Leon Gradoń

Control of the morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol.

The control of the morphology of nanostructured particles prepared by the spray drying of nanoparticle sol was investigated experimentally and the results are qualitatively explained based on available theory. A theoretical analysis indicates that the structural stability of the droplet and the hydrodynamic effects during the drying process play important roles in controlling the morphology of the resulting particles. The size of the sol in the droplet, droplet size, viscosity of droplet, drying temperature, gas flow rate, and addition of surfactant are all crucial parameters that affect the morphology of particles. Experimentally, nanostructured silica particles were prepared from a nanosize silica sol under various preparation conditions. Doughnut-shaped particles can be produced when the droplet size is large, in conjunction with high temperature, high gas flow rate and in the presence of an added surfactant. Appropriate choice of the spray drying method permits control of the particle size and shape, ranging from spheres to ellipsoids as well as doughnut-shaped particles by varying the preparation conditions. The results open a new route to controlling the formation of a wide variety of nanostructured particles.

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.

Deposition of inhaled aerosol particles in a generation of the tracheobronchial tree

Abstract An equation for the diffusion and convection of aerosol particles in the three-dimensional space of the tracheobronchial tree bifurcation has been solved. A geometric model of a bifurcation of the tracheobronchial tree and the results of computations of the stationary air velocity field in such a system have been used. Values of the local deposition fluxes of aerosol particles have been obtained. Localization of the so-called ‘hot spots’ in the bifurcation has been established.

Lattice-Boltzmann approach for description of the structure of deposited particulate matter in fibrous filters

Abstract The rational design of filtration process should be based on reliable predictions of the dependence on the effluent concentration and on the pressure drop variations with time for a given set of the operating conditions, i.e. particle concentration and size, filter packing density, size of filter element, gas velocity, etc. The pattern of filling of the internal space with the porous structure of fibrous filters strongly influences the behavior of the filter at the stage of non-steady-state filtration. The cellular automata probabilistic model extended to the lattice-Boltzmann approach was used for description of the local structures of deposited particles forming clusters on the surface of a single fibre of the filter. The fractal dimension of deposited structure and its local porosity were calculated for the Peclet number ranging from 0.5 to10. The results of calculations show that deposits, for which diffusion is a controlling mechanism of deposition, have higher fractal dimension, are strongly branched and are distributed around the filter fibre. Deposits obtained for the conditions related to the higher Peclet numbers are situated at the front of the fibre and are more regular than those obtained for diffusion-controlled deposition. The pressure drop of the aerosol flow through a loaded fibre increases more rapidly, during loading, for diffusion-controlled deposition than that for the higher contribution of convection during the deposition process.

Deposition and Filtration of Nanoparticles in the Composites of Nano- and Microsized Fibers

Filtration of aerosol particles using composites of nano- and microsized fibrous structures is a promising method of effective separation of nanoparticles from gases. The multiscale physical system describing the flow pattern and particles deposition in it requires other than a continuous approach for the process analysis. The lattice-Boltzmann method was used for the calculation of deposition efficiency on nanosized particles for the system consisting of two nano- and microsized fibers. The proposed method allows to calculate the deposition efficiency of nanoparticles on both fibers for a very wide range of Knudsen numbers in the case of each nanofiber considering molecular, slip, and continuous flow patterns. The nanofiber is a significant attractor for collecting particles as an element of multiscale fibers of the filtration composite. The results of particle deposition efficiency calculated for the microfiber, using proposed method, are similar to those obtained from the classical continuum approach (Filippova and Hanel 1997; Przekop et al. 2003). The proposed model was extended to calculate the performance of bilayer filter structures consisting of a nanofibrous front layer and a microfibrous backing layer of the filter. Filtration efficiency, pressure drop and quality factors for uniform and non-uniform distributions of nanofibers in the front filter layer were calculated for a wide range of Knudsen and Peclet numbers.

