution cellulose derivatives, i.e. carbamates and acetates, containing finely dispersed sub-micron scaled NaCl particles (d₁₆ = 269 nm, d₅₀ = 275 nm, d₈₄ = 283 nm) serving as templates were coated on textiles. By wet milling of NaCl particles in a 12.5 wt% solution of polyvinylpyrrolidone in dimethylacetamide (DMAc) as dispersing agent, a stable, processable dispersion was obtained, which could be diluted with LiCl/DMAc without any flocculation. For the preparation of the coating solution, the NaCl/DMAc dispersions were diluted with LiCl/DMAc and added to the DMAc-swollen cellulose derivatives. After application onto the textiles, the NaCl particle-containing coating had to be coagulated directly after application in a solvent bath, otherwise slow replacement of hygroscopic DMAc by water lead to the dissolution and recrystallisation of NaCl on the surface of the coating, thereby changing particle distribution and diameter. The solvent for the coagulation bath was chosen in a way that it allows for a high coagulation speed for the cellulose derivative matrix while possessing a low solubility product for NaCl (e.g., 2-propanol) in order to prevent any loss of the NaCl particles. Due to the highly porous structure created, increased water retention values and increased water vapour permeabilities were observed under preservation of the number of accessible hydroxyl groups of the cellulose derivatives. Both the templated and non-templated coatings could be processed on various textile substrates (e.g., on PET and PP). An important feature of these new materials, i.e. the possibility to apply an antibacterial finish, is discussed within the context of a potential use in the medical sector.     

Adsorption of Corrosion Inhibitors onto Iron Carbonate (FeCO3) Studied by Zeta Potential Measurements

The adsorption of cetyl trimethyl ammonium bromide (CTAB) and two commercial inhibitor base chemicals, an oleic imidazoline salt (OI) and a phosphate ester (PE), onto iron carbonate (FeCO₃), was studied by zeta potential measurements in a 0.1 wt% sodium chloride (NaCl) solution under 1 bar CO₂ at 22°C, in the absence and presence of a refined low-aromatic oil. The zeta potential of oil-in-water emulsion droplets was also determined. Surface tension of 0.1 wt% and 3 wt% brines was measured as a function of inhibitor concentration. The isoelectric point was pH 6.0 in the 0.1 wt% NaCl solution under 1 bar CO₂. The results show that all three inhibitor compounds adsorbed onto the iron carbonate particles both at pH 4.0 and pH 6.0. Adsorption on both negatively charged surfaces and surfaces with no charge were thus found for all inhibitors. The addition of oil had no significant effect on the measured zeta potential on iron carbonate particles.     

Synthesis of VO2 Nanopowders. Part II. Hydrolysis of Vanadium Alkoxide/Citric Acid Premixes: VO2 Nanostructures of Controlled Shape

Reaction of VO(OiPr)₃/citric acid premixes with excess water produces stable, blue dispersions of V_xO_y gel nanoparticles (5–100 nm in diameter) that can be isolated via acetone precipitation. Annealing under reducing conditions transforms these gel particles into crystalline, faceted VO₂ nanoparticles of similar size. Larger V_xO_y gel particles (75–200 nm in diameter) form when V_xO_y nanogel dispersions are aged with aqueous ammonia. Upon annealing, these larger gel particles transform into crystalline VO₂ rods of 50 nm–10 μm in length. Hysteresis loops confirming a semiconductor-to-metal phase transition near 68 °C expected for crystalline VO₂ particles are recorded by variable-temperature electrical resistance and powder X-ray diffraction measurements.     

An experimental study of the stability of TiO2 particles in organic–water mixtures

The stability of TiO₂ (Anatase) particles in various organic-water mixtures is examined experimentally. The results obtained reveal that the addition of AlCl₃ to a methanol–water dispersion leads to charge reversal on particle surface. If the concentration of methanol is high, CaCl₂ also leads to charge reversal, but NaCl does not have this effect. This implies that if the concentration of methanol is low, the coagulation between TiO₂ particles is due to double-layer compression for Na⁺ and Ca²⁺, and due to charge adsorption and neutralization for Al³⁺. A methanol dispersion is unstable without the addition of electrolyte, and the addition of both CaCl₂ and AlCl₃ has the effect of stabilizing the dispersion; the addition of NaCl does not have this effect. The qualitative behaviors of an acetone–water dispersion are similar to those of a methanol–water dispersion. It is interesting to observe, however, that the absolute mobility of a pure acetone dispersion has a maximum as the concentrations of both CaCl₂ and AlCl₃ vary, but charge reversal does not occur. Among the dispersions without the addition of electrolyte, a 50% organic–water mixture is most stable. Also, a methanol–water dispersion is more stable than an acetone–water dispersion, which can be explained based on the degree of dissociation of an electrolyte.     

Stability and Flow-Induced Flocculation of Fumed Silica Suspensions in Mixture of Water-Glycerol

A systematic investigation has been performed to relate the effect of glycerol composition to the rheological properties of aqueous suspensions of hydrophilic fumed silica at pH far from the isoelectric point. Steady state/dynamic rheology and electrophoresis measurements are compared to correlate the stability of the suspension with particle-particle and particle-solvent interactions. Although the extent of electrostatic stability is reduced by addition of glycerol, the rheological properties show a transition from a highly flocculated gel to stable dispersions containing no microstructures. This is attributed to a high degree of hydrogen-bonding between glycerol and the Aerosil surface silanol groups. Small dissociation of NaCl and particles reduce the effect of ion exchange and particle bridging mechanisms when the suspensions destabilise in the presence of glycerol. The high viscosity of glycerol is important with respect to the formation of a thick solvation layer around the particles. These parameters give rise to short-range, non-DLVO repulsive solvation forces, which stabilise the dispersion. At intermediate concentrations of glycerol (30–60 wt%) the apparent viscosity increase abruptly and irreversibly as both the extent and time of shearing are increased. The shear rate for the onset of the shear thickening is found to be retarded by decreasing the particle and salt concentration as well as by increasing the glycerol concentration. It is postulated that at intermediate glycerol concentration, where the height of the energy barrier is small, mechanical forces can activate the particles to overcome the energy barrier to enter the region where attractive forces dominate. Here, domination of the hydrodynamic forces to the colloidal forces under the shear results in formation of irreversible gels which does not relax to its initial condition.     

Cellulose gel dispersions: fascinating green particles for the stabilization of oil/water Pickering emulsion

A facile approach for the preparation of cellulose gel dispersions with particle size less than 5 μm has been developed. The particles were obtained by dissolving cellulose in NaOH/urea solvent, followed by regeneration in ethanol/H₂O mixed solution with homogenizer shearing. The characteristics of the cellulose gel dispersions were evaluated in terms of particle dimensions and crystalline structure, size distribution and rheology behavior. The cellulose gel dispersions had low crystallinity, and the concentration of the cellulose solution had little influence on the particle size of the gel dispersions. Furthermore, the cellulose gel dispersions could be well dispersed in deionized water, and they could be used to stabilize oil/water emulsion without addition of any surfactant. The formed Pickering emulsion had typical shear-thinning behavior and higher storage modulus. The concentration of cellulose gel dispersions had a significant influence on the emulsion stability. The Pickering emulsion stabilized by the cellulose gel dispersions would open opportunities for the development of food emulsion systems or environmentally friendly functional materials.     

Dry reforming of greenhouse gases CH4/CO2 over MgO-promoted Ni–Co/Al2O3–ZrO2 nanocatalyst: effect of MgO addition via sol–gel method on catalytic properties and hydrogen yield

