Bimodal Diameter Distribution Research Articles

Electrospun carboxylated MWCNTs modified PMIA tree-like nanofibrous membrane with excellent thermal stability and chemical resistance for efficient particulate matter removal

The aim of this study is to fabricate nanofibrous membranes with excellent filtration and mechanical properties for application in the field of flue gas purification. Carboxylated Multiwalled carbon nanotubes (MWCNTs-COOH) were used to enhance the performance of PMIA nanofibrous membranes. The results showed that the average particle size D50 of MWCNTs-COOH in the PMIA electrospining solution was significantly reduced from 644 nm to 361 nm, the stability and dispersibility of MWCNTs-COOH were significantly enhanced. The resultant membranes exhibit a tree-like structure with a bimodal distribution of diameters and interconnected bonding points, where the trunk nanofibers exhibit an average diameter of 134.80 nm, while the branch nanofibers demonstrate an average diameter of 27.19 nm. The MWCNTs-COOH/PMIA nanofibrous membranes exhibited a filtration efficiency of 99.98 % for the most penetrating particle size (MPPS), while maintaining a tensile strength of 46.736 MPa. Notably, they retained significant strength even under harsh conditions, e.g. 56.46 % at 250 °C, 58.26 % with 30 wt% H2SO4, and 82.71 % with 10 wt% NaOH. The filtration efficiency remained at approximately 88.97 % even at 250 °C. These findings expand PMIA's application to harsh environments and offer insights for designing high-performance filters for high-temperature settings.

Biomimetic grafts from ultrafine fibers for collagenous tissues.

The ligament is the soft tissue that connects bone to bone and, in case of severe injury or rupture, it cannot heal itself mainly because of its poor vascularity and dynamic nature. Tissue engineering carries the potential to restore the injured tissue functions by utilization of scaffolds mimicking the structure of native ligament. Collagen fibrils in the anterior cruciate ligament (ACL) have a diameter ranging from 20 to 300nm, which defines the physical and mechanical properties of the tissue. Also, the ACL tissue exhibited a bimodal distribution of collagen fibrils. Currently, the ability to fabricate scaffolds replicating this structure is a significant challenge. This work aims at i) measuring the diameter of collagens of bovine ACL tissue, ii) investigating the fabrication of sub-100nm fibers, and iii) fabricating aligned scaffolds with bimodal diameter distribution (with two peaks) resembling the healthy ACL structure. It is hypothesized that such scaffolds can be produced by electrospinning polycaprolactone (PCL) solutions. To test the hypothesis, various PCL solutions were formulated in acetone and formic acid in combination with pyridine, and electrospun to generate sub-100nm fibers. Next, this formulation was adjusted to produce nanofibers with a diameter between 100nm and 200nm. Finally, these solutions were combined in the co-electrospinning process, i.e., two-spinneret electrospinning, to fabricate biomimetic scaffolds with a bimodal distribution. Electrospinning of 8% and 15% PCL solutions, respectively, resulted in the production of fibers with diameters below and above 100nm. The combined scaffold exhibited a bimodal distribution of aligned fibers with peaks around 80 and 180nm, thus mimicking the collagen fibrils of healthy ACL tissue. This research is expected to have a society-wide impact because it aims to enhance the health condition and life quality of a wide range of patients.

Fabrication of Poly(Lactic Acid)@TiO2 Electrospun Membrane Decorated with Metal-Organic Frameworks for Efficient Air Filtration and Bacteriostasis.

