Laponite Platelets Research Articles

The Diffusion Role in Adsorption of Hexavalent Chromium on Solid Olive Mill Waste

The removal of Cr(VI) ions from aqueous solutions with wet pomace treated with laponite was investigated. A direct comparison with untreated biomass revealed an increase in both the rate of adsorption and the amount adsorbed. A cooperative interaction between the laponite platelets and biomass surface making more adsorption sites accessible was suggested. In this process, a key role is played by intraparticle diffusion. The experimental results indicate that intraparticle diffusion plays an important role in the adsorption process. A simple diffusion-binding model is presented to discuss the experimental results. The diffusion lifetime is linearly related to the adsorbent mass. The model combined with experimental results allowed us to estimate the average free path of a Cr(VI) molecule. Particularly, it was obtained that, in 1 dm3 of solution, the diffusion path increased by nearly 1 cm per gram of adsorbent. However, this did not imply that the amount of Cr(VI) removed decreased because the total number of adsorption sites also increased.

Nanoscale Thin Film Corrosion Barriers Enabled By Multilayer Polymer Clay Nanocomposites

Ultrathin nanocomposite films fabricated by layer-by-layer (LbL) assembly are an emerging class of coatings with remarkable barrier performance. Here, we examine LBL polymer-clay nanocomposite (PCN) coatings that afford anti-corrosion properties comparable to those exhibited by more traditional films that are orders of magnitude thicker. PCN barrier thin films comprised of up to 40 bilayers of polyethyleneimine (PEI) and exfoliated laponite (LAP), montmorillonite (MMT), or vermiculite (VMT) clay platelets were coated onto steel plates using a scalable LBL dip-coating process. A combination of electrochemical impedance spectroscopy and ex-situ electron and vibrational spectroscopy were used to evaluate coating performance during exposure in 0.6 M NaCl for up to 7 days. A PEI/VMT crosslinked coating of only 250 nm thick slowed the corrosion rate of mild steel by three orders of magnitude (Rct = 106 vs. 103 Ω-cm2) after seven days in 0.6 M NaCl. This performance exceeded the reported performance of other LBL coatings along with much thicker multilayer composite coatings and several conventional pretreatments on mild steel under similar test conditions. The exceptional performance is attributed to the effective barrier properties imparted by a high loading (>80 wt%) of orientated, high aspect ratio (2000:1) platelet layers in a nanobrick wall morphology. Substitution of VMT with lower aspect ratio clay platelets of either MMT (400:1) or LAP (30:1) showed that coated steel corrosion rates and apparent coating permeability scales with platelet size following LAP > MMT >> VMT. Thus, this study has for the first time shown that platelet aspect ratio is a primary means of improving the performance LbL nanocomposite coatings which is in line with the expected behavior of conventional nanocomposites. Given film debonding from the substrate was observed as a common failure mode during exposure for all coating types, replacement of the PEI polymer component with a more debonding-resistant polymer may be an additional pathway to further improve LbL PCN anticorrosion performance.

Innovative Method for Laponite Encapsulation into Polymer Latex Particles by Clay Cluster-Seeded Emulsion Polymerization

We herein report an innovative pathway for the encapsulation of Laponite platelets into polymer nanoparticles via free radical polymerization in heterogeneous aqueous medium. Hydrophobization of the Laponite platelets was performed via double functionalization of the clay basal surfaces and edges by a cationic surfactant and an organosilane, respectively. The hydrophobized platelets were then dispersed in toluene and ultrasonicated with an aqueous solution of an anionic surfactant to form clay-loaded toluene droplets. The droplets were subsequently transformed into clusters by toluene evaporation and finally encapsulated into polymer latex particles using a seeded-emulsion polymerization process. Two different copolymers were synthesized: poly(styrene-co-methyl acrylate), as a model system and poly(vinylidene chloride-co-methyl acrylate), a specialty film-forming copolymer. Stable composite particles with a diameter ranging from 150 to 180 nm were obtained for both copolymers. Transmission electron microscopy analysis showed that the Laponite clay platelets were successfully encapsulated into the polymer latex particles. The films cast from the composite suspensions of poly(vinylidene chloride-co-methyl acrylate)/clay particles showed spherical inclusions of clay tactoids dispersed within the polymer matrix.

