Surface Tension polymer particles

Alkaline reaction leads to the formation of the corresponding fatty-acid salts (anion-active surface-active substances), adsorbed on the surface of polymer particles. Surface tension of the investigated latex determined by tensometric method was of 46.2 mN/m thus defining an extra aggregative stability of Indian rubber latex during air-ozone bubbling. 

The circular cross section of the polymer blobs does not prove that the polymer existed in solution as a tangled coil (although this is the case). The shape displayed by the particles in the photograph is probably due in part to surface tension occurring during the drying of the sample. 

Another application based on a polymer s increased ease of flow in the presence of ultrasound is the atomisation of polymers. Here the particles are fed through an extruder then atomised (Fig. 5.51). The size of droplets (D) are governed by Eq. 5.44, where X is the surface tension, p is the density and F is the exciting frequency. 

Since the surface tension y of mercury is 0.485 N m at 20 °C with a contact angle of 9= 130°, a pore of d= 1 pm and greater will be filled if a pressure p of 1.25 MPa is applied. Hence, the amount of mercury forced into pores increases with pressure (intrusion), but releasing the pressure, the pores are emptied again (extra-sion). Typical intrusion and extrusion curves are represented schematically in Fig. 1.16A. The intrusion branches in this illustration are typical for samples such as suspension polymerized polymer particles ( 200 pm). 

When the polymerization has proceeded to such an extent that all of the monomer droplets have vanished, which occurs after 60-80% conversion, all of the residual monomer is located in the latex particles. The monomer concentration in the particles now declines as polymerization proceeds further, i.e., in this final period the reaction is first order. At the end of the polymerization, the emulsion consists of polymer particles with a size distribution between 50 and 150 pm, which is larger than the original micelles, but smaller than the original monomer droplets. The changes of surface tension and overall rate of polymerization with conversion are schematically shown in Fig. 2.2. 

A very recent development is encapsulation of actives in colloidosomes [16, 41]. The method is analogous to liposome entrapment. Selectively permeable capsules are formed by surface-tension-driven deposition of solid colloidal particles onto the surface of an inner phase or active ingredient in a water-in-oil or an oil-in-water emulsion composed of colloidal particles. Initially synthetic polymer microparticles were used but more recently a natural alternative has been described based on small starch particles. After spray-drying, redispersible emulsions can be formed. 

This method has been applied successfully in the determination of the surface tensions of polymer particles (140,141,1591, coal particles (160,161). and biological cells [162-168], Contact angles predicted from these surface tensions involving solids agree well with experimental contact angles f 159]. 

Our understanding of miniemulsion stability is limited by the practical difficulties encountered when attempting to measure and characterize a distribution of droplets. In fact, most of the well-known, established techniques used in the literature to characterize distributions of polymer particles in water are quite invasive and generally rely upon sample dilution (as in dynamic and static laser light scattering), and/or shear (as in capillary hydrodynamic fractionation), both of which are very likely to alter or destroy the sensitive equihbrium upon which a miniemulsion is based. Good results have been obtained by indirect techniques that do not need dilution, such as soap titration [125], SANS measurements[126] or turbidity and surface tension measurements [127]. Nevertheless, a substantial amount of experimental evidence has been collected, that has enabled us to estabhsh the effects of different amounts of surfactant and costabihzer, or different costabilizer structures, on stabihty. 

Relationship between the variation of surface tension of aqueous phase of reaction mixture and the number of polymer particles produced ... 

Once a micelle is stung, polymerization proceeds very rapidly. The particle can accommodate more monomer as its polymer content increases and the water-polymer interfacial surface increases concuirently. Tlie new surface adsorbs emulsifier molecules from the aqueous phase. This disturbs the equilibrium between micellar and dissolved soap, and micelles will begin to disintegrate as the concentration of molecularly dissolved emulsifier is restored to its equilibrium value. Thus the formation of one polymer particle leads to the disappearance of many micelles. The initial latex will usually contain about 10 micelles per milliliter water, but there will be only about 10 particles of polymer in the same volume of the final emulsion. When all the micelles have disappeared, the surface tension of the system increases because there is little surfactant left in solution. Any tendency for the mixture to foam while it is being stirred decreases at this time. 

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