Laponite Surface Research Articles

Synthetic-Clay-Assisted Carrier Transport in Solid Polymer Electrolytes for Enhanced All-Solid-State Lithium Metal Batteries.

As a potential alternative to liquid organic electrolytes, solid polymer electrolytes provide good processability and interfacial properties. However, insufficient ionic conductivity limits its further development. To overcome these challenges, we propose the solution of synthetic clay Laponite as a filler in this work. Specifically, the ionic conductivity increases to 1.71×10-4 S cm-1 (60 °C) after adding 5 wt.% of Laponite to the PEO-LiClO4 system. The Laponite surface's negative charge enhances lithium ions dissociation and transport in the electrolyte: the lithium-ion transference number increases from 0.17 to 0.34, and the exchange current density increases from 46.84 μA cm-2 to 83.68 μA cm-2 . The improved electrochemical properties of composite electrolytes improve the symmetric cell's stability to at least 600 h. Meanwhile, the Li||LiFePO4 cells' rate and long-cycle performance are also significantly enhanced. This work's concept of Laponite filler demonstrates a novel strategy to enhance ion transport in polymer-based electrolytes for solid-state batteries.

Intelligent Films from Chitosan and Biohybrids Based on Anthocyanins and Laponite®: Physicochemical Properties and Food Packaging Applications

Colorimetric films containing anthocyanins can be used as intelligent food packaging materials. The present research aims to develop, characterize, and apply chitosan films containing a biohybrid based on anthocyanins from eggplant (Solanum melongena L.) peel and laponite®. Anthocyanins were adsorbed on the laponite surface to produce biohybrids (BH) and then used to manufacture edible films by casting method. The BH increased the thickness and reduced the solubility in water of chitosan films. Furthermore, the residual mass and opacity of films increased with the presence of BH. Chitosan films containing BH showed change color properties from grey (initial film color) to red or yellow colors when exposed to buffer solutions with acid and basic pH, respectively. Finally, chitosan films containing BH were used to monitor meat freshness at different temperatures (− 20, 4, and 20 °C) by means of film color alterations which was correlated with total volatile basic nitrogen produced in meats during the storage. Based on physicochemical and colorimetric results, the BH based on anthocyanins and laponite® is an interesting material to manufacture intelligent films for the food packaging sector.

Interaction of Cationic, Anionic, and Nonionic Macroraft Homo- and Copolymers with Laponite Clay.

The functionalization of Laponite RD platelets with different cationic, anionic, and nonionic homo- and copolymers synthesized by reversible addition-fragmentation chain transfer (RAFT) has been investigated. The effective interaction of the macromolecular RAFT agents (macroRAFTs) with the inorganic particles is known to be of crucial importance for the successful coating of minerals with polymers via RAFT-mediated emulsion polymerization to produce polymer-encapsulated inorganic particles. The macroRAFT agents synthesized in the present work contain carefully selected reinitiating R groups, which bear either ionizable tertiary amine or quaternary ammonium moieties (from 2-(dimethylamino)ethyl methacrylate, DMAEMA), negatively charged acrylic acid (AA) repeat units, or neutral polyethylene glycol (PEG) side chains, and are capable of interacting with Laponite via different adsorption mechanisms. The equilibrium adsorption of these RAFT (co)polymers was investigated by the plotting of adsorption isotherms, and either L-type or H-type curves were obtained. The hydrophobicity of the macroRAFT was shown to promote adsorption, as did the pending configuration of the PEG block. Charge repulsion between AA and the negatively charged surface of Laponite at pH 7.5, on the other hand, was prejudicial for adsorption, while the strong electrostatic interaction between the cationic DMAEMA molecules and the Laponite surface led to high-affinity-type curves.

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.

Reinforcement of polyacrylamide hydrogel with patched laponite-polymer composite particles

The application of patched laponite-polymer composite particles (LCPs) in hydrogel reinforcement has been proposed and such hydrogels (LC hydrogels) were successfully prepared. LCPs can be well dispersed in hydrogel matrix to rather high particle concentration and at the same time, form chemical bonding with polymer matrix through copolymerization of surface CC groups. The obtained LC hydrogels showed more homogeneous microstructure and significantly higher mechanical strength comparing with the hydrogel containing bare laponite or laponite surface modified with CC groups at same particle content. A series of control experiments reveals that both the surface chemistry and patched morphology were essential to produce such good reinforcement performance.

