Hectorite Clay Research Articles

Molecularly imprinted polymer doped with Hectorite for selective recognition of sinomenine hydrochloride

In this work, a new and facile method was introduced to prepare molecularly imprinted polymers (MIPs) based on nano clay hectorite (Hec) for sinomenine hydrochloride (SM) analysis. Hec was firstly dissolved in distilled water in order to swell adequately, followed by a common precipitation polymerization with SM as the template, methacrylic acid as monomer, ethylene glycol dimethacrylate as a crosslinker and 2,2-azobisisobutyronitrile as an initiator. Hec@SM-MIPs were characterized by Fourier transform infrared spectrometer, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The maximum binding capacity of Hec@SM-MIPs, SM-MIPs and non-imprinted polymers (NIPs) (Hec@NIPs) was 57.4, 16.8 and 11.6 mg/g, respectively. The reason for this result may be that Hec@SM-MIPs have more binding sites and imprinted cavities for template molecule. Equilibrium data were described by the Langmuir and Freundlich isotherm models. The results showed that the Hec@SM-MIPs adsorption data correlated better with the Langmuir equation than the Freundlich equation under the studied concentration range. In vitro drug release experiment, Hec@SM-MIPs have a better ability to control SM release than SM-MIPs. Therefore, Hec@SM-MIPs were successfully applied to extraction of SM and used as the materials for drug delivery system.

Room-temperature storage of microalgae in water-in-oil emulsions: influence of solid particle type and concentration in the oil phase.

Water-in-oil emulsions containing silica nanoparticles (Aerosil R974) have the potential to stabilize microalgae for long-term storage. Studies were completed to determine if smectite clays could be used as an alternative to Aerosil R974. Emulsions were prepared with Aerosil R974, and hectorite and bentonite clays in the continuous phase and Chlorella sorokiniana was added to the aqueous phase to monitor the effects of solid particles on emulsion stability. Biological stability (cell viability) was determined using cell density measurements, and physical stability was measured from water droplet size distributions obtained by light scattering measurements and by examining phase separation over time. Measurements were also made to determine the effects of particles in the oil phase on emulsion viscosity. Particle concentrations greater than 0.25 wt% in the oil phase were required for maintaining physical stability. In emulsions containing 1 wt% solid particles and microalgae, biological stability of cells could be sustained for 340 days, regardless of particle type. At 1 wt% particles in the oil phase, apparent viscosity was 165% greater for samples containing hectorite and bentonite clays compared to samples containing Aerosil R974. The higher viscosity would need to be considered in large-scale production of emulsions for commercial application.

133Cs Nuclear Magnetic Resonance Relaxometry as a Probe of the Mobility of Cesium Cations Confined within Dense Clay Sediments

133Cs nuclear magnetic resonance is used to quantify the mobility of cesium counterions confined within the interlamellar space of synthetic Hectorite clay under controlled hydration conditions. The degree of lamellae ordering within the macroscopic clay sediment is determined by analyzing the variation of the 133Cs NMR spectra as a function of the sample orientation in the static magnetic field. Furthermore, a detailed analysis of the 133Cs NMR spectra allows one to determine the order of magnitude of the quadrupolar and heteronuclear dipolar couplings monitoring the NMR relaxation of the cesium cations confined within clay sediments. Finally, a lower limit to the average residence time of the cesium cations within the clay interlamellar space is determined by using 133Cs NMR relaxation measurements under spin-locking conditions.

Investigation of Mechanical Properties and Dye Adsorption Capacities of Novel Hydrophobic Association Nanocomposite Hydrogels

The preparation of high performance hydrogels has always been one of the research focuses in the area of soft matters and functional polymers. In this paper, a facile method was developed for the preparation of high performance hydrophobic association nanocomposite hydrogels (HANC gels) via in situ copolymerization of acrylamide (AM) and octadecyl methacrylate (OMA) in the aqueous suspension of hectorite clay Laponite HZ-200 (clay) with sodium dodecyl benzene sulfonate (SDBS). Tensile hysteresis curves showed that the hysteresis degrees between HANC gels and conventional hydrophobic association hydrogels (HA gels) were almost the same, but the tensile strength of the HANC gel reinforced by just 0.4 wt% clay at the strain of 1500% was already as 630% as the strength of the HA gel, which indicated that the mechanical properties of the HA gel were greatly enhanced by the introduction of a small amount of clay without increasing the internal friction in the hydrogel network. The effects of clay on the structure of HANC gels were further confirmed by swelling test, it was found that the addition of clay effectively maintained the structural integrity of HANC gels in watery environment and prevented the collapse of gel network. Moreover, HANC gels exhibited superior cationic dye adsorption capacity compared to HA gels due to the existence of abundant negative charges on the surfaces of clay nanosheets

