Layered Double Hydroxide Platelets Research Articles

Highly Porous Layered Double Hydroxide and Mixed Metal Oxide by Sacrificial Bio-Template, Egg White Foam

Highly porous layered double hydroxide (LDH) and its calcined mixed metal oxide (MMO) were obtained by utilizing egg white (EW) as a biogenic porous template. The LDH was prepared through coprecipitation under the existence of a beaten EW meringue, and the corresponding MMO was obtained by calcining LDH at 500 °C. According to X-ray diffraction, the crystal structure of LDH and MMO was well-developed with or without EW. In contrast, the crystallinity analyses and microscopic investigations clearly showed differences in the particle orientation in the presence of EW; the protein arrangement in the EW foam induced the ordered orientation of LDH platelets along proteins, resulting in well-developed inter-particle pores. As a result, the distinctive particle arrangement in EW-templated samples compared with non-templated ones showed dramatically enhanced specific surface area and porosity. The nitrogen adsorption–desorption isotherm exhibited that the high specific surface area was attributed to the homogeneous nanopores in EW-templated LDH and MMO, which originated from the sacrificial role of the EW.

Layered double hydroxides bundled Agar-g-PAN/Ag nanocomposite films: A strategy to improve thermal, barrier and antibacterial properties

With an aim of designing a biodegradable packaging material with considerable stability, herein, layered double hydroxides (LDH) bundled agar grafted polyacrylonitrile nanocomposites (Agar-g-PAN/Ag/LDH) incorporated with silver nanoparticles (Ag Nps) have been synthesized using surfactant free in situ polymerization method. The LDH platelets form a laminating structure around the Agar-g-PAN copolymeric network while the Ag Nps are dispersed throughout the material. The prepared nanocomposite films exhibit high thermal stability because of the sandwiching of polymeric chains in between the LDH platelets which also evidences the improvement in fire retardancy. The comparative analysis of limiting oxygen indices of Agar-g-PAN/Ag/LDH nanocomposites with PAN and Agar-g-PAN clearly indicates the fire-repellent nature of the materials. Proper exfoliation and partial intercalation of the LDH platelets as well as presence of Ag Nps result in almost five-fold enhancement in oxygen barrier properties of Agar-g-PAN/Ag/LDH nanocomposite films as compared to the copolymeric matrix. The combination of LDH with Ag Nps shows a synergistic effect in improving the biodegradability and chemical resistance of the nanocomposite films. The antibacterial studies indicate remarkable antibacterial properties of the Agar-g-PAN/Ag/LDH nanocomposites which are more pronounced for gram negative bacterial strains. The synthesized nanocomposite films are biodegradable and chemically inert with enhancement in thermal, barrier and antibacterial properties, making them suitable candidates for packaging applications.

NMR Investigation of Water Molecular Dynamics in Sulfonated Polysulfone/Layered Double Hydroxide Composite Membranes for Proton Exchange Membrane Fuel Cells.

The development of nanocomposite membranes based on hydrocarbon polymers is emerging as one of the most promising strategies for overcoming the performance, cost, and safety limitations of Nafion, which is the current benchmark in proton exchange membranes for fuel cell applications. Among the various nanocomposite membranes, those based on sulfonated polysulfone (sPSU) and Layered Double Hydroxides (LDHs) hold promise regarding their successful utilization in practical applications due to their interesting electrochemical performance. This study aims to elucidate the effect of LDH introduction on the internal arrangement of water molecules in the hydrophilic clusters of sPSU and on its proton transport properties. Swelling tests, NMR characterization, and Electrochemical Impedance Spectroscopy (EIS) investigation allowed us to demonstrate that LDH platelets act as physical crosslinkers between -SO3H groups of adjacent polymer chains. This increases dimensional stability while simultaneously creating continuous paths for proton conduction. This feature, combined with its impressive water retention capability, allows sPSU to yield a proton conductivity of ca. 4 mS cm-1 at 90 °C and 20% RH.

