不同类型的乳胶粒子的制备和性能
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Table 1. Different types of polystyrene latices Initiator Type 1 Type 2 Type 3 Type 4 KPS KPS KPS KPS Emulsifier SDS SDS Comonomer KSS KSS SPP
of water was 225 ml. Dispersion was held at 100 ~ for 6 h, cooled, and filtered first through glass wool then through a paper filter. Part of the dispersion was dialyzed against water [11]. The volume fraction of solid polymer, ~ao, increases strongly with the amount of initiator a d d e d to the emulsion (Table 2a). (The volume fraction r was obtained from the mass of the residue after drying 1 or several ml of the dispersion at 60 ~ ~ for 48 h, and the density of 1.06 gcm -3 for the latex material. A m o u n t s of soluble c o m p o u n d s (salts and emulgator) were taken into consideration). Type 2: Polystyrene latices of type 2 were formed from emulsions of styrene stabilized by sodium dodecyl sulfate with and without KPS as initiator [10, 12, 13] (Table 2b). The latices were prepared at 100 ~ from 25 ml styrene and 0.10-2.0 g sodium dodecyl sulfate in a total of 225 ml water [11] (Table 2b). These dispersions were used undialyzed, because dialysis strongly reduces the stability of the dispersion. Table 2b. Preparation of type-2 polystyrene latices at 100 ~ Latex I E 103 (f/M) 1.9 4.7 9.5 9.5 9.5 9.5 9.5 9.5 103 (E/M) 4.4 8.9 17.7 35.4 4.4 4.4 4.4 4.4 1.8 4.4 8.0 17.7 35.4 ~a o pH
Abstract: The boundary region separating a latex particle from the surrounding medium has a great influence on the properties of latex dispersions. Four types of polystyrene and polystyrene/comonomer latices differing greatly in the structure of the boundary region were prepared. The first part of a series of papers reports on the preparation of the various latex dispersions. Mean particle sizes were obtained from simple turbidity measurements, quasi-elastic light scattering, and electron micrographs. The behavior of the particles in the centrifugal force field is a simple tool for detecting aggregation tendencies that are not directly related to salt stability. The BET-surface area agrees with the area calculated from the mean particle size when a sharp boundary and smooth surface is developed between the particle and the surrounding medium. In the case of particles with extended boundary regions (core/shell particles or particles with hairy envelopes), film formation reduces the specific surface area. Removal of soluble oligomers and polymers from the boundary region during subsequent treatments (purification and centrffugation before freeze-drying) can increase the surface area considerably. Key words: Emulsion polymerization, light scattering, particle size, polystyrene latices, surface-area determination.
பைடு நூலகம்
Zimehl et al., Latex preparation
925
further important point is that purification processes can strongly change the chemical composition of the particles and, as a consequence, particle structure and stabilization mechanisms. Latex dispersions produced in technical scale contain a large variety of compounds, and macromolecular materials remaining in solution may add an amount of depletion stabilization or destabilization. It is generally difficult to determine the factors that contribute mainly to the stability of technical latex dispersions. In laboratory runs, latex dispersions can be prepared in a more transparent way (see also [2]), so that the structure/property relation becomes more lucid. This will be illustrated by four types of polystyrene particles prepared from styrene monomers in different ways (Table 1).
R. Zimehl, G. Lagaly, and J. Ahrens 1)
Institut ffir anorganische Chemie der Universitfit Kiel, FRG 1) Institut ffir angewandte Physik der Universitfit Kid, FRG
GL767
iv) Polymerization in the presence of preformed polymers (template polymerization or in situ grafting polymerization). In cases ii)-iv), an additional repulsive force can be operative, which arises from thin emulsifier layers (case ii)) or from oligomers and macromolecules at the particle surface (cases iii) and iv)). The different stabilization mechanisms during particle growth sensitively influence the properties of the final latex dispersion, such as particle shape, size and size distribution, particle structure (core/shell structure), aggregation behavior, shear stability, thermal stability, and stability against salts. During particle growth, the influence of electrostatic and steric or electrosteric stabilization [1] can change, so that the degree of steric or electrosteric stabilization in the final dispersion not only depends on the composition of the starting emulsion, but also on the way the particles form during synthesis. A
Colloid & Polymer Science
Colloid Polym Sci 268:924-933 (1990)
Colloid Science
Some aspects of polymer colloids I. Preparation and properties of different types of latex particles
Introduction
Preparation of stable polystyrene latices in aqueous media needs a well balanced composition of the polymerization mixture. The dispersions in statu nascendi can be stabilized by different mechanisms: i) Creation of electrostatic repulsion forces between the polymer particles by adding an initiator, which adds charged groups to the growing macromolecular chains (emulsifier-free emulsion polymerization of hydrophobic monomers). ii) Addition of emulsifying agents (classical emulsion polymerization). iii) Copolymerization of a hydrophobic monomer and readily polymerizable emulsifying agents or hydrophilic derivatives of the hydrophobic monomer (in situ polymerization of surface active agents or in situ grafting).
