Laponite Dispersions Research Articles

Investigation of electrostatic interactions in laponite-polyacrylic acid nanocomposites

Nanocomposites provides a unique opportunity to enhance thermal, mechanical, and waterproof resistance properties of polymer. The effectiveness of these enhancements typically depends on the optimal dispersion and interaction of nanofillers within the polymer matrix. The primary objective of this study is to provide direct chemical evidence for electrostatic interactions between Laponite nanofiller and polyacrylic acid. Samples were prepared by mixing Laponite dispersion and aqueous polyacrylic acid (PAA) that were adjusted to various pH conditions. We observed, an IR peak shift in the carbonyl peak of PAA and Si–O peak of Laponite to lower wave number in nanocomposite, with the maximum shift at pH 7. UV–Vis results also showed a hypsochromic shift in the carbonyl peak of PAA due to the interaction with Laponite. The extent of peak shift in IR, and UV–Vis region for the PAA-Laponite dispersion was found to be influenced by the molar mass of PAA used in the formulation of Laponite-PAA nanocomposite and pH of the medium. These results along with zeta potential measurements strongly suggest that electrostatic forces are in play between deprotonated PAA and the positively charged rim of Laponite in promoting electrostatic interactions between Laponite and PAA. The findings of the study can have a strong bearing on the design of next generation high performance coatings, sealants, and adhesives.

Tribological and Rheological Study of Thixotropic Gels of 2D Nanoparticles.

A thixotropic colloidal gel constituting an aqueous dispersion of synthetic clay Laponite with varying concentrations of salt has been studied for its rheological and tribological performance as a lubricant. We observed that the incorporation of NaCl induces notable enhancements in the colloidal gel's relaxation time, elastic modulus, and yield stress. Although an increase in NaCl concentration decreases the material's relaxation time dependence on waiting time (tw), overall, the strength of its thixotropic character has been observed to increase with an increase in salt concentration. The analysis of friction and wear indicated that the utilization of a thixotropic colloidal gel of Laponite with a higher concentration of NaCl resulted in progressively greater reductions in both the coefficient of friction and specific wear rates under various load-speed conditions. Severe abrasive wear on disc surface under dry test, gradually mitigated upon the introduction of these lubricants. Two simultaneous lubricating mechanisms, first, the smooth sliding of the friction pair, facilitated by the alignment of Laponite particles in the direction of shear forces, and second, the stable structure of Laponite, coupled with the addition of NaCl, enabling continuous replenishment of the wear track with lubricant, are attributed to lubrication effectiveness.

Aqueous Laponite® dispersions are attractive gels, not repulsive Wigner glasses: A critical commentary

An aqueous dispersion of Laponite® has been studied in the literature for over the past three decades. Typically, the aqueous dispersion of Laponite® undergoes incessant evolution of its microstructure, wherein its elastic modulus and the mean relaxation time show a continuous increase as a function of time. A considerable amount of discussion has revolved around the nature of this dispersion, specifically whether it can be classified as a repulsive Wigner glass state, characterized by disconnected Laponite® particles stabilized by electrostatic repulsions, or an attractive gel state, in which the particles form a percolated space-spanning network. The proponents of the Wigner glass state also conjecture that this system experiences a glass–glass transition after a period of 2 days has elapsed since its preparation. In this Commentary, we explore this topic from a rheological point of view, analyzing the published literature and performing new experiments. Aided by additional evidence from the literature, we propose that rheological behavior overwhelmingly suggests that an aqueous dispersion of Laponite® undergoes a sol–attractive gel transition and remains in the attractive gel state over at least up to 7 days without undergoing any additional transition. Importantly, rheology, despite being a macroscopic tool governed by principles of mechanics, offers profound insight into the microstructure of this particular system. The corresponding analysis conclusively determines the state of an aqueous dispersion of Laponite® to be an attractive gel.

