Spongy Gels by a Top-Down Approach from Polymer Fibrous Sponges

Abstract

Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge.

Keywords: electrospinning; gels; sponges.

Figure 1

Sponge made of electrospun fibers with mass of 0.03 g (a) and the sponge after uptake of 30 g of mineral oil (b).

Figure 2

Drawing of the formation of organogels by action of organogelators on liquids (a) and by filling of electrospun fiber sponges with liquids (b).

Figure 3

Cross‐section morphology of the P‐SG1 (a, b) and P‐SG2 (c, d). Scale bar: 100 μm. Insert of (a) and (c) are the water contact angle of the corresponding sponges.

Figure 4

Evaporation of ethanol and water from P‐SG1 and P‐SG2.

Figure 5

Evaporation from the sponges. a) Non‐wettable sponge, 7.57 mg of water; T _s=12 °C. b) Non‐wettable sponge, 6.38 mg of water; T _s=11 °C. c) Wettable sponge, 4.2 mg of ethanol; T _s=12 °C. d) Wettable sponge, 190.66 mg of ethanol; T _s=18 °C. In all of the cases, the humidity was assumed to be zero.

Figure 6

Dynamic oscillatory shear rheological properties of P‐SG2 gel loaded with ethylene glycol as functions of strain (a), temperature (b), and frequency at 25 (c) and 50 °C (d).