Measurement of Particle Size Distribution of Polymer Latexes

GUGLIOTTA, L. M.; VEGA, J. R.

SIGNPOST RESEARCH

Lugar: KERALA, INDIA; Año: 2009 p. 254

978-81-308-0413-2

The particle size distribution (PSD) of a polymer latex is an important characteristic because it usually affects several processing, formulation, and end-use properties of materials when used as adhesives, coatings, and inks. The PSD can also influence particle-nucleation, particle-growth, and particle-interaction in emulsion and dispersion polymerization processes, and the stability of the resulting polymer colloids. In the case of latexes for coatings formulation, the PSD can modify characteristics such as the gloss or the opacity of the film, its hardness, and the drying time. This book includes review chapters written by specialists in the field of measurement of PSD of polymer latexes, and provides the reader with most important concepts regarding available techniques and measurement interpretation. Main characterization techniques are critically discussed, including Direct Observation Methods, Ensemble Techniques, and Fractionation Methods. Chapter 1 introduces the beginner to the problem of particle size characterization of polymer colloids, giving an overview of main methodologies and data treatment required to transform the measurements into PSDs. Definitions of the PSD and its averages are presented, and analytical techniques are classified and revised. Ensemble techniques such as turbidimetry (T), elastic light scattering (ELS) and dynamic light scattering (DLS), are thoroughly treated and evaluated; and the effect of uncertainties in the particle refractive index (PRI) on the PSD estimation is considered. Fractionation techniques based on sedimentation, column chromatography, and field flow fractionation principles are also presented. Particle characterization by standard electron microscopy (EM) is briefly considered, as well as new EM developments for the characterization of wet samples in their environment, and the analysis of latex nanoparticles by atomic force microscopy. Chapter 2 describes some mathematical methods useful for solving the ill-conditioned inverse problems involved in the estimation of latex PSD from light scattering (LS) measurements. In particular, the regularization methods known as Truncated Singular Value Decomposition and Phillips-Tikhonov are presented in detail, together with some techniques normally used to select the regularization parameters, such as Morozov´s Discrepancy Principle, L-curve, and Generalized Crossed Validation. The simultaneous estimation of the PSD and the PRI from ELS measurements is also considered. Chapter 3 gives an overview on the use of combined LS techniques for improving the resolution of the PSD estimates. It is showed that the involved non-linear inverse problem can be, in some cases, transformed into a linear (better conditioned) problem, which is able to be solved by means of standard regularization methods. Several combined LS measurements are analyzed, including multiangle dynamic light scattering (MDLS), ELS+MDLS, ELS+T, and MDLS+T, on the basis of both simulated and experimental examples. Applications of fractionation techniques for the particle size analysis of polymer latexes are described in Chapters 4-6. Chapter 4 reviews the hydrodynamic chromatography (HDC) technique; and some characteristics and experimental improvements regarding accuracy, sensitivity, and stability are presented. Turbidity detection at single wavelength is employed for quantifying the particle number; and its limitations together with the potential advantages of multiwavelength detectors are discussed. Results obtained by HDC are also compared with those obtained from other analytical techniques. Chapter 5 considers the use of fractionation techniques combined with absolute multiangle light scattering (MALS) detection for determining the PSD and the concentration of polymer latexes. Several fractionation methods are discussed, including HDC, capillary hydrodynamic fractionation, disk centrifugation, and asymmetric flow field flow fractionation. Chapter 6 presents the use of the analytical ultracentrifugation technique (AUC) for particle characterization, including not only size determination of polymer latexes, but also size-density correlations, density distributions, and swelling degrees. The estimation of chemical homogeneity and/or copolymer composition from density distributions is also considered. Chapter 7 presents an overview of the Rayleigh-Debye-Gans theory for the analysis of small angle scattering (SAS) data of different types of particle systems, including concentrated polymer-polymer dispersions, in which particles are formed by a phase separation induced by polymerization. Both monodisperse and polydisperse systems are considered, which involve not only spherical but also non-spherical particles. Some methods are presented for analyzing SAS data with the aim of extracting information on particle size and shape, PSD, and particle concentration. We want to express our deepest thankfulness to our families for their patience and understanding along the project. Luis G. specially acknowledges his wife Claudia and his daughters María Florencia and Agustina. Their love and guidance have sustained him throughout the work. Jorge V. expresses his gratitude to María and Nicolás for their support; and to his parents, Andrés and Beatriz, in the year of their golden wedding anniversary. We wish to dedicate this book to all of them. We also manifest our sincere appreciation to the contributing authors, whose efforts and cooperation have made the present book possible. Finally, we dedicate this book to our colleague and friend, Professor Gregorio R. Meira, who is celebrating his 30 anniversary as the head of the Polymer and Polymerization Reactors Group at INTEC, Santa Fe, Argentina.   Dr. Luis M. Gugliotta Polymer and Polymerization Reactors Group INTEC (Universidad Nacional del Litoral and CONICET), and Facultad de Ingeniería Química (Universidad Nacional del Litoral) Santa Fe, Argentina   Dr. Jorge R. Vega Polymer and Polymerization Reactors Group INTEC (Universidad Nacional del Litoral and CONICET), and Facultad Regional Santa Fe (Universidad Tecnológica Nacional) Santa Fe, Argentina    Santa Fe, December 2009