Self-Assembled Monolayers as Nucleating Surfaces to Study Early Formation Pathways of Crystallographic Polymorphs

Publication Reference: 
Author Last Name: 
Hui Du and Ulrich B. Wiesner
Report Type: 
ARR - Annual Report
Research Area: 
Particle Formation
Publication Year: 
United States

Executive Summary
Understanding and control of crystallographic polymorphism and crystal habit of organic
as well as inorganic compounds are scientifically and technologically important to a
number of industries. This project has moved to the formation of alkane-thiols on gold
based self-assembled monolayers (SAMs) with different terminal (omega) functional
groups (-OH and -CH3) as nucleating surfaces for the organic model system 5-methyl-2-
[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) in toluene as solvent.
Crystallization by cooling experiments were conducted to allow, for the first time in this
project, control over the degree of supersaturation. SAMs were placed vertically in the
solution and the nucleation was induced on the SAM surface by generating a temperature
jump at three different levels of supersaturation. Raman microscopy was applied for
polymorph characterization of nucleated crystals. First experimental results demonstrated
that yellow crystal (Y) was the dominating polymorph on both -OH and -CH3 terminated
surfaces. However, hydroxyl and methyl terminated SAMs showed a different tendency
for selection of additional polymorphs. Besides Y, hydroxyl SAMs preferred the nucleation
of yellow needles (YN), while methyl SAMs preferred red prisms (R). Next experimental
steps will include changing sample angle in order to increase the low number of observed
crystals on the SAM surface, as well as exploration of other SAM surface functional
groups, including carboxylates and amines, and other solvents.