Polyacrylamide Layer Research Articles

Depth profiling via nanoindentation for characterisation of the elastic modulus and hydraulic properties of thin hydrogel layers

The accurate determination of the mechanical properties of hydrogels is of fundamental importance for a range of applications, including in assessing the effect of stiffness on cell behaviour. This is a particular issue when using thin hydrogel layers adherent to stiff substrate supports, as the apparent stiffness can be significantly influenced by the constraint of the underlying impermeable substrate, leading to inaccurate measurements of the elastic modulus and permeability of thin hydrogel layers. This study used depth profiling nanoindentation and a poroelastic model for spherical indentation to identify the elastic moduli and hydraulic conductivity of thin polyacrylamide (PAAm) hydrogel layers (∼27 μm–782 μm thick) on impermeable substrates. The apparent stiffness of thin PAAm layers increased with indentation depth and was significantly greater than those of thicker hydrogels, which showed no influence of indentation depth. The hydraulic conductivity decreased as the geometrical confinement of hydrogels increased, indicating that the fluid became more constrained within the confinement areas. The impact of geometrical confinement on the apparent modulus and hydraulic conductivity of thin PAAm hydrogel layers was then established, and their elastic moduli and intrinsic permeability were determined in relation to this effect. This study offers valuable insights into the mechanical characterisation of thin PAAm hydrogel layers used for the fundamental study of cell mechanobiology.

Facile fabrication of fabric-based membrane for adjustable oil-in-water emulsion separation, suspension filtration and dye removal

Special wettability fabrics-based membranes have shown excellent performance in emulsified oil/water separation, however, their application in separating industrial oil-in-water emulsions still remains a great challenge due to the complexity of multifarious surfactant components. In this work, we demonstrate a simple and facile approach to fabricate fabric-based membranes (P(AM-DMC-AA)@CFs) for complex emulsified oil/water (printing and dyeing wastewater) separation with combining the advantage of amphoteric polyacrylamide layer and cotton fabric in a single system. The amphoteric polyacrylamide surface and tortuous fabric channels synergistically provide the membranes with demulsification adjustability for separating emulsified oil in water which stabilized by anionic/cationic surfactants. Meanwhile, the incorporating of amphoteric polyacrylamide into cotton fabrics had remarkable advantages of both flexible and stable superhydrophilic/underwater superoleophobic. Consequently, the obtained P(AM-DMC-AA)@CFs membranes are endowed with robust superhydrophilicity, underwater superoleophobicity and switchable zeta potential, which make it capable of highly efficient separation of oil/water emulsion (anionic: 94.05%, cationic: 96.19%), suspension filtration (kaolin: 89.5%, hematite: 93.1%,) and concurrent dye removal in 5 min (14.3 mg/g). In addition, the prepared membrane is still effective in separating simulated printing and dyeing wastewater containing multiple pollutants. The facile and versatile design of the P(AM-DMC-AA)@CFs membrane offers new prospects for exploiting fabric-based membranes with extraordinary features for industrial oily wastewater treatment.

A stretchable and conductive design based on multi-responsive hydrogel for self-sensing actuators

Intelligent hydrogel materials have significant potential for soft robotic applications due to their sharply and reversibly responding to various external stimuli. However, obtaining a biomimetic hydrogel actuator with integrated self-sensing and self-actuation properties is still a great challenge. Herein, a multifunctional conductive hydrogel is fabricated by incorporating a conductive polymer polyaniline (PANI) into a double network poly(N-isopropylacrylamide-co-acrylamide)/poly(vinyl alcohol) (PNA/PVA) hydrogel. The as-prepared conductive PNA/PVA/PANI hydrogel could span a wide range of mechanical properties and phase transition temperatures by simply tuning polymer composition. When combined the active PNA/PVA/PANI layer with a passive polyacrylamide (PAAM) layer, a bilayer hydrogel actuator exhibits superior actuation ability with high bending speeds by the thermal stimulation. In addition, the introduction of PANI component endows the PNA/PVA/PANI hydrogel with excellent electrical conductivity up to 3.91 ± 0.15 S/m and ultrahigh-efficiency of photothermal conversion. Consequently, the PNA/PVA/PANI hydrogel not only exhibits piezoresistive strain/pressure sensing in motion recognition and physiological signal monitoring, but also displays a variety of precise and remotely driven photo-responsive locomotion such as contraction, bending, light tracking and weightlifting by locally near-infrared (NIR) illumination. Furthermore, this hydrogel can simultaneously detect these actuation states via real-time resistance change, achieving closed-loop monitoring and sensing feedback. The self-sensing actuation performance has been fully demonstrated by remotely controlling a hydrogel octopus’s grasping and object moving activities. The multi-responsiveness and real-time sensory feedback will inspire this material to be applied in novel soft biomimetic actuating materials and systems.