Time-dependent clay gels: Stepdown shear rate behavior, microstructure, ageing, and phase state ambiguity

To study the time-dependent properties of clay gels in the structural rejuvenation mode, a combination of the stepdown shear rate method and an ageing test is advocated. In this mode, the structural development process at two different initial equilibrium states during the low stepdown shear rate and the rest period of the ageing test were followed. The roles played by the electric double layer (EDL) repulsive force in this structural development process with and without shear, for platelet sodium montmorillonite or NaMnt, hectorite and Laponite gels, and fibrous sepiolite gels were assessed. The response of the stepdown shear stress and ageing yield stress reflects the action of these forces on the structural rejuvenation kinetics and the type of structure formed. The platelet clay gels with their strong EDL repulsive particle interaction commenced the structural development process immediately and formed an open network structure. This process is short in shear and takes years when without. The fibrous sepiolite gel with its weak EDL repulsive interaction did not display structural rejuvenation in shear and only showed a significant yield stress increase after the first few hours of ageing. An additional issue concerning the stability of the isotropic liquid (IL) phase state of dilute Laponite dispersions was addressed. These dispersions aged for >9 years, displaying that yield stress and network structure confirmed that the IL phase is unstable. A low energy path available for Laponite particles to aggregate was discussed. A new method for determining the flocculate phase state was also presented.

Anticipating gelation and vitrification with medium amplitude parallel superposition (MAPS) rheology and artificial neural networks

Anticipating qualitative changes in the rheological response of complex fluids (e.g., a gelation or vitrification transition) is an important capability for processing operations that utilize such materials in real-world environments. One class of complex fluids that exhibits distinct rheological states are soft glassy materials such as colloidal gels and clay dispersions, which can be well characterized by the soft glassy rheology (SGR) model. We first solve the model equations for the time-dependent, weakly nonlinear response of the SGR model. With this analytical solution, we show that the weak nonlinearities measured via medium amplitude parallel superposition (MAPS) rheology can be used to anticipate the rheological aging transitions in the linear response of soft glassy materials. This is a rheological version of a technique called structural health monitoring used widely in civil and aerospace engineering. We design and train artificial neural networks (ANNs) that are capable of quickly inferring the parameters of the SGR model from the results of sequential MAPS experiments. The combination of these data-rich experiments and machine learning tools to provide a surrogate for computationally expensive viscoelastic constitutive equations allows for rapid experimental characterization of the rheological state of soft glassy materials. We apply this technique to an aging dispersion of Laponite® clay particles approaching the gel point and demonstrate that a trained ANN can provide real-time detection of transitions in the nonlinear response well in advance of incipient changes in the linear viscoelastic response of the system.

Influence of carboxymethyl cellulose solutions on rheological properties of Laponite dispersions

Influence of carboxymethyl cellulose solutions on rheological properties of Laponite dispersions

Regulation of oil well cement paste properties by nanoclay: Rheology, suspension stability and hydration process

Enhanced grid reconstruction ability of oil well cement paste has been confirmed as a promising solution to inhibit particle sedimentation caused by the uncontrolled rheological property at high temperatures. The effect of nanoclay dispersions of Bentonite and Laponite on the rheological property, suspension stability and hydration process of the cement pastes was examined. The nanoclay dispersions (especially Laponite) enhanced the dynamic reversible gel structure and improved its reconstruction ability. The addition of nanoclay effectively inhibited the sedimentation of solid particles at high temperatures due to form a gel structure by polymer admixtures, nanoclay and cement colloidal particles. Moreover, the nanoclay facilitated the cement hydration and enhanced the mechanical property for the nucleation and filler effect. Accordingly, the nanoclay can enhance thixotropy and suspension stability of the early cement paste and increase the mechanical strength of hardened cement stones, which contributes to improving the sealing integrity of cement sheath.

Dynamics and microrheology of colloidal clay-polymer glasses and gels: Size-dependent phenomena and re-entrant behavior at early aging times.

