Polyethylene water clusters

Polyethylene samples were also exposed to conditions which created 0.4% clustered water and dielectric data taken at low temperatures on the samples. The same loss maximum noted In polycarbonate and polysulfone near -100 C at 1 kHz was also noted In polyethylene. A special polyethylene sample was molded around a PTFE sheet. The PTFE was removed and replaced with distilled water. This sample was equivalent to a thin water layer between polyethylene sheets. The dielectric behavior of this sample was quantitatively equivalent to that of the polyethylene containing spherical clusters of water if the difference in geometry of the water phase is taken into account. Figure 7 shows the logarithm of the frequency of loss maxima due to water clusters versus reciprocal temperature for polyethylene, polycarbonate, poly(vlnyl acetate and polysulfone. The polysulfone data from Allen are shown for comparison and It Is seen that the data can be Interpreted as a single mechanism with an activation energy of 7 kcal/ mole. 

Water absorbed in a polymer can exist in an unassociated state or as a separate phase (cluster). In this investigation the DSC technique of water cluster analysis was used in conjunction with coulometric water content measurements to characterize the water sorption behavior of polysulfone and poly(vinyl acetate) The polysulfone had to be saturated above its Tg (190°C) and quenched to 23°C for cluster formation to occur while cluster formation occurred isothermally at 23°C in the poly(vinyl acetate) Both polymers showed an enchancement of their low temperature 3-loss transitions in proportion to the amount of unclustered water present. Frozen clustered water produced an additional low-temperature dielectric loss maximum in PVAc and polysulfone common to polyethylene and polycarbonate as well. Dielectric data obtained on a thin film of water between polyethylene sheets was in quantitative agreement with the clustered water data. 

Bair and co-workers have considered the phenomenon of water clustering in polyethylene (11) and other polymers (12). In polyethylenes soaked in water at elevated temperatures, they observed a low temperature crystallization exotherm upon cooling the sample in a DSC. A melting endotherm near 0 C was found when the sample was reheated. They attributed these results to clustered water that resulted from supersaturation of the sample when the polymer was removed from the water bath and cooled to room temperature (10). In the DSC experiment, the water crystallized at ca -40°C, which was due to the extremely small size of the clusters, ca. 2 ym. 

Inspection of the five water clusters (see Figure 7.1) around a cytidine unit shows, however, that most of the water molecules are situated in the immediate neighborhood of the cytosine molecules (forming the larger part of their first hydration shell) while only some of the water molecules are further apart than in the case of a cytosine stack. Therefore, the error is less than one would expect without looking at the details. When the motivation of this model calculation is understood in the sense discussed above, it can be regarded as the next step after the work of Clementi, who calculated the band structure of polyethylene in the field of periodic point charges situated around it in different ways. 

Mixtures of a protein (usually myoglobin) and some smaller peptides can be used polyethylene glycols and polypropylene glycols are also widely used for calibration. Anacleto et al. have summarized different options and have proposed protonated water clusters and salt clusters generated by pneumatically assisted electrospray. Water clusters provided a calibration range up to miz 1000 in the SCIEX API III mass spectrometer. Alkali metal halides (sodium iodide) allow calibration on cluster ions Na (Nal) or I (NaI) up to at least m/z 2000, the fiiU mass range of this instrument. 

Porat et al. performed TEM (zero-loss bright field) studies of very thin Nation films that were cast from ethanol/water solutions, and some of the conclusions are as follows. It was suggested that the backbone had a planar zigzag conformation in large orthorhombic crystallites as in polyethylene, in contrast with the helical conformation found in poly(tetra-fluoroethylene). This is an interesting result, although there are no other studies that support this view. Sulfur imaging indicated the presence of sulfonate clusters that are 5 nm in size. 

Figure 3.3.5 (A) Chemical structure of sulfonated perfluorinated polyethylene (Nafion ). (B) Schematic illustration of the microscopic structure of hydrated Nafion membrane perfluorinated polyethylene backbone chains form spherical hydrophobic clusters. Sulfonic end groups interface with water-filled channels and mediate the migration and diffusion of protons. The channels are filled with water and hydronium ions. Figure adapted from [4].

