1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

A unified approach to physica adsorption of heterogeneous solids is presented. In the case of single-gas adsorption the overall adsorption isotherms, derived by solving the fundamental integral equation for Langmuir's local isotherm and different energy distributions, are discussed. These isotherm equations are extended for Fowler-Gugaenheim and BET local adsorption isotherms. Moreover, the overall isotherms for single-gas adsorption are generalized for mixed-gas adsorption, adsorption from solutions of non-electrolytes and multi-solute adsorption from dilute solutions. The last section of this paper is devoted to the kinetics of localized adsorption of cases, the gas and liquid mixtures on energetically heterogeneous solid surfaces.

Physical Adsorption on Heterogeneous Solids

Localized adsorption on heterogeneous surfaces

Recent progress in determination of energetic heterogeneity of solids from adsorption data

Desorption and scattering of a helium atom from dynamic surfaces are studied using a generalized Langevin equation formalism for the bulk solid and time dependent quantum mechanical propagation of the helium. The motion of the bulk solid enters the Schrodinger equation as a time dependent potential coupling the solid surface to the atom. The propagation of the atomic wave packet is then followed in coordinate space using a Fourier transform technique to evaluate the kinetic energy operator. An attenuating grid is used to remove the wave packet in the asymptotic region thus permitting stable calculations for long duration times. Rates for one dimensional desorption from tungsten as a function of temperature are computed which display a change in mechanism. Three dimensional scattering from platinum at two temperatures shows significant nonspecular amplitude. These results indicate the utility of this time dependent technique.

Dynamical atom/surface effects: Quantum mechanical scattering and desorption

Theory of localized and non-localized adsorption

A theory is developed for adsorption of gases on patchwise heterogeneous surfaces with the assumption of a discrete distribution of site energies. The lateral interactions between adatoms in the first layer are neglected, but those in the second layer are accounted by the cluster expansion theorem. The heterogeneity effect on the isotherm is studied via the renormalization of the first layer coverage. The representation of the first layer coverage in the form of a pade approximant is introduced to determine the distribution of site energies. There is established a set of inequalities for the coefficients of the Pade approximant, which is essential in the analysis of experimental data. The theory is successfully applied to the systems of gases adsorbed on rutile reported by Drain and Morrison. It is found that the rutile surface primarily consists of three kinds of patches, the relative extent of which is proportional to that of cleavage planes of rutile. The distribution of site energies is discussed in comparison with the distribution functions previously obtained by other authors. The cluster integrals for the second layer are determined. The theory is also applied to the systems of gases on porous silver given by Hobson.

Theory of localized and nonlocalized adsorption of gases on heterogeneous surfaces

The maxima, minima, and inflection points of the thermodynamic functions are calculated from the theory of localized and nonlocalized adsorption. Experimental determinations of the molecular thermodynamic functions, which depend on temperature alone, are discussed. Existing empirical methods of determining monolayer capacity from entropies and isosteric heat are examined. The inflection point of isosteric heat or of differential entropy directly gives monolayer capacity within an error less then 5% for ordinary systems. Similar results obtained for the BET theory are given in the Appendix; it is noted that the inflection point of the isosteric heat occurs at the coverage θ = 1−2c−1.

Characteristic properties of thermodynamic functions for the theory of localized and nonlocalized adsorption

A study has been made of fluctuations in adsorbed phase coverage based on a model which assumes localized adsorption for the first layer and nonlocalized mobile adsorption for the second layer. For a homogeneous surface the envelopes, extremum locations, and limiting knee point of the fluctuation are calculated. An s‐shaped semiloop exists in the fluctuation, if the adsorption strength c is larger than the critical value cK=28.43. The molar fluctuation (fluctuation divided by coverage) has always one minimum. In the case of adsorption on a heterogeneous surface with s‐different patches there exist s maxima and minima in the fluctuation provided that [Mi]ci/Mi−1ci−1≳cK=28.43, i=2, 3,..., s, where ci and Mi are the adsorption strength and the number of lattice sites for the ith patch, respectively, and [Mi]=Jsk=iMk. From these extrema in the fluctuation we can estimate the characteristic constants ci’s and Mi’s of an adsorbed phase. The theory is in excellent agreement with the observed fluctuations of argo...

Fluctuation in adsorbed phases

The problem of rotational diffusion of a polar cylinder about its long axis in an electric field has been solved. The solutions apply to the high as well as the low field limits. The results are presented as a function of a reduced time and the variable κ, which is a measure of the ratio of mean electrical energy to thermal energy. Asymptotic expansions are obtained for the distribution function and the fractional polarization. The eigenvalues and even solution of a Whittaker–Hill–Ince differential equation have been calculated as functions of κ. Asymptotic expansions of the eigenvalue and solution of this equation are given.

Byung K. Oh

Papers

Theory of localized and non-localized adsorption

Theory of localized and nonlocalized adsorption of gases on heterogeneous surfaces

Characteristic properties of thermodynamic functions for the theory of localized and nonlocalized adsorption

Fluctuation in adsorbed phases

Relaxation of polar cylinders in strong electric fields