Colloidal clay Laponite forms a variety of arrested states that display interesting aging behavior. Microrheology has been applied to Laponite-based glasses and gels, but few studies evaluate the influence of probe particle size. In this work, we report the dynamics and microrheology of Laponite-polymer dispersions during aging using passive microrheology with three different probe particle sizes. At early aging times, the neat Laponite dispersion forms an arrested state; the nature of this state (e.g., a repulsive glass or gel) has remained the subject of debate. The addition of polymer retards gelation and melts the arrested state. While this melting has been observed at the macroscale and has been attributed to a re-entrant transition of a repulsive glass to a liquid state, to our knowledge, it has not been observed at the microscale. The delay of the gelation time needed to form an arrested state was found to depend on the polymer concentration and could vary from ∼24 h for neat Laponite to seven days for some Laponite-polymer samples. Significant effects of probe particle sizes are observed from the mean-squared displacement (MSD) curves as small and intermediate probe particles show diffusive motion, while the motion of large particles is restricted. By examining the factor of ⟨Δr2 (τ)⟩a, structural heterogeneity can be confirmed through the strong size-dependence displayed. Different MSD trends of probe particles are obtained at longer aging times, but no significant changes occur after 30 days of aging. Our microrheology results also reveal significant effects of probe particle size.

Infiltration of laponite: An effective approach to improve the mechanical properties and thermostability of collagen hydrogel

AbstractRapid aggregate precipitation of collagen and laponite in solution restricted the development of corresponding hybrid materials. Herein, a facile method of immerging collagen hydrogel into laponite dispersion was adopted to prepare hybrid collagen/laponite hydrogel, avoiding the precipitation. Collagen hydrogel shrunk and water content decreased dramatically after laponite solution treatment. According to the images of Scanning electron microscopy and energy dispersive system, the uniformly dispersed laponite in collagen hydrogel was observed, demonstrating infiltration of laponite into collagen hydrogel. X‐ray photoelectron spectroscopy results revealed that coordination bonds generated between magnesium in laponite and collagen. Thermogravimetric analysis and Differential scanning calorimetry results displayed thermal decomposition temperature of collagen hydrogel increased from 321 to 342°C, and denaturation temperature rose from 43.8 to 50.8 °C after laponite infiltration. Rheological and compressive tests showed the elastic modulus, fracture stress, compressive modulus and rupture point of hydrogel treated by 10% laponite were 695.2 Pa, 253.3 kPa, 13.5 kPa and 76.7%, respectively, which were about 3.5, 5.5, 45.0, and 1.4 times larger than those of pristine collagen hydrogel. Besides, enzyme degraded rate of collagen was decelerated, and the hydrogel was still nontoxic with the infiltration of laponite. The promising data demonstrated infiltration of laponite was an effective way to fabricate collagen/laponite hybrid materials with desirable properties.

Effect of polymer-polymer interactions on the flow behavior of some polysaccharide-based hydrogel blends

This study is the continuation of our previous work (Kopač, Abrami, et al., 2021) where the theoretical approach of polymer-polymer interaction to predict the crosslink density of hydrogels was introduced. This theory is further extended to the flow properties of hydrogels that allow the analysis of synergistic effect in hydrogel systems and the understanding of possible anomalous behavior of certain mixtures. Various hydrogel structures were prepared accordingly by blending scleroglucan, anionic nanocellulose, Laponite dispersions and alginate solution. The relationship between mechanical and flow properties of the hydrogel network was carefully studied and eventually described by mathematical model. The linear model equation to predict yield stress of hydrogels in relation to the crosslink density was designed showing a satisfactory agreement between experimental data and model predictions. The correlation was adjusted by defining a proportionality coefficient, representing the energy defined per moles of crosslinks that can be used to restore the deformation.

Liquid phase hydrogenation of furfural to biofuel over robust NiCu/Laponite catalyst: A study on the role of copper loading

