Volume 130, Issue 12, 28 March 2009
Index of content:
130(2009); http://dx.doi.org/10.1063/1.3109691View Description Hide Description
The discovery of a first-order phase transition in fluid phosphorus aroused renewed interest in polyamorphism in liquids with a locally tetrahedral molecular structure. We have performed in situ synchrotron x-ray diffraction measurements on tin tetraiodide, which consists of tetrahedral molecules at ambient pressure, and established that the liquid forms existing above and below 1.5 GPa, where the slope of the melting curve of the solidphase changes abruptly, have different structures. This discovery offers evidence of thermodynamically stable polyamorphism in general compounds as well as in elements. A possible phase diagram that includes the two amorphous states already found is proposed based on the pseudobinary regular solution model. The vertex-to-face orientation between the nearest molecules plays a key role in the transition from the low-pressure to the high-pressure liquid phase.
130(2009); http://dx.doi.org/10.1063/1.3090484View Description Hide Description
We present results of temperature dependent measurements of dynamics of polymer grafted nanoparticles with high grafting density with star polymerlike morphology. We observed for the low grafting density and hence low functionality sample, a dynamically arrested state with lowering of temperature, similar to what was conjectured earlier. However the high grafting density sample shows liquidlike relaxation at all measuredtemperatures. Possible origin of dynamical arrest in the two grafting density sample is discussed.
130(2009); http://dx.doi.org/10.1063/1.3106762View Description Hide Description
The growth of glycine film by thermal evaporation on at room temperature has been studied by X-ray photoemission. In contrast to common carboxylic acids, glycine is found to adsorb on dissociatively through cleavage of a N–H bond instead of O–H bond. The intricate evolution of the observed N features at 399.1, 401.4, and 402.2 eV with increasing film thickness demonstrates the existence of a transitional adlayer between the first adlayer and the zwitterionicmultilayer. This transitional adlayer is estimated to be 1–2 adlayer thick and is characterized by the presence of intermolecular hydrogen bond. An intramolecular proton transfer mechanism is proposed to account for the adsorption process through the amino group.