The Physics of Cleaning
By Ed Kanegsberg, BFK Solutions LLC, Reprinted with Permission from Clean Source, a BFK Solutions Newsletter
Think like a physicist; and, by understanding how cleaning works, your cleaning process can be much more effective. As a physicist, I tend to view the processes of cleaning, washing, rinsing, and drying, in terms of physical actions. Before you cower and run away, let me assure you that the concepts are pretty easy to understand.
The processes of cleaning involve forces, and they involve energy. Soil is matter out of place. The purpose of cleaning is to remove soils from the surface (or sometimes from beneath the surface) of a product. In cleaning, there is a “tug of war” at the molecular level. The soils are held to the product by forces; and it takes energy to overcome those forces and to separate the soil from the product.
Forces
The forces involved are intramolecular forces of chemical bonds, those that hold atoms together to form molecules, or the intermolecular forces that hold molecules together to form liquids or solids rather than a gas. In general, intermolecular forces are weaker than intramolecular forces, and most soils are held to the product by the weaker intermolecular forces. Even though the soils are held to the product by the weaker forces, that does not necessarily make cleaning easy, since the molecules of the product are also held together by intermolecular forces, and the goal in cleaning is usually to remove the unwanted soils without unduly removing or altering the product from which the soils are removed.
Opposites Attract
The adage that opposites attract holds true in cleaning. Virtually all the forces that are involved in the processes of cleaning arise from electronic charges that are associated with the atoms and molecules of interest. Since like charges repel and unlike charges attract, a molecule with a portion that is predominantly positively charged will be attracted to a predominantly negatively charged portion of another molecule.
No Energy, No Cleaning
You don’t clean without energy, even if you clean by soaking the product in solvent at room temperature. It takes energy to separate molecules that are bonded by forces. That energy can come from rearranging chemical bonds to change molecular identity (chemical reactions), from electrical current, or from the motion of atoms and molecules. Heat is an example of energy associated with the motion of atoms and molecules. More heat means molecular motion, and that means there is more energy available to dislodge soil.
Editor’s Note: To read more about The Physics of Cleaning, visit Clean Source at BFK Solutions for additional articles in this series.
Dr. Ed Kanegsberg is a consultant in manufacturing process development and modification with a concentration in critical cleaning, surface preparation, process design, and failure analysis/resolution. As Vice President of BFK Solutions, he uses his 35 years of experience in chemical physics and engineering to address production yield issues through process improvement, materials substitution, and component modification. His background is in the design, development, testing, and manufacture of critical precision instruments. He utilizes this background to rapidly and effectively troubleshoot an array of fabrication process problems; he has been known to pinpoint the source of equipment problems more rapidly than the equipment supplier. He also coordinates the transition of the product from the engineering laboratory to the fabrication facility or factory. His concerns include issues of scale-up, technical training, procedures and documentation, customer requirements (including military requirements if applicable), and regulatory issues. Ed conducts site visits and audits. He is involved in research in environmental policy. His activities include cost/benefit analyses for economic and regulatory applications. Ed specializes in the technical and analytical evaluation that allows optimal resolution of regulatory permitting problems. Ed is co-editor of the comprehensive “Handbook for Critical Cleaning,” CRC Press, 2001. He also co-authors a column that appears regularly in Controlled Environments Magazine; he specializes in explaining the practical importance and the basis of operation of new analytical technology. His presentations and publications emphasize the physics of general cleaning, critical cleaning, and surface quality. As a confirmed believer that most of rocket science can be understood by non rocket scientists, he has extensive publications and has conducted scores of workshops, both public and for individual companies as well as for the military. He is a technical adviser, working with all levels of interest and sophistication including technicians, other engineers, and upper management. Ed has been awarded numerous U.S. and foreign patents. He has a B.S. in Physics from Massachusetts Institute of Technology and a Ph.D. in Physics from Rutgers University.
