Dimensional control of brittle nanoplatelets. A statistical analysis of a thin film cracking approach.

Nanoparticles are essential building blocks for nanotechnology. In this paper we demonstrate a novel method to create nanoplatelets by thin film cracking. The thickness of the resulting platelets is determined by the film thickness, and their aspect ratio is controlled by the total strain and the elastic mismatch between substrate and thin film. Platelets can be created from any brittle film independently of microstructure and materials class. The feasibility of this method is substantiated by a statistical analysis of the fracture process.

Experimental investigation of equibiaxial extension and breakup of drops in a molten two-phase polymer blend.

We experimentally investigate the breakup of an equibiaxially elongated polystyrene (PS) drop in a poly(methyl methacrylate) (PMMA) matrix during relaxation after melt elongation. In equibiaxial elongation, the initially spherical PS drop is deformed into an ellipsoidal disclike shape for our test parameters. Using a hotstage in combination with a light microscope, we observe the evolution of the drop shape during relaxation. In the initial stage of relaxation, fingers and holes are formed. The holes are located preferentially near the rim of the drop. The number and the size of the holes increase with time such that the elongated PS drop attains a complex shape during relaxation. The fingers form bulbous ends which separate from the fingers. We discuss the dynamics of this breakup process by taking into account the interfacial energy between PS and PMMA. Our analysis shows that a very large number of small PS droplets can be generated by the sequential breakup of the elongated PS drop.

Disorder and plasticity in the fragmentation of coatings.

Using a one-dimensional model that takes into account ideal plasticity of the surface layer, we investigate the fragmentation of thin coatings under uniaxial tension. The coating is modeled as a chain of plastically deforming elements that are connected via leaf springs to a uniformly stretched substrate. Each coating element can only withstand a maximum elongation, which is randomly distributed. From simulations of the fragmentation process we find that the average crack spacing scales with applied strain epsilon, i.e., proportional to epsilon(-kappa). Simulations and analytical arguments show that the scaling exponent kappa depends on the disorder parameters of the model.