Soft materials like hair gel, lotion, and shaving cream aren’t as settled as they look. Even when a gel appears stable after mixing, it can still harbor “mechanical memory,” i.e., hidden stresses from the manufacturing process that linger long after the product seems uniform, reports Tech Xplore.
Crystal Owens, a postdoc at MIT’s CSAIL, set out to measure these residual stresses using a simple protocol and a benchtop rheometer. She mixed soft glassy materials in the rheometer’s rotating plates, then let them sit well beyond the typical one-minute QC window. She found that the materials remained stressed. If they were twisted one way during mixing, their internal structure held onto that twist, and when released, they gradually drifted in the opposite direction, even days later.
That subtle shift explains real-world inconsistencies: why two batches of hand cream or gel feel different, even when the process is “identical.” Owens models how these materials will evolve over time based on their residual stress, opening the door for smarter design choices. One target: asphalt. Mixed when molten, roadway materials might retain stress that contributes to pavement cracking. Reducing that built-in stress could make surfaces last longer.
These soft materials aren’t passive; they carry the memory of how they were mixed. A simple rheometer test can reveal that and arms manufacturers with insight to design longer-lasting, more reliable products.