Wettability of paracetamol polymorphic forms I and II.

Area of Science:

• Solid-state chemistry
• Materials science
• Surface science

Background:

• Polymorphic materials are known to possess diverse physicochemical properties.
• Understanding the surface energetics and wetting behavior of these materials is crucial for various applications.
• Previous studies have indicated anisotropic wetting, but detailed comparisons between polymorphs are lacking.

Purpose of the Study:

• To investigate and report for the first time the variations in wetting and surface energetics of two organic polymorphic solids (paracetamol forms I and II).
• To directly measure advancing contact angles for water and diiodomethane on specific facets of paracetamol polymorphs.
• To explore the relationship between molecular packing, crystal structure, and surface properties.

Main Methods:

• Growth of macroscopic single crystals of paracetamol (facet area >1 cm²).
• Direct measurement of advancing contact angles (θA) using water and diiodomethane.
• Analysis of wetting behavior on specific Miller indexed faces: (001), (010), and (110).

Main Results:

• Anisotropic wetting behavior was observed for both paracetamol forms I and II.
• Significant variations in wetting behavior were found for the same Miller indexed faces between the two polymorphs.
• Facet wettability was confirmed to be independent of Miller indices and sensitive to local surface chemistry, influenced by molecular packing.

Conclusions:

• The surface chemical behavior of different polymorphs is distinct, precluding inference of properties from one form to another.
• Anisotropic surface energies are a common characteristic of organic crystalline solids.
• The study highlights the complex surface chemistry of polymorphic solids and the importance of polymorph-specific characterization.