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How Surface Active?

by Dom Ruggeri

August 2003:

For a number of reasons this past weekend caused me to reflect a bit.  As some of you readers know, my nephew is starting college this fall and as luck would have it he decided to attend my alma mater LaSalle University.  It was then I realized I am getting old.  But that happens to us all.  As I began to think back to my days as an undergraduate, I remembered someone once told me I would look back on those times and say “those were the good old days.”  They were right.

I remember one Thursday of my junior year in particular; I was almost kicked out.  It was a strange day none of us slept well due to a P-Chem. Test, and none of us were ready.  So what else was new?  The Professor was Dr. Max Barth; aptly called Max the Ax.  By a stroke of his pen he could convert Chemistry majors into English majors or worse, Business majors.  Once again, we vowed to pull the famous all night study session in the hopes of passing.  Thursday was the Analytical Chemistry lab day.  This particular lab was rather difficult but we got it done and needed to blow off some steam. 

Unfortunately for all, we found the Analytical Professor’s bicycle.  One of us proceeded to ride it around the Chemistry Department to the delight of all of us.  That day I brought my fencing equipment to school for a later scheduled match.  Someone slapped me in the head and began to run after the bicycle.  I grabbed my foil and gave chase brandishing the weapon high above my head.  The scene was something out of the old Keystone Cops comedies, a bicycle rider being chased by a man, both being chased by another runner with a sword; such a sight in the hallowed halls of LaSalle University. 

On about the fifth lap as we passed the main stairwell and there stood the head of the Chemistry department with the Dean of Sciences.  The department head turned bright red and yelled something like “Jiminy Crickets.”  Normally I would have laughed out loud but this time we knew we were in big trouble.  So we scattered and met in the cafeteria for an extended lunch.

About three o’clock we all met back in as we called it the department.  We waited in the Chemistry Library until the Doctor entered.  His voice was stern and clear as he said, “Between hockey in the halls, bikes, and now swords I am going to have to start chaining people down because this department is becoming a loony bin.”  It would have been a good time to  keep quiet but instead I answered, “But Doctor, who runs this loony bin?” He replied, “Ruggeri my office - 5 minutes.”  I blew it big time, three years of college gone.  After saying my goodbyes I stood before the Doctor to await my fate.  He was calm.  He looked at me and in a clear but firm voice he said, “The dean said I was going to miss you guys when you graduate, and I said ‘hardly.  Now get out of my office!”  My luck had held.  I promised I would be a model student from then on.  (So I lied.)

SURFACTANTS are perhaps the most versatile and useful products known to the chemical industry today.  These molecules can make the insoluble soluble, the milky emulsion clear, and the unstable neat product stable.  Many will foam and many slick marketing people will try to convince unsuspecting women that this foam will give them clean dishes and soft hands, but that is fuel for another article. 

Those readers who have read my articles on formulating realize that I prefer surfactants with an HLB of about 8 and use them as co-emulsifiers.  However, surfactants can be used as primary emulsifiers as long as you realize that you will have to use them at the 8 to 10 percent levels.  Further, you should monitor the long-term emulsifiability.  I remember one product I worked with where the material emulsified well for ninety days, and after ninety days you could not make it emulsify.  Obviously there was a reaction of some sort that rendered the surfactant useless. 

In my experience, an HLB of about 8 yielded a stable emulsion, so you would use ten percent of a surfactant with an HLB of 8.  That would work but you could do better by blending your surfactants, such as fifty percent of a surfactant with an HLB of 12 and fifty percent of a surfactant with an HLB of 4.  This combination would not only give you an HLB of 8 but you would get the benefits of the low HLB and high HLB surfactants.  For example:
The low HLB surfactant will be better at emulsifying the oil portion of the product.
The high HLB surfactant will assist in keeping the oil droplets from lensing or splitting in the emulsion

How to Calculate and Use HLB:

As you know, I devoted an entire article on this topic so for right now I will use the surfactant blend above as an example:

HLB=((.50*4) + (.50*12))
HLB=    2 + 6
HLB=    8

So how do we use this in a typical formulation:

            Surfactant HLB 12 – 5.0%
            Surfactant HLB   4 – 5.0%
            50% Cl Paraffin - 10%
            Napthenic Oil - QS
            Grotan - 3%
            Na Omadine - 0.3%

As I said above you will have to be around the eight to ten percent total surfactant content and once again monitor your emulsion carefully.  Last but not least choose your surfactant package carefully since not all surfactants are good emulsifiers but all can have an HLB value.  Naturally, with the millions of formulations out there it is impossible to discuss all the possible scenarios but, as always, should you have any questions please feel free to e-mail me directly in care  of the magazine at Email Dom.

Good Luck,