Abstract
Honeycomb-like porous chitosan (CS) films are attractive tools for developing functional materials for filters, catalyses, adsorbents, biomaterials, etc. A simple method for fabricating honeycomb-like porous CS films without special reagents, facilities, and techniques would make them accessible. Here we introduce an easily available method for fabricating honeycomb-like CS films without a strong acid/base, toxic reagents, or special facilities/techniques. An aqueous solution containing CS and poly(N-isopropylacrylamide) (PNIPAm) was allowed to stand at 25 °C to evaporate water. After 3 days, CS–PNIPAm composite films with homogenously phase-separated PNIPAm particles were obtained. The PNIPAm particles were removed by immersion in methanol, and the resulting films dried under reduced pressure to become honeycomb-like porous CS films. The pore size could be varied in the range of 0.5–3.0 μm by altering the CS concentration and the molecular weight of CS where the pore size was reduced under conditions with stronger interaction between CS molecules. We reveal that the key to success with this system is the decrease of lower critical solution temperature (LCST) of PNIPAm with water evaporation. In addition, we confirmed the removed PNIPAm was recyclable in this system. Furthermore, we found this method was also applicable to alginate. The proposed facile method for fabricating honeycomb-like porous polymeric films could provide various functional porous materials.
Highlights
Honeycomb-like CS lms with 0.1–1.0 mm pores prepared via the template-imprinting method with scari ed polystyrene colloid crystals have been reported,[32] the phenomenon we found provides a novel strategy for fabricating honeycomb-like CS lms, i.e., the homogenously phase-separated PNIPAm particles in the CS lm are used as templates to make honeycomb-like pores
The 1H Nuclear magnetic resonance (NMR) spectrum of the materials removed by methanol showed PNIPAm and acetic acid (Fig. S4†), proving the observed
The honeycomb-like pores were formed via the removal of the PNIPAm particles by immersion in methanol
Summary
Macroporous polymer lms with interconnected macropores (>50 nm)[1] have attracted a great deal of attention, from separation science,[2,3,4] and catalysis, battery,[5,6] and biomaterial elds,[7,8] because they can be used as supports for catalysis, drugs, or living cells, and as frameworks[9] in the fabrication of hierarchical porous materials.Honeycomb structures inspired by bee honeycombs are a superior design used in various elds including architecture, and mechanical, acoustic, and chemical engineering, because they offer lighter material, high structural stability, large surface area, high permeability, and heat and sound-insulation.[10]. We investigate the preparation of honeycomb-like CS lms via phase transition of PNIPAm during water evaporation at 25 C and subsequent removal of PNIPAm particles to establish a novel methodology for fabricating honeycomb-like porous CS lms. Preparation of the honeycomb-like porous lms CS and PNIPAm aqueous solutions were prepared as follows: CS (2.0 g) and acetic acid (0.5 g) were dissolved in 97.5 mL of water, and PNIPAm (2.0 g) was dissolved in 98 mL of water.
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