Hollow Aggregates Research Articles

The Effect of Dense and Hollow Aggregates on the Properties of Lightweight Self-Compacting Concrete.

The development of self-compacting lightweight concretes is associated with solving two conflicting tasks: achieving a structure with both high flowability and homogeneity. This study aimed to identify the technological and rheological characteristics of the flow of concrete mixtures D1400…D1600 based on hollow microspheres in comparison with heavy fine-grained D2200 concrete and to establish their structural and physico-mechanical characteristics. The study of the concrete mixtures was carried out using the slump flow test and the rotational viscometry method. The physical and mechanical properties were studied using standard methods for determining average density and flexural and compressive strength. According to the results of the research conducted, differences in the flow behaviors of concrete mixtures on dense and hollow aggregates were found. Lightweight concretes on hollow microspheres exhibited better mobility than heavy concretes. It was shown that the self-compacting coefficients of the lightweight D1400...D1600 concrete mixtures were comparable with that of the heavy D2200 concrete. The rheological curves described by the Ostwald-de Waele equation showed a dilatant flow behavior of the D1400 concrete mixtures, regardless of the ratio of quartz powder to fractionated sand. For D1500 and D1600, the dilatant flow behavior changed to pseudoplastic, with a ratio of quartz powder to fractional sand of 25/75. The studied compositions of lightweight concrete can be described as homogeneous at any ratio of quartz powder to fractional sand. It was shown that concrete mixtures with a pronounced dilatant flow character had higher resistance to segregation. The value of the ratio of quartz powder to fractional sand had a statistically insignificant effect on the average density of the studied concretes. However, the flexural and compressive strengths varied significantly more in heavy concretes (up to 38%) than in lightweight concretes (up to 18%) when this factor was varied. The specific strength of lightweight and heavy concrete compositions with a ratio of quartz powder to fractional sand of 0/100 had close values in the range of 20.4...22.9 MPa, and increasing the share of quartz powder increased the difference between compositions of different densities.

Modeling and Optimizing the Effect of 3D Printed Origami Bubble Aggregate on the Mechanical and Deformation Properties of Rubberized ECC

A recent development in the production of lightweight concrete is the use of bubble or hollow aggregates. Due to its exceptional energy absorption and ductility properties, engineered cementitious composite (ECC) is increasingly recommended and used for structural applications, particularly in earthquake-prone regions. As a result, researchers have started looking into the benefits of lightweight ECC for such applications. However, the strength is considerably compromised due to the use of lightweight fillers such as perlite, cenospheres, glass microbubbles, and crumb rubber (CR). This study evaluates an origami-shaped bubble aggregate (OBA) novel application in rubberized ECC (RECC) to achieve density reduction at a relatively lower strength loss. The experiment is designed using response surface methodology (RSM) with the spacing of the OBA at 10, 15, and 20 mm and its quantity at 9, 15, and 21 as the input factors (independent variables). The dependent variables (responses) assessed are density, compressive strength, modulus of elasticity, and Poisson’s ratio. The results showed that adding the OBA lowered the density of the RECC by 20%. It was revealed that using up to 15 OBAs with spacings between 15 and 20 mm, a lightweight OBA-RECC with substantial strength could be produced. Similarly, utilizing 15 and 21 OBAs at 20 mm spacing, a lightweight OBA-RECC with a comparable modulus of elasticity as the control could be developed. Models for predicting the responses were developed and validated using analysis of variance (ANOVA) with high R2 values. The spacing and quantity of the OBA’s optimal input levels were determined using the RSM multi-objective optimization to be 20 and 9, respectively. These levels produced optimal responses of 1899 kg/m3, 45.3 MPa, 16.1 GPa, and 0.22 for the density, compressive strength, modulus of elasticity, and Poisson ratio, respectively.

