Viscosity during spin coating

The method used for the preparation of thin films of PPV or its derivatives depends on the specific potymer. For those that present high solubility in common organic solvents, very simple procedures, such as casting, doctor-blade technique [98], or spin-coating of the polymer solution with further solvent evaporation can be used. In the case of spin-coating, the film morphology is sensitive to the solvent evaporation rate, density, viscosity, polarity, and solubility during the process [99]. 

The three-dimensional displacements inherent to NIL require resist materials that easily deform under an applied pressure and/or elevated temperature. These resists must have a low viscosity during imprinting, a Young s modulus less than that of the mold, and a low sheer modulus. It should also be mentioned that the resist material should have excellent adhesion to the substrate, provide high-quality, uniform film thickness through deposition via spin-coating, and have sufficient thermal and mechanical properties for subsequent processes. When determining the type of NIL resist to use, one should consider the critical dimensions of the pattern, pattern density, release properties from the mold, required imprint temperature and pressure, etch selectivity for subsequent pattern transfer, and route to eventual removal by dissolution or other processes. 

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