Effect of Cosolvent in a Nucleophilic Substitution Reaction Using Organoclay in Triphase Catalytic System

A remarkable rate enhancement technique has been devised for a typical nucleophilic displacement reaction by using triphase catalytic materials based on tetraoctylammonium exchange forms of hectorite clay. Pseudo-first order rate constants (kobs) for the conversion of 1-bromobutane to the corresponding chloride under triphase conditions using the clay catalyst in the presence of various polar cosolvents have been observed. The results here have shown that the addition of a cosolvent increases the catalytic activity of the triphase system by several fold. In addition, the results have demonstrated that each cosolvent has a unique concentration for achieving an optimum reaction rate.

Binding interaction and gelation in aqueous mixtures of poly(N-isopropylacrylamide) and hectorite clay.

The binding interaction between poly(N-isopropylacrylamide) (PNIPAm) chains and hectorite clay platelets was directly detected by quartz crystal microbalance with dissipation (QCM-D) to explore the cross-linking mechanism in the strong nanocomposite hydrogel (NC gel), which is in situ polymerized with NIPAm in the clay suspension. PNIPAm chains were allowed to be adsorbed on the gold surface of the QCM electrode. A large frequency shift Δf in the QCM as introducing the clay indicated that a large amount of clay platelets were adsorbed on the deposited PNIPAm layer. The relationship between the dissipation shift ΔD and Δf revealed that the adsorption included two steps of fast initial buildup and following densification of the clay platelets. In dilute aqueous mixtures, the PNIPAm chain and clay formed aggregates as observed from the hydrodynamic diameter. A gelation state diagram was established for concentrated aqueous PNIPAm-clay mixtures. The Raman spectrum pointed out the conformation change of the PNIPAm chains in aqueous solutions when the clay was added, which would be caused by the adsorption of PNIPAm chains to the clay platelets.

Temperature dependence of aging kinetics of hectorite clay suspensions

The aging of salt-free hectorite suspensions with different concentrations (cL=2.9, 3.2 and 3.5wt%) stored for 2days or 4days was studied by rheology at different temperatures. The evolution of storage and loss moduli G′ and G″ during aging followed aging time–temperature superposition. The temperature dependence of the shift factor aT, which reflected the aging kinetics, was interpreted by the reaction-limited colloidal aggregation (RLCA) mechanism with counterion condensation in calculating the double-layer interaction of the charged clay particles. Temperature dependence of the plateau modulus and yield stress of the suspension aged for 800s was modeled with the soft glassy rheology (SGR) theory. The estimated noise temperature x indicated that the sample aged at higher temperature corresponded to a deeper quench in the nonergodic state. Under larger amplitude of oscillatory shear, the suspension exhibited a strain rate-frequency superposition (SRFS). The shearing eliminated the effects of aging and heating.

A facile method for reinforcing poly(N‐isopropylacrylamide)‐hectorite clay nanocomposite hydrogels by heat treatment

A facile method was explored to reinforce the poly(N‐isopropylacrylamide) (PNIPAm)‐hectorite nanocomposite hydrogel (NC gel) by heat treatment at temperature above the volume phase transition temperature (VPTT), which enhanced mechanical strength and reduced swelling capacity with denser microporous structure as compared with the non‐treated NC gel. This reinforcement effect was increased by increasing treating temperature and/or treating time, which still remained even after swelling, indicating an irreversible structure change in the treated NC gels. Heat treatment became more effective when the NC gel contained higher clay content. The quartz crystal microbalance (QCM) data showed that the interaction between PNIPAm chains and clay platelets became stronger at temperatures higher than the VPTT, causing an increase in the crosslinking density of the treated NC gels. A strong hydrogel was obtained by heat treatment of the aqueous mixture of PNIPAm and hectorite clay for the first time. POLYM. COMPOS., 37:1557–1563, 2016. © 2014 Society of Plastics Engineers

