Abstract
Young's law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This has been used to explain why colloids often bind to liquid interfaces, and has been exploited in emulsification, water purification, mineral recovery, encapsulation and the making of nanostructured materials. However, little is known about the dynamics of binding. Here we show that the adsorption of polystyrene microspheres to a water/oil interface is characterized by a sudden breach and an unexpectedly slow relaxation. The relaxation appears logarithmic in time, indicating that complete equilibration may take months. Surprisingly, viscous dissipation appears to play little role. Instead, the observed dynamics, which bear strong resemblance to ageing in glassy systems, agree well with a model describing activated hopping of the contact line over nanoscale surface heterogeneities. These results may provide clues to longstanding questions on colloidal interactions at an interface.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 138-142 |
| Number of pages | 5 |
| Journal | Nature materials |
| Volume | 11 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 2012 |
Funding
We thank S. Ghosh for his help in the work that inspired these experiments; L. DeLorenzo for her work on sample cell prototypes; S. Rubinstein and H. Stone for critical discussions; and J. MacArthur and S. Cotreau for guidance in construction of the apparatus. This work was supported by the National Science Foundation under CAREER award number CBET-0747625 as well as through the Harvard MRSEC under award number DMR-0820484.
ASJC Scopus subject areas
- General Chemistry
- General Materials Science
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering