Latex particles nature

The ionic nature of the radicals generated, by whatever technique, can contribute to the stabilisation of latex particles. Soapless emulsion polymerisations can be carried out usiag potassium persulfate as initiator (62). It is often important to control pH with buffets dutiag soapless emulsion p olymerisation. 

A method of impregnating textile fibres with latex. There is no natural affinity between the textile fibre and the latex particle this is overcome by making the latex slightly acid and the surface of the textile strongly alkaline. 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

Before applying the ideas summarised in the first section to polymer latices it is appropriate to consider the nature of polymer latex particles. We know, for example, that each particle is composed of a large number of polymer chains, with the chains having molecular weights in the range of about 105 to 107. Moreover, the particles themselves can be amorphous, crystalline, rubbery, glassy or monomer swollen, either extensively or minutely. It follows, therefore, that the properties of the system on drying depends directly on the physical state of the particles, for example, if the particles are soft, coalescence can occur to form a continuous film, whereas with hard particles their individuality is retained. The nature of the particle obtained is directly related to the preparative method employed and the surface properties are often determined by s-... 

Figure 2. Schematic of the nature of the surface on various types of latex particles...

These applications require a good knowledge of the nature and magnitude of interactions between nucleic acids and polymer particles. To that purpose, many systematic studies were carried out by different authors and in this lab on the adsorption behavior of various nucleic acids onto various type latex microspheres, mostly cationic and anionically-charged polystyrene or hydrophilic (i.e. poly[N-isopropylacrylamide]) latex particles. 

Marcus et al. [23 used EWDLS to study Brownian motion of dilute solutions of latex particles (diameter 1 gm) between two glass surfaces separated by 3 /cm. The light was detected in a plane perpendicular to the interface, but due to the two-dimensional nature of the cell only in-plane fluctuations were expected to be important. Typical measurements are shown in Fig. 6. where the different... 

CEe data obtained by Brodnyan and Kelly (11) on adsorption of water-soluble macrcmiolecules on latex particles indicate that both the nature of macromolecules and that of the substrate are essential for adsorption. 

In general, the types of surfactant added to a latex will be either anionic, cationic, or nonionic as classified by the nature of the head group. If it is assumed that the latex particle has a sur ce free of adsorbed materials and is negatively charged, then the various possibilities of adsorption of the surfectant can be envisaged by the schematic diagram given in Fig. 17. The discussion of the various phenomena observed can then he based on these models. 

Here n(square matrix formed from the kinetic parameters p, k, and c. The nature of O may be recognized by expressing Eq. (2) in matrix form and identifying the resulting square matrix with O. O is called here the Smith Ewart coupling matrix because its elements in Eq. (5) describe bow latex particles change state as a consequence of the Smith-Ewart mechanisms (entry, exit, and bimolecular termination). 

The fundamental difficulty in constructing a theory for the MWD in emulsion polymers is to account for the compartmentalized nature of the system- In the commouly occurring situation where particles contain only a few free radicals at any given time, it is obviously incorrect to consider that each latex particle behaves like a mini-bulk reaction vessel, and so the conventional methods used for bulk polymerizations are inapplicable. Nevertheless, some assumptions which introduce only minor errors may often be made. The most important such assumptions is that the evaluation of the MWD may be separated from that of the PSD. In other words, provided that the MWD being produced at any given moment is the same as would be formed in an equivalent set of monodispersed latex particle systems [as expressed in Eq. (27) below], then the MWD evolved in a system that is polydispersed in size may be computed trivially. Formally, this is expressed as follows. Let S(M,a,t) be the MWD formed in a monodisperse system of size o at time f here M is the molecular weight variable. In a polydisperse system with PSD n([Pg.115]

The development here follows that of Lichti et af. (1980). By analogy with the MWD calculation for bulk and solution polymerizations presented earlier, the MWD formalism for monodisperse emulsion systems requires the evaluation of certain types of free-radical growth time distributions. Because of the variable nature of the reaction loci (depending on the state i), a separate growth time distribution is required for the population of particles in each state i. It is therefore convenient to define the distribution of singly distinguished latex particles in state i. denoted as the... 

Under dynamic conditions of emulsion polymerization the process of formation and aggregation of primary particles is accompanied by estab-Hshment of an equilibrium adsorption of the emulsifier on the polar surface of particles. As a result of competition of these processes, secondary" panicles of complex structure are formed (Figs. 11 and 14). The rate of attainment of equilibrium adsorption, depending on monomer polarity and the nature of the emulsifier, determines the degree of limited flocculation of primary particles at which aggregate stability of the secondaiy" latex particles is reached. The formation of nuclei from micelles during the... 

---