Small additives help achieve “water-based” polyimide electrospinning

Sponge-like porous materials based on electrospinning technology have the advantages of high porosity, light weight and versatility. With the continuous advancement of short fiber technology and polymer functional material preparation technology in recent years, electrospun sponge materials have received widespread application attention as a new open-pore three-dimensional material. Among them, polyimide (PI)-based electrospun sponge porous materials have become a research hotspot in this field based on their excellent mechanical properties and thermal stability. However, in the past, PI electrospinning technology mostly used non-aqueous solvents such as 1,4-dioxane as the medium, and the toxicity of the solvent caused inevitable environmental pollution and human health hazards. On the other hand, the surface of PI porous electrospun materials prepared by traditional organic solvent electrospinning technology is mostly hydrophobic, which greatly limits the expansion of its application fields.

Recently, Andreas Greiner of the University of Bayreuth in Germany and the Il-Doo Kim research team of the Korea Institute of Science and Technology (KAIST) collaborated to use an aqueous solution containing sodium dodecyl benzene sulfonate (SDBS) surfactant as a solvent system. , a breakthrough was achieved in the preparation of PI electrospun sponge porous materials (sPI) with hydrophilic surface characteristics. Based on the addition of SDBS additives, the surface of the prepared porous PI material exhibits controllable hydrophilic characteristics. The porous PI has excellent dimensional stability in aqueous solution and has a water absorption capacity of 5000%. This research result is a milestone in the preparation of hydrophilic electrospun sponge materials and has broad technical application prospects in biological tissue engineering, oil-water separation and other fields.

PI electrospun sponge preparation process and surface performance display. Image source: ACS Appl. Mater. Interfaces

Long PI fibers are cut into short fibers through high shear mixing, and a small amount (e.g., 1 wt %) of SDBS surfactant is added as a dispersion aid to achieve stable dispersion in aqueous solutions. After further adding the polyamic acid solution, the mixed solution also showed good compatibility; the polyamic acid played the role of a binder in the subsequent electrospinning process to prepare sPI sponge materials. After the SDBS surfactant was introduced, the sPI imine The curing temperature is increased to 280°C. These two factors are the key to ensuring the excellent mechanical properties of PI sponge materials.

SPI sponge material surface affinity and absorption performance control. Image source: ACS Appl. Mater. Interfaces

Different from traditional electrospinning technology, the surface of the sPI sponge material prepared after adding SDBS as an additive shows obvious hydrophilic characteristics (the time required for complete wetting of water droplets is <100 ms). At the same time, systematic research shows that the hydrophilicity (water contact angle) and water absorption capacity of sPI sponge materials can be controlled by regulating the concentration of SDBS surfactant and the content of PI short fibers in the solution. Among them, research shows that the addition of 2.0 wt% SDBS is sufficient to ensure that the surface of the prepared PI material is hydrophilic.

Mechanical property testing of sPI sponge materials. Image source: ACS Appl. Mater. Interfaces

At the same time, although traditional PI materials are inherently hydrophobic, the sPI sponge material prepared in this study shows excellent water absorption capacity and cycle test performance stability; when the SDBS content is 10 wt% of the PI fiber mass, the sPI sponge material (SDBS(10%)-sPI) initial water absorption reaches 5000 wt % (optimal). In addition, cyclic compression performance testing shows that the sPI sponge material system exhibits excellent mechanical properties.performance and porous dimensional stability. Expansion of preparation and application of polyacrylonitrile porous sponge. Image source: ACS Appl. Mater. Interfaces

To demonstrate the universality of this electrospinning technology, the researchers further used SDBS to assist in the preparation of polyacrylonitrile (PAN) sponge materials. By adding 10 wt % SDBS, the prepared PAN porous material has a density of 5.7 mg cm-3, a strongly hydrophilic surface and excellent performance stability in compression cycle tests (more than 100 times). In addition, based on the hydrophilic properties of the surface of the sPI sponge material, the porous material can be used as a bacterial membrane substrate for the cultivation of biofilms with different functions, and has important potential applications in fields such as biofuel cells.

Bacterial culture application of sPI sponge material. Image source: ACS Appl. Mater. Interfaces

Summary

As a typical amphiphilic macromolecular compound, surfactants are widely used in industrial production and daily life. This study creatively used a trace amount of traditional SDBS as a solution additive to achieve a simple “water-based” electrospinning preparation of polymer material systems such as polyimide. The porous material surface hydrophilic modification technology and the universality of the strategy in this research result will greatly break through the application limitations caused by the inherent hydrophobic properties of traditional polymer materials.