Simulation of XPS C1s Spectra of Organic Monolayers by Quantum Chemical Methods

Several simple methods are presented and evaluated to simulate the X-ray photoelectron spectra (XPS) of organic monolayers and polymeric layers by density functional theory (DFT) and second-order Møller–Plesset theory (MP2) in combination with a series of basis sets. The simulated carbon (C1s) XPS spectra as obtained via B3LYP/6-311G­(d,p) or M11/6-311G­(d,p) calculations are in good agreement (average mean error <0.3 eV) with the experimental spectra, and good estimates of C1s spectra can be obtained via <i>E</i>_C1s(exp) = 0.9698<i>E</i>_C1s(theory) + 20.34 (in eV) (B3LYP/6-311G­(d,p)). As a result, the simulated C1s XPS spectra can elucidate the binding energies of the different carbon species within an organic layer and, in this way, greatly aid the assignment of complicated C1s XPS spectra. The paper gives a wide range of examples, including haloalkanes, esters, (thio-)­ethers, leaving groups, clickable functionalities, and bioactive moieties

Generic Top-Functionalization of Patterned Antifouling Zwitterionic Polymers on Indium Tin Oxide

This paper presents a novel surface engineering approach that combines photochemical grafting and surface-initiated atom transfer radical polymerization (SI-ATRP) to attach zwitterionic polymer brushes onto indium tin oxide (ITO) substrates. The photochemically grafted hydroxyl-terminated organic layer serves as an excellent platform for initiator attachment, and the zwitterionic polymer generated via subsequent SI-ATRP exhibits very good antifouling properties. Patterned polymer coatings can be obtained when the surface with covalently attached initiator was subjected to photomasked UV-irradiation, in which the C–Br bond that is present in the initiator was broken upon exposure to UV light. A further, highly versatile top-functionalization of the zwitterionic polymer brush was achieved by a strain-promoted alkyne–azide cycloaddition, without compromising its antifouling property. The attached bioligand (here: biotin) enables the specific immobilization of target proteins in a spatially confined fashion, pointing to future applications of this approach in the design of micropatterned sensing platforms on ITO substrates

Synergistic Stiffening in Double-Fiber Networks

Many biological materials are composite structures, interpenetrating networks of different types of fibers. The composite nature of such networks leads to superior mechanical properties, but the origin of this mechanical synergism is still poorly understood. Here we study soft composite networks, made by mixing two self-assembling fiber-forming components. We find that the elastic moduli of the composite networks significantly exceed the sum of the moduli of the two individual networks. This mechanical enhancement is in agreement with recent simulations, where it was attributed to a suppression of non-affine deformation modes in the most rigid fiber network due to the reaction forces in the softer network. The increase in affinity also causes a loss of strain hardening and an increase in the critical stress and stain at which the network fails