Polystyrene particles

We will focus on one experimental study here. Monovoukas and Cast studied polystyrene particles witli a = 61 nm in potassium chloride solutions [86]. They obtained a very good agreement between tlieir observations and tire predicted Yukawa phase diagram (see figure C2.6.9). In order to make tire comparison tliey rescaled the particle charges according to Alexander et al [43] (see also [82]). At high electrolyte concentrations, tire particle interactions tend to hard-sphere behaviour (see section C2.6.4) and tire phase transition shifts to volume fractions around 0.5 [88]. 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

An example of a Maugis-Pollock system is polystyrene particles having radii between about 1 and 6 p.m on a polished silicon substrate, as studied by Rimai et al. [64]. As shown in Fig. 4, the contact radius was found to vary as the square root of the particle radius. Similar results were reported for crosslinked polystyrene spheres on Si02/silicon substrates [65] and micrometer-size glass particles on silicon substrates [66]. 

All this being said, perhaps the most definitive study of the relative roles of electrostatic and van der Waals forces was performed by Gady et al. [86,101,102]. In their studies, they attached a spherical polystyrene particle, having a radius between 3 and 6 p.m, to the cantilever of an atomic force microscope. They then conducted three distinct measurements that allowed them to distinguish between electrostatic and van der Waals forces that attracted the particle to various conducting, smooth substrates. 

As previously discussed, the JKR theory predicts that the detachment force is independent of the Young s modulus. Yet despite that, when Gady et al. [117] measured the detachment force of polystyrene particles from two elastomeric substrates having Young s moduli of 3.8 and 320 MPa, respectively, they found that the detachment force from only the more compliant substrate agreed with the predicted value. The force needed to separate the particle from the more rigid substrate was about a factor of 20 lower. Estimates of the penetration depth revealed that the particles would penetrate into the more compliant substrate more deeply than the heights of the asperities. Thus, in that case, the spherical particle approximation would be reasonable. On the other hand, the penetration depth... 

Capture efficiency is the fraction of generated contaminant that is directly captured by the hood. Measurement of capture efficiency involves measuring concentration of process-generated contaminant or a tracer material. Using process-generated contaminant requires use of instruments suited to each specific contaminant and its conditions (temperature, pressure, concentration, form, etc.). In order to facilitate these measurements, a tracer is often substituted for the process-generated contaminant. The tracer is usually a gas (sulfur hexafluoride, nitrous oxide, helium, or similar), but an aerosol (particles) can also be used (potassium iodide, polystyrene particles, microbiological particles, etc.). The chosen tracer should be as similar to the real contaminant as possible, but at the same time should... 

Monosized polystyrene particles in the size range of 2-10 /am have been obtained by dispersion polymerization of styrene in polar solvents such as ethyl alcohol or mixtures of alcohol with water in the presence of a suitable steric stabilizer (59-62). Dispersion polymerization may be looked upon as a special type of precipitation polymerization and was originally meant to be an alternative to emulsion polymerization. The components of a dispersion polymerization include monomers, initiator, steric stabilizer, and the dispersion medium... 

In-column solvents Column size (mm) Theoretical plate number Exclusion limit Polystyrene" Particle size (pm) Flow rate (ml/min) Maximum pressure (kgf/cm ) Maximum temperature (X)... 

The polymerization reaction is conducted at the desired temperature with a slow stirring regime for a certain period. A typical recipe for the emulsion polymerization of styrene is exemplified in Table 1 [40]. As seen here, potassium persulfate and sodium dodecyl sulfate were used as the initiator and the stabilizer, respectively. This recipe provides uniform polystyrene particles 0.22 /Lim in size. 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

Figure 14 The variation of average size of the polystyrene particles by the average solubility parameter of the homogeneous alcohol-water dispersion medium. (From Ref. 89. Reproduced with the permission of John Wiley Sons, Inc.)...

Sheu and coworkers [111] produced polysty-rene-polydivinylbenzene latex interpenetrating polymer networks by the seeded emulsion polymerization of styrene-divinylbenzene in the crosslinked uniform polystyrene particles. In this study, a series of uniform polystyrene latexes with different sizes between 0.6 and 8.1... 

Removal of diluent by an extraction process To obtain the final stable macroporous structure, the liquid organic diluents and the linear polymer are removed from the crosslinked structure by extraction with a good solvent for the inert diluents and particularly for the linear polymer. Toluene or methylene chloride are usually preferred for the removal of linear polystyrene from the divinylbenzene crosslinked macroporous polystyrene particles [125,128]. The extraction is carried out within a Soxhelet apparatus at the boiling point of the selected solvent over a period usually more than 24 h. 

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

Sometimes it can be advantageous to use mixtures of alkanesulfonates and nonionic surfactants, such as Triton X-100, to prepare monodisperse polystyrene particles [95]. 

Figure 6.5. Experiments involving mimics of sporopollenin (the principal component of spore walls] demonstrate that patterns very similar, if not identical to those of natural spores and pollen, can be produced from mixtures containing colloidal particles. All scales refer to bar in (a. (a Spore-like structures of polystyrene particles and particle aggregates formed around a droplet of hydrocarbon. Scale = 10 p.m. (b A broken structure like that shown in (a. Scale =...

Figure 2. Effect of ionic strength on Rp for different polystyrene particle sizes using SLS or AM A in eluant.

Recently it has been reported that even colloidal particle suspensions themselves, without added polymers, can form dissipative structures. Periodic stripes of colloidal particles (monodisperse particles of diameter 30 nm and 100 nm, respectively) and polystyrene particles (monodisperse diameters from 0.5 to 3 pm) can be formed from dilute aqueous suspensions. The stripes are parallel to the receding direction of the edge of the suspension droplet and thus indicate that a fingering instability... 

Bocek, P. and Chrambach, A., Electrophoretic size separations in liquidified agarose of polystyrene particles and circular DNA, Electrophoresis, 12, 620, 1991. 

Fig. 31. Fractal structures obtained experimentally at different stages of aggregation of a colloidal monolayer of 1 /im sulfonated polystyrene particles on the surface of an aqueous calcium chloride solution, initially uniformly distributed (Robinson and Earnshaw, 1992).

As mentioned in the introduction, the particle composition has an effect on the release velocity. In particular, from Figure 6 it is clear that 10 pm glass particles release more easily than 10 pm polystyrene particles. 

Plastic products are known to eventually break down into smaller and smaller pieces (nanoparticles) until they are small enough to enter the cells of living organisms. Because the amount of discarded plastic is so substantial, nanoplastic particles pose an emerging environmental concern. The health effects of nanoplastics are not thoroughly understood, but polystyrene particles up to 240 nm in diameter have been proven to be transportable through placental cells [52],... 

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