of water was 225 ml. Dispersion was held at 100 ~ for 6 h, cooled, and filtered first through glass wool then through a paper filter. Part of the dispersion was dialyzed against water [11]. The volume fraction of solid polymer, ~ao, increases strongly with the amount of initiator a d d e d to the emulsion (Table 2a). (The volume fraction r was obtained from the mass of the residue after drying 1 or several ml of the dispersion at 60 ~ ~ for 48 h, and the density of 1.06 gcm -3 for the latex material. A m o u n t s of soluble c o m p o u n d s (salts and emulgator) were taken into consideration). Type 2: Polystyrene latices of type 2 were formed from emulsions of styrene stabilized by sodium dodecyl sulfate with and without KPS as initiator [10, 12, 13] (Table 2b). The latices were prepared at 100 ~ from 25 ml styrene and 0.10-2.0 g sodium dodecyl sulfate in a total of 225 ml water [11] (Table 2b). These dispersions were used undialyzed, because dialysis strongly reduces the stability of the dispersion. Table 2b. Preparation of type-2 polystyrene latices at 100 ~ Latex I E 103 (f/M) 1.9 4.7 9.5 9.5 9.5 9.5 9.5 9.5 103 (E/M) 4.4 8.9 17.7 35.4 4.4 4.4 4.4 4.4 1.8 4.4 8.0 17.7 35.4 ~a o pH
Abstract: The boundary region separating a latex particle from the surrounding medium has a great influence on the properties of latex dispersions. Four types of polystyrene and polystyrene/comonomer latices differing greatly in the structure of the boundary region were prepared. The first part of a series of papers reports on the preparation of the various latex dispersions. Mean particle sizes were obtained from simple turbidity measurements, quasi-elastic light scattering, and electron micrographs. The behavior of the particles in the centrifugal force field is a simple tool for detecting aggregation tendencies that are not directly related to salt stability. The BET-surface area agrees with the area calculated from the mean particle size when a sharp boundary and smooth surface is developed between the particle and the surrounding medium. In the case of particles with extended boundary regions (core/shell particles or particles with hairy envelopes), film formation reduces the specific surface area. Removal of soluble oligomers and polymers from the boundary region during subsequent treatments (purification and centrffugation before freeze-drying) can increase the surface area considerably. Key words: Emulsion polymerization, light scattering, particle size, polystyrene latices, surface-area determination.
பைடு நூலகம்
Zimehl et al., Latex preparation
925
further important point is that purification processes can strongly change the chemical composition of the particles and, as a consequence, particle structure and stabilization mechanisms. Latex dispersions produced in technical scale contain a large variety of compounds, and macromolecular materials remaining in solution may add an amount of depletion stabilization or destabilization. It is generally difficult to determine the factors that contribute mainly to the stability of technical latex dispersions. In laboratory runs, latex dispersions can be prepared in a more transparent way (see also [2]), so that the structure/property relation becomes more lucid. This will be illustrated by four types of polystyrene particles prepared from styrene monomers in different ways (Table 1).
R. Zimehl, G. Lagaly, and J. Ahrens 1)
Institut ffir anorganische Chemie der Universitfit Kiel, FRG 1) Institut ffir angewandte Physik der Universitfit Kid, FRG
GL767
iv) Polymerization in the presence of preformed polymers (template polymerization or in situ grafting polymerization). In cases ii)-iv), an additional repulsive force can be operative, which arises from thin emulsifier layers (case ii)) or from oligomers and macromolecules at the particle surface (cases iii) and iv)). The different stabilization mechanisms during particle growth sensitively influence the properties of the final latex dispersion, such as particle shape, size and size distribution, particle structure (core/shell structure), aggregation behavior, shear stability, thermal stability, and stability against salts. During particle growth, the influence of electrostatic and steric or electrosteric stabilization [1] can change, so that the degree of steric or electrosteric stabilization in the final dispersion not only depends on the composition of the starting emulsion, but also on the way the particles form during synthesis. A
Colloid & Polymer Science
Colloid Polym Sci 268:924-933 (1990)
Colloid Science
Some aspects of polymer colloids I. Preparation and properties of different types of latex particles
Introduction
Preparation of stable polystyrene latices in aqueous media needs a well balanced composition of the polymerization mixture. The dispersions in statu nascendi can be stabilized by different mechanisms: i) Creation of electrostatic repulsion forces between the polymer particles by adding an initiator, which adds charged groups to the growing macromolecular chains (emulsifier-free emulsion polymerization of hydrophobic monomers). ii) Addition of emulsifying agents (classical emulsion polymerization). iii) Copolymerization of a hydrophobic monomer and readily polymerizable emulsifying agents or hydrophilic derivatives of the hydrophobic monomer (in situ polymerization of surface active agents or in situ grafting).