Crystalline ZnO photocatalysts with different morphologies prepared at ambient temperature

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Dithioesters and Trithiocarbonates Monolayers on Gold

We show that dithioester and trithiocarbonate compounds, used as chain transfer agents in reversible addition fragmentation chain transfer polymerization, form monolayers on gold. We evidence that the monolayers are slightly less dense than those formed by long alkanethiols on gold, but show a surface coverage that is close to the one obtained for short alkanethiols. Since the grafting density of polymer brushes is limited by the steric hindrance which inhibits the diffusion of large free polymer chains to opensurface reactive sites, the relatively high grafting density of dithioesters and trithiocarbonates anchoring groups is not expected to limit the density of the brushe

Erratum

International audienc

Influence of Network Topology on the Viscoelastic Properties of Double Dynamics Hydrogels

Dual-cross-linked networks (DCNs), interpenetrating polymer networks (IPNs), and IPN-derived double networks (DNs) are increasingly utilized to fabricate hydrogels with unique mechanical properties. However, the relationship between the topology of these networks and the resulting dynamics is rarely compared and little understood. To tackle this shortcoming, this work presents a systematic investigation of the viscoelastic properties of DCN, IPN, and DN hydrogels as well as their corresponding single networks by oscillatory shear rheology using both frequency and strain sweeps. All the hydrogels are based on the same orthogonal combination of a supramolecular interaction: zinc(II)-terpyridine bis-complexes, and of a reversible covalent bond: oxime, as cross-links. To understand the contribution of each sub-network to the properties of the DCN, IPN, and DN hydrogels, the corresponding single networks, i.e., cross-linked by only one type of bond, are first studied in detail. All double dynamics hydrogels have a plateau modulus much higher than the sum of the plateau modulus of the single networks, evidencing a synergetic effect between the sub-networks. However, the origin of this modulus increase varies according to the network topology. We also show that the relaxation behaviors of the DCN, IPN, and DN hydrogels are influenced by the dynamics of the corresponding single dynamic networks. Finally, the strain sweeps reveal that, for all network topologies, the amplitude of deformation at which the linear viscoelastic region of the double dynamics networks stops is governed by the oxime network, while the metallo-supramolecular network governs the amplitude of deformation up to which the sample can resist before starting to break

Controlling the cross-linking density of supramolecular hydrogels formed by heterotelechelic associating copolymers

Associating polymers constitute a fascinating class of materials because of the richness in their rheological behaviors. They may find application in numerous areas, provided that their mechanical properties can be tailored to fulfill specific requirements. In this context, this study aims to control the magnitude of the viscoelastic response of coordination micellar hydrogels built through the hierarchical assembly of heterotelechelic poly(N- isopropylacrylamide). The influence of different variables on the rheological properties of those materials is investigated and discussed in term of cross-linking density. In this respect, two distinct regimes are distinguished that correspond to the well percolated network, with a high cross-linking density, and the weakly percolated network, with a low cross-linking density. © 2014 American Chemical Society