Thermo-Responsive Nanocomposite Hydrogels Based on PEG-b-PLGA Diblock Copolymer and Laponite.

Poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) (PEG-b-PLGA) diblock copolymers are widely known as polymeric surfactants for biomedical applications, and exhibit high solubility in water compared to PLGA-b-PEG-b-PLGA triblock copolymers known as gelation agents. In order to overcome the difficulties in the preparation of thermo-responsive hydrogels based on PLGA-b-PEG-b-PLGA due to the low solubility in water, the fabrication of thermo-responsive hydrogels based on PEG-b-PLGA with high solubility in water was attempted by adding laponite to the PEG-b-PLGA solution. In detail, PEG-b-PLGA with high solubility in water (i.e., high PEG/PLGA ratio) were synthesized. Then, the nanocomposite solution based on PEG-b-PLGA and laponite (laponite/PEG-b-PLGA nanocomposite) was fabricated by mixing the PEG-b-PLGA solutions and the laponite suspensions. By using the test tube inversion method and dynamic mechanical analysis (DMA), it was found that thermo-responsive hydrogels could be obtained by using PEG-b-PLGA, generally known as polymeric surfactants, and that the gelation temperature was around the physiological temperature and could be regulated by changing the solution composition. Furthermore, from the structural analysis by small angle neutron scattering (SANS), PEG-b-PLGA was confirmed to be on the surface of the laponite platelets, and the thermosensitive PEG-b-PLGA on the laponite surface could trigger the thermo-responsive connection of the preformed laponite network.

Morphological and physical properties of nano-biocomposite films based on collagen loaded with laponite®

Abstract The objective of the present study was to analyze the effects of laponite concentrations (CLap) on surface morphology and physical properties of nano-biocomposite films based on collagen loaded with laponite. Films microstructure, thickness, moisture content (MC), gloss, color, opacity, crystallinity, chemical structure, thermal and mechanical properties (MP), water vapor permeability (WVP), and the water contact angle (WCA) were determined. A considerable impact of CLap on the surface roughness of the nano-biocomposite films was observed, without effect on its thickness, MC, gloss, color, opacity, MP, WVP, and WCA results. Laponite platelets were exfoliated into collagen chains, provoking a reduction in helix-coil formation, leading to a decrease in the enthalpy melting values of the nano-biocomposite films. This research reports for the first time information regarding films based on collagen loaded with laponite with potential use as food packaging.

Inorganic surface chemistry and nanostructure controls lipolytic product speciation and partitioning during the digestion of inorganic-lipid hybrid particles

HypothesisSolid-state lipid formulations, whereby liquid lipids are encapsulated in inorganic particle matrices, have attracted significant interest for drug/nutrient delivery in recent years. We hypothesized that the surface chemistry of the inorganic material used to encapsulate lipids impacts the lipase-mediated digestion and partitioning of lipolytic species between the solubilized aqueous and insoluble pellet phases. ExperimentsMedium chain triglycerides were spray dried with silica nanoparticles, montmorillonite or laponite platelets to form inorganic-lipid hybrid particles. In vitro lipolysis studies were conducted under gastric (pH 1.6) and intestinal (pH 7.5) conditions, and the speciation and partitioning of lipolytic products between the aqueous and pellet phases was characterized using solution-state proton nuclear magnetic resonance and fourier transform infrared spectroscopy. FindingsUnder gastric conditions, greater than 80% of all lipid species remained adsorbed within each lipolysis pellet after 60 min. Approximately 40%, 50–60% and 80–90% of all lipid species were adsorbed from solution by silica-, montmorillonite- and laponite-based particle matrices during intestinal lipolysis. Monoglycerides were preferentially adsorbed by silica, whereas triglycerides and fatty acids were adsorbed by montmorillonite and laponite. Adsorption of lipolytic products from solution is expected to impact significantly on drug/nutrient solubilization and absorption in vivo. To the best of our knowledge, this is the first report characterizing the speciation and phase behavior of lipolytic products released from solid-state lipid formulations during in vitro lipolysis studies.