Constructing Fast Transmembrane Pathways in a Layered Double Hydroxide Nanosheets/Nanoparticles Composite Film for an Inorganic Anion-Exchange Membrane

Anion-exchange membranes (AEMs) with high conductivity are crucial for realizing next-generation energy storage and conversion systems in an alkaline environment, promising a huge advantage in cost reduction without using precious platinum group metal catalysts. Layered double hydroxide (LDH) nanosheets, exhibiting a remarkably high hydroxide ion (OH-) conductivity approaching 10-1 S cm-1 along the in-plane direction, may be regarded as an ideal candidate material for the fabrication of inorganic solid AEMs. However, two-dimensional anisotropy results in a substantially low conductivity of 10-6 S cm-1 along the cross-plane direction, which poses a hurdle to achieve fast ion conduction across the membrane comprising restacked nanosheets. In the present work, a composite membrane was prepared based on mixing/assembling micron-sized LDH nanosheets with nanosized LDH platelets (nanoparticles) via a facile vacuum filtration process. The hybridization with nanoparticles could alter the orientation of LDH nanosheets and reduce the restacking order, forming diversified fast ion-conducting pathways and networks in the composite membrane. As a result, the transmembrane conductivity significantly improved up to 1000-fold higher than that composed of restacked nanosheets only, achieving a high conductivity of 10-2 to 10-1 S cm-1 in both in-plane and cross-plane directions.

(Invited) Ions Transport Properties and Carbonation Process Investigation of Nanocomposite Anion Exchange Membranes Containing Layered Double Hydroxide

Electrochemical energy conversion and storage (EECS) technologies such as fuel cells and electrolyzers are expected to play a pivotal role owing to their compatibility with the environment and high energy conversion efficiency. Anion-exchange membranes (AEMs) have received increased interest in recent years as the electrolyte separator in different EECS devices.[1] They have numerous advantages respect to the proton-exchange membranes, such as operation at high pH conditions, significantly lower cost (based on low-cost raw materials), less corrosive environment, and significantly lower fuel crossover (one order of magnitude lower than the acidic counterparts). AEM fuel cells and electrolyzers devices can reach the performance level required by applications with electrocatalysts that do not require a high loading of platinum-group metals (PGMs) due to the alkaline environment at the electrodes.However, the AEM based EECS development and implementation is significantly hindered by the anion exchange membrane (AEM) stability during cell operation, their low OH- conductivity and the low kinetics of the electrocatalysts. In fact, the electrolytic anion-exchange membrane (AEM) is a crucial component which should allow good charge and water transport, i.e. high ionic conductivity, but should also guarantee good chemical, thermal and mechanical stability and high durability. [2]We report on an extensive study on nanocomposite AEMs based on tetramethylammonium Polysulfone ionomer (PSU) and Layered Double Hydroxide (LDH) as nanofiller. [3] PSU is a thermoplastic polymer with high thermal stability, good chemical resistance and mechanical properties. However, since it has two activated positions per repetition unit for electrophilic aromatic substitution, it can undergo high degrees of functionalisation, which reduce the mechanical properties. We developed a two steps procedure, with allow a functionalization degree of about 80%, preserving its stability. Concerning the LDHs, these mineral anionic clays are excellent inorganic anionic conductors with elevated ion exchange capacity (IEC). They consist of the positively charged metal hydroxide layers with anions located in the interlayer space. This allows strong hydration of the material together with a large number of hydroxyls on the host layers forming a dense network of hydrogen bonds along the two-dimensional surface, therefore facilitating OH- ion conduction by diffusion mechanism.PSU/LDH AEMs were investigated in both OH- and forms, comparing swelling capacity, ionic conductivity and water diffusion. The latter was studied by NMR spectroscopy, measuring the self-diffusion coefficient by the Pulse Field Gradient (PFG) NMR techniques. The nanocomposite membranes are able to maintain good hydration at high temperatures, and to create an adequate nanostructure with the polymer chains, which favour the Grotthuss diffusion mechanism for the OH- ions. Such feature is reflected in the ionic conductivity and in the alkali stability, where they demonstrated the highest conductivity and a reduced membrane degradation rate.In addition, the 13C-NMR technique was used to investigate carbonation processes in the presence of CO2, showing that the presence of the LDH platelets into the AEM remarkably reduces the conversion rate of hydroxyl groups, as much as slow down the diffusion of carbonate ions.Finally, electrolysis cell tests were conducted on MEAs based on these hybrid membranes, and preliminary results showed very promising performance. Acknowledgments This work has been supported by the Italian Ministry for University and Research (MUR) for funding through the FISR 2019 project AMPERE (FISR2019_01294). References Vincent, I. and Bessarabov, D. (2018) Renewable and Sustainable Energy Reviews 81, 1690–704G. Arges, L. Zhang, ACS Appl. Energy Mater. 1 (2018) 2991–3012,Simari, C.,...and Nicotera, I. (2022) Electrochimica Acta, 403, p. 139713.