Comparison of the properties of polyimide nanocomposites containing three different nanofillers: Organoclay, functionalized graphene, and organoclay/functionalized graphene complex

Polyimide nanocomposites containing three different types of nanofillers were compared in terms of their thermal properties, morphology, and oxygen permeability. Organically modified hectorite clay (STN), functionalized hexadecylamine-graphene sheets, and an STN/hexadecylamine-graphene sheets complex were utilized as nanofillers in the fabrication of polyimide nanocomposite films. Hybrid films were obtained from blended solutions of the precursor polymer and the three types of nanofillers, and the filler content with respect to the polyimide was varied from 0 to 20 wt%. The variations in the properties of the polyimide matrix with respect to the filler content are discussed. Transmission electron microscopy photographs confirmed that most of the STN and hexadecylamine-graphene sheets were dispersed homogeneously throughout the matrix polymer on the nanoscale, although some agglomerate STN/hexadecylamine-graphene sheet complex particles were also formed. The coefficients of thermal expansion and the O2 transmission rates of the hybrid materials were found to improve linearly as the filler content of the polyimide matrix increased.

Comparison of the properties of colorless polyimide nanocomposites containing saponite or organically modified hectorite

Poly(amic acid) (PAA) was prepared by the reaction of 4,4′-(hexafluoro isopropylidene) diphthalic anhydride with 2,2′-bis(trifluoromethyl) benzidine in N, N-dimethylacetamide. Hybrid films were obtained from blended solutions of the precursor polymer and saponite (SPT) or organically modified hectorite (STN) clays, and the clay content was varied from 0 to 40 wt%. The cast film of PAA was heat treated at different temperatures to create polyimide (PI) hybrid films. The nanostructure of the hybrid films was observed using transmission electron microscopy, which showed that the clay layers were well dispersed into the matrix polymer, although some clusters or agglomerated particles were also detected. The addition of SPT was more effective than the addition of STN with regard to improving the thermal properties, whereas the addition of STN was more effective with regard to improving the optical transparency and gas barrier characteristics of the PI matrix.

Notch insensitive and self-healing PNIPAm–PAM–clay nanocomposite hydrogels

In the present work, hydrophilic monomer acrylamide (AM) was copolymerized with N-isopropylacrylamide (NIPAm) in an aqueous hectorite clay suspension to prepare PNIPAm-PAM-clay nanocomposite hydrogels (NC gels). With increasing AM content, the elongation at break of the copolymerized NC gels increased but the strength as well as the hysteresis during the loading-unloading cycle decreased, showing faster relaxation due to the more hydrophilic copolymer chains with the AM segments. The elongation at break of the copolymerized NC gels was independent of the notch length and notch type, while the fracture energy was greatly increased to 3000-5000 J m(-2) from 700 J m(-2) for the pure PNIPAm NC gels. The copolymer chains resulted in this notch insensitivity by easily dispersing the stress concentration at the notch tip through disorientation of the copolymer chains and clay platelets. The copolymerized NC gels also exhibited excellent self-healing capability; the cut surfaces were connected together by simply keeping in contact for a period of time (about 4 days at 20 °C). This self-healing was accelerated by increasing the treatment temperature (about 4 h at 80 °C).

A novel model to predict the fatigue life of thermoplastic nanocomposites

In this article, a new model was developed to predict the fatigue life and stiffness reduction in thermoplastics filled with two-dimensional nanoparticles. The established model is a combination of micromechanics model and the normalized stiffness degradation approach. It was assumed that under fatigue loading condition, only stiffness of thermoplastic resin was degraded due to the temperature rise and thermal softening phenomena, while the stiffness of the nanofillers remains unchanged. The developed model is capable of predicting the fatigue life of thermoplastic nanocomposites based on the experimental data of the neat thermoplastic resin without nanofillers. The results obtained by the new model are in very good agreement with the experimental data of polyamide-6 pellets and hectorite clay nanocomposites under constant stress amplitudes fatigue loading conditions.