Carbon dioxide adsorbents from flame-made diesel soot nanoparticles

Carbon dioxide (CO2) is the top contributor to global warming. On the other, soot particles formed during fuel combustion and released into the atmosphere are harmful and also contribute to global warming. It would therefore be highly advantageous to capture soot and make use of it as a feedstock to synthesize carbon-based materials for applications such as carbon dioxide adsorption. In this work, flame-made diesel soot nanoparticles were used to produce a variety of activated carbons by combined oxidative treatment with hydrogen peroxide (H2O2) and potassium hydroxide (KOH), and their performance towards CO2 adsorption was evaluated. The effect of the chemical activation of soot with H2O2 for different reaction times and with KOH on the physicochemical properties of the activated carbons was investigated and compared to fresh soot. Interestingly, hollow aggregates of carbonaceous nanoparticles of a high interplanar distance, reduced polycyclic aromatic hydrocarbons (PAH) size, shorter PAH stacks, mesoporous structure, and a high content of oxygen functionalities along with other structural defects in PAHs were obtained in the synthesized activated carbons. Among the various analysis techniques employed, Raman spectroscopy indicated that the ID/IG ratio in soot decreased after simultaneous chemical treatment, though it did not indicate any enhancement in the graphitic character since the carbonyl and carboxylic containing PAHs and monovacancies (which cause defects in PAHs) also contribute to the increase in the intensity of the graphitic band. The activated carbons possessed promising CO2 adsorption capacities, adsorption kinetics and CO2/N2 selectivity. For example, one of the activated carbons, following H2O2 treatment for 9 h and a subsequent KOH activation, exhibited a CO2 adsorption capacity of 1.78 mmol/g at 1 bar and 25 °C, representing an increase of 161 % in capacity as compared to fresh soot. Hollow aggregates of carbonaceous nanoparticles consisting of shorter PAHs with a larger number of defects led to enhanced CO2 adsorption rate and CO2/N2 selectivity on activated carbons.

The preparation of mono- and multicomponent nanoparticle aggregates with layer-by-layer structure using emulsion templating method in microfluidics

We report on the preparation of multicomponent hollow aggregates by an emulsion templating method adapted to microfluidic format. The method exploits partial miscibility of aqueous colloidal solutions as discrete phase and n-butanol as continuous phase. The aggregates consisted of an inner inorganic shell composed of iron oxide (IO) and gold nanoparticles (Au NPs) covered with polycaprolactone (PCL) NPs. The aggregates of smaller sizes were prepared compared to immiscible phases due to the diffusion-controlled shrinkage of aqueous droplets. The aggregate surface properties were controlled by using different mobilities and affinities of IO, Au, and PCL NPs to the water:n-butanol interface. The biocompatible surface layer enclosing an inorganic shell with a core space for possible cargo loading endowed these constructs with properties appreciated in medicinal applications. A computational fluid dynamics model enabled the prediction of the droplet size and formation frequency together with flow field properties at the point of droplet detachment.

Study on Permanent Thermal Insulation Formwork of Mass Concrete Prepared by Different Types of Nano-modified Lightweight Aggregate

Aiming at the problems of low strength, flammability, easy falling off, and aging of traditional organic thermal insulation materials, inorganic thermal insulation materials of different types of nano-modified lightweight aggregates were prepared in this paper. The feasibility of preparing permanent thermal insulation formwork of mass concrete with nano-modified lightweight aggregate was studied through experiments and calculation analysis of mechanical, durability, and thermal properties. The results show that the water absorption of shale ceramsite modified by nano-permeable hydrophobic agent is reduced to 1.21%, and the water absorption rate of inorganic precast hollow aggregate produced by nano-silica powder is lower, which is 0.79%. Inorganic precast hollow aggregate concrete, modified shale ceramsite concrete, and organic foamed aggregate concrete have the characteristics of high strength, fire resistance, aging resistance and low thermal conductivity. Inorganic precast hollow aggregate concrete and modified shale ceramsite concrete have excellent impermeability and frost resistance. Organic foamed aggregate concrete has the lowest thermal conductivity and good thermal insulation effect and its durability can be improved by surface protection technology. According to the principle of equivalent surface heat release coefficient, it is feasible to use lightweight aggregate precast formwork as permanent insulation formwork of mass concrete with thickness between 50 and 100 cm. The permanent thermal insulation formwork of nano-modified lightweight aggregate concrete can also be used as the formwork for concrete construction to realize the temperature control measures of tracking thermal insulation and slow cooling of mass concrete, reduce the risk of cracking, and improve the construction efficiency.

Chiral Supramolecular Polymers Assembled by Amphiphilic Oligopeptide-Perylene Diimides and High Electrochemical Sensing.

