Solvent Casting Process Research Articles

Massive electrical conductivity enhancement of multilayer graphene/polystyrene composites using a nonconductive filler.

We report a massive increase in the electrical conductivity of a multilayer graphene (MLG)/polystyrene composite following the addition of nonconducting silica nanoparticles. The nonconducting filler acts as a highly effective dispersion aid, preventing the sheetlike MLG from restacking or agglomerating during the solvent casting process used to fabricate the composite. The enhanced dispersion of the MLG leads to orders of magnitude enhancement in electrical conductivity compared to samples without this filler.

The comparison between the effects of solvent casting and melt intercalation mixing processes on different characteristics of polylactide‐nanographite platelets composites

This study investigates the influence of enhanced dispersion of nanographite platelets (NGP) fillers through solvent casting mixing process on rheological, electrical and thermal properties of polylactide (PLA)/NGP composites. PLA/NGP composites were fabricated at 1 to 5 wt% filler contents by means of three processing techniques: (i) dry mixing and melt intercalation; (ii) solvent casting using dichloromethane organic solvent; and (iii) combination of solvent casting and melt intercalation techniques. The extent of dispersion of nanofillers within polymer matrix was evaluated through X‐ray diffraction and transmission electron microscopy analysis of the composites. Morphological studies of the samples revealed that the maximum extent of dispersion of NGP fillers within PLA matrix was achieved when the combination of solvent casting and melt intercalation processes occurred. Rheological analyses of the samples were indicative of deterioration in the composites produced through solvent casting mixing process. Despite of initial reduction in electrical resistivity of the composites after the addition of 1 wt% of NGP fillers, further addition of nanofillers did not exhibit a considerable enhancement in their electrical conductivity of the composites. Thermogravimetric analysis of the composites was demonstrative of enhancing impact of nanofiller loading, along with detrimental effect of solvent casting on the thermal stability of the PLA matrix. POLYM. ENG. SCI., 55:1560–1570, 2015. © 2014 Society of Plastics Engineers

Synthesis of Chitin Nano Particles for Preparation of Nano PF Composites

Preparation of Phenolic nanocomposites with the help of solvent casting technique was carried out by dispersing the chitin nano particles in water soluble phenol formaldehyde (PF). The nanocomposites were prepared by using water suspended chitin whisker as the reinforced phase and water soluble phenol formaldehyde (PF) as matrix. In the present work, crab shell originated chitin whisker was processed by acid hydrolysis method to prepare the chitin whiskers. The whiskers suspension consists of parallelepiped slender rod shape which can be used for mixing it with any water soluble thermosetting cross linking polymer. The suspension can be mixed with the water soluble aqueous solution of PF so that the suspension quantify for the varying fraction of chitin whisker particles ranging from 1 to 20 percent. Thus the varying fraction, whisker chitin reinforced phenol formaldehyde composites can be prepared by solvent casting process.

Extrusion of xylans extracted from corn cobs into biodegradable polymeric materials

Solvent casting technique, which comprises multiple energy demanding steps including the dissolution of a polymer in a solvent followed by the evaporation of the solvent from the polymer solution, is currently the main technique for the production of xylan based polymeric materials. The present study shows that sufficient water content renders arabinoglucuronoxylan (AGX) polymers extrudable, enabling the production of AGX based polymeric materials in a single step via extrusion, which is economically advantageous to solvent casting process for mass production. AGX polymers with water content of 27% were found to yield extrudates at an extrusion temperature of 90°C. The extruded strips showed very good mechanical properties with an ultimate tensile strength of 76 ± 6 MPa and elongation at break value of 35 ± 8%, which were superior to the mechanical properties of the strips obtained from polylactic acid.

PLLA/PMMA blends: A shear-induced miscibility with tunable morphologies and properties?