Sustainable production of biofuel and chemical feedstock through catalytic hydrogenation has now received increased attention due to the expeditious depletion of crude oil. In the present investigation, we developed a cost-effective and base metal-based NiCu/Laponite catalyst for liquid-phase hydrogenation of furfural into fuel range components. The robust catalysts were prepared by a simple co-impregnation method with constant loading of 5 wt% NiO with different wt.% of CuO (x) loadings (where x = 8, 10, 12 & 14%) on the Laponite support. The textural properties, surface acidity, and reduction of the synthesized catalysts were studied by employing various physicochemical characterizations such as XRD, N2 sorption analysis, NH3-TPD, H2-TPR, and TGA. The obtained results revealed that optimum loading of 12% CuO and 5% NiO catalyst aids fine dispersion of copper and nickel oxide on the surface of the support. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images displayed the delamination of Laponite particles and dispersion of Ni-Cu catalyst on the support surface. The hydrogenation efficiency of the synthesized catalysts was tested in a bench top stainless steel autoclave reactor by liquid phase reaction condition of furfural at 150–210 °C under 10–25 bar H2 pressure for 1–6 h. The excellent activity of 5Ni-12Cu/Laponite catalysts was compared and correlated with the physicochemical characteristics of the catalyst.

Structural evolution of salt-free aqueous Laponite dispersions: A study based on low-field NMR relaxometry and rheological investigations

The combination of Low-Field NMR relaxometry (LF-NMR) and rheological analyses was used to investigate the kinetics of aging and structural evolution of salt-free aqueous Laponite dispersions with concentrations ranging from 0.33 to 2.00 wt%. The examination of LF-NMR results reveals that the rate of nanoclay delamination increases with increasing Laponite concentration while its degree decreases. Furthermore, the LF-NMR results were interpreted together with rheological results to assess the kinetics of processes occurring on different length scales reflecting on the time evolution of the three-dimensional structure. The structural evolution is described by the definition and comparison of three different characteristic times. The LF-NMR decay time (tr) designates the time required for Laponite delamination. The induction time (ti) indicates when interparticle edge-face interactions become effective enough for incipient networking. The gelation time (tg) corresponds to sufficiently high degree of interparticle connectivity for the development of a macroscopic gel behavior. The comparison of ti and tg, on one hand, and tr, on the other hand, allows to conclude that for low concentration Laponite dispersions nanoclay delamination is a prerequisite for the formation of the new dispersion structure with a macroscopic gel behavior. Interestingly, the development of the new structure, based on orientation of clay disks into edge-to-face pattern and mutual interparticle attractive interactions, starts when the delamination process is still running.

The use of a laponite dispersion to increase the hydrophilicity of cobalt-ferrite magnetic nanoparticles

In the literature, several attempts have been made to synthesize and later to modify magnetic nanoparticles to make them feasible for several applications. For biomedical applications, magnetic nanoparticles and clay minerals were combined to form a material that is both stable and biocompatible. In this context, composites with ratios of 4.70, 2.35 and 1.17 (weight/weight) of Cobalt Ferrite and Laponite were synthesized and characterized. These composites were treated with acid, and consequently the laponite was converted into an amorphous silica matrix around the magnetic nanoparticles. This morphology was confirmed using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). The particle size distribution, obtained by Transmission Electron Microscopy (TEM), was used as an input parameter for the polydispersity function in the Small Angle X-ray Scattering (SAXS) analysis. The latter was also applied to verify the particle shapes and aggregates for each composite. It was demonstrated by Thermal Gravimetric Analysis (TGA), that these materials, except for the composite with the highest ratio, adsorbed at least one order of magnitude more water than pure Cobalt Ferrite nanoparticles. Thus, increasing the hydrophilicity properties of the Cobalt Ferrite - laponite/silica system. A preliminary magnetization experiment corroborated with these findings and showed that a fraction of the system is not in the superparamagnetic regime at room temperature.

Rheology of aqueous dispersions of Laponite and TEMPO-oxidized nanofibrillated cellulose

The viscoelastic and flow properties of aqueous Laponite/TEMPO-oxidized nanofibrillated cellulose (TEMPO-NFC) systems are investigated with the aim to study the effect of content and proportion of both components on the properties. Both Laponite and TEMPO-NFC aqueous dispersions can find numerous applications in different fields (from industrial to biomedical one) due to their structural and rheological properties. The most important effects of blending are observed at low Laponite fractions, also with qualitative changes in the shape of the flow curves and mechanical spectra. Positive synergistic effects are ascribed to the interpenetration and electrostatic interactions between TEMPO-NFC fibrils and Laponite nanodisks. These mechanisms are more effective in Laponite-poor blends when a minority of clay nanoparticles and its aggregated forms are distributed within the nanocellulose matrix, acting as bridging agents between polymer nanofibrils. The synergistic effects are compared to those observed for Laponite blends with a nonionic biopolymer, scleroglucan.

