1 copyright © 2011, elsevier inc. all rights reserved. atomic force microscopy for characterization...

Copyright © 2011, Elsevier Inc. All rights Reserved. 1

Atomic Force Microscopy for Characterization of Surfaces,

Particles, and Their Interactions

Chapter 6

Frank M. Etzler and Jaroslaw Drelich


FIGURE 6.1 Schematic drawing of an atomic force microscope. The scanner moves in threedirections and the deflection of the cantilever is detected by the photodetector.


FIGURE 6.2 5 µm 5 µm images of topography (left) and phase (right) for polyurethane/polyethylene composite. The Z-scale was 200 nm (topography) and 150° (phase), and the drive phase is 40°. The dark circles in the phase image show the areas of high concentration polyurethane (dispersed phase, nodular shape, diameter: 0.5–1.5 µm). The bright continuous areas indicate polyethylene (matrix phase, continuous area).


FIGURE 6.3 Hypothetical force curve for probe–surface interaction. Dashed curve represents probe advancing toward surface. Solid curve represents probe receding from surface. A is probe snap-off force representing the force of adhesion between probe and surface. C is the probe surface contact position with advancing motion. The shaded area has sometimes been used as a method for determining the adhesion strength [19].


FIGURE 6.4 Left – AFM cantilever tip. Right – AFM cantilever with lactose particle mounted asa colloidal probe.


FIGURE 6.5 Comparison of particle diameters determined by AFM to other methods. Left axis –particles on impactor plates. Plate number is given on x-axis. Data on the left axis by Gwaze et al.[42]. Right axis comparison particle diameters were determined by AFM and TEM. Data on theright axis by Lacava et al. [45].


FIGURE 6.6 Pull-off force of insulin particles on PP and ABS surfaces versus relative humidity.Figure redrawn from data by Beach and Drelich [51]. Results indicate that surface roughness andcapillary forces contribute significantly to the adhesion force. See text and original work [51] fordetails.


FIGURE 6.7 Height and friction images of gelatin capsule surfaces [32]. Surfaces are frominterior of the capsule. Capsules from Manufacturer A have pits in the surfaces that presumablyresult from bubbles entrapped near the surface during capsule manufacture. Light areas in thefriction image result from surface contamination by mold release agent.


FIGURE 6.8 Adhesion force of lactose particles on capsule surfaces [54]. Numbers in legend are capsule lot numbers. Upper curve represents normal capsules (Manufacturer A) and lower curve represents capsules cleaned with supercritical CO2, or capsules made by Manufacturer B.

Capsules that have clean surfaces exhibit lower adhesion force.


FIGURE 6.9 Surface free energy parameters for various lots of lactose as determined using IGC[52]. γLW is the Lifshitz –van der Waals component of the surface free energy. Ka and Kd are the

acid and base parameters describing the lactose surface using Gutmann’s acid–base model (seeEtzler [40] for an explanation of acid–base models). The figure suggests that the surface chemistryof various lots of lactose is variable.


FIGURE 6.10 Surface acidity (Ka) for various lots of lactose and retention in capsule for various

lots of lactose versus ratio of OCO carbons to aliphatic (CH) carbons on lactose surfaces [52]. CHcarbons represent surface contamination. The oxidation states of surface carbons were determinedusing x-ray photoelectron spectroscopy (XPS) (or ESCA, Electron Spectroscopy for ChemicalAnalysis).


FIGURE 6.11 Phase image of lactose surface showing surface contamination (dark area and white specks) [54].


FIGURE 6.12 Normalized adhesion force (F/R) between drug (Ibr) and lactose particles withother particles and surfaces [54]. Both normal capsules (Cap) and cleaned capsules (Cap E) werestudied. Normalized force is the measured force divided by particle radius. Particle – capsuleinteractions are strongest. Drug – capsule interactions are stronger than lactose capsule interactions.


FIGURE 6.13 In-vitro deposition measurements of the percentage of dose retained in device (% Ret. Device), the fine particle fraction relative to the emitted dose (% FPF ED), and fine particle fraction relative to the total dose (% FPF Total) for salbutimol and mixtures of salbutimol with force control agents. Figure redrawn from the data by Begat et al. [55]. Addition of a flow control agent has a small effect on retention of the powder in the device, but significantly reduces adhesion between particles, thus improving dispersion of the powder and FPF.


FIGURE 6.14 Normalized adhesion force for chemically modified AFM tips against modified surfaces. Modification reagents are CH-octyltrichlorosilane, COC-3-methoxy propyltrimethoxysilaneand COOC-2-acetoxyethyltrichlorosilane. Non-CH-modified surfaces are vastly different in hydrocarbon and HFA media. COC and COOC allow for more interaction with HFA media and show lower forces than CH in this media.


FIGURE 6.15 Height (left) and phase (right) images of Al canister used for an MDI formulation.A 10 μm 10 μm area is shown. Banding pattern is clearly observed in the phase image andpresumably results from the canister manufacturing process.


FIGURE 6.16 Topographic (left) and phase image (right) of a silicon wafer contaminated withan oil that came from a dust-remover moisture-free cleaning can, commonly used in coarsecleaning of substrates (E. Beach and J. Drelich, unpublished work).

1 copyright © 2011, elsevier inc. all rights reserved. atomic force microscopy for characterization...

Documents

force of adhesion

lower adhesion force

phase right

hypothetical force curve

force of insulin particles

surface contamination

surface roughness

jaroslaw drelich slide