Polystyrene, wettability

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. 

Tn the last decades many attempts have been made to obtain attractive - materials by intimate mixing of two polymers with opposite or complementary properties. For example, the impact resistance of brittle polystyrene is increased by mixing with a rubber the wettability of polyacrylonitrile fiber is increased by mixing with hydrophilic saponified cellulose acetate, and the inconvenient flat-spotting of nylon-reinforced tires is suppressed by mixing stiffer polyester fibrils into the nylon fibers. In practically all cases these products acquire their final shape via the liquid state. Thus, the viscous properties of these liquid mixtures are important. 

Wettability and Constitution of Photooxidized Polystyrene and other Amorphous Polymers... 

The effect of ultraviolet irradiation in air on the wettability of thin films of amorphous polymers has been studied. With poly(vinyl chloride), poly(methyl methacrylate), poly(n-butyl methacrylate), poly (ethylene terephthalate), and polystyrene the changes in contact angles for various liquids with irradiation time are a function of the nature of the polymer. A detailed study of polystyrene by this technique and attenuated total reflectance spectra, both of which are sensitive to changes in the surface layers, indicates that the contact angle method is one of the most sensitive tools for the study of polymer photooxidation in its early stages. The method is useful in following specific processes and in indicating solvents to be used in the separation and isolation of photooxidation products. 

Once laid, the polystyrene films were further purified by exhaustive extraction with methanol or n-heptane the progress of extraction was followed by the ultraviolet spectra of the extracts. These preirradiation extractions showed considerable variation in purity among the three polystyrenes in spite of reprecipitation measures. The degree to which solvents can remain with a 20/ film is suggested by the need of seven days of continuous methanol or n-heptane extraction to remove all of the extractable benzene from a film laid from that solvent and dried in vacuum at 65°C. for 24 hours. For film laid from methylene chloride, an optically clean n-heptane extract was obtained from the AIBN-ini-tiated sample within a few hours, but up to 48 hours were required for the benzoyl peroxide-initiated samples. The extracted 20/ polystyrene films were essentially non-absorbing above 285 m/, no absorption attributable to material other than polystyrene could be observed, and only one peak (337 m/ ) was seen in the fluorescence spectrum in methylene chloride. Once the films were purified by extraction, the products and wettability changes resulting from irradiation were the same for all polystyrene samples and were independent of the solvent from which the films were laid. 

To relate the wettability changes more firmly to the photooxidation processes and products, a detailed study was carried out with polystyrene. This polymer was selected because the formation of oxidation products in the hydrocarbon surface gave rise to large changes in wettability and because these products would be readily accessible to optical methods of analysis. The ultraviolet absorption spectrum of polystyrene shows a sharp cut-off, and the extinction coefficients for the radiation absorbed are sufficiently high that almost all of the photochemical reaction should be confined to the surface layers. 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

Compatibility of polymers implies a semi-quantitative measure can be used to predict whether two or more polymers are compatible. The use of one of the semi-quantitative approaches, solubility parameter, was demonstrated by Hughes and Britt (22). It was concluded (8) that one parameter was insufficient to predict the compatibility. In this paper, we now introduce critical surface tension which is determined from the surface properties of a polymer. Though both of these parameters have been related by Gardon (15), we are inclined to use the latter because we can further describe the wettability between two polymers. For instance, by the use of yc, we can predict equally well that compatibility between polystyrene and polybutadiene can be improved if butadiene is... 

Another important property - wettability was followed by SEM analysis on PS/MWCNTs nanocomposite prepared by in-situ bulk-suspension polymerization (54). Figure 8.7 presents a micrograph of fracture surface of the prepared nanocomposite. The picture very clearly evidences that the nanotubes are covered by a thick layer of polystyrene. Parts of original nanotubes can be identified at the end of the fracture noteworthy is also the smaller diameter at the end of tubes. 

Figure 8.7. Evidence of wettability of polystyrene matrix on the surface of MWCNT nanocomposite prepared by in- situ polymerization with assistance of sonication (54).

RFGD polystyrene was oxidized, wettable, and of a decreased aromatic character as determined by analysis of XPS C-ls satellite spectra. The RFGD oxidation process etches the surface as witnessed by scanning electron micrographs. 

The curves obtained at various concentrations are almost parallel. This observation means that the rate of change of voltage with respect to temperature is independent of the solids concentration. By cross-plotting the results shown in Figure 24, a set of calibration curves can be prepared with temperature as a parameter. When such curves were prepared, they indicated that the value of e at C = 0, obtained by extrapolation, was lower than the corresponding value obtained for tap water at the same temperature. A review of the procedure of this experiment indicated that the only possible reason for this difference was the fact that a small amount of a wetting agent (an anionic surfactant) was added with the solids to increase the wettability of the polystyrene particles. 

A wettability change was also observed when triphenylmethane leucohydroxide was introduced [47]. The contact angle with water of the surface of polystyrene having triphenylmethane leucohydroxide chromophores increased from 0.2 to 0.8. This increase in wettability is due to an enhanced hydrophilicity of the film surface brought about by ionic dissociation of the chromophores. 

Paper wettability by polystyrene based toner has been studied by Lee (3). Wax/polymer coating of paper and paperboard has been investigated by Swanson and Becher (4), Glossman (5 ), and more recently by Fredholm and Westfelt (60. In the coating studies it was believed that surface energetics of the paper structure played a fundamental role in the spreading process and subsequent adhesion of polymer to the paper surface. 

Other flexible substrates than polystyrene and PVA may have better properties in terms of coating nucleation and wettability and so allow the continuous production of membranes by a reel-to-reel process. 

CF4, CF4 h O2 1. Enhancement of wettability of plastic surfaces Polyethylene (PE), polyoxymethylene (aeetal), polystyrene (PS), polypropylene (PP), polytetrafluoroethylene (PTFE), polymethylmethacrylate (PMMA), polyimide (PI)... 

Ma and Dai [121] reported the synthesis of polystyrene latexes armored with silica nanoparticles (10-15nm in diameter, PA-ST silica sol, Nissan Chemicals) via solids-stabilized emulsion polymerization. They used VA-086, 2,2 -azobis [2-methyl-lV-(2-hydroxyethyl)propionamide], as nonionic initiator. Whereas we found that Pickering emulsion polymerization of styrene using Ludox TM-40 and a low flux of radicals generated from potassium persulfate did not result in an armored latex, the hydroxyethyl groups probably enhance the wettability of the surface of the latex particles to promote silica adhesion. This was confirmed by a... 

A reduction in nucleation density of dewetted holes was also fotmd for such polystyrene films on homogeneous substrates [5]. Thus, a threshold film thickness hi can be determined for which the nucleation density of dewetted holes is identical to the number density of imprinted non-wettable domains. Obviously, h[Pg.31]

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