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Shi-yow Lin - One of the best experts on this subject based on the ideXlab platform.

  • the impalement of water drops impinging onto hydrophobic superhydrophobic graphite surfaces the role of dynamic pressure hammer pressure and liquid Penetration Time
    Applied Surface Science, 2014
    Co-Authors: Paola G. Pittoni, Ya-chi Lin, Shi-yow Lin
    Abstract:

    Abstract Droplet impingement experiments at low Weber numbers were conducted by digitizing silhouettes of impacting water drops onto unlike graphite substrates, typified by different advancing water contact angles ( θ a ): 140 and 160°. The relaxation of wetting diameter, dynamic contact angle, and drop shapes were measured. The purpose was to carefully investigate the phenomenology and possible causes of the failure of the superhydrophobicity. During impact and spreading phases, all the drops impinging onto both graphite substrates showed a similar behavior. Then, after an initial free recoil, drops impinging at lower impact velocities onto graphite substrates characterized by θ a  = 140° clearly exhibited Time intervals in which the wetting diameter appeared to be almost constant. The duration of this pinned phase was observed decreasing with increasing the impact height and almost completely disappearing for drops impinging at higher impact velocities. This behavior has never been reported before, and, contrariwise, water droplets impinging at lower impact velocities onto hydrophobic and superhydrophobic surfaces have been generally observed more freely retracting, and ultimately rebounding, compared to drops impacting at higher velocities. In the present study, this latter behavior was recorded just for drops impinging onto graphite surfaces characterized by θ a  = 160°. A theoretical description of the experimental results was proposed, specifically investigating the role of dynamic pressure, hammer pressure and liquid Penetration Time during the impact, spreading and recoil stages.

  • The impalement of water drops impinging onto hydrophobic/superhydrophobic graphite surfaces: the role of dynamic pressure, hammer pressure and liquid Penetration Time
    Applied Surface Science, 2014
    Co-Authors: Paola G. Pittoni, Ya-chi Lin, Shi-yow Lin
    Abstract:

    Abstract Droplet impingement experiments at low Weber numbers were conducted by digitizing silhouettes of impacting water drops onto unlike graphite substrates, typified by different advancing water contact angles ( θ a ): 140 and 160°. The relaxation of wetting diameter, dynamic contact angle, and drop shapes were measured. The purpose was to carefully investigate the phenomenology and possible causes of the failure of the superhydrophobicity. During impact and spreading phases, all the drops impinging onto both graphite substrates showed a similar behavior. Then, after an initial free recoil, drops impinging at lower impact velocities onto graphite substrates characterized by θ a  = 140° clearly exhibited Time intervals in which the wetting diameter appeared to be almost constant. The duration of this pinned phase was observed decreasing with increasing the impact height and almost completely disappearing for drops impinging at higher impact velocities. This behavior has never been reported before, and, contrariwise, water droplets impinging at lower impact velocities onto hydrophobic and superhydrophobic surfaces have been generally observed more freely retracting, and ultimately rebounding, compared to drops impacting at higher velocities. In the present study, this latter behavior was recorded just for drops impinging onto graphite surfaces characterized by θ a  = 160°. A theoretical description of the experimental results was proposed, specifically investigating the role of dynamic pressure, hammer pressure and liquid Penetration Time during the impact, spreading and recoil stages.

Karen Hapgood - One of the best experts on this subject based on the ideXlab platform.

  • Percolation Concentration Threshold: Connecting the Murky Region between Hydrophilic and Hydrophobic Wet Granulation
    2010
    Co-Authors: Thanh Nguyen, Wei Shen, Karen Hapgood
    Abstract:

    Wet granulation is the agglomeration of particles, encouraged by agitation forces and the addition of a liquid binder. Although wet granulation is seemingly a simplistic process, complex interactions between heterogeneous-wetting particles can exist. This is of great concern to the pharmaceutical industry in achieving content uniformity in tablets, especially for hydrophobic drugs. Much is known about hydrophilic or hydrophobic granulation, but a murky region remains in between. The objective of this research is to understand heterogeneous-wetting granulation. A formulation consisting of lactose (hydrophilic) and salicylic acid (hydrophobic) powders, in varying concentrations, was investigated. Single drop nucleation experiments examined the droplet/powder interaction through the drop Penetration Time, while wet granulation and sieve fraction assays were performed to examine the drug distribution. The drop Penetration Time showed that hydrophobic components significantly affects the formulation wettability, even at low concentrations ( 10wt%). The drop Penetration Time also undergoes a steep increase at a critical hydrophobic concentration, which was defined as the concentration threshold, pc, and marks the boundary between hydrophilic and hydrophobic behaviour. Wet granulation experiments revealed that the drug distribution is more uniform for good (θ < 90 ) or transitional wetting (θ ≈ 90 ) formulations, while hydrophobic formulations resulted in poor drug distribution. Hence there is a correlation between the concentration threshold and the drug distribution, demonstrating the importance of the concentration threshold in defining the granulation wetting behaviour and the drug distribution uniformity. The percolation concentration threshold is anticipated to help bridge the gap between hydrophilic and hydrophobic granulation.

