Making Sense of Milling: the Role of Water on the Micro-Structural Relaxation-Like of Cryo-Milled Griseofulvin
Feng T1, Stanciu L2, and Carvajal MT1,3*
1Department of Industrial and Physical Pharmacy, Purdue University, West Lafayette, IN 47907, USA
2Material Sciences Engineering, Purdue University, West Lafayette, IN 47907, USA
3Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA
*Correspondence E-mail: tcarvaja@purdue.edu
Key Words: Griseofulvin, Relaxation, Temperature, Humidity, Annealing, Water, Crystal defects, Relative humidity
Received February 8th, 2012; Accepted March 25th, 2012; Published July 29th, 2012; Available online August 3rd, 2012
Summary
The purpose of this investigation was to study the effect of different annealing conditions (moisture and temperature) on the relaxation-like or rearrangement of cryogenic milled griseofulvin (cMG). Different analytical tools were used to characterize the structural changes and to monitor the stability of cMG. The cMG is thermodynamically unstable because it apparently contains some defective crystals. Due to the high Gibbs free energy acquired upon milling, the material was susceptible to relaxation or annealing upon exposure to favorable environmental conditions of temperature and humidity. Upon storage under certain conditions, the cMG restored some of its original arrangement of the molecules and/or crystal growth (sintering) which was dependent on the annealing temperature and duration. Possible relaxation-like regimes can be explored to explain the proposed findings. The isothermal annealing behavior of cMG may be important for milled powders where the material presents regions that are physically distinct from amorphous (totally disordered), hence the crystal defects (dislocated) are suggested.