Sol–gel method was employed to prepare Ni–Co/Al₂O₃–MgO–ZrO₂ nanocatalyst with various loadings of MgO (5, 10 and 25 wt%) for dry reforming of methane. The physiochemical properties of nanocatalysts were characterized by XRD, field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), BET and fourier transform infrared spectroscopy (FTIR) analysis. Evaluation of catalytic performance was conducted in atmospheric pressure, stoichiometric feed ratio, GHSV of 24 l/g_cat h and temperature range from 550 to 850 °C. XRD patterns represented that as MgO content increases, the amorphous behavior slightly intensifies and also dispersion of active phase improves which probably caused by strong metal–support interaction. Furthermore, FESEM analysis confirmed that all of prepared samples are nano scale. EDX results besides verifying the declared claim about the dispersion of samples proved the presence and detected the position of the various elements. In addition, based on the FESEM analysis, narrow particle size distribution, uniform morphology and dispersion without agglomeration were found for Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO. Moreover, smallest average particle size 11.6 nm (close to the critical size for Ni–Co catalyst to avoid carbon formation) was obtained for this nanocatalyst. Also, according to the BET analysis, MgO rich nanocatalyst represented the higher surface area than the other ones. Based on the excellent characterizations, Ni–Co/Al₂O₃–MgO–ZrO₂ with 25 wt% MgO exhibited the best products yield through all of the investigated temperature e.g. H₂ = 96.9 % and CO = 97.1 % at 850 °C. Furthermore, this nanocatalyst demonstrated the stable yield with H₂/CO close to unit during 1,440 min stability test.     

Hybrid silica-organic material with immobilized amino groups: surface probing and use for electrochemical determination of nitrite ions

A sol–gel based hybrid process was developed by manipulating different techniques in sol–gel process to synthesize γ-alumina and (CuO, CuO + ZnO) doped γ-alumina spherical particles. Catalysts having spherical geometry have an important advantage over powders or pellets which are impervious to fluids, when packed in a reactor. Boehmite sol was used as alumina precursor for synthesizing porous γ-alumina and doped materials. γ-alumina particles having 5 wt% CuO, 4 wt% CuO + 1 wt% ZnO, 3 wt% CuO + 2 wt% ZnO and 2 wt% CuO + 3 wt% ZnO were prepared by adding required amounts of Cu(NO₃)₂ and Zn(NO₃)₂ solutions prior to gelation of the sol. Methanol dehydration studies were carried out by employing these synthesized catalysts. Hundred percent conversion of methanol to dimethyl ether was observed with (4 wt% CuO + 1 wt% ZnO)-γ-alumina and (5 wt% CuO)-γ-alumina microspheres at 325 and 350 °C, respectively.     

Preparation of monodisperse PMMA microspheres in nonpolar solvents by dispersion polymerization with a macromonomeric stabilizer

We discuss a dispersion polymerization procedure for preparing monodisperse and micron-sized poly(methyl methacrylate) (PMMA) particles in hexanes with methacryloxypropyl-terminated polydimethylsiloxane stabilizers. We investigate the effects of the stabilizer molecular weight, stabilizer concentration, and monomer concentration on the particle size and polydispersity. We find that a minimum molecular weight of 10 000 g/mol is necessary to synthesize colloidally stable PMMA dispersions. The particle polydispersity is minimal (=5%) for stabilizer to monomer weight ratios of 0.02 to 0.1, while PMMA particles prepared under conditions outside this range are polydisperse. The particle diameter can be varied from 0.4 to 1.5 µm by appropriate choices of stabilizer and monomer concentrations. Stable PMMA suspensions can be prepared at up to 26.3% solids. The dispersions are stable in most liquid aliphatics, and are monodisperse enough to form ordered domains at high concentration. This single-stage synthesis, requiring only commercially available materials, may be of interest to those seeking a simple way to prepare highly monodisperse non-aqueous dispersions in the micron size range.     

Effects of synthetic lipids on solubilization and colloid stability of hydrophobic drugs

