Comparison of Crystalline Phase Transitions in Fluorniated vs Nonfluorinated Parylene Thin Films

Abstract

Thermally induced morphological changes in thin (1−5 μm) films of poly(α,α,α‘,α‘-tetrafluoro-p-xylylene, (C6H4CF2) n ) (Parylene-F or PPX-F) are characterized using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and thermal stress measurements. A reversible crystalline phase transition is observed between 360 and 400 °C, which to our knowledge has not been reported previously. The transition is accompanied by an increase of the in-plane tensile stress of the film, which is attributed to contraction of the in-plane polymer structure during the transition to the high-temperature crystalline form. The stress and thermal behavior are qualitatively similar to those occurring in the more extensively studied nonfluorinated material, poly(p-xylylene, (C6H4CH2) n ) (Parylene-N or PPX-N), which undergoes a shift in stress during the β1−β2 transition (270−300 °C).

Electrical Conductivity of Parylene F at High Temperature

“…As reported in the literature for PA-N, recrystallization could be accompanied by a possible change in the PA-F polymorphism, even if this has not been demonstrated to date. 19 The small peak at an angle near 2h = 16.4°that appears after annealing is due to diffraction of K b radiation from the same hightemperature crystalline plane that gives rise to the main K a peak. The length of the repeat units (d-spacing) for both as-deposited and annealed films was calculated using the Bragg equation:…”

“…These results are consistent with the works of Morgen et al, where T c was found in the range from 395°C to 403°C. 19 Figure 7 shows XRD measurements of PA-F films before and after annealing at 400°C for 1 h in N 2 . The as-deposited film presents a wide, low-magnitude diffraction peak (centered at 2h = 19.14°) characteristic of a poorly crystallized structure.…”

“…These values are in agreement with those reported by Morgen et al and Blackwell et al, where the d-spacings in equivalent annealing conditions (400°C and 450°C) were 4.33 Å and 4.4 Å , respectively. 19,27,28 As a consequence of progressive crystallization from the glassy state, semicrystalline polymers often exhibit chain arrangements in the form of lamellae (i.e., parallel chain arrangements, $10 nm in thickness), which often organize in spherulites (i.e., spherical semicrystalline regions approximately 1 lm to 100 lm in diameter inside nonbranched linear polymers). Spherulites consist of arrangements of dense lamella stacks consisting of both crystalline lamellae and amorphous regions.…”

“…The main reasons are the difficulty encountered in film synthesis (process, cost) and the only recent availability of commercial films (since 2004). The work reported in the literature deals mainly with film synthesis and the resulting chemical structure (CF 2 formation, crystallization kinetics, and oxygen impurity content), 8,9,[17][18][19] and sometimes with thermal properties. 11,12 In fact, studies regarding the electrical properties of PA-F are almost nonexistent.…”

Structure and optical properties of thin poly(p-xylylene) – Silver nanocomposite films prepared by low-temperature vapor deposition polymerization

“…[36,38] that reversible behavior can also be observed under certain circumstances. More specifically, it was suggested that, the a to b 1 phase transition in PPX is kinetically slow and can occur in the temperature range between þ200 and þ250 C, with its reversibility being dependent on the annealing conditions [38]. Perhaps, the low temperature of the a to b 1 transition observed in our study can be accounted for by the film thickness.…”