Polymer blends and alloys represent an interesting approach to implement bio-based poly(l-lactic acid) (PLLA) into high-value applications. Here, a re-evaluation of the miscibility extent between both biobased PLLA and petro-based poly(methyl methacrylate) (PMMA) is proposed in order to tune morphologies and properties of resulting blends upon either a solvent-casting method or a twin-screw extrusion. The solvent-casting process proved only able to produce immiscible blends with matrix–droplet or co-continuous morphologies in function of the blend composition and the immiscibility–miscibility transition is not observed for temperature lower than 250 °C. When melt-processed via extrusion technique, only miscible PLLA/PMMA blends were recovered all over the composition range, as observed by a single glass transition and a single α-relaxation transition at intermediate temperature between pure PLLA and pure PMMA as determined by DSC and DMTA, respectively. Miscibility was also observed at low shear rate with a phase-reversibility, demonstrating the absence of any reactions between PMMA and PLLA phases and the existence of a shear-sensitive clarity point. Homogenous and transparent PLLA/PMMA blends were easily produced with tunable thermomechanical and barrier properties against the blend composition. Glass transition temperature, α-relaxation temperature, thermal resistance and gas permeability were accurately controlled by the PMMA content, while maintaining impact strength and storage modulus in the same range than PLLA itself.

Elaboration of cellulose acetate nanobiocomposites using acidified gelatin‐montmorillonite as nanofiller: Morphology, properties, and biodegradation studies

Nanobiocomposites were successfully prepared from cellulose acetate (CA) and a novel organoclay based on montmorillonite and acidified gelatin as bio‐modifier (AGe‐MMT), at room temperature via solvent casting process. The formation of AGe‐MMT was confirmed by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), differential Scanning Calorimetry (DSC), and thermogravimetric analysis (TGA). From both XRD and transmission electron microscopy (TEM) analyses of these nanohybrids, it was suggested a partially exfoliated/intercalated structures, with small clay tactoïds remaining. Glass transition (Tg) and melting (Tm) temperatures of the nanobiocomposites, evaluated by DSC analysis, were slightly affected by clay loading compared to neat CA. Significant improvement in their thermal stabilities was observed from TGA, as evidenced by the shift of their Tdonset toward higher values. Otherwise, the optical clarity of these nanohybrids films, measured by UV–vis spectroscopy, has showed a decline in the transmittance in the visible region with the increase of clay content, indicating that clay platelets are not fully exfoliated. The impact of AGe‐MMT on biodegradability of CA under compost was also studied by gravimetric and Scanning Electron Microscopy (SEM). The CA matrix biodegradability was retarded by both MMT and bio‐modifier, except for 5 wt% AGe‐MMT loading. POLYM. COMPOS., 34:1515–1524, 2013. © 2013 Society of Plastics Engineers

Polybenzimidazole containing ether units as electrolyte for high temperature proton exchange membrane fuel cells

A rapid method to synthesize poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) through a solution polycondensation under microwave irradiation is explored. Synthesis parameters affecting the molecular weight (Mw) of OPBI, including the mass ratio of solvent to P2O5, the monomer concentration, and reaction time, are optimized. The main characteristics of OPBI are studied, and the corresponding membrane is prepared through a solvent casting process. A series of sulfuric acid doped OPBI (H2SO4/OPBI) hybrid membranes with different acid doping levels (ADLs) are developed. The effects of H2SO4 on microstructure, ADL and electrochemical properties of these membranes are explored. Herein, the hybrid membrane shows high proton conductivity (190 mS cm−1) at elevated temperature (160 °C) and anhydrous conditions, high ADL (18.73 mol of H2SO4 for OPBI per repeat unit, i.e., ADL = 18.73 mol PRU−1) and excellent dimensional stability (40.3%). All these properties demonstrated that H2SO4/OPBI hybrid membrane can be used as an alternative membrane for high temperature proton exchange membrane fuel cells (HT-PEMFCs).

Nafion®/ODF-silica composite membranes for medium temperature proton exchange membrane fuel cells

