Drying of foam under microgravity conditions

Foams have recently been characterised as ideal products for pharmaceutical and topical use applications for the delivery of topical active agents. Foams are usually produced in a wet form but in a number of applications moderately dry foams are required. Drying of foam under terrestrial conditions proceeds under the action of gravity, which is impossible under microgravity condition. Below a new method of drying foams under microgravity condition is suggested. According to this method foam should be placed on a porous support, which will absorb the liquid from foam based on capillary forces only. The final liquid content inside the foam can be achieved by a proper selection of the porous support. The suggested method allows drying foams under microgravity conditions. Interaction of foams with porous support under terrestrial conditions was developed only recently and theoretically investigated (Arjmandi-Tash, O.; Kovalchuk, N.; Trybala, A.; Starov, V. Foam Drainage Placed on a Porous Substrate. Soft Matter2015, 11 (18), 3643–3652) followed by a theory of foam drainage on thin porous substrates (Koursari, N.; Arjmandi-Tash, O.; Johnson, P.; Trybala, A.; Starov, M. V. Foam Drainage Placed on Thin Porous Substrate. Soft Matter, 2019, (submitted)), where rate of drainage, radius of the wetted area inside the porous layer and other characteristics of the process were predicted. The latter model is modified below to investigate foam drying under microgravity conditions. Model predictions are compared with experimental observations for foam created using Triton X-100 at concentrations above CMC. Wetted radius inside the porous substrate was measured and results were compered to model predictions. Experimental observations for spreading area versus time show reasonable agreement with theoretical predictions for all investigated systems

Kinetics of Wetting and Spreading of Droplets over Various Substrates

There has been a substantial increase in the number of publications in the field of wetting and spreading since 2010. This increase in the rate of publications can be attributed to the broader application of wetting phenomena in new areas. It is impossible to review such a huge number of publications; that is, some topics in the field of wetting and spreading are selected to be discussed below. These topics are as follows: (i) Contact angle hysteresis on smooth homogeneous solid surfaces via disjoining/conjoining pressure. It is shown that the hysteresis contact angles can be calculated via disjoining/conjoining pressure. The theory indicates that the equilibrium contact angle is closer to a static receding contact angle than to a static advancing contact angle. (ii) The wetting of deformable substrates, which is caused by surface forces action in the vicinity of the apparent three-phase contact line, leading to a deformation on the substrate. (iii) The kinetics of wetting and spreading of non-Newtonian liquid (blood) over porous substrates. We showed that in spite of the enormous complexity of blood, the spreading over porous substrate can be described using a relatively simple model: a power low-shear-thinning non-Newtonian liquid. (iv) The kinetics of spreading of surfactant solutions. In this part, new results related to various surfactant solution mixtures (synergy and crystallization) are discussed, which shows some possible direction for the future revealing of superspreading phenomena. (v) The kinetics of spreading of surfactant solutions over hair. Fundamental problems to be solved are identified

Foams built up by non-Newtonian polymeric solutions: Free drainage

A mathematical model of free drainage of foam built up by a power-law non-Newtonian liquid is developed. The theory predictions are compared with the experimental data on the drainage of foams formed using commercially available Aculyn™22 and Aculyn™33 polymeric solutions. The rheological parameters of the polymeric solutions were independently measured and used in the calculations. The deduced dimensionless equations were solved using finite element method with appropriate boundary conditions. The numerical simulations show that the decrease in the foam height and liquid content is very fast in the very beginning of the drainage; however, it reaches a steady state at longer time. The predicted values of the time evolution of the foam height and liquid content are in good agreement with the measured experimental data

A novel method for the analysis of particle coating behaviour via contact spreading in a tumbling drum: Effect of coating liquid viscosity