  • Drop Penetration Time in heterogeneous powder beds
    Chemical Engineering Science, 2009
    Co-Authors: Thanh Nguyen, Wei Shen, Karen Hapgood
    Abstract:

    Abstract Wet granulation is a technique in which enlarged particles or ‘granules’ are produced from the coalescence of fine particles, with the intention of improving the powder properties. High shear granulators are often used to carry out the granulation process where the powder mass is agitated in a vessel by mechanical means while liquid is sprayed from above onto the powder bed surface. When the binder droplets impact the powder surface, the drop Penetration Time of the droplet into the powder is important for uniform binder dispersion and the prediction of the formation of granule nuclei from the nucleation map, which depends on the dimensionless spray flux. Previous studies on the drop Penetration Time were carried out on predominantly hydrophilic powder beds. Although this gives a good prediction of the nucleation behaviour in granulation, it does not reflect the condition where hydrophobic drugs are used in the formulation without surfactants. This paper aims to look at the effects of powder bed hydrophobicity on the drop Penetration Time. Single drop nucleation experiments using a syringe and a small powder bed were carried out on varying ratios of salicylic acid and lactose powders to study the kinetic of drop Penetration. As expected, the drop Penetration Time increased as the proportion of hydrophobic component increased in the powder mixture. However, long drop Penetration Times were observed for low degrees of drug loading, showing that hydrophobicity strongly influences the drop Penetration Time. The wettability of the powder mixture also has a pronounced affect on the granule properties in which the hydrophobicity of the powder mixture is proportional to the granule strength and inversely proportional to the granule size. These findings have important implications in terms of the design of the granulation process where conditions of minimum spray flux or efficient mechanical forces are recommended to produce a more uniform granulation batch.

  • A method to predict nuclei size distributions for use in models of wet granulation
    Advanced Powder Technology, 2009
    Co-Authors: Karen Hapgood, Melvin X.l. Tan, Darren W.y. Chow
    Abstract:

    Abstract Models of granulation and agglomeration are becoming more sophisticated and accurate, but nucleation is poorly understood. Models of granulation processes typically either use simplistic nucleation assumptions; complex multi-phase simulations or deliberately focus on the final granulation stages only. Here, we validate a simple method to generate nuclei size distributions using the dimensionless spray flux parameter, for future use in granulation models in the drop controlled regime. Dimensionless spray flux describes the spray density in the spray zone, which is closely related to the Poisson distribution. A simple model to estimate the nuclei size distribution at a range of spray flux conditions was compared with data generated in a previous study. The simulations were in reasonable agreement with experimental data at low Penetration Time and low spray flux ( Ψ a 0.5. For a longer Penetration Time system, the simulations and experimental results agreed up to Ψ a  = 0.5. Multi-modal experimental results could not be modeled. Spray flux derived models of nuclei size distributions are useful nucleation granulation models, provided that the simulations are restricted to the drop controlled regime ( Ψ a

  • Foam and drop Penetration kinetics into loosely packed powder beds
    Chemical Engineering Science, 2009
    Co-Authors: Melvin X.l. Tan, Ling Shyong Wong, Kwan Hoe Lum, Karen Hapgood
    Abstract:

    Abstract Foam granulation is a new liquid delivery method for wet granulation, where the liquid binder is delivered as an aqueous foam, rather than as an atomised spray to the powder bed. This paper reports for the first Time the similarities and differences between wet granulation via foamed and sprayed binder addition methods. The kinetics of single foam and single drop (of HPC and HPMC solutions) Penetrations into loosely packed powder beds (of glass ballotini and lactose powders) were studied. Specific Penetration Time (defined as Penetration Time per unit of binder mass) and nucleation ratio (defined as the ratio of nuclei granule mass to liquid binder mass) were compared between foam and drop nucleation methods. The impact of particle size and binder concentration on both parameters was also studied. The results indicate that the foamed binder addition method allows a greater mass of binder fluid to be absorbed into the particle bed and uses less liquid binder to nucleate the same number of gram of powder, which indicates improved nucleation efficiency compared to the drop addition method.

