Clay Mineral Dispersions Research Articles

Effect of blunging process on purification of halloysite ore from ferrous impurities by dry magnetic separation

The objective of this research is to study the effects of feed particle size, splitter angle, and washing process on Fe<sub>2</sub>O<sub>3</sub> removal efficiency in the separation of ferrous impurities from halloysite ore by dry magnetic separation in order to increase the purity of halloysite sample after crushing and blunging processes separately. Firstly, after crushing ore in a jaw crusher and sizing to -2+1 mm, -1+0.5 mm, and -0.5+0.212 mm fractions, the sized materials were fed to REMS-type dry magnetic separator at a constant belt speed of 300 rpm with the splitter angles of 0, 15, 30º separately. Maximum Fe<sub>2</sub>O<sub>3</sub> removal efficiency (FRE) (97.1%) was obtained in the nonmagnetic product at -0.5+0.212 mm size fraction and 0º splitter angle. The minimum Fe<sub>2</sub>O<sub>3</sub> content (1.3%) was reached in the nonmagnetic product obtained in the experiment with the feed size of -2+1 mm and a splitter angle of 0º. Secondly, dry magnetic separation was applied to the washed -2+0.212 mm size fraction after drying at room temperature to evaluate the coarse particle-sized halloysite ore that was gained by mechanical dispersion in the aqueous medium towards sodium hexametaphosphate (SHMP), while a significant part of the clay minerals went into fine size after the dispersion process. In the experiment performed with a 0º splitter angle after washing, it was determined that halloysite concentrate of 0.4% Fe<sub>2</sub>O<sub>3</sub> content could be obtained with 98.8% Fe<sub>2</sub>O<sub>3</sub> removal efficiency. As a result of dry magnetic separation experiments, it was seen that Fe<sub>2</sub>O<sub>3</sub> removal efficiency decreased as the splitter angle increased, while Fe<sub>2</sub>O<sub>3</sub> content in magnetic and nonmagnetic products increased. It was determined that washing and cleaning of fine-sized minerals plastered on particle surfaces after mechanical dispersion and particle release of minerals with different magnetic properties increased the dry magnetic separation efficiency, and nonmagnetic products with very low Fe<sub>2</sub>O<sub>3</sub> (0.4%) and high Al<sub>2</sub>O<sub>3</sub> (31.9%) content was obtained. The blunging process in the presence of dispersant caused the dispersion of clay minerals and allowed to liberating of the ferrous minerals from the halloysite ore, hence the increase in the FRE for the magnetic separation.

Terminal amine‐based hyperbranched polymer‐modified metal oxide particles for improving the stability of water‐based drilling fluids in interaction with shales

AbstractWhen oil and gas extraction is drilled into water‐sensitive shale formations, water intrusion leads to hydration expansion and dispersion of shale clay minerals, which in turn leads to well wall instability. Two nanomaterials, PET and PEF, were synthesized using Hyperbranched polyethyleneimine (HPEI) as shell‐coated metal oxide nanoparticles (MONPs), and the nanomaterials were characterized in terms of molecular structure, thermal stability, and particle size distribution. The blocking and inhibition properties of PET and PEF were tested and investigated by analytical methods such as linear swelling experiments, shale rock chip rolling recovery experiments, and American Petroleum Institute (API) filtration loss experiments, the effects of PET and PEF on the rheology and filter loss reduction of water‐based drilling fuilds (WBDFs) were also investigated. PET and PEF have good blocking and inhibition properties, which somewhat ameliorate the effect of NPs on the rheology of WBDFs, while significantly improving the stability of shale in WBDFs.

Correlation of pesticide ecotoxicity with clay mineral dispersion effect on adsorption and ozonation – An approach through impact assessment on Lemna minor

An unprecedented approach allowed correlating the pesticide fate in clay-containing media under air exposure with their ecotoxicity. This constitutes the novelty of this work and involves the study of the toxicity of ozonized pesticide-containing waters towards an aquatic plant, Lemna minor. The behavior of diazinon (DAZ) and atrazine (ATR) in natural clay-containing media was simulated in plant growth media fulfilling the Swedish Institute for Standards (SIS) containing Na+ and Fe2+-exchanged montmorillonite (Mt). The exchangeable cation was found to influence the pesticide ozonation and toxicity towards Lemna minor. Pesticide interactions appear to promote high catalytic surface through a compromise between low pH and high Mt dispersion. These results provide valuable findings for predicting pesticide ecotoxicity according to their natural oxidative degradation in the host clay suspension.