A series of composite membranes were prepared by dispersing fluorinated polyoxadiazole oligomer (ODF)-functionalized silica nanoparticles in a Nafion® matrix. Both melt-extrusion and solvent casting processes were explored. Ion exchange capacity, conductivity, water uptake and dimensional stability, thermal stability and morphology were characterized. The inclusion of functionalized nanoparticles proved advantageous, mainly due to a physical crosslinking effect and better water retention, with functionalized nanoparticles performing better than the pristine silica particles. For the same filler loading, better nanoparticle dispersion was achieved for solvent-cast membranes, resulting in higher proton conductivity. Filler agglomeration, however, was more severe for solvent-cast membranes at loadings beyond 5 wt.%. The composite membranes showed excellent thermal stability, allowing for operation in medium temperature PEM fuel cells. Fuel cell performance of the composite membranes decreases with decreasing relative humidity, but good performance values are still obtained at 34% RH and 90 °C, with the best results obtained for solvent cast membranes loaded with 10 wt.% ODF-functionalized silica. Hydrogen crossover of the composite membranes is higher than that for pure Nafion® membranes, possibly due to porosity resulting from suboptimal particle-matrix compatibility.

Formation of H* Phase in Chiral Block Copolymers: Morphology Evolution As Revealed by Time-Resolved X-ray Scattering

The ordering of a chiral block copolymer (BCP*) polystyrene-b-poly(d-lactide) during the solvent-casting process was studied in real time using in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) simultaneously. Three different solvents, namely benzene, dimethylformamide, and 1,3-dioxolane, were used. It was found that, according to the solution phase behavior of these BCPs*, there were three different stages of morphology development during solvent removal. Initially, the development of the morphology during solvent removal was the same for all solvents studied. However, for strongly selective solvents, crystallization dominated and no H* phase formed. For moderately selective solvents, crystallization was initially suppressed, a microphase separated H* phase formed, and then crystallization occurred, leading ultimately to a crystalline H* phase. The results clearly showed that crystalline ordering is not required for the H* phase to form in mutually good solvents. Consequently, the preferred handedness of molecular packing of the chiral block in the amorphous state necessarily underpins the transfer of chirality from the segmental level to the microphase-separated morphology level.

Development of hydroxyapatite nanorods-polycaprolactone composites and scaffolds derived from a novel in-situ sol-gel process

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which displays splendid biocompatibility and bioactivity properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL) was employed as a matrix and hydroxyapatite nanorods were used as a reinforcement element of the composite. HA/PCL nanocomposites were synthesized by a new in-situ sol-gel process using low cost chemicals. Chemical and physical characteristics of the nanocomposite were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analyses. XRD analysis revealed that pure hydroxyapatite with no undesirable compound was formed within the nanocomposite. Moreover, hydroxyapatite had low crystallinity with the average crystallite size of 62.5 nm. FE-SEM images showed dispersion of HA nanorods in PCL matrix with suitable interaction were obtained. The average length and diameter of HA nanorods were calculated 167 nm and 53 nm, respectively. It was found that HA/PCL nanocomposite had marcoporous structure and high surface area which are essential parameters for cell attachment and protein absorption. Biological properties of HA/PCL scaffolds, prepared through a solvent casting process, were investigated under in vitro condition. Bioactivity of these scaffolds was studied in a saturated simulated body fluid (5×SBF). It was confirmed that HA/PCL scaffold was uniformly covered with a layer of calcium phosphate crystals with the thickness of few microns and phase composition of hydroxyapatite. Consequently, scaffolds met the requirements of materials for bone tissue engineering and could be used for many clinical applications in orthopedic and maxillofacial surgery.

Characterization of controlled highly porous hyaluronan/gelatin cross-linking sponges for tissue engineering

This study examines the suitability of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride for use as a cross-linker in the preparation of highly porous hyaluronan (HA)/gelatin sponges through the solvent casting and particulate leaching (SCPL) process. The modulus, water absorption rate, bonding, morphology, cell viability, and chondrocyte mRNA expression of the HA/gelatin sponges were measured and compared. Water uptake by the sponges resulted in pores with spherical diameters ranging from 100μm to 200μm. With higher porosity, the strength and modulus declined. Larger salt leaching amounts resulted in higher water uptake. The cross-linking bonds in the HA/gelatin sponges were mostly ester bonds. According to our study, the amount of salt in the SCPL process was the main factor that influenced strength, pore interconnectivity, and water uptake ability. The results also showed that the scaffold had a non-viability effect on human chondrocytes, but the mRNA expression level of aggrecan and type II collagen in the cartilage was significantly higher than that of the control group after 5d of culture. The sponges developed in the present study are potential candidates for chondrocyte proliferation and differentiation in cartilage regeneration.