Structure of the Cluster. Definition of variables is important in the following discussions we use the following notations c, molar concentration of the cluster p, distance from its center v, 0, 1, volume, cross-section, and length of one monomer. These values are obtained from crystallographic data. The chains are treated as ideal free jointed rods of monomers. For numerical applications, we generally use the case of polyethylene v = 50 A3, 0 = 20 X2, 1 = 2,5 I. (1 + a)v will be taken as the volume of one neutralized charged ionomer. In many applications we shall take, for simplicity, a = 0 for the dry state. If the cations are solvated by V water molecules for each of volume vQ (30 AJ), a simple additivity rule for the volumes give av = WQ. 

The perfluorinated, carboxylated and sulfonated ionomer membranes form the ionic clusters of a few nm in size, as in the case of the hydrocarbon-based ionomers such as polyethylene,polystyrene and polybutadiene(9). The ionic clusters strongly affect physical properties of the membranes, e.g., the swelling behavior of the membranes (amount of water uptaken by the membranes, W and... 

The dielectric loss behavior of both polyethylene s Y transi-tion and polycarbonate s 0-transltion was enhanced by the presence of unassociated water. The area under the associated loss peak was found to increase in direct proportion to the concentration of unassociated water. In addition a secondary dielectric loss peak associated with frozen clustered water occurred in polycarbonate about 40°C below Its g-transition. Liquid clustered water at... 

The determination of clustered water and water molecule clusters trapped in polyethylene have been described by Baker (209). This water has been related lo a loss in the dielectric properties of polyethylene used in a submarine cable core. When DSC is employed, as shown by the curve in Figure... 

The effect of technological additives on permeability of pol3Tuers is connected with variations in their sorption capacity, formation of defects and interactions of the electrolyte and additives. Impregnation of fillers improves, as a rule, permeability of polymers and intensifies clusterization of water and the penetrant. When polyethylene is filled by talc, HCl and H2O clusters formed in the polymer can be observed in microscope. Water and HCl sorption increases proportionally to the volume content of talc up to 17% concentration. Further increase in talc concentration does not result in sorption growth because of filler particle aggregation in the polymer binder. 

In PVP containing 10% w/w water, as shown previously in MD simulations (Fig. 13.5), water molecules tend to self-associate to form clusters or chains [24a]. This tendency for water to self-associate as its concentration inaeases has been reported in several other polymer glasses, including HPMCAS, polyimide [102], polyethylene [103], as well as in sugars above their T [96] and in monoglyceride/ triglyceride lipid vehicles [2b]. 

Waterproof boxes, in crossing style, with 3-mm aluminum walls, with various thiCkness-2S, SO, 100 mm-were interposed between four 18 X 18 rod fuel clusters (square pitch 13.S mm). Several hydrogenous compounds were put inside the boxes air, expanded polystyrene (CgH )n. powder and small balls of polyethylene (CHj)n, and water. The critical approach p arameter is the heigiit of water that immerses the whole. These compounds are at the same level as water in clusters. 

In the case of a mixture of surfactant and polymer, the surface tension method has become popular and has had a significant impact in this area since 1967, when Jones published his work [14] on mixtures of polyethylene oxide (PEO)/SDS by using the surface tension method. From the plot of surface tension versus -log concentration at a certain concentration of polymer, one can evaluate whether and where the surfactant and polymer associate (some call it clusters) in the bulk solution and at the air/water interface. 

Because the thermospray interface contains a dedicated ion source block, tuning and calibration of the source and analyser parameters is obligatory. Calibration and tuning cannot be performed with common calibrants like perfluorokerosene. Diluted solutions of polyethylene glycols are used in most cases, although a tuning and calibration based on clusters of ammonium acetate, ammonium trifluoro-acetate and even simply water was proposed and used as well. 

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