Disc-like Particles Research Articles

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4– 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Dynamics Simulation of Self-assembly of Disc-like Nanoparticles

Brownian dynamics of self-assembly of disklike nanoparticles is simulated with a generalized aspherical model using tabulated method of force field parameters. The present model uses the force field of all-atom objects using tabulated table parameters which inherently reflects the specification of shape and component of nanoparticle. We study the self-assembly of disc-like particles. The transition mechanism is analyzed and discussed.

Shape-Tunable Biconcave Disc-Like Polymer Particles by Swelling-Induced Phase Separation of Seeded Particles with Hydrophilic Shells.

Anisotropic shape-tunable polymer particles have gained significant attention for their wide applications, and their performances are usually strongly correlated to their shapes. In contrast to convex particles, the synthesis of highly uniform concave polymer particles remains a great challenge. Here, we present a facile and effective route to synthesize biconcave polystyrene (PS) discs by swelling-induced phase separation of hydrophilically modified PS microspheres and report an unexpected finding that even a tiny amount of hydrophilic units that were incorporated into PS microspheres can significantly change the shape of phase interfaces, resulting in the transformation of disc shapes from convex to flat to concave. This is realized by several typical hydrophilic monomers, such as sodium styrene sulfonate (NaSS), acrylic acid (AA), or (2-(methacryloyloxy)ethyl)trimethylammonium chloride (METAC). The effect of the distribution of hydrophilic units in microspheres was investigated, and the mechanism of shape tuning has been discussed. The curvatures of the bottom surfaces of discs show a strong correlation to the content of hydrophilic units. In particular, we emphasize that the shape control method is general since it does not depend on specific hydrophilic units. This research paves the way for precisely structuring polymer particle shapes, which is important for polymer particles to be used for self-assembly, diffusion, rheology, transport, filler, and many other applications.

Superhydrophilic/air-superoleophobic diatomite porous ceramics for highly-efficient separation of oil-in-water emulsion

Facile, eco-friendly and effective separation of oil-in-water emulsion under various conditions is urgently desired. In this work, novel 3D superhydrophilic/air-superoleophobic diatomite porous ceramics (3DSSPC) with superior separation performance for surfactant-stabilized oil-in-water emulsions were successfully fabricated via a foam gelcasting-freeze drying and subsequent surface modification approach. SiO2 whiskers in-situ generated on the surface of disc-like diatomite particles increased the roughness of the porous ceramics, which, along with the organic film formed on their surface, conferred excellent superhydrophilic and air-superoleophobic properties. The continuous separation efficiency of the 3DSSPC for the surfactant-stabilized edible oil-in-water emulsion (oil concentration of 5 wt%) was higher than 99%, with a flux of 5.06 kg·m−2·s−1 ( 18,200 L·m−2·h−1), more importantly, the separation flux for an industrial oil-in-water emulsion containing suspended particles was as high as 5.69 kg·m−2·s−1 ( 20,500 L·m−2·h−1). In addition, the microstructure, superoleophobicity and separation efficiency of the 3DSSPC changed little even after 20 separation cycles. The good mechanical strength and outstanding chemical stability in strong acidic, alkaline, concentrated salty solutions and at high/low-temperature make the 3DSSPC a promising candidate for future treatments of industrial wastewater containing emulsified oil-in-water liquids.

Hemocompatibility, biodegradability and acute toxicity of acetylated cellulose nanocrystals of different types in comparison

Promotion of promising cellulose nanocrystals (CNC) is largely dependent on the relationship between their morphology, surface chemical composition, and supramolecular structure with toxicity, hemocompatibility, and biodegradability. This paper outlines comparative and integrated analysis of the mentioned biocompatibility aspects of partially acetylated rod-, and disc-lake morphology of CNC with crystalline cellulose allomorphs I and II. These data have also included the study of CNC obtained from the sulfuric acid solutions. The aqueous solution of all types of tested CNC has not been toxic to mice after oral administration. Morphology of internal organs has not changed. However, in case of disc-like particles, the kidney mass coefficient noticeably changed. CNC have neither triggered platelet aggregation nor destroyed the red cell membrane. Intravenous administration to rabbits has not affected the plasma clotting time. Rod-like CNC are more resistant, and the disc-like particles are more susceptible to degradation under the influence of cellulases.

