Surface tension, polymer samples

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. 

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). 

The densities of polymers can be determined by the pyknometer technique or by the flotation method. In the pyknometer technique the liquid volume displaced by the polymer sample is determined by weighing. Most polymers have a density larger than that of water, which can, therefore, be used as the liquid. Polymers in the form of powders or pressed discs tend to adsorb or occlude air bubbles, which can lead to serious errors. This can be largely prevented by careful degassing of the pyknometer and polymer sample under vacuum before filling with liquid, and/or by addition of a small amount (0.1%) of commercial detergent to lower the surface tension of the water. 

Critical surface tensions of functional polymers were experimentally determined. This set of data and the data on elastomers obtained previously were used to elucidate the proposed solubility parameter-surface tension relationship and the proposed parachor-surface tension relationship. The results show that the former has a higher correlation coefficient than the latter. The correlation coefficients, including three highly hydrogen-bonded polymers, are 0.731 for the former and 0.299 for the latter. Otherwise, they are 0.762 for the former and 0.178 for the latter. For the size of samples examined, we can conclude that the proposed solubility parameter-relationship is more effective than the proposed parachor-relationship in calculating critical surface tension of a polymer. 

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. 

Chap. 2, altered surface tensions of surface-treated polymers are directly accessible. In addition, laterally resolved maps of adhesive interactions are useful to investigate heterogeneous samples, such as multicomponent systems, or to record local functional group distributions. For quantitative AFM work, calibration procedures for the cantilever spring constant and the AFM detection system become important. In addition, the use of modified tips will be discussed as a means to enhance the applicability of AFM for chemically sensitive imaging. 

The predicted y values follow the same order as the experimental values of y extrapolated from the melt [2] for the four polymers for which such data are available. In addition, the absolute magnitudes of three of the predicted values are very close to the experimental values. Poly[oxy(methylphenylsilylene)] is the only polymer for which there is a significant difference between the predicted and measured values of y. The surface tension increases asymptotically to a limiting value with increasing number-average molecular weight Mn. The relatively low experimental value for poly[oxy(methylphenylsilylene)] may therefore be at least partially due to the possibly very low Mn of the sample, as suggested by its very low viscosity. 

The mechanical behavior of polymers is well recognized to be rate dependent. Transitions from ductile to brittle mode can be induced by increasing the test speed. The isotactic PP homopolymer with high molecular weight is ductile at low speed tensile tests. It is brittle at tension under high test speeds at room temperature. Grein et al. (62) determined the variation of Kiq with test speed for the a-PP CT samples (Fig. 11.22). The force-displacement (F-J) curves and the schematic diagrams of the fracture surfaces of CT samples are presented in Fig. 11.23. At a very low test speed of 1 mm s , the F-d curve exhibits a typical ductile behavior as expected. At 10 mm s, the F-d curve stiU displays some nonlinearity before the load reaches its maximum value, but this is substantially suppressed as test speeds increase further. The samples fail in brittle mode at test speeds >500 mm s . From Fig. 11.22, the Kiq values maintain at 3.2 MPam at test velocities from 1 to... 

Four polymers with different surface compositions were used in this study—polystyrene (PS), poly(methyl methacrylate) (PMMA), polyacrylamide (PAM), and a poly(vinylidene chloride) (PVeC) copolymer (containing 20% polyacrylonitrile). Polystyrene has essentially a hydrocarbon surface, whereas the surfaces of poly (methyl methacrylate) and polyacrylamide contain ester and amide groups, respectively. The surface of the poly(vinylidene chloride) copolymer on the other hand will contain a relatively large number of chlorine atoms. The presence of acrylonitrile in the poly(vinylidene chloride) copolymer improved the solubility characteristics of the polymer for the purposes of this study, but did not appreciably alter, its critical surface tension of wetting. Values of y of these polymers ranged from 30 to 33 dynes per cm. for polystyrene to approximately 40 dynes per cm. for the poly(vinylidene chloride) copolymer. No attempt was made to determine e crystallinity of the polymer samples, or to correlate crystallinity with adsorption of the fluorocarbon additives. 

