Swollen structure

A large amount of water is added to the dehydrated material in order to cause it to swell the swollen structure is preserved when the material is frozen and subsequently dried in vacuo (in the frozen state) to a low moisture content. Some leaching occurs during the treatment with water and this, undoubtedly, further contributes to the increase in the porosity of the solid. Drying of the lyophilized substance can.be completed in a relatively short time in a vacuum oven at an elevated temperature, or at room temperature in the presence of an efficient water adsorbent. 

The in situ bulk polymerization of vinyl monomers in PET and the graft polymerization of vinyl monomers to PET are potential useful tools for the chemical modification of this polymer. The distinction between in situ polymerization and graft polymerization is a relatively minor one, and from a practical point of view may be of no significance. In graft polymerization, the newly formed polymer is covalently bonded to a site on the host polymer (PET), while the in situ bulk polymerization of a vinyl monomer results in a polymer that is physically entraped in the PET. The vinyl polymerization in the PET is usually carried out in the presence of the swelling solvent, thereby maintaining the swollen PET structure during polymerization. The swollen structure allows the monomer to diffuse in sufficient quantities to react at the active centers that have been produced by chemical initiation (with AIBM) before termination takes place. 

It was shown (8,9) that the pretreatment of PET yarns with certain strongly interacting solvents can lead not only to swelling but also to irreversible modifications of polymers structure. The basis of structural modification during the DMF treatment of PET is solvent-induced crystallization which occurs while the PET structure is swollen by DMF. At low treatment temperatures (i.e., 50-100°C, Table I), only small crystallites are formed and after removal of the solvent the swollen structure cannot be supported by the small crystallites and consequently collapses. 

Polyelectrolyte films are comprised of the polyelectrolytes, solvent and ions, the latter mainly located at the film/solution interface, see below. Solvent content in PEMs can beaproximately40% ]94,95], being the actual value dependent on film history (drying and reswelling steps) and for dry films on environmental humidity ]95,96]. PEMs are therefore highly swollen structures, but its water content is below that found in... 

This reaction can be utilized to determine Fe(lll) at potentials where it is not redox-active at an unmodified glassy carbon electrode. The mediation of this reaction in two different electrolytes, i.e. 1 M perchloric acid and 0.1 M sulfuric acid, will be discussed. EQCM and neutron reflectivity measurements have shown that, while in H2SO4 a swollen structure is obtained, in perchloric acid a much more closed morphology is obtained which inhibits ion movement. 

In order to define this accessibility curve clearly it is necessary to use a number of solute molecules which range in size over the whole range of pore sizes anticipated in the swollen structure. We have found the most suitable solutes to be the dextrans marketed by Pharmacia (Uppsala) Ltd. supplemented by a few low molecular weight sugars. Grotte (7) has reviewed evidence to show that these dextrans behave in solution as hydro-dynamic spheres, and that the diameters of these molecules in solution may be calculated from their diffusion coefficients according to the Einstein-Stokes formula ... 

In conclusion, it should be also said that the origin of the hysteresis loop of the adsorption—desorption isotherms of porous polymers is stiU debated and can be interpreted in different ways. For example, there exists an opinion that hysteresis is not related to traditional capillary condensation in the pores, but may be a consequence of the out-of-equihbrium character of phase transitions in real disordered mesoporous polymers [255]. A failure to reach equilibrium under the given experimental conditions may be caused by the slow diffusion rate of the sorbate [256] or slow swelling of the polymeric sorbent on adsorption and slow relaxation of its swollen structure on desorption. Quite often, a subsequent adsorption on the same material results in larger adsorption capacity values. It is the so-called conditioning effect [256] that may imply a nonequihbrium character of the process. Even the reproducibihty of the shape and location of a hysteresis loop of the isotherms may indicate the estabhshment of fast... 

If the solvent is nonselective, the anchor has a swollen structure similar to an adsorbed homopolymer. In the case of adsorption of an AB block copol5mier from nonselective solvents there are two possible cases (38) The first is referred to as the buoy regime, in which the anchor are small and adsorption is dominated by repulsive interactions between the buoys. Increasing the length of the anchor will increase the amount adsorbed. The second case is called the anchor regime, in which the anchor layer is saturated and the buoys are small in size. Here, increasing the length of the anchor block will not increase the adsorbed amount. 

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