The development of high-performance filtration materials is essential for the effective removal of airborne particles, and metal-organic frameworks (MOFs) anchored to organic polymer matrices are considered to be one of the most promising porous adsorbents for air pollutants. Nowadays, most air filters are generally based on synthetic fiber polymers derived from petroleum residues and have limited functionality, so the use of MOFs in combination with nanofiber air filters has received a lot of attention. Here, a conjugated electrostatic spinning method is demonstrated for the one-step preparation of poly(lactic acid) (PLA) nanofibrous membranes with a bimodal diameter distribution and the anchoring of Zeolitic Imidazolate Framework-8 (ZIF-8) by the introduction of TiO2 and in situ generation to construct favorable multiscale fibers and rough structures. The prepared PLA/TZ maintained a good PM2.5 capture efficiency of 99.97%, a filtration efficiency of 96.43% for PM0.3, and a pressure drop of 96.0 Pa, with the highest quality factor being 0.08449 Pa-1. Additionally, ZIF-8 was uniformly generated on the surface of PLA and TiO2 nanofibers, obtaining a roughened structure and a larger specific surface area. An enhanced filtration retention effect and electrostatic interactions, as well as active free radicals, can be generated for the deep inactivation of bacteria. Compared with the unmodified membrane, PLA/TZ prepared antibacterial characteristics induced by photocatalysis and Zn2+ release, with excellent bactericidal effects against S. aureus and E. coli. Overall, this work may provide a promising approach for the development of efficient biomass-based filtration materials with antimicrobial properties.

Enhancing creep formability and mechanical properties of creep-aged AA2050 alloys via slow heating

In this work, a new creep aging route (pre-deformation+slow-heated creep aging, PSHCA) of AA2050 alloys was developed by the slow heating (20 °C/h) from 120 °C to 180 °C. The PSHCA alloy exhibits high creep strain with a simultaneous increase of strength and plasticity. The yield strength, ultimate tensile strength, and elongation reached 544 MPa, 581 MPa, and 11.1%, respectively. Both the rolling pre-deformation before aging and stress field during aging promoted the increased dislocation density and dense precipitation of T1 phases in the aged alloys, hence, the strength was improved at the expense of plasticity. Meanwhile, the bimodal diameter distribution of T1 phase of the PSHCA alloy and the enrichment of Ag atoms at T1/matrix interface was promoted by slow heating, slowing down the thickening of T1 phases. This further promoted the plasticity of PSHCA alloys while maintaining high strength. Additionally, the slow precipitation of T1 phase at the early stage of aging promoted dislocation slip and thus improving the creep strain of PSHCA alloys. These findings pave a way in designing large-curved and high-performance Al-Li components by creep aging technology.

Modelling ‘Type B’ ejecta formation reveals reactor Unit 1 conditions during the Fukushima Daiichi Nuclear Disaster

For the first time, a model was developed to simulate the cooling of the Fukushima Daiichi Nuclear Power Plant reactor Unit 1-derived, ‘Type B’ radiocaesium bearing microparticles, distributed into the environment during the 2011 nuclear meltdown. By establishing an analogy between ‘Type B’ CsMP and volcanic pyroclasts, the presented model simulates the rapid cooling of an effervescent silicate melt fragment upon atmospheric release. The model successfully reproduced the bi-modal distribution of internal void diameters observed in ‘Type B’ CsMP, however, discrepancies resulted primarily due to the neglection of surface tension and internal void coalescence. The model was subsequently utilised to estimate the temperature within reactor Unit 1 in the instant preceding the hydrogen explosion—between 1900 and 1980 K. Such a model demonstrates the accuracy of the volcanic pyroclast—‘Type B’ CsMP analogue, and confirms radial variations in cooling rate as the cause of the vesicular texture of Unit 1 ejecta. The presented findings provide scope to further explore the comparison between volcanic pyroclasts and ‘Type B’ CsMP via experimentation, which will provide a deeper understanding of the specific conditions within reactor Unit 1 during the catastrophic meltdown at the Japanese coastal plant.

Polylactic Acid/Poly(vinylpyrrolidone) Co-Electrospun Fibrous Membrane as a Tunable Quercetin Delivery Platform for Diabetic Wounds.

Diabetic wound infections (DWI) represent one of the most costly and disruptive complications in diabetic mellitus. The hyperglycemic state induces a persistent inflammation with immunological and biochemical impairments that promotes delayed wound healing processes and wound infection that often results in extended hospitalization and limb amputations. Currently, the available therapeutic options for the management of DWI are excruciating and expensive. Hence, it is essential to develop and improve DWI-specific therapies able to intervene on multiple fronts. Quercetin (QUE) exhibits excellent anti-inflammatory, antioxidant, antimicrobial and wound healing properties, which makes it a promising molecule for the management of diabetic wounds. In the present study, Poly-lactic acid/poly(vinylpyrrolidone) (PP) co-electrospun fibers loaded with QUE were developed. The results demonstrated a bimodal diameter distribution with contact angle starting from 120°/127° and go to 0° in less than 5 s indicating the hydrophilic nature of fabricated samples. The release QUE kinetics, analyzed in simulated wound fluid (SWF), revealed a strong initial burst release, followed by a constant and continuous QUE release. Moreover, QUE-loaded membranes present excellent antibiofilm and anti-inflammatory capacity and significantly reduce the gene expression of M1 markers tumor necrosis factor (TNF)-α, and IL-1β in differentiated macrophages. In conclusion, the results suggested that the prepared mats loaded with QUE could be a hopeful drug-delivery system for the effective treatment of diabetic wound infections.

