Whenever molecules get closer to adhesive surfaces, they always move faster. However, this is not a permanent effect. Such was the perplexing conclusion reached by Simone Napolitano and his co-workers in the Laboratory of Polymers and Soft Matter Dynamics at the Université libre de Bruxelles (ULB). The study has been published in Physical Review Letters.
For more than two decades, a number of Researchers have been investigating the behavior of specific liquid crystals, polymers and biomolecules at the nano-scale close to an absorbing medium. In this situation, slower movement rates would be expected, but the experiments demonstrated the opposite effect: as molecules get closer to an adhesive surface, they move faster.
The ULB Researchers reported that this unusual movement is caused by a phenomenon called the 'nanoconfinement effect'. While the molecules that remain in direct contact with the adhesive surface certainly move slower, or even not at all, this consequently increases the movement rate of the subsequent molecules because they have more amount of free space around them.
Now, writing in PRL, Napolitano and his colleagues show that this is just a temporary effect: as new molecules stick to the surface and fill in the available spaces, their rate of movement steadily slows down. After sometime, the molecules move as if they were far from the sticky surface. Interestingly, the time required to return to usual molecular movement rate is found to be longer than what would be expected by any present theory of polymer physics.
It was therefore proposed by the Researchers that the amount of space available at the interface between the sticky wall and polymer is a critical parameter to regulate the behavior of nanomaterials.