Development of imidazolium-type alkaline anion exchange membranes for fuel cell application

This study reports the development of imidazolium-type alkaline anion exchange membranes (Im-AAEMs) based on the functionalization of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) using 1-methylimdazole. Aromatic polymers bearing bromomethyl, instead of chloromethyl, functional groups were employed as base materials to avoid complicated chloromethylation which require toxic reagents. H NMR and FT-IR spectroscopic data indicated the synthesis of a series of membranes with controlled IECs (achieved by varying the amount of 1-methylimdazole). Due to the conjugated structures of imidazolium cations, the novel Im-AAEMs display enhanced short-term thermal and chemical stabilities compared with classical quaternary ammonium-type AAEMs. In addition, the imidazolium salts exhibit excellent solubility in polar solvents, such as NMP and DMSO, which allowed the exploitation of a pre-functionalized strategy for the synthesis of the AAEMs. Accordingly, the Im-AAEMs displayed conductivities up to >100mScm at 80°C, which derived from the establishment of a nano-scale phase-separated morphology as directed by the solvent casting process. A H /O fuel cell test yielded a peak power density of 30mWcm at a current density of 76mAcm ; this will be improved on development of a chemical compatible imidazolium-based alkaline ionomer for use as ionic polymer binder in the electrodes' catalyst layers. © 2012 Elsevier B.V.

Microstructure and nonisothermal cold crystallization of PLA composites based on silver nanoparticles and nanocrystalline cellulose

Poly(lactic acid) (PLA) based high performance nanocomposites, were prepared using an innovative combination of nanocrystalline cellulose and silver nanoparticles. Binary and ternary systems were prepared by solvent casting process and their morphological, mechanical and thermal responses were investigated. Pristine (CNC) and surfactant modified cellulose nanocrystals (s-CNC) and silver (Ag) nanoparticles were used, and the effect of cellulose crystal nano-dimension, cellulose modification, and the combination of cellulose nanostructures with silver nanoparticles, was investigated. The important industrial problem of slow crystallization of PLA was addressed by the use of cellulose nanocrystals as biobased nucleating agents and the nonisothermal cold crystallization behaviour of reinforced binary and ternary systems was studied.The presence of surfactant on the nanocrystal surface favoured the dispersion of CNC in the PLA matrix while the thermal investigations and the nonisothermal crystallization studies underlined the ability of s-CNC to act as nucleation agent in both binary and ternary nanocomposites.

Synthesis of soluble copolymers bearing ionic graft for alkaline anion exchange membrane

In this study, we report firstly the synthesis of a soluble quarternary ammonium salt and the corresponding graft copolymer P(VDF-g-QVBC) (poly(vinylidene fluoride-graft-quaternary ammonium-functionalized 4-vinylbenzyl chloride)), via atom transfer radical polymerization (ATRP) of QVBC from a PVDF macroinitiator. 1H NMR spectra indicate the successful synthesis of a series of copolymers with different graft ratios by varying the amount of monomers. The soluble quarternary ammonium-containing copolymers are composed of hydrophobic backbones and hydrophilic graft chains, which allow for favorable nano-scale phase separation during the solvent casting process. As a consequence, the resultant membrane exhibits excellent ionic conductivity as high as 45 mS cm−1, which suggests its potential application in alkaline anion exchange membrane fuel cells. In addition, semi-crystalline nature of PVDF macromolecules imparts the graft membrane excellent thermal and mechanical stability which are required for fuel cell application. Different from available studies of AEMs based on insoluble quarternary ammonium-containing copolymers, this study served as a model system for improving hydroxide conductivity from the viewpoint of self-generated nano-phase separation, and gives pioneering understanding of the morphology–property relationship in novel graft copolymer AEMs.

