The Science of Chocolate: interactive activities on phase transitions, emulsification, and nucleation

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Entry by Andrew Capulli, AP225 Fall 2011


A. C. Rowat, K. A. Hollar, H. A. Stone, and D. Rosenberg, "The Science of Chocolate: Interactive Activities on Phase Transitions, Emulsification, and Nucleation," J. Chem. Educ. 88 (1), 29-33 (2011).

Introduction: Motivation

A change in a system being studied can be generally viewed as a phase change and although much of this sort of physics studied in academia seems like far-out irrelevant work, as we all know, its really not... in fact, it can be related to common materials and phenomena we see everyday (remember to Cheerios Effect!?... see a couple wiki entries ago). And what better, in terms of explaining 'science' than food? Stone et al. use chocolate as their 'everyday' material to explain some fundamental physics to the community (ages 6+); chocolate being a very complex food that deliciously illustrates the authors' points (discussed below). But even to the graduate student, the demonstrations used by the authors and the seemingly simple physics being covered is easily recognizable as an opening of the door to a far more complicated subject. In the past few weeks in Soft Matter we have covered some introductory material on surfactants and phase diagrams/transitions and this 'paper' addresses those subjects while further demanding more investigation of the reader. Because this paper is more so an instructive layout on how to teach/demo the subjects to a general audience, I'll focus my wiki not only on what the paper had to say, but some further investigation into the phases of chocolate.

Summary: Educational Points of the Paper

This paper, unlike the typical methods or experimental account we're used to reading and discussing, is an instructive summary on how to address some relatively simple but very important explanations (the physics) behind some common phenomena we see everyday. It should be noted that while the 'take homes' from the summarized demonstrations seem fundamental... even as graduate students we re-learn the concepts. The authors aim to address three main concepts:

  • Phase Changes (Solid, Liquid, Vapor)
  • Surfactant/Emulsification
  • Crystallization (More Phase Change)
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