The Physics
of Cleaning, Part 1—Forces and Energy
Ed Kanegsberg
BFK Solutions LLC
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. In upcoming articles
in this
series, I will go into greater detail on the types of intermolecular
forces and how they impact the ability of some materials to remove soils
more
readily than others.
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 more molecular motion
and that means there is more energy available to dislodge soil. In upcoming
articles, I will expand on the role and type of energy involved in cleaning
processes.