Aqueous miconazole (MCZ) aggregates were solubilized and/or colloidally stabilized by bilayer-forming synthetic amphiphiles such as dioctadecyldimethylammonium bromide (DODAB) or sodium dihexadecylphosphate (DHP) dispersions. Particle sizing, light absorption and scattering from drug particles, zeta-potential determination, and drug aggregation kinetics from turbidity changes in the presence or absence of lipid dispersions were obtained over a range of drug and lipid concentrations. The very low solubility of MCZ in water made possible the determination of size distributions for drug particles in water and comparison to those in the presence of DODAB or DHP nanosized bilayer fragments or entire and closed bilayer vesicles. Large drug aggregates disappeared upon incubation with nanosized bilayer fragments produced by ultrasonic dispersion with tip. Light-absorption spectra for MCZ in a poor solvent (water), in a good organic solvent (methanol), and in different lipid dispersions showed that solubilization depended on the presence of bilayer fragments. MCZ was poorly soluble in dispersions formed of closed bilayers (vesicles) of DODAB or DHP in the gel state and in phosphatidylcholine (PC) vesicles in the liquid-crystalline state. Increased hydrophobicity at the borders of bilayer fragments explained MCZ solubilization. At [MCZ]>0.4 mM, kinetics of drug aggregation, zeta-potential measurements, and size minimization were obtained upon addition of minute amounts of oppositely charged bilayer fragments ([DHP]=0.05 mM), making possible determination of a remarkable stabilizing effect of drug particles by coverage with anionic bilayer fragments. High drug colloid stability in the presence of charged bilayer fragments was achieved by two different means: (1). at large drug concentrations and small concentrations of bilayer fragments, coverage of large drug particles with bilayer fragments; (2). at large amounts of bilayer fragments, drug solubilization in its monomeric form at the borders of bilayer fragments. Inexpensive, synthetic bilayer fragments offered a large area of hydrophobic nanosurfaces dispersed and electrostatically stabilized in water, opening new prospects for drug solubilization and colloid stabilization of insoluble drug particles.     

Hofmeister Salts Affect Buildup of Thin Multilayer Films Surrounding Oil Droplets

The layer-by-layer electrostatic deposition method is a novel technique to precisely control the interfacial properties of multilayered films such as charge, thickness, permeability, and composition. The formation and stability of multilayered emulsions is however often plagued by extensive droplet flocculation and aggregation even at ideal polyelectrolyte concentrations where saturation should occur. Addition of salts may reduce the degree of attractive interactions ions and thus improve deposition. To test this hypothesis, the influence of different Hofmeister salts (KCl, NaCl, LiCl, and NH₄Cl) at various salt concentrations (0–2500 mM) on the aggregation behavior of multilayered emulsions was investigated. A simple coating process of fish gelatin interfacial membranes with sugar beet pectin was used. Our results show that mean particle diameter and particle size distribution of emulsions initially decreased from 600 nm to 328 nm with increasing salt concentrations up to 250 mM. Above a critical level (>500 mM), heavy aggregation of emulsions at the presence of chaotropic salts occurred whereas kosmotropes reduced flocculation and creaming. Microscopic images and isothermal titration calorimetry confirmed particle size measurements. Results thus suggest that addition of salts may be an extremely useful tool to modulate and improve depositioning of alternatingly charged polymers on surfaces.      

Double inversion of emulsions induced by salt concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.     

Polymer nanoparticles with a sensitive CO2‐responsive hydrophilic/hydrophobic surface

Poly(methyl methacrylate) (PMMA) nanoparticles with a sensitive CO₂‐responsive hydrophilic/hydrophobic surface that confers controlled dispersion and aggregation in water were prepared by emulsion polymerization at 50 °C under CO₂ bubbling using amphiphilic diblock copolymers of 2‐dimethylaminoethyl methacrylate (DMAEMA) and N‐isopropyl acrylamide (NIPAAm) as an emulsifier. The amphiphilicity of the hydrophobic–hydrophilic diblock copolymer at 50 °C was triggered by CO₂ bubbling in water and enabled the copolymer to serve as an emulsifier. The resulting PMMA nanoparticles were spherical, approximately 100 nm in diameter and exhibited sensitive CO₂/N₂‐responsive dispersion/aggregation in water. Using copolymers with a longer PNIPAAm block length as an emulsifier resulted in smaller particles. A higher concentration of copolymer emulsifier led to particles with a stickier surface. Given its simple preparation and reversible CO₂‐triggered amphiphilic behavior, this newly developed block copolymer emulsifier offers a highly efficient route toward the fabrication of sensitive CO₂‐stimuli responsive polymeric nanoparticle dispersions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2149–2156     

