Montmorillonite Nanoplatelets Research Articles

Silicone elastomer dielectric composites by introducing novel O-MMT@TiO2 nanoparticles for energy harvesting application

Dielectric elastomers have attracted attention in emerging advanced electromechanical applications. However, how to simultaneously improve the dielectric constant and the breakdown strength of dielectric composite needs to be solved. In this paper, we propose a new strategy to anchor TiO2 nanoparticles onto organically modified montmorillonite (O-MMT) nanoplatelets through dehydration reaction to synthesize a novel filler O-MMT@TiO2. Then, the O-MMT@TiO2 is incorporated into methyl vinyl silicone rubber (MVSR) matrix to obtain O-MMT@TiO2/MVSR dielectric composites. Comparing with the composites by direct mixing of TiO2 and O-MMT in MVSR (O-MMT/TiO2/MVSR), O-MMT@TiO2/MVSR composites significantly increase mechanical and dielectric and energy storage properties. 30 wt% O-MMT@TiO2/MVSR composite achieves the highest energy storage density of 118.65 kJ/m3, which is 142.9 % higher than that of 15 wt%O-MMT/15 wt%TiO2/MVSR (48.84 kJ/m3). This study offers an effective method for the preparation of high-performance dielectric elastomer materials, which can be exploited for the energy harvesting application.

Development of multilayer PVA-MMT and PVA-CS film structures by spin coating-assisted layer-by-layer technique: Effect of PVA, CS and MMT nanoclay orientation on oxygen barrier properties

The orientation of biopolymer macromolecules and nanoclay, specifically Montmorillonite (MMT) nanoplatelets, plays a crucial role in controlling the properties of multi-layer film structures. Understanding the impact of macromolecule and nanoclay platelets’ orientation on barrier properties of packaging films is essential. To investigate the influence of hydrogen bonding in multilayer films structures, two polymers, namely polyvinyl alcohol (PVA) and chitosan (CS), were selected and laminated nanocomposite films were fabricated using the spin coating-assisted layer-by-layer (Spin-LbL) assembly technique. This technique facilitates the production of highly oriented nanocomposite films, where polymer chains and nanoclay particles align parallel to the film surface. Multi-directional 2-D wide-angle X-ray diffraction (2D-WADX) was successfully used to accurately assess the orientation and distribution of MMT nanoplatelets. Additionally, the films underwent characterization using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The 2D-WADX analysis revealed a parallel alignment of both the PVA chains and MMT clay nanoplatelets parallel to film surface. The XRD results confirmed the formation of intercalated nanolaminate structures, hydrogen-bonding interactions, and adjustments in the crystalline structure of PVA matrix. Through contact angle and oxygen permeability measurements, we observed that all quadri-layer film structures exhibited hydrophobic properties and reduced oxygen permeability compared to neat PVA films. Furthermore, the integration of MMT nanoclay, even at low concentrations, contributed to the development of nanocomposite films with improved oxygen barrier properties. Consequently, the quadri-layer films demonstrate great potential for food packaging applications.

Possible selective physisorption of lower molecular mass of epoxy-vinyl ester chains on the montmorillonite nanoplatelets: A rheological approach

Na+-montmorillonite nanoplatelets were surface functionalized by triethoxyvinylsilane through sol-gel reactions. The functionalized, and pristine nanoplatelets were then impregnated by Octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, a primary phenolic antioxidant, to be used in an epoxy vinyl ester resin. The FTIR, Raman and, TGA results confirm that the functionalization reactions, and the antioxidant impregnation process have been successfully carried out. FE-SEM micrographs demonstrate that particle morphology significantly changed as a result of the processes. In the next step, three different concentrations of the obtained nanofillers were added to an epoxy vinyl ester resin, and the attained colloids underwent rheological assessment. Both steady-shear, and dynamic complex viscosity diagrams showed significantly increased values, by two orders of magnitude, for untreated Na+-montmorillonite compared to the other nanofillers, i.e. vinyl-functionalized, and antioxidant-loaded ones. It was then demonstrated that such an increase is most certainly attributed to a proposed theory as possible selective physisorption of lower molecular mass of epoxy vinyl ester chains on the untreated montmorillonite nanoplatelets.

