Going inside colored solutions: The optical microscope as a tool for studying the chemistry of hydrophilic and hydrophobic materials

Two of the most common student questions concerning polar-apolar liquid interfaces are the following: Why do not oil and water mix? How do soaps and detergents work to remove dirt? The questions can best be answered by incorporating concepts such as hydrophilic and hydrophobic properties of materials, emulsions, liposomes, and surfactants. A two-part laboratory experiment was developed to help students answer these questions. In the first part of the laboratory, students visually explore the behavior of different materials with various lipophilic-hydrophilic properties. An optical microscope is used to examine the dissolution mode of various food colors into both water-in-oil (W/O) and oil-in-water (O/W) emulsions, using phosphatidylcholine as a surfactant. In the second part of the laboratory, the size of the liposome structures is reduced from microscale to nanometer scale (400 nm) using a simple apparatus called the miniextruder. The students examine the change in solution transparency when the size of the liposomes is reduced. Two different student groups carried out the laboratory: a group of 20 upper-level high school students majoring in biotechnology and a group of 20 first-year college students majoring in chemistry.