Biodegradable Scaffolds for Vascular Regeneration Based on Electrospun Poly(L-Lactide-co-Glycolide)/Poly(Isosorbide Sebacate) Fibers.

Vascular regeneration is a complex process, additionally limited by the low regeneration potential of blood vessels. Hence, current research is focused on the design of artificial materials that combine biocompatibility with a certain rate of biodegradability and mechanical robustness. In this paper, we have introduced a scaffold material made of poly(L-lactide-co-glycolide)/poly(isosorbide sebacate) (PLGA/PISEB) fibers fabricated in the course of an electrospinning process, and confirmed its biocompatibility towards human umbilical vein endothelial cells (HUVEC). The resulting material was characterized by a bimodal distribution of fiber diameters, with the median of 1.25 µm and 4.75 µm. Genotyping of HUVEC cells collected after 48 h of incubations on the surface of PLGA/PISEB scaffolds showed a potentially pro-angiogenic expression profile, as well as anti-inflammatory effects of this material. Over the course of a 12-week-long hydrolytic degradation process, PLGA/PISEB fibers were found to swell and disintegrate, resulting in the formation of highly developed structures resembling seaweeds. It is expected that the change in the scaffold structure should have a positive effect on blood vessel regeneration, by allowing cells to penetrate the scaffold and grow within a 3D structure of PLGA/PISEB, as well as stabilizing newly-formed endothelium during hydrolytic expansion.

Preparation of fluffy bimodal conjugated electrospun poly(lactic acid) air filters with low pressure drop.

Electrospun nanofiber membranes have been extensively studied as air filters. However, their limited filtration efficiency for submicron inhalable particulate matter (PM), high resistance to filtration, and limited capacity to hold dust have hindered their widespread use. The majority of materials come from petroleum, and the use of organic solvents during the spinning process has a significant negative impact on the environment. In this work, a sustainable method has been proposed for producing filters using poly(lactic acid) (PLA) with a bimodal diameter distribution through conjugated electrospinning. This technique allows for the continuous production of interconnected micro/nano hybrid porous membranes, resulting in reduced resistance and improved dust holding capacity. The filtration efficiency, pressure drop, long-term filtration performance, and actual performance of the conjugated bimodal membrane (CBM) were extensively investigated. The results indicate that the filter has a high capacity for retaining particles, with filtration efficiencies of 99.94% for PM 0.3 and 99.96% for PM 2.5. It also demonstrates a high quality factor (0.078 Pa-1 for PM 0.3 and 0.084 Pa-1 for PM 2.5), long-term stability (a decrease of 2.35% for PM 0.3 and 0.05% for PM 2.5 over a period of 60 days) and outstanding dust holding capacity (9.17 g m-2). The conjugated bimodal membrane (CBM) shows a 22.64% decrease in resistance compared to the non-conjugated bimodal membrane (BM). In general, the approach outlined in this work provides valuable insights into the development of high-performance biodegradable air filters. These filters have improved filtration efficiency and reduced resistance.

