Powder Adhesion Measurement

Introduction

The NanoTest instrument utilises a pendulum assembly with an electromagnetic loading arrangement. Movement of the probe is monitored with very high resolution by determining the simultaneous change in capacitance of a parallel plate capacitor. For adhesion measurement, a force is first applied to the probe such that the probe is pressed onto the surface; the force is then slowly reduced until the probe is detached and the pendulum moves rapidly away from the surface. The force at this point is identified on the computer screen by means of a moving cursor.

The following parameters are defined prior to each test:

• Maximum load or maximum depth

• Contact load

• Loading rate

• Dwell time at maximum load

Experimental

Adhesion forces between two different pharmaceutical powder samples were measured. The method employed produced contact between a number of particles, thus ensuring a statistically more meaningful result than would be obtained from single particle contact experiments.

The powders were applied to 1mm diameter wires as shown.

Four tests were performed using a maximum applied load of approximately 250 mN prior to load reversal for specimen separation. Tests 1 and 2 were carried out at the same position, whereas Tests 3 and 4 were carried out after moving the sample stage to new contact areas