Combined Effect of Layered Double Hydroxides and Nano silver on Bacterial Inhibition and Gas Barrier Properties of Chitosan Grafted Polyacrylonitrile Nanocomposites

ABSTRACT Herein, chitosan-grafted-poly(acrylonitrile) (CS-g-PAN) nanocomposites are prepared by emulsifier-free emulsion polymerization technique with dispersion of layered double hydroxides(LDHs) and nano silver(AgNPs). The interactions of AgNPs and LDH with co-polymeric matrix are investigated by FTIR and XRD. It is noticed that LDH platelets are intercalated and partially exfoliated within the copolymeric matrices. Dispersion of fillers creates tortuous path which enhances the gas barrier properties up to seven folds. Antibacterial behavior of nanocomposites is achieved due to incorporation of silver nanoparticles and LDH. Thermal stability, chemical resistance and biodegradable properties of the synthesized material are also increased due to combined effect of LDH and AgNPs.

Novel Nanocomposites Reinforced with Layered Double Hydroxide Platelets: Tribofilm Growth Compensating for Lubrication Insufficiency of Oil Films

Growth of solid tribofilms between moving parts substantially reduces friction and wear, and this is true especially for boundary-lubricated sliding contacts. However, efficacy of the tribofilms relies upon antiwear additives in formulated oil, typically zinc dialkyldithiophosphate, that usually gives rise to adverse environmental impacts. It is desirable to reduce the use of environmentally harmful additives by designing materials of moving parts so that they function properly with base oil lubrication. Herein, CoAl layered double hydroxide (LDH) nanoplatelets were synthesized via a one-step hydrothermal approach. When being lubricated with polyalphaolefin base oil (PAO 4), epoxy nanocomposites reinforced with low-loading LDH exhibit excellent tribological performance. In comparison to neat epoxy, wear of the nanocomposite is reduced by an order of magnitude and friction is decreased by 32%. Our work provides direct evidence that LDH released onto a friction interface facilitates tribofilm growth compensating for lubrication insufficiency of the oil film. This work paves a route for minimizing the dependency on harmful antiwear additives by optimizing tribomaterials.

Effect of LDH platelets on the transport properties and carbonation of anion exchange membranes

We report on an extensive study on nanocomposite Anion Exchange Membranes (AEMs) based on tetramethylammonium Polysulfone ionomer and Layered Double Hydroxide (LDH) as nanofiller. The AEMs were investigated in both OH− and HCO3− forms, comparing swelling capacity and transport properties. Ionic conductivity measurements were performed both by Electrochemical Impedance Spectroscopy and Ziv and Dekel's method, while the water and ions mobility by 1H Pulse Field Gradient (PFG) NMR spectroscopy.One of the most serious problems to be addressed in AEMs fuel cell technology is that of the significant loss of performance when CO2 is present in the reaction oxidant gas (e.g., air) due to the phenomenon of carbonation. In this work, the carbonation kinetics of AEMs and the effect of LDH filler were addressed through 13C NMR spectroscopy (including diffusometry and relaxometry measurements). The presence of LDH platelets in the AEM significantly reduces the conversion rate of hydroxide groups. The interaction between the polymer chains and the anionic clay lamellae creates a suitable network that benefits the membrane's ionic conductivity, its mechanical properties (DMA tests), and finally reduces the rate of alkaline degradation.

Functionalization of cellulose fibers alongside growth of 2D LDH platelets through urea hydrolysis inspired Taro wettability

Here, Cotton fabric was functionalized via hybrid coating including 2D MgAl LDH (layered double hydroxide) and SA (stearic acid). The urea hydrolysis was employed for construction of vertically aligned LDH on surface of cellulose fibers under hydrothermal condition. The in situ formation mechanism of LDH on cotton surface was nucleation, growth, and interaction with activated cellulose chains. The partial cellulose ionization in the alkaline solution led to nucleophilic behavior towards electron deficient atom. The effect of different ageing, synthesis temperature, and amount of SA were investigated and optimized at 100 °C for 24 h with 0.05 M. The superhydrophobic surface architecture of treated cotton with hierarchical micro/nanostructure was inspired from the Taro leaf structure with continuous contact line presented WCA of 154 ° and CAH of 9 °. The Cotton@LDH@SA exhibited efficient oil/water separation after several washes (>90%) with good stain resistant. Also, the physico-mechanical properties were studied.