Tailoring bimodal protein fabrics for enhanced air filtration performance

Natural material-based nanofiber air filters promise to minimize any adverse impacts on the environment after use, but the nanofiber structure causes poor airflow performance, i.e. high airflow resistance. Constructing bimodal structures reduces airflow resistance without compromising removal efficiency but has been rarely studied for natural nanofiber air filters. In this study, we fabricate bimodal protein fabric air filters and carefully tailor their bimodal structure to achieve higher removal efficiency with significantly lowered airflow resistance. The bimodal structures are generated by co-spinning of denatured zein protein in two solvent systems, via controlling the protein denaturation degree and fiber shape/size. The bimodal structures with bimodal diameter distributions are then carefully adjusted by varying the feed rates. It is revealed that a bimodal fabric shows an optimized filtration performance when the fiber diameters locate at 2.44 and 0.13 μm, reducing the airflow resistance by up to 56.47 Pa (from 84.97 Pa to 28.5 Pa) with a high PM2.5 removal efficiency of 98.43%. The bimodal fabric treated with TX-100 shows a further improved filtration performance of filtering PM0.3 of 97.01% and PM2.5 of 99.15% at an ultralow airflow resistance of 21.1 Pa. Moreover, the treated bimodal fabric presents better long-term performance and higher removal efficiency in a humid environment. This work develops a simple and viable method for fabricating and tailoring bimodal air filters made of abundant natural protein for broad applications.

Effects of silvicultural selection treatments on spatial pattern and dynamics in a Pinus palustris Mill. woodland

Natural disturbance-based silviculture emphasizes harvest methods that emulate the timing and structural changes of natural disturbances. Longleaf pine woodlands are ecologically important ecosystems of the southeastern U.S. that support high biodiversity. Options for multi-aged silviculture include individual tree and group selection methods to promote regeneration—the latter method may be modified by retention of reserve trees. To explore the extent to which selection methods are congruent with natural disturbance regimes, we evaluated how treatments in mature second-growth longleaf pine woodlands affected overstory structure, pattern, and dynamics, and we made comparisons to an old-growth longleaf stand. In 2010, stands were harvested using individual tree selection, group selection, or group selection with reserves. We compared treatment effects on spatial pattern of residual trees, recruitment of trees into the 10 cm diameter class (hereafter “recruitment”), and tree mortality 8 years after harvest. Basal area and residual volume were similar among treatments, but the individual tree selection treatment had lower density and a unimodal rather than bimodal diameter distribution compared to other treatments. Group selection and group selection with reserves increased spatial aggregation, compared to individual tree selection which reduced aggregation. Recruitment was similar across treatments but usually occurred near existing trees in the group selection treatments and was further from existing trees in the individual tree selection treatment. Tree mortality primarily occurred as single trees rather than tree groups for all treatments. These results indicate that natural disturbance-based treatments vary in their effects on overstory spatial pattern and alter forest dynamics. In longleaf pine woodlands, the rationale for individual tree selection emphasizes maintaining a continuous input of needles as fine fuels for control of resprouting hardwoods with prescribed fire. This method, may simplify overstory spatial structure and alter forest dynamics after initial harvest. Maintenance of vertical and horizontal complexity is a central tenet of natural disturbance-based management, thus attention to spatial pattern must be given when individual tree selection methods are used. In longleaf pine woodlands, natural disturbance-based techniques such as group selection with reserves may better mimic spatial patterns seen in old-growth stands while preserving continuity of fine fuels.

Solubilization of artificial mitochondrial membranes by amphiphilic copolymers of different charge

Certain amphiphilic copolymers form lipid-bilayer nanodiscs from artificial and natural membranes, thereby rendering incorporated membrane proteins optimal for structural analysis. Recent studies have shown that the amphiphilicity of a copolymer strongly determines its solubilization efficiency. This is especially true for highly negatively charged membranes, which experience pronounced Coulombic repulsion with polyanionic polymers. Here, we present a systematic study on the solubilization of artificial multicomponent lipid vesicles that mimic inner mitochondrial membranes, which harbor essential membrane-protein complexes. In particular, we compared the lipid-solubilization efficiencies of established anionic with less densely charged or zwitterionic and even cationic copolymers in low- and high-salt concentrations. The nanodiscs formed under these conditions were characterized by dynamic light scattering and negative-stain electron microscopy, pointing to a bimodal distribution of nanodisc diameters with a considerable fraction of nanodiscs engaging in side-by-side interactions through their polymer rims. Overall, our results show that some recent, zwitterionic copolymers are best suited to solubilize negatively charged membranes at high ionic strengths even at low polymer/lipid ratios.

