Mechanics of Contact Printing: System geometry, interface adhesion and material constitutive laws.

Sanjay Nana Lakshamana, Advised by John Lambropoulos

Hopeman 224

Contact printing is an emerging technology used to pattern a range of materials including metals, solvents, DNA and even cells. The technique characteristically involves the use of a patterned elastomeric stamp to "contact print" the material layer desired on a rigid substrate.

Due to the versatility of the material that can be patterned and its cost effectiveness, contact printing lends itself well as a technology to print organic layers that make up OLED displays. This research concentrates on the viability of using shape memory polymers (SMPs) as stamps in contact printing. SMP stamps may thermally trigger shape change and thus a means to control adhesion between the stamp and substrate.

Simulation of compression of different stamp geometries with variable backing layer compliance on a rigid substrate allows us to isolate the contribution of the backing layer in different stamp geometries. This lends insight into the deformation mechanics of the stamp.

The nonlinear behavior of one stamp material was investigated at different temperatures and strains. This data allows understanding the behavior of the material when it undergoes thermal cycling as is the case in contact printing. Rheological models simulate viscoplastic materials and provide a good foundation to simulate such materials effectively over various strains and temperatures.

Critical strain energy release rate, a fracture mechanics concept, can be used to study the delamination mechanics of two surfaces in adhesive contact. Delamination of cylindrical stamps made of PCL (polycaprolactone) from a rigid substrate was simulated in ABAQUS using a traction-separation law which dictates the interfacial adhesion mechanics between the surfaces. An accurate estimate of the surface energy of the stamp material was made possible by examining the local traction-separation relation. This approach demonstrates an easily applicable method to estimate surface energy.