Highly-performing and low-cost nanostructured membranes based on Polysulfone and layered doubled hydroxide for high-temperature proton exchange membrane fuel cells

The low cost, reduced fuel crossover and ease of preparation make sulfonated Polysulfone (sPSU) a potential candidate to replace Nafion electrolyte in proton exchange membrane fuel cells (PEMFCs). To reach a satisfactory proton conductivity the general strategy involves the preparation of macromolecules with high ion exchange capacity (IEC), even at the cost of sacrificing their mechanical properties. In this study, sPSU with relatively low IEC was used as polymer matrix for the preparation of nanocomposite electrolytes by dispersing Mg/Al–NO3- Layered Double Hydroxides (LDH). sPSU-LDH membranes were prepared by solution intercalation method and characterized by XRD, TGA and DMA, whereas water dynamics and proton conductivity were investigated by NMR (PFG and T1) and EIS spectroscopies, respectively. The complete exfoliation and nanodispersion of the LDH platelets into the polymer enhance the thermo-mechanical resistance, the dimensional stability and the water retention capacity of the electrolytes. The formation of highly connected ion channels promotes an effective Ghrotthus-type mechanism for the proton transport also under dehydrating environment. Such features allowed proton conductivity values and electrochemical performances in single cell PEMFC distinctly higher than the Nafion recast, demonstrating the possibility to prepare cost-effective and high performing sPSU-based membranes able to operate under low-humidification and high temperatures conditions.

Barrier properties of sulfonated polysulfone/layered double hydroxides nanocomposite membrane for direct methanol fuel cell operating at high methanol concentrations

High performing and cost effective nanocomposite membranes for DMFC application are synthesized by incorporating hygroscopic layered double hydroxides (LDH) particles into sulfonated polysulfone (sPSU). A significant improvement in the dimensional stability as well as in the water and methanol molecular dynamics of the sPSU_LDH composite membrane is observed in comparison with both pristine sPSU and Nafion 212. The strong electrostatic interaction occurring between positively charged LDH platelets and negatively charged polymer chains of sPSU alters the microstructure of the ionic domains, allowing an effective reduction of the methanol permeability whilst improving the proton conductivity. The methanol crossover measurements confirmed that sPSU_LDH membranes are able to withstand high methanol concentration without significant aftermath on the chemical stability of the electrolyte. The features enable the single DMFC assembled with the sPSU_LDH nanocomposite to achieve the remarkable power density of 150 mW cm−2 at 80 °C in 5 M methanol solution.

Revisiting fluorescein and layered double hydroxide using a synergistic approach: A complete optical study

The luminescence of Fluorescein, an inexpensive dye, ought to be interesting for lighting application devices such as commercial LEDs. However, the molecule suffers from severe instability, making it inappropriate for such applications. As previously studied, fluorescein molecules may be hosted in a layered double hydroxide (LDH), and the role of such an inorganic material in stabilizing the dye has been underlined. However, a deep understanding of the resulting optical properties is still required. Using extremely small amounts of fluorescein, it is demonstrated here that Zn2Al cation-based LDH tethering acts as a «solid solvent » for the dye, enabling its luminescence even in powder form, whereas fluorescein molecules on their own emit no luminescence at all in the solid state. However, aggregations of the dye occur in the interlamellar space, leading to non-radiative emission. Emission and excitation spectra, as well as fluorescence decays, are studied to explain the difference between the hybrid LDH-Fluorescein material and an aqueous solution of fluorescein. Additionally, LDH platelets are found to help the dispersion of the intercalated fluorescein in silicone to obtain a homogeneous composite film, which exhibits luminescent properties. Finally, an accelerated photoaging study demonstrates that the LDH-fluorescein filler has a pro-degradant effect on polymer aging under UV radiation.

