Mechano-Chemical Coupling in the Adhesion of Thin Shell Structures: Transitions Between Weakly- and Well- Bonded States

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Mechano-chemical Coupling in the Adhesion of Thin Shell Structures:Transitions between Weakly- and Well- Bonded States (CMMI ? 0900058)PI: John L. BassaniDepartment of Mechanical Engineering and Applied MechanicsUniversity of Pennsylvania, PA 19104Bonding of thin films and adhesion of biological cells are important topics with certain common mechanical, chemical, and thermodynamic characteristics that motivate the proposed research. The overall objective is to understand how the adhered state between a thin film or shell and a substrate is controlled by intrinsic physical and chemical properties. For non-conforming bodies, these states are constrained by kinematical compatibility, force equilibrium, and chemical equilibrium. Molecular information, for example, the effects of stress on the kinetics of the bond, will be incorporated into macroscopic models. Transitions between weakly and strongly adhered states, what are referred to in the proposal as a snap-in/snap-out phenomena, have broad implications. The control of snap-in and snap-out adhesive transitions, with and without the influence of various dissipative mechanisms including the effects of diffusion and of stress on bonding, offer potential in applications ranging from micro-electro-mecahnical systems (MEMS), medical treatments, and even data storage. Snap debonding of wafers due to fabrication defects or due to moisture is a problem for MEMS technologies. Snap transitions also may be key to the attachment-detachment mechanism that are present in the natural cycles of white blood cells. Another exciting application is tissue engineering in which cells can be aligned by adhering to patterned substrates. One additional example: there have been many clinical trials for cancer treatment that attempt to breakdown the adhesion of tumor cells, and perhaps a better understanding of the mechano-chemistry of adhesion can point the way to other therapeutic advances.