Deformation controlled assembly of binary microgel thin films

We describe the assembly of two-component, hydrogel microparticle (microgel) monolayer films onto solid substrates via passive Coulombic adsorption from solution. By using two different microgel types with nearly identical sizes but different degrees of softness, the influence of particle deformation on film composition was determined. Determination of the microgel properties using a variety of light scattering techniques allowed for predictions of the film composition as a function of solution composition using a random sequential adsorption (RSA) model. The films were then studied via atomic force microscopy (AFM), and surface coverage and population statistics were determined from the images and compared to the model predictions. Deviations from the predicted particle adsorption behavior can be directly traced to differences in particle softness, deformation, and particle footprint following adsorption, which biases the particle coverage to the more rigid (smaller footprint) particles. Furthermore, by using a mixture of degradable and nondegradable core/shell particles, the identity of the particles can be unambiguously determined by measuring AFM height changes following erosion of the core from the microgels. These results show that, regardless of the solution diffusion properties of soft particles, their competition for surface adsorption from a binary mixture is largely dictated by their interactions with the surface and their deformation at the surface.     

High Magnetic Moments in Manganese‐Doped Silicon Clusters

We report on the structural, electronic, and magnetic properties of manganese‐doped silicon clusters cations, Si_nMn⁺ with n=6–10, 12–14, and 16, using mass spectrometry and infrared spectroscopy in combination with density functional theory computations. This combined experimental and theoretical study allows several structures to be identified. All the exohedral Si_nMn⁺ (n=6–10) clusters are found to be substitutive derivatives of the bare Si_n+1⁺ cations, while the endohedral Si_nMn⁺ (n=12–14 and 16) clusters adopt fullerene‐like structures. The hybrid B3P86 functional is shown to be appropriate in predicting the ground electronic states of the clusters and in reproducing their infrared spectra. The clusters turn out to have high magnetic moments localized on Mn. In particular the Mn atoms in the exohedral Si_nMn⁺ (n=6–10) clusters have local magnetic moments of 4 μ_B or 6 μ_B and can be considered as magnetic copies of the silicon atoms. Opposed to other 3d transition‐metal dopants, the local magnetic moment of the Mn atom is not completely quenched when encapsulated in a silicon cage.     

Reversible Inter- and Intra-Microgel Cross-Linking using Disulfides

Thermoresponsive hydrogel nanoparticles composed of poly(N-isopropylmethacrylamide) (pNIPMAm) and the disulfide-based cross-linker N,N'-bis(acryloyl)cystamine (BAC) have been prepared using a redox-initiated, aqueous precipitation polymerization approach, leading to improved stability of the disulfide bond compared to traditional thermally-initiated methods. The resultant particles demonstrate complete erosion in response to reducing conditions or thiol competition. This stands in contrast to the behavior of thermally-initiated particles, which retain a cross-linked network following disulfide cleavage due to uncontrolled chain-branching and self-cross-linking side reactions. The synthetic strategy has also been combined with the non-degradable cross-linker N,N-methylenebisacrylamide (BIS) to generate "co-cross-linked" pNIPMAm-BAC-BIS microgels. These particles are redox-responsive, swell upon BAC cross-link scission and present reactive thiols. This pendant thiol functionality was demonstrated to be useful for conjugation of thiol-reactive probes and in reversible network formation by assembling particles cross-linked by disulfide linkages.     

Electron deficient carbon-titanium triple bonds: formation of triplet XC/TiX3 methylidyne complexes

Laser-ablated titanium atoms react with CX4 (X = F and Cl) to produce triplet state XC/TiX3 complexes trapped in an argon matrix. Products are identified by their infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C(3v) symmetry structures for these lowest-energy products. The two unpaired electrons in the carbon 2p orbitals are shared with empty titanium d orbitals leading to degenerate singly occupied pi molecular orbitals and an electron-deficient triple bond between the carbon and titanium centers, on the basis of DFT bonding analysis and spin density calculations. The carbon-titanium distances are near typical C=Ti double bond lengths, and the C-X bonds in the resulting products are shorter than in the CX4 precursors. It appears that X lone-pair conjugation contributes to the C-X bond strength and somewhat to the C-Ti bond, and Cl does better in this regard than F.     

Cluster organization in co-sputtered platinum-carbon films as revealed by grazing incidence X-ray scattering

Nanostructured platinum-carbon thin films were prepared by magnetron co-sputtering method for designing efficient catalytic thin films, like fuel cells electrodes. The in-depth morphology of composite films was studied using surface sensitive X-ray techniques (grazing incidence small-angle scattering and reflectivity), consolidated by electron microscopy investigations. This study elucidates the growth mode of co-sputtered platinum-carbon thin film: 2-nm-sized platinum clusters are growing in surrounding simultaneously growing carbon columns (20-nm diameter range). In particular, the platinum cluster growth and distribution in the plane of the substrate surface are driven by surface diffusion and coalescence phenomena. Finally, this anisotropic distribution of platinum clusters correlated to the textured morphology of carbon matrix leads to a catalytic thin film morphology very suitable for electrochemical processes in fuel cell electrodes.