The structure of water near a charged crystalline surface

The structure of water near a synthetic clay surface, Laponite, is probed experimentally by total neutron scattering, in both liquid and arrested states. It is shown that the crystalline structure of the Laponite platelets and their charge distribution determine polarization of the closest water layers, with a local density higher than that of bulk water. Interestingly these layers show long range order in the plane parallel to the Laponite surface, while no indication of strong hydrogen bonding between water and Laponite is found.

Clay-Based Colloidosomes

Poly(ethylene imine) (PEI) has been adsorbed onto the surface of Laponite clay nanoparticles from aqueous solution at pH 9 in order to produce an efficient hybrid Pickering emulsifier. This facile protocol allows formation of stable sunflower oil-in-water Pickering emulsions via homogenization at 12,000 rpm for 2 min at 20 °C. The effect of varying the extent of PEI adsorption on the Pickering emulsifier performance of the surface-modified Laponite is investigated for five oils of varying polarity using aqueous electrophoresis, thermogravimetric analysis, and laser diffraction studies. A minimum volume-average emulsion droplet diameter of around 60 μm was achieved at a Laponite concentration of 0.50% by mass when utilizing a PEI/Laponite mass ratio of 0.50. Such emulsions proved to be very stable toward droplet coalescence over time scales of months, although creaming is observed on standing within days due to the relatively large droplet size. These conditions correspond to submonolayer coverage of the Laponite particles by the PEI, which ensures that there is little or no excess PEI remaining in the aqueous continuous phase. This situation is confirmed by visual inspection of the underlying aqueous phase of the creamed emulsion when using fluorescently labeled PEI. These Pickering emulsions are readily converted into novel clay-based colloidosomes via reaction of the primary and/or secondary amine groups on the PEI chains adsorbed at the Laponite surface with either oil-soluble poly(propylene glycol) diglycidyl ether or water-soluble poly(ethylene glycol) diglycidyl ether cross-linkers. These colloidosomes were sufficiently robust to survive the removal of the internal oil phase after washing with excess alcohol, as judged by both optical and fluorescence microscopy. However, dye release studies conducted with clay-based colloidosomes suggest that these microcapsules are highly permeable and hence do not provide an effective barrier for retarding the release of small molecules.

Structural and mechanical properties of Laponite–PEG hybrid films

Inorganic/organic hybrids were obtained by the sol–gel type organic modification reaction of Laponite sidewalls with poly(ethylene glycol) (PEG) bearing alkoxysiloxy terminal functionality. By casting an aqueous dispersion of the hybrid, the flexible and transparent hybrid films were obtained. Regardless of the inorganic/organic component ratio, the hybrid film had the ordered structure of Laponite in-plane flat arrays. The mechanical strength of hybrid films was drastically improved by the presence of cross-linking among alkoxysilyl functionalities of PEG terminals and the absence of PEG crystallines. Hybrid films, especially those that consisted of PEG with short chain, showed good mechanical properties that originate from quasi-homogeneous dispersion of components due to anchoring of PEG terminal to Laponite sidewall and interaction of PEG to Laponite surface.

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

AbstractWe report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Long-term aging effects on the rheology of neat laponite and laponite–PEO dispersions

We observe aging behavior of neat laponite systems over the course of 1,000 or more days. Under basic conditions, low laponite concentrations (1 wt%) slowly evolve from a viscoelastic liquid to a glass made of clusters acting as constituent elements interacting via long-range repulsion. Higher concentrations of laponite (3 wt%) quickly form a glass of individual particles. Intermediate concentrations of laponite form a glass that is a combination of clusters and individual particles. The aging rheological response and upturn of the loss modulus at low frequencies are well predicted by models of soft glassy systems (Fielding et al., J Rheol, 44(2):323–369, 2000; Sollich, Phys Rev E, 58(1):738–759, 1998). If low amounts of high-molecular-weight (Mn ≥ 163 kg/mol) poly(ethylene oxide) (PEO) are added, the aging behavior follows the dynamical response of the clay. Above a critical ratio, φ, of the free polymer chains in solution to the total laponite surface area, the PEO dynamics dominate at high frequencies. It appears that the dynamics of these complex laponite-PEO systems are governed by the parameter φ.

