(341g) Relationship Between Material Properties and Structure of Nanocoated Organic Crystals
Anisotropy between orientations of organic crystals and their different faces have been studied with respect to the material properties of bulk pharmaceutical powders. In the first stage, experimental measurements were adopted to study various techniques to grow single pure crystals of acetaminophen. The influence of operating conditions on the geometry of crystal habit was investigated in order to control the growth rate of crystals. Surface properties of crystals were characterized by surface wetting, contact angle measurements, atomic force microscope (AFM) measurements of force separation curves, lateral force microscope (LFM) measurements of frictional forces and electron microscopy of crystal structure and morphology. The mechanical response of the crystal surface with respect to the functionalized groups was obtained. Influence of humidity on the mechanical response of both empty and functionalized AFM tips was obtained on crystal surfaces. In the second stage, crystal surfaces were modified by coating with nanoparticles of colloidal silica. The particle size of nanocoating was controlled to obtain a uniform layer deposition. Atomic Layer Deposition (ALD) was performed to deposit uniform thin films of nanosilica with atomic precision on a carefully mounted crystal surface. Control of the atomic scale deposition based on self-limited ALD film growth through chemisorption and sequential surface reaction was performed. In addition, another method of Pulse Layer Deposition (PLD) was also used to deposit the thin film on the substrate (crystal). The thin film of nanosilica was grown on crystal surface due to the direct flow of ablation particles. Nucleation and growth of the thin film on the substrate surface resulted in a sequential monolayer deposition of nanosilica. The mechanical response of thin nanosilica layers on crystal surfaces was estimated by functionalizing AFM tips with both hydrophilic and hydrophobic terminal groups. In the next stage, binding energies or molecular forces of nanosilica layers as a function of extent of coverage of nanolayer was reported.