On the gular sac tissue of the brown pelican: Structural characterization and mechanical properties

The brown pelican (Pelecanus occidentalis) wields one of the largest bills of any bird and is distinguished by the deployable throat pouch of extensible tissue used to capture prey. Here we report on mechanical properties and microstructure of the pouch skin. It exhibits significant anisotropy, with the transverse direction having maximum nominal tensile strains of 200% to 300%, triple the value in the longitudinal direction. This is a higher extensibility than most conventional skin and is the result of the requirement of the sac to net fish; it should expand laterally, with controlled longitudinal stretch. Transmission electron microscopy provides microstructural evidence of the directionality of the collagen fibers and reveals the individual collagen fibrils with a bimodal diameter distribution having peaks at 100 and 170 nm. These dimensions are similar to collagen in mammal skin. In the lateral direction, the fibers form a curvy pattern with a radius of approximately 2 µm wherein the fibrils reorient, straighten, slide, and stretch elastically under tensile load. A second mechanism operates in the transverse direction; the membrane forms a corrugated pattern that, upon straightening of collagen fibrils, confers additional extensibility. This elicits the anisotropic response observed in tensile testing. This work focuses on the mechanical characterization based on the effect of relative bird age, sample location on the pouch, and strain rate. Anterior-posterior location and strain rate are not major influencers on exhibited strengths and extensibilities. However, bird age and dorsal-ventral location are found to affect the mechanical response of the pouch significantly. A physically-based constitutive model is developed for the middle layer of the gular sac, based on observations, which predicts maximum stresses, strains, and the shape of the stress-strain curve consistent with the experimental results.

Encapsulation of Bioactive Compounds from Aloe Vera Agrowastes in Electrospun Poly (Ethylene Oxide) Nanofibers.

Aloe Vera is an ancient medicinal plant especially known for its beneficial properties for human health, due to its bioactive compounds. In this study, nanofibers with antioxidant activity were successfully obtained by electrospinning technique with the addition of a natural Aloe Vera skin extract (AVE) (at 0, 5, 10 and 20 wt% loadings) in poly(ethylene oxide) (PEO) solutions. The successful incorporation of AVE into PEO was evidenced by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging (ABTS) and ferric reducing power (FRAP) assays. The incorporation of AVE introduced some changes in the PEO/AVE nanofibers morphology showing bimodal diameter distributions for AVE contents in the range 10-20 wt%. Some decrease in thermal stability with AVE addition, in terms of decomposition onset temperature, was also observed and it was more evident at high loading AVE contents (10 and 20 wt%). High encapsulation efficiencies of 92%, 76% and 105% according to DPPH, FRAP and ABTS assays, respectively, were obtained at 5 wt% AVE content, retaining AVE its antioxidant capacity in the PEO/AVE electrospun nanofibers. The results suggested that the obtained nanofibers could be promising materials for their application in active food packaging to decrease oxidation of packaged food during storage.

Groove-shaped polypropylene/polyester micro/nanofibrous nonwoven with enhanced oil wetting capability for high oil/water separation

Enhancing oil wettability is an effective way to improve the performance of removing oil from water efficiently and rapidly. In this study, an ordered groove-like rough morphology was exploited to engrave on polypropylene/polyester (PP/PET) micro/nanofiber surface using a three-step tailored process of blending, drawing and etching. The results showed PP/PET micro/nanofibers possessed a bimodal diameter distribution and an ordered groove-like rough morphology with groove-diameter of 100–200 nm. Additionally, the groove-like fiber surface roughness reached up to 1.13 and endowed the prepared nonwovens with a rapid oil wetting capability for separating oil and water mixtures. Furthermore, a separation efficiency of 99% was obtained, driven solely by gravity, in which the nonwovens had high stability. The proposed nonwovens may provide an efficient and fast alternative the industry strategy to large-scale oil spill cleanup.

