ABSTRACT
Morphology and structure of aqueous block copolymer solutions based on polystyrene-block-poly(ethylene oxide) (PS-b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H2PtCl6.6H2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H2O was replaced with D2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H2PtCl6.6H2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS-b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D2O solutions, revealing good agreement of AUC and SANS data.
Subject(s)
Micelles , Polyethylene Glycols , Polystyrenes , Calorimetry, Differential Scanning , Microscopy, Electron , Models, Molecular , Surface-Active Agents , UltracentrifugationABSTRACT
Polymer colloids with internal ordering were synthesized using hydrolytic condensation of octadecyl-dimethyl(3-trimethoxysilylpropyl)ammonium chloride (ODMACl) and a mixture of ODMACl and the trisodium salt of the triacetic acid N-(trimethoxysilylpropyl)ethylenediamine (TANED). The structure and morphology of these colloids were studied with small-angle X-ray scattering, transmission electron microscopy, nuclear magnetic resonance, sedimentation in ultracentrifuge; and other methods. When polymer colloids are obtained from a single precursor (ODMACl), their local structure, molecular weight characteristics, and morphology strongly depend on the reaction conditions, while lamellar ordering remains nearly unaffected. Use of a mixture of cationic and anionic silanes (ODMACl and TANED) as precursors in hydrolytic condensation results in novel zwitterionic copolymer colloids with two-dimensional hexagonal packing. Interaction of the ODMACl quaternary ammonium groups with the three carboxy groups of TANED leads to replacement of sodium and chloride ions and formation of gegenions, resulting in a molar ratio ODMACl:TANED = 3:1 (each TANED molecule contains three carboxy groups). Due to their ordered interior, polyODMACl (PODMACl) and PODMACl-TANED colloids can be used as templates for controlled positioning of nanoparticles within these colloids. For example, lamellar ordering controls Pt nanoparticle formation within PODMACl colloids providing Pt nanoparticle alignment within the lamellar structure. Loading of PODMACl-TANED colloids with iron salts followed by pH increase results in the formation of iron oxide nanoparticles located within PODMACl-TANED cylinders.