Cylindrical Couette flow of Laponite dispersions

Abstract Taylor-Couette flow of aqueous dispersions of nanometric Laponite platelets was studied by dynamic light scattering and direct observation. Despite high rotation rates, gel growth was observed starting from the stator, and filling almost the whole gap after some period of time depending on the angular velocity of the rotor. SEM microscopy observations of the flowing liquid showed the presence of spheres in the micrometer range. A mechanism for gel growth is proposed, where lumps of gel are formed in the sheared liquid and form spherical aggregates which eventually adhere to the side of the gel, with a progressing gelling front.

A Printing‐Centric Approach to the Electrostatic Modification of Polymer/Clay Composites for Use in 3D Direct‐Ink Writing

AbstractPolymer/clay composite inks are exceptionally useful materials for fabrication processes based on 3D direct‐ink writing, however, there remains an insufficient understanding of how their physiochemical dynamics impact printability. Using a model system, N‐isopropylacrylamide/Laponite, the electrostatic interactions between Laponite platelets are modified to tune critical rheological properties in order to improve printability. Rheological measurements and X‐ray scattering experiments are carried out to monitor the nano/micro‐structural dynamics and complex physicochemical interactions of Laponite as it impacts complex modulus in the linear region, flow behavior, thixotropy, and yield stress of the composite ink. Modification of the electrostatic interactions between platelets reduces the yield stress of the material, while maintaining a complex microstructure that allows for sufficient recovery times upon removal of stress to form stable, and thus printable, filaments. A printing‐centric approach is established based on a fundamental understanding of electrostatic inter‐particle interactions, harnessing the innate microstructure of Laponite in 3D direct‐ink writing of composites.

Microstructure and physical properties of nano-biocomposite films based on cassava starch and laponite

The aim of this research was to study the effects of laponite concentrations on some properties of nano-biocomposite films based on cassava starch, focusing mainly the relation between the properties of the surface microstructure and roughness, water contact angle and gloss. Nano-biocomposite films were produced by casting. We analyzed gloss, color, opacity, water contact angle, crystallinity by X-ray diffraction, and microstructure by scanning electron microscopy and atomic force microscopy. Texture parameters (energy, entropy and fractal dimension) were extracted from micrographs. We observed a great impact of laponite in the morphology of nano-biocomposite films. Texture parameters correlated with surface heterogeneity and roughness. Finally, surface roughness affected the surface hydrophilicity of nano-biocomposite films. Laponite platelets were exfoliated and/or intercalated with amylose and amylopectin chains. This research reports new information on the effects of laponite concentrations on the morphological, optical and wetting properties of nano-biocomposite films aiming future industrial applications.

Fabrication of amino-containing hollow polymer latex and its composite with inorganic nanoparticles

Using N,N′-dimethylaminoethyl methacrylate (DMAEMA) as functional co-monomer and styrene (St) as main monomer, the amino-containing hollow latexes were fabricated via one-step emulsion copolymerization and following stepwise acid-alkali post-treatment. Influences of DMAEMA content and post-treatment condition on the morphology and volume expansion of the P(St-co-DMAEMA) latex particles were investigated based on the TEM characterization, and the hollow-forming mechanism was proposed. Results showed that the introduction of 2-butonane promoted the mobility of the polymer chains and the hollow structure generated under moderate post-treatment conditions. Many factors should be balanced to obtain fine hollow particles, an appropriate content of DMAEMA was 15 mol% to all the monomers, and the optimized post-treatment conditions were at 70 °C for 1 h both for acid treatment (initial pH 4.0) and for alkali treatment (initial pH 9.0). Under the optimized conditions, the mean diameter and volume expansion of the resulted hollow particles were 264 nm and 934%, respectively. Finally, the hollow P(St-co-DMAEMA)/laponite composite latex particles were fabricated simply by electrostatic adsorption process, and the resulted composite hollow particles loaded 4.1 wt% of laponite platelets and showed better thermal stability. This simple and facile method can be applied to fabricate the functional hollow latex particles with amino groups including polymeric and polymeric-inorganic composite materials.

