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Method for Determining the Activation Energy Distribution Function of Complex Reactions by Sieving and Thermogravimetric Measurements. J Phys Chem B 2016; 120:244-9. [PMID: 26671287 DOI: 10.1021/acs.jpcb.5b10448] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A method for studying the kinetics of thermal degradation of complex compounds is suggested. Although the method is applicable to any matrix whose grain size can be measured, herein we focus our investigation on thermogravimetric analysis, under a nitrogen atmosphere, of ground soft wheat and ground maize. The thermogravimetric curves reveal that there are two well-distinct jumps of mass loss. They correspond to volatilization, which is in the temperature range 298-433 K, and decomposition regions go from 450 to 1073 K. Thermal degradation is schematized as a reaction in the solid state whose kinetics is analyzed separately in each of the two regions. By means of a sieving analysis different size fractions of the material are separated and studied. A quasi-Newton fitting algorithm is used to obtain the grain size distribution as best fit to experimental data. The individual fractions are thermogravimetrically analyzed for deriving the functional relationship between activation energy of the degradation reactions and the particle size. Such functional relationship turns out to be crucial to evaluate the moments of the activation energy distribution, which is unknown in terms of the distribution calculated by sieve analysis. From the knowledge of moments one can reconstruct the reaction conversion. The method is applied first to the volatilization region, then to the decomposition region. The comparison with the experimental data reveals that the method reproduces the experimental conversion with an accuracy of 5-10% in the volatilization region and of 3-5% in the decomposition region.
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Some physicochemical remarks on spontaneous emulsification of vitreal tamponades. BIOMED RESEARCH INTERNATIONAL 2014; 2014:243056. [PMID: 25133159 PMCID: PMC4123479 DOI: 10.1155/2014/243056] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Revised: 06/03/2014] [Accepted: 06/16/2014] [Indexed: 11/18/2022]
Abstract
The importance of gravitational instability in determining the emulsification of vitreal tamponades is discussed. Theoretical results and numerical simulations indicate that the spontaneous formation of water-silicon oil is a rare event and that the very low concentration of surface active agents cannot justify the systematic formation of emulsions. The gravitational instabilities seem to play the main role. Our theoretical results seem in agreement with the experimental evidences; furthermore they indicate a future research line for the improvement of endotamponades. Indeed, the use of biodegradable antifoam may avoid the formation of bubbles and delay the formation of emulsions.
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Ambrosone L, Murgia S, Cinelli G, Monduzzi M, Ceglie A. Size Polydispersity Determination in Emulsion Systems by Free Diffusion Measurements via PFG-NMR. J Phys Chem B 2004. [DOI: 10.1021/jp046480o] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Luigi Ambrosone
- Consorzio Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology, Università del Molise, via De Sanctis, I-86100 Campobasso (CB), Italy, Department of Chemical Science, Università di Cagliari, s.s. 554 Bivio Sestu, 09042 Monserrato (CA), Italy
| | - Sergio Murgia
- Consorzio Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology, Università del Molise, via De Sanctis, I-86100 Campobasso (CB), Italy, Department of Chemical Science, Università di Cagliari, s.s. 554 Bivio Sestu, 09042 Monserrato (CA), Italy
| | - Giuseppe Cinelli
- Consorzio Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology, Università del Molise, via De Sanctis, I-86100 Campobasso (CB), Italy, Department of Chemical Science, Università di Cagliari, s.s. 554 Bivio Sestu, 09042 Monserrato (CA), Italy
| | - Maura Monduzzi
- Consorzio Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology, Università del Molise, via De Sanctis, I-86100 Campobasso (CB), Italy, Department of Chemical Science, Università di Cagliari, s.s. 554 Bivio Sestu, 09042 Monserrato (CA), Italy
| | - Andrea Ceglie
- Consorzio Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology, Università del Molise, via De Sanctis, I-86100 Campobasso (CB), Italy, Department of Chemical Science, Università di Cagliari, s.s. 554 Bivio Sestu, 09042 Monserrato (CA), Italy
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Hollingsworth KG, Johns ML. Measurement of emulsion droplet sizes using PFG NMR and regularization methods. J Colloid Interface Sci 2003; 258:383-9. [PMID: 12618109 DOI: 10.1016/s0021-9797(02)00131-5] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The droplet size distributions of emulsions have been measured using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) for many years. This technique finds particular application with emulsions that are concentrated and/or opaque, since such emulsion systems are difficult to characterize by other methods. Most studies employing PFG techniques assume a lognormal form when extracting the droplet size distribution from the experimental data. It is clearly desirable to retrieve a droplet size distribution from the experimental data without assuming such a functional form. This is achieved for the first time using regularization techniques. Regularization based on the distribution area and on its second derivative are compared and assessed along with the following techniques for selecting the optimal regularization parameter: the L-curve method, generalized cross validation (GCV), and the discrepancy principle. Regularization is applied to both simulated data sets and experimental data. It is found that when the experimental error can be estimated accurately, the discrepancy principle with area regularization is the best approach. When the error is not known the GCV method, with second derivative regularization and allowing only nonnegative values, is most effective.
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Affiliation(s)
- K G Hollingsworth
- Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, CB2 3RA, UK
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Vergara A, Paduano L, Mangiapia G, Sartorio R. Diffusion Coefficient Matrix in Nonionic Polymer−Solvent Mixtures. J Phys Chem B 2001. [DOI: 10.1021/jp011034b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Affiliation(s)
- Alessandro Vergara
- Dipartimento di Chimica dell’Università “Federico II” di Napoli, Complesso Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy
| | - Luigi Paduano
- Dipartimento di Chimica dell’Università “Federico II” di Napoli, Complesso Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy
| | - Gaetano Mangiapia
- Dipartimento di Chimica dell’Università “Federico II” di Napoli, Complesso Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy
| | - Roberto Sartorio
- Dipartimento di Chimica dell’Università “Federico II” di Napoli, Complesso Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy
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