Mechanism of microorganisms to relieve reservoir water sensitivity damage

Reservoir water sensitivity damage means that the contact between the external fluid and reservoir rock lead to the hydration, expansion, dispersion, and migration of clay minerals, thereby reducing the formation permeability and causing damage to the reservoir. In this study, the transformation of smectite to illite (S-I) is promoted by endogenous microorganisms to achieve anti-swelling of the clay minerals and reduce the water sensitivity damage of the reservoir. The microbial community reducing Fe(III) was enriched from the samples of Karamay Oilfield, Xinjiang, and microbial community diversity was analyzed by the 16S rRNA gene sequencing. The Fe(II) ion concentration in the interaction medium was monitored, and the maximum iron reduction rates reached 60.2%. The structural changes of smectite before and after microbial treatment were observed by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The result demonstrated that the reduction of Fe(III) was accompanied by the transformation of S-I. There may be some endogenous microorganisms that transform S-I in low permeability reservoirs. This study is of great significance for oilfields to realize clay mineral anti-swelling and eliminate reservoir water sensitivity damage by endogenous microorganisms.

Enhanced the permeability of water invasion sandstone by effectively inhibiting the swelling and dispersion of montmorillonite

The long-term effect of protecting water-sensitive reservoirs and enhancing permeability of water invasion reservoir is still an urgent practical problem to be solved. Here, an imidazolium Gemini ionic liquid (IL), PEG-DC8Im, with octyl as tail chain and polyoxyethylene chain as bridging group, was synthesized to inhibit the hydration, swelling and dispersion of clay minerals. The PEG-DC8Im could exert excellent anti-swelling ability (93.82 %) and outstanding washable capacity (cumulative decrease of anti-swelling rate after being washed five times: 1.32 %) at the concentration of 60 mmol/L. The inhibition effect of 20 mmol/L PEG-DC8Im was significantly better than that of 250 mmol/L KCl at 90 °C. And the PEG-DC8Im could intercalate into the interlayer space of MMT through cation exchange to play an inhibition effect, where zeta potential of MMT particles was reduced and then the dispersion ability of MMT was weakened. Subsequently, the anionic polymer poly(AM/AA) was found to cooperate with PEG-DC8Im to improve the inhibition effect for MMT swelling and dispersion, in which poly(AM/AA) was not intercalated into the interlayer of MMT, and only adsorbed on the surface of the particles to encapsulate the MMT particles. Simultaneously, the apparent viscosity and thixotropy of the composite solution were enhanced. Besides, after the treatment of PEG-DC8Im, the displacement pressure decreased and the permeability of sandstone cores increased due to the inhibition of clay mineral hydration, revealing the enhancement of injectivity. Finally, the pore connectivity of the core increased and the water wettability was weakened. The treatment of PEG-DC8Im was conducive to the discharge of invasive water in reservoir and the improvement of the reservoir permeability. Overall, PEG-DC8Im has a good application prospect as permeability-enhancing clay stabilizers.

In situ preparation of compounds using silanized mPEG inspired by talc-like structures.

Composite materials show improved properties compared to pristine materials, in particular when the filler is dispersed homogeneously in the matrix. For polymer-clay composites, different strategies exist to improve clay mineral dispersion in the polymer matrix. In this study, an innovative approach is suggested which consists of forming a talc-like structure directly in a polymer matrix using a silanized polymer as the silicon source. Poly(ethylene glycol) methyl ether of different average molar masses (Mn = 350, 500, 750, 1900 g mol-1) were functionalized with (3-isocyanatopropyl)triethoxysilane and added to the ethanolic solutions of magnesium nitrate. 1H-29Si CPMAS solid state NMR experiments revealed partial condensation of silane compounds, and FTIR analysis confirmed the presence of both Si-O and Mg-O bonds, but an additional proof of the Si-O-Mg bond is needed to prove the formation of such a structure.

