(208g) Particle Shape and Roughness Characterization by Focused Ion Beam Tomography for Adhesion Simulation

Particle cohesion and adhesion interactions have far-ranging impacts within the pharmaceutical industry with regard to both the manufacturing of particulate solids and the delivery of active pharmaceutical ingredients.  The ability to measure and model these interactions can aid material selection, improve the design of process equipment, and increase the accuracy of various process simulations and models.

The accuracy of particle adhesion models and simulations is highly dependent on particle geometry and roughness which are often either oversimplified estimates or hybrids of estimates and measured data.  A novel method for the simultaneous characterization of particle geometry and roughness was developed in which the particle of interest is serially sectioned using a focused ion beam (FIB) and the cross sections are imaged with a field emission electron microscope (FESEM).  Subsequently, the cross-sectional data are used to synthesize a 3-dimensional particle surface mesh which contains micron- and nanometer-scale information.

Colloidal probe microscopy (CPM) using an atomic force microscope (AFM) was used to examine particle-substrate adhesion interactions between individual 10 μm diameter silicon dioxide particles and a polished stainless steel substrate.  Individual particles were mounted as probes on tipless AFM cantilevers.  The force of adhesion was measured in various locations across the polished stainless steel substrate in an electrostatically neutral and humidity controlled environment.  Finally, the particles were serially sectioned and imaged in microscope housing both a FIB column and FESEM column.  The cross sectional data were used to synthesize 3D mesh surface models for each particle, and a simulation assisted particle adhesion model was used to estimate the value of the Hamaker constant.