Effects of inorganic cations on the steric force between polyacrylamide layer physically adsorbed on SiO2 wafer and poly (ethylene oxide) layer

The physical adsorption of polyacrylamide on the SiO2 wafer in high salty solutions was investigated by an improved AFM steric force measurement. The colloid probe was modified by poly (ethylene oxide) layer and used to determine the steric force between adsorbed polyacrylamide and poly (ethylene oxide) layer in NaCl, KCl, MgCl2 and CaCl2 solutions. Assuming the adsorbed polyacrylamide complies with the self-similar model, the surface excesses, the thicknesses of the proximal regions, and "free energies of sticking" were estimated. Take the case of 5000 mg/L NaCl for example. The concentration profile was deduced from the corresponding steric force profile. The polyacrylamide concentration next to the SiO2 wafer was estimated to be about 147 g/L and the average concentration in the proximal region was estimated to be about 100 g/L. Based on the above estimations, interaction strength between the adsorbed cations and polyacrylamide was established, Mg2+ > Ca2+ > K+ > Na+. Moreover, the conformations of the adsorbed polyacrylamide were changed from "lying flat" to folded ones by the stronger interactions between the adsorbed cations and polyacrylamide.”

Multifunctional polymeric surface coatings of carbon fibre electrodes for enhanced energy storage performance

We report a proof-of-concept study on the development of multifunctional surface coatings for carbon fibre (CF) electrodes in structural energy composites, which for the first time addresses three key properties of CF: capacitance, tensile properties and interfacial adhesion, simultaneously. Multifunctional coatings have been designed by covalently grafting conductive and redox active poly(o-phenylenediamine) (PoPD) on CF via surface electro-initiated polymerisation using different diazonium salts. This has resulted in improvements in specific capacitance, tensile strength, tensile modulus and interfacial shear strength (IFSS) up to 30 F g−1, 4.58 GPa, 276 GPa and 43.5 MPa, respectively, all of which are higher than the values reported for pristine CF. To further improve the IFSS, a bilayered polymeric coating has been designed by electro-grafting polyacrylamide on top of the conductive PoPD layer, which led to specific capacitance, tensile strength, tensile modulus and IFSS (up to 9 F g−1, 4.28 GPa, 256 GPa and 55.6 MPa, respectively). The non-conductive polyacrylamide layer on top of the PoPD layer is thought to be the reason for depressed capacitive performance, though this does come at a trade-off for improved fibre–matrix adhesion. Thus, a means to tailor this material based on end user priorities is presented herein. In contrast to the conventional methods of surface activation for improving the capacitance of CF, which often result in a trade-off between electrochemical and mechanical/interfacial properties of CF, this method offers a means to simultaneously enhance the electrochemical, mechanical, and interfacial performance of CF with great tunability.

A strategy that combines a hydrogel and graphene oxide to improve the water-lubricated performance of ultrahigh molecular weight polyethylene

The use of water-lubricated materials is important in efforts to protect the environment and conserve resources. However, the low bearing capacity and insufficient lubrication of ultrahigh molecular weight polyethylene (UHMWPE), which is an important water-lubricated material, restrict its application in engineering fields. In order to improve the properties of UHMWPE under water lubrication, we propose a strategy that combines a soft polyacrylamide (PAAm) hydrogel with hard graphene oxide (GO). PAAm-GO flakes were synthesized and UHMWPE composites reinforced with GO or PAAm-GO were prepared. The mechanical properties and tribological performances of the composites were tested and analyzed. The results show that the PAAm layers grafted onto GO played an important role in improving the bearing capacity and lubrication conditions of the composites. The strategy of integrating hard GO flakes modified with soft PAAm layers will provide a method for designing reinforced composites used in the manufacturing of water-lubricated bearings.