An in situ investigation of the thermal decomposition of metal-organic framework NH2-MIL-125 (Ti)

Abstract Titanium based metal-organic frameworks (MOFs) are interesting self-sacrificial precursors to derive semiconducting porous nanocomposites for highly efficient heterogeneous catalysis. However, there is a lack of systematic and in-depth mechanistic understanding of the pyrolytic conversion of MOF precursors into the desired functional composite materials. In this work, TGA-MS and in situ STEM/EDX combined with other characterization techniques were employed to investigate the evolution of the structural, physicochemical, textural and morphological properties of NH2-MIL-125(Ti) pyrolysis at different temperatures in an inert gaseous atmosphere. In situ thermal analysis of NH2-MIL-125(Ti) reveals the presence of 3 rather defined stages of thermal transformation in the following order: phase-pure, highly porous and crystalline MOF → intermediate amorphous phase without accessible porosity → recrystallized porous phase. The three stages occur from room temperature till 300 °C, between 350 and 550 °C and above ~550 °C respectively. It is found that the framework of NH2-MIL-125(Ti) starts to collapse around 350 °C, accompanied with the cleavage of coordination and covalent bonds between organic linkers [O2C–C6H3(NH2)–CO2]6 and the Ti oxo-cluster Ti8O8(OH)4. The organic linker continues fragmentation at 450 °C causing the shrinkage of particle sizes. The dominant pore size of 0.7 nm for NH2-MIL-125(Ti) gradually expands to 1.4 nm at 800 °C along with the formation of mesopores. The derived disc-like particles exhibit an approximately 35% volume shrinkage compared to the pristine MOF precursor. Highly crystalline N and/or C self-doped TiO2 nanoparticles are homogeneously distributed in the porous carbon matrix. The original 3D tetragonal disc-like morphology of the NH2-MIL-125(Ti) remains preserved in derived N and/or C doped TiO2/C composites. This study will provide an in-depth understanding of the thermal conversion behavior of MOFs to rationally select and design the derived composites for the relevant applications.

Effect of particle shape on bubble dynamics in bubbling fluidized bed

Particle shape can significantly affect the bubble dynamics of bubbling fluidized beds (BFB). In this paper, findings obtained from simulations using CFD-DEM are summarized to discuss the effect of particle shape on bubble dynamics and bubble properties such as bubble size, shape and velocity at a single orifice and uniform fluidized bed. Particles with aspect ratios at 0.5 (oblate), 1 (spherical) and 2 (prolate) are employed to represent disc-like, spherical and rod-like particles, respectively. Both single jet and uniform fluidized bed simulations demonstrate that the bubble forming/rising regions, bubble coalescence locations, and bubble splitting phenomena are significantly influenced by particle shape. The CFD-DEM results for bubble size and bubble velocity show good agreement with literature correlations.

Formation of Colloidal Superstructures of Disc-like Particles Utilizing Hydrogen Bonding Interactions between Steric Stabilizers

The colloidal structure without a template was demonstrated using disc-like polystyrene (PS) particles, which had the colloidal stabilizer only on the lateral side of the discs. Disc-like PS partic...

Solvothermal synthesis of nanoscale disc-like gadolinium doped magnesium zirconate for highly efficient photocatalytic degradation of rhodamine B in water

Highly ordered nanoscale disc-like cubic gadolinium doped magnesium zirconate (Gd:MgZrO3) was synthesized by facile solvothermal route. The reaction time was found to be crucial in determining the final morphology of disc-like Gd:MgZrO3. After studying the particles from time-dependent experiments, it is observed that, the formation of disc-like particles involved a complex process, in which rod-like or agglomerate particles were favorably formed after the initial thermal treatment. Owing to the chemical instability, they would turn into disc-like particles. After calcination, the generated product possessed good photocatalytic performance for the degradation of Rhodamine B (50 mg l−1) under UV light irradiation in contrast to morphologies of Gd:MgZrO3 and other related state-of-the-art photocatalysts (e.g., TiO2, ZnO, WO3, BiVO4, Fe2O3, and g-C3N4). The catalyst could be used for five cycles, maintaining its efficiency above 94.2%. These capacities made the disc-like Gd:MgZrO3 a potential candidate for polluted water treatment. Also, the underlying photocatalysis mechanism of Gd:MgZrO3 was proposed through radical trapping experiments.