Spray coating is a common method of distributing liquids over powders, especially in the pharmaceutical, detergent and food industries. During this process, liquid drops are deposited on the surface of particles. Liquid is then transferred between particles via particle collisions, in a process called liquid contact spreading. This contact spreading process facilitates inter-particle coating, in which wetting, de-wetting, mixing and drying are occurring simultaneously. This work presents the first experimental study of the mechanism of liquid contact spreading. In this work, a novel experimental method has been developed to investigate the mechanism of contact spreading, incorporating a newly developed image analysis technique, based on colourimetric measurements, to quantitatively determine coating behaviour via contact spreading. Here, experiments designed to isolate the contact spreading coating mechanism were performed in a tumbling drum using a model material system; alumina particles and dyed polyethylene glycol solutions of varying viscosities. The coating uniformity was quantified by the variation in inter-particle coating; the coefficient of variation (CoV). For all systems, the uniformity of the coating increased with time until the CoV decreased to an asymptotic value. The rate of the decrease in the CoV was successfully fitted using an exponential decay function. The viscosity of the coating solution had a significant effect on the rate of liquid transfer; the lower the viscosity the faster the contact spreading process. This effect is attributed to differences in the formation and stability of liquid bridges between the particles, influencing the extent of liquid transfer. The results also show that in most cases examined here, viscous forces play a main role in the contact spreading process, and the contribution of capillary forces are minimal. This understanding could assist the design and scale up for the wet coating processes

Mechanistic modelling of spherical agglomeration processes

Spherical agglomeration is emerging as an important unit process for pharmaceutical manufacturing. However, at present, quantitative process design to control agglomerate attributes is impossible. A new population balance model to predict agglomerate attributes is presented where for the first time, all of the key rate processes that control agglomerate properties are included. A parameter sensitivity analysis is undertaken to study the effect of process parameters on agglomerate attributes. Bridging liquid droplet size and bridging liquid to solids ratio (BSR) are critical controlling parameters. Good quality agglomerates are formed over a relatively narrow range of BSR. Within this range, bridging liquid droplet size can be used to tune agglomerate size. Primary crystal size and process mixing intensity have only a modest effect on equilibrium agglomerate attributes but do impact agglomerate formation kinetics. This new model provides the basis for improved process understanding and quantitative process design of spherical agglomeration

Interaction of foam with a porous medium: Theory and calculations

A new theory of foam drainage in the presence of a porous support was introduced and accordingly, a mathematical model which combines the foam drainage equation with the equation describing imbibition into the porous substrate was developed. Proposed dimensionless equations were solved using finite element method. Boundary conditions were zero liquid flux on the top of the foam and continuity of flux on foam/substrate interface. It was found that the kinetics of foam drainage depends on three dimensionless numbers. The result indicated that there are two possible scenarios for the interaction of foam with a porous substrate: (i) a rapid imbibition, the liquid volume fraction at the bottom of the foam is a decreasing function of time. In this regime the imbibition into the porous substrate dominates and it is faster as compared with the foam drainage; (ii) a slow imbibition, the liquid volume fraction at the interface experiences a peak point and imbibition into the porous substrate is slower for some time as compared with the foam drainage

Integrated continuous process design for crystallisation, spherical agglomeration, and filtration of lovastatin

Purpose This work seeks to improve the particle processability of needle-like lovastatin crystals and develop a small-footprint continuous MicroFactory for its production. Methods General conditions for optimal spherical agglomeration of lovastatin crystals and subsequent product isolation are developed, first as batch processes, and then transferred to continuous MicroFactory operation. Results Methyl isobutyl ketone is a suitable bridging liquid for the spherical agglomeration of lovastatin. Practical challenges including coupling unit operations and solvent systems; mismatched flow rates and inconsistent suspension solid loading were resolved. The successful continuous production of lovastatin spherical agglomerates (D50 = 336 µm) was achieved. Spherical agglomeration increased the density of the bulk lovastatin powder and improved product flowability from poor to good, whilst maintaining lovastatin tablet performance. Conclusion A continuous, integrated MicroFactory for the crystallisation, spherical agglomeration, and filtration of lovastatin is presented with improved product particle processability. Up to 16,800 doses of lovastatin (60 mg) can be produced per day using a footprint of 23 m2

Interaction of foam with a porous medium: Theory and calculations

Closed accessA new theory of foam drainage in the presence of a porous support was introduced and accordingly, a mathematical model which combines the foam drainage equation with the equation describing imbibition into the porous substrate was developed. Proposed dimensionless equations were solved using finite element method. Boundary conditions were zero liquid flux on the top of the foam and continuity of flux on foam/substrate interface. It was found that the kinetics of foam drainage depends on three dimensionless numbers. The result indicated that there are two possible scenarios for the interaction of foam with a porous substrate: (i) a rapid imbibition, the liquid volume fraction at the bottom of the foam is a decreasing function of time. In this regime the imbibition into the porous substrate dominates and it is faster as compared with the foam drainage; (ii) a slow imbibition, the liquid volume fraction at the interface experiences a peak point and imbibition into the porous substrate is slower for some time as compared with the foam drainage