Aqueous Nonionic Copolymer-Functionalized Laponite Clay. A Thermodynamic and Spectrophotometric Study To Characterize Its Behavior toward an Organic Material

The affinity of functionalized Laponite clay toward an organic material in the aqueous phase was explored. Functionalization was performed by using triblock copolymers based on ethylene oxide (EO) and propylene oxide (PO) units that are EO(11)PO(16)EO(11) (L35) and PO(8)EO(23)PO(8) (10R5). Phenol (PhOH) was chosen as organic compound, which represents a contaminant prototype. To this purpose, densities and enthalpies of mixing as well as PhOH UV-absorption spectra were determined. The enthalpy and the spectrophotometry revealed PhOH-Laponite interactions whereas the volume did not. It emerged that the area occupied by PhOH on the Laponite surface is equal to that computed from the partial molar volume of PhOH in water, corroborating the insensitivity of the experimental volumes to the adsorption process. The situation where both PhOH and copolymer are simultaneously present in the aqueous Laponite suspension was also investigated. It turned out that the copolymer replaces PhOH from the water/Laponite clay interface, resulting in L35 being the more efficient. Moreover, the lateral copolymer-phenol interactions enhance the anchoring of PhOH to the solid surface. The reverse copolymer exercises the most important relevant effect. The UV-absorption spectra of PhOH in the water + copolymer + Laponite mixtures provided information that is consistent with those given by the calorimetric experiments. In conclusion, the aqueous copolymer-functionalized Laponite presents surface properties very different from the bare Laponite, favoring the removal of the organic compound from the solid surface.

Organo-Laponites as Novel Mesoporous Supports for Manganese(III) salen Catalysts

A Mn(III) salen complex was immobilized onto the Laponite surface using three different methodologies: method A, direct immobilization of the complex on the parent Laponite; method B, covalent anchoring through cyanuric chloride (CC); and method C, covalent anchoring through CC into a 3-aminopropyl)triethoxysilane (APTES) modified Laponite. All of the materials were characterized by FTIR, XPS, thermogravimetry, XRD, and nitrogen isotherms at 77 K, to gather information on the modifications introduced by the organo spacers within the Laponite surface, as well as on the anchored complex integrity; the Mn based materials were screened in the heterogeneous epoxidation of styrene. The results have shown that the immobilization of the manganese(III) salen complex by methods B and C have occurred at the edges of the clay particles through the spacers (APTES and CC) that have been anchored onto the Si-OH groups, whereas in method A, the complex is distributed throughout the clay surface, including the interlayer region. Therefore, the manganese loadings on the Laponites were as follows: materials prepared by method A >> method B > method C. All of the heterogeneous catalysts showed high styrene epoxide selectivity, with that prepared by method A showing comparable styrene epoxide selectivity as the homogeneous phase reaction. The styrene epoxide yields decrease in the following order: materials prepared by method A > method B > method C (1st cycles), which parallel the respective support catalytic activity and decreasing of manganese content. The heterogeneous catalysts prepared using methods B and C could be reused at least for four times, with the former exhibiting the most stable catalytic activity, but that prepared by method A showed a significant decrease after two catalytic cycles.

Thermodynamic Study of the Acid−Base Equilibrium on the Surface of a Synthetic Clay, Laponite. Adsorption of Dimethyldodecylamine-N-oxide onto Laponite at Various pHs, in Aqueous Media, at 298 K

Adsorption isotherms were determined for dimethyldodecylamine-N-oxide (DDAO) onto Laponite dispersed in water. The isotherms were obtained at pH 3.5 and 4.5 and at various NaCl concentrations (0.1, 0.2, and 0.3 M) by potentiometry, using an electrode sensitive to the nonionic surfactant. The stability of the synthetic clay at the pH values and for the durations of the measurements used was initially verified in preliminary tests. At the acidities used, DDAO in aqueous solution is bound in an acid-base equilibrium with its protonated form (DDAOH + ). For a given pH, adsorption isotherms, determined for different ionic strengths, showed a common intersection point. Coordinates of this point were compared to those obtained for its cationic homologue, dodecyltrimethylammonium (DTA + ), in the same conditions. We used these data to deduce the value of the acid-base constant of DDAOH + /DDAO pairs on the Laponite surface: α pK a = 3.9. The acid, DDAOH + , seems to be stronger when adsorbed than when in solution (pK a = 4.95).

NMR Visibility and Alkali–Tetraalkylammonium Cation Competition in Laponite Suspensions

Abstract Competition experiments between alkali counterions and tetraalkylammonium cations for interaction with a clay (laponite) surface have been monitored by7Li and23Na NMR. As a result of a stronger interaction of sodium cations, an increase of the23Na NMR visibility is observed with the addition of the organic salt. Multiple-quantum-coherence spectra have been used to investigate the behaviors of the alkali cations. The variation in both7Li and23Na half bandwidths reflects the monolayer formation of tetraalkylammonium cations at the laponite surface.