Cell proliferation and cell sheet detachment from the positively and negatively charged nanocomposite hydrogels

The charged nanocomposite hydrogels (NC gels) were synthesized by copolymerization of positively or negatively chargeable monomer with N-isopropylacrylamide (NIPAm) in the aqueous suspension of hectorite clay. The ionic NC gels preserved the thermo-responsibility with the phase-transition temperature below 37°C. The L929 cell proliferation was sensitive to charge polarity and charge density. As compared to the PNIPAm NC gel, the cationic NC gels with <5 mol % of 2-(dimethylamino)ethyl methacrylate (DMAEMA) showed improved cell proliferation, whereas the cells grew slowly on the gels with negatively charged 2-acrylamido-2-methylpropane sulfonic acid (AMPSNa). By lowering temperature, rapid cell sheet detachment was observed from the surface of ionic NC gels with 1 mol % of ionizable monomers. However, lager amount of AMPSNa or DMAEMA did not support rapid cell sheet detachment, probably owing to the adverse swelling effects and/or enhanced electrostatic attraction.

Fluorescent colored material made of clay mineral and phycoerythrin pigment derived from seaweed

In order to obtain a fluorescent colored powder, composites of phycoerythrin pigment extracted from seaweed and clays (hectorite and montmorillonite) were examined. The pigment adsorbed easily on synthetic hectorite in an aqueous solution and a composite with bright fluorescence was obtained. On the other hand, the adsorption of the pigment on natural montmorillonite was not sufficient, and a salt had to be added to the pigment solution to obtain the composite. Low heat and light fastness, which are serious drawbacks of phycoerythrin for practical usage, were increased by the adsorption to the hectorite clay.

Anisotropy of Water Dynamics in Clays: Insights from Molecular Simulations for Experimental QENS Analysis

We measure H2O dynamics in a well-defined synthetic hectorite clay by the neutron spin echo technique, in the temperature range from 240 to 347 K. The interlayer spaces of this anisotropic material contain two layers of confined water, corresponding to the so-called bihydrated state. We analyze the experimental data in light of parallel molecular dynamics simulations. Simulations demonstrate that H2O diffusion in the direction perpendicular to the clay layers is not negligible and has to be taken into account in the experimental data analysis. A diffusive model with only two fitting parameters D⊥ and D∥ is well adapted for such analysis. A clear physical meaning for the two fitting parameters exists, in view of the geometry of the system. Experimentally, the diffusion coefficients parallel to the clay layers D∥ were estimated to be slowed down by a factor of 5 compared to bulk water. Further, the activation energy of the diffusion process is higher than in bulk water especially toward the lower temperatur...

Functionalized hectorite clay mineral for Ag(I) ions extraction from wastewater and preparation of silver nanoparticles supported clay

A novel clay mineral-based adsorbent for Ag(I) ions extraction was obtained by modifying hectorite with 2-(3-(2-aminoethylthio)propylthio)ethanamine (AEPE-hectorite). The modified hectorite was used to recover Ag(I) ions from wastewater for further preparation of silver nanoparticles supported hectorite. The parameters affecting silver ions extraction by AEPE-hectorite were investigated. The adsorbent could extract Ag(I) ions from solution in a wide pH range (1–8) and high extraction efficiencies were achieved in the solution pH ranged from 4 to 9. AEPE-hectorite showed a good selectivity toward Ag(I) ions over Co(II), Ni(II) and Cd(II) ions and the solution ionic strength had no significant effect on extraction efficiency. The adsorption of Ag(I) ions onto AEPE-hectorite followed the Freundlich isotherm model with maximum adsorption capacity observed in the experiment of 49.5mgg−1. The adsorbent was successfully used to recover silver ions from a wastewater containing high concentration of silver and silver nanoparticles supported hectorite was obtained after reducing with NaBH4. These results show an alternative in the preparation of silver nanoparticles supported clay.

Robust and thermo-response graphene–PNIPAm hybrid hydrogels reinforced by hectorite clay

Graphene oxide (GO) based hydrogels were proposed to be used as biomaterials and stimuli-response materials, but their poor mechanical properties restricted their applications. We enhanced GO–poly(N-isopropylacrylamide) (PNIPAm) hydrogels by hybrid with the hectorite clay through in situ polymerization for the first time. This clay was found to stabilize the GO in the aqueous suspension when a reducer was added in a redox initiating pair. These GO–clay–PNIPAm hybrid hydrogels exhibited a high mechanical strength and extensibility with the GO sheets as the cross-linker and with the hectorite clay as both the cross-linker and reinforcing agent. They were thermal-responsive with the volume phase transition at ∼34°C. Reduction of the GO with l-ascorbic acid under environmental friendly conditions resulted in a high conductivity to the graphene–clay–PNIPAm hydrogels. These graphene–clay–PNIPAm hydrogels still had desirable mechanical properties. This finding has provided an easy method to prepare strong and stimuli-response graphene–polymer hydrogels to meet the demand for the newly developed soft matter.