Self-Assembly Behavior of Benzotriazole in Water

The self-assembly behavior of ¹H-benzotriazole (BTA) in aqueous solutions below its solubility limit has been revealed for the first time using NMR and light scattering techniques. Relaxation time, diffusion and chemical shift NMR techniques in addition to various light scattering techniques were used to study the aqueous behavior of ¹H-Benzotriazole (BTA). These studies have revealed the self assembly of BTA molecules in water. Results show that BTA molecules tend to aggregate in water to form nanoparticles with radius in the range of 5 nm. The critical aggregation concentration (CAC) is estimated based on NMR data to be ～16–20 mM. Such a critical aggregation concentration is comparable with the typical critical micelle concentration (CMC) for surfactants that have moderate aqueous solubility. The self-assembly behavior of BTA may not be limited to benzotriazole. It might be generally true for all poorly water soluble species to aggregate at concentrations below their solubility.     

Protein ultrafiltration concentration polarization layer flux resistance I. Importance of protein layer morphology on flux decline with gelatin

The effect of added ethanol and (NH₄)₂SO₄ on the morphology of the gelatin concentration polarization (CP) layer during ultrafiltration (UF) was analyzed using protein ternary phase diagrams, as well as turbidity and intrinsic viscosity measurements. CP layer resistance was characterized by measuring the flux decline index (FDI) of a 0.10 wt% gelatin solution in a dead-end UF system at 40°C. Ethanol concentrations up to 30 wt% produced an aggregated CP layer morphology with a moderate FDI. However, above 30 wt%, a swollen macromolecular gel formed on the membrane surface, resulting in a lower FDI. Low salt levels led to the formation of compact protein particles in the CP layer that had a moderate FDI. In contrast, a concentration of 8 wt% produced a high FDI coacervate structure. The highest FDI was observed at salt concentrations above 12 wt%, where the surface morphology consisted of a dense particulate gel. Overall, the FDI could be altered by a factor of ∼3 by manipulating the concentration of solute in the solution.     

Formation of Vesicles and Micelles in Aqueous Systems of Tetrameric Acids as Determined by Dynamic Light Scattering

A comprehensive dynamic light scattering (DLS) study on the system BP10Na₄/water is presented. BP 10Na₄ is a tetrameric fatty acid in sodium form. In order to change molecular packing conditions both electrolyte (NaCl) and alcohol (1-butanol, 1-pentanol) are added to the surfactant system. Phase diagrams of the systems reveal not only an extensive micellization, but also the occurrence of a lamellar liquid crystalline D phase. The DLS study shows an existence of vesicles at very dilute BP10Na₄ concentrations ( ?cmc) and also a co-existence of micelles and vesicles at higher BP10Na₄ concentrations. Cryo-TEM pictures verify the existence of the vesicles. Based on the DLS and SLS experiments the weight-average molar mass of the micelles are estimated to be 13500 g/mol at 100 mM NaCl and 22700 g/mol at 600 mM. The corresponding aggregation numbers are 13 and 22, respectively.     

Study on Rheologic Properties and Molecular Configuration in the Mixed Systems of Polyacrylamide and a Gemini Surfactant

The rheological properties and the microconformations of the mixed system of hydrophobically modified polyacrylamide and a Gemini surfactant, O,O′-bis(sodium 2-lauricate)-p-benzenediol, in water, 5000 mg/L NaCl, 1.2 wt% NaOH, and 5000 mg/L NaCl with 1.2 wt% NaOH solutions were investigated, respectively. Scan electron microscopy of the samples prepared with the vacuum sublimation freezing–drying technique shows much more polymer aggregation information. The mixed system of polyacrylamide and an anionic surfactant, sodium dodecyl benzene sulfonate, was also investigated for comparison. The experimental results reveal that the rheological properties have a close relation with aggregation micostructure of the polymer. The Gemini surfactant is much more effective to affect the molecular interaction and aggregation of hydrophobically modified polyacrylamide, and thus has a higher viscosity increasing effect than the conventional surfactants.