Physisorption

Definition - What does Physisorption mean?

Physisorption is the physical bonding of gas molecules to the surface of a solid or liquid that the gas comes into contact with at low temperatures. This occurs due to Van der Waals forces. The weak, long-range bonding is not surface specific and takes place between all gas molecules on any surface. The process, which does not involve any surface reaction, is achieved quickly at low temperatures, but surface coverage reduces with temperature increase. Physisorption is used when measuring the total surface area and in pore size analysis of mesopores, micropores and nanopores.

Physisorption is also known as physical adsorption.

Corrosionpedia explains Physisorption

Most of the atoms making up a solid are bounded by other atoms on all sides. Atoms on the solid's surfaces, however, are not bounded completely. Van Der Waals interactions cause these surface atoms to be reactive, causing them to attract liquids, vapors and gases in order to satisfy their atomic force imbalance. The attracted molecules fill in the pores on the surface of the solid when adsorption occurs.

This adherence of gas or liquid molecules to the surface of a solid does not affect the particle’s electronic and geometrical characteristics. However, a slight but reversible deformation of the atoms may occur. There is no chemical specificity in physisorption and any gas is adsorbed on any solid surface, provided that sufficiently low temperature or high pressure conditions are satisfied.

The adherence molecules (adsorbate) are not limited to gases as a source, and can be from liquids or solids. In fact, this physical adsorption of gas molecules occurs on both solid and liquid surfaces (adsorbents). Liquid molecules can also adhere to solid surfaces, and solid-to-solid adherence also occurs.

The physisorption effect is used in determining surface areas and the porosity of solid surfaces. The surface area determined using this analysis is more complex, but a true measurement, as opposed to the area determined by the width and length of an object. The analysis takes into account all the additional areas due to ripples, pores and other imperfections.

Physisorption analysis is widely used in research, development and quality control in industries such as:

  • Nanotechnology
  • Metallurgy
  • Pharmaceutical
  • Material science
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