Nanocomposite polymeric films

Figure 7.6 The scheme of the press for molding the nanocomposite polymeric films 1, nanocomposite material 2, optical glasses 3, spring 4, foil disc.

Thin-film metal (metal oxide)/polymer nanocomposites with different inorganic phase contents were obtained by using the cold-wall vacuum co-deposition technique. A range of metals was shown to be applicable to form nanocomposite thin films with PPX, i.e., Al, Ti, Pd, and Sn. AFM studies show the metal nanoparticles to have a size of 7-50 nm. Within the composite the polymer forms more or less spherical globules with a maximum size of about 200 nm. The interfacial regions between neighbouring polymeric spherulites contain nanoparticles of the inorganic filler. 

PANI/exfoliated graphene nanoplatelets (GNs) composites were prepared by similar in-situ polymerization [13]. A paper-like nanocomposite flexible film was obtained by controlling vacuum filtration of an aqueous dispersion of PANI-decorated GNs as shown in Figure 6.6 [14]. 

Ihe ECP/CNM nanocomposites can be prepared mainly in two ways (i) in-situ chemical oxidative polymerization, and (ii) in-situ electrochemical polymerization. In an in-situ chemical polymerization, CNM is added into the dispersion containing monomers and oxidant, and the reaction takes place over a period of time. Even a mixture of CNMs can also be used simultaneously. The monomers are polymerized on the surfaces of CNMs. In an in-situ electrochemical polymerization, CNMs are added into the dispersion containing monomer, and the polymerization takes place by the application of electric field for a short period of time, and the nanocomposite films are deposited onto the surface of substrate. Any electrically conducting substrate can be used, such as metal plates. The polarity of substrate and the charges present on the CNM should be accounted for the effective formation of nanocomposites. The thickness of ECP/CNM nanocomposite thin films deposited on the substrate can be controlled by varying the electric field and deposition time. 

For NR nanocomposite filled with silica, it has always been known that the hydrophilicity-hydrophobicity issue is a challenge since silica is hydrophilic and NR is hydrophobic. The usual method to overcome this issue is by adding coupling agent. In 1987 Wu and coworkers introduced admicellar polymerization where a thin polymeric film will be formed on the silica s surface. This process yields a thin film of polymer on the silica which can further enhance the adhesion between the surfaces of silica and rubber. The steps involved in admicellar polymerization are outlined in Scheme 7.7. In principle, a bilayer of surfactant, i.e. the admicelle, is first formed on the surface of the silica. Monomer will then penetrate the admicelle, i.e. the adsolubilization of monomer. Upon addition of initiator to the reaction system, in situ polymerization occurs in the admicelles. Finally, the surfactant is removed by washing with water and an ultrathin polymer layer is formed on the surface of the silica. The polymerization of the monomer in the admicelles can be induced by thermal process, chemical initiators or radiation. ... 

Elsewhere, Tai et al. used PANI/Ti02 nanocomposites prepared by in-situ chemical oxidation polymerization synthesis in the presence of T1O2 nanoparticles to fabricate a gas sensor [317]. The responses of the PANI/T1O2 nanocomposite thin film to toxic NH3 and CO gas were investigated. It was found that the response, reproducibility, and stability of nanocomposite thin film to NH3 were superior those for CO gas. The gas-sensing properties of the PANI/T1O2 thin film to NH3 and CO indicated that the PANI/Ti02 thin film was an excellent candidate for NH3 detection, but not for the fabrication of a CO gas sensor [317]. 

The third-order nonlinear susceptibility of the polymerized nanocomposite thin films was evaluated by a CA Z-scan technique [22], Figure 22.22 shows the Z-scan results of high-quality PbS QDs uniformly dispersed in an organic-inorganic hybrid photosensitive polymer [24]. Figure 22.22a presents the setup used for the Z-scan experiment A femtosecond laser beam operating at 800 nm, with a pulse width of 100 fs and a repetition rate of 1 kHz, was used to excite the sample. The signal was collected by detector 1 (Dl) and the reference beam was collected by detector 2 (D2), to eliminate laser fluctuations. The sample was... 

However, and without any doubt, the in situ monomer polymerization in the presence of pre-prepared magnetic nanoparticles is the most common strategy to prepare nanocomposites based on conducting polymers. In this sense the polymerization can be carried out in either homogeneous medium or heterogeneous medium, i.e., in emulsion using surfactants, providing different types of nanocomposites, from films to core-shell particles. 

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

Scheme 6 Formation of hyperbranched thin film nanocomposites using an electrophilic polymeric reagent 14 and a nucleophilic amine-functionalized PAMAM dendrimer 15...

Surface engineering of polymers by infusion. Supercritical-fluid contact can reversibly swell some polymer surfaces and films thus helping to enhance impregnation by monomers with subsequent polymerization to form nanocomposite anchored layers. - ... 

Simultaneous evaporation of metal with organic and inorganic substances followed by vapor deposition on a substrate allows the production of composite films containing M nanoparticles stabilized in various dielectric matrices [2, 28]. The use of monomer molecules in this process polymerizing during deposition or as a result of the subsequent reactions yields polymeric nanocomposite films with metal inclusions [2, 3, 28, 37]. The new low-temperature synthesis of polymeric nanocomposite films has been elaborated recently. This synthesis is based on the deposition of M/SC and monomers vapors at temperature 80 K followed by low-temperature solid-state polymerization of obtained films in conditions of frozen thermal movement of molecules (cryochemical synthesis) [2], This synthesis has important features, which will be considered further. 

At the co-deposition of nanocomposite components formation of M/SC particles proceeds simultaneously with formation of a dielectric matrix, and the relationship between these processes determines the nanocomposite structure. This problem has been in detail investigated for the case of M/SC nanoparticles formation in polymer matrices. Synthesis of nanocomposite films by simultaneous PVD of polytetrafluoroethylene (PTFE) and Au has been carried out in works [62-64], Polymer and metal were sputtered under action of Ar ions and then the obtained vapors were deposited on substrates (quartz, glass, silica, mica, etc.) at various temperatures. Here, it is necessary to note that polymer sputtering cannot be considered as only physical process PFTE polymer chains destruct under action of high-energy ions, and formed chemically active low-molecular fragments are then deposited and polymerized on a substrate surface. 

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