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My research partners and I have studied the possibility of building a material system with controllable properties using two interpenetrating polymer networks (IPNs). This study is part of a project to build a rapid prototyping system that allows for the printing of objects with predefined spatial distribution of properties, with the goal that property distributions are controlled though interactions at the molecular level.
One can change the properties of an IPN by adjusting the ratio of interpenetrating networks present in a given cured mixture. This is similar to how one obtains different shades of the color green by gradually changing the ratio of blue and yellow pigments when mixing paint. In much the same way as one can use mixing to change colors along the surface of a painting, one may change the properties of a body along a direction in space by changing the ratio of networks in the IPN. To achieve this, we studied how to make an IPN and how to control it in a way that will allow controlled grading of material properties in space.
An IPN is constructed by curing two polymer networks in the same space. Unlike separated systems, the IPN shows behavior and properties that result from the close interaction of the networks, a feature that inhibits the expression of the individual network properties in favor of a property resulting from the close interaction of the networks. The properties of a given IPN system change based on the ratio of the networks present in the system and the order and kinetics of the curing process.
At first, we studied and demonstrated the construction of an IPN using two networks that are both photo-cured in the same space. Most IPNs are constructed using a combination of rapid photo-curing of one network and then slow thermal curing of the second network, which is constructed from molecules that are trapped in the first network. The ability to photo-cure both networks speeds up the curing process, a point deemed desirable for rapid prototyping. Once constructed, Fourier-Transform Infra-Red spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Atomic Force Microscopy (AFM) were used to show that the resulting system is a true IPN and we used Thermal Gravimetric Analysis (TGA), AFM, Dynamic Mechanical Analysis (DMA), and tensile testing to further characterize its properties.
Advisers: Mehrdad Negahban and Li Tan