Researchers at the Massachusetts Institute of Technology (MIT) have identified a phenomenon termed 'mechanical memories' in soft materials, which could significantly impact the manufacturing of products ranging from cosmetics to construction materials.
The discovery, led by postdoctoral researcher Crystal Owens at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL), reveals that common soft materials like hand lotions and hair gels retain residual stresses from their manufacturing processes for extended periods. These embedded stresses can subtly alter the material's properties over time, potentially causing changes such as lotions becoming runnier.
Owens developed an innovative method using a standard rheometer to precisely measure these residual stresses. Her research indicates that these materials can recall the direction and duration of their initial mixing. This internal stress, when released, can cause the material to revert to a prior state. This phenomenon is a key reason why different batches of cosmetics or food products might exhibit varying behaviors even when subjected to seemingly identical manufacturing conditions.
The study found that hair gel and shaving cream possess longer mechanical memories, retaining these stresses for longer durations than previously assumed. The implications of this finding are significant for the manufacturing of soft materials. By understanding and quantifying these inherent stresses during production, companies can engineer products with enhanced durability and more consistent performance. For example, minimizing residual stresses in asphalt production could lead to more resilient and longer-lasting roads.
This research, published in the journal Nature Materials, offers crucial insights into the complex behavior of soft materials and opens new avenues for improving product quality and extending their functional lifespan. The concept of mechanical memory has also been observed in other fields, such as studies on stem cells, where they can 'remember' past physical signals, influencing their fate and differentiation. Furthermore, shape memory polymers and alloys are being developed for applications ranging from soft robotics to biomedical devices, showcasing the utility of materials that can adapt and return to previous states.