Polyamide-6,6/in situ silica hybrid nanocomposites by sol-gel technique: synthesis, characterization and properties

The organic-inorganic hybrid nanocomposites comprising of poly(iminohexamethyleneiminoadipoyl), better known as Polyamide-6,6 (abbreviated henceforth as PA66), and silica (SiO₂) were synthesized through sol-gel technique at ambient temperature. The inorganic phase was generated in situ by hydrolysis-condensation of tetraethoxysilane (TEOS) in different concentrations, under acid catalysis, in presence of the organic phase, PA66, dissolved in formic acid. Infrared (IR) spectroscopy was used to monitor the microstructural evolution of the silica phase in the PA66 matrix. Wide angle X-ray scattering (WAXS) studies showed that the crystallinity in PA66 phase decreased with increasing silica content. Atomic force microscopy (AFM) of the nanocomposite films revealed the dispersion of SiO₂ particle with dimensions of <100 nm in the form of network as well as linear structure. X-ray silicon mapping further confirmed the homogeneous dispersion of the silica phase in the bulk of the organic phase. The melting peak temperatures slightly decreased compared to neat PA66, while an improvement in thermal stability by about 20 °C was achieved with hybrid nanocomposite films, as indicated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) exhibited significant improvement in storage modulus (E′) for the hybrid nanocomposites over the control specimen. An increase in Young's modulus and tensile strength of the hybrid films was also observed with an increase in silica content, indicating significant reinforcement of the matrix in the presence of nanoparticles. Some properties of the in situ prepared PA66-silica nanocomposites were compared with those of conventional composites prepared using precipitated silica as the filler by solution casting from formic acid.     

Grafting of vinyl monomers onto natural rubber,II. Graft copolymerization of methyl methacrylate onto natural rubber using tetravalent ceric ions

The use of tetravalent ceric ions to initiate graft-copolymerization of methyl methacrylate onto natural rubber (NR) has been investigated. The rate of grafting has been determined by varying the concentration of monomer and cerium(IV), the temperature and the solvents. The graft yield increases with increasing monomer concentration up to 1.877 M, with further increase of the monomer, the graft yield decreases. The percentage of grafting increases with increasing cerium(IV) concentration up to 0.035 M, thereafter it decreases. With increasing temperature the graft yield increases. The effect of CuSO₄ on the rate of grafting has also been investigated. A plausible mechanism has been suggested and the kinetic rate expressions have been derived.     

Preparation and properties of styrene–butadiene rubber based nanocomposites: The influence of the structural and processing parameters

Rubber‐based nanocomposites were prepared with octadecyl amine modified sodium montmorillonite clay and styrene–butadiene rubber with different styrene contents (15, 23, and 40%). The solvent used to prepare the nanocomposites, the cure conditions, and the cure system were also varied to determine their effect on the properties of the nanocomposites. All the composites were characterized with X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies revealed exfoliation for the modified clay–rubber composites. The TEM photomicrographs showed a uniform distribution of the modified clay in the rubber matrix. The thickness of the particles in the exfoliated composites was around 10–15 nm. Although the FTIR study of the unmodified and modified clays showed extra peaks due to the intercalation of the amine chains into the gallery, the spectra for the rubber–clay nanocomposites were almost the same because of the presence of a very small amount of clay in the rubber matrix. All the modified clay–rubber nanocomposites displayed improved mechanical strength. The styrene content of the rubber had a pronounced effect on the properties of the nanocomposites. With increasing styrene content, the improvement in the properties was greater. Dicumyl peroxide and sulfur cure systems displayed similar strength, but higher elongation and slightly lower modulus values were obtained with the sulfur cure system. The curing of the samples at four different durations at 160°C showed that the cure time affected the properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 698–709, 2004     

Measurement of intrinsic rates for homogeneous gas‐phase reactions at high temperatures

A coiled quartz tubular reactor has been designed to measure the intrinsic reaction kinetics for homogeneous reactions at high temperatures up to 1100°C. Actual gas residence times were less than 100 ms. A simple and well‐studied test reaction (i.e., the decomposition of nitrous oxide, N₂O), with published intrinsic kinetics, was used to verify the operation of the experimental reactor. For this system, Peclet numbers (Pe = uL/DL) computed from experimental conversion data were greater than 1000, indicating that the plug flow assumption could be used with this reactor system to determine intrinsic rate expressions with errors of less than 5% for the conditions studied.     

Melt‐processable rubber: Chlorinated waste tire rubber‐filled polyvinyl chloride

Chlorinated ground rubber tire (Cl‐GRT) particles were used as filler in a plasticized polyvinylchloride (PVC) to develop a melt‐processable rubber composition. Physical properties of the Cl‐GRT‐filled PVC compound showed improvement compared to the nonchlorinated counterpart. Interaction between Cl‐GRT and PVC was examined on the basis of results of stress relaxation, dynamic mechanical thermal analysis, and solvent swelling studies. The Cl‐GRT could be loaded upto 40 parts per hundred parts of PVC, and the composition still retains the elastomeric characteristics. The Cl‐GRT‐filled composite was found to be reprocessable like the unfilled PVC compound. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 622–631, 2002; DOI 10.1002/app.10352     

Scalable P2P bot detection system based on network data stream

P2P Botnets are one of the most malevolent threats to the Internet users due to their resiliency against takedown efforts. In this paper, we propose a bot detection system that is capable of detecting stealthy bots in a network. This system treats network traffic as a data stream, segregating the traffic into two parallel streams. The detection is based on failure traffic and communication traffic. The traffic is analyzed during small time window, and the infected hosts are reported immediately. The network administrator can monitor the status of hosts in the network and can take the necessary action before the infected hosts harm the system or can involve in the attacks. Experiments and evaluation of the proposed system on a variety of P2P data transfer applications and P2P botnets have demonstrated high accuracy of detection. The scalability of the proposed system is exhibited through its implementation on Hadoop MapReduce.     

Trading privacy with incentives in mobile commerce: A game theoretic approach

In mobile commerce, companies provide location based services to mobile users, who report their locations with a certain level of granularity to maintain a degree of anonymity. This level of granularity depends on their perceived risk as well as the incentives they receive in the form of monetary benefits or improved mobile services. This paper formulates a quantitative model in which information theoretic metrics such as entropy, quantify the anonymity level of mobile users. The individual perceived risks of users and the benefits they obtain are defined as functions of their chosen location information granularity. The interaction between the mobile commerce company and its users is investigated using mechanism design techniques as a privacy game. The user best responses and optimal strategies for the company are derived under budgetary constraints on incentives, which are provided to users in order to convince them to share their private information at the desired level of granularity. Information limitations in the system are analyzed to capture more realistic scenarios where the companies do not have access to user utility functions. Iterative distributed algorithm and regression learning methods are investigated to design mechanisms that overcome these limitations. The results obtained are demonstrated with a numerical example and simulations based on real GPS data.