Surface vs. bulk composition

Films of the three block copolymers were cast from chloroform, a mutual solvent for PS and PEO,( ) and the measured and 0. core level spectra are shown in Figure 2. The spectra show the characteristic peak of PEO, the shake-up satellite of PS, and an easily deconvoluted doublet for the core levels in PS and PEO. It is apparent from the spectra that he PS concentration at the copolymer surface increases as the PS in the copolymer increases. More importantly, however, an analysis of the spectral data clearly shows that the surface compositions are significantly richer in PS than would be predicted based on a knowledge of the bulk compositions of the block copolymers. In Figure 3 is shown a plot of the surface-vs-bulk compositions for the diblock copolymers. ... 

Figure 3. Surface vs. bulk compositions for PS/PEO diblock (9) and triblock (/S) copolymers (XPS ( ) = 0°)...

Figure 10. Comparison of the surface-vs.-bulk composition for the blends (0) and the diblock copolymers (A) (from CHCb)...

Acidified water surfaces degree of surface sensitivity, 111 experimental description, 107-109 stratospheric significance, 107 sulfuric acid, 109-111 surface composition, 111-113 surface vs. bulk composition, 113-114 Adsorption... 

FIGURE 435. Surface vs. bulk composition of Cr-doped CoO. (From Haber, J., Nowotny, J., Sikora, I., and Stoch, J., J. Appl. Phys., 1984, 17, 321 330. With permission.)... 

Figure 1. Catalyst composition surface vs. bulk. Reproduced with permission from Ref. 2. Copyright 198A, Acaddmic Press.

Katrlfk et al. [25] Wine Alcohol dehydrogenase (ADH) and diaphorase (DP)/added either to the bulk composite or to the surface Graphite-solid binding matrix composite modified with NAD+ and the mediator/+300 mV vs. SCE Organic dyes, vitamin K3, h exacyan oferrate(III), ferrocene... 

Fig. 19.a Local d66 volume fraction as a function of depth z, determined for the d66/h52 blend monolayers with different initial compositions following 2 h of annealing at 99 °C [16]. Horizontal solid and dashed lines indicate the respective binodal values and ( )2 and their estimated uncertainty. The hatched area marks the d66 surface excess z. The inset marks on the phase diagram bulk compositions ([) for which z was determined. Solid curve in the inset denotes binodal determined previously [91] and described by %= (0.327/T+3.48X10 4)(l+0.222( )). b Segregation isotherm data [16] plotted as normalized surface excess z /[w(( )2-< )i)] vs normalized bulk volume fraction (1) (1),. Solid lines are generated by Eq. 44 to fit the data. Dashed horizontal lines are normalized surface excess values for the bulk phase enriched at the surface to the compositions ( )s such that (([>2—s)/(ct)2— ())1)=10%, 5%, and 1%, respectively... 

Fig.24.a-b Typical d52 volume fraction (1—<))) vs depth z profiles indicating a a depletion b an enrichment in the h66 component, obtained for 90%h66/10%d52 and 30%h66/70%d52 monolayers annealed at 71 °C for 16 and 43 h, respectively [175]. Hatched areas mark positive (b) and negative (a) values of the h66 surface excess z. The free surface locus (z=0) is yielded by - the profile itself (a) - a profile of the control layer measured prior to the annealed sample (as in Fig. 21 a) - the interface created by a reference layer positioned on top of the annealed sample (b) c a phase diagram as outlined by previously determined coexistence compositions [91] (solid line described by %=(0.452/T-1.2Xl(T4)(l+0.031)) and coexistence temperatures [138] (X points). Bulk compositions in one phase region are marked where the surface enrichment (A symbols) or depletion ( points) in h66 is concluded... 

Fig.26.a Composition ( ) vs depth z profiles of x=86% copolymer through annealed to equilibrium films of d86/h75 mixture (O points and a dashed line, T=106°C, [16]) and of h86/d75 blend ( points and a solid line, T=86 °C, [145]). The surface excess z (shaded area marked for h86/d75) increases when h86/d75 mixture is exchanged for d86/h75 blend in line with the shift of phase diagram presented in the inset (solid and dashed lines for h86/d75 and d86/h75, respectively). In the inset the symbols O and mark the bulk compositions of profiles presented for d86/h75 and h86/d75 blends, respectively, b Composition vs depth z profiles of x=66% copolymer through annealed to equilibrium films of d66/h52 (O points and a dashed line,1=99 °C, [16]) mixture andh66/d52 ( points and solid line, T=89 °C, [175]) blend. The surface peak (and the excess z ) increases when h66/d52 mixture is exchanged for d66/h52 blend in line with the shift of phase diagram presented in the inset (solid and dashed lines for h66/d52 and d66/h52, respectively). In the inset the symbols O and mark the bulk compositions of profiles presented for d66/h52 and h66/d52 blends, respectively... 

Fig. 22. Surface MA oxygen concentration vs bulk MA content for thermally pressed poly(ethylene-co-methyl acrylate) films as determined from XPS at three different take-off angles. The bold line would be obtained for a surface composition identical with the bulk.