Combined effect of cetyltrimethylammonium bromide and laponite platelets on colloidal stability of carbon nanotubes in aqueous suspensions

The combined effect of cationic surfactant (cetyltrimethylammonium bromide, CTAB) and laponite platelets (laponite RD) on the stability of aqueous suspension of carbon nanotubes (NTs) has been investigated. The experimental methods include measurements of electrokinetic potential, radius of particles and aggregation stability. In individual suspensions the concentration of NTs was Cn=0.003% and concentration of laponite was Cl=0.5% and 2%. In hybrid NT+laponite suspensions the concentration of NTs was Cn=0.003% and 0.01% and the laponite/NT mass ratio, X=ml/mn, was varied within the range of X=0–1. For individual NTs and laponite species the increase of the CTAB concentration, Cs, changed the electrokinetic potential from negative to positive. However, the different effects of CTAB on stability of this species were observed: addition of CTAB stabilized the individual NTs and enhanced aggregation of laponite. The CTAB-induced overcharging was also typical for hybrid NT+laponite suspensions. Surprisingly, the minimum of a position of an isoelectric point Cs(IEP) (≈3·10−6M) at X≈0.1–0.3 was observed. This behavior can reflect the impact of CTAB on adhesion interactions between NTs and laponite platelets and adsorption of CTAB on individual NT and laponite species and their hybrids.

Laponite as a rheology modifier of alginate solutions: Physical gelation and aging evolution

The rheological behavior of alginate and Laponite/alginate solutions was studied. It was observed that the Cross viscosity model successfully describes the steady-state shear behavior of this polysaccharide. The scaling behavior analyzed for the entangled regime is in good agreement with polyelectrolyte solutions (Ge∼cp3/2), with interactions generated between the alginate and the charged surfaces of the Laponite platelets. Therefore, the effect of Laponite as a rheology modifier is influenced by the alginate concentration. Higher alginate concentrations hindered the formation of the house of cards microstructure. Frequency sweep tests were performed to analyze the transition from solid-like to liquid-like behavior in a solid-like dominated domain. Soft physical gels were obtained at low alginate concentrations. The gel point was determined (1.65wt.% of alginate and 2wt.% of Laponite) through the Kramers–Krönig damping factor, and time sweep tests revealed the evolution of the storage (G′) and loss modulus (G″) as functions of the waiting time (tw). The growing elasticity revealed that Laponite/alginate solutions undergo aging.

Investigation of cationic soapless P(St-co-DMAEMA) latex and its electrostatic adsorption of laponite

Cationic poly(styrene-co-N,N-dimethylaminoethyl methacrylate) (P(St-co-DMAEMA)) latexes were prepared in the absence of surfactant by using 2,2’ -azobis (2-methylpropionamidine) dihydrochloride (AIBA) as the initiator. The effects of the AIBA concentration, HCl/DMAEMA molar ratio and DMAEMA amount on the emulsion polymerization and the latex properties were investigated. The particle morphology and size, the zeta potential and the amino distribution of the P(St-co-DMAEMA) latexes were characterized by transmission electron microscope (TEM), dynamic light scattering (DLS) and conductometric titration, respectively. Results showed that the emulsion polymerization performed smoothly with high monomer conversion and narrow particle size distribution under the optimized conditions with AIBA concentration of 1 wt%, HCl/DMAEMA molar ratio of 1.2 and DMAEMA content of 5 wt%. The diameter of the dried latex particles decreased and the density of amino groups on the particle surfaces increased with increasing the DMAEMA content. The zeta potential of the P(St-co-DMAEMA) latexes was pH-dependent and the zero point was around at pH 7.2. A facile method was developed to fabricate P(St-co-DMAEMA)/laponite hybrid nanoparticles via electrostatic adsorption, in which the loading capacity of laponite platelets reached 17.7 wt%, and the resultant hybrid nanoparticles showed good thermal stability.

Minimizing Corrosion of Outdoor Metalworks Using Dispersed Chemically Stabilized Nanoclays in Polyvinylidene Fluoride Latex Coatings.