Various secondary structures, for example, β-sheet hydrogen bonds formed by oligopeptides exhibiting high directionality and selectivity provide a new avenue to regulate optoelectronic performances of supramolecular assemblies constructed by π-conjugated chromophores. In this work, oligopeptide-perylene diimides (AUPDIs) are synthesized to generate β-sheet strands which guide the formation of chiral supramolecular polymers with a diversity of morphologies in combination with the π-π stacking even in aqueous media. Complex morphology transitions are successfully controlled by simply adjusting the water volume fraction in the binary solvent of water and tetrahydrofuran from spherical hollow aggregates to long helical nanowires and to short nanofibers. The mechanism of the assembly changes from cooperative to the isodesmic model relying on AUPDI concentrations. This originates from the transformation in the β-sheet that regulates profoundly the arrangement of the AUPDI molecules. Prominently efficient and positive electronic sensing to triethylamine for highly helical nanowires engenders due to the highly ordered helical arrangement within the nanowires, fourfold of the short nanofibers.

Dopant-Assisted Control of the Crystallite Domain Size in Hollow Ternary Iridium Alloy Octahedral Nanocages toward the Oxygen Evolution Reaction

The dissolution of Ir-oxide-based catalysts remains a roadblock in the development of durable electrocatalytic oxygen evolution reaction (OER) catalysts. Both the activity and stability of Ir-based catalysts are critically dependent on the ratio of stable rutile IrO2 and unstable amorphous Ir oxide (a-IrOx), as well as the spatial relationship between them. Here, we report that the domain size in hollow ternary Ir alloy nanocages can be fine-tuned by the introduction of dopant elements during the growth of parent core-shell nanoparticles, [email protected] After electrochemical oxidation under OER conditions, Ir alloy nanocages possessing multiple crystallites in their structure are transformed into hollow aggregates of loosely knit crystalline IrO2@a-IrOx domains, whereas single-crystalline Ir alloy nanocages are transformed to hollow Ir oxides with a random mixture of a-IrOx and IrO2. The loosely knit IrO2@a-IrOx structure achieves high OER activity and long-term stability, which is not feasible with the random mixture of a-IrOx and IrO2.

Numerical study on rheological properties for dispersed and aggregated particle systems

Shear thinning behavior of colloidal suspensions is a direct consequence of shear-induced structural variation of aggregates. This study numerically simulates the shear-induced deformation of spherical aggregates of particles with close-packed and hollowed-out structures to evaluate its rheological effects on the bulk suspension. Simulations are performed by the discrete element method (DEM) coupled with direct numerical simulation (DNS), herein referred to as the “DEM–DNS method.” This method can be used to simultaneously evaluate adhesive force and contact force acting on particles, which play an essential role in aggregate breakup, combined with the two-way particle–fluid interaction. The simulations show that the weakly sheared suspensions for both aggregates, subjected to no structural rearrangement, yield the same shear viscosity. In contrast, under strong shear where both aggregates undergo an irreversible breakup, the suspension of the hollow aggregate shows greater shear thinning than that of the close-packed aggregate. This bifurcation in shear thinning suggests the mechanism underlying the oft-encountered large shear thinning: the shear-induced breakup of aggregates enables a release of the fluid caged inside the aggregates and thus a substantial decrease in the apparent volume fraction of the solid phase. We thereby demonstrate the sophisticated capacity of the DEM–DNS method for experimentally unachievable correlation of shear-induced deformation of aggregates with a macroscopic viscosity evaluation.

Template-free hydrothermal synthesis of 3D hollow aggregate spherical structure WO3 nano-plates and photocatalytic properties

A new kind of 3D hollow aggregate spherical structure WO3 nano-plates was prepared via a simple hydrothermal synthesis without any template. In this paper, the effects of HNO3 addition on the preparation of WO3 powder were systematically investigated. With HNO3 concentration increasing, the product was converted from WO3(H2O)0.33 to monoclinic WO3·H2O until the reaction to complete. Meanwhile, the morphology and size of particles changed from mocro-scale spheres to nano-plates. In the WO3·H2O structure, H2O integrates the H2O molecules via hydrogen bond, while WO3 bonds with other WO3 molecules and finally form a hollow spherical structure. During subsequent drying, WO3·H2O is deprived of crystal water to become monoclinic WO3, remaining this porous spherical structure. Compared with the industry-use catalyst of Degussa P25 TiO2, the as-prepared WO3 exhibits the wonderful photocatalytic activity due to the plate-like morphology and porous structure.