Linear and nonlinear viscoelasticity of water-in-oil emulsions: Effect of droplet elasticity

The effect of droplet elasticity on the linear and nonlinear viscoelasticity of water-in-oil emulsions was studied by comparing two kinds of emulsions: one with pure water as droplets, the other with a suspension of hectorite clay as droplets. The clay-filled emulsion had high droplet elasticity due to the gelation of the clay suspension. As the water-to-oil volume ratio ϕ increased, the emulsions changed from liquid-like state to solid-like state as the droplets formed a jammed state. Effect of droplet elasticity was most significant in the jammed state, where the clay-filled emulsion showed a much higher plateau modulus than the clay-free one. Nonlinear viscoelasticity was observed by the large amplitude oscillatory shear (LAOS) rheology. The Lissajous curve was dissected into the cage-yielding and cage-restructuring parts, and the cage modulus Gk in the nonlinear viscoelastic regime was higher for clay-filled emulsion than the clay-free one in the jammed state due to the contribution of the droplet elasticity. The droplet elasticity was found to contribute to the nonlinear viscoelasticity of the emulsions.

Binding mechanism of Cu(II) at the clay–water interface by powder and polarized EXAFS spectroscopy

The sorption mechanism of Cu(II) on the 2:1 magnesian clay hectorite, the 2:1 aluminous clay montmorillonite, and the 1:1 aluminous clay kaolinite was investigated at pH 5.4–6.0 and 0.5M NaCl ionic strength by solution chemistry and powder and polarized XANES and EXAFS spectroscopy. Divalent copper was not photoreduced under the intense synchrotron X-ray beam and retained its usual square (bi)pyramidal coordination with four equatorial oxygens (Oeq) at 1.93–1.96Å and one to two axial oxygens (Oax) at 2.56–2.58Å. The angular dependence of XANES spectra, the measured angle of 57–58° between the Cu–Oeq atomic pair and the direction perpendicular to the clay layer plane ([001]∗), and the detection and polarization dependence of neighboring Al/Mg and Si cationic shells, together indicate that Cu(II) is bonded to the edges of the clay layers as an inner-sphere complex. Based on the number of Mg/Al and Si nearest neighbors, the Cu(Oeq)4(Oax)1–2 polyhedron is attached to the clay surface by sharing one to three edges with the structural Al/Mg octahedra and zero to three corners with the Si/Al tetrahedra. Copper has an unusually high coordination on the two dioctahedral aluminous clays, explained by the presence at their surface of distorted empty cavities which can accommodate irregular coordination polyhedra. The steric match between the distorted empty octahedral cavities and the Jahn–Teller distorted Cu polyhedra provides a rationale to explain the higher affinity of Cu(II) for Al octahedral sheets, including the hydrargillite sheet of lithiophorite ([Al,Li][MnO2]O2[OH]2) as observed in nature.

Promoted cell proliferation and mechanical relaxation of nanocomposite hydrogels prepared in cell culture medium

Nanocomposite hydrogels (NC gels) were synthesized through in situ polymerization of N-isopropylacrylamide (NIPAm) in the hectorite clay suspension made from cell culture medium Dulbecco’s modified Eagle medium (DMEM). Cell cultured on these NC gels (D-NC gels) surface proliferated faster compared with that on the NC gels synthesized in water due to the nutrients in the D-NC gels. Cells attached and proliferated faster on the D-NC gels with higher modulus. In addition, cell sheets with good viability spontaneously detached from the gel surface by lowering temperature. Their tensile elongation at break was higher than 7 and the true strength σtrue was up to 800kPa. The stress–strain curves of the D-NC gels were described quantitatively with the Mooney–Rivlin equation. A stretched exponential stress equation was adopted to express the stress relaxation of the D-NC gels with an average relaxation time τ (∼102s) estimated from data fitting, showing a broad distribution (polydispersity k∼0.4). The τ value, which was used in simulation for the tensile creep compliance of the D-NC gels, became shorter with increasing clay concentration due to the decrease in the network chain length. The relaxation process was similar to the natural articular cartilage. This work provides a facile way to produce hydrogels with improved cell compatibility and satisfactory mechanical properties for biomedical applications.