Naga B. Gundrati, Graduate Student, University at Buffalo, The State University of New York
Deborah D.L Chung PhD, Professor, University at Buffalo, The State University of New York
Three-dimensional (3D) printing involves layer-by-layer build-up of a structure. A novel capacitance method has been developed to probe the microstructure of the printed material within and between the layers. The capacitance is measured in the through-thickness and in-plane directions, using an RLC meter at 100 Hz. The printing involves bottom-up stereolithography, using an acrylic ester UV-curable resin. The degree of in-plane preferred orientation of the polymer molecules increases with decreasing layer thickness (10-50 µm) and is higher for the layers deposited later. The preferred orientation increases the electric permittivity, thereby increasing the capacitance. Preferred orientation is known to affect the mechanical properties. The through-thickness permittivity is higher than that of the bulk polymer, due to the preferred orientation. Stress relaxation decreases the through-thickness permittivity for three hours after printing, after which the permittivity increases gradually for three hours (probably due to additional curing). The through-thickness capacitance of the interlayer interface is infinity, which indicates that this interface does not contribute to the capacitance of the printed material (which amounts to capacitors in series, with each layer corresponding to a capacitor) and reflects the high quality of this interface. This method can also be applied to monitor the printing process in-situ.