Lignosulfonate Improves Photostability and Bioactivity of Abscisic Acid under Ultraviolet Radiation.

Abscisic acid (ABA), as a commonly used plant growth regulator, is easy to be degraded and lose its bioactivity under sunshine. To select an eco-friendly and efficient photoprotectant for the improvement of photostability and bioactivity of ABA when exposed to ultraviolet (UV) light, we tested the effects of three biodegradable natural-derived high polymers, sodium lignosulfonates 3A [molecular weight (MW) > 50000, with degree of sulfonation (DS) of 0.48] and NA (20000 < MW < 50000, with DS of 0.7) and calcium lignosulfonate CASA (MW < 20000, with DS of 0.7), on the photodegradation of ABA. Lignosulfonates 3A, NA, and CASA showed significant photostabilizing capability on ABA. Lignosulfonate 3A showed preferable photostabilizing effects on ABA compared to CASA, while NA showed an intermediate effect. That indicated that lignosulfonate with a high MW and low DS had a stronger UV absorption and the hollow aggregate micelles formatted by lignosulfonate protect ABA from UV damage. Approximately 50% more ABA was kept when 280 mg/L ABA aqueous solution was irradiated by UV light for 2 h in the presence of 2000 mg/L lignosulfonate 3A. The bioactivity on wheat (JIMAI 22) seed germination was greatly kept by 3A in comparison to that of ABA alone. The 300 times diluent of 280 mg/L ABA plus 2000 mg/L 3A after 2 h of irradiation showed 20.8, 19.3, and 9.3% more inhibition on shoot growth, root growth, and root numbers of wheat seed, separately, in comparison to ABA diluent alone. We conclude that lignosulfonate 3A was an eco-friendly and efficient agent to keep ABA activity under UV radiation. This research could be used in UV-sensitive and water-soluble agrichemicals and to optimize the application times and dosages of ABA products.

Solvent-Induced Molecular Folding and Self-Assembled Nanostructures of Tyrosine and Tryptophan Analogues in Aqueous Solution: Fascinating Morphology of High Order.

Hydrophobic derivatives of tyrosine and tryptophan, viz. octyl and dodecyl esters of tyrosine and octyl ester of tryptophan, are synthesized, and the interfacial and bulk properties in aqueous media are investigated as models for the membrane proteins. Molecular modeling by the density functional theory method is carried out to understand the molecular conformation and geometry for the purpose of determining the packing parameters. Water-induced molecular folding of the esters of both tyrosine and tryptophan, as observed using rotating frame nuclear Overhauser effect spectroscopy, indicates that the segregation of the hydrophobic and hydrophilic blocks in water is the key to the development of fascinating interfacial property displayed by the aromatic amino acid esters. The unusually high-order morphology of the aggregates, as observed using high-resolution transmission electron microscopy, is highly uncommon for single-chain amphiphiles and points to the fact that the self-assembly behavior of the present systems resembles that of block copolymers. The study of the growth of mesosized hollow aggregates with internal bilayer structures from tyrosine and tryptophan-based model systems would add to the understanding of biochemistry and biotechnology relevant to the cell membrane. The potential of biocompatible nanostructured motifs as the drug carriers is discussed. The highly functional role played by the aromatic amino acids at the membrane-water interface will be considered with the present amphiphilic models for future perspective.

New large-scale production route for synthesis of lithium nickel manganese cobalt oxide

The spray roasting process is recently applied for production of catalysts and single metal oxides. In our study, it was adapted for large-scale manufacturing of a more complex mixed oxide system, in particular symmetric lithium nickel manganese cobalt oxide (LiNi1/3Co1/3Mn1/3O2—NMC), which is already used as cathode material in lithium-ion batteries. An additional lithiation step was coupled with the main process in order to obtain the desired layered structure. Thermogravimetric analysis and high-temperature X-ray diffractometry built the basis for determining suitable synthesis temperature regions for the used chloride precursors and the post-treatment step. The optimized process was proven on an industrial pilot line where a setup for minimum production capacity of 12 kg h−1 was possible. The powder obtained directly after roasting had a very striking morphology compared to the final lithiated product. Hollow aggregates (≥250 μm) with overall 10.926 m2 g−1 surface area and a pore diameter of 3.396 nm were observed. Their well-faceted primary particles were converted into nanosized spheres after lithiation, building a few micrometer big high-porous agglomerates. Actual composition was verified by inductively coupled plasma atomic emission spectroscopy analysis, and the crystal structure and corresponding unit cell parameters were identified and confirmed by Rietveld fit of the derived X-ray diffraction pattern. The initial electrochemical measurements show a 149-mAh g−1discharge capacity, as determined from cyclic voltammetry.