Aggregation and thermal properties of nanostructured montmorillonite covered with mixed adsorption layers of cationic polyacrylamide and hazardous lead(II) ions

The aim of the study was to investigate the influence of nanostructured montmorillonite surface modification by the cationic polyacrylamide and the lead(II) ions on the thermal and aggregation properties of solid particles covered with mixed adsorption layers. The effects of cationic groups content in the polymeric macromolecules, the order of individual adsorbates addition, and lead(II) ions concentration were determined. Using spectrophotometry, potentiometric titration, microelectrophoresis, turbidimetry, DCS (Differential Centrifugal Sedimentation) and thermal analysis methods, the adsorption, electrokinetic, aggregation properties, as well as the thermal stability of studied montmorillonite—CT PAM—Pb(II) systems were established. It was shown that applied polymeric substance (soil flocculant) causes accumulation of lead(II) ions, which are hazardous at very low concentrations. Nevertheless, the chemical nature of these interactions may limit the bioavailability of this heavy metal for plants.

Shape Morphable Hydrogel/Elastomer Bilayer for Implanted Retinal Electronics.

Direct fabrication of a three-dimensional (3D) structure using soft materials has been challenging. The hybrid bilayer is a promising approach to address this challenge because of its programable shape-transformation ability when responding to various stimuli. The goals of this study are to experimentally and theoretically establish a rational design principle of a hydrogel/elastomer bilayer system and further optimize the programed 3D structures that can serve as substrates for multi-electrode arrays. The hydrogel/elastomer bilayer consists of a hygroscopic polyacrylamide (PAAm) layer cofacially laminated with a water-insensitive polydimethylsiloxane (PDMS) layer. The asymmetric volume change in the PAAm hydrogel can bend the bilayer into a curvature. We manipulate the initial monomer concentrations of the pre-gel solutions of PAAm to experimentally and theoretically investigate the effect of intrinsic mechanical properties of the hydrogel on the resulting curvature. By using the obtained results as a design guideline, we demonstrated stimuli-responsive transformation of a PAAm/PDMS flower-shaped bilayer from a flat bilayer film to a curved 3D structure that can serve as a substrate for a wide-field retinal electrode array.

New type of montmorillonite compatibilizers and their influence on viscoelastic properties of ethylene propylene diene and methyl vinyl silicone rubbers blends

Montmorillonite modified with a grafted polyacrylamide layer (Mt-g-PAm) was used as an effective compatibilizer for the blends of ethylene propylene diene (EPDM) and methyl vinyl silicone (MVQ) rubbers. PAm was prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) in such a way that varied PAm content and Mt. surface coverage was achieved, which was confirmed by FTIR, TGA, XRD and TEM measurements. The morphology of the hybrid compatibilizers influenced the elastic behavior of the composite blends during samples deformation which was due to varied polymer-filler-rubber network interactions as well as the varied chains entanglements effects. The selective location of Mt-g-PAm within MVQ phase as well as at the EPDM/MVQ interphase affected the dynamic mechanical properties of the composites (storage and loss modulus G', G" and tan delta values). Tan delta values were used to investigate the damping properties of the composites. The highest values were observed for hybrid compatibilizers grafted with dense brushes. Compared to the values of the neat matrix, an improvement of 118% and 161% was reported for long dense and short dense brushes, respectively.

Antifreezing and Stretchable Organohydrogels as Soft Actuators.

Inspired by the freezing tolerance performances found in living creatures, an effect approach is presented to develop novel antifreezing polymeric organohydrogel actuators. Through construction of a bilayer hydrogel including a nonresponsive polyacrylamide (PAAm) layer and a pH-responsive polyacrylic acid (PAA) layer in the presence of a mixed solvent of water and glycerol, organohydrogel actuators that could produce various shape deformations at subzero temperatures have been achieved, and the actuating speed could be tuned by adjusting the temperature and the ratio between glycerol and water. Moreover, a series of application demonstrations including a weightlifting robot, artificial valve, and robotic arm have been displayed. In addition, by introducing the ionic compound KI into the glycerol-based organogel, flexible conductors that could perform stable sensing performance over a wide range of temperatures from -30°C to 60°C have been developed.

