Preparation Of Free-standing Films Research Articles

Preparation of freestanding films from SWCNT/PANI nanocomposites using different blending techniques and characterization of their EMI shielding effectiveness in X-band

Synthetic polyvinyl alcohol (PVA) was used as a matrix, and polyaniline/SWCNT (PS) was used as a filler in the composite to create thin films for electromagnetic interference (EMI) shielding. The blending methods, namely mechanical stirring and ultrasonication, were used to produce composites (commercially available polyaniline (PANI) and single-walled carbon nanotube (SWCNT)). A solution casting process was used to create the composite films, which had a thickness of 0.5 mm. X-ray diffraction and field-emission scanning electron microscopy were used to examine the structural and morphological properties of the as-prepared composite films. Using a vector network analyzer, the effect of PANI/SWCNT composition on microwave shielding effectiveness (SE) of PVA was investigated and the efficiency of the EMI shield was evaluated. To select the effective films, the losses due to absorption, reflection, and total SE of the samples were measured. These findings show that absorption dominated total shielding effectiveness (SET) up to −18 dB in the 8.2–12.4 GHz (X-band) frequency range, implying their usefulness as microwave absorbers.

A new approach for preparation of free-standing nano-porous SiO2 films with a large area

Free-standing nano-porous SiO2 films with high porosity on the scale of hundreds of microns were obtained by combing a parting agent method and layer-by-layer assembly method where betaine was employed as soluble layer and PAMS (poly-α-methylstyrene) was used as protective and thermal degradation sacrificial layer, respectively. The surface morphology, roughness, chemical composition and physical properties of the films were studied in this work. The thermal degradation property of PAMS and its effect on the preparation of free-standing film were also analyzed. The results indicated that the PAMS effectively protected the SiO2 films from damage during the detachment and transfer processes, and it can be completely removed after the film being calcined at 330 °C for 4 h. The thickness of the SiO2 films can be adjusted between 534 and 297 nm. Before calcination, the SiO2 film was hydrophobic and the process of dissolving betaine would not damage its structure nor influence its smoothness. After being calcined, the SiO2 film became hydrophilic, the refractive index increased from 1.19 to 1.20, and the porosity decreased from 56 to 53 %; the calcination process contributed to progress condensation of the polysiloxane network and removed organic groups from silica film. Employing PAMS as protective and thermal degradation sacrificial layer provides a new approach for preparation of other large-area free-standing films.

Layer-by-layer self-assembly, controllable disintegration of polycarboxybetaine multilayers and preparation of free-standing films at physiological conditions

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.

Preparation of Free-Standing Films from Kafirin Protein Microparticles: Mechanism of Formation and Functional Properties

A method of preparing free-standing films using kafirin microparticles made by phase separation from acetic acid is described. Film preparation involved the suspension of the microparticles in acetic acid solution containing plasticizer. On evaporation of the acetic acid, a complete, smooth, flexible, transparent film was formed. A minimum concentration of acid was required to form a cohesive film relative to the concentration of kafirin. This was approximately 10.8:1, percent acetic acid to percent kafirin. Film formation appears to be by controlled aggregation of kafirin microparticles, followed by dissolution of the microparticles in acetic acid and drying into a cohesive film. The functional properties of microparticle films were generally superior to films cast directly from a solution of kafirin, at the same protein content. Kafirin microparticle films were very thin (<15 microm), relatively strong but not very extensible, with better water barrier properties and lower protein digestibility than conventionally cast kafirin films.

Metal ion mixing in diamond

We have carried out some investigations of the mixing of thin metal films into diamond by energetic metal ion bombardment. Free-standing diamond films were made by microwave plasma-assisted CVD, onto which films of Nb or Ta, approximately 100-Å thick, were deposited using a filtered vacuum arc plasma technique. The metalized diamond was then bombarded with a Ta and Nb ion-beam, respectively, at an energy of 150 keV and to an applied dose of ∼7×10 16 ions/cm 2. The Nb and Ta depth profiles were measured by 2 MeV He + Rutherford backscattering spectrometry. Intense intermixing was produced between the original metal overlay, the diamond matrix, and the implanted atoms; and the concentration depth profiles were found to be well-described by the predictions of the TRIM code. Here, we outline the techniques used for diamond synthesis and the preparation of free-standing films, the vacuum arc plasma deposition of Nb and Ta thin films, and the Ta and Nb ion implantations; and we describe our observations of the ion-mixed films formed in this way.