Swollen particles

However, in most cases the AW(D) dependencies are distinctly nonlinear (Fig. 9), which gives impulse to further speculations. Clearly, dependencies of this type can result only from mutual suppression of the hydrogel particles because of their nonuniform distribution over the pores as well as from the presence of a distribution with respect to pore size which does not coincide with the size distribution of the SAH swollen particles. A considerable loss in swelling followed from the W(D) dependencies, as shown in Fig. 9, need a serious analysis which most probably would lead to the necessity of correlating the hydrogel particle sizes with those of the soil pores as well as choice of the technique of the SAH mixing with the soil. Attempts to create the appropriate mathematical model have failed, for they do not give adequate results. 

The polymerizations were conducted in a 20-liter stainless steel reactor with a pitched-blade turbine agitator and four side-wall baffles. The monomer was polymerized at the same temperature, initiator and monomer concentration in two different inert diluents. The data (Figure 6) illustrate the substantial lowering of the overall heat transfer coefficient for the system with the more highly swollen particles. 

For bioadhesive applications, anionic polymers appear to provide the most effective balance between adhesiveness and toxicity, with carboxylic materials preferred over sulfonic polymers [400]. Polyfacrylic acid) microparticles have been identified as particularly effective bioadhesive materials [402]. Studies with poly(acrylic acid) microparticles have indicated that, while water-swollen particles exhibit good bioadhesion, dry polymer particles give no adhesion at all. In addition, adhesive strength increases as the degree of ionization of the polymer is increased [402]. Thus the expanded nature of the polymer network is important to mucoadhesion, probably via polymer interdiffusion and entanglement with mucin [403],... 

Special reference should be made to resin-liquid systems, where the phenomenon of swelling makes the case more complex. A resin s matrix is flexible and when immersed in a liquid, its volume expands, leading to an increase in its particle diameter and in turn, to a decrease in particle density (mass of diy resin per volume of swollen particle). Furthermore, the loading of the resin with ions results in further changes in its volume (Helfferich, 1995). Thus, in these cases, the particle density and diameter as well as the hydraulic density should be referred to for the swollen and loaded resin. In practice, a mean value is frequently used. 

Menoud et al. (1998) studied the adsoiption of copper from aqueous solutions by using the chelating resin Chelamine. The resin used is spherical, with an average diameter of 0.305 mm, swollen particle density of 158.4 kg/m3 (dry) and hydraulic particle density (wet density) of 1064 kg/m3. 

Note that in this relationship, we use the swollen particle density, i.e. 158.4 kg/m3, because the resin volume changes when immersed in the solution. Then, the solid-phase diffusion coefficient is 6.9 X 10 10 m2/s. 

Note that the swollen particle density, which is 158.4 kg/m3, is used for all calculations except the hydraulic ones, where the hydraulic density is used. Then, we have K = 22.61 and = 0.0006. According to the mechanical parameter criterion, if is zero (practically much lower than 1), then fluid-film diffusion controls the process rate, while if infinite (practically much higher than 1), then solid diffusion is controlling the process rate. It is obvious that the controlling mechanism is the fluid-film diffusion. 

The HEC powder was added to the desired amount of bidistilled dust-free water at 4°C, using a fast-stirring device. The rate of addition was very slow to avoid the formation of lumps. The substrate particles were further allowed to swell at 4°C during at least 12 hr. The swollen particles are then completely dissolved. One hour before use, the solution is swirled again and brought to the working temperature of 25.0°C. A supplementary correction can be needed for evaporation. This solution is stable for four days when kept at 4°C. 

The emulsion polymerization system consists of three phases an aqueous phase (containing initiator, emulsifier, and some monomer), emulsified monomer droplets, the monomer-swollen micelles, and monomer-swollen particles. Water is the most important ingredient of the emulsion polymerization system. It is inert and acts as the locus of initiation (the formation of primary and oligomeric radicals) and the medium of transfer of monomer and emulsifier from monomer droplets or the monomer-swollen particle micelles to particles. An aqueous phase maintains a low viscosity and provides an efficient heat transfer. 