Temporary and spatial deposition of aerosol particles in the upper human airways during breathing cycle

The k–e model was used to describe of airflow structure in the sequence of the two first bifurcations of the human respiratory system. Local and temporary distributions of the linear air velocity were calculated for a cyclic breathing pattern corresponding to symmetrical hyperventilation with spontaneous deep breathing. For such a flow, deposition efficiency of particles with diameters of 0.01, 0.1, 1 and was calculated using particle trajectories including random displacement of particles due to the Brownian motion. For each type of particles, the “hot spots” of deposition were identified. A specific temporary deposition pattern during breathing cycle was found. The enhancement of deposition was observed at the moment of transition between inspiratory and expiratory parts of the breathing curve.

Production of morphology-controllable porous hyaluronic acid particles using a spray-drying method

Hyaluronic acid (HA) porous particles with controllable porosity and pore size, ranging from 100 to 300 nm, were successfully prepared using a colloidal templating and spray-drying method. HA powder and polystyrene latex (PSL) particles, which were used as the precursor and templating agent, respectively, were mixed in aqueous solution and spray-dried using a two-fluid nozzle system to produce HA and PSL composite particles. Water was evaporated during spray-drying using heated air with a temperature of 120 degrees C. This simple process was completed within several seconds. The prepared particles were collected and washed with an organic solvent to dissolve the PSL templating agent. The porosity and pore size of the resulting particles were easily controlled by changing the initial mass ratio of precursor to templating agent, i.e., HA to PSL, and by altering the size of the PSL template particles.

Dynamics of Oropharyngeal Aerosol Transport and Deposition With the Realistic Flow Pattern

Aerosol flow and deposition in the model of human oropharynx was studied theoretically and experimentally for two realistic inspiratory patterns. The three-dimensional (3D) airflow structure in the sample geometry was solved with the computational fluid dynamics (CFD) code (Fluent), used to calculate dynamic distribution of particle deposition (0.3–10 μm). Experiments were done for the same flow conditions using the silicone-rubber cast with the matching geometry. Nonsteady breathing flows were reproduced with the computer-controlled artificial lung apparatus. Results of computations show that particles smaller than 3 μm easily pass the oropharynx during inspiration, while particles with a size close to 10 μm are substantially deposited, preferentially in the region of the naso-pharyngeal bend. For particles in the submicrometer size range, the spatial and temporal deposition pattern is more complicated, and strongly depends on breathing dynamics. The experiments confirmed that the mass median diameter (MMD) of the aerosol that penetrates the oropharynx and flows to the tracheobronchial tree is reduced. Measured total mass efficiency of deposition of the tested aerosol was in the range of 35–60%, depending on the breathing pattern. These findings are consistent with the CFD results. The methods and the preliminary results enable a more realistic analysis of dynamic effects during the flow of inhaled particles through the complex geometry of the oropharynx. Such analysis is needed for estimation of toxic potential of aerosols, related to their local deposition in different parts of the respiratory tract.

Hydrodynamical model of pulmonary clearance

The theoretical description of the behaviour of a thin liquid film covered with a monomolecular surfactant layer is presented. This film is subjected to oscillatory compressions and tensions. It follows from the solution of this model that a net outflow of liquid from the film takes place. The size of this outflow has been estimated for variable parameters of the model. The optimum value of the displacement as a function of the Ma/Re Sc factor has been found. The model was adapted to the phenomenon of alveoli clearance.

Diffusional Particle Deposition in the Human Nose and Mouth

Human nose and mouth serve as an effective filter for particles inhaled into the lung. For sufficiently small particles, particle loss to the wall surface of the air pathways is expected to be significant owing to the presence of strong Brownian diffusion. In this paper, we present the filtration results of ultrafine particles obtained from a simulation experiment in a cast of human oropharynx. It was found from the convective diffusion process that at normal breathing rate the inspiratory deposition efficiency of particles of diameter 0.001 μm in nose and mouth is 28.5% and 16.5%, respectively. These deposition fractions rapidly decrease to 0.1% and 0.05% for particles of diameter 0.1 μm.