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We present a versatile synthetic route leading toward generating surface-attached polyacrylamide gels, in which the cross-link density varies continuously and gradually across the substrate in two orthogonal directions. We employ free radical polymerization to synthesize random copolymers comprising -5% of photoactive methacrylyloxybenzophenone (MABP), -5% of thermally active styrene sulfonyl azide (SSAz), and -90% of N-isopropylacrylamide (NIPAAm) units. The presence of MABP and SSAz in the copolymer facilitates control over the cross-link density of the gel in an orthogonal manner using photoactivated and thermally activated cross-linking chemistries, respectively. Spectroscopic ellipsometry is employed to determine the degree of swelling of the gel in water and methanol as a function of position on the substrate. Network swelling varies continuously and gradually across the substrate and is high in regions of low gel fractions and low in regions of high gel fractions. [ABSTRACT FROM AUTHOR]

The resemblance between colloidal and molecular polymerization reactions is very useful in fundamental studies of polymerization reactions, as well as in the development of new nanoscale systems with desired properties. Future applications of colloidal polymers will require nanoparticle ensembles with a high degree of complexity that can be realized by hetero-assembly of NPs with different dimensions, shapes, and compositions. A method has been developed to apply strategies from molecular copolymerization to the co-assembly of gold nanorods with different dimensions into random and block copolymer structures (plasmonic copolymers). The approach was extended to the co-assembly of random copolymers of gold and palladium nanorods. A kinetic model validated and further expanded the kinetic theories developed for molecular copolymerization reactions. [ABSTRACT FROM AUTHOR]

The self‐assembly of colloidal analogues of molecular copolymers can greatly benefit fundamental studies of molecular copolymerization and nanotechnology. In their Communication on page 2648 ff., K. Liu, E. Kumacheva, et al. present microscopy and spectroscopy analyses to develop design rules and a kinetic model for the growth of colloidal random and block copolymers made from plasmonic nanorods with different lengths and compositions. [ABSTRACT FROM AUTHOR]

Die Selbstorganisation kolloidaler Analoga von molekularen Copolymeren kann grundlegende Erkenntnisse für die Gebiete der molekularen Copolymerisation und der Nanotechnologie liefern. In ihrer Zuschrift auf S. 2686 ff. präsentieren K. Liu, E. Kumacheva et al. eine mikroskopische und spektroskopische Analyse, mit deren Hilfe sie Design ‐ Regeln und ein kinetisches Modell für das Wachstum kolloidaler Zufalls ‐ und Blockcopolymere aus plasmonischen Nanostäben unterschiedlicher Länge und Zusammensetzung formulieren. [ABSTRACT FROM AUTHOR]

The utility and lifetime of materials made from polymer networks, including hydrogels, depend on their capacity to stretch and resist tearing. In gels and elastomers, those mechanical properties are often limited by the covalent chemical structure of the polymer strands between cross-links, which is typically fixed during the material synthesis. We report polymer networks in which the constituent strands lengthen through force-coupled reactions that are triggered as the strands reach their nominal breaking point. In comparison with networks made from analogous control strands, reactive strand extensions of up to 40% lead to hydrogels that stretch 40 to 50% further and exhibit tear energies that are twice as large. The enhancements are synergistic with those provided by double-network architectures and complement other existing toughening strategies. [ABSTRACT FROM AUTHOR]