It is accepted that the radical entry rate coefficient for miniemulsion droplets is substantially lower than for the monomer-swollen particles. This is attributed to a barrier to radical entry into monomer droplets which exists because of the formation of an interface complex of the emulsifier/coemulsifier at the surface of the monomer droplets [24]. The increased radical capture efficiency of particles over monomer droplets is attributed to weakening or elimination of the barrier to radical entry or to monomer diffusion by the presence of polymer. The polymer modifies the particle interface and influences the solubility of emulsifier and coemulsifier in the monomer/polymer phase and the close packing of emulsifier and co emulsifier at the particle surface. Under such conditions the residence time of entered radical increases as well as its propagation efficiency with monomer prior to exit. This increases the rate entry of radicals into particles. 

F than that for a more fully swollen particle, because of less likelihood for termination of the adsorbed oligoradical. 

Actually, information regarding the internal structure of the swollen particle is not necessary since the change in particle volume is equal to the volume of water absorbed, and the expanded particle settles slower, as its average density decreases, according to Equation 2 in either case. As with other hydrodynamic methods, sedimentation does not offer easy access to information regarding particle morphology. 

A and were subsequently swollen with monomer to the extent of 150-175 parts of monomer per hundred parts of polymer. The surfactant level was adjusted to 45% of saturation on the swollen particle surface so that each experiment was equivalent in surface density of surfactant at the start of the reaction. That maintained a stable latex throughout the polymerization and avoided new particle formation. 

Where S is the sedimentation coefficient of the particle at an adjusted pH, S0 is the sedimentation coefficient of the unswollen particle (low pH), r is the unswollen particle radius, and x is the increase in radius of the swollen particle. In this study, the model latexes were diluted with distilled water to 1 percent solids by weight. Individual samples were adjusted to various pH values with sodium hydroxide and allowed to equilibrate for at least 24 hours. Sedimentation rates were obtained at 30°C using a Beckman Model E analytical ultracentrifuge. 

The substrate particles are further allowed to swell at 4°C for at least 12 hours. The swollen particles are then completely dissolved. One hour before use the snhiHrm m swirled again and is brought to 25.0PC. The solution is stable far 4 days when kept at 4°C. 

The description of phase 1 of the SE theory was refined by Gardon [133] and Harada et al. [134] the effect of particles in which polymerization has been terminated by radical entrance is included. Paris et al. [135] and Sautin et al. [136] calculate the balance of micelles and of the growing and dead particles. Pismen and Kuchanov [137] and Sundberg and Eliassen [138] included the effect of particle size distribution in their calculations. According to Fitch and Tsai [134] and Roe [140], the monomer swollen particles are produced by the polymerization of the monomer which is dissolved in water. 

Because the performance within the extmder and the nature of the post-die extru-date will be influenced by the properties of the final viscous fluid produced, many workers have attempted to characterise the rheology of this melted mass (e.g., Jao et al. 1978 Akdogan et al. 1997). Since its stmcture is either that of a polymer melt or a dispersion of highly swollen particles within a polymer melt, then complex... 

The effect of mass transfer of vinyl versatate on the mini/macroemulsion polymerization of VAc/VEOVA in batch and semibatch systems was explored. For the batch experiments, the addition of neat VEOVA formed poor dispersions of VEOVA, which resulted in smaller particles, lower polymerization rates and different polymer composition tracks compared to normal mini/macroemulsion polymerization of VAc/VEOVA. The well-dispersed VEOVA seemed to help the monomer-swollen particle to gain more radicals in the nucleation period. 

The monomer chemical potential in the particles is lower than that in the droplets, so that the monomer in the droplets will diffuse across the aqueous phase and into the particles, leading to changes in the monomer chemical potentials of the the particles and droplets. The change in the monomer chemical potential is illustrated in Fig. 21, where Y is defined as the swelling capacity the ratio of the weight of a swollen particle to its weight before it is swollen. 

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