Open Nanoporous Morphologies from Polymeric Blends by Carbon Dioxide Foaming

Abstract

We report the formation of open nanoporous polymer films composed of homogeneous polysulfone/polyimide blends. Porosity is introduced by expansion of carbon dioxide-saturated films at elevated temperatures. To interpret details of the porous morphologies in terms of the experimental conditions during expansion, the glass transition temperature and carbon dioxide solubility of the dense film were examined at various blend compositions. We find that above a critical threshold of the carbon dioxide concentration the porous structure obtained changes from microcellular into open nanoporous. This critical carbon dioxide concentration is independent of the blend composition. Remarkably, it resembles the value previously reported on different polymers.

Controlling the Pore Structure of Polyimide Films Prepared by Exposure to High-Pressure CO₂ and UV Light

“…To clarify the effect of monomer concentration on pore structure, the monomer concentration was reduced from that used in the standard formulation. 2 Porous polyimide films were prepared utilizing UV light irradiation in high-pressure CO 2 , as reported in previous studies [7,8].…”

“…However, the small number of produced pores resulted in low porosity. Another approach to forming pores involves physical foaming, featuring thermal phase-separation of CO 2 gas dissolved in a polymer matrix to induce bubble nucleation in the glassy and rubbery polymer state [8,9]. This method allows dielectric constants as low as 1.77 to be achieved, corresponding to an ultralow-k level [9].…”

Cover-layering a Porous Polyimide Flexible Print Circuit with a Porous Polyimide Layer

“…The preparation of a porous PI film has been continuously studied by several researchers. Some of the studies have succeeded in creating ultra-low k porous material in which the relative dielectric constant is less than two [3][4][5][6][7][8][9][10][11][12].…”

Development of a High-Intensity UV Exposure Apparatus under a High-Pressure CO₂ Gas Atmosphere to Manufacture Large-Area Porous Ultralow-k Polyimide Substrates for Flexible Print Circuits

“…Voids were successfully formed in the PI, although the porosity was limited by the small number of pores. Another approach to forming pores involves the physical foaming technique, wherein CO 2 gas dissolved in a polymer matrix is thermally phase-separated to induce bubble nucleation in the glassy and rubbery state of the polymer [8,9]. The dielectric constant achieved using this method is 1.77, which is known as the ultralow-k level [9].…”