Novel nanocomposite coating for dental implant applications in vitro and in vivo evaluation

This study aimed at preparation and in vitro and in vivo evaluation of novel bioactive, biodegradable, and antibacterial nanocomposite coating for the improvement of stem cells attachment and antibacterial activity as a candidate for dental implant applications. Poly (lactide-co-glycolide)/bioactive glass/hydroxyapatite (PBGHA) nanocomposite coating was prepared via solvent casting process. The nanoparticle amounts of 10, 15, and 20 weight percent (wt%) were chosen in order to determine the optimum amount of nanoparticles suitable for preparing an uniform coating. Bioactivity and degradation of the coating with an optimum amount of nanoparticles were evaluated by immersing the prepared samples in simulated body fluid and phosphate buffer saline (PBS), respectively. The effect of nanocomposite coating on the attachment and viability of human adipose-derived stem cells (hASCs) was investigated. Kirschner wires (K-wires) of stainless steel were coated with the PBGHA nanocomposite coating, and mechanical stability of the coating was studied during intramedullary implantation into rabbit tibiae. The results showed that using 10 wt% nanoparticles (5 wt% HA and 5 wt% BG) in the nanocomposite could provide the desired uniform coating. The study of in vitro bioactivity showed rapid formation of bone-like apatite on the PBGHA coating. It was degraded considerably after about 60 days of immersion in PBS. The hASCs showed excellent attachment and viability on the coating. PBGHA coating remained stable on the K-wires with a minimum of 96% of the original coating mass. It was concluded that PBGHA nanocomposite coating provides an ideal surface for the stem cells attachment and viability. In addition, it could induce antibacterial activity, simultaneously.

Physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly(lactic acid)

A range of nanocomposites were prepared using cellulose nanowhiskers (CNWs) and poly(lactic acid) (PLA) via a solvent casting process. Acid hydrolysis process was used to produce CNWs from bleached cotton. Structural morphology and surface topography of the CNWs and nanocomposites were examined using transmission (TEM) and scanning electron microscopy. TEM images revealed rod-like whiskers in the nano-scale region which were dispersed within the PLA matrix. The presence of the functional groups of CNWs and PLA were confirmed via FTIR analysis. Tensile tests were conducted on thin films and the nanocomposites containing 1 wt% CNWs showed a 34 and 31% increase in tensile strength and modulus, respectively, compared to pure PLA. The dynamic mechanical analysis showed that the tensile storage modulus also increased in the visco-elastic temperature region with increasing CNWs content in the nanocomposites. Thermogravimetric analysis showed that all the materials investigated were thermally stable from room temperature to 210 °C. A positive effect of CNWs on the crystal nucleation of PLA polymer in the nanocomposites was observed using differential scanning calorimetry and X-ray diffraction analysis. The degradation profiles of the nanocomposites in deionised water over 1 week revealed a mass loss of 1.5–5.6% at alternate temperatures (25, 37 and 50 °C) and at the same conditions the swelling ratio and water uptake were seen to increase with CNWs content in the nanocomposites, which was strongly influenced by the presence of crystalline CNWs.

New Sulfonated Poly(p-phenylenesulfone)/Poly(1-oxotrimethylene) Nanocomposite Proton-Conducting Membranes for PEMFCs

Two series of membranes, A and B, were prepared by the following synthesis protocols. A-type membranes were obtained by a solvent casting process from solutions prepared by dissolving three different blends of poly(1-oxotrimethylene) (PK) and sulfonated poly(p-phenylenesulfone) (sPSO2) in DMAc. B-type materials were prepared using a two-step process. First, an inorganic–organic hybrid nanofiller was synthesized by CO-ethene copolymerization in the presence of silica nanoparticles. From this synthesis, a hybrid nanofiller, [SiO2/(PK)0.65], with 35 wt % of SiO2 was obtained. Membranes were produced by a solvent casting process from solutions prepared by dispersing different amounts (10, 20, 30 wt %) of the [SiO2/(PK)0.65] nanofiller in a sPSO2/DMAc solution. As compared to pristine sPSO2 and the A-type materials, the presence of the hybrid nanofiller in the B-type membranes reduces the water uptake and membranes' swelling and increases the proton conductivity at low membrane hydration levels.