The XPS results indicated that there were about 3-5 at. % sulfur and 27-47 at. % oxygen incorporated onto the sulfur dioxide plasma treated LDPE substrate surfaces (Table 1). The sulfur atomic concentration reached a maximum at about 50 A from the sample surface (0 = 30°) right after the plasma treatment (Figure 3). (The uncertainty of the XPS multiplex scan for atomic concentration analysis is believed to be 0.5-1.0 at. %.) The sulfur-containing species diffused into the bulk of the polymer (> 100 A) as shown from the XPS data collected eleven days after the plasma reaction. This phenomenon is due to the mobility of the polymer surface. s After the sulfur dioxide plasma modification, the hydrophilic sulfonyl groups on the LDPE backbone diffuse away from the polymer surface toward the bulk of the material so that a lower surface energy can be attained. Because the air/LDPE interface has a low surface tension, thermodynamic equilibrium favors a hydrophobic surface. As a result, the sulfur atomic concentrations in the top 100 A of the substrates decreased with time as the sulfonyl groups diffused away from this surface layer. 

Monomer conversion can be adjusted by manipulating the feed rate of initiator or catalyst. If on-line M WD is available, initiator flow rate or reactor temperature can be used to adjust MW [38]. In emulsion polymerization, initiator feed rate can be used to control monomer conversion, while bypassing part of the water and monomer around the first reactor in a train can be used to control PSD [39,40]. Direct control of surfactant feed rate, based on surface tension measurements also can be used. Polymer quality and end-use property control are hampered, as in batch polymerization, by infrequent, off-line measurements. In addition, on-line measurements may be severely delayed due to the constraints of the process flowsheet. For example, even if on-line viscometry (via melt index) is available every 1 to 5 minutes, the viscometer may be situated at the outlet of an extruder downstream of the polymerization reactor. The transportation delay between the reactor where the MW develops, and the viscometer where the MW is measured (or inferred) may be several hours. Thus, even with frequent sampling, the data is old. There are two approaches possible in this case. One is to do open-loop, steady-state control. In this approach, the measurement is compared to the desired output when the system is believed to be at steady state. A manual correction to the process is then made, based on the error. The corrected inputs are maintained until the process reaches a new steady state, at which time the process is repeated. This approach is especially valid if the dominant dynamics of the process are substantially faster than the sampling interval. Another approach is to connect the output to the appropriate process input(s) in a closed-loop scheme. In this case, the loop must be substantially detuned to compensate for the large measurement delay. The addition of a dead time compensator can... 

Nanosubstrate, rather than particle, approaches have been utilized in a handful of experiments [33, 34]. HCCA has been crosslinked to SU-8 photoresist polymer via cationic photoiortization, forming a hydrophobic surface. When aqueous sample droplets are applied to this support, surface tension during evaporation essentially concentrates the samples and thus improves the analysis sensitivity [34]. Another engineering approach has been to pre-deposit CHCA matrix crystals by vacuum sublimation onto an ultra-phobic surface. The resultant disposable chips contain an array of matrix spots which concentrate analytes from aqueous matrixes during the drying process. The approach has been applied to the quantitation of drug compounds in biofluids such as serum or urine [31]. 

GPEs contain organic solvents as plasticizers and the reduction of vapor pressure is crucial. The amount of vaporized solvents from our GPE was measured in the experiment described here. Microporous polyethylene separator and the polymer matrix were soaked in the electrolyte solution and heated at various temperatures for 60 min. The vapor amounts from both samples were measured and compared. Figure 2.5 clearly shows that the vapor pressure of solvents in our GPE was significantly low even at the temperature of TOO °C, while microporous separator could hold the solution at low temperature probably due to large surface tension in the micropores, but vaporization of solvents increased steeply as the temperature rose. 

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