Nanosponge

This review will discuss the possibility to control and improve the reactivity of Titania by design of new tailored nano-architecture. Specifically, analyses quasi-ID Ti02 nanostructures, e.g. nanorods, nanowires and nanofibres, nanotubes and nanopillars. 2D Titania nanostructures, e.g. columnar-type films, ordered arrays of nanotubes or nano-rods/-wires, nanobowl array, nanomembranes (called also nanohole array) and nanosponge, and Ti-based ordered mesoporous matrices will be instead discussed in a consecutive review paper. 

The nanoball of the type M0132 shows such molecule-response activity. It can be compared to a nanosponge with a multitude of open pores accessible for a specific substrate, for example, guanidinium cation guests in the case of M0132 ... 

A. Muller, B. Botar, H. Bogge et al., A Potassium Selective Nanosponge with Well Defined Pores, Chem. Commun. 2002, 2944-2945. 

Bogge et al.. Changeable Pore Sizes Allowing Effective and Specific Recognition by a Molybdenum-Oxide Based Nanosponge En Route to Sphere-Surface and Nanoporous-Cluster Chemistry, Angew. Chem. Int. Ed. Engl. 2002, 41, 3604-3609. 

StiU, our conclusion on the restricted overlapping of individual polystyrene coils in the hypercrossHnked network and in the initial polymer solution was further corroborated by a direct experiment, namely by the preparation of a hypercrossHnked material deHberately constructed from individual polystyrene macromolecules. The initial Hnear polystyrene was first crosslinked intramolecularly in a very ddute solution and then the individual intramolecularly crossHnked cods, nanosponges, were additionally crosslinked intermolecularly in a concentrated solution, thus giving a bulk hypercrossHnked material. Both the nanosponges and the final polymeric material were subjected to electron microscopic investigation. 

Soluble intramolecularly hypercrossHnked polystyrene (nanosponges) represent a fundamentady new macromolecular object that wdl be described in detail in Chapter 8. For the above two-step modeling experiments, nanosponges were prepared from the industrial Hnear polystyrene having a molecular weight of 300 000 Da and a wide molecular weight... 

Figure 7.33 Texture of three-dimensional material based on hypercrosslinked nanosponges additional crosslinking degree with monochlorodimethyl ether is 11% ultrathin section, transmission electron microscopy, 42,000x. (After [198]).

This chapter introduces a novel macromolecular species, the intramolecularly hypercrosshnked polystyrene (IHPS) or nanosponge, which differs fundamentaUy from the above four basic types... 

Figure 8.1 Schematic representation of four known types of macromoiecuiar species and the nanosponge.

We introduce the term nanosponge for the IHPS species, since it refers to the macromolecular range of about 10—20 nm of the species sizes it is also associated with the low density and porosity of the material, its ability to readily incorporate large amounts of any liquid, as well as the rigidity of the species, both in dry and in swollen state. 

As discussed, the intensive crosslinking of polystyrene cods in ddute solutions results in the formation of the soluble polymeric species, nanosponges, which can be expected to reproduce on the molecular level the major properties of the hypercrosslinked networks prepared from semi-dduted polystyrene solutions. Since the nanosponges present a novel type of macromolecular objects, their physico-chemical characterization could be of great theoretical interest. 

Table 8.3 demonstrates the extremely high sedimentation constants, Sq, of IHPS molecules, compared to the parent linear polystyrene and chlor-omethylated polystyrene, aU examined with an ultracentrifuge. The difference implies a significant contraction of polymeric coils in the course of their crosslinking. In this respect, the nanosponges resemble globular... 

On crosslinking, the molecular wei t of the polystyrene macromolecules of330 kDa should rise to 370 kDa for sample IHPS-18, due to the introduction of one additional —CH2- poup per styrene repeat unit (at the formal degree of crosshnking of the nanosponge of 200% attained). It could even amount to 390 kDa if the residual 6% chlorine is also taken into consideration. 

In order to estimate the molecular dimensions of nanosponges, we appHed dynamic light scattering and size-exclusion chromatography (SEC) to the solutions of the new species and low-angle X-ray scattering, electron microscopy, and scanning atomic force microscopy to the dry material [236, 238-240]. 

Figure 8.2 Zimm diagrams for the solution of PS-330 before (PS) and after intramolecular crosslinking (N-SP = nanosponge). Solvent tetrahydrofuran. (Reprinted from [236] with permission of the American Chemicai Society.)...

Indeed, when examined by low-angle X-ray scattering technique, the nanosponge powder scattered X-rays as a material with fluctuations in its density having a lattice spacing period of about 12 nm. SEC in tetrahydrofuran or chloroform, on both analytical and preparative scale [236], was carried out on a silica gel Diasorb Si 400 column having an acceptable performance (over 9000 theoretical plates for naphthalene in acetonitrile)... 

Figure 8.3 Preparative size-exclusion chromatography of the bulk intramolecular crosslinking product. Fractions 1, 2, and 3 correspond to microgels, clusters, and nanosponge, respectively. (Reprinted from [239] with permission of Wiley Sons, Inc.)...

Dynamic tight scattering [236] of fractions 3 and 2 allowed estimation of the diameter of the nanosponges as 17 nm and that of the clusters as 34 nm. Indeed, transition electron micrographs reveal the spherical shape and a distinct size difference of the two types of dry species, approximately 15-20 nm and up to 40-50 nm, respectively [236, 238]. 

By using the technique of an artificial boundary in the ultracentrifiige cell, diffusion coefficients Do for the clusters (firaction 2) and the nanosponges (fiaction 3) were determined at a single concentration of 2 g/L (Table 8.4). It has been shown earlier that the hydrodynamic parameters of these species do not depend on the concentration. This is not the case with the initial linear polystyrene, where several measurements in the concentration range of 2.5-1.0 g/L were needed, in order to extrapolate to the limiting value of the diffusion constant Dq at zero concentration. 

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