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Characterization of Emulsion Polymerizations Through Ultrasound Propagation Velocity-measurements
No full textThe application of the measurement of ultrasound waves propagation velocity for characterizing emulsion polymerization systems is discussed. The ultrasound velocity sensor provides informations about various properties of interest in emulsion polymerization systems. These include the evaluation of monomer solubility and emulsifier critical micellar concentration in water, the in-situ and on-line monitoring of conversion in homo- and co-polymerizations, the investigation of the polymer glass transition and finally the measure of monomer solubility in submicron polymer particles
Estimation of Critical Micellar Concentration Through Ultrasonic Velocity-measurements
No full textA technique based on ultrasound propagation velocity measurements has been developed to investigate surfactant's behavior in aqueous solutions. Applications to the estimation of the critical micellar concentration of two emulsifiers, sodium dodecyl sulfate and dodecylbenzene sulfonic acid sodium salt, and a mixture of them are discussed. A simple model was developed to interpret the experimental ultrasound propagation velocity measurements. The model provides a theoretical foundation to the experimental results as well as a valuable tool for smoothing out the disturbances affecting the experimental data. (C) 1995 John Wiley and Sons, Inc
Densimetry For Online Conversion Monitoring In Emulsion Homopolymerization and Copolymerization
No full textThe use of on-line densimetry to monitor conversion in batch emulsion polymerization reactors are investigated. Some characteristics of the sampling circuit connecting the reactor to the densitometer, which allow one to obtain reliable on-line estimations of monomer conversion in the whole range of conversion, are discussed in detail. Moreover, the amount of collected data provides a practically continuous monitoring of the system evolution in time, which allows one to estimate directly the rate of conversion as a function of time. The technique has been applied both to homopolymerization systems [i.e., styrene (STY) and methyl methacrylate (MMA)] as well as to copolymerization systems [ i.e., STY-MMA, acrylonitrile (ACN) -MMA, vinyl acetate (VAC) -MMA]. In the latter case, the density measurements are combined with a reliable model which provides for polymer composition as a function of conversion, in order to obtain accurate measurements of monomers conversion
Online Conversion Monitoring Through Ultrasound Propagation Velocity-measurements In Emulsion Polymerization
No full textAn on-line sensor for estimating conversion from measurements of ultrasound propagation velocity in emulsion polymerizations has been developed. The sensor does not require a sampling circuit, because it can be directly plugged in the reacting mixture. The performance of the sensor has been tested by comparison with off-line gravimetric measurements of conversion under various operating conditions. These include the homopolymerization of methyl methacrylate and vinyl acetate, with different values of the monomer to water ratio and the initial concentrations of emulsifier and initiator. The results obtained using either an empirical calibration curve or a suitable a priori model indicate excellent reliability of the sensor with somewhat lower accuracy at low conversion values, i.e., when monomer droplets are present. (C) 1995 John Wiley & Sons, Inc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Composition Control in Emulsion Copolymerization. 2. Application to Binary and Ternary Systems
No full textThe optimal monomer feed policy for producing in a semibatch reactor a given amount of polymer with constant instantaneous composition, in the minimum reaction time and complete monomer depletion, as developed in Part I of this work, has been implemented experimentally. Conversion has been monitored on-line using a densitometer suitably connected to the laboratory reactor. The procedure has been applied to two binary and one ternary systems. The composition of the polymer produced has been characterized through various experimental techniques. The composition control procedure is insensitive to most types of irreproducibilities that arise in batch reaction performed in industrial applications. (C) John Wiley & Sons, Inc
Composition Control in Emulsion Copolymerization. 1. Optimal Monomer Feed Policies
No full textThe problem of producing polymers with constant instantaneous composition in semibatch reactors has been addressed in the most general terms. A rigorous procedure for determining a priori the monomer feed policy that allows one to produce, with a minimum reaction time, a given amount of polymer, with constant instantaneous composition and complete monomer depletion, has been developed. The procedure involves the knowledge of only the monomer reactivity ratios and the interphase partition laws. Its practical implementation needs the on-line monitoring of conversion. The reliability of the theoretical approach has been tested by comparison with the optimal policies obtained in the literature, for three different binary systems, as the result of various experimental iterative procedures. (C) 1994 John Wiley and Sons, Inc
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