The electrospinning process was used successfully to fabricate nanofibers of poly(ethylene oxide) (PEO) in which multiwalled carbon nanotubes (MWCNT) are embedded. Initial dispersion of MWCNTs in water was achieved using amphiphiles, either as small molecules (sodium dodecyl sulfate, SDS) or as a high molecular weight, highly branched polymer (Gum Arabic). These dispersions provided separation of the MWCNTs and their individual incorporation into the PEO nanofibers by subsequent electrospinning. The focus of this work is on the development of axial orientations in these multicomponent nanofibers. A theoretical model is presented for the behavior of rodlike particles representing CNTs in electrospinning. Initially the rods are randomly oriented, but due to the sinklike flow in a wedge they are gradually oriented mainly along the stream lines, so that straight CNTs are almost oriented upon entering the electrospun jet. The degrees of orientation of polymer, surfactant, and MWCNT were studied using X-ray diffraction and transmission electron microscopy. Oriented ropes of the nanofibers were fabricated in a converging electric field by a rotating disk with a tapered edge. A high degree of alignment of PEO crystals was found in electrospun nanofibers containing only PEO, as well as PEO/SDS. The latter also exhibited a high degree of alignment of the SDS layers. The axial orientation of PEO and SDS is significantly reduced in MWCNT-containing nanofibers. Transmission electron microscopy (TEM) images indicated that the MWCNTs were embedded in the nanofibers as individual elements, mostly aligned along the fiber axis. Nevertheless, there are also many cases in which the nanotubes appear twisted, bent, or with other irregularities. Comparison of cryo-TEM images of vitrified MWCNT dispersions with TEM images of the raw nanotubes indicated that sonication during the dispersion process may be responsible for the irregularities observed in some of the nanotubes.

No abstract

The electrospinning process was used successfully to embed single-walled carbon nanotubes (SWCNTs) in a poly(ethylene oxide) (PEO) matrix, forming composite nanofibers. Initial dispersion of SWCNTs in water was achieved by the use of an amphiphilic alternating copolymer of styrene and sodium maleate. The resulting dispersions were stable, having a dark, smooth, ink-like appearance. For electrospinning, the dispersions were mixed with PEO solution in an ethanol/water mixture. The distribution and conformation of the nanotubes in the nanofibers were studied by transmission electron microscopy (TEM). Oxygen plasma etching was used to expose the nanotubes within the nanofibers to facilitate direct observation. Nanotube alignment within the nanofibers was shown to depend strongly on the quality of the initial dispersions. Well-dispersed and separated nanotubes were embedded in a straight and aligned form, while entangled nonseparated nanotubes were incorporated as dense aggregates. X-ray diffraction demonstrated a high degree of orientation of the PEO crystals in the electrospun nanofibers with embedded SWCNTs. This result is in pronounced distinction to the detrimental effect of incorporation of multiwalled carbon nanotubes on polymer orientation in electrospun nanofibers, as reported previously.

Nylon‐6,6 nanofibers were electrospun at an elongation rate of the order of 1000 s−1 and a cross‐sectional area reduction of the order of 0.33 × 105. The influence of these process peculiarities on the intrinsic structure and mechanical properties of the electrospun nanofibers is studied in the present work. Individual electrospun nanofibers with an average diameter of 550 nm were collected at take‐up velocities of 5 and 20 m/s and subsequently tested to assess their overall stress–strain characteristics; the testing included an evaluation of Young's modulus and the nanofibers' mechanical strength. The results for the as‐spun nanofibers were compared to the stress–strain characteristics of the melt‐extruded microfibers, which underwent postprocessing. For the nanofibers that were collected at 5 m/s the average elongation‐at‐break was 66%, the mechanical strength was 110 MPa, and Young's modulus was 453 MPa, for take‐up velocity of 20 m/s—61%, 150 and 950 MPa, respectively. The nanofibers displayed α‐crystalline phase (with triclinic cell structure). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1482–1489, 2006

Beta-casein is an intrinsically unstructured amphiphilic protein that self-assembles into micelles at neutral pH. This paper reports that beta-casein self-organizes into micelles also under acidic conditions. The protein association behavior and micelle characteristics at pH 2.6, well below the p I, are presented. The pH was found to strongly affect the micelle shape and dimensions. Cryogenic transmission electron microscopy (cryo-TEM) experiments revealed disk-like micelles of 20-25 nm in length and approximately 3.5 nm in height in acidic conditions. An aggregation number of 6 was determined by sedimentation equilibrium under these conditions. Isothermal titration calorimetry experiments verified the association below the p I and allowed determination of the micellization enthalpy, the critical micellar concentration, and the micellization relative cooperativity (MR). Small-angle X-ray scattering results at concentrations below the critical micellization concentration (CMC) suggest that the monomeric protein is likely in a premolten globule state at low pH. Calculations of the protein charge at acidic and neutral pH reveal a similar high net charge but considerable differences in the charge distribution along the protein backbone. Overall the results show that beta-casein is amphiphilic at low pH, but the distribution of charge along the protein chain creates packing constraints that affect the micelle organization, leading at concentrations above the CMC to the formation of disk micelles.