Tough and Variable-Band-Gap Photonic Hydrogel Displaying Programmable Angle-Dependent Colors.

One-dimensional photonic crystals or multilayer films produce colors that change depending on viewing and light illumination angles because of the periodic refractive index variation in alternating layers that satisfy Bragg’s law. Recently, we have developed multilayered photonic hydrogels of two distinct bulk geometries that possess an alternating structure of a rigid polymeric lamellar bilayer and a ductile polyacrylamide (PAAm) matrix. In this paper, we focus on fabrication of composite gels with variable photonic band gaps by controlling the PAAm layer thickness. We report programmable angle-dependent and angle-independent structural colors produced by composite hydrogels, which is achieved by varying bulk and internal geometries. In the sheet geometry, where the lamellae are aligned parallel to the sheet surface, the photonic gel sheet exhibits strong angle-dependent colors. On the other hand, when lamellae are coaxially aligned in a cylindrical geometry, the gel rod exhibits an angle-independent color, in sharp contrast with the gel sheet. Rocking curves have been constructed to justify the diverse angle-dependent behavior of various geometries. Despite varying the bulk geometry, the tunable photonic gels exhibit strong mechanical performances and toughness. The distinct angle dependence of these tough photonic materials with variable band gaps could benefit light modulation in displays and sensor technologies.

Water-Triggered Ductile–Brittle Transition of Anisotropic Lamellar Hydrogels and Effect of Confinement on Polymer Dynamics

We study the effect of dehydration on the structure and mechanical properties of anisotropic lamellar hydrogels, consisting of alternative stacking of several thousands of nanoscale rigid bilayers from amphiphilic poly(dodecyl glyceryl itaconate) (PDGI) and submicroscale soft hydrogel layers from hydrophilic polyacrylamide (PAAm) networks. We found that the layered microstructure is well preserved with dehydration, and a ductile–brittle transition occurs at the critical water content. This transition is related to the rubbery–glassy transition of the PAAm layers, which occurs at 58 wt % water content and is much higher than 26 wt % of bulk PAAm hydrogels. Such specific behavior of the lamellar hydrogels indicates that the dynamics of the submicroscale PAAm hydrated layer intercalated between the rigid bilayers are very different from its bulk state.

High Oxygen Barrier Polyethylene Films

“Layer by layer” technology was used to create transparent, thin and high barrier polyethylene films to use in food packaging. These films were made by inserting successive layers of polyacrylamide and montmorillonite (Cloisite Na+, non-organic modification) grown onto a low density polyethylene (LDPE) film substrate submitted to corona treatment. Excellent oxygen permeability results were reached with only 9 bilayers, with a reduction of 99.92%, compared to the pure polyethylene. This allowed the oxygen barrier film to change from poor to high (3.66 cm3/m2·day), with a total thickness of 48 microns, due to the structure formed over the film to create a tortuous path for oxygen molecules. Optical properties were analysed, showing a ≥92% transparency in all samples. Thermal stability of polyethylene was slightly improved and this was attributed to nanoclays presence forming an insulating layer. The result of this research is a thin structured film which is a good candidate for common barrier films replacement in food packaging thanks to its high oxygen barrier capacity, optical transparency, microwaveability and recyclability.

Abstract A36: Study of stromal mechanoregulation of tumor metabolism and growth dynamics

