Synthetic Nanoclay Research Articles

Nacre Mimetic with Embedded Silver Nanowire for Resistive Heating

Nacre mimetics show great potential as lightweight, mechanically robust, and functional materials. Here, we introduce highly reinforced nacre-mimetic nanocomposite (NC), prepared via self-assembly of poly(vinyl alcohol) polymer-coated synthetic nanoclay from aqueous dispersions, as a transparent and mechanically robust substrate to prepare silver nanowire (AgNW) embedded thin-film resistive heater. AgNW is a promising substitute for widely used brittle and expensive indium tin oxide (ITO) due to its high electrical conductivity, excellent optical transparency, and good mechanical flexibility. However, current AgNW-based electrodes mostly suffer from limitations such as surface roughness and weak adhesion of AgNWs to flexible plastic substrates (e.g., poly(ethylene terephthalate), PET). We demonstrate that AgNW can be embedded in nacre-mimetic NC substrate by simple hot-pressing as compared to PET, leading to excellent stability against scotch tape peeling without any encapsulation layer. The AgNW/NC resistive heater shows uniform sheet resistance varying from 10 to 80 Ω/sq with 70 to 91% transmittance at 550 nm on decreasing AgNW density from 111 to 23 mg/m2. Moreover, AgNW/NC heater can generate rapid (10 s) and repetitive long-term heating response at low input voltages. It shows only small variation in temperature (4 °C) and sheet resistance during bending at 14 mm diameter for 2000 cycles as well as under various extreme mechanical deformations. Taking advantage of the conformability, mechanical deformability, and fast thermal response of the resistive heater, we demonstrated the in vitro temperature-triggered release of antibiotics (i.e.,vancomycin) from phase change material-coated, antibiotic-loaded hydrogels. Hence, we envision that the resistive heater can be introduced as a potential candidate into flexible electronics and wearable devices.

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.

Cyclic behavior and pore pressure generation in sands with laponite, a super-plastic nanoparticle

The paper examines the effect of the presence of small percentages (1–5%) by dry mass of the sand of laponite – a synthetic nanoclay with plasticity index exceeding 1000% – on the cyclic response of sand with relative density in the 15–25% range. The work is based on cyclic triaxial tests performed on specimens prepared pluviating sand and laponite under dry conditions and then permeated with water. 1% laponite impacts all stages of the cyclic tests, from the response during the first loading cycle to liquefaction, increasing the cyclic resistance. Further benefits are observed with a longer pre-shear aging period or higher dosages (3–5%) of laponite.The observed behavior is associated with reduced mobility of the sand particles during cyclic loading, which can be ascribed to two mechanisms: (1) bonding/bridging at the particle contacts due to the charged laponite fines which are attracted to the sand grains; and (2) formation of a pore fluid with solid like properties. The first appears to control the behavior with 1% laponite, while it is proposed that the second is responsible for the response with higher dosages of laponite.The results presented provide new insight into the effects of high plastic fines on the cyclic response of sands, the “extreme” effects of the plasticity of the fines, and are significant in light of the possible use of laponite for liquefaction mitigation, an idea first put forth by the authors.

Hierarchical Nacre Mimetics with Synergistic Mechanical Properties by Control of Molecular Interactions in Self-Healing Polymers.

Designing the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass-transition temperature T(g) and bonded by quadruple hydrogen-bonding motifs, and subsequently assembled with high-aspect-ratio synthetic nanoclays to generate nacre-mimetic films. The high dynamics and self-healing of the polymers render transparent films with a near-perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σ(UTS)≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.

Hierarchical Nacre Mimetics with Synergistic Mechanical Properties by Control of Molecular Interactions in Self‐Healing Polymers

AbstractDesigning the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass‐transition temperature Tg and bonded by quadruple hydrogen‐bonding motifs, and subsequently assembled with high‐aspect‐ratio synthetic nanoclays to generate nacre‐mimetic films. The high dynamics and self‐healing of the polymers render transparent films with a near‐perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σUTS≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.

