Solvophilic-solvophobic interactions

This chapter describes supramolecular assemblies in mesoscopic dimension and their recent developments. It also compliments earlier reviews [21,22]. The mesoscopic supramolecular assemblies are defined as hierarchically self-assembled amphiphilic supramolecular structures whose ternary and the higher assembly structures are controlled through solvophilic-solvophobic interactions. Here, pairs of molecules brought by secondary interactions are designed that acquire amphiphilicity upon complexation. They become units of self-assembly and hierarchically grow into mesoscopic-scale supermolecules that are dispersed stably in aqueous or in organic media. 

The integration of molecular-recognition-directed self-assembly and chemistry of bilayer membranes has lead to the development of mesoscopic supramolecular assemblies. The impartment of amphiphilicity to supermolecules drives their hierarchical self-assembly. The solvophilic-solvophobic interactions play a pivotal role in the determination of the supramolecular architecture, and this is a distinct feature from the earlier supramolecular chemistry. The combinatorial supramolecular approach is also effective to develop functional mesoscopic assemblies. In addition, combination of supramolecular polymers and solvent engineering will give a new perspective in the design of mesoscopic materials. 

Self-assembly offers an attractive strategy to construct functional nanofibers. Amphiphilic self-assembly of components that belong to different molecular families or disciplines allows development of unique properties that have not been created in the framework of conventional studies. The solvophilic-solvophobic interactions play a pivotal role in the determination of mesoscopic-scale supramolecular architectures, and this is a feature not appreciated in classical supramolecular chemistry. Since many supramolecular nanofibers have been developed, one of the next issues would obviously be finding functions unique to their nano architectures. Introduction of biological molecules as essential components for nanofiber self-assembly has been shown to provide bridges that link materials science and in vivo applications. 

In addition, medium effects play an important role through the interaction of solvent molecules with p and a as well as with each other thus the two partners should present geometrically matched hydrophobic/hydrophobic or hydrophilic/hydro-philic (solvophobic, solvophilic, more generally) domains. 

In this context we note that the formation of nanostructures by amphiphilic molecules represents a careful balance between the solvophobic and the solvophilic interactions. A dominance of either can lead to either phase separation or complete solubility of the amphiphile in the solvent. While the subtle balance between these forces is recognized in the current literature, the crossover from one behavior to the next remains to be understood in a quantitative fashion. 

If two such sparsely coated layers are brought into close contact, the pinned micelles from each surface interact and form novel structures. Little is known of the interactions in systems that involve both solvophobic and solvophilic (solvent-compatible) chains at low grafting densities [19,20,28]. Probing the structure and energies between these layers can yield insight into the nature of the adhesive forces between polymer-coated substrates and provide guidelines for tailoring the interactions between the interfaces. 

The solubility of SPs in a given solvent is often controlled (cf. Section III.A) by the use of side chains compatible with the particular solvent. For instance, columnar assemblies of m-phenylene ethynylene rings having apolar aliphatic substituents are (poorly) soluble only in nonpolar solvents. More polar substituents result in increased solubility in polar solvents. While the side chain experiences a solvophilic interaction with the solvent, the core of the molecule experiences a solvophobic environment that may actually reinforce the contact forces. 

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