No abstract

No abstract

No abstract

No abstract

No abstract

The dynamics of low molecular weight polymer mixtures, in terms of concentration fluctuations near a critical point, in the homogeneous region, has shown a nonlinear behavior in a number of physical properties.1-2 For high molecular weight mixtures, i.e., polymer blends and block copolymers, most of the studies dealt with the dynamics of phase separation and spinodal decomposition and its incidence on the scattering properties of these mixtures.3 For the viscoelastic properties, Bates,[4][5][6] Gouinlock and Porter,6 and Han7-8 have studied block copolymers and observed important discontinuities of their dynamic properties (G' and *) near the microphase separation temperature (TB) when performing temperature steps. Also, an important increase of these properties was observed at low frequencies for temperatures close to TB.

No abstract

Core-shell structured PEO-chitosan nanofibers have been produced using a coaxial electrospinning setup. PEO and chitosan solutions, both in an aqueous acetic acid solvent, were used as the inner (core) and outer (shell) layer, respectively. Uniform-sized defect-free nanofibers of 150-190 nm diameter were produced. In addition, hollow nanofibers could be obtained subsequent to PEO washing of the membranes. The core-shell nanostructure and existence of chitosan on the shell layer were confirmed by TEM images obtained before and after washing the PEO content with water. The presence of chitosan on the surface of the composite nanofibers was further supported by XPS studies. The chitosan and PEO compositions in the nanofibrous mats were determined by TGA analysis, which were similar to their ratio in the feed solutions. The local compositional homogeneity of the membranes and the efficiency of the washing step to remove PEO were also verified by FTIR. In addition, DSC and XRD were used to characterize the crystalline structure and morphology of the co-electrospun nonwoven mats. The prepared coaxial nanofibers (hollow and solid) have several potential applications due to the presence of chitosan on their outer surfaces.