Adsorption and in vitro release of vitamin B1 by synthetic nanoclays with montmorillonite structure

Modelling experiments on vitamin B1 (thiamine hydrochloride) intercalation into synthetic montmorillonite (Mt) structures of the systematically varied compositions Na2x(Al2(1–x),Mg2x)Si4O10(OH)2∙nH2O (where 0<x<1) were performed. Mt samples were prepared by hydrothermal synthesis during 72h at the temperature 350°C and a pressure of 70MPa. In vitro release of vitamin B1 (VB1) in simulated gastric (SGF) and intestinal (SIF) fluids was performed. It was established that the intercalation of VB1 depends primarily on the composition and cation-exchange capacity of Mt and, to a lesser extent, on the pH of the solution. The adsorption data were fitted with several common isotherms, but the best regression parameters were obtained for the Langmuir model. Adsorption type was determined as the cation-exchange reaction according to the Dubinin–Radushkevich model. The release profile of VB1 from the VB1–Mt composite followed the Higuchi model. The maximum amount of released VB1 reached 54wt.% and 19wt.% in SGF and SIF, respectively, for synthetic Mt. For natural Mt K10, these values reached 37wt.% and 11wt.%, respectively. For the first time, the optimal Mt compositions for further drug delivery systems development were chosen.

Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios.

Nacre-mimetics hold great promise as mechanical high-performance and functional materials. Here we demonstrate large progress of mechanical and functional properties of self-assembled polymer/nanoclay nacre-mimetics by using synthetic nanoclays with aspect ratios covering three orders in magnitude (25-3,500). We establish comprehensive relationships among structure formation, nanostructuration, deformation mechanisms and mechanical properties as a function of nanoclay aspect ratio, and by tuning the viscoelastic properties of the soft phase via hydration. Highly ordered, large-scale nacre-mimetics are obtained even for low aspect ratio nanoplatelets and show pronounced inelastic deformation with very high toughness, while those formed by ultralarge nanoplatelets exhibit superb stiffness and strength, previously only reachable for highly crosslinked materials. Regarding functionalities, we report formerly impossible glass-like transparency, and excellent gas barrier considerably exceeding earlier nacre-mimetics based on natural nanoclay. Our study enables rational design of future high-performance nacre-mimetic materials and opens avenues for ecofriendly, transparent, self-standing and strong advanced barrier materials.

Synthetic nanoclays with the structure of montmorillonite: Preparation, structure, and physico-chemical properties

Nanosized layered silicates with a montmorillonite structure of varying composition were synthesized under hydrothermal conditions (350°C, 700 atm). The hydrothermal treatment was applied to gels with the compositions calculated with the use of an ideal formula of the final product Na2x (Al2(1 − x), Mg2x ) Si4O10(OH)2 · nH2O (0 ≤ x ≤ 1). The obtained samples were investigated by X-ray diffraction, IR and NMR spectroscopy, electron microscopy, and mercury porosimetry. The values of the cation-exchange capacity and specific surface are determined. The mean size of the particles of the synthesized samples is 40 ± 7 nm. A gradual substitution of aluminum for part of the magnesium in the initial gel made it possible to obtain samples with well-defined composition-dependent characteristics.

Rheological Behavior of Nanoclay Containing Nanofluids

ABSTRACTA synthetic hectorite nanoclay, Laponite®, with a disc shape (20 – 30 nm in diameter and 1 nm in thickness) was used as a model nanoparticle to prepare dispersions in water and different organic solvents. Although up to 20 wt% of nanoclay can be dispersed in water to form a low-viscosity stable colloidal sol, dispersions in organic solvents behave differently. The effect of the dielectric constant of the medium on the viscosity of the dispersion was studied systematically using two series of water-organic solvent miscible blends. Changes in the rheological behavior of the dispersions suggest that the dielectric constant of the organic solvent is a determining factor in the sol-gel transition of a nanoclay-containing nanofluid.