Effect of van der Waals force on bubble dynamics in bubbling fluidized beds of ellipsoidal particles

This paper presents a numerical analysis of the combined effect of cohesive van der Waals force and particle shape on bubble dynamics in gas fluidization. The van der Waals force is incorporated into the CFD-DEM model and the magnitude varies from 0 to 20 times Hamaker constant (Ha = 2.1 × 10−21 J), representing non-cohesive to highly cohesive particles. Particles with aspect ratios at 0.5 (oblate), 1 (spherical) and 2 (prolate) are employed to represent disc-like, spherical and rod-like particles, respectively. The results show that under the influence of cohesive force, features such as bubble splitting and coalescence are affected significantly by aspect ratios of ellipsoidal particles. With the increase of Hamaker constant, bubble size and rising velocity decrease, and the bubble shape becomes irregular and vertically oblong. Moreover, the increase of van der Waals force leads to the transformation to non-bubbling fluidization for ellipsoids, but channelling occurs for spheres.

Orientation of spheroidal particles in single jet bubbling fluidized beds

Particle shape has a significant effect on the characteristics of fluidized beds due to the anisotropy of non-spherical particles. In particular, particle shape can affect the bubble dynamics such as bubble size, shape and velocity. However, the relationship between bubble dynamics and the orientation of non-spherical particles is not clear. This paper presents a detailed analysis on orientation of spheroids in a gas-solid fluidized bed operated with a continuous central jet. Spheroids with aspect ratios at 0.5 (oblate) and 2 (prolate) are employed to represent disc-like and rod-like particles, respectively. The results show that the orientation of spheroids is directly related to bubble motion. The orientation evolves with bubble progression and prefers to align in the bed horizontally or vertically depending upon the bubble position. Further, frequency distributions of spheroids orienting parallel/perpendicular with fluid flow direction were analysed in terms of several hydrodynamic parameters such as particle position and velocity, and fluid drag force. The results indicate that spheroids have different orientations depending upon the hydrodynamic parameters. The findings obtained from this study can aid to better understand fluidization dynamics associated with non-spherical particles.

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

ABSTRACTWe study the structure and liquid-crystalline phase behaviour of a model of confined non-convex circular soft-repulsive nanorings in a planar slit geometry using molecular-dynamics simulation. The separation distance between the structureless parallel soft-repulsive walls is made large enough to allow for the formation of a distinct bulk phase in the central region of the box which is in coexistence with the adsorbed fluid thus allowing the analysis of single-wall effects. As the density of the particles is increased, the fluid adsorbs (wets) onto the planar surfaces leading to the formation of well-defined smectic-A layers with a spacing proportional to the diameter of the rings. An analysis of the nematic order parameter at distances perpendicular to the surface reveals that the particles in each layer exhibit anti-nematic behaviour and planar (edge-on) anchoring relative to the short symmetry axis of the rings. This behaviour is in stark contrast to the behaviour observed in convex disc-like particles that have the tendency to form nematic (discotic) structures with homeotropic (face-on) anchoring. The smectic phases formed by nanorings in the bulk and under confinement are characterised by the formation of low-density layered liquid-crystalline states with large voids, referred to here as lacuna smectic phases. In contrast to what is typically found for confined liquid-crystalline systems involving convex particles, no apparent biaxiality is found for nanorings in planar confinement. We argue that formation of the low-density lacuna smectic layers with planar anchoring is a consequence of the non-convex shape of the circular rings that allow for interpenetration between the particles as observed for nanorings under bulk conditions [C. Avendaño, G. Jackson, E.A. Müller and F.A. Escobedo, Proc. Natl. Acad. Sci. U.S.A. 113, 9699 (2016); H.H. Wensink and C. Avendaño, Phys. Rev. E 94, 062704 (2016)].

Scratching a 50-year itch with elongated rods

ABSTRACTThe classical Oseen–Frank theory of liquid crystal elasticity is based on the experimentally verified fact that there are three independent modes of distortion, each with its associated elastic constant. On the other hand, the arguably more first-principles order parameter-based Landau–de Gennes theory only involves two independent elastic modes. The resulting ‘elastic constants problem’ has led to a considerable amount of vexation among theorists. In a series of papers at the turn of the century, Fukuda en Yokoyama suggested that the resolution of this problem could be found in the proper treatment of non-local effects in the ideal part of the free energy. They used an ingenious, but technically complex, technique based on a field-theoretic approach to semi-flexible polymers. Here we revisit their idea but now in the more accessible framework of density functional theory of rigid particles. Our work recovers their main results for rod-like particles, in that generically an ordered assembly of non-interacting rods has three independent elastic constants associated to it that all scale as the square of the length of the particles and obey the inequalities . We also consider the case of disc-like particles, and then find in line with expectations that .

