Self‐Assembly from Surfactants to Nanoparticles – Head vs. Tail

Surfactant molecules possess an intrinsic duality in their molecular characteristics because they are composed of a hydrophilic headgroup covalently linked to a hydrophobic tail. The forced coexistence of the head and the tail, despite their mutual antipathy, provides the foundation for the self-assembly behavior of classical low molecular weight surfactants in solutions and at interfaces, generating nanoscale structures of different sizes and shapes. High molecular weight block copolymers with a solvophilic polymer block functioning as the headgroup and a solvophobic polymer block functioning as the tail also display self-assembly behavior analogous to classical surfactants. Despite evident analogies between surfactants and block copolymers, theoretical models predicting their self-assembly behavior have evolved independent of one another. The classical theory of surfactants assigns a critical role to the headgroup interactions in controlling the pattern of self-assembly. In contrast, the early theories of block copolymers assigned a controlling role to the elastic stretching of the solvophobic block, namely, the tail, in determining aggregate shape variations. In this chapter, we focus on how the concepts from the surfactant and block copolymer studies have merged to emphasize the importance of both the head and the tail and the consequent ability of theories to predict more accurately the self-assembly and shape transitions in the classical surfactant and block copolymer systems. Further, we show that these ideas have broad generality and provide a rational way to understand the self-assembly behavior of a variety of non-classical amphiphilic systems involving dendrimers, DNA, peptides, proteins, and nanoparticles as critical head or tail components.