Experimental study of water imbibition characteristics of the lacustrine shale in Sichuan Basin

Through the stimulation method of large-scale hydraulic fracturing, the spontaneous imbibition capacity of the water phase in the shale reservoir has great influence on the effect of stimulation. Generally, the lacustrine shale has the characteristics of high clay minerals content, strong expansibility, development of nanopores and micro-pores, and underdevelopment of fractures, which leads to the unclear behavior of spontaneous imbibition of aqueous phase. The lacustrine shale of Da'anzhai Member and marine shale of Longmaxi Formation in Sichuan Basin were selected to prepare both the shale matrix sample and fractured shale sample, and the spontaneous imbibition experiment of simulated formation water was carried out. By means of an XRD test, SEM observation, nuclear magnetic resonance test and linear expansion rate test, the mineral composition, the structure of pores and fractures, the capacity of hydration and expansion of both lacustrine and marine shale are compared and analyzed. The results show that the average spontaneous imbibition rate of lacustrine shale is 60.8% higher than that of marine shale within the initial 12 hours of imbibition. The lacustrine shale has faster imbibition rate than the marine shale in the initial stage of spontaneous imbibition. However, the lacustrine shale has underdeveloped pores and fractures, as well as poor connectivity of pores. Besides, the strong hydration and expansion of clay minerals can easily lead to dispersion and migration of clay minerals on the fracture surface, which will plug up the seepage channels, resulting in poor capacity of spontaneous imbibition. The spontaneous imbibition rate in the middle and late stage of Lacustrine shale is obviously lower than that of the marine shale. The overall spontaneous imbibition rate ability of the lacustrine shale is less than that of the marine shale. According to the characteristics of water imbibition of lacustrine shale, considering the dual effects of hydration expansion of clay minerals on the effective reconstructed volume, the microfractures can be initiated and extended by fully utilizing the hydration of shale. Acidification treatment, oxidation treatment or high temperature treatment can be used to expand pore space, enhance water phase imbibition capacity and improve multi-scale mass transfer capacity of the lacustrine shale.

Investigation on the microscopic damage mechanism of fracturing fluids to low-permeability sandstone oil reservoir by nuclear magnetic resonance

Hydraulic fracturing has become an essential stimulation treatment for improving the development efficiency of low-permeability oil reservoirs. However, fracturing fluid inevitably causes reservoir damage. This study proposed a combined method of microscopic and macroscopic experiments to investigate the nature of formation damage of fracturing fluid by quantifying its influence on porosity, permeability, and pore structure. Nuclear magnetic resonance technology combined with core flooding test and parallel sample comparison method was applied to quantitatively evaluate the damage degree and identify the main damage types of hydroxypropyl guar (HPG) fracturing fluid and slickwater fracturing fluid. The microscopic damage mechanisms of these fracturing fluids were analyzed by thin section petrography, X-ray diffraction, rate-controlled mercury intrusion, scanning electron microscopy, and wettability tests. The results show that the total permeability damage degree of HPG fracturing fluid filtrate is 30.43%, of which water sensitivity, water lock, and macromolecule adsorption account for 6.06%, 23.26%, and 1.11%, respectively. Water lock is the major damage factor. Regarding the damage of slickwater fracturing fluid filtrate, water sensitivity causes the severest damage, corresponding to 39.08% of core permeability loss, whereas macromolecule adsorption and water lock contribute 13.21% and 0.97%, respectively. Water sensitivity damage causes reduced porosity, decreased permeability, and narrower pores, resulting from hydration, swelling, dispersion and migration of clay minerals. Water lock damage increases the movable pore volume, decreases the permeability, increases the pore radius, decreases the throat radius, and increases the pore throat ratio, which increases the flow resistance to the oil phase. The magnitude of water lock damage is closely related to the surfactant content and performance, rock wettability, and pore throat radius ratio. Macromolecule adsorption damage leads to a decrease in permeability, a reduction in the number of large pores, an increase in the number of small throats, and an increase in the pore throat radius ratio due to the absorption and retention of macromolecules on the surfaces of the pores and throats. Increasing the flowback volume of slickwater fracturing fluid can recover part of the macromolecule absorption damage. This research can provide a reliable reference for the optimization of fracturing fluid performance, enhancement of the fracturing effect and reservoir protection of low-permeability reservoirs.