Micro foaming performance of scCO2-aid glutaraldehyde/hexametaphosphate/thermoplastic starch foams modified by alkali treatment and montmorillonite nano-platelets

The micro foaming performance, moisture resistance and dynamic viscosity of scCO2-aid glutaraldehyde/hexametaphosphate/thermoplastic tapioca starch (GA/SHMP/TOS) foams were considerably improved by proper NaOH treatment. The expansion ratio, resilience rate, dynamic viscosity values of these NaOH modified foams improved to a maximum, as the time for NaOH treatment approached a proper value. The dynamic viscosity, expansion ratio and resilience rate of the scCO2-aid GA/SHMP/TOS foams modified using 110 atm scCO2-pressure, the proper alkali treatment time, SHMP loading and varying montmorillonite (MMT) loadings improved further, as their MMT loadings approached a proper value of 2.5 part per hundred parts of tapioca starch (PHTOS). Relatively large dynamic viscosity (7.1x104 Pa·s), extremely large expansion ratio (∼75), cell density (1.1x109 cells/cm3) and/or resilience rate (∼80%) were acquired for the scCO2-aid GA/SHMP/TOS/MMT foam modified using the proper alkali treatment time and MMT loading. Thermal analyses results showed that crystallization onset temperatures and crystallization rates of scCO2-aid GA/SHMP/TOS/MMT foams modified using the proper alkali treatment time and varying MMT loadings improved to a highest value by adding 2.5 PHTOS of MMT nano-platelets. Possible reasons accounting for the considerably improved micro foaming performance of scCO2-aid GA/SHMP/TOS/MMT foams modified using the proper alkali treatment time and MMT loading are proposed in this study.

Green and Fire Resistant Nanocellulose/Hemicellulose/Clay Foams

AbstractLightweight polymer foams from synthetic polymers are commonly used in a wide‐spread spectrum of application fields. Their intrinsic flammability coupled with restrictions on flame retardant chemicals poses a severe threat to safety. Here, fire resistant foams comprising biobased components capable of replacing petroleum‐based foams are investigated. Cellulose nanofibers are combined with 2D montmorillonite nanoplatelets and a native xyloglucan hemicellulose binder, using a water‐based freeze casting approach. Due to the silicate nanoplatelets, these lightweight foams self‐extinguish the flame during flammability tests. The limiting oxygen index is as high as 31.5% and in the same range as the best fire‐retardant synthetic foams available. In cone calorimetry, the foams display extremely low combustion rates. Smoke release is near the detection limit of the instrument. In addition, the foams are withstanding the penetration of a flame torch focused on one side of the specimen (Ton surface 800 °C) and structural integrity is maintained. At the same time, the unexposed side is insulated, as demonstrated by a through‐thickness temperature drop of 680 °C cm−1. The results represent a tremendous opportunity for the development of fire‐safe foams combining excellent sustainability with multifunctional performance.

Magnetic κ-carrageenan/chitosan/montmorillonite nanocomposite hydrogels with controlled sunitinib release

This work aimed to design montmorillonite-incorporated pH-responsive and magnetic κ-carrageenan/chitosan hydrogels via a completely green route for controlled release of sunitinib anticancer drug. This was accomplished by ionic cross-linking of two biopolymers, κ-carrageenan and chitosan, in the presence of magnetic montmorillonite (mMMt) nanoplatelets. Interestingly, it was observed that the amount of mMMt affected not only the microstructure of hydrogels, but also the drug loading efficiency of nanocomposite hydrogels was noticeably increased by introducing mMMt (from 69 to 96%). The in vitro sunitinib release experiments showed that a low content of loaded sunitinib was released from all hydrogels in the buffered solution with pH 7.4. In contrast, a relatively sustained release with a high content of drug release was observed in the acidic solution of pH 5.5. During 48 h, the hydrogels nanocomposite containing a high content of mMMt showed cumulative release of 64.0 and 8.6% at pH 5.5 and 7.4, respectively. During two days, while the cumulative release of sunitinib was obtained 84.3% for the magnetic-free hydrogel, the magnetic ones showed 74.4 and 64% with the low and high contents of magnetic MMt, respectively. The developed κ-carrageenan/chitosan hydrogels with a high capacity of drug loading and subsequent pH-sensitive drug release can be considered in prolonged cancer therapy with reduced side effects.

Surface Charges Control the Structure and Properties of Layered Nanocomposite of Cellulose Nanofibrils and Clay Platelets.