Nanoclays are small enough to appear optically transparent, yet they have large surface-to-volume and high aspect ratios that can significantly inhibit water diffusion when incorporated into protective coatings. Clear coatings, which minimally affect the aesthetics of metalworks, are commonly applied to outdoor metalworks, such as sculptures, to prevent and slow corrosion. In recent years, waterborne clear coatings, rather than solvent-based clear coatings, are increasingly used in many applications to reduce the quantity of volatile organic components in the formulation, yet the performance of dry films produced from waterborne colloidal suspensions is generally poorer. In this work, we aim to improve the barrier properties of a highly weatherable waterborne acrylic/polyvinylidene fluoride emulsion by adding a synthetic nanoclay, Laponite, into the formulation. To improve clay–polymer compatibility, the clay was covalently modified using an acetoxy or perfluoroalkyl silane monomer that is reactive with the hydroxyl groups at the edges of the Laponite platelets. Cation exchange on the clay faces using phosphorylcholine was conducted to increase the stability in water and characterized by zeta potential. Resulting changes in barrier properties of the polymer nanocomposite films were characterized by gravimetry, colorimetry, and electrochemical impedance spectroscopy. Surface ablation after accelerated artificial weathering was monitored by attenuated total internal reflectance Fourier transform infrared microspectroscopy and Raman microspectroscopy, thin film X-ray diffraction (TF-XRD) and gloss and thickness measurements. The composite films showed many improved properties: reduced water sensitivity and ultraviolet-induced polymer degradation, which increased the barrier properties and reduced the diffusion constants over both short- and long-term weathering studies compared with films without nanoclays. The diffusion constant measured for the highest performing composite film showed that the performance gap between relevant water- and solvent-borne coatings used to protect outdoor metals was narrowed by half.

Investigation of Four Different Laponite Clays as Stabilizers in Pickering Emulsion Polymerization.

Clay-armored polymer particles were prepared by emulsion polymerization in the presence of Laponite platelets that adsorb at the surface of latex particles and act as stabilizers during the course of the polymerization. While Laponite RDS clay platelets are most often used, the choice of the type of clay still remains an open issue that is addressed in the present article. Four different grades of Laponite were investigated as stabilizers in the emulsion polymerization of styrene. First, the adsorption isotherms of the clays, on preformed polystyrene particles, were determined by ICP-AES analysis of the residual clay in the aqueous phase. Adsorption of clay depended on the type of clay at low concentrations corresponding to adsorption as a monolayer. Adsorption of clay particles as multilayers was observed for all the grades above a certain concentration under the considered ionic strength (mainly due to the initiator ionic species). The stabilization efficiency of these clays was investigated during the polymerization reaction (free of any other stabilizer). The clays did not have the same effect on stabilization, which was related to differences in their compositions and in their adsorption isotherms. The different grades led to different polymer particles sizes and therefore to different polymerization reaction rates. Laponite RDS and S482 gave similar results, ensuring the best stabilization efficiency and the fastest reaction rate; the number of particles increased as the clay concentration increased. Stabilization with Laponite XLS gave the same particles size and number as the latter two clays at low clay concentrations, but it reached an upper limit in the number of nucleated polymer particles at higher concentrations indicating a decrease of stabilization efficiency at high concentrations. Laponite JS did not ensure a sufficient stability of the polymer particles, as the polymerization results were comparable to a stabilizer-free polymerization system.

Partitioning of Laponite Clay Platelets in Pickering Emulsion Polymerization.

Partitioning of laponite disklike clay platelets between polymer particles and bulk aqueous phase was investigated in Pickering surfactant-free emulsion polymerization of styrene. Adsorption of laponite clay platelets plays an important role in the stabilization of this system, influencing the particle size and the number of particles, and, hence, the reaction rate. Adsorption isotherms show that, while the laponite clay platelets are almost fully exfoliated in water, they form multilayers on the surface of the polymer particles by the end of polymerization, as confirmed by transmission electron microscopy (TEM). This observation is supported by quartz crystal microbalance, conductivity, and TEM measurements, which reveal interactions between the clay and polystyrene, as a function of the ionic strength. The strong adsorption of clay platelets leaves a low residual concentration in the aqueous phase that cannot cause further nucleation of polymer particles, as demonstrated during seeded emulsion polymerization experiments in the presence of a high excess of clay. A Brunauer-Emmett-Teller (BET)-type model for laponite adsorption on polystyrene particles matches the adsorption isotherms.

