Brief Concepts of Surface Chemistry.

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S u r fa c e C h A n mr aicsi vt rcyn c e e att t e s ie

A few words on the history and future of surface chemistry For more than 400 years, important scientists and mathematicians like Leonardo da Vinci, Isaac Newton, Pierre Simon Laplace, Thomas Young, Siméon Denis Poisson, Josiah Willard Gibbs, Frederick M. Fowkes have done valuable pioneer work for the explanation of surface tension, capillarity, wetting and other interfacial problems. As a sector of physical chemistry, surface chemistry in connection with colloid chemistry established itself as an independent science about 70 years ago. Important milestones in modern theory and practice of wetting properties are the works of Girifalco/Good and Fowkes from the 50s and 60s of this century. They formed the basis for the analysis and optimization of solid and liquid interfaces frequently applied today. Although most of us don't realize it, interfacial processes rule our everyday life wherever we go. A multitude of processes, whether in a household or in industrial production, is influenced by interfaces and their chemical state. All known high technologies with a promising future, like wafer and chip production, biochemistry and gene technology as well as micro-system technology benefit in particular from the increasing understanding of interfacial correlations. The DataPhysics team would like to take you on a little tour of this exciting world.

S c i e n sc oet i n t r o d u c t i o n t o s u r f a c e c h e m i s t r y A h r

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About interfacial interactions When talking about the wetting behavior of liquids and solids; this is in fact surface chemistry. Apart from such properties as density or viscosity, liquids also have the property of surface tension, which specifies the amount of work necessary to create a piece of new surface. It is equivalent to the surface free energy of solids.

A series of inter- and intra-molecular interactions rules the surface phenomena, all of which have their origin in Coulomb's attraction or repulsion of differently or equally charged particles, electrons and nuclei. Phenomenologically, a distinction is made between static and induced dipole moments, which are named after their discoverers Keesom (1912), Debye (1920) and London (1930). The ratio of forces of the three interaction types in water for instance is 190:11:47.

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In summary they are known as »van der Waals interactions« and manifest themselves for example, in the deviation of gasses from ideal behavior. Since the works of Latimer and Rodebush (1920) the additional possibilities of interaction in polar media such as water, alcohol or acetic acid are known. Water molecules especially are exemplary representatives of the formation of so-called hydrogen bonds, whose presence shows in the known density anomaly of water (e.g. floating icebergs). The hydrogen bonds causing the formation of an orderly cage structure in water are the basis of all organic life. The bonding forces between the nucleic acids in the chromosome molecule DNS are naturally hydrogen bonds, too.

1 Molecular interactions on the liquid surface – Surface tension 2 Interaction of two dipoles (parallel position) 3 Interaction of two dipoles (head-on position) 4 p- and s-electron orbital gaining proximity 5 Cage structure of a water cluster 6 Ca l c u l at i o n o f a s i m u l at e d co n t a c t a n g l e – Wat e r on a polymer (polyethylene terephtalate PET)

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8 L o n g - c h a i n s u r f a c t a n t m o l e c u l e C TA ⊕ – Cetyltrimethylammonia cation

7 Electrostatic potential of a water molecule

Today, the Schrödinger equation as the physical basis of quantum chemistry forms the firm theoretical foundation of surface chemistry. Many numerical methods of approximation (e.g. ab initio, semi-empirical) have in recent years been continuously developed with the aim of understanding chemical bonding forces and courses of reaction with the help of the...
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