One-pot fabrication of multiporous polymer particles by phase inversion in emulsions

Relatively monodisperse spherical poly(styrene-co-acrylonitrile) (SAN) particles may be prepared using phase inversion from water-in-oil (W/O) to oil-in-water (O/W) emulsions containing water-soluble methyl ethyl ketone (MEK) as the oil phase. In this study, we investigate how mixed solvents containing MEK and water-insoluble methylcyclohexane (MCH) affect the shape of SAN particles produced by the same phase-inversion process. We demonstrate that phase separation between MEK-rich and MCH-rich phases in oil droplets of O/W emulsions occurs during phase inversion and that the state of phase separation is controlled by the MCH:MEK ratio and concentration of SAN. In addition, SAN heterogeneously distribute in the oil droplets of O/W emulsions because SAN is soluble in MEK but not in MCH. We show that the uneven distribution of SAN in the oil droplets produces semispherical, disc-like, and multiporous SAN particles.

Enhanced encapsulation and bioavailability of breviscapine in PLGA microparticles by nanocrystal and water-soluble polymer template techniques

Poly (lactide-co-glycolide) (PLGA) microparticles are widely used for controlled drug delivery. Emulsion methods have been commonly used for preparation of PLGA microparticles, but they usually result in low loading capacity, especially for drugs with poor solubility in organic solvents. In the present study, the nanocrystal technology and a water-soluble polymer template method were used to fabricate nanocrystal-loaded microparticles with improved drug loading and encapsulation efficiency for prolonged delivery of breviscapine. Breviscapine nanocrystals were prepared using a precipitation-ultrasonication method and further loaded into PLGA microparticles by casting in a mold from a water-soluble polymer. The obtained disc-like particles were then characterized and compared with the spherical particles prepared by an emulsion-solvent evaporation method. X-ray powder diffraction (XRPD) and confocal laser scanning microscopy (CLSM) analysis confirmed a highly-dispersed state of breviscapine inside the microparticles. The drug form, loading percentage and fabrication techniques significantly affected the loading capacity and efficiency of breviscapine in PLGA microparticles, and their release performance as well. Drug loading was increased from 2.4% up to 15.3% when both nanocrystal and template methods were applied, and encapsulation efficiency increased from 48.5% to 91.9%. But loading efficiency was reduced as the drug loading was increased. All microparticles showed an initial burst release, and then a slow release period of 28days followed by an erosion-accelerated release phase, which provides a sustained delivery of breviscapine over a month. A relatively stable serum drug level for more than 30days was observed after intramuscular injection of microparticles in rats. Therefore, PLGA microparticles loaded with nanocrystals of poorly soluble drugs provided a promising approach for long-term therapeutic products characterized with preferable in vitro and in vivo performance.

Shear-rate-dependent viscosities of nematic and disc-like particles perfectly aligned in arbitrary relative directions to the shear layer

The shear-rate-dependent viscosity coefficients of hard ellipsoids are derived for arbitrary relative orientations to the shear flow geometry. Each of the nine components of the coefficients scaled by the Newtonian shear viscosity agrees with the previous result for the viscosity in the zero-shear-rate limit. Among the components, the shear viscosity is graphically displayed for nematic ellipsoids with an axis ratio greater than 1 and for disc-like ellipsoids with an axis ratio less than 1 over the whole range of relative orientations of the axis of ellipsoid to the plane shear layer. As the primary axis of the ellipsoid rotates from the x-axis to the y-axis in the x-y plane, the shear viscosity increases or decreases for nematic or disc-like ellipsolids, respectively.

Dual-seeded dispersion polymerization: Effect of different polymerization conditions on the shape of the produced particles

Dual-seeded dispersion polymerization (DSDP) of 2-ethylhexyl methacrylate with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed beads in the presence of saturated hydrocarbon droplets followed by evaporation of the hydrocarbon was studied. The effect of various polymerization conditions including initiator type and content, stabilizer type and concentration, and different hydrocarbon’s content on the shape of the obtained particles was investigated. The increase of concentration of 2,2'-azobis(isobutyronitrile) (AIBN) had no effect on the shape of the produced almond-shell-like PS particles, although it contributes in the formation of associated composite particles along with larger poly(2-ethylhexyl methacrylate) (PEHMA) beads produced by secondary nucleation. The experimental results showed that other initiators led to the formation of stable golf-ball-like PMMA particles as well as PS ones with symmetric shape. The type of stabilizer did not affect the shape of the particles. This observation suggests that unique almond-shelllike PS particles can be produced through a stabilizer-free DSDP process. The lowering of the concentration of hydrocarbons with long alkyl chains yielded stable disc-like PMMA particles. The formation of functional almond-shell-like particles by using light hydrocarbons was another interesting finding of this research.

