Polymers, critical surface tension

The data, when compared with a model, suggested that bare areas of polymer exist after adsorption (i.e., the protein film forms in "islands ") and that the degree of coverage of the polymer surface with adsorbed protein increases with increasing polymer critical surface tension. 

The surface properties of polymers are important in technology of plastics, coatings, textiles, films, and adhesives through their role in processes of wetting, adsorption, and adhesion. We will discuss only surface tensions of polymer melts that can be measured directly by reversible deformation or can be inferred from drop shapes. Those inferred from contact angles of liquids on solid polymers ( critical surface tension of wetting ) are excluded, as their relations to surface tensions are uncertain. 

Other methods of surface characterization are discussed in Infrared spectroscopy attenuated total reflection. Infrared spectroscopy RAIR, Surface characterization by contact angies - metais. Surface characterization by contact angles - polymers. Critical surface tension, and Electron probe microanalysis (EPMA). 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

Wettability—coupling agents improve the wetting between polymer and substrate (critical surface tension factor). 

Organofunctional group Chemical structure OSi-Specialties Germany GmbH product Critical surface tension of glass with silane treatment [dyne/cm] Applied polymers (abbreviations according ASTM 1600)... 

Complete wetting of a solid is only possible if a drop of the liquid spreads spontaneously at the surface, i.e. for 9 = 0 or cos 9=1. The limiting value cos 6 = 1 is a constant for a solid and is named critical surface tension of a solid y... Therefore, only liquids with yl < Vc have the ability to spontaneously spread on surfaces and wet them completely. Tab. 4.2 gives an overview of critical surface tension values of different polymer surfaces [40]. From these data it can be concluded that polytetrafluoroethylene surfaces can only be wetted by specific surfactants with a very low surface tension, e.g. fluoro surfactants. 

The ability of a liquid to "wet" the membrane material is an indication of that liquids ability