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

Executive Summary

to extend our work to other model compounds.

since the methodologies worked out in our studies to date have been effective, we consider

become relevant for the development of molecular dynamics simulations. Furthermore,

With that knowledge, we are now in the course of collecting new data that we hope will

first results are quite exciting and warrant further in-depth studies of these phenomena.

the project, we are on target with achieving the goal of the original project brief. These

ACM on SAMs as revealed by in situ synchrotron x-ray experiments in the third year of

By providing first insights into the earliest formation stages of the crystallization of

these early stages.

nucleation and growth, pointing to the possible existence of structural transformations at

along scattering vector, q, of isolated scattering peaks at the earliest time points of crystal

spontaneous crystallization events in a simple droplet of form I we identified unusual shifts

verified that crystallization originates at the substrate-solution interface. Studying

crystals and moving the x-ray beam vertically through the elongated film sample we

Energy Synchrotron Source (CHESS). Using seeded crystallization events of form II

means of time-resolved in situ wide-angle x-ray scattering (WAXS) at Cornell’s High

have studied the early formation stages of these form I and II crystallization events by

dioxane produce the less favored orthorhombic form II. In the third year of this project, we

thermodynamically stable, monoclinic polymorph form I, while mixtures of water and 1,4-

hydrophobic SAMs, pure solvent systems such as ethanol, water, and 1,4-dioxane yield the

• (i) both solvent and substrate work together to control crystal polymorph, and that
• (ii) on (gold, silicon oxide/silicon). In the first two years of this project, we have established that

and -silanes, with different terminal (omega) functional groups, on various substrates

(ACM) as our model system, on arrays of self-assembled monolayers (SAMs) from alkanethiols

We have successfully worked with a pharmaceutical compound, acetaminophen

understanding of early crystal formation pathways and mechanisms are highly desirable.

a polymorph is determined at the nucleation of a crystal, methods that lead to an advanced

(crystalline solids with different arrangements of the same constituents) is difficult. Since

a number of industries. To date, however, the experimental control of polymorphs

organic as well as inorganic compounds is scientifically and technologically important to

Understanding and control of crystallographic polymorphism and crystal habit of