Bimodal Nanofiber and Microfiber Nonwovens by Melt-Blowing Immiscible Ternary Polymer Blends

Most nonwoven fiber mats are produced with a uniform, narrow fiber diameter distribution. However, building evidence suggests that a bimodal diameter distribution (i.e., comprised of two populations of fibers, one with a smaller average diameter (dₐᵥ), d, and the other with a larger dₐᵥ, D, where D ≥ 5d), has certain advantages in applications such as filtration media. To the best of our knowledge, all previous reports describing production of bimodal fiber diameter distributions have relied on solution-based electrospinning, a much less common fiber-spinning technique, compared to melt blowing, which currently produces more than 10% of nonwovens globally (an approximately $50 billion market). In this study, we demonstrate a facile method for producing bimodal fiber diameter distributions by melt blowing immiscible ternary polymer blends, with the two minority blend components being randomly dispersed as isolated, bimodally sized particles within the continuous matrix. Such a ternary blend can be obtained by selecting a matrix phase that preferentially wets/encapsulates both dispersed phases having vastly different viscosity ratios. Specifically, two model immiscible ternary blends comprised of polystyrene/polyethylene/Nylon-6 (PS/PE/Nylon) and poly(ethylene oxide)/polyethylene/Nylon-6 (PEO/PE/Nylon) with the desired morphologies and PS or PEO as the matrix were examined. During melt blowing of the blends, the PE minority domains (∼8 μm in diameter) and Nylon minority domains (∼70 μm in diameter) dispersed within the matrix were transformed to PE nanofibers (dₐᵥ ≈ 560 nm) and Nylon microfibers (dₐᵥ ≈ 8 μm) embedded in the elongated PS matrix fibers, and similarly for fibers made with a PEO matrix. Subsequent removal of the matrix polymer with an appropriate solvent (tetrahydrofuran for PS or water for PEO) produced a macroscopic mat of randomly distributed, bimodal nanofibers and microfibers. The nanofiber and microfiber compositions of the bimodal-diameter fiber mats were effectively tuned by varying the composition of the minority components of the original ternary polymer blends. Interestingly, the resulting bimodal-diameter fiber mats possessed few nanofiber bundles; we hypothesize that this is due to the presence of Nylon microfibers that are intrinsically intermixed among the PE nanofibers that physically restrict the formation of nanofiber bundles. Overall, this versatile method could provide a high-throughput route to scalable quantities of fiber mats with a bimodal distribution of fiber diameters, thus promoting the application of hierarchically structured nonwovens.

A transmission electron microscopy (TEM) study of silver nanoparticles associated with mine waste from New Caledonian nickel deposits: potential origins of silver toxicity in a World Heritage Site

The nature of silver nanoparticles associated with nickel-laterite ore deposits in New Caledonia (SW Pacific Ocean) is explored using transmission electron microscopy. The silver nanoparticles, dispersed in a matrix of amorphous silica, display complex textures such as linear aggregation and bimodal diameter distributions of 3–12 and 20–60 nm for one sample and 2–30 and 150–650 nm for the other, indicative of Ostwald ripening. These features as well as chemical heterogeneity (31–82% Ag—normalized X-ray energy dispersive spectrum), destructive assemblage interfaces, and amorphous and nanoparticle silica phases are consistent with those observed in epithermal gold deposits, potentially indicating a similar origin. Silver is highly toxic to a wide variety of organisms, and therefore, its significant presence in material directly related to mine runoff is a major threat to the New Caledonian environment, particularly the lagoons, which are listed as a World Heritage Site. Potential exists that the silver nanoparticles observed here provide the key to the origin of the toxic silver accumulation observed in New Caledonian reef organisms.

Mesoscale porosity at the dentin-enamel junction could affect the biomechanical properties of teeth.

In this paper, the 3D-morphology of the porosity in dentin is investigated within the first 350μm from the dentin-enamel junction (DEJ) by fluorescence confocal laser scanning microscopy (CLSM). We found that the porous microstructure exhibits a much more complex geometry than classically described, which may impact our fundamental understanding of the mechanical behavior of teeth and could have practical consequences for dental surgery. Our 3D observations reveal numerous fine branches stemming from the tubules which may play a role in cellular communication or mechanosensing during the early stages of dentinogenesis. The effect of this highly branched microstructure on the local mechanical properties is investigated by means of numerical simulations. Under simplified assumptions on the surrounding tissue characteristics, we find that the presence of fine branches negatively affects the mechanical properties by creating local stress concentrations. However, this effect is reduced by the presence of peritubular dentin surrounding the tubules. The porosity was also quantified using the CSLM data and compared to this derived from SEM imaging. A bimodal distribution of channel diameters was found near the DEJ with a mean value of 1.5-2μm for the tubules and 0.3-0.5μm for the fine branches which contribute to 30% of the total porosity (∼1.2%). A gradient in the branching density was observed from the DEJ towards the pulp, independently of the anatomical location. Our work constitutes an incentive towards more elaborate multiscale studies of dentin microstructure to better assess the effect of aging and for the design of biomaterials used in dentistry, e.g. to ensure more efficient bonding to dentin. Finally, our analysis of the tubular network structure provides valuable data to improve current numerical models.