Structure and properties of ZrO2-MgO powders

It have been studied magnesia stabilized zirconia (ZrO2-MgO) powders produced by high-frequency decomposition of water salt solutions. It have been shown that due to precursor dissociation powders consist of spherical particles with smooth surface and irregular hollow aggregates resembling foam. An increase in the magnesium concentration in the precursor has an effect on the powder properties, namely, the specific surface decreases significantly and the bulk density increases. Zirconia in the nanostructured state is present only in the powders with 8.6 and 13.9 mole% MgO, with the size of the c-ZrO2 crystallites in them no more than 100 nm. In powder with 43.3 mole% of MgO the magnesia content in c-ZrO2 solid solution corresponds to its solubility limit of 22.2 mole% at temperature 2100°C.

Structure and Properties of ZrO2–MgO Powders

It have been studied magnesia stabilized zirconia (ZrO2-MgO) powders produced by high-frequency decomposition of water salt solutions. It have been shown that due to precursor dissociation powders consist of spherical particles with smooth surface and irregular hollow aggregates resembling foam. An increase in the magnesium concentration in the precursor has an effect on the powder properties, namely, the specific surface decreases significantly and the bulk density increases. Zirconia in the nanostructured state is present only in the powders with 8.6 and 13.9 mole% MgO, with the size of the c-ZrO2 crystallites in them no more than 100 nm. In powder with 43.3 mole% of MgO the magnesia content in c-ZrO2 solid solution corresponds to its solubility limit of 22.2 mole% at temperature 2100°C.

EDTA-assisted template-free synthesis and improved photocatalytic activity of homogeneous ZnSe hollow microspheres

Abstract Homogeneous ZnSe hollow microspheres were synthesized on a large scale through an EDTA-assisted mixed solvothermal strategy without any surfactants and templates. The as-synthesized ZnSe microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis absorption spectroscopy. The results of photodegradation of methylene blue (MB) indicate that the hollow microspheres exhibit a visible-light-responsive photocatalytic behavior. As compared with the bulk ZnSe, the photocatalytic efficiency for the hollow microspheres was enhanced remarkably, which might be related with the hollow aggregates of ZnSe nanocrystallites.

Formation of Highly Ordered Nanostructures by Drying Micrometer Colloidal Droplets

Nanoparticles with well-defined chemical compositions can act as building blocks for the construction of functional structures, such as highly ordered aggregates, as well as porous and hollow aggregates. In this work, a spray-drying technique is used to form a crystal-like structure with nanoparticle building blocks. When spray-drying uniform spherical particles, tightly packed aggregates with either simple or broken symmetries (quasicrystalline) were formed. Using polystyrene (PS) particles with varied zeta potentials as templates, it is also possible to form highly ordered porous and hollow aggregates from inorganic colloidal particles. Essential to the production of quasicrystalline structures is the use of monodisperse colloidal particles in spray drying, as the quasicrystalline form is not achievable when two different sizes of colloidal particles are used in the precursor suspension. With varying colloidal particles sizes, smaller colloidal particles fill the spaces formed between the larger particles, resulting in adjustment of colloidal crystallization. A geometric model that considers the tight packing of several spheres into frustrated clusters (quasicrystal form) with short-range icosahedral symmetry is compared to experimentally produced structures and found to quantitatively explain experimental observations.

Wall panel application of fibre-reinforced lightweight concrete

In this study, material properties of lightweight concrete reinforced with randomly distributed poly vinyl alcohol (PVA) fibres are discussed, on account of a possible structural use. Flexural, compressive and cyclic performances of the material are tested and the results are presented. The effect of fibres on high-strength lightweight concrete is investigated, and the expected performance of any wall panel produced with the mentioned material is compared with commercially-available wall panels. In the frame work of the study, hollow sphere aggregates are used to produce lightweight concrete and PVA fibres are used to increase ductility. Using 1.5% fibre volume fraction caused an increase in the flexural strength by up to 2.5 times compared to lightweight concrete, and using lightweight aggregate provides considerable decrease in density depending amount of lightweight aggregate used. Using this type of aggregate with a range between 20% to 40% of lightweight aggregate content provided densities in a range between 1.2 to 1.6 g/cm3. It is found that the matrix design of PVA fibre-reinforced lightweight concrete produced for this study has 5% to 15% higher flexural strength than the ones commercially available for approximately the same density range.