New Insights into Ionic Aggregate Morphology in Zn-Neutralized Sulfonated Polystyrene Ionomers by Transmission Electron Tomography

The three-dimensional microstructure of ionic aggregates in Zn-neutralized sulfonated polystyrene ionomers was characterized, for the first time, by transmission electron tomography. Two methods were used in order to prepare ionomer films: the hot-pressing and solvent-casting. With the first method, spherical aggregates with a mean diameter of about 5 nm are observed within the material. They are heterogeneously dispersed within the matrix and tend to form a network. When the second processing method is used, a nanoplatelet shape (with a thickness of about 6 nm) is unambiguously observed for the ionic aggregates. A preferential alignment of these aggregates parallel to the film plane is induced by this method. The solvent-casting process is a very slow method where the medium viscosity is gradually increasing; such an aggregate morphology is assumed to represent a complete aggregation state for the ionic groups.

수용성 고분자를 이용한 항균 필름의 제조 및 특성 연구

본 연구에서는 폴리비닐알코올(Polyvinyl alcohol : PVA)와 메틸셀룰로오스(Methyl cellulose: MC)를 사용하여 항균성을 갖는 필름을 제조하였다. 메틸셀룰로오스와 폴리비닐알코올 필름에 항균성을 부여하기 위해 ampicillin(0.025~1wt%)과 streptomycin(0.1~1.0 wt%)을 첨가하여 함량에 따른 기계적인 물성과 항균활성을 확인하였다. 중합도와 검화도에 따른 PVA 필름의 기계적인 물성을 보면 중합도와 검화정도에 따라 필름의 인장강도가 20.2~51.5 <TEX>$N/mm^2$</TEX>이었고, 메틸셀룰로오스 필름의 경우 점도에 따라 15.44~21.70 <TEX>$N/mm^2$</TEX>이었다. 사용한 균주와 항균제의 함량정도에 따라 그 기계적인 물성과 항균활성에 차이를 보였지만 함량이 늘어날수록 전체적으로 기계적인 물성은 약간 저하되는 경향을 보였지만 항균필름의 항균활성은 우수하였다. Ampicillin과 streptomycin을 사용하여 제조한 항균필름의 항균활성은 포도상 구균과 대장균을 disc diffusion test로 확인하였다. 메틸셀룰로오스와 폴리비닐알코올 필름 모두 streptomycin보다 ampicillin을 함유할 때 항균활성이 우수한 경향을 보였다. This study was performed to develop antimicrobial films using polyvinyl alcohol and methyl cellulose. Methyl cellulose and polyvinyl alcohol films plasticized with PEG(polyethylene glycol) were prepared by solvent casting process under addition of 0.025~1.0 wt% ampicillin and 0.1~1.0 wt% streptomycin as an antimicrobial agent. The mechanical properties of prepared films were examined by universal testing machine(UTM). Tensile strength of methyl cellulose films was 15.44~21.70 <TEX>$N/mm^2$</TEX>. Tensile strength of PVA(15 wt%) film was 20.2~51.5 <TEX>$N/mm^2$</TEX>, and the tensile strength of the antimicrobial films were decreased linearly with increasing the antibiotic loading amount up to 1 wt%. Antimicrobial activities of PVA and methyl cellulose films containing ampicillin and streptomycin through the disc diffusion test for the Staphylococcus aureus and Escherichia coli. The antimicrobial activity of methyl cellulose films and PVA containing ampicillin were higher than that of containing streptomycin methyl cellulose films. The results indicate the films may be a proper materials for antimicrobial packing applications.

Effects of casting solvent on microstructrue and ionic conductivity of anhydrous sulfonated poly(ether ether ketone)-inoic liquid composite membranes

As the key component of polymer electrolyte membrane fuel cells, the membrane has significant effect on the performance of fuel cells. The commonly used approach for preparation of membrane is solvent casting. In this paper, high temperature polymer electrolyte membranes consisting of sulfonated poly(ether ether ketone) and 1-butyl-3-methylimidazolium tetrafluoroborate were prepared using solvent casting process from N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone solutions to understand the solvent effect on the nature of formed membranes. It was found that solvents used for casting process strongly affect the microstructure and ionic conductivity of formed membranes. The composite membrane cast from DMF solution has clearly inter-connected ionic clusters with diameters of several hundreds nanometers to about 1.5 μm and exhibits the highest ionic conductivity, reaching 1.04 × 10 −2 S cm −1 at 170 °C under anhydrous conditions.