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Infection Control

Science-based Steps Of The Cleaning Process: Part Four

September 19, 2010
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Separating Matter From The Environment Or Sub-compartment

Effective cleaning requires separating unwanted matter or its parts from the compartment being cleaned.

Understanding how moving or displacing this matter occurs requires a basic knowledge of energy, physical force and chemical action.

What Is The Difference Between Energy And Force?

Energy — required for cleaning — is the capacity to move matter (a substance with mass) a known distance.

Potential energy is matter that is ready to move.

Gravitational energy is the attraction of two objects with known mass and distance.

Kinetic energy is moving matter with an identified mass and velocity.

Heat energy is the sum of kinetic energies in which multiple masses move randomly in all directions.

Force sets matter into motion.

Mechanical force often is used when displacing matter from a compartment or environment.

In cleaning, wiping or brushing and water or air flows are common forms of displacement.

Friction is a force derived from two connected objects moving in different directions.

This force moves matter and generates heat.

Abrasion occurs when friction erodes a solid surface film.

An abrasive cleaner removes matter with a scouring action.

Agitation through brushing normally moves matter and chemical cleaning agents to dissolve solids and liquids.

For example, agitation and heat energy cause faster interaction between cleaning solvent molecules and the dissolved substances.

Agitation also separates particles by providing the initial momentum for the bodies of charged particles to separate and rearrange themselves according to their electrostatic charges.

What Is Cleaning Chemistry?

Chemistry — or the "science of substance" — examines the matter''s structure, the substance''s properties and reactions that change them into other substances.

Chemical action makes separating matter during cleaning effective.

Matter consists of atoms or small particles while elements contain similar atoms.

Compounds form when atoms of same or different elements bind together in a definite proportion.

A molecule is a compound''s smallest particle that exists and exhibits that compound''s properties.

Compounds are a pure substance decomposed by chemical change.

Atoms continuously cycle or rearrange themselves into different compounds and substances and release or absorb energy.

Polluting substances differ in their dissolvability in various solutions.

For example, oil does not dissolve in water, only in another organic solution, such as naphtha.

Sodium chloride (table salt) dissolves in water but not gasoline.

In cleaning it is important to understand how matter dissolves and becomes suspended before being removed.

Most chemical action in cleaning occurs when polluting substances dissolve in solutions.

Solutions are a homogeneous mixture or have the same chemical structure.

Mixtures can consist of air or water.

Cleaning solutions often combine water containing soaps, detergents or an organic solvent in liquid or gas form.

Substances or pollutants are soluble if they cannot be dissolved.

A cleaning solution is a solvent if its chemical nature is maintained while dissolving the substance or pollutant.

Upon dissolution molecules or ions are distributed and occupy the positions normally held by the dissolving solution''s molecules.

A liquid''s molecules are closely packed.

Compared to solutions in air, they interact strongly with neighboring molecules.

These molecules separate and interface weakly in gaseous solutions.

How easily a dissolved substance''s molecule is replaced by a dissolving solution depends on the attraction forces.

Benzene dissolves in carbon tetrachloride solutions.

Each substance''s attraction forces are nearly equal.

The benzene molecules easily can replace those of the carbon tetrachloride solution.

Two completely soluble substances are miscible.

This same chemical relationship explains why oils and grease effectively dissolve in other dry cleaning agents.

Carbon tetrachloride dissolves benzene but should never be used when cleaning indoors because it is carcinogenic.

Are There Varying Degrees Of Solubility In Cleaning Chemistry?

Consider what happens when a solid dissolves in a liquid.

A solid''s molecules are arranged in a regular pattern to maximize attraction forces.

For the solid to dissolve, the dissolving solution''s molecular forces must overcome those forces holding the solid together.

Sugar consists of molecules held tightly together by hydrogen bonding.

It will not dissolve in gasoline.

The gasoline''s carbon-based molecular forces are too weak to overcome the sugar''s hydrogen-based molecules.

The sugar, however, dissolves in water because of its hydrogen-based molecules.

It has one oxygen and two hydrogen atoms and attraction forces equivalent to sugar molecules.

When sugar and water combine their molecules become interchangeable.

Water alone dissolves many water-soluble substances, such as solids containing positive and negative ions.