Preparation of Highly Oil-Absorbing Resins Consisting of Hollow Nanoparticle Aggregates by Spray Drying

We report on the preparation of a novel poly(styrene-dodecyl methacrylate) (P(St-DMA)) absorbent resin by spray drying. The microstructures of the prepared resins have been examined by scanning electron microscope (SEM), showing that the resins consisted of hollow micrometer-sized spheres that were aggregated by nanoparticles. Meanwhile, the effects of the content of the cross-linker divinybenzene (DVB) on the oil absorption capacity, the desorption efficiency and the resin microstructures have also been studied. The absorption performance and the hydrophobic properties of the resins prepared by spray drying and vacuum drying have been studied and compared.

Globulin 11S and Its Mixture with l-Dipalmitoylphosphatidylcholine at the Air/Liquid Interface

Langmuir films of globulin 11S protein, l-dipalmitoylphosphatidylcholine (L-DPPC), and mixtures of both on water and on buffer subphases were studied. Brewster angle microscopy (BAM) was used to characterize in situ the films morphology along Pi-A isotherms at the air/liquid interface. The L-DPPC monolayer on water behaved as has been reported extensively in the literature but a slight increase on surface pressure and a notable change in domain morphology is observed on buffer. This difference in domain behavior is due to the stabilization interaction of the LE phase by the buffer ions. On the other hand, the protein monolayer was prepared by direct deposit or injection below the surface. Both methods formed mostly a condensed film, with a multilayer formed by globular aggregates in the first method with the two subphases. However, the second method showed different behavior of the protein films depending on the subphase; on water the protein formed a homogeneous film with some globule aggregates, but on buffer a remarkably well-organized monolayer was observed by atomic force microscopy (AFM). Mixtures of globulin 11S and L-DPPC were prepared using both methods for the protein film formation at the air/fluid interface. BAM showed that the mixtures formed coexistence regions between two condensed phases, whose domains of both phases behave like liquids. Fingering phenomena were observed at the interface between protein-rich and L-DPPC-rich domains, which indicates that both phases are fluid. AFM images of the mixtures show the formation of protein- or L-DPPC-rich domains. The liquidlike behavior could be explained due to different sizes of the protein and the L-DPPC, the minority compound in each kind of domain produces defects making them behave as liquids. Interestingly enough, as the monolayer is compressed to higher surface pressure, the lipid molecules are squeezed out and complete separation of the protein and L-DPPC is produced. Furthermore, we present evidence that the protein/L-DPPC mixtures produce films with holes, which might indicate its tendency to form hollow aggregates that could have some relevance in water-channel formation for in vivo seed germination.

Spray drying formulation of hollow spherical aggregates of silica nanoparticles by experimental design

The present work employs an experimental design methodology to optimize the spray-drying production of micron-size hollow aggregates of biocompatible silica nanoparticles that are aimed to serve as drug delivery vehicles in inhaled photodynamic therapy. To effectively deliver the nanoparticles to the lung, the aerodynamic size ( d A) of the nano-aggregates, which is a function of the geometric size ( d G) and the degree of hollowness, must fall within a narrow range between 2 and 4 μm. The results indicate that (1) the feed concentration, (2) the feed pH, and (3) the ratio of the gas atomizing flow rate to the feed rate are the three most significant parameters governing the nano-aggregate morphology. Spray drying at a low pH (<7) and at a low feed concentration (<1%, w/w) generally results in nano-aggregates having small geometric and aerodynamic sizes ( d A = d G ≈ 3 μm) with a relatively monodisperse size distribution. Spray drying at a higher feed concentration produces nano-aggregates having a larger d G but with a multimodal particle size distribution. A trade-off therefore exists between having large d G to improve the aerosolization efficiency and obtaining a uniform particle size distribution to improve the dose uniformity.