Abstract As tumors develop and mature they are subjugated to compressive forces and a rigid stroma. This is particularly true in pancreatic cancer where its defining feature is a particularly rigid and fibrous stroma. The mechanical properties of the stroma can have a large influence on the growth behavior and invasiveness of tumors. An intriguing recent example of this is that the PI3K pathway is activated via integrin engagement on a rigid stroma and can affect some metabolic pathways. What makes this exciting is that both the stromal stiffness and reprogrammed metabolism have long been known to be features of cancer and this showed that these features may be intertwined in a feedback loop. From another angle, tumors are subjugated to high compressive forces and many have shown that this force can alter spheroid growth dynamics and shift cells to a more invasive phenotype. While compressive stress on spheroid growth certainly influences its growth dynamics, it is unclear whether it is due to stress or strain on the spheroid. Additionally, it implicates compressive force in altering the cellular metabolism as well. Going a step further, extracellular acidity is a well-known phenotype of solid tumors and is intrinsically linked to an altered metabolism. To study this feedback loop between stromal mechanical properties and metabolism/acidity we will utilize two different models alongside the pH dependent fluorophore, SNARF. The first is a hybrid gel model that is constructed of a base polyacrylamide (PA) layer that is covalently bound to select ECM proteins such as matrix gel and collagen. The second is a spheroid embedded in agarose model in which a base coat of agarose is applied to the bottom of each well in a multiwall plate and after setting, an ungelled mixture of spheroids, agarose and fluorescently labelled latex beads are poured over the base coat and allowed to set. The agarose is bio inert and cannot be broken down by cells. Thus it effectively acts like a compressible, non-integrin activating, isotropic media that completely surrounds the embedded spheroid. To study the cell packing density we will explore a model that predicts strain on an embedded spheroid due to compressive stress drives the cell density in spheroids. To experimentally explore this model, we will use the spheroid embedded in agarose model and vary starting implanted spheroid sizes, but remove them from the agarose at identical stress levels. All of this together will lead us to a better understanding of how the cell metabolism/pHe and tumor cell packing are mechanoregulated by the stroma. Citation Format: Michael Anderson, Jonathan Celli, Hamid El-Hamidi. Study of stromal mechanoregulation of tumor metabolism and growth dynamics. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A36.

Investigation of Removal Possibilities of Colloidal Alumina from Aqueous Solution by the Use of Anionic Polyacrylamide

Purification of drinking and industrial water required usage of high molecular weight polymer to cause flocculation process of dispersed suspension of contaminants. Polyelectrolytes, including ionic polyacrylamide are especially appropriate for these purposes, because in this case the suspension stability can be controlled by both steric and electrostatic forces. Thus the influence of solution pH and hydrolysis degree (carboxyl groups content) of anionic polyacrylamide (PAM) on the alumina (Al2O3) suspension stability were studied. The turbidimetry was applied for determination of the examined systems stability. The mechanism of suspension stabilization or destabilization in the polymer presence was proposed on the basis of determined parameters: adsorbed amount of PAM, its adsorption layer thickness, linear dimensions of macromolecules in the solution and zeta potential of alumina particles covered with the polyacrylamide layer. The greatest decrease of the alumina suspension stability in the polymer presence in comparison to that without the polymer was obtained at pH 6 after the addition of PAMs with higher molecular weight (i.e. 14 000 0000) and hydrolysis degrees 20 and 30% (efficient neutralization of solid surface charge). In turn, the most unstable alumina system proved to be that prepared at pH 9 containing PAM with the highest molecular weight and the greatest hydrolysis degree (causing the most effective bridging flocculation).

Fabrication and Optimization of ChE/ChO/HRP-AuNPs/c-MWCNTs Based Silver Electrode for Determining Total Cholesterol in Serum.

The developed method used three enzymes comprised of cholesterol esterase, cholesterol oxidase, and peroxidase for fabrication of amperometric biosensor in order to determine total cholesterol in serum samples. Gold nanoparticles (AuNPs) and carboxylated multiwall carbon nanotubes (cMWCNTs) were used to design core of working electrode, having covalently immobilized ChO, ChE, and HRP. Polyacrylamide layer was finally coated on working electrode in order to prevent enzyme leaching. Chemically synthesised Au nanoparticles were subjected to transmission electron microscopy (TEM) for analysing the shape and size of the particles. Working electrode was subjected to FTIR and XRD. The combined action of AuNP and c-MWCNT showed enhancement in electrocatalytic activity at a very low potential of 0.27 V. The pH 7, temperature 40°C, and response time of 20 seconds, respectively, were observed. The biosensor shows a broad linear range from 0.5 mg/dL to 250 mg/dL (0.01 mM–5.83 mM) with minimum detection limit being 0.5 mg/dL (0.01 mM). The biosensor showed reusability of more than 45 times and was stable for 60 days. The biosensor was successfully tested for determining total cholesterol in serum samples amperometrically with no significant interference by serum components.