  • Foam Granulation: Comparison of Nucleation via Drops and Foams
    2008
    Co-Authors: Melvin X.l. Tan, Ling Shyong Wong, Kwan Hoe Lum, Karen Hapgood
    Abstract:

    A new approach to wet granulation process has been developed, where the liquid binder is delivered to the powder bed as an aqueous foam rather than as an atomised spray. This paper compares nucleation of powder between foamed and sprayed binder addition methods. Nucleation behaviours of several grades of glass ballotini and lactose powder via HPC and HPMC foamed solutions were studied and compared with the nucleation via single drops of the same fluids. Specific Penetration Time (Penetration Time per unit mass of liquid drop or foam) and nucleation ratio (ratio of mass of nucleus to mass of liquid binder) for both foam and drop addition methods were compared. The effects of powder particle size and liquid binder concentration on both parameters were examined. Some powder-fluid combinations showed faster specific Penetration Times for foam, while for others liquid drops were faster. Using a less viscous foamed liquid binder and/or a larger particle size of powder creates a larger final nucleus size. The study of nucleation ratio suggests that foam addition method provides better liquid distribution efficiency and uses less liquid binder to nucleate the same number of grams of powder.

Xuechao Cao - One of the best experts on this subject based on the ideXlab platform.

Paola G. Pittoni - One of the best experts on this subject based on the ideXlab platform.

  • the impalement of water drops impinging onto hydrophobic superhydrophobic graphite surfaces the role of dynamic pressure hammer pressure and liquid Penetration Time
    Applied Surface Science, 2014
    Co-Authors: Paola G. Pittoni, Ya-chi Lin, Shi-yow Lin
    Abstract:

    Abstract Droplet impingement experiments at low Weber numbers were conducted by digitizing silhouettes of impacting water drops onto unlike graphite substrates, typified by different advancing water contact angles ( θ a ): 140 and 160°. The relaxation of wetting diameter, dynamic contact angle, and drop shapes were measured. The purpose was to carefully investigate the phenomenology and possible causes of the failure of the superhydrophobicity. During impact and spreading phases, all the drops impinging onto both graphite substrates showed a similar behavior. Then, after an initial free recoil, drops impinging at lower impact velocities onto graphite substrates characterized by θ a  = 140° clearly exhibited Time intervals in which the wetting diameter appeared to be almost constant. The duration of this pinned phase was observed decreasing with increasing the impact height and almost completely disappearing for drops impinging at higher impact velocities. This behavior has never been reported before, and, contrariwise, water droplets impinging at lower impact velocities onto hydrophobic and superhydrophobic surfaces have been generally observed more freely retracting, and ultimately rebounding, compared to drops impacting at higher velocities. In the present study, this latter behavior was recorded just for drops impinging onto graphite surfaces characterized by θ a  = 160°. A theoretical description of the experimental results was proposed, specifically investigating the role of dynamic pressure, hammer pressure and liquid Penetration Time during the impact, spreading and recoil stages.

  • The impalement of water drops impinging onto hydrophobic/superhydrophobic graphite surfaces: the role of dynamic pressure, hammer pressure and liquid Penetration Time
    Applied Surface Science, 2014
    Co-Authors: Paola G. Pittoni, Ya-chi Lin, Shi-yow Lin
    Abstract:

    Abstract Droplet impingement experiments at low Weber numbers were conducted by digitizing silhouettes of impacting water drops onto unlike graphite substrates, typified by different advancing water contact angles ( θ a ): 140 and 160°. The relaxation of wetting diameter, dynamic contact angle, and drop shapes were measured. The purpose was to carefully investigate the phenomenology and possible causes of the failure of the superhydrophobicity. During impact and spreading phases, all the drops impinging onto both graphite substrates showed a similar behavior. Then, after an initial free recoil, drops impinging at lower impact velocities onto graphite substrates characterized by θ a  = 140° clearly exhibited Time intervals in which the wetting diameter appeared to be almost constant. The duration of this pinned phase was observed decreasing with increasing the impact height and almost completely disappearing for drops impinging at higher impact velocities. This behavior has never been reported before, and, contrariwise, water droplets impinging at lower impact velocities onto hydrophobic and superhydrophobic surfaces have been generally observed more freely retracting, and ultimately rebounding, compared to drops impacting at higher velocities. In the present study, this latter behavior was recorded just for drops impinging onto graphite surfaces characterized by θ a  = 160°. A theoretical description of the experimental results was proposed, specifically investigating the role of dynamic pressure, hammer pressure and liquid Penetration Time during the impact, spreading and recoil stages.

Zhonghou Shen - One of the best experts on this subject based on the ideXlab platform.