Soft Materials Hold Onto “Memories” Of Their Past
Hand lotions, hair gels, and shaving creams can become runny because they retain “mechanical memory” from the mixing process. These materials can hold internal stresses that cause them to shift back toward their original, pre-mixed state, even after setting.
An MIT engineer developed a way to measure these residual stresses in soft materials. Research shows that products like hair gel and shaving cream can hold these stresses longer than manufacturers might expect. Using a standard benchtop rheometer, MIT postdoc Crystal Owens found that gels mixed in one direction keep a memory of that direction. Even days later, internal stress can make the gel return to its earlier state.
