**2. Crystallization on SAMs**

Crystallization refers to the formation of solid crystals from a solution, melt or more rarely, directly from gas. Crystallization consists of two processes – nucleation and crystal growth. Nucleation is the formation of small clusters of molecules. These clusters may re-dissolve in the crystallizing solution or go on to become a crystal, depending on their size. Beyond a critical size, they are stable and form crystal nuclei. Crystal growth refers to the subsequent addition of molecules to the formed nuclei. The nucleation can be homogenous, occurring spontaneously or heterogenous, induced by foreign particles such as dust particles or vessel walls. Primary nucleation occurs in the absence of crystals in solution whereas secondary nucleation occurs on seeds or existing crystals present in the crystallizing solution.

The ability to control crystallization is a critical requirement in many technologies such as in the food, pharmaceutical and chemical industries. Crystallization parameters such as particle size, particle shape, particle morphology and polymorph selectivity determine the crystal properties and uses. The solution concentration, crystallization time, crystallization temperature, solvent and crystallization vessel all have an effect on the crystal parameters. In the past few decades, researchers have been busy searching for new ways to control crystallization. Self assembled monolayers are showing great promise in this field. The

The self assembled adsorbate has a great influence on the SAM outcome and can be tailored according to the desired SAM properties. The molecule used can possess a number of functional groups in addition to the molecule's headgroup. These functional groups can be distributed within the monolayer interior and located at the terminus of the molecule. Manipulation of the monolayer interior affects its degree of order and how easily electrons are conducted through it. For example, the molecular chain length and the steric crowding of the organic groups affect the density of the organic layer and the tilt angle of the molecule away from the surface normal. In general, longer chains and less robust organic groups yield denser, more organized SAMs, allowing high degrees of van der Vaals interactions (and in some cases, hydrogen bonds) with the neighboring molecules. The molecular constituent exposed at the SAM surface is critical to the SAM's interfacial properties. It affects the surface's general hydrophobic/hydrophilic character, adhesive properties and reactivity. In addition, it determines the surface interaction with other molecular species that

SAMs are of prime technological interest, as the presence of molecules chemically bound to the surface renders the properties of the modified interface (i.e., wetting, conductivity, adhesion, and chemistry) to be entirely different than those of the bare substrate. The incorporation of functional moieties such as chromophores, electroactive groups, or molecules that can bond within the SAM (i.e., covalent cross-linking between adjacent molecules or non-covalent hydrogen bonding) enable capabilities in sensing, electron

This review will focus on the use of SAMs in crystallization processes. We will begin with a short introduction on crystallization on SAMs. Then, we will review the latest advances in crystallization on patterned SAM's and effects of SAMs on crystal morphology and crystal polymorphism. This chapter will also include a description of chiral SAMs and their role in

Crystallization refers to the formation of solid crystals from a solution, melt or more rarely, directly from gas. Crystallization consists of two processes – nucleation and crystal growth. Nucleation is the formation of small clusters of molecules. These clusters may re-dissolve in the crystallizing solution or go on to become a crystal, depending on their size. Beyond a critical size, they are stable and form crystal nuclei. Crystal growth refers to the subsequent addition of molecules to the formed nuclei. The nucleation can be homogenous, occurring spontaneously or heterogenous, induced by foreign particles such as dust particles or vessel walls. Primary nucleation occurs in the absence of crystals in solution whereas secondary

The ability to control crystallization is a critical requirement in many technologies such as in the food, pharmaceutical and chemical industries. Crystallization parameters such as particle size, particle shape, particle morphology and polymorph selectivity determine the crystal properties and uses. The solution concentration, crystallization time, crystallization temperature, solvent and crystallization vessel all have an effect on the crystal parameters. In the past few decades, researchers have been busy searching for new ways to control crystallization. Self assembled monolayers are showing great promise in this field. The

nucleation occurs on seeds or existing crystals present in the crystallizing solution.

come in contact when placed on the surface of the SAM.

enantioselective crystallization.

**2. Crystallization on SAMs** 

transfer, molecular recognition, and other areas (Smith *et al.*, 2004).

SAMs interact with the crystallizing molecules and thus, affect their organization, ultimately affecting the crystallization outcome. SAMs have been reported to affect crystal orientation, morphology, polymorphism and crystal size. The interaction between SAMs and molecules in solution has usually been rationalized on the basis of hydrogen bonding and/or strong ionic interactions.