Size distribution and volume fraction of T1 phase precipitates from TEM images: Direct measurements and related correction

Transmission Electron Microscopy (TEM) can be used to measure the size distribution and volume fraction of fine scale precipitates in metallic systems. However, such measurements suffer from a number of artefacts that need to be accounted for, related to the finite thickness of the TEM foil and to the projected observation in two dimensions of the microstructure. We present a correction procedure to describe the 3D distribution of disc-like particles and apply this method to the plate-like T1 precipitates in an Al–Li–Cu alloy in two ageing conditions showing different particle morphologies. The precipitates were imaged in a High-Angular Annular Dark Field Microscope (HAADF-STEM). The corrected size distribution is further used to determine the precipitate volume fraction. Atom probe tomography (APT) is finally utilised as an alternative way to measure the precipitate volume fraction and test the validity of the electron microscopy results.

Towards a Mechanistic Understanding of Cellular Uptake

Budding of cell membranes initiates intracellular vesicle transport and has been studied for a variety of soft matter systems. Using a continuum model, we study wrapping of a single nano-particle as an interplay of the membrane deformation energy and the adhesion energy between particle and membrane. With the help of numerical energy minimization using triangulated surfaces, we investigate the role of shape and size of the particle as well as of the membrane's elastic parameters on nano-particle wrapping.For rod-like and disc-like particles, we find a higher binding-affinity to the membrane compared with spherical particles. However, such particles have a lower uptake to cells, as confirmed by experiments. All more complex particle shapes, such as a Hauser's cube and supereggs, have stable partially-wrapped states with shallow and high wrapping fractions for sufficiently high adhesion strengths. Partially-wrapped particles can be advantageous both from an application point of view as well as from a biological point of view. Rod-like particles, for example filamentous-viruses like Ebola and Marburg, preferentially bud in tip-first orientation.Similarly, a mechanistic understanding of how the malarial merozoite invades the erythrocyte is lacking. Assuming an asymmetric egg-like shape for the parasite, we have investigated the role of the membrane properties for the invasion mechanism. We propose a concentration gradient of adhesive molecules to be responsible for reorientation of the merozoite towards the tip before invasion and membrane spontaneous curvature from cytoskeletal re-modelling or secretion of unstructured membranes to assist motor forces for the parasite to invade a red blood cell.

Orientation dynamics of small, triaxial–ellipsoidal particles in isotropic turbulence

AbstractThe orientation dynamics of small anisotropic tracer particles in turbulent flows is studied using direct numerical simulation (DNS) and results are compared with Lagrangian stochastic models. Generalizing earlier analysis for axisymmetric ellipsoidal particles (Parsa et al., Phys. Rev. Lett., vol. 109, 2012, 134501), we measure the orientation statistics and rotation rates of general, triaxial–ellipsoidal tracer particles using Lagrangian tracking in DNS of isotropic turbulence. Triaxial ellipsoids that are very long in one direction, very thin in another and of intermediate size in the third direction exhibit reduced rotation rates that are similar to those of rods in the ellipsoid’s longest direction, while exhibiting increased rotation rates that are similar to those of axisymmetric discs in the thinnest direction. DNS results differ significantly from the case when the particle orientations are assumed to be statistically independent from the velocity gradient tensor. They are also different from predictions of a Gaussian process for the velocity gradient tensor, which does not provide realistic preferred vorticity–strain-rate tensor alignments. DNS results are also compared with a stochastic model for the velocity gradient tensor based on the recent fluid deformation approximation (RFDA). Unlike the Gaussian model, the stochastic model accurately predicts the reduction in rotation rate in the longest direction of triaxial ellipsoids since this direction aligns with the flow’s vorticity, with its rotation perpendicular to the vorticity being reduced. For disc-like particles, or in directions perpendicular to the longest direction in triaxial particles, the model predicts noticeably smaller rotation rates than those observed in DNS, a behaviour that can be understood based on the probability of vorticity orientation with the most contracting strain-rate eigendirection in the model.