Mechanism of Methylene Blue adsorption on hybrid laponite-multi-walled carbon nanotube particles

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue (MB) on hybrid laponite-multi-walled carbon nanotube (NT) particles in aqueous suspensions were determined. The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB. Experiments were performed at room temperature (298K), and the laponite/NT ratio (Xl) was varied in the range of 0–0.5. For elucidation of the mechanism of MB adsorption on hybrid particles, the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured. Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage I (adsorption time t=0–10min), a slower intermediate stage II (up to t=120min) and a long-lasting final stage III (up to t=24hr). The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles, as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs. The analysis of experimental data on specific surface area versus the value of Xl evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs. It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations.

Multiphase coexistence in mixed suspensions of large and small hard platelets

The phase behaviour of mixed suspensions of large and small hard platelets is treated by osmotic equilibrium theory. Depending on the size ratios of the small and large platelets, three distinct phase behaviour scenarios appear: isotropic–isotropic–nematic, isotropic–nematic and isotropic–nematic–nematic coexistence regions, in agreement with computer simulations. The experimental multiphase coexistence observed in mixed suspensions of large Titanate platelets and small Laponite platelets can be reproduced semi-quantitatively using osmotic equilibrium theory calculations.

Spray Layer-by-Layer Assembled Clay Composite Thin Films as Selective Layers in Reverse Osmosis Membranes.

Spray layer-by-layer assembled thin films containing laponite (LAP) clay exhibit effective salt barrier and water permeability properties when applied as selective layers in reverse osmosis (RO) membranes. Negatively charged LAP platelets were layered with poly(diallyldimethylammonium) (PDAC), poly(allylamine) (PAH), and poly(acrylic acid) (PAA) in bilayer and tetralayer film architectures to generate uniform films on the order of 100 nm thick that bridge a porous poly(ether sulfone) support to form novel RO membranes. Nanostructures were formed of clay layers intercalated in a polymeric matrix that introduced size-exclusion transport mechanisms into the selective layer. Thermal cross-linking of the polymeric matrix was used to increase the mechanical stability of the films and improve salt rejection by constraining swelling during operation. Maximum salt rejection of 89% was observed for the tetralayer film architecture, with an order of magnitude increase in water permeability compared to commercially available TFC-HR membranes. These clay composite thin films could serve as a high-flux alternative to current polymeric RO membranes for wastewater and brackish water treatment as well as potentially for forward osmosis applications. In general, we illustrate that by investigating the composite systems accessed using alternating layer-by-layer assembly in conjunction with complementary covalent cross-linking, it is possible to design thin film membranes with tunable transport properties for water purification applications.

Luminescence enhancement after adding organic salts to nanohybrid under aqueous condition.

Lanthanide-based organic-inorganic hybrid materials (LnOIH) are of immense importance for various applications nowadays, while it still remains a significant challenge to achieve high luminescence efficiency in aqueous environment. Herein we present a simple and environmentally friendly two-step strategy to prepare strongly red-light emitting nano-LnOIH by first in situ forming Eu(3+)-β-dikeonate complexes on Laponite platelets and subsequently increasing the coordination number of the complexes via the modification with a silane-functionalized imidazolium salt, which can fully protect Eu(3+) ions from the water molecule quenching. The mechanism of how the imidazolium salt favors the formation of Eu(3+)-β-dikeonate complex with large coordination number was elucidated. The result is that the removal of the abundant protons on the Laponite platelets through a mechanism of synergic effect of ion exchange and neutralization drives the formation of Eu(3+)-β-diketonate complexes with high coordination number. The high efficiency of the resulting luminescent nano-LnOIH in water endows the nanohybrid with good aqueous solution processability and opens the possibility of using them under complicated aqueous conditions for biorelated applications.