Mixed polymer nanofibers

PAN blends changed with different amount of PANA of the mixed polymers. The morphologies of electrospun nanofibers are presented in Fig. 6.24a-d. According to the SEM images, the diameters of the PANA/PAN nanofibers are dependent on initially added PANA concentrations. The diameter of PANA/PAN fibers was smaller than for pure PAN fibers. The average nanofiber diameter decreased from 113 23 nm for pure PAN fibers to 105 23 nm for PANA/PAN (10 w/v %), 102 20 nm for PANA/PAN (15 w/v %), and 94 16 nm for PANA/PAN (20 w/v %), as shown in Table 6.6. 

Blending is the simplest and easiest method anployed to functionalize a polymer. This is a physical approach with the addition of blending ligand molecules into the polymer solution and then electrospinning the polymer solution. No chemical bonding or attachment is involved between the polymer material and the modified species (Figure 8.3). It is a simple mixing of two or more materials that has been proven to be an effective method for polymer nanofiber modification. Nevertheless, blend molecules are susceptible to detachment and the technique is neither reproducible nor controllable. 

Composites of carbon nanofibers and thermoplastic polyurethanes with shape memory properties prepared by chaotic mixing. Polym. Eng. Sd., 49,... 

In the previous sections, organic solutions are already mentioned a few times, and many of the techniques that allow polymer nanofibers to be produced, as described in Chapters 2 and 3, rely on systems composed of macromolecules in solution. Investigating the properties of polymer solutions is the subject of an entire sub-field of chemical physics, and we give here only introductory background information. A solution involves two or more chemical species that are intimately mixed, i.e. in which the mutual interaction between the components is at the molecular level. In other words, a solution is homogenously composed of only one phase. Polymer solutions comprise at least one polymeric material and the solvent (water, organic solvents, etc.) in... 

A dispersion is instead a mixture in which the less abundant compound is dispersed, but not molecularly dissolved, in the other component. Examples are a dispersion of a solid phase (powder, nanoparticles, nanocrystals, nanotubes, etc) in a solvent, which is called a suspension, or a dispersion of an immiscible liquid phase in a second liquid, which is called an emulsion. Milk and mayonnaise are familiar examples of emulsions. Aerosols are dispersions of tiny liquid droplets or solid particles in a continuous gaseous phase. The science of aerosols is particularly relevant in order to design filter elements able to remove droplets and particles from air, which can be performed with very high efficiency by polymer nanofibers (Section 4.3.1). Finally, another way to indicate homogeneously mixed dispersions, emulsions or aerosols of nano- or microparticles is colloids. Colloidal dispersions of inorganic nanocrystals or organic nanofibers are familiar examples for nanotechnologists. 

In this study, a novel proach is plied to prepare polymer composites reinforced by both nanoparticles and long fibers. Carbon nanofibers were pre-boimd onto glass fiber mats, and then unsaturated polyester conposites were synthesized through vacuum assisted resin transfer molding. These composites were compared with those synthesized by pre-mixing carbon nanofibers into the polymer resin. Mechanical and thermal properties of composites were measured. Flexural strength and modulus of composites were improved with the incorporation of nanoparticles. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficients of imsaturated polyester resin. 

Techniques to produce multiscale biomaterial scaffolds with designer geometries are the need of the hour to provide improved biomimetic properties for functional tissue replacements. While micrometer fibers generate an open pore stnicture, nanofibers support cell adhesion and facilitate cell-cell interactions. This was further proven by cell penetration studies, which showed superior ingrowth of cells into hierarchical structures. Mixed bimodal scaffolds of two different polymers are another promising approach, because they exhibit hierarchical pore/ surface systems and combine the beneficial properties of both polymers at two different scales. Vaiious 3D micro- and nanoscale multiscale scaffolds have been fabricated through various techniques and were found to have the potential to essentially recreate natural bone, cardiac, neural, and vascular tissues. 

The above polyolefin copolymers have also been used to prepare conventional composites and nanocomposites. However, similar to the case of polymer blends, not too many studies have been reported thus far. Recently, Kelarakis et al. (49) have mixed 10 wt% of surface-modified carbon nanofiber (MCNF) with propylene-ethylene random copolymer (propylene 84.3%). The MCNF acted as a nucleating agent for crystallization of the a-form of PP in the matrix. During deformation at room temperature, strain-induced crystallization took place, while the transformation from the 7-phase to a-phase also occurred for both unfilled and 10 wt% MCNF-filled samples. The tensile strength of the filled material was consistently higher than that of pure copolymer. These results are illustrated in Fig. 8.27. 

HGURE 4.4 Electrical properties of polymer composites. (A) The electrical conductivity of the PS/graphene composite as a function of graphene volume fraction. (B) The electrical conductivity of directly mixing (DM) CNT/PANI and CNT/ PANI nanofibers with different CNT contents in the directions being parallel and perpendicular to the fiber axis. 

To determine the activity of a single drug in different polymer matrices, the prepared polymer solutions are mixed with 1.5 wt% of each drag alone and electrospun into nanofibers. Then 5-mm circular sections of nanofibers are... 

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