Counterion-Induced Control of the Colloidal State of Polyamic Acid Nanoparticles for Electrophoretic Deposition

Abstract

Optimizing the colloidal state of polyamic acid (PAA) nanoparticles is essential for achieving a uniform and high-performance polyimide coating by electrophoretic deposition (EPD) on metal substrates of various shapes. In this paper, we report two important roles of the counterions in the formation of PAA colloids for EPD, which, to date, have not been recognized. First, when tertiary alkyl amines are used to neutralize PAA, the polarity of neutralizing counterions determines the size and stability of the PAA colloidal particles. The polarity can be finely tuned by using two different tertiary alkyl amines containing polar and nonpolar groups and adjusting the molar ratio. Depending on the polar/nonpolar ratio, various states of PAA colloids were obtained, including dissolved state, stable colloid, and aggregates. Second, we observed that the confined counterions inside PAA nanoparticles can act as an imidization catalyst during the thermal annealing process. It is revealed that some fraction of the counterion species, mostly having nonpolar groups, is not drawn toward the counter electrode and remains inside the PAA nanoparticles during the EPD process. Optimizing the polarity eventually allowed us to form uniform EPD coatings with high dielectric strengths.

Bioinspired polyimide film with fire retardant and gas barrier properties by gravity‐induced deposition of montmorillonite

“…By observing the results of DABPPI and MMT-PI, the characteristic absorption peaks of the imide ring both appeared around 1771 cm −1 (C=O stretching vibration) and around 1370 cm −1 (C-N stretching vibration). [37,38] Due to the existence of DABA, both DABPPI and MMT-PI have characteristic peaks at 1642 cm −1 ("Amide I") and 1513 cm −1 ("Amide II"). [39] For MMT-PI, there are also absorption peaks at 3623 and 3351 cm −1 , which are caused by the hydrogen bonding interaction between MMT and PI, respectively.…”

Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

“…PAAS has opposite ions, and at proper concentration will form stable electrostatic repulsion and will be well dispersed in the GO matrix. The electrostatically stable state can be broken, and aggregation will occur due to the attraction of GO to counter‐ions, which is proportional to the concentration of PAAS 38 . There is a critical concentration for PAAS to maintain an aligned structure and prevent phase separation (Scheme 1).…”

“…The electrostatically stable state can be broken, and aggregation will occur due to the attraction of GO to counter-ions, which is proportional to the concentration of PAAS. 38 There is a critical concentration for PAAS to maintain an aligned structure and prevent phase separation (Scheme 1). 39…”

Preparation of Nacre‐Like Polyimide/Montmorillonite Composite Films with Excellent Water Vapor Barrier Properties by Gravity‐Induced Deposition

“…For NC50, the appearance of peaks at ≈1775 cm −1 and ≈1380 cm −1 are corresponding to the imide group and the disappearance of the amide group peak at ≈1540 cm −1 indicates the occurrence of imidization. [ 36 ] Additionally, there are no obvious peaks at 3500–3300 cm −1 for NH stretching, which implies the completion of imidization.…”