The interfacial bonding and structure at the nanoscale in the polymer–clay nanocomposites are essential for obtaining desirable material and structure properties. Layered nanocomposite films of cellulose nanofibrils (CNFs)/montmorillonite (MTM) were prepared from the water suspensions of either CNFs bearing quaternary ammonium cations (Q-CNF) or CNFs bearing carboxylate groups (TO-CNF) with MTM nanoplatelets carrying net surface negative charges by using vacuum filtration followed by compressive drying. The effect of the ionic interaction between cationic or anionic charged CNFs and MTM nanoplatelets on the structure, mechanical properties, and flame retardant performance of the TO-CNF/MTM and Q-CNF/MTM nanocomposite films were studied and compared. The MTM nanoplatelets were well dispersed in the network of TO-CNFs in the form of nanoscale tactoids with the MTM content in the range of 5–70 wt %, while an intercalated structure was observed in the Q-CNF/MTM nanocomposites. The resulting TO-CNF/MTM nanocomposite films had a better flame retardant performance as compared to the Q-CNF/MTM films with the same MTM content. In addition, the effective modulus of MTM for the TO-CNF/MTM nanocomposites was as high as 129.9 GPa, 3.5 times higher than that for Q-CNF/MTM (37.1 GPa). On the other hand, the Q-CNF/MTM nanocomposites showed a synergistic enhancement in the modulus and tensile strength together with strain-to-failure and demonstrated a much better toughness as compared to the TO-CNF/MTM nanocomposites.

Assembly of cellulose nanocrystals and clay nanoplatelets studied by time-resolved X-ray scattering.

Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d ∝ φ-1/2 scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.

Super‐crosslinked ionic liquid‐intercalated montmorillonite/epoxy nanocomposites: Cure kinetics, viscoelastic behavior and thermal degradation mechanism

AbstractSuper‐crosslinked epoxy nanocomposites containing N‐octadecyl‐N′‐octadecyl imidazolium iodide (IM)‐functionalized montmorillonite (MMT‐IM) nanoplatelets were developed and examined for cure kinetics, viscoelastic behavior and thermal degradation kinetics. The structure and morphology of MMT‐IM were characterized by FTIR, XRD, TEM, and TGA. Synthesized MMT‐IM revealed synergistic effects on the network formation, the glass transition temperature (Tg) and thermal stability of epoxy. Cure and viscoelastic behaviors of epoxy nanocomposites containing 0.1 wt% MMT and MMT‐IM were compared based on DSC and DMA, respectively. Activation energy profile as a function of the extent of cure was obtained. DMA results indicated a strong interface between imidazole groups of MMT‐IM and epoxy, which caused a significant improvement in storage modulus and the Tg of epoxy. Network degradation kinetics of epoxy containing 0.5, 2.0, and 5.0 wt% MMT and MMT‐IM were compared by using Friedman, Kissinger‐Akahira‐Sunose (KAS), Flynn‐Wall‐Ozawa (FWO) and the modified Coats‐Redfern methods. Although addition of MMT to epoxy was detrimental to the Tg value, as featured by a fall from 94.1°C to 89.7°C detected by DMA method, and from 103.3°C to 97.9°C by DSC method, respectively. By contrast, meaningful increase in such values were observed in the same order from 94.1°C to 94.7°C and from 103.3°C to 104.7°C for super‐crosslinked epoxy/MMT‐IM systems.

Effect of Natural Nanostructured Rods and Platelets on Mechanical and Water Resistance Properties of Alginate-Based Nanocomposites.

A series of biopolymer-based nanocomposite films were prepared by incorporating natural one-dimensional (1D) palygorskite (PAL) nanorods, and two-dimensional (2D) montmorillonite (MMT) nanoplatelets into sodium alginate (SA) film by a simple solution casting method. The effect of different dimensions of nanoclays on the mechanical, water resistance, and light transmission properties of the SA/PAL or MMT nanocomposite films were studied. The field-emission scanning electron microscopy (FE-SEM) result showed that PAL can disperse better than MMT in the SA matrix in the case of the same addition amount. The incorporation of both PAL and MMT into the SA film can enhance the tensile strength (TS) and water resistance capability of the film. At a high content of nanoclays, the SA/PAL nanocomposite film shows relatively higher TS, and better water resistance than the SA/MMT nanocomposite film. The SA/MMT nanocomposite films have better light transmission than SA/PAL nanocomposite film at the same loading amount of nanoclays. These results demonstrated that 1D PAL nanorods are more suitable candidate of inorganic filler to improve the mechanical and water resistance properties of biopolymers/nanoclays nanocomposites.

