Fabrication of amorphous lamellar freestanding poly(N‐dodecyl acrylamide) films and their mechanical properties

Abstract

AbstractAn amorphous lamellar freestanding film composed of poly(N‐dodecyl acrylamide) (pDDA) was prepared by annealing a micrometer‐thick film under humid conditions (humid‐annealing). pDDA was blade‐coated onto a glass substrate, and its lamellar formation was studied by XRD and polarized optical microscopy (POM). The XRD pattern indicates that pDDA formed a highly oriented lamellar structure by humid‐annealing at 80 °C for 6 h. Moreover, the POM image of the cross‐section of the film indicates that lamellar formation started at the polymer–substrate interface, and the amorphous lamella covered the entire film area without randomly oriented regions. In contrast, the open Nicol microscopic image exhibited large cracks in the highly oriented film owing to shrinkage of the film. A crack‐free film was prepared using water‐saturated chloroform as the solvent for blade coating. Water is thought to adsorb to an amide moiety to induce a ‘pre‐lamellar’ structure in the solution. The formation of pre‐lamellae and the decrease in the humid‐annealing temperature reduced the shrinkage of the film by lamellar formation to form a crack‐free film. The mechanical properties of the crack‐free, freestanding pDDA films were studied using a simple tensile test. The film became increasingly stronger with the formation of an amorphous lamellar structure. These results indicate that the mechanical properties of polymer films can be improved without crystallization. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.