Polymer Thin Film Dewetting

Spontaneous Instability or Spinodal Dewetting Theoretical Aspects 

The condition of instability vis-a-vis stability of a thin film in terms 6 or II (or AG) as a function of h emerges from linear stability analysis (LSA) [33-38,65]. In order to facilitate the discussion of LSA, a brief summary of the kqr theoretical results on thin film instability is presented here. 

Each of the constituent terms of Equation 11.1 represents a distinct force field. From left to right the terms represent the contributions of viscous forces, surface tension forces due to the curvature at the free interface (Laplace pressure), and the excess intermolecular forces (disjoining pressure) respectively [37, 38, 65, 67]. The viscous force in no way influences the stability as it merely controls the dynamics of the system. For tangentially immobile films, the prefactor of the viscous term 3 is replaced by 12 [38, 65]. The Laplace pressure arising from surface tension has a stabilizing influence, as already discussed. Thus, the only term that may induce an instability in the system is the one representing the excess intermolecular interactions [37,38,65]. 

The major practical use of Equation 11.1 lies in testing whether a film of uniform initial thickness ho remains stable or eventually become unstable with time. The solution of linearized equations of motion incorporating the effect of intermolecular forces, can be simplified by the lubrication approximation (non-inertial laminar flow in thin films) and admit space periodic solutions for the film thickness h(x, t) = ho + E sin(kx) exp(cof) with  

Equation 11.2 represents the Hnear dispersion relation for the initial growth coefficient (co) of an axis-symmetric perturbation on the free liquid surface with a small (e ho) initial amplitude having wavenumber of instabflily k [65]. The parameter 

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Meredith JC, Smith AP, Karim A, Amis EJ (2000) Combinatorial materials science for polymer thin-film dewetting. Macromolecules 33 9747-9756... 

Pattern Formation in Polymer Thin Film Dewetting... 

Xu L, Sharma A, Joo SW. Substrate heterogeneity induced instability and slip in polymer thin films Dewetting on silanized surfaces with variable grafting density. Macromolecules 2010 43 7759-7762. 

Kanemoto, R., Anas, A., Matsumoto, Y, Ueji, R., Itoh, T., Baha, Y, Nakanishi, S Ishikawa, M. and Biju, V. (2008) Relations Between dewetting of polymer thin films and phase-separation of encompassed quantum dots. J. Phys. Chem. C, 112, 8184-8191. 

Pattern Formation by Rim Instability in Dewetting Polymer Thin Films... 

Roy, S., Mukherjee, R. Ordered to isotropic morphology transition in pattern-directed dewetting of polymer thin films (m substrates with different feature heights. ACS Appl. Mater. Interfaces 4.5375-5385 (2012)... 

Hence, the stabilization of polymer thin films against dewetting is of great importance to a number of technological applications. The likelihood that films will either wet or dewet solid surfaces is related to the value of the spreading parameter S ... 

Recently, our group reported a new application of dewetting of polymer thin films as time-temperature integrator. The idea stems from the knowledge that dewetting of a solid film is an irreversible process exhibiting an activation energy and whose characteristic... 

G. Lee, B. Yoon, H. Acharya, C. Park, and J. Huh, Ordered micropatterns by confined dewetting of an imprinted polymer thin film and their microlens application, Macromol. Res., 17,181-186 (2009). 

Xue LJ, Han YC. Pattern formation by dewetting of polymer thin film. Prog Polym Sci 2011 36 269-293. 

The bilayer morphology of thin asymmetric films of may be unstable. A regularly corrugated surface structure of the films was ascribed to spinodal transition into a laterally phase separated structure, where the surface morphology depended on the polymer incompatibility and the interfacial interactions [347, 348]. Recently, the phase separation and dewetting of thin films of a weakly incompatible blend of deuterated PS and poly(p-methylstyrene) have been monitored by SFM [349, 350]. Starting from a bilayer structure, after 454 h at T= 154 °C the film came to the final dewetting state where mesoscopic drops of... 

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