Solution self-assembly

Hamley IW, Ansari A, Castelletto V et al (2005) Solution self-assembly of hybrid block copolymers containing poly(ethylene glycol) and amphiphilic beta-strand peptide sequences. 

Zhang L, Bartels C, Yu Y, Shen H, Eisenberg A. Mesosized crystal-like structure of hexagon-ally packed hollow hoops by solution self-assembly of diblock copolymers. Phys Rev Lett 1997 79 5034-5037. 

Solution self-assembly is a thermodynamically controlled equilibrium reaction in which components are able to sift through a variety of possible structures until they find the one of the maximum stability. There is effectively infinite time available for the reaction and mistakes in the assembly process may be rectified by decomplexation and recomplexation steps. 

In examining a crystalline structure as revealed by diffraction experiments it is all too easy to view the crystal as a static entity and focus on what may be broadly termed attractive intermolecular interactions (dipole-dipole, hydrogen bonds, van der Waals etc., as detailed in Section 1.8) and neglect the actual mechanism by which a crystal is formed, i.e. the mechanism by which these interactions act to assemble the crystal from a non-equilibrium state in a super-saturated solution. However, it is very often nucleation phenomena that are ultimately responsible for the observed crystal structure and hence we were careful to draw a distinction between solution self-assembly and crystallisation at the beginning of this chapter. For example paracetamol, when crystallised from acetone solution gives the stable monoclinic crystal form I, but crystallisation from a molten sample in the absence of solvent... 

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Brown MD, Gray AI, Tetley L, Santovena A, Rene J, Schatzlein AG, Uchegbu IF (2003) In vitro and in vivo gene transfer with poly(amino add) vesicles. J Contr Release 93(2) 193-211 Zhang L, Bartels C, Yu Y, Shen H, Eisenbeig A (1997) Mesosized crystal-Uke stmcture of hexagonally packed hollow hoops by solution self-assembly of diblock copolymers. Phys Rev Lett 79 5034-5037... 

Kuo S-W, Lee H-F, Huang W-J, Jeong K-U, Chang F-C (2009) Solid state and solution self-assembly of helical polypeptides tethered to polyhedral oligomeric silsesquioxanes. Macromolecules 42 1619-1626... 

An ABC triblock terpolymer was successfully synthesized by a sequential three-step RAFT polymerization process of N-n-propylacrylamide, N-isopropylacrylamide and N,N-ethylmethylacrylamide monomers [41], The different cloud points of the respective blocks, present in the terpolymer, are responsible for the rich temperature depended solution self-assembly of the sample in aqueous media. 

NUH Nuhn, H. and Klok, H.-A., Aqueous solution self-assembly of polystyrene-Z>-poly(L-lysine) diblock oligomers, Eur. Polym. J., 47, 782, 2011. 

Solution self-assembly nsnally involves an amphiphilic multiblock copolymer in which the blocks display different solubility properties. The self-assembly process involves the association of an insolnble segment or segment(s) of the copolymer chain, when the copolymer is placed in a solvent system that solvates only a portion of the overall chain, at concentrations, at or above the critical micelle concentration (cmc). The cmc is a critical parameter in determining the stability of the assembly and is often significantly lower for block copolymer assemblies than surfactant assemblies. A simple solution thermodynamic measure of aggregate stability or cmc can be expressed in terms of n, the degree of polymerization, by (1). 

Figure 3 Correlation of packing parameter for a given amphiphile with the resultant solution self-assembled micelle morphology. (Reproduced from Ref. 3. Elsevier, 2005.)...

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