Ji-Woong Park, Jae-Suk Lee and colleagues from the Gwangju Institute of Science and Technology, investigated the structures formed when amphiphilic rod-coil block copolymers were dissolved in a solvent specific for the rod block of the copolymer.
Park and colleagues have discovered that placing the rod-coil block copolymer in toluene, a solvent in which the rod component of the amphiphile is soluble, leads to the aggregation of the coil block. The tangential packing of the rod block forms spherical, membrane bound structures that have a shielded core of approximately 20 to 50 nm in diameter, with a thin shell of only 4 nm thickness. This tangential packing, or so-called 'chain wrapping', of the soluble part of the copolymer has not been observed previously; it is the only plausible packing arrangement as the rod block of the copolymer is 38 nm long, so a wrapped (tangential) arrangement is the only way that the rod shell could be confined to a thickness of only 4 nm.
The membrane bound structures are reversibly interchangeable between a vesicular and micellar state, depending on the concentration of the copolymer in the solvent. The hollow cores of the aggregates were shown to be effectively protected from the surrounding solvent.
The chain wrapping of the soluble rod block was indirectly evidenced by the successful use of the aggregates as nano-sized reactors for the production of two types of gold nanoparticles. The team also envision that these aggregates may be formed with any type of rod coil block copolymer and could be conjugated with a variety of molecules, making them potentially useful for a broad range of applications.
Original publication: Haeng-Deog Koh, Ji-Woong Park, M. Shahinur Rahman, Mohammad Changez and Jae-Suk Lee, Chem. Commun., 2009, 4824.