A facile approach to obtain highly tough and stretchable LAPONITE®-based nanocomposite hydrogels.

LAPONITE® sheets have been widely used for the preparation of tough nanocomposite hydrogels for enticing applications; however, their inferior dispersion in aqueous media resulting from electrostatic interactions between the nanosheets remarkably limits further improvements in the mechanical performances of the nanocomposite hydrogels. Here, we show a simple approach to dramatically accelerate the dispersion of LAPONITE® sheets in water, and in turn further improve the mechanical performances of the resulting nanocomposite hydrogels. Upon addition of poly(acrylic acid) (PAA), the electrostatic interactions between the LAPONITE® sheets were effectively reduced due to the adsorption of PAA onto the positively charged edges of the LAPONITE® sheets, thereby accelerating the dispersion of the LAPONITE® sheets in water. On this basis, a series of polyacrylamide (PAAm) hydrogels with a high content of LAPONITE® sheets was prepared, showing excellent tensile strength, stretchability, and anti-fatigue properties. This study will be beneficial for the preparation of LAPONITE®-based nanocomposite hydrogels bearing excellent mechanical properties for new applications.

Preparation and characterization of carrageenan/silver nanoparticles/Laponite nanocomposite coating on oxygen plasma surface modified polypropylene for food packaging.

In this work, the nano composites of carrageenan/AgNPs/Laponite were prepared and coated on the oxygen plasma surface modified polypropylene film to enhance the barrier and adhesion properties. The mechanical, barrier, adhesion and antimicrobial properties were also studied to use for food packaging applications. The polypropylene film was surface modified with oxygen plasma treatment for 60s. The AgNPs are prepared by green synthesis method from the Digitalis purpurea plant. Then the carrageenan based nanocomposites were coated by roller coating method with the thickness of 24μm. By using scanning electron microscopy, the morphology of the coating was investigated. The Laponite and AgNPs dispersion was analyzed by X-ray diffraction analysis. The tensile and adhesion strength of the coated film was increased and the OTR and WVTR were decreased after the incorporation of Laponite and AgNPs. It exhibited the strong antimicrobial activity against the E. coli and S. aureus.

Effect of Network Parameters of Preformed Particle Gel on Structural Strength for Water Management

Summary Preformed particle gel (PPG) is an appropriate solution for conformance control and water management in low permeability reservoirs. In this paper, the network parameters of PPGs are evaluated through swelling tests and rheology and by determining their role in maintaining structural strength. Several PPG hydrogels were prepared by varying the concentrations of polyacrylamide and chromium triacetate [Cr(OAc)3] as copolymer and crosslinker, respectively, using a central composite design. The characterization of these hydrogels was performed using a scanning electron microscope (SEM), electron dispersion X-ray (EDX), and environmental scanning electron microscope (ESEM). The correlation between reaction conditions and the network parameters of polymer networks, such as the molecular weight of the polymer chain between two neighboring crosslinks (Mc¯), the crosslink density, and the size fraction, have been determined. In addition, swelling of the hydrogels took place through the Fickian diffusion mechanism. Structural states of Laponite dispersions strongly depend on concentration and ionic strength. Based on the rheological tests, the dynamic modulus of the PPG was strongly dependent on the initial concentration and resulting network parameters of the hydrogel. The results showed an effective interaction between Mc¯ and the elastic modulus of the gel network. Through the optimization of the network parameters, the appropriate composition was presented on the basis of the factors of strength (complex modulus of 4×104 Pa in the plateau region), the formation of a 3D network, and the preservation of the viscoelastic structure in the presence of Na+, Ca2+, and Mg2+, at a salt sensitivity of 0.5. In addition, the optimum sample structure was confirmed on the basis of microscopic images. Based on the coreflooding data, the optimal PPG showed a disproportionate permeability reduction (DPR) index of 17.01 and indicated the dual performance of these materials against water and oil. Also, the permeability diagrams of the core showed wettability of the oil-wet core could shift to more water-wet after PPG injection. To summarize this research, we present the determination and analyses of the network parameters as a novel technique for predicting the performance of hydrogels in porous media, and for investigating their strength under harsh reservoir conditions. In other words, determination of the network parameters can be used to ensure the success of the gel performance in porous media.