Ions are positively or negatively charged particles.

Sometimes they are called ionic crystals. Salt — or sodium chloride — is one.

When ionic substances dissolve in water the adjoining ions in the solid separate and are surrounded by water molecules.

Water molecules are two positive charged hydrogen atoms joined by a single oxygen atom.

The water molecule is called a polar molecule meaning opposing molecule ends carry opposite electrical charges.

Not all molecules are polar.

Water is, however, because of its positive and negative ends.

The electrostatic attraction of opposite charges holds the water molecules together to form water bodies.

Its molecular polarity makes it particularly useful in cleaning because of its dissolvability.

Salt also dissolves in water when a positive charged sodium ion is surrounded by water molecules.

Their negative ends are directed at the sodium and a negatively charged chloride ion surrounded by water molecules.

Their positive ends are directed at the chloride.

The ions comprising table salt are in cages of water molecules.

When water molecules surround an ion that way the ion is hydrated.

The cage of water molecules surrounding an ion neutralizes or insulates its charge.

It also keeps the solution''s oppositely charged ions from attracting each other over distances.

In the case of water, Na+ and Cl- cannot form a salt crystal.

In contrast, non-polar molecular solutions cannot dissolve ionic solids, such as salt, since solids cannot be separated by positive and negative charged forces.

They also cannot insulate the solid''s ions from each other.

When ionic solids are in non-polar molecular solutions they quickly attract each other and separate from the solution as solids.

They congregate rather than dissolve.

The result is an important fact of cleaning chemistry.

Substances similar in molecular attraction forces generally are soluble in one another.

Polar solvents, such as water, dissolve ionic substances, like salt.

Solvents comprised of non-polar molecules dissolve non-polar substances.

Chemistry explains many cleaning mechanisms.

Soap is made when animal fats react with water and a strong base, like lye or caustic soda.

When the base and the acids'' fats react an ion is released that has a negatively charged head connected to a long hydrocarbon chain.

Typically, soap has a negatively charged carbon dioxide unit.

This head connects to a long hydrocarbon tail resembling those in oil, gasoline, grease and animal fat.

The soap ion''s hydrocarbon tail is not water soluble.

It will, however, dissolve in like hydrocarbons, such as grease and animal fat.

Hydrophobic substances aren''t water soluble either.

In solutions containing soap the hydrophobic hydrocarbon tails of fatty acid ions interlace forming an oil-like glob.

Meanwhile, the ion''s charged head points toward the surrounding water molecules.

This charged head has an affection for water.

Fatty acid ions called micelles are formed by this love-fear relationship with water.

Soap decomposes and removes oils and fats in fabrics and surfaces because "like dissolves like."

The soap ions'' hydrocarbon tails dissolve in the hydrocarbons being removed.

That hydrocarbon substance is overlaid by the soap ions'' hydrocarbon tails.

Gradually it separates as the charged, water-loving ion head is drawn toward surrounding water molecules.

The attraction forces of the water molecules and the head of the long hydrocarbon chain pull the glob apart.

As the breakdown occurs, the soap solution holds bits of unwanted substance in colloidal suspension.

The heads of the soap ions are the same charge and repulse each other.

This prevents the substance being dissolved from reforming.

The suspended substance is emulsified and carried away in wash water.

Synthetic detergents act like soap by breaking apart and dissolving the same substances.

Instead of animal fat, however, they consist of man-made chemicals, such as sodium alkylbenzenesulfonates.

Detergents'' main advantage is they work better than soap in hard water, the common state of ground water in urban and rural environments.

The electrostatic states in detergents vary more than in soaps.

Detergent ions have positive heads called cations or negative heads called anions.

Other detergents are non-ionic or polar compounds with positive and negative ends.

A synthetic detergent''s anions don''t become solids in hard water like in soap.

Consequently, hard water does not affect their cleaning action.


Michael D. Berry, Ph.D., was chairman of the Science Advisory Council for the Cleaning Industry Research Institute (CIRI) in 2006. The information contained in this article was extracted from Dr. Berry''s papers and presentations at CIRI''s 2007 Cleaning Science Conference and Symposium. His entire paper and PowerPoint presentation, as well as those of other symposium presenters, are available at www.ciri-research.org.

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