Why an oil phase heats faster than a water phase

I was sent an email asking me about what the best set-up was for heating batches.  It seemed that this formulator was having a hard time getting her batches to heat up quickly.  I told her the setup I typically use includes the following

  • 1.  Beaker (for the batch ingredients)
  • 2.  Stainless steel short pot filled with water (for the water-bath)
  • 3.  Hot plate

Then you should also cover the batch with Aluminum foil and plastic wrap.  This set-up works well.

However, in considering this question it occurred to me that there is a phenomena that most emulsion formulators will experience some time in their formulating career.  When you are heating your oil phase, it will get hotter much faster than the water phase.  In fact, it can almost seem like it gets hotter twice as fast.

The reason?

Our good old friend the Hydrogen Bond.

The temperature of a system is a reflection of the speed at which the molecules in it are moving.  Water molecules tend to stick to each other better than oils stick to each other.  That is because of hydrogen bonding between molecules.  So, it takes more energy to break the hydrogen bonds and speed up the molecules.  In an oil phase, there isn’t that extra bonding between the individual molecules so it requires less energy to make the molecules go faster and heat up.

And if you want to test this for yourself, try this water oil heat capacity experiment.

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