SMALL-ANGLE NEUTRON SCATTERING STUDY OF THREE-LAYER MICELLES

  J.Plestil1, H.Pospisil1, B.Masar1, M.A.Kiselev2

1 Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq.2, 162 06 Prague 6, Czech Republic
2 Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia  

Keywords: block copolymer micelle, ABC copolymer, solubilization, small-angle neutron scattering  

Block copolymer micelles are polymolecular nanoparticles with a dense core formed by insoluble blocks and a protective corona formed by swollen soluble blocks. Most of potential applications of the micelles are based on or use loading of sparingly soluble compounds into micellar cores (solubilization). It was shown that characteristics of this process correlate with the affinity between solubilizate and the core-forming constituent of block copolymer [1]. Results of DLS and fluorescence study reported by Kiserow et al. [2] and our recent SANS and NMR experiments revealed that also the properties of the micelle corona can strongly affect kinetics and the extent of solubilization [3]. This extends the variability of micellar properties of particular copolymer and enables one to control the processes of uptake and release of solubilizates to some extent.

The commonly studied micelles have usually a two-component core/corona structure. The possibility to control transport processes in micellar systems can be further extended if three-layered (onion-type) micelles are available. Preparation of two such micellar systems has been recently reported [4,5]. For various reasons, however, these systems are not well suited to the purpose of controlled transport.

In the present contribution, results of small-angle neutron scattering (SANS) study of onion-type micelles in aqueous media will be reported. The copolymer used (poly(styrene)-block-poly(2-vinyl pyridine)-block-poly(ethylene oxide) , PS-b-P2VP-b-PEO) is an ABC block copolymer with one hydrophobic (PS) and one hydrophilic (PEO) outer block. The middle block (P2VP) is soluble in water at low pH but insoluble at high pH. Thus, the copolymer is expected to form micelles with PS core and PEO corona. At low pH, the middle P2VP blocks are swollen and contribute to the formation of the corona. Upon increasing pH, the P2VP chains collapse and form an outer core. These conjectures are supported by the structure characteristics obtained using SANS technique.

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