Soil Wetting Pattern from Subsurface Drip Irrigation as Affected by Application of a Polyacrylamide Layer†

AbstractA soil box was used to investigate the water movement and soil water distribution around subsurface drip laterals with two emitters in the presence of a thin layer of polyacrylamide (PAM). Sandy soil was uniformly packed into a soil box. The PAM was applied at a rate of 29.3 kg ha‐1 as a 0.01% solution by spraying it directly onto the soil surface at the required depths. With an operating pressure of 150 kPa and no PAM layer, the water consumption with a dripper line depth of 0.15 m was 12% lower than with a dripper line depth of 0.10 m. The greatest improvement in soil water‐holding capacity after the addition of a PAM layer (47%) was observed when the dripper line was placed at a depth of 0.15 m under an operating pressure of 100 kPa. With a dripper line depth of 0.15 m and an operating pressure of 100 kPa, the average moisture content in the vertical planes below and above the dripper line directly increased by about 7.4 and 20%, respectively, with PAM layers at 0.25 and 0.30 m depths when compared with the moisture content with no PAM layer. The combination of a dripper line depth of 0.15 m, a PAM layer depth of 0.30 m and an operating pressure of 100 kPa will achieve optimal water management. Copyright © 2015 John Wiley & Sons, Ltd.

Stabilization of activity of cellulase and hemicellulase enzymes by covering with polyacrylamide layer

Enzymes (β-d-xylosidase, endoxylanase and endocellulase), isolated from Thermobifida fusca moderate thermophile organism, have been stabilized as single enzyme nanoparticles. During the stabilization process every individual enzyme molecule is covered with a thin polyacrylamide polymer layer. This polymer layer has a cross-linked spatial structure but thin and porous enough to allow the diffusion of substrate molecules to the active centrum of the enzyme molecule and the enzymatic function of the pretreated enzyme. A new, easily realizable two-step process was used to prepare enzyme nanoparticles. The catalytic activity of these three native enzymes and enzyme nanoparticles prepared were measured as a function of the incubation time, with 150rpm shaking at 50°C as optimal temperature. All enzymes are significantly more stable in form of enzyme nanoparticles than in their natural state. Heat stability of β-d-xylosidase enzyme was also investigated at 80°C and 150rpm. The half-life time of activity of enzyme nanoparticles obtained was about two-order of magnitude longer than that of the natural ones.

Self-assembled reduced graphene oxide/polyacrylamide conductive composite films.

Substrate supported conductive thin films are prepared by the self-assembly of graphene oxide (GO) on a cationic polyacrylamide (CPAM) layer followed by a subsequent chemical reduction. During self-assembly, the dispersed GO nanosheets with a negative zeta potential from solution are spontaneously assembled onto the positively charged CPAM adsorption layer. In addition, CPAM adsorption on the substrate is studied with an electrochemical quartz crystal microbalance (EQCM), showing adsorption stabilization could be established in less than 150 s. The electrostatic interactions between GO and CPAM are investigated by changing the polarization potential with EQCM for the first time, and optimal conditions for facilitating self-assembly are determined. The self-assembled GO/CPAM films are further characterized by Raman spectroscopy, infrared spectroscopy and atomic force microscopy. Importantly, reduced GO (R-GO)/CPAM composite films exhibiting a sheet resistance of 3.1 kΩ/sq can be obtained via in situ reduction in sodium borohydride for 20 min at room temperature. This provides a simple, highly effective, and green route to prepare conductive graphene-based composite thin films.

Impact of polyacrylamide with different contents of carboxyl groups on the chromium (III) oxide adsorption properties in aqueous solution

The main goal of experiments was determination of solution pH and contents of anionic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of chromium (III) oxide suspension. The spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry were applied. They enabled determination of polymer adsorbed amount, surface and diffusion charges of solid particles with and without PAM, thickness of polymer adsorption layer, macromolecule dimensions in the solution and stability of the Cr2O3 – polymer systems, respectively. It was found that adsorption of anionic PAM decreases and thickness of polymeric adsorption layer increases with the increasing pH. Slightly higher adsorption was obtained for the PAM samples containing a greater number of carboxyl groups. At pH 3 and 9 insignificant deterioration of stability conditions of Cr2O3 particle covered with polyacrylamide was observed (neutralization of solid positive charge by the adsorbed polymeric chains (pH 3) and single polymeric bridges formation (pH 9)). The electrosteric repulsion between the solid particles covered with PAM layers at pH 6, is the main reason for significant improvement of Cr2O3 suspension stability in the polymer presence.