Fabrication of functional biomass carbon aerogels derived from sisal fibers for application in selenium extraction

Selenium (Se) is a rare element, usually in ionic form in aqueous media. The separation of selenium from aqueous solution has received considerable attention due to the large-batch application of selenide. In this work, the Mg–Al layered double hydroxides (LDHs)-functionalized biomass carbon aerogels (CAs) were fabricated by combining freeze-drying, carbonization with in-situ growth method. And the process for extracting selenium based on adsorption of CAs and “memory effect” of LDHs nanosheets has been developed. Firstly, CAs was prepared by alkalization, bleaching, freeze-drying and carbonization using the sisal fiber as precursor. Then, Mg–Al LDHs-functionalized CAs were fabricated by in situ growth of LDHs platelets on the CAs surfaces. The physical and chemical properties of the LDHs-functionalized CAs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET). The SEM results showed that sisal cellulose fibers used in this paper have a smooth surface with a diameter about 8μm and a length of several millimeters. Furthermore, the flowerlike nanosheets are uniform in both size and shape, with each LDHs nanoplatelet grafted to the CAs. The nitrogen sorption analysis confirmed that LDHs-functionalized CAs is mesoporous structure with the mesopores centered at about 3.5–5nm and BET surface area of 165.26m2/g. It is indicated that the maximum adsorption capacity of selenium on LDHs-functionalized CAs reached 73.6mg[Se]/g. The adsorption time profile of selenium onto LDHs-functionalized CAs ndicates that the adsorption equilibrium was achieved within 4h. After recycling 9 times, the regenerated LDHs-functionalized CAs still displayed high selenium absorption properties. Therefore, the high absorption capacity and excellent recycling capabilities of LDHs-functionalized CAs composites give the material an ideal choice for the selenium recovery in practical applications.

Low molecular weight hindered amine light stabilizers (HALS) intercalated MgAl-Layered double hydroxides: Preparation and anti-aging performance in polypropylene nanocomposites

A low molecular weight hindered amine light stabilizer (HALS), contains 2, 2, 6, 6-tetramethyl piperidine functional group has been successfully prepared and intercalated into the interlayer region of Mg-Al layered double hydroxides (LDH) via a co-precipitation method to produce HALS-LDH. Furthermore, a series of HALS-LDH/PP nanocomposites were fabricated by dispersing HALS-LDH in poly(propylene) (PP) in a solvent casting route. Through the accelerated aging test method, the morphological properties, the thermal-oxidative degradation and photo-oxidative degradation behavior of HALS-LDH/PP composites were carefully investigated. The results show that the thermal stability of HALS in HALS-LDH was improved compared to that of HALS free of LDH dispersed into PP, and there is no negative effect on the crystallization behavior of PP after the addition of HALS-LDH. Besides, the HALS-LDH significantly enhances synergistically the thermal- and photo-stability of PP compared when LDH platelets CO3-LDH or HALS are used separately. Under the experimental conditions, a mass loading of HALS-LDH optimized as 4 wt % in respect to PP was found to exhibit an excellent anti-aging performance for potential applications.

Ultrathin and Vacancy-Rich CoAl-Layered Double Hydroxide/Graphite Oxide Catalysts: Promotional Effect of Cobalt Vacancies and Oxygen Vacancies in Alcohol Oxidation

Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to afford a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co–O and Co····Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (VO) and cobalt vacancies (VCo), CoAl-ELDH/GO also contains negatively charged VCo–Co–OHδ− sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h–1; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h–1) precursor. O2-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged VCo–Co–OHδ− sites. A kinetic isotope effect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O–H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols.

Size Effect of Layered Double Hydroxide Platelets on the Crystallization Behavior of Isotactic Polypropylene.

Layered double hydroxide (LDH) platelets with nanosized and microsized level were synthesized and used as fillers in an isotactic polypropylene (PP) matrix. The nucleation and crystallization behavior of PP/LDH composites (denoted as 1-PPLx and 2-PPLx for composites containing nanosized and microsized LDH, respectively; x represents the mass percentage of LDH) was investigated by differential scanning calorimetry and polarized optical microscopy techniques. It is found that the crystallization temperature of PP/LDH composites is largely enhanced and the half crystallization time is reduced remarkably relative to pure PP, especially for 2-PPLx composite. The 2-PPLx composite exhibits stronger heterogeneous nucleating ability and faster crystallization rate than 1-PPLx samples with the same LDH loading. In addition, the crystallized PP/LDH composites possess significantly enhanced thermal stability, gas barrier, and flame-retardant properties relative to neat PP, which would show a broad application prospect in engineering plastics and packing industry.