Stable graphene oxide-based composite membranes intercalated with montmorillonite nanoplatelets for water purification

Graphene oxide (GO) membranes have great potential in separation technology. However, their instability under aqueous environments hinders their separation performance and practical application. Herein, we present a facile and environmentally friendly method to fabricate stable GO-based membranes via the intercalation of montmorillonite (MMT) nanoplatelets. The as-prepared membranes remain stable under water (neutral, acidic, and alkaline) in a fully hydrated state and exhibit a high pure-water flux up to 139.5 L·m−2·h−1 under 0.09 MPa. Furthermore, they also show high organic molecule rejection (98.75% for Congo red, 99.44% for rhodamine B, 99.90% for crystal violet, 99.94% for methylene blue, 96.26% for phenanthracene, and 51.32% for phenol) as well as good removal rate of heavy metal ions (100% for Ag(I), 100% for Cu(II), and 27.04% for Cr(VI)). Moreover, an outstanding recycling ability of the membranes also has been obtained. These significant performances make our membranes a good candidate in water purification.

Nanoplatelet reinforcement of cavity cell walls in polymer foams using carbon dioxide supercritical fluid

ABSTRACTReinforcing the cavity cell walls of polymer foams using nanoparticles can offer a new era for the property‐structure‐processing field in the development of functionalized ultra‐light components and devices manufactured from foam. When the nanoparticles are exfoliated in polymers, the viscosity substantially increases and thus mixing or foaming usually becomes almost impossible. We use CO2 supercritical fluid (CO2 SCF) for the mixing and foaming of poly(ethylene‐vinyl acetate) copolymer (EVA) with montmorillonite (MMT) nanoplatelets. The in situ evaporation of CO2 induces robust cavity cells of the EVA/MMT nanocomposite foam in a stable form of spherical shapes, which are seldom achieved by other methods. As the bubble grows and becomes stabilized in CO2 SCF, the exfoliated MMT nanoparticles are aligned at the cell walls by the Gibbs adsorption principle to minimize the surface energy at the gas–liquid interface and increase the rupture strength of the cavity walls. It is demonstrated that the developed methodology can be successfully used for foaming EVA containing high vinyl acetate (VA) content (>40%). Since EVA is too soft to construct cell walls of foam using conventional methods, the applicability of the developed methodology is extensively broadened for superior adhesion and compatibility with other materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46615.

Enhanced dielectric property and energy storage density of PVDF-HFP based dielectric composites by incorporation of silver nanoparticles-decorated exfoliated montmorillonite nanoplatelets

Dielectric constant and breakdown strength are two key factors influencing the energy density of a dielectric material. This paper reports a promising strategy to increase both the dielectric constant and breakdown strength of the PVDF-HFP upon incorporating a low content of silver-deposited exfoliated montmorillonite nanoplatelets (Ag-OMMT). Incorporation of the Ag-OMMT nanoplatelets forms a large number of nanocapacitors, resulting in more interfacial polarization compared to the bare PVDF-HFP under the same applied electric field. Meanwhile, the OMMT nanoplatelets act as the insulating barriers, increasing the breakdown strength of the PVDF-HFP. Consequently, great improvements in the energy storage density are achieved in these dielectric composites. The PVDF-HFP/Ag-OMMT composite film with 4 vol% Ag-OMMT shows an energy density of 10.51 J cm−3 at 400 MV m−1, which is ∼ 2.25 times that of the pure PVDF-HFP film.

Improvement of Food Packaging-Related Properties of Whey Protein Isolate-Based Nanocomposite Films and Coatings by Addition of Montmorillonite Nanoplatelets