Performance evaluation of laponite as a mud-making material for drilling fluids

In this study, laponite was tested as a mud-making material for drilling fluids. Laponite is a synthetic smectite clay with a structure and composition closely resembling the natural clay mineral hectorite. Commercially available laponite was characterized by X-ray diffractometry, scanning electron microscopy and infrared spectrometry. Its dispersibility, salt resistance and high-temperature resistance were evaluated. The results showed that laponite possessed superior cation exchange capacity (140.4 mmol/100 g) with interlayer cations of Na+ and Li+. Laponite could easily be dispersed in water to yield increased viscosity with no influence from hydration time or temperature. On the other hand, laponite dispersions displayed an excellent heat resistance, with invariant apparent viscosity at high temperatures. For instance, the apparent viscosity of the 2 wt% laponite dispersion underwent changes between 22 and 24 mPa s after hot rolling at 180–240 °C for 16 h. Compared to existing mud-making materials, laponite exhibited better mud-making properties. Furthermore, laponite revealed good compatibility with other additives, and the water-based drilling fluids prepared with laponite as mud-making material showed an excellent stability at elevated temperatures and superior performance–cost ratios. Overall, these findings indicated that laponite had an excellent dispersibility at high temperatures and hence would have promising applications as high-temperature mud-making material for preparing water-based drilling fluids designed for ultra-high-temperature environments.

Centrifuge testing of liquefaction mitigation effectiveness on sand foundations treated with nanoparticles

In the last decade there has been a significant research focus on developing non-disruptive methods to mitigate liquefaction in soil foundations beneath infrastructure. One such method involving the use of nanoparticles has been recently proposed to reduce liquefaction potential without changing the soil skeleton. To explore its effectiveness and mechanisms of anti-liquefaction, an advanced centrifuge test is presented. The test involves a sand model treated with laponite (a clay nanoparticle) which is measured for dynamic responses at appropriate spatial and temporal scales. Following treatment, various pore pressure and acceleration response trends are observed and analyzed. Marked reductions in excess pore pressure, settlement and lateral displacement are evident from the treatment. In combination with laboratory tests, amplitude reduction and trend changes are found to be closely related to the properties of laponite dispersion. Laponite dispersion appears to induce rheological changes in the pore fluid, thus reducing the permeability coefficient and strengthening the restraint of soil particles. This is especially evident in terms of delayed build-up of excess pore pressure. Overall, pore fluid modification using this nanoparticle method shows excellent performance and has potential for future applications in non-disruptive liquefaction mitigation.

Rapid Recovery Hydrogel Actuators in Air with Bionic Large-Ranged Gradient Structure.

Fast recovery in a nonaqueous environment is a big challenge for hydrogel actuators. In this work, a temperature-responsive hydrogel actuator with outstandingly rapid recovery in air was reported. The hydrogel with bionic large-ranged gradient structure was fabricated by copolymerization of hydrophilic monomer hydroxyethyl acrylate (HEA) and N-isopropylacrylamide in the dispersion of Laponite utilizing a facile electrophoretic method. The deformation degree and time can be regulated by varying the concentration of HEA to change the lower critical solution temperature (LCST) and swelling of the hydrogel. A dynamic equilibrium between the water into and out of the hydrogel was observed, and the hydrogel showed no shrink above LCST. The synthesized hydrogels showed fast response in hot water and rapid recovery in air. Such nonshrink characteristics and excellent reversibility made it possible for these hydrogels to be used as temperature-controlled microfluidic switches. This work provided an approach to design fast recovery hydrogel actuators by the incorporation of hydrophilic monomers and extend the application of the hydrogel actuators into fields such as soft robots, micromanipulation, microfluidics and artificial muscles in various environments.