Latex diameters

PARTICLE SIZE AVERAGES FOR PMMA LATEXES DIAMETERS IN NANOMETERS... 

Latex Diameter Charge Number Charge Density... 

As discussed there, the normalized scattering intensity is expected to become independent of concentration above a certain q-value related to the diameter of the particles. This can be shown easily by measuring the SAXS-intensities at different volume fractions. Figure 15 displays the normalized scattering intensities of a PS latex (diameter 80 nm) measured at three different volume fractions [46]. 

Fig. 1 Left, (a-d) Different morphologies of heterocoagulate particles that can be obtained when the relative sizes of the two colloids are varied. Right Micrographs obtained from heterocoagulation of an amphoteric latex (diameter 250 nm) at pH 5.6, at which it has a cationic surface charge, with negatively charged silica particles of various diameters 1590 (a), 960 (b), 460 (c), and 240 (d) nm. Reproduced from Figs. 2 and 3 from [17]...

FIG. 10 Neutron-scattering intensity for poly(ethylene oxide) adsorbed on deuterated polystyrene latex in D2O. Molecular weight 28 x 10, E =1.21 mg/m, and latex diameter was 240run [17]. 

Figure 55 Comparative flocculation efficiency W of food biopolymers (latex diameter 88 nm, particle density 4.5 X lO Vcm , sodium chloride concentration 6.7 X 10 mol/ dm, 28°C, pH 5.9). D, dextran 7500 C, caseinate A, gum arabic X, xanthan G, guar.

The commercial use of 2,4-D has decreased substantially and (ca 1993) it has general use for home lawns to control broadleaved weeds it also is used on a limited basis to control broadleaved weeds in commercial moncotyledonous crops, eg, sugarcane. 2,4-D is used on citms when the fmit is 1/3 to 1 inch in diameter to increase fmit size and to limit fmit drop on trees more than six years old. It should not be appHed to trees that are in fliU flush. A further use includes treatment of harvested lemons at 500 mg/L to improve storage properties and to delay yeUowing (23). It is used in certain parts of the world to increase latex flow in old mbber tree plantations. 

A typical recipe for batch emulsion polymerization is shown in Table 13. A reaction time of 7—8 h at 30°C is requited for 95—98% conversion. A latex is produced with an average particle diameter of 100—150 nm. Other modifying ingredients may be present, eg, other colloidal protective agents such as gelatin or carboxymethylcellulose, initiator activators such as redox types, chelates, plasticizers, stabilizers, and chain-transfer agents. 

Emulsions Emulsions have particles of 0.05 to 5.0 [Lm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce massive polymers. Figures 23-23d and 23-23 show bead and emulsion processes for vinyl chloride. Continuous emulsion polymerization of outadiene-styrene rubber is done in a CSTR battery with a residence time of 8 to 12 h. Batch treating of emulsions also is widely used. 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Poly(vinyl chloride) is commercially available in the form of aqueous colloidal dispersions (latices). They are the uncoagulated products of emulsion polymerisation process and are used to coat or impregnate textiles and paper. The individual particles are somewhat less than 1 p,m in diameter. The latex may be coagulated by concentrated acids, polyvalent cations and by dehydration with water-miscible liquids. 

Lest I leave the erroneous impression here that colloid science, in spite of the impossibility of defining it, is not a vigorous branch of research, I shall conclude by explaining that in the last few years, an entire subspeciality has sprung up around the topic of colloidal (pseudo-) crystals. These are regular arrays that are formed when a suspension (sol) of polymeric (e.g., latex) spheres around half a micrometre in diameter is allowed to settle out under gravity. The suspension can include spheres of one size only, or there may be two populations of different sizes, and the radius ratio as well as the quantity proportions of the two sizes are both controllable variables. Crystals such as AB2, AB4 and AB13 can form (Bartlett et al. 1992, Bartlett and van... 

Rubber media appear as porous, flexible rubber sheets and microporous hard rubber sheets. Commercial rubber media have 1100-6400 holes/in. with pore diameters of 0.012-0.004 in. They are manufactured out of soft rubber, hard rubber, flexible hard rubber and soft neoprene. The medium is prepared on a master form, consisting of a heavy fabric belt, surfaced on one side with a layer of rubber filled with small round pits uniformly spaced. These pits are 0.020 in. deep, and the number per unit area and their surface diameter determine the porosity of the sheet. A thin layer of latex is fed to the moving belt by a spreader bar so that... 

New methods of emulsion polymerization, particularly the use of swelhng agents, are needed to produce monodisperse latexes with a desired size and surface chemistiy. Samples of latex spheres with uniform diameters up to 100 pm are now commercially available. These spheres and other mono-sized particles of various shapes can be used as model colloids to study two- and three-dimensional many-body systems of very high complexity. 

Hydration of Phospholipids with Solutions of Very Low Ionic Strength Very large unilamellar and oligolamellar vesicles can be prepared when a thin lipid film is dispersed in a solution of very low ionic strength (Reeves and Dowben, 1969). The formation of vesicles with diameters up to 300 pm enclosing latex beads with a diameter of 20 pm have been reported (Antanavage et al., 1978). 

The first study utilizing this method was reported by Schuller in 1966 [65]. Schuller used polystyrene latex beads that were spread on a salt-containing aqueous subphase in order to keep the particles at the interface. tt-A plots of the floating particles were determined, which showed several phase regions with reproducible transition points. The author determined the particle diameters from the A-value, at which a steep rise in the isotherm occurred. Moreover, Schuller also spread millimeter-sized Styropor particles and found isotherms of similar shape [66]. By taking pictures at different surface pressure, he was able to correlate the shape with different states of order in the monolayer. Shortly after that. 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

Hollow and porous polymer capsules of micrometer size have been fabricated by using emulsion polymerization or through interfacial polymerization strategies [79,83-84, 88-90], Micron-size, hollow cross-linked polymer capsules were prepared by suspension polymerization of emulsion droplets with polystyrene dissolved in an aqueous solution of poly(vinyl alcohol) [88], while latex capsules with a multihollow structure were processed by seeded emulsion polymerization [89], Ceramic hollow capsules have also been prepared by emulsion/phase-separation procedures [14,91-96] For example, hollow silica capsules with diameters of 1-100 micrometers were obtained by interfacial reactions conducted in oil/water emulsions [91],... 

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