Among the surface-modified CNTs materials, a bulk-modified CNT paste (CNTP) has also been reported [126]. The new composite electrode combined the ability of CNTs to promote adsorption and electron-transfer reactions with the attractive properties of the composite materials. The CNTP was prepared by mixing MWCNTs powder (diameter 20-50 nm, length 1-5 jim) and mineral oil in a 60 30 ratio. The oxidation pretreatment [performed in ABS (pH 5.0) for 20 s at 1.30 V, vs Ag/AgCl] proved to be critical in the state of the CNTP surface. Pretreatments improved the adsorption and electrooxidation of both DNA and DNA bases, probably due to the increase in the density of oxygenated groups. 

Taking the 25% sizing additive composition as a model for the interphase near the fiber surface, the interphase consisting of this epoxy with this commercial sizing agent would have a lower Tg than the bulk by about 70°C (176°C vs. 100°C),... 

FIG. 14. Number of d holes on Pd atom vs. composition in Pd-Ag 15-atom model for one bulk and two surface atoms. 

Despite all simplifications the model of particle in the rectangular potential well, extended to include the population of excited le els. describes quite well the dependence of ortho-positronium lifetime on the pore radius. In this model the o-Ps lifetime is ruled entirely by geometrical factors, however, maybe the chemical composition of the medium should be taken into account. The lifetime vs. average radius dependence is particularly steep below 5 nm. and in this range the positron annihilation method can be useful for determination of average pore radii. The specific surface determines the distribution of o-Ps between small voids in the bulk and pores. 

Another insight into the wetting phenomena, alternative to that yielded by the contact angle 0, has been given by the profile (]>(z) (composition < > vs depth z) [8,53,61,153,158]. The surface of a two component liquid mixture which favors one of the components will be enriched in that component, A say. When the region far from the surface (bulk region) is occupied by the B-rich phase the surface concentration < >s (( >ls or < >2S in Fig. 14) is higher than this binodal value... 

We have studied binary blends dxx/hx2 of random olefinic copolymers x=(Ex x EEx)n, with one blend constituent protonated (hx) and the other deuterated (dx). The blends examined were grouped in four pairs of structurally identical mixtures xx/x2 but with a swapped isotope labeled component (dxx/hx2 and hxx/dx2). For such blend pairs the bulk interaction parameter % (and hence also the critical point Tc) has been found (see Sect. 2.2.3 and references therein) to be higher when the more branched (say xx>x2) component is deuterated, i.e., X(dx /hx2)>x(hx /dx2) or Tc(dxx/hx2)>Tc(hxx/dx2) (see Fig. 9). An identical pattern is exhibited here by the force driving the segregation at the free surface. This is illustrated in Fig. 26a,b where the composition vs depth profiles of the more branched (xx) component are shown for blend pairs with swapped isotope... 

Example 13-5 Using the one-dimensional method, compute curves for temperature and conversion vs catalyst-bed depth for comparison with the experimental data shown in Figs. 13-10 and 13-14 for the oxidation of sulfur dioxide. The reactor consisted of a cylindrical tube, 2.06 in. ID. The superficial gas mass velocity was 350 lb/(hr)(ft ), and its inlet composition was 6.5 mole % SO2 and 93.5 mole % dry air. The catalyst was prepared from -in. cylindrical pellets of alumina and contained a surface coating of platinum (0.2 wt % of the pellet). The measured global rates in this case were not fitted to a kinetic equation, but are shown as a function of temperature and conversion in Table 13-4 and Fig. 13-13. Since a fixed inlet gas composition was used, independent variations of the partial pressures of oxygen, sulfur dioxide, and sulfur trioxide were not possible. Instead these pressures are all related to one variable, the extent of conversion. Hence the rate data shown in Table 13-4 as a function of conversion are sufficient for the calculations. The total pressure was essentially constant at 790 mm Hg. The heat of reaction was nearly constant over a considerable temperature range and was equal to — 22,700 cal/g mole of sulfur dioxide reacted. The gas mixture was predominantly air, so that its specific heat may be taken equal to that of air. The bulk density of the catalyst as packed in the reactor was 64 Ib/ft. ... 

Two different stages for silver deposition on platinum can be described one at 1.1 V vs. RHE responding to a silver-platinum alloy electrodissolution (overlapped with the oxygen electroadsorption at free platinum sites) and the other at 0.65 V due to the silver oxidation (from the onset of the bulk deposition process) deposited on the former surface alloy [88,89]. The former process splits into two peaks when the potentiostatic ageing is performed. The spectroscopic techniques such as XPS and ARXPS (angle resolved x-ray photoelectron spectroscopy) were used to determine the chemical composition of the silver films on the platinum in an acid solution [92], The technique was not able to discern between the presence of silver oxides and sulfates, only an energy shift of the clean silver 3d5/2 band at a upd level of —0.5 eV was detected. 

Tin oxide-based materials are potent oxidation and isomerization catalysts. Their bulk and surface properties, as well as their presumed mechanism in oxidation catalysis, have been reviewed (53j. Considerable uncertainty remains concerning the phase compositions, solid-solution range, and the redox behavior (Sn / Sn" vs. Sb WSb ) of these materials. Structural investigations have so far concentrated on the use of " Sn and Sb Mossbauer spectroscopy. Surprisingly, no " Sn solid-state NMR studies have appeared to date on this system, although it was recently demonstrated that isotropic " Sn chemical shifts and chemical shift anisotropies give characteristic fingerprints of the various tin coordination environments in Sn(IV) oxide compounds [54]. In situ C NMR has been used to study the double bond shift of 1-butene to t /.s-2-butene, and the subsequent cis-trans isomerization over tin antimony oxide catalysts [55 j. 

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