Organic nanoparticles whose size and rigidity are finely tuned by cross-linking the end groups of dendrimers

Dendrimers with molecular weights ranging from ca. 2700 to 11 000 and from 16 to 64 homoallyl ether end groups were cross-linked using the Grubbs ring-closing metathesis reaction. A combination of SEC, MALDI-TOF-MS, and AFM were used to characterize the cross-linked nanoparticles. The data suggest a significant decrease in volume with cross-linking and a concomitant increase in rigidity, both of which can be controlled independently with a fair degree of precision.     

Evolution of the interface and metal film morphology in the vapor deposition of Ti on hexadecanethiolate hydrocarbon monolayers on Au

The combination of in situ X-ray photoelectron spectroscopy, infrared reflection spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry are used to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a CH(3)(CH(2))(15)S/Au{111} self-assembled monolayer (SAM) at ambient temperature. The results show that for a deposition rate of approximately 0.15 Ti atom.nm(-2).s(-1) a highly nonuniform Ti overlayer is produced via a process in which a large fraction of impinging Ti atoms do not stick to the bare SAM surface. The adsorbed atoms form isolated Ti clusters and react with CH(3) groups to form carbide products at the cluster-SAM interfaces. Further growth of Ti clusters appears to be concentrated at these scattered reaction centers. The SAM molecules in the local vicinity are subsequently degraded to inorganic products, progressing deeper into the monolayer as the deposition proceeds to give an inorganic/organic nanocomposite. A continuous overlayer does not form until metal coverage approaches approximately 50 Ti atoms per SAM molecule. These data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic, suffering from both a highly nonuniform contact area and the presence of extensive inorganic products such as nonstoichiometric carbides and hydrides.     

Tunable and rapid crystallisation of phase pure Bi2MoO6 (koechlinite) and Bi2Mo3O12 via continuous hydrothermal synthesis

Herein, we report the rapid single step hydrothermal synthesis of phase pure Bi₂MoO₆ (koechlinite) and Bi₂Mo₃O₁₂, via a continuous hydrothermal flow synthesis (CHFS) reactor, which uses supercritical water of 375–450 °C at a pressure of 24.1 MPa as a crystallising medium. The product being obtained as highly crystalline nano-materials with high surface area. Simple variation in synthesis condition and appropriate solution stoichiometry were shown to be sufficient to select the phase of the product. The materials synthesised showed significant photcatalytic activity towards the decolourisation of methylene blue in comparison to a commercial gold standard photocatalyst.     

Relaxations and rheology near jamming

We determine the form of the complex shear modulus G* in soft sphere packings near jamming. Viscoelastic response at finite frequency is closely tied to a packing's intrinsic relaxational modes, which are distinct from the vibrational modes of undamped packings. We demonstrate and explain the appearance of an anomalous excess of slowly relaxing modes near jamming, reflected in a diverging relaxational density of states. From the density of states, we derive the dependence of G* on the frequency and distance to the jamming transition, which is confirmed by numerics.     

Poly-α-ester degradation studies. I. Introduction: Design and construction of equipment

The various types of polyester degradation known to occur at elevated temperature are briefly summarized with particular reference to features of potential diagnostic value. Although little is known of poly-α-ester degradation in particular, examination of work on other linear polyesters indicates the spectrum of analytical and kinetic information that will be needed to characterize the degradation of poly-α-esters of various structures. On the basis of this review, an apparatus has been designed which enables kinetic information to be simultaneously obtained by thermogravimetry, gas evolution analysis, and rheological studies of the residual polymer melt. In addition a gas sampling procedure enables twin-column gas-liquid chromatographic analysis to be carried out on the degradation products. Samples of the chromatographically separated degradation products are collected in a microcollector cell for infrared and mass spectrometric analysis. Other refinements include in-line filament and Curie-point pyrolysis techniques.     

The dynamics of noble metal atom penetration through methoxy-terminated alkanethiolate monolayers

We have studied the interaction of vapor-deposited Al, Cu, Ag, and Au atoms on a methoxy-terminated self-assembled monolayer (SAM) of HS(CH(2))(16)OCH(3) on polycrystalline Au[111]. Time-of-flight secondary ion mass spectrometry, infrared reflection spectroscopy, and X-ray photoelectron spectroscopy measurements at increasing coverages of metal show that for Cu and Ag deposition at all coverages the metal atoms continuously partition into competitive pathways: penetration through the SAM to the S/substrate interface and solvation-like interaction with the -OCH(3) terminal groups. Deposited Au atoms, however, undergo only continuous penetration, even at high coverages, leaving the SAM "floating" on the Au surface. These results contrast with earlier investigations of Al deposition on a methyl-terminated SAM where metal atom penetration to the Au/S interface ceases abruptly after a approximately 1:1 Al/Au layer has been attained. These observations are interpreted in terms of a thermally activated penetration mechanism involving dynamic formation of diffusion channels in the SAM via hopping of alkanethiolate-metal (RSM-) moieties across the surface. Using supporting quantum chemical calculations, we rationalized the results in terms of the relative heights of the hopping barriers, RSAl > RSAg, RSCu > RSAu, and the magnitudes of the metal-OCH(3) solvation energies.