Process–Structure–Property Relationships for Porous Membranes Formed by Polymerization of Solid Monomer by a Vapor-Phase Initiator

Nano- and Microscale Design of Electrically Conductive Bacterial Cellulose/PEDOT Cryogels for Electromagnetic Interference Shielding

Exploiting conductive biobased polymer nanocomposites for electromagnetic interference (EMI) shielding is a rapidly evolving research area. In this study, we systematically fine-tune the nano- and microstructural features of bacterial cellulose (BC) modified with poly(3,4-ethylenedioxythiophene) (PEDOT) for EMI shielding applications. First, to investigate the effect of nanostructure, PEDOT is incorporated into the BC matrix using two methods: chemical vapor polymerization (CVP) and in situ polymerization. The CVP method produces more uniform and denser BC-PEDOT nanocomposites, resulting in cryogels with higher electrical conductivity and total EMI shielding effectiveness (SET) (52 ± 2 S/m, 37 dB) compared to those of the in situ polymerized BC-PEDOT cryogels (7 ± 1.5 S/m, 27 dB). The cryogels' microstructure is then adjusted to control the EMI shielding mechanisms by applying different drying methods: freeze-drying, air-drying, and hybrid freeze- and air-drying. Our results indicate that the more energy-efficient air-drying method enhances the reflection-dominant EMI shielding mechanism, with a slight increase in total shielding effectiveness. The drying conditions also affect the final mechanical properties of the samples. Overall, this study demonstrates that BC-PEDOT nanocomposites are excellent candidates for EMI shielding applications.

Influence of Oblique Angle Deposition on Porous Polymer Film Formation

In this study, we applied oblique angle deposition to a modified initiated chemical vapor deposition (iCVD) process to synthesize porous poly(methacrylic acid) (PMAA) films. During the modified iCVD process, frozen monomer molecules are first captured on a cooled substrate, then polymerization occurs via a free radical polymerization mechanism, and finally, the excess monomer is sublimated, resulting in a porous polymer film. We found that delivering the monomer through an extension at an oblique angle resulted in porous films with three morphological regions. Region 1 is located nearest to the monomer extension outlet and consists of porous polymer pillars; region 2 consists of densified pillars, which occur due to the recapturing and polymerization of the sublimated monomer; and region 3 is located furthest from the monomer extension outlet and consists of dendritic structures, which occur due to low monomer concentration. We investigated the role of substrate temperature and monomer deposition time on the growth process. We found that changing the extension angle influenced the location of the regions and the film coverage across the substrate. Our results provide useful guidelines for tuning the structures within porous polymer films by varying the angle of monomer delivery.

Vapor phase polymerization for electronically conductive nanopaper based on bacterial cellulose/poly(3,4-ethylenedioxythiophene)

Eco-friendly conductive polymer nanocomposites have garnered attention as an effective alternative for conventional conductive nanocomposites. Here, we report the fabrication and optimization of flexible, self-standing, and conductive bacterial cellulose/poly(3,4-ethylene dioxythiophene) (BC/PEDOT) nanocomposites using the vapor phase polymerization (VPP) method. Eco-friendly bacterial cellulose (BC) is used as a flexible matrix, and the highly conductive PEDOT polymer is introduced into the BC matrix to achieve electronic conductivity. We demonstrate that vapor phase polymerized BC/PEDOT composites exhibit more than 10 times lower sheet resistance (18 Ω/square) compared to solution polymerized BC/PEDOT (188 Ω/square). The resultant BC/PEDOT fabricated could be bent up to 100 times and completely rolled up without a notable decrease in electronic performance. Moreover, bent BC/PEDOT films enable operation of a green light-emitting diode (LED) light, indicating the flexibility and stability of conductive BC/PEDOT films. Overall, this study suggests a strategy for the development of eco-friendly, flexible, and conductive nanocomposite films.