Applications of the Atomic Force Microscope in the Development of                    Propellant-based Inhalation Formulations

Wu, Libo; Rocha, Sandro R. P. da

doi:10.14356/kona.2008011

Cited by 5 publications

(10 citation statements)

References 83 publications

(292 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Experiments must be designed to reflect the heterogeneous character of the passivated nanoparticle surfaces. The use of atomic force microscopy, as suggested recently by a research group, 53 promises to yield more reliable criteria.…”

Section: Reasons For Effectiveness Of Ethane Over Comentioning

confidence: 99%

Understanding the Relative Effectiveness of Alkanethiol Ligands in Dispersing Nanoparticles in Supercritical Carbon Dioxide and Ethane

2010

View full text Add to dashboard Cite

There is considerable interest in developing a nonfluorous capping ligand that is effective in dispersing nanoparticles in supercritical carbon dioxide. To augment the experimental search for such a molecule, a simulation protocol is developed, involving atomistic molecular dynamics simulations, which captures the relevant physical phenomena related to the effectiveness of capping ligands in stabilizing nanoparticle dispersions, evidenced by a consistency with empirical observation. The method is used to determine why the cheap and benign alkanethiol ligands are effective in supercritical ethane and several organic solvents but not in supercritical CO 2 at convenient conditions of temperature and pressure; n-dodecanethiol is used as the representative ligand. We conclude that the ineffectiveness of the alkanethiol ligands in CO 2 is primarily because they cannot compensate for the quadrupolar interactions which account for a substantial portion of the cohesive energy of bulk CO 2 , which is lost to the CO 2 molecules when transitioning from bulk solvent to the confined region between approaching nanoparticles, thus reducing the degree of osmotic repulsion. Ethane, which largely lacks significant electrostatic interactions, is adequately compensated for transitioning into the confinement by surface dispersion interactions. Hence, ligands that would be more effective in stabilizing nanoparticle dispersions in supercritical CO 2 should interact with CO 2 not only via dispersion interactions but also via its quadrupole. We find that the solvent does not penetrate the densely packed ligandpassivation layer at the nanoparticle surface, and solvent interacts only with the ligand tips. Hence, experiments intended to screen for effective ligands should probe ligand behavior not in an isotropic bulk system but in heterogeneous conditions similar to the ligand-solvent interface.

show abstract

Section: Reasons For Effectiveness Of Ethane Over Comentioning

confidence: 99%

Understanding the Relative Effectiveness of Alkanethiol Ligands in Dispersing Nanoparticles in Supercritical Carbon Dioxide and Ethane

2010

View full text Add to dashboard Cite

show abstract

“…CFM is a variation of Atomic Force Microscopy (AFM) that utilizes functionalized tips and substrates to determine the cohesive forces ( F ad ) between chemical groups [29] . The chemical modification on the surfaces can be performed by self‐assembled monolayers (SAMs) of covalently attached organosilanes [15,24] . SAMs of a large enough number of carbons in the tail group are expected to be highly oriented and ordered upon deposition, irrespective of the functional groups at the end of the monolayer [48] .…”

Section: Resultsmentioning

confidence: 99%

“…W tms was estimated based on individual interfacial free energies between the modified tip and the medium γ tm , that between the substrate and the medium ( γ tm ), and that between the modified substrate and tip ( γ st ) [15] –: …”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…To overcome solubility limitations, the industry has resorted to a large extent to the use of cosolvents, especially ethanol, [12] not only as solubility enhancer for drugs in the development of solution formulations, but also as solubility enhancer for other excipients, for both solution and suspension formulations [12,15] . However, there are also many issues surrounding the use of ethanol [1,7,12,15,16] . In solution‐based formulations, ethanol may reduce the chemical stability of the system and, depending on its concentration, the presence of such a low‐volatile compound mixed with the propellant can adversely impact the aerosol characteristics of the formulation [12,13,17] .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations