Nanoindentation studies of polyimide thin films with various internal linkages in the diamine component

Abstract

Polyimide thin films were synthesized from 3,3Ј,4,4Ј-biphenyltetracarboxylic acid dianhydride (BPDA) and four different diamines (p-phenylene diamine, 4,4Јoxydiphenylene diamine, 4,4Ј-biphenylene diamine, and 4,4Ј-sulfonyldiphenylene diamine). The nanoindentation behavior of the resulting polyimides, namely, poly(pphenylene biphenyltetracarboximide) (BPDA-PDA), poly(4,4Ј-biphenylene biphenyltetracarboximide) (BPDA-BZ), poly(4,4Ј-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), and poly(4,4Ј-sulfonyldiphenylene biphenyltetracarboximide) (BPDA-DDS), were investigated. Also, the morphological properties were characterized with a prism coupler and wide-angle X-ray diffraction and were correlated to the nanoindentation studies. The nanoindentation behavior and hardness varied quite significantly, depending on the changes in the chemical and morphological structures. The hardness of the polyimide thin films increased in the following order: BPDA-DDS Ͻ BPDA-ODA Ͻ BPDA-BZ Ͻ BPDA-PDA. For all the polyimide thin films, except that of BPDA-BZ, the hardness decreased with an increase in the load. The birefringence, a measure of the molecular in-plane orientation, increased in the following order: BPDA-DDS Ͻ BPDA-ODA Ͻ BPDA-PDA Ͻ BPDA-BZ. The X-ray diffraction studies revealed that the crystallinity of the polyimide thin films varied with the changes in the chemical structure. The studies showed that the indentation response with an applied load and the hardness by nanoindentation for the BPDA-based polyimides were closely related to the morphological structure. The nanoindentation and birefringence results revealed that the mechanical properties of the polyimide thin films were dependent on the crystallinity, which arose because of the chain order along the chain axis and the molecular packing order.

Residual stress and mechanical properties of polyimide thin films

“…The elastic–plastic behavior of the polyimide thin films with various backbone structures is best illustrated in Figure 3. For the different structure polyimide films, the characteristic kickback (elbow) appears in the unloading curves, which indicates that all the polyimide films exhibit an elastic–plastic response 9, 10, 19–21. Figure 3 clearly shows that with an increase in the applied load, both the maximum indentation depth and the plastic response of the polymer increased.…”

“…For the different structure polyimide films, the characteristic kickback (elbow) appears in the unloading curves, which indicates that all the polyimide films exhibit an elasticplastic response. 9,10,[19][20][21] Figure 3 clearly shows that with an increase in the applied load, both the maximum indentation depth and the plastic response of the polymer increased. Their results are summarized in Table II. As the applied load increases from 0.08 to 0.162 mN, the penetration depth of the polyimide thin films varied from 86 to 123 nm for BPDA-PDA, from 88 to 127 nm for PMDA-PDA, from 103 to 151 nm for BPDA-ODA, and from 130 to 183 nm for PMDA-ODA, respectively.…”

Nanoindentation and optical properties of poly(4,4′‐oxydiphenylene p‐phenylene pyromellitimide) copolyimide thin films according to the p‐phenylene diamine content

“…This shows that the hardness and modulus of the polyimide thin films were significantly affected by their morphological structure, such as the crystallinity, molecular order (chain and packing order), and orientation, according to the PDA content. A similar trend of variation in the nanoindentation behavior with changes in the chemical and morphological structures was observed in our previous work 12…”

“…Variations in the polymer microhardness have been correlated to differences in the crystallinity, molecular weight, cohesive energy density, microstructure, elastic modulus, and yield stress 10, 11. Despite the insight that microhardness testing provides, far fewer studies of the nanoscale indentation of polymeric materials have been reported 12. In this nanoindentation study, the effect of the p ‐phenylene diamine (PDA) content on the mechanical properties (hardness and modulus) of polyimide thin films was investigated.…”

ATR-FTIR and Nanoindentation Measurements of PMDA-ODA Polyimide Film under Different Curing Temperature

“…The nano-hardness and nano-elastic modulus of soft film on hard substrate can be determined from the continuous stiffness measurement (CSM) technique of dynamic indentation test, the detailed description of simplified hardness and elastic modulus equation, 18) and the complex hardness and elastic modulus equation also can be seen elsewhere. [19][20][21][22][23] …”