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Center for Polymer Microfabrication (CPM)

MIT Laboratory for Manufacturing Productivity

NTU Biochemical Process Engineering Laboratory

materials and process modeling

Demolding: surface adhesion and release mechanics

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This research effort is aimed at understanding the adhesion of workpiece material to various tool mateirals, and to also understand the mechanical and thermo-mechanical effects of part processing on demolding. Adhesion is a complex phenomenon that involves several different mechanisms:  chemical interaction by covalent bonding, acid-base interaction, or inter-diffusion; molecular interactions such as Van der Waals forces or hydrogen bonding; and mechanical interaction of asperities.  Many of these adhesion mechanisms have been the subject of extensive study in the context of commercial adhesives, but they have received relatively little attention in the polymer-imprinting field.  The surface energies of various material pairs are being investigated and the use of high temperature polymer tools, such as PEEK and Teflon has been explored experimentally.  For example, the we have found that the work of adhesion (a key component of adhesion) can be up to 5 times lower for a PTFE tool forming PMMA than the typical silicon – PMMA combinations.

In another set of experiments, the concept of high temperature de-molding was tested to see if the locking strains from thermal contraction could be avoided.  While the results show that thermally induced locking strains are large (see Figure  1.), they can be avoided with higher temperature demolding and careful tooling design.

Figure 1. Effect of elevated de-molding temperature on channel geometry in embossing.

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