Supramolecular functional materials [1] with 3D fibrous network structures formed by interconnecting nanosized fibrils have important applications in, for example, drug delivery, coatings, lithography, catalyst supporters, scaffolds for tissue engineering, the engineering of nanostructural and self-supporting porous materials, and novel separation for macromolecules. [1Β±5] Macroscopic properties, in particular, the rheological properties of supramolecular functional materials are determined by the microstructure of fibrous networks. The fibrous networks with permanent interconnections will effectively entrap and immobilize liquid in the meshes and promote the formation of self-supporting rigid gels, which possess the elastic properties of ideal solids and the viscosity properties of a Newtonian liquid. [2,4, 6] In contrast, systems consisting of nonpermanent or transient interconnecting (such as entangled) fibrils or needles reveal only viscous weak gels at low concentrations. [2] Significant efforts have been devoted to the identification of novel systems with a desirable microscopic structural organization that can enable formation of such functional materials. [2,4,5] One such route includes the screening of a large number of potential gelator/solvent systems capable of forming 3D self-organized interconnecting fibrous networks. [2, 4Β±7] However, through the lack of suitable of materials, screening is very difficult. Thus for a given system, it would be extremely desirable to construct or engineer interconnecting 3D fiber networks at the micro-or nanolevel with such organization that materials with the expected functionalities can be created. We aim to illustrate a completely new approach to engineering such materials by constructing permanent 3D interconnecting nanofibrous networks from a system consisting of separate fibers.
The materials to be examined were obtained by dissolving lanosta-8,24-dien-3b-ol:24,25-dihydrolanosterol (L/DHL), 56:44 molar ratio, Sigma) in diisooctylphthalate (DIOP, 99 % purity, Aldrich) at approximately 125 8C, and then cooling the sample to approximately room temperature.
Scanning electronic microscopy (SEM) coupled with a CO 2 super-critical fluid-extraction technique (Thar Design) was applied to examine the micro-and nanostructure of the fibrous networks. The latter technique is used to remove the liquid captured in the networks without disturbing their overall structure. [8] An opaque and viscous paste was obtained on cooling the aforementioned system (10 wt % L/DHL) to room temperature (Figure 1 a, inset). The system consists of only nonbranched fibers or needles, which are in temporary contact with each other (Figure 1 a).
Our strategy is to create networks with permanent interlinking from such a system. An additive, ethylene/vinyl acetate copolymer (EVACP, (C 4 H 6 O 2 Β₯C 2 H 4 ) n , M W ΒΌ ca. 100 000, 40 % in vinyl acetate), is introduced to achieve the microstructured architecture. Surprisingly, under identical ZUSCHRIFTEN