In the present study the effects of the addition of montmorillonite (MMT) nanoplatelets on whey protein isolate (WPI)-based nanocomposite films and coatings were investigated. The main objective was the development of WPI-based MMT-nanocomposites with enhanced barrier and mechanical properties. WPI-based nanocomposite cast-films and coatings were prepared by dispersing 0 % (reference sample), 3 %, 6 %, 9 % (w/w protein) MMT, or, depending on the protein concentration, also 12 % and 15 % (w/w protein) MMT into native WPI-based dispersions, followed by subsequent denaturation during the drying and curing process. The natural MMT nanofillers could be randomly dispersed into film-forming WPI-based nanodispersions, displaying good compatibility with the hydrophilic biopolymer matrix. As a result, by addition of 15 % (w/w protein) MMT into 10 % (w/w dispersion) WPI-based cast-films or coatings, the oxygen permeability (OP) was reduced by 91 % for glycerol-plasticized and 84 % for sorbitol-plasticized coatings, water vapor transmission rate (WVTR) was reduced by 58 % for sorbitol-plasticized cast-films. Due to the addition of MMT- nanofillers the Young’s modulus and tensile strength improved by 315 % and 129 %, respectively, whereas elongation at break declined by 77 % for glycerol-plasticized cast-films. In addition, comparison of plasticizer type revealed that sorbitol-plasticized cast-films were generally stiffer and stronger, but less flexible compared glycerol-plasticized cast-films. Viscosity measurements demonstrated good processability and suitability for up-scaled industrial processes of native WPI-based nanocomposite dispersions, even at high nanofiller-loadings. These results suggest that the addition of natural MMT- nanofillers into native WPI-based matrices to form nanocomposite films and coatings holds great potential to replace well-established, fossil-based packaging materials for at least certain applications such as oxygen barriers as part of multilayer flexible packaging films.

All-Inorganic Intumescent Nanocoating Containing Montmorillonite Nanoplatelets in Ammonium Polyphosphate Matrix Capable of Preventing Cotton Ignition.

In the present manuscript a new concept of completely inorganic intumescent flame retardant nanocoating comprised of sodium montmorillonite nanoplatelets embedded in an ammonium polyphosphate matrix has been investigated using cotton as model substrate. The coating, deposited by multistep adsorption from diluted water-based suspensions/solutions, homogenously cover each cotton fibers with average thicknesses below 50 nm and add-on up to 5% in weight. Combustion characterization evidences the interesting properties: indeed, the so-treated fabrics reached self-extinguishing during horizontal flame spread tests. Furthermore, when the coating add-on reaches 5%, no ignition has been observed during cone calorimetry tests under 35 kW/m2 heat flux. Residue analyses pointed out the formation of an expanded all-inorganic coating capable of greatly improving char formation by exerting barrier function towards volatile release and heat transfer.

Multifunctional hybrid films prepared by aqueous stabilization of graphene sheets viaing cellulose nanofibers and exfoliated montmorillonite system

In this paper, reduction of graphene oxide (RGO) nanosheets were stably dispersed in water directly in the presence of montmorillonite (MMT) nanoplatelets and cellulose nanofibers (CNFs). This could be attributed to the steric hindrance of CNFs and the repulsion between different charges which exist in RGO nanosheets, MMT nanoplatelets and CNFs. Taking advantage of these stable hybrids, the films with unique microstructure have been fabricated successfully via vacuum filtration. For the highly oriented layer structures, the films have been given excellent fire resistance, high thermal stability and good flexibility. Meanwhile, because of the excellent electrical property of RGO nanosheets and the dielectric property of MMT nanoplatelets, there are lots of micro-capacitors in the film which has unique microstructure, and these micro-capacitors can impart the film high dielectric constant and relatively low dielectric loss.

Gastroretentive montmorillonite-tetracycline nanoclay for the treatment of Helicobacter pylori infection

The paper aims to explore the potential benefits provided by an organically modified montmorillonite (nanoclay) in the problematic management of the Helicobacter pylori gastric infection that is one of the most prevalent infectious diseases worldwide. Two nanoclay samples were produced by the intercalation of tetracycline (TC) into the interlayer of montmorillonite (MM) under two different pH reaction conditions (pH 3.0 and 8.7). MM/TC nanoclays were characterized by EDX, XRD, FTIR, DSC, drug adsorption extent, in vitro mucoadhesiveness and desorption in simulated gastric media. The reaction between MM and TC led to a complete MM cation (Na+ and Ca2+) exchange process, an increase of MM characteristic interlayer spacing as well as an involvement of NHR3+ group of TC, regardless of the reaction pH value. However, MM/TC nanoclay obtained under alkaline conditions provided a lower TC adsorption as well as a drug fraction weakly linked to MM in comparison with the nanoclay obtained in acidic conditions. Both the nanoclays exhibited good mucoadhesion properties to porcine mucin and TC desorption occurring mainly via a cation exchange process by H+ ions. Based on the results obtained, TC intercalation into MM nanoplatelets could represent a potential advantageous approach allowing the antibiotic to distribute homogeneously on the gastric mucosa, diffuse through the gastric mucus layer and achieve the microorganism localization.

