Interface coverage

FIG. 5 Interface coverage with CTAB molecules vs. CTAB average concentration in the water phase. Experimental data are shown as squares, and the calculated Langmuir adsorption isotherm is the solid line. 

Interface Coverage [ML] Site Td [K] Ead [eV/atom] Method Refererrce... 

Luu X-C, Yu J, Striolo A Nanoparticles adsorbed at the water/oil interface coverage and composition effects on stmcture and diffusion, Langmuir 29 122 -1 T2, 2013a. 

Chemical constitution Concentration Solubility in continuous phase, absorption behavior at solid-liquid interface. Coverage of the surface, viscosity of the continuous phase, IJ0... 

SHG Optical second-harmonic generation [95, 96] A high-powered pulsed laser generates frequency-doubled response due to the asymmetry of the interface Adsorption and surface coverage rapid surface changes... 

Because of the generality of the symmetry principle that underlies the nonlinear optical spectroscopy of surfaces and interfaces, the approach has found application to a remarkably wide range of material systems. These include not only the conventional case of solid surfaces in ultrahigh vacuum, but also gas/solid, liquid/solid, gas/liquid and liquid/liquid interfaces. The infonnation attainable from the measurements ranges from adsorbate coverage and orientation to interface vibrational and electronic spectroscopy to surface dynamics on the femtosecond time scale. 

We now consider how one extracts quantitative infonnation about die surface or interface adsorbate coverage from such SHG data. In many circumstances, it is possible to adopt a purely phenomenological approach one calibrates the nonlinear response as a fiinction of surface coverage in a preliminary set of experiments and then makes use of this calibration in subsequent investigations. Such an approach may, for example, be appropriate for studies of adsorption kinetics where the interest lies in die temporal evolution of the surface adsorbate density N. ... 

The applications of this simple measure of surface adsorbate coverage have been quite widespread and diverse. It has been possible, for example, to measure adsorption isothemis in many systems. From these measurements, one may obtain important infomiation such as the adsorption free energy, A G° = -RTln(K ) [21]. One can also monitor tire kinetics of adsorption and desorption to obtain rates. In conjunction with temperature-dependent data, one may frirther infer activation energies and pre-exponential factors [73, 74]. Knowledge of such kinetic parameters is useful for teclmological applications, such as semiconductor growth and synthesis of chemical compounds [75]. Second-order nonlinear optics may also play a role in the investigation of physical kinetics, such as the rates and mechanisms of transport processes across interfaces [76]. 

Later it was found that the polluting lubricant droplets originating from the transport belts used in the production they had fallen into the paint bath and prevented adhesion of the paint to the metal. It can be concluded that the high sensitivity of SSIMS in the detection of submonolayer coverage of organic species makes it an extremely powerful tool for solving such interface problems. 

In which we summarize the terms as CTq = cohesive fracture strength of A = modulus of A, h = thickness of A layer L = influx length to a maximum length Lc, I — influx coverage of the A-B interface (/ < 1) = fraction of elastic energy dissipated in the A layer ( < 1). 

A particularly simple lattice model has been utilized by Harris and Rice [129] and subsequently by Stettin et al. [130] to simulate Langmuir mono-layers at the air/water interface chains on a cubic lattice which are confined to a plane at one end. Haas et al. have used the bond-fluctuation model, a more sophisticated chain model which is common in polymer simulations, to study the same system [131]. Amphiphiles are modeled as short chains of monomers which occupy a cube of eight sites on a cubic lattice and are connected by bonds of variable length [132], At high surface coverage, Haas et al. report various lattice artefacts. They conclude that the study... 

An adsorption isotherm gives the relatiortship between the coverage of an interface With an adsorbed species (the amount adsorbed) and the pressure of gas or concentration of the species in solution in electrochemical reactions the coverage will depend alisO on the potential diHbrcnce at the... 

Previous Considerations have been confined to the effect of pressure and concentration upon coverage, but in an electrochemical equilibrium the activity and chemical potentials of the species adsorbing at the interface will also be a function of the potential difference A4>. For a solution containing unit activity of the species the effective pressure of the species at the interface is given by... 

Figure 5-16. XPS C(ls), S(2p), and Al(2p) spcclra of llie AI/ -6T interface for increasing Al coverage. Tlic C(ls) and S(2p) spccua of the pristine system is al the bottom and increasing Al coverage upwards (from Kef. 184 ).

Figure 5-17. XPS S(2p) spectra of the Cu/P3HT interface for increasing Cu coverage. The S(2p) spectrum of the pristine system is at the lop and increasing Cu coverage downwards (adapted from Ref. 188]).

Section 8 deals with reactions which occur at gas—solid and solid—solid interfaces, other than the degradation of solid polymers which has already been reviewed in Volume 14A. Reaction at the liquid—solid interface (and corrosion), involving electrochemical processes outside the coverage of this series, are not considered. With respect to chemical processes at gas-solid interfaces, it has been necessary to discuss surface structure and adsorption as a lead-in to the consideration of the kinetics and mechanism of catalytic reactions. 

Figure 8 shows an example of the most common behavior of AEam/0 as a function of adsorbate coverage. Linear behavior, if ever observed, is seen at the air/solution interface.93 At metal/solution interfaces, if chemical interactions with the metal can be ruled out, electrostatic interactions cannot be avoided, and these are responsible for the downward curvature.91 Upward curvatures are often observed at air/solution interfaces as a consequence of lateral interactions.95... 

Figure 2.8. STM image (unfiltered) of a Pt( 111) surface of a Pt single crystal interfaced with P"-A1203, a Na+ conductor showing different domains of Na coverage. The Pt(l 11 )-(2x2)-0 surface was initially covered by the Pt(ll l)-(2x2)-Na adlattice (domain A) and was intentionally only partly electrochemically cleaned (via positive UWR=1V potential application and Na+ removal into the P"-A1203 lattice) leading to the formation of clean domains (domain B) and of higher Na coverage domains (domain C) corresponding to a (V3 x V3 )-Na adlattice.

We consider the adsorption of a single molecule, j, on a metal film M. The film is deposited on a solid electrolyte, e.g. YSZ, or is partly covered by a promoter, or simply has a significant coverage of adsorbed reactants and products on its surface, so that we may consider (Chapter 5) that an effective double layer is present at the the metal-gas interface (Fig. 6.15). 

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