Effect of water intrusion on the characteristics of surface morphology and pore fracture spaces in argillaceous meagre coal

Dry coal samples and coal samples with different water invasion times (DWITs) were prepared, and X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and low-pressure nitrogen adsorption (LPNA) experiments were carried out to analyze the pore fracture volume and distribution. The fractal dimension of the aperture surface was calculated with the MIP and LPNA data of these coal samples. We found that the pore diameter of macropores decreases, and the fractal dimensions of macropores and mesopores change greatly, on the score of the dispersion of clay minerals and clay expansion; in addition, water intrusion has little effect on the pore size and fractal dimension of minipores and micropores with increasing water invasion time. We conclude that long-term water invasion greatly damages the pore diameter and surface morphology of macropores and mesopores and reduces the permeability of the fractures in coal seams. Long-term water invasion causes little damage to the pore diameter and surface morphology of minipores and micropores. Water plays an important role in sealing off gas and competing for gas adsorption position in minipores and micropores. In addition, by combining the fractal dimension data of MIP and LPNA, we found that water invasion for 20 days was an effective time point to change the pore structure and surface morphology of coal particles. We anticipate that the research conclusions could save coal seam water injection time, and the conclusions could improve the efficiency of natural gas extraction and improve coal and gas outburst prevention engineering.

Colloidal interactions of micro-sized biochar and a kaolinitic soil clay

Fine-sized biochars and clay minerals co-present in various circumstances, e.g., agricultural land and water treatment. Because both of these materials are scavengers for nutrients, agrochemicals and other toxicants, their dispersibility and transportability have received much attention. However, little is documented about their colloidal interactions and to what extent biochar particles can stimulate the dispersion of clay minerals. Here, the effect of engineered micro-sized biochar amendment on the surface charge (SC) and colloidal dynamics of the clay fraction of a kaolinite-rich soil was determined. The engineered biochars showed distinctive SC and colloidal properties depending on their pyrolysis conditions (e.g., oxygen level and temperature) and solution chemistry (i.e., pH and cation type). Two types of biochars prepared under non-biochar-oriented pyrolysis (open heating, ‘O-biochar’) and biochar-oriented pyrolysis (N2-supported heating, ‘N2-biochar’) showed contrasting effects on the colloidal dynamics of clay. The O-biochars provoked aggregation due to their higher content of soluble salts, which increased ionic strength and provided multivalent cations, inducing bridging between negatively charged colloids. In contrast, the N2 biochars low in soluble salts and rich in negatively charged burned organic matter compounds favoured the dispersion of clay. The adjustment of biochar production methods can therefore be highlighted as the way to customize biochar for specific uses or to reduce the risk of clay loss from soils in the short term. In the long term, when soluble salts are removed by leaching, it is likely that dispersion is facilitated and the risk for erosion increases.

Study on the cross-sectional microstructure of a thin ceramic coating on stainless steel surface fabricated by the application and calcination of an aqueous clay mineral paste

In this study a technique is described that enables the ceramic coating on stainless steel with good adhesion via a simple application, drying, and calcination process using an aqueous paste based on clay mineral dispersion. On the basis of this technique, the cross-sectional microstructure of the interfacial area between the clay-derived ceramic coating and stainless steel was analyzed in detail, and the mechanism behind the coating of the ceramic layer with good adhesion was investigated. From the results of elemental mapping using transmission electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, it was discovered that iron from the stainless steel diffuses into the ceramic coat, and the specific passivation film of the stainless steel integrates with the clay mineral-derived ceramic coating during the calcination, revealing that such chemical reactions are effective in promoting strong adhesion between the coat and stainless steel surface. In addition, a unique advantage of using this coating method was discovered in that even if there are small natural scratches on the raw stainless steel, the clay mineral paste can be used to cover these, resulting in a good, flat surface.