Polystyrene‐montmorillonite core–shell particles via Pickering emulsion polymerization and their use as reinforcing additives for polypropylene and ethylene vinyl acetate

Solid particles can be used as stabilizers for oil/water (o/w) emulsions instead of the conventional surfactants. Emulsion polymerization of styrene, as an example of polymerizable oil, was started in the current study after ultrasonication of the monomer into aqueous phase with aid of montmorillonite nanoplatelets as solid stabilizer. Imaging using a field emission scanning electron microscopy equipped with energy dispersive X‐ray unit as well as transmission electron microscopy proved the formation of polystyrene/montmorillonite as core–shell hybrid latex particles via Pickering mode of emulsification. The mechanical properties of polypropylene (PP) and ethylene vinyl acetate copolymer (EVA) were studied after addition of various loadings of these hybrids (2, 4, 8, 12, and 14 wt%). It could be ensured that the tolerance of PP towards phase separation caused by the insertion of the core–shell particles was higher than that of EVA, which translates into different extents of reinforcements. POLYM. ENG. SCI., 55:1546–1552, 2015. © 2015 Society of Plastics Engineers

Wet-spinning of continuous montmorillonite-graphene fibers for fire-resistant lightweight conductors.

All-inorganic fibers composed of neat 2D crystals possessing fascinating performance (e.g., alternately stacking layers, high mechanical strength, favorable electrical conductivity, and fire-resistance) are discussed in detail. We developed a wet-spinning assmebly strategy to achieve continuous all-inorganic fibers of montmorillonite (MMT) nanoplatelets by incorporation of a graphene oxide (GO) liquid crystal (LC) template at a rate of 9 cm/s, and the templating role of GO LC is confirmed by in situ confocal laser scanning microscopy and polarized optical microscopy inspections. After protofibers underwent thermal reduction, the obtained binary complex fibers composed of neat 2D crystals integrate the outstanding fire-retardance of MMT nanoplatelets and the excellent conductivity of graphene nanosheets. High-resolution transmission electron microscopy and scanning electron microscope observations reveal the microstructures of fibers with compactly stacking layers. MMT-graphene fibers show increaing tensile strengths (88-270 MPa) and electrical conductivities (130-10500 S/m) with increasing graphene fraction. MMT-graphene (10/90) fibers are used as fire-resistant (bearing temperature in air: 600-700 °C), lightweight (ρ < 1.62 g/cm(3)) conductors (conductivity: up to 1.04 × 10(4) S/m) in view of their superior performance in high-temperature air beyond commercial T700 carbon fibers. We attribute the fire-resistance of MMT-graphene fibers to the armor-like protection of MMT layers, which could shield graphene layers from the action of oxidative etching. The composite fibers worked well as fire-resistant conductors when being heated to glowing red by an alcohol lamp. Our GO LC-templating wet-spinning strategy may also inspire the continuous assembly of other layered crystals into high-performance composite fibers.

Polymerization of octamethylcyclotetrasiloxane between montmorillonite nanoplatelets initiated by surface anions

Research deals with the assessment of grafting of cyclosiloxanes onto organically modified montmorillonite (MMT) layers through anionic ring-opening polymerization (AROP) without additional catalyst or initiator. Pristine Na+-MMT was organically modified by systematically varying the hexadecyltrimethylammonium bromide (HDTMABr) loading level. X-ray diffraction and thermogravimetric analysis of differently modified MMTs (OMMTs) showed that HDTMABr cations that exchanged sodium cations were strongly attracted to the silicate platelet surfaces. Part of HDTMABr formed a sandwiched HDTMABr layer between organically modified silicate platelets. The obtained OMMTs were tested as initiator material for AROP of octamethylcyclotetrasiloxane (D4) in the bulk, since the D4 polymerization may be initiated by oxygen anions located on the silicate surfaces. The highest monomer conversion (91 % after 24 h at 80 °C) was observed when OMMT with HDTMABr amount equal to cation exchange capacity was used. At lower amounts of HDTMABr, the MMT was less organically modified and thus less compatible with D4. On the other hand, when the HDTMABr sandwiched layer was thicker, lower rates of polymerization were observed due to the hindered transport of monomer to silicate platelet surfaces. The active function of surface anions in MMT platelets in the initiation process was confirmed experimentally by varying the OMMT/D4 ratio. It was observed that monomer conversion increased with increasing OMMT/D4 ratio. The obtained composites were exfoliated. In the last part of the research, OMMT was added to the formulation for D4 emulsion polymerization, where HDTMABr was also used as an emulsifier. The obtained composite material had a significantly improved thermal stability.