Effect of a capillary force induced network on the development of cracks in nanoparticle films

• Applicant: Professor Dr. Norbert Willenbacher, since 10/2016
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263644168

Cracks are a major problem in the manufacture of uniform thin films from nanoparticle dispersions onto rigid substrates. Particle mobility and formation of cracks can degrade the film properties or even result in a total loss of functionality. Cracks are usually formed through the movement of particles near the drying front (as in coffee stains) or from the accumulated stress associated with the shrinkage as the solvent is evaporated (as in dried mud). Cracks are often prevented by reducing the rate of evaporation with sophisticated temperature and humidity profiles or fixed using repeated annealing; both methods increase the time and cost of manufacturing. We propose that the strong particle network found in capillary suspensions can be used to increase the material strength and reduce particle mobility, thereby reducing the formation of cracks under fast drying conditions. Preliminary investigations have revealed that the addition of small amounts of a secondary fluid to a suspension, forming so-called capillary suspensions, can reduce cracking in thin films. In this project, the extent of cracking will be investigated as a function of the secondary fluid content, drying conditions, and material properties. The cracking will be correlated to the rate of evaporation of the two fluids as well as microstructural changes as monitored using particle tracking. This cracking will also be correlated with rheological measurements of the suspension. We will then investigate the mechanism of cracking and determine the parameters controlling the formation and size of cracks. Finally, these control parameters will be applied towards the creation of model crack-free films for printable thin film solar cells and flexible electronics.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Professorin Dr. Erin Koos, until 9/2016