Swelling of clay minerals during the leaching process of weathered crust elution-deposited rare earth ores by magnesium salts

To ensure the safety of leaching process in the weathered crust elution-deposited rare earth ore, it is of great importance to decrease the swelling of clay minerals in the rare earth ore for preventing landslides and other hazards. Meanwhile, it is also necessary to ensure the leaching efficiency of rare earth ores during industrial production. In this study, the effect of the magnesium ion concentrations and acidity of magnesium salts on the swelling process was investigated. The inhibiting properties of the optimized magnesium salts were evaluated by anti-swelling experiments. The results show that the relation between the linear swelling ratio of the clay minerals and time correspond with the equation δ = A·e-B/t when the rare earth minerals were recovered from weathered crust elution-deposited rare earth ore with magnesium salts. The optimal leaching conditions were determined to be 0.2 mol/L of magnesium nitrate with a pH below 6.0, with the kinetic equation: δ = 1.5995·e-5.5170/t. According to the evaluations, magnesium nitrate shows a strong capacity to inhibit the hydration swelling and dispersion of clay minerals at room temperature; the anti-swelling rate of 0.2 mol/L magnesium nitrate was 65%, the highest among the magnesium salts. Decreasing the pH and leaching temperature of the magnesium salt solution could effectively reduce the swelling of clay minerals during leaching. The results of the experiment could lead to an improvement in the in-situ leaching technology and reduce the risk of hazards, which has a significant meaning in the safe operations of the mining process.

Amidocyanogen silanol as a high-temperature-resistant shale inhibitor in water-based drilling fluid

To meet the technical requirements of high-temperature deep wells, highly inhibitive, high-temperature-resistant shale inhibitors are essential. This paper reports for the first time the use of amidocyanogen silanol (ANS-1), a newly developed oligomer with an amino siloxane structure, as a potential shale inhibitor. Its inhibitive properties were evaluated by linear swell testing, cutting dispersion testing, bentonite inhibition testing, and mud pellet disintegration testing, and the results were compared with the properties of other current conventional inhibitors. The inhibition mechanism was investigated by X-ray diffraction, adsorption, Fourier transforms infrared spectroscopy, contact angle, zeta potential and transmission electron microscope. The results indicated that ANS-1 can inhibit the hydration swelling and dispersion of water-sensitive clay minerals effectively, performing better than other inhibitors. Furthermore, ANS-1 provides reliable thermal stability as high as 140 °C and has potential application in high-temperature deep wells. ANS-1 can adsorb into the surface of clay, which changes the wettability of the clay surface and increases the resistance of water molecules to bond with the clay. In addition, ANS-1 can intercalate into the clay interlayer, occupying water adsorption sites, and into the interlayer channel, thus inhibiting the hydration swelling of clay. The introduction of siloxane groups in the ANS-1 molecular chain led to a firm chemical adsorption between ANS-1 and clay, which increased the adsorption capacity of ANS-1 at high temperature, thus improving its inhibition performance.

Hyperbranched polyethylenimine modified with silane coupling agent as shale inhibitor for water-based drilling fluids

Hyperbranched polyethylenimine modified with a silane coupling agent (Si-HPEI) as a shale inhibitor was synthesized by the Michael addition reaction of hyperbranched polyethylenimine (HPEI) and methacryloxypropyltrimethoxysilane. The structure of Si-HPEI was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The inhibitory properties of Si-HPEI in comparison with currently available inhibitors were evaluated using linear swelling tests, cuttings dispersion tests, and bentonite inhibition tests. The inhibitory mechanism was investigated via X-ray diffraction measurements, adsorption measurements, and atomic force microscopy observations. The results indicated that Si-HPEI effectively inhibited the hydration and expansion of shale and exhibited excellent temperature resistance in comparison with HPEI and traditional shale inhibitors. The shale cuttings recovery in the case of Si-HPEI remained above 68% up to a hot rolling aging temperature of 140 °C, which demonstrated an excellent ability to inhibit hydration and dispersion that was significantly less affected by the hot rolling aging temperature than in the cases of other inhibitors. In addition, Si-HPEI inhibited the formation of a bentonite slurry more effectively at high temperatures. A mechanistic analysis showed that the siloxane groups present in the molecular chains of Si-HPEI caused strong and stable chemical adsorption of Si-HPEI on water-sensitive clay minerals, which thus hindered the penetration of water molecules and ultimately inhibited the hydration expansion and dispersion of water-sensitive clay minerals. In field application, Si-HPEI was successfully applied on Su 4-4HF well.

