Formation of nanoscale networks: selectively swelling amphiphilic block copolymers with CO2-expanded liquids

Abstract

Polymeric films with nanoscale networks were prepared by selectively swelling an amphiphilic diblock copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), with the CO(2)-expanded liquid (CXL), CO(2)-methanol. The phase behavior of the CO(2)-methanol system was investigated by both theoretical calculation and experiments, revealing that methanol can be expanded by CO(2), forming homogeneous CXL under the experimental conditions. When treated with the CO(2)-methanol system, the spin cast compact PS-b-P4VP film was transformed into a network with interconnected pores, in a pressure range of 12-20 MPa and a temperature range of 45-60 °C. The formation mechanism of the network, involving plasticization of PS and selective swelling of P4VP, was proposed. Because the diblock copolymer diffusion process is controlled by the activated hopping of individual block copolymer chains with the thermodynamic barrier for moving PVP segments from one to another, the formation of the network structures is achieved in a short time scale and shows "thermodynamically restricted" character. Furthermore, the resulting polymer networks were employed as templates, for the preparation of polypyrrole networks, by an electrochemical polymerization process. The prepared porous polypyrrole film was used to fabricate a chemoresistor-type gas sensor which showed high sensitivity towards ammonia.

Nanophase separation and structural evolution of block copolymer films: A “green” and “clean” supercritical fluid approach

“…24 scCO2 can also be used to fabricate nanocellular structures and nanopores in block copolymer thin and thick films. 5,[25][26][27][28] Much attention has been paid to ordering and kinetics of BCP thick and thin films by scCO2, examined from both a theoretical and an experimental perspective. 23,25,[29][30] However, to-date surface periodic arrangements of two blocks has only been realized by annealing polymers above their melting points.…”

Highly mesoporous metal–organic framework assembled in a switchable solvent

“…Therefore, by varying CO 2 pressure, a continuum of liquid media ranging from the neat organic solvent to CXL is generated, and their properties can be adjusted by tuning the operating pressure. Until now, CXLs have been shown to be optimal solvents in a variety of fields, including facilitating polymer processing23242526, serving as reaction media2728293031, precipitating fine particles323334, inducing separations3536 and so on.…”

Fabrication of Silica Membrane through Surface‐Induced Condensation on Porous Block Copolymer

“…Of particular, BCP templates with bicontinuous porosities can been used to induce inorganic porous materials that have potential applications such as separation, sensing, biomedicine, catalysis, electrochemical devices and optics . Various approaches, including atomic layer deposition (ALD),, chemical vapor deposition, sol‐gel process, and electrodeposition have been developed to obtain inorganic porous materials by using BCPs as templates. For example, H−Y.…”