Nanofiber-Structured TiO2 Nanocrystals as a Scattering Layer in Dye-Sensitized Solar Cells

We developed a scattering layer composed of TiO2 nanocrystals assembled into a densely packed three-dimensional network of nanofibers to localize light within a photoanode used in dye sensitized solar cells (DSSCs). The electro-netting approach was applied to obtain polyamide 6 nanofibers with bi-modal diameter distribution, followed by solvothermal synthesis for the coating of TiO2 nanocrystals on the polymer template. The resulting nanofiber-structured scattering layer (NFSL) is composed of TiO2 nanofibers (200–300 nm in diameter) supporting an ultrathin nanofiber network (diameters within 10–50 nm) and exhibits strong light scattering in the visible range (400 to 700 nm). This NFSL was applied on top of a transparent active TiO2 layer (TL) forming the photoanode in DSSCs. The performance of the bi-layered photoanode was compared to its analogue, fabricated with commercial scattering layers containing different sizes of nanoparticles. The DSSCs assembled with the NFSL showed an 18% enhancement in power conversion efficiency (PCE) compared to that of DSSCs whose photoanode contained only a TL. This enhancement factor was improved up to 31% when the bi-layered structure was post-treated with TiCl4. The PCE improvement was mainly associated with the light harvesting efficiency within the photoanode because of scattering from the NFSL and increased dye adsorption due to the addition of this top layer. These conclusions were inferred from diffuse reflectance behavior, dye loading measurements, external quantum efficiency and electrochemical properties. Our work demonstrates a promising approach without the requirement of time consuming and complicated procedures for the fabrication of a densely packed 3D nanofiber network scattering layer for diverse energy conversion devices and photocatalytic applications.

Mesoscopic simulations of coarsening kinetics within block-copolymer/homopolymer thin films

The simulated evolution of thin-film blends of immiscible AB diblock-copolymers and C homopolymers are presented and analyzed in terms of the time-dependent evolution of the three respective domains. In the current model, all polymer species are mutually incompatible, however the C homopolymers are considered to be less incompatible with the B-block of the diblock copolymer relative to the A-block, hence B-C interfaces develop rather than A-C interfaces. The collective phase-separation within these films leads to microdomains of the AB diblock copolymers along with macrodomains of C homopolymers, in which a growing disparity in domain length scales develops. Technologically, such films may be exploited to fabricate porous membranes with a bimodal distribution of through-thickness pore diameters.

Studies on air permeability of multi-constituent nonwovens

In this work, a series of multi-constituent nonwovens possessing multi-modal fiber diameter distribution was prepared and the air permeability of such nonwoven structures was measured. This approach was extended to bi-constituent nonwovens consisting of fibers with bi-modal diameter distribution and mono-constituent nonwovens composed of fibers with mono-modal diameter distribution. The multi-constituent nonwovens exhibited highest air permeability, followed by the bi- and mono-constituent nonwovens for the same mean fiber diameter. This was explained in terms of the mean pore diameter of the multi-, bi-, and mono-constituent nonwoven structures. An analytical expression of mean fiber diameter of multi-constituent nonwoven structures was derived. The square of the mean fiber diameter in the multi-constituent nonwovens was found to be the harmonic mean of the volume-weighted square of the mean fiber diameter of the individual constituents. The mean fiber diameter coupled with Kozeny–Carman equation was found to predict the air permeability of the multi-, bi-, and mono-constituent nonwovens very well. It was observed that the mono-constituent nonwoven displayed the highest value of Kozeny–Carman coefficient, followed by the bi- and multi-constituent nonwovens.