Application of electrospray spreading to a modified Langmuir–Blodgett technique for organo-clay hybrid film preparation

A clay mineral, montmorillonite, is exfoliated into discrete clay nanosheets bearing negative charges in aqueous dispersions. When amphiphilic cations are spread on a surface of a clay mineral dispersion, clay nanosheets adsorb onto a floating film of the amphiphilic cations, forming a hybrid film. In conventional procedures, a solution of an amphiphilic cation is spread on a dispersion by manual operation. In this work, we instead applied an electrospray (ES) spreading method. A chloroform solution of octadecylammonium chloride (ODAH+Cl−) was spread on clay mineral dispersions by ES method at different infusion rates. The surface pressure-molecular area isotherm curves of the films exhibited the unusual dependence on the infusion rates; the curves shifted to a larger molecular area with the increase of infusion rate, while they shifted back to a smaller area with the further increase of infusion rate. The following formation mechanism was proposed. In case of the low infusion rate, the solution drops were so fine that some evaporated before they arrived at the interface. Under these conditions, the hybrid film contained ODAH+Cl− salt particles. In case of the high infusion rate, the large solution drops hit violently the dispersion surface, affording a hybrid film with multi-layered domains.

A novel method for surface wettability modification of talc through thermal treatment

Silica tetrahedron (also called siloxane) is an important structure of clay minerals, the percentage of which influences the hydrophobicity, polarity and other surface properties on clay mineral surfaces. In this study, a novel method for surface wettability modification of talc through thermal treatment has been put forward. In this method, the symmetrical siloxane structures on talc basal surfaces were broken by transforming the nonpolar siloxane structure into a polar structure during the thermal treatment process, thus to decrease the hydrophobic components on talc surfaces, and therefore achieve the goal of surface wettability modification. This study was performed through the measurements of thermosgravimetric analysis and differential scanning calorimetry (TG-DSC), contact angle and wetting heat measurements, fourier transform infrared spectroscopy (FTIR), and 29Si-nuclear magnetic resonance spectroscopy (29Si NMR) as well as molecular dynamic simulations (MDs). The results indicate that the thermal treatment at 960 °C for only a very short time could greatly decrease the contact angle of water on talc surfaces. The mechanism could be attributed to that the thermal treatment leads to the disorder of some of the SiO bond length and O-Si-O bond angle in talc silica tetrahedron structure, which finally results in the disorder of the symmetrical siloxane structure and the formation of the amorphous silica phase. And the decrease of hydrophobic siloxane structures on talc surface gives rise to the relatively strong hydrophilicity on talc surfaces. This current method improves the wettability of talc without any addition of modifiers, which would be helpful of many applications of clay minerals, such as clay-polymer composites, filler materials, clay mineral dispersion in aqueous suspensions or mineral processing, etc.

Formation of Arrested States in Natural Di- and Trioctahedral Smectite Dispersions Compared to Those in Synthetic Hectorite — A Macro- and Microrheological Study

AbstractThe effect of natural clay-mineral properties on the rheological behavior of dispersion is very important in new geotechnical and industrial applications. The colloidal behavior of natural clay minerals with various octahedral structures was investigated using macro- and microrheological measurements and compared with the behavior of synthetic hectorite. In the present study montmorillonite (dioctahedral smectite of Volclay), natural hectorite (trioctahedral smectite of SHCa-1 Source Clay), and the synthetic trioctahedral smectite Laponite®, with lateral layer dimensions of 277, 100, and 30 nm, respectively, were used. The structure formation, kinetics of aging, and broad bandwidth viscoelastic response (10-2 — 106 rad/s) of their dispersions were obtained using mechanical shear and squeeze flow rheometry combined with diffusing wave spectroscopy (DWS) and multiple particle tracking (MPT) microrheology. State diagrams were determined at inherent pH considering the clay-mineral and NaCl concentrations as well as the kinetics of structure formation and sample aging. Due to the larger mean layer diameter and greater layer-charge density of natural clay-minerals, their sol—gel transitions occurred at higher solid and NaCl concentrations than those of Laponite®. Structure formation was faster at pH < pHPZC,edge than at pH > pHPZC,edge (point of zero charge at the edge). The long-term aging of natural clay-mineral samples was less pronounced in the glass state than in the gel state, in contrast to the findings for Laponite®. The storage modulus, G’, of clay-mineral dispersions in arrested states remained essentially constant in a wide frequency range (up to 100 rad/s), as expected. The corresponding plateau value of G’ depends on the number of particle contacts per volume and, hence, increased with decreasing particle size at a given concentration. The dissipation mechanisms determining the high-frequency loss modulus, G", however, are independent of particle size and, accordingly, the high-frequency crossover of G’ and G" shifted to higher values when the particle size decreased. The MPT data revealed structural refinement on the submicrometer length scale during the aging of weak hectorite gels, which was similar to the results for Laponite®. No refinement, however, occurred for montmorillonite in the glass or strong gel state.

