Much is known about the structure and order-disorder transitions of linear block copolymers.1-3 Detailed information about the kinds of microphase domain morphologies that can be found in block polymers, the composition of copolymer that display each structure, and the conditions for the transitions between these morphologies, as well as into a disordered state, is available. For graft polymers, there has been only one theoretical treatment

No abstract

Diblock copolymers show a menagerie of morphologies1 as a function of the relative lengths of the blocks and the temperature (or the magnitude of x-N, where x is the Flory interaction parameter and N the degree of polymerization). These structures range from spheres to hexagonally ordered cylinders and lamellae, corresponding to decreasing mean curvature of the interphase boundary. More recently2 a three-dimensionally ordered structure called the ordered bicontinuous double diamond (OBDD) phase is found at styrene compositions 4>s between 0.62 and 0.66 for polystyrene-6-polyisoprene diblock copolymers. When a homopolymer is mixed with a diblock copolymer, the occurrence of macrophase separation adds a new dimension to the possible morphological variations that can be realized, and the phase diagrams of such blends exhibit fascinating complexities.3,4 Even when the amount of added homopolymer is below its solubility limits so that a single macroscopic phase is realized, a range of structure,

The absolute binding energies of Pt on the stoichiometric and reduced TiO 2 ͑110͒ surfaces should be lower by 0.48 eV compared to the values reported in our paper. This results in a uniform shift of the energy scale in Fig. 2͑a͒ and Fig. 3͑a͒. The new Fig. 2͑a͒ and 3͑a͒ with the updated energy scale are shown below. The correct binding energies of Pt to the stoichiometric and reduced surfaces at the most favorable sites should be 2.03 eV ͑2.14 eV for 3 ϫ 2 cells͒ and 3.80 eV ͑3.55 eV for 4 ϫ 2 cells͒, respectively. This does not change the main conclusions of the paper, since the conclusions involve relative binding energies of Pt, which remain the same, and the Pt-Au binding energy differences are still large, ϳ1.5 eV. FIG. 2a. ͑Color online͒ The potential energy profile for Pt on the stoichiometric TiO 2 ͑110͒ surface. The profile is doubled along the ͓001͔ direction ͑compared to the chosen rectangular grid mentioned in the original paper͒ to have the same size as the profiles in Fig. 3͑a͒. FIG. 3a. ͑Color online͒ The potential energy profiles for Pt on the reduced TiO 2 ͑110͒ surface. PHYSICAL REVIEW B 73, 039902͑E͒ ͑2006͒

No abstract

A comparative first principles pseudopotential study of the adsorption and migration profiles of single Pt and Au atoms on the stoichiometric and reduced TiO 2 rutile (110) surfaces is presented.Pt and Au behave similarly with respect to (i) most favorable adsorption sites, which are found to be the hollow and substitutional sites on the stoichiometric and reduced surfaces, respectively, (ii) the large increase in their binding energy (by ∼ 1.7 eV) when the surface is reduced, and (iii) their low migration barrier near 0.15 eV on the stoichiometric surface. Pt, on the other hand, binds more strongly (by ∼ 2 eV) to both surfaces. On the stoichiometric surface, Pt migration pattern is expected to be one-dimensional, which is primarily influenced by interactions with O atoms. Au migration is expected to be two-dimensional, with Au-Ti interactions playing a more important role. On the reduced surface, the migration barrier for Pt diffusion is significantly larger compared to Au.

The characterization of Pt/TiO2 (Degussa P25) catalyst system using atomic resolution Z-contrast images and electron energy loss spectroscopy in the scanning transmission electron microscope has recently revealed that Pt particles have a strong tendency to nucleate on the rutile phase of TiO2 rather than anatase. Comparative ab initio pseudopotential calculations for Pt and Pt2 on the stoichiometric and reduced TiO2 surfaces, and oxygen vacancy (VO) formation energies are performed to address the microscopic origin of this finding. The results, which show that Pt actually binds more strongly to anatase surfaces, indicate that the selective growth of Pt on rutile must be controlled by the lower formation energy of VO on rutile, and possibly by the stronger tendency of VO sites on rutile to trap large Pt clusters compared to anatase.The fundamental and technological importance of TiO 2 , stemming to a large extent from its wide spread use as a catalyst and catalyst support, has made it the subject of many experimental and theoretical studies over the last decade.[1] As one of the most active catalysts for CO oxidation reactions and photocatalysis, in addition to being the prototype system for the strong-metalsupport-interaction (SMSI) phenomenon, [2] Pt/TiO 2 has recently received particular attention. The catalytic properties of Pt/TiO 2 and the occurrence of SMSI has a strong dependence on the phase of TiO 2 (rutile versus anatase). For example, it was recently shown that anatase titania palladium supported catalyst presents SMSI at low H 2 pre-reduction temperatures, while rutile does not.[3] It is also well known that anatase is more efficient than rutile as an oxidative photocatalyst.[4] The presence of a small amount of rutile, however, such as in commercial mixed-phase titania samples results in an unusually high activity.[5] A fundamental comparative study of the interaction of Pt with both rutile and anatase TiO 2 surfaces will, therefore, contribute to our understanding of the catalytic properties of this system and the occurrence of SMSI.Recently, using a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), we examined the atomic and electronic structure of the Pt/TiO 2 interface.[6] The experiments were performed on a commercial mixed-phase titania sample, known as Degussa P25, which is composed of about 80 % anatase and 20 % rutile. We observed rather unexpectedly that Pt particles were not uniformly distributed over the titania particles, but showed a selective distribution, as shown in Fig. 1(a). The oxygen−K edges of these specific particles [ Fig. 1 Oxygen K−edge EEL spectra taken at the locations specified in (a). Note the difference in the shape of the secondary peaks (from 538 eV to 548 eV) for particles 1 and 2 in comparison to particle 3. (c) O K−edge EEL spectra of bulk rutile and anatase shown for comparison with the spectra in (b), showing that particles 1 and 2 with few Pt clusters are of anatase and the d...

Simultaneous and molecularly selective parts-per-billion detection of benzene, toluene, and xylenes (BTX) using a thermal desorption (TD)-FTIR hollow waveguide (HWG) trace gas sensor is demonstrated here for the first time combining laboratory calibration with real-world sample analysis in field. A calibration range of 100-1000 ppb analyte/N(2) was developed and applied for predicting the concentration of blinded environmental air samples within the same concentration range, and demonstrate close agreement with the validation method used here, GC-FID. The analyte concentration prediction capability of the TD-FTIR-HWG trace gas sensor also compares well with the industrial standard and other experimental techniques including GC-PID, ultrafast GC-FID, and GC-DMS, which were simultaneously operated in the field. With the advent of a quantum cascade laser with emission frequencies specifically tailored to efficiently overlap benzene absorption as the most relevant analyte, the overall sensor footprint could be considerably reduced to ultimately yield hand-held trace gas sensors facilitating direct and real-time detection of BTX in air down to low ppb levels.