Dynamics and Pattern Formation in Evaporating Polymer Solutions

These two examples show that regular patterns can evolve but, by definition, dissipative structures disappear once the thermodynamic equilibrium has been reached. When one wants to use dissipative structures for patterning of materials, the dissipative structure has to be fixed. Then, even though the thermodynamic instability that led to and supported the pattern has ceased, the structure would remain. Here, polymers play an important role. Since many polymers are amorphous, there is the possibility to freeze temporal patterns. Furthermore, polymer solutions are nonlinear with respect to viscosity and thus strong effects are expected to be seen in evaporating polymer solutions. Since a macromolecule is a nanoscale object, conformational entropy will also play a role in nanoscale ordered structures of polymers. 

Dynamics and Pattern Formation in Evaporating Polymer Solutions 

Recently it has been reported that even colloidal particle suspensions themselves, without added polymers, can form dissipative structures. Periodic stripes of colloidal particles (monodisperse particles of diameter 30 nm and 100 nm, respectively) and polystyrene particles (monodisperse diameters from 0.5 to 3 pm) can be formed from dilute aqueous suspensions. The stripes are parallel to the receding direction of the edge of the suspension droplet and thus indicate that a fingering instability 

One possibility to prepare regular dewetted patterns on rough substrates is by pattern transfer. A regular pattern is formed on mica, on which then another substrate is placed. The pattern is released from the mica and fixed on the other substrate at the original droplet positions [49]. 

In order to allow for more control during the evaporation, the solution can be placed in a motor-controlled sliding [ 50] or rolling apparatus [51] which uses capillary force to confine the solution between two glass surfaces. The motor determines the speed at which the solution edge is drawn over the substrate and is one of the main parameters to control patterning. Droplet, stripe and ladder patterns have been observed. 

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