Comparison of the Critical Coagulation Concentrations of Allophane and Smectites

Clays consist of fine particles (clay minerals) which under certain conditions can be dispersed in water, forming a fairly stable dispersion. The stability of the clay mineral dispersions depends on the pH, solid/liquid ratio, and most of all on the type and concentration of dissolved ions. The difference between the dispersibility of different clays is not yet understood. In the present study allophane and smectite (main constituent of bentonite) are compared. Allophane surfaces are dominated by aluminol groups. Therefore, they can be used to investigate the properties of the edges of platy dioctahedral clay minerals. Dispersion and coagulation of allophane was understood based on the charge of the surface functional groups. Dispersion of allophane was only possible at pH < 5 where the aluminol groups became positive and at low ionic strength (critical coagulation concentrations (CCC) < 10 mmol/L NaCl). Dispersion at high pH may also be possible but this was not tested in the present study. In contrast to allophane, bentonite dispersions coagulated when the edges of the smectites became positive. This is probably caused by heterocoagulation leading to edge (+)/face (−) aggregation. CCC values of different bentonite dispersions ranged from 10 to 750 mmol/L. Most of the Wyoming bentonite dispersions were more stable and even above the CCC, sedimented much slower compared to other bentonites. The reason for this phenomenon could not be identified and needs further research.

Effect of mixing parameters, postcuring, and stoichiometry on mechanical properties of fiber reinforced epoxy–clay nanocomposites

The influence of processing variables was experimentally studied for glass fiber reinforced epoxy–clay nanocomposites manufactured using vacuum-assisted wet layup method. The tensile strength, flexural strength, and interlaminar shear strength of these nanocomposites were significantly influenced by the processing variables including the temperature of resin–clay mixture, speed of homogenization, and ultrasonic probe amplitude during premixing of clay minerals in epoxy. The glass transition temperature of glass fiber reinforced composites increased with incorporation of clay minerals in epoxy. Also, the postcuring of the laminates was carried out at three different temperatures, e.g. 100, 130, and 150 ℃ for 3 h. A decrease in tensile modulus, tensile strength, and flexural strength of nanocomposites postcured at 130 and 150 ℃ was observed. Also, the use of non-stoichiometric epoxy resin and hardener ratios had an adverse effect on mechanical properties of fiber reinforced epoxy–clay nanocomposites. In fiber reinforced composites incorporating clay minerals, a uniform dispersion of clay minerals besides a strong interfacial adhesion between clay minerals and polymer and optimum conditions of curing of matrix is a crucial aspect for improved performance over conventional fiber reinforced composites.

Modified aggregation pattern of cresyl violet acetate adsorbed on nano clay mineral layers in Langmuir Blodgett film

Present work investigated the modified aggregation behavior of a cationic oxazine dye, Cresyl violet acetate (CVA) in presence of Laponite nano clay mineral layers in aqueous clay mineral dispersion as well as in ultra thin organo-clay hybrid Langmuir Blodgett (LB) films. The presence of non-fluorescent H-dimeric sites in aqueous solution of CVA even at very low concentration diminishes its fluorescence intensity and CVA ceases to emit any fluorescence in solid state and in the ultrathin films due to the abundance of H-dimeric sites. Incorporation of clay in aqueous solution drastically modified the absorption spectrum of CVA. Organo-clay hybrid film of CVA, fabricated at higher clay concentration, showed intense J-aggregated band due to the formation of J-aggregated species. UV–vis absorption and fluorescence spectroscopy as well as in-situ Brewster angle microscopic (BAM) studies were employed in this investigation.