Vapor-Deposited Thin Films: Studying Crystallization and α-relaxation Dynamics of the Molecular Drug Celecoxib

Abstract

Crystallization is one of the major challenges in using glassy solids for technological applications. Considering pharmaceutical drugs, maintaining a stable amorphous form is highly desirable for improved solubility. Glasses prepared by the physical vapor deposition technique got attention because they possess very high stability, taking thousands of years for an ordinary glass to achieve. In this work, we have investigated the effect of reducing film thickness on the α-relaxation dynamics and crystallization tendency of vapor-deposited films of celecoxib (CXB), a pharmaceutical substance. We have scrutinized its crystallization behavior above and below the glass-transition temperature ( T g ). Even though vapor deposition of CXB cannot inhibit crystallization completely, we found a significant decrease in the crystallization rate with decreasing film thickness. Finally, we have observed striking differences in relaxation dynamics of vapor-deposited thin films above the T g compared to spin-coated counterparts of the same thickness.

Influence of Surface Roughness on the Dynamics and Crystallization of Vapor-Deposited Thin Films

“…Considering films under geometric confinement, the influence of the surface region will be much pronounced compared to bulk films. Our group has also reported a similar behavior for confined vapor-deposited films of CXB . We have observed faster α-relaxation dynamics for CXB films with decreasing thickness.…”

“…The melting and the glass-transition values are in well agreement with the literature data . The details of the DSC thermogram for bulk CXB are given in our previous article . Conductive silicon wafers (purchased from SIL’TRONIX, France) with a native oxide layer are used as the substrate.…”

“…Our group has also reported a similar behavior for confined vapor-deposited films of CXB. 38 We have observed faster α-relaxation dynamics for CXB films with decreasing thickness. However, in that case, CXB was deposited on the native silicon surface.…”

“…The vapor deposition technique is reported to be a novel method that can slow down the crystallization of organic glasses. , The reduction in the crystallization rate upon vapor deposition is observed both above and below the glass-transition temperature. ,, Here, we investigate the influence of both confinement and roughness on the crystallization behavior of vapor-deposited CXB.…”

“… 37 The details of the DSC thermogram for bulk CXB are given in our previous article. 38 Conductive silicon wafers (purchased from SIL’TRONIX, France) with a native oxide layer are used as the substrate. The wafers are oriented in (1 0 0) and possess a resistivity value from 0.001 to 0.003 Ω cm.…”