Hybrid effects in graphene oxide/carbon nanotube-supported layered double hydroxides: enhancing the CO2 sorption properties

Graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) have been previously used independently as active supports for layered double hydroxides (LDH), and found to enhance the intrinsic CO2 sorption capacity. However, the long-term stability of the materials subjected to temperature-swing adsorption (TSA) cycles still requires improvement. In this contribution, GO and MWCNT are hybridized to produce mixed substrates with improved surface area, and compatibility for the subsequent deposition of LDH platelets, compared to either phase alone. The incorporation of a robust and thoroughly hybridized carbon network considerably enhances the thermal stability of activated, promoted LDH over twenty cycles of gas adsorption-desorption (96% of retention of the initial sorption capacity at the 20th cycle), dramatically reducing the sintering previously observed when either GO or MWCNT were added separately. Detailed characterization of the morphology of the supported LDH, at several stages of the multicycle adsorption process, shows that the initial morphology of the adsorbents is more strongly retained when supported on the robust hybrid GO/MWCNT network; the CO2 adsorption performance correlates closely with the specific surface area of the adsorbents, with both maximized at small loadings of a 1:1 ratio GO:MWCNT substrate.

Porous Layered Double Hydroxides Synthesized using Oxygen Generated by Decomposition of Hydrogen Peroxide

Porous magnesium-aluminium layered double hydroxides (LDH) were prepared through intercalation and decomposition of hydrogen peroxide (H2O2). This process generates oxygen gas nano-bubbles that pierce holes in the layered structure of the material by local pressure build-up. The decomposition of the peroxide can be triggered by microwave radiation or chemically by reaction with iodide (I−) ions. The carbonate LDH version [Mg0.80Al0.20(OH)2](CO3)0.1∙mH2O was synthesized by microwave-assisted urea coprecipitation and further modified by iodide or H2O2 intercalation. High resolution Scanning Electron Microscopy (HR-SEM) and Brunauer-Emmet-Teller (BET) analysis were used to assess the morphology and surface area of the new porous materials. The presence of H2O2 in the interlayer region and later decomposition triggered by microwave radiation generated more pores on the surface of the LDH platelets, increasing their specific surface area from initially 9 m2/g to a maximum of 67 m2/g. X-Ray Diffraction showed that the formation of the pores did not affect the remaining crystal structure, allowing possible further functionalization of the material.

Analysis of dynamic oscillatory rheological properties of PP/EVA/organo-modified LDH ternary hybrids based on generalized Newtonian fluid and generalized linear viscoelastic approaches

A comprehensive investigation was performed on single-step melt processed polypropylene (PP)/(ethylene vinyl acetate copolymer (EVA)/organo-modified layered double hydroxide (LDH) counterpart ternary hybrids to explore the effect of LDH loading on small-amplitude oscillatory shear (SAOS) rheological properties and to correlate the properties with microstructure. The rheological results were analyzed in detail from qualitative and quantitative perspectives. Using qualitative interoperation of storage modulus and complex viscosity alteration against LDH loading, and also quantitative analysis by viscosity models based on both the generalized Newtonian fluid (GNF) and generalized linear viscoelastic (GLVE) approaches, detailed predictions were carried out on the microstructure of samples and also partitioning of the organo-modified LDH particles and their intercalation and exfoliation extent within hybrids. By comparing the elasticity and relaxation spectrum of PP-rich/LDH with those of EVA-rich/LDH hybrids, it was predicted that organo-modified LDH platelets, in the case of PP-rich samples, have been located at the interface or within the EVA dispersed particles, while in the case of EVA-rich samples, they mainly localized within the matrix. In addition, the crossover frequency and slope of G′ and G″ curve at terminal region were correlated with the extent of intercalated and exfoliated structures of filler. The validity of these predictions on microstructure of the developed hybrids was confirmed visually using transmission electron microscope (TEM) micrographs.

Layered double hydroxides: Efficient fillers for waterborne nanocomposite films

Using Layered double hydroxides (LDH) nanoparticles and film-forming latexes, waterborne nanocomposite films were produced by simply a heterocoagulation and solvent casting process. Self-standing and transparent films with LDH contents from 2.5 to 15vol% were prepared. The structure, microstructure and mechanical behavior were thoroughly investigated by powder X-ray diffraction (PXRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), scanning electron microscopy (FIB–SEM) and dynamic mechanical analysis (DMA). Favorable electrostatic interactions between pristine LDH and the latex ensured a good dispersion of the bidimensional LDH platelets in the films. Above a certain content of LDH, the formation of a well-defined cellular LDH network following the starting latex morphology was observed. Such a percolating microstructure induces a large mechanical reinforcement significant of a mechanical percolation behavior.