Sepiocite, Sepiolite-Like Nanoclay Derived from Hydrotalcite-Like Layered Double Hydroxide

Sepiocite, a synthetic sepiolite-like nanoclay, was derived from hydrotalcite-like Mg2Al(CO3)0.5-layered double hydroxide (LDH) under phase transformation at 270 +/- 3 degrees C. The crystal structure of sepiocite is conceptually very similar to that of sepiolite derived from montmorillonite clay because sepiocite is formed through the alternation of the blocks and tunnels along the crystallographic c-axis, with a partial dehydroxylation of the octahedral Mg-(OH)-Al configuration into tetrahedral ones. Three important findings regarding sepiocite were arrived at: (i) its high specific surface area of 128.25 m2/g with an average particle size of 200 nm, which is approimately equal to 3.5 times larger than the specific surface area of the pristine LDH (34.21 m2/g); (ii) its non-swelling property; and (iii) its strongly reduced anion-exchange capacity.

Effect of nanoclay on relaxation of poly(vinylidene fluoride) nanocomposites

AbstractThe effect of Lucentite™ STN nanoclay on the relaxation behavior of poly(vinylidene fluoride) (PVDF) nanocomposites was investigated using dielectric relaxation spectroscopy (DRS) and wide‐ and small‐angle X‐ray scattering. Lucentite™ STN is a synthetic nanoclay based on hectorite structure containing an organic modifier between the hectorite layers. The addition of this nanoclay to PVDF results in preferential formation of the beta‐crystallographic phase. When the STN content increased to 5% and 10%, only the beta‐phase was observed. Bragg long period and lamellar thickness both decrease with STN addition. The relaxation rates for processes termedαa(glass transition, related to polymer chain motions in the amorphous regions) andαc(related to polymer chain motions in the crystalline regions and fold surfaces) can be described either with the Vogel‐Fulcher‐Tamman equation or with Arrhenius behavior, respectively. DRS shows that theαarelaxation rate increases with the concentration of STN because of the reduction of intermolecular correlations between the polymer chains, caused by the presence of layered silicate nanoclay particles, which serve to segregate polymer chains in the amorphous regions. Comparing samples with beta‐crystal phase dominant, the relaxation rate for theαcrelaxation also increases with concentration of STN in all nanocomposite samples. Dielectric properties at low frequencies are dominated by the dc conductivity, and as more STN is added, the conductivity increases rapidly. The addition of 10% STN makes the dc conductivity increase by almost four decades when compared with neat PVDF. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2520–2532, 2009

Poly(ethylene glycol) layered silicate nanocomposites for retarded drug release prepared by hot-melt extrusion

Composites of paracetamol loaded poly(ethylene glycol) (PEG) with a naturally derived and partially synthetic layered silicate (nanoclay) were prepared using hot-melt extrusion. The extent of dispersion and distribution of the paracetamol and nanoclay in the PEG matrix was examined using a combination of field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and wide-angle X-ray diffraction (WAXD). The paracetamol polymorph was shown to be well dispersed in the PEG matrix and the nanocomposite to have a predominately intercalated and partially exfoliated morphology. The form 1 monoclinic polymorph of the paracetamol was unaltered after the melt mixing process. The crystalline behaviour of the PEG on addition of both paracetamol and nanoclay was investigated using differential scanning calorimetry (DSC) and polarised hot-stage optical microscopy. The crystalline content of PEG decreased by up to 20% when both drug and nanoclay were melt blended with PEG, but the average PEG spherulite size increased by a factor of 4. The time taken for 100% release of paracetamol from the PEG matrix and corresponding diffusion coefficients were significantly retarded on addition of low loadings of both naturally occurring and partially synthetic nanoclays. The dispersed layered silicate platelets encase the paracetamol molecules, retarding diffusion and altering the dissolution behaviour of the drug molecule in the PEG matrix.

Dual Functions of Clay Nanoparticles with High Aspect Ratio in Dye-Sensitized Solar Cells

We have prepared a quasi-solid-state electrolyte for dye-sensitized solar cells (DSSCs) that consist of a liquid electrolyte and a synthetic nanoclay in order to solidify a liquid electrolyte and to induce a light-scattering effect to increase cell performance. These clay-based quasi-solid-state electrolytes offer unexpected benefits over liquid electrolyte due to their light-scattering effect. The best DSSC result is a short-circuit current of 15.4 mA/cm 2 , an open-circuit voltage of 0.723 V, a fill factor of 0.64, and an overall energy-conversion efficiency of 7.10% at 100 mW/cm 2 [air mass (AM) 1.5].