Composite films, synthesized

Chapter 10 deals with composite films synthesized by the physical vapor deposition method. These films consist of dielectric matrix containing metal or semiconductor (M/SC) nanoparticles. The film structure is considered and discussed in relation to the mechanism of their formation. Some models of nucleation and growth of M/SC nanoparticles in dielectric matrix are presented. The properties of films including dark and photo-induced conductivity, conductometric sensor properties, dielectric characteristics, and catalytic activity as well as their dependence on film structure are discussed. There is special focus on the physical and chemical effects caused by the interaction of M/SC nanoparticles with the environment and charge transfer between nanoparticles in the matrix. 

FIGURE 15.1 Dependence of sensitivity on frequency and humidity of poly(DOCDA 0DA)/Fc304 composite films synthesized at 300°C, at 20 wt% Fe304 contents. (Adapted from Nica Simona Luminita et al. Polym. hit., 64, no. 9, 1172-1181, 2015.)... 

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

Polysilane-based nanostructured composites were synthesized by the inclusion of poly(di-w-hexylsilane) (Mw = 53,600) into mesoporous, Si-OH-rich silica with a pore size of 2.8 nm.81 Two PL bands are observed for the composite. A narrow band at 371 nm, assigned to a PDHS film on a quartz substrate is blue shifted by 20 nm, a shift attributed to the polymer being incorporated into the pores.82 The size of the monomeric unit of the PDHS is about 1.6 nm, so only one polymer chain can be incorporated into a mesopore with a diameter of 2.8 nm. The narrow PL band at 350 nm is due to the reduction of the intermolecular interactions between polymer chains. This narrow PL band at 350 nm is assigned to the excited state of the linear polymer chain.81 Also, a new broad band of visible fluorescence at 410 nm appeared, which is assigned to localized states induced by conformational changes of the polymer chains caused by its interaction with the silanol (Si-OH) covered pore surface. Visible luminescence in nanosize PDHS is observed only when the polymer was incorporated in hexagonal pores of 2.8 nm and is not seen for the polymer incorporated into cubic pores of 2.8 nm diameter or hexagonal pores of 5.8 nm diameter. 

Percolation threshold pc corresponding transition to metal conductivity in composite films from Teflon with Au nanoparticles is 30 vol.% [36]. The similar transition to semiconductor conductivity in films of polyvinyl alcohol containing nanocrystals CuS takes place at pc 15-20 vol.% [88]. In cryochemically synthesized films PPX with Ag nanocrystals conductivity of metal type is achieved already in films with Ag content 7 vol.% conductivity of these composite films increases with the lowering temperature proportional to (1 — j.Ty1 similarly to that of block metals, but coefficient a is 2.5 times less than value x0, characteristic for block silver [86]. 

Benoit et al. 2001 (41) SWCNT Arc Discharge As-synthesized Casting CNT Loading levels 0.1 to 8 wt% Film Electrical conductivity increases with CNT content by 9 orders of magnitude from 0.1 to 8% mass fraction with percolation threshold 0.33 wt%. Temperature dependence of resistivity for 0.2 to 8 wt% SWCNT composite films showed that percolating network is affected at low temperature, enhancing the relative resistivity ... 

The effects of substrate temperature (Ts b) on cubic boron nitride (c-BN) films synthesized using magnetron sputtering were studied. Fourier transform infrared (FTIR) spectroscopy. X-ray photoelectron spectroscopy (XPS) were employed to characterize the structure and composition of the films. It is found that Ts , plays a crucial role on the formation of cubic phase, and an appropriate T, , can lead to a high content. A tentative explanation on the mechanism of such Ts b effects is reported with the most details. 

Summary PDMS-6-PEO short-chain diblock copolymers were prepared via anionic ring-opening polymerization of cyclosiloxanes. Applying this method, various well-defined block copolymers with different compositions were synthesized and their phase behavior was investigated. The polymers predominantly showed lamellar phases in aqueous solutions. At small surfactant concentrations, vesicles were formed, as observed via cryogenic TEM. The aggregates of the diblock copolymers were used for the formation of lamellar thin films, applying the evaporation-induced self-assembly approach. 

When metal particles are isolated in a polymer so that the interaction between them can be neglected, the conductivity of a composite is determined by that of a polymer matrix. In such composites, metal nanoparticles can only inject carriers into a polymer but do not influence substantially the conductivity process [59], This is the case of metal-PPX films prepared by the cryochemical vapor deposition teclmique if such films contain metal or semiconductor nanocrystals in amounts less than 4—5 vol. % [30]. The conductivity of such composites follows classical olmfic current-voltage relationship [30] and Arrheiuus dependence on temperature [57]. At higher metal contents the mechaiusm of conductivity in synthesized composite films changes under influence of the interparficle interaction. In PPX films containing Pb nanoparficles in amounts from 5 to 10 vol. %, the dependence of current I on voltage U looks like In / [30]. This dependence is characteristic for a... 

Cryochemically synthesized PPX films containing metal or semiconductor nanocrystals have a fine porous structure caused by features of solid-state polymerization. Due to this structure, molecules of gaseous substances readily penetrate into polymer film from the environment. Synthesized composite films demonstrate valuable strong sensor effects resulting from a marked influence of some low-molecular-weight molecules, diffusing into the polymer and adsorbed onto nanocrystals, on the film conductivity [4, 30, 62-64]. Such effects are characteristic of films whose conductivity is governed by electron transfer between nanoparticles. 

Yang,Y., Wang, C.,Yue, B., Gambhlr, S.,Too, C.O., Wallace, G.G., 2012. Electro chemically synthesized polypyrrole/graphene composite film for Uthium batteries. Adv. Energy Mater. 2, 266-272. 

LSM, SDC and LSCF powders synthesized by the above mentioned methods were used to prepare LSM-SDC and LSCF-SDC composite films onto YSZ substrates. A previous study performed by Ye and co-workers (Ye et al., 2007) demonstrated that the amount of ethyl cellulose in LSM-SDC slurries is restricted by cracking of the surface of the films. These authors observed that cracking took place when the amount of pwre former reached 15 wt.% and is caused by the large amount of organics which evaporates during sintering. Therefore, in the present study, LSM-SEXT slurries with a maximum of 10 wt.% ethyl cellulose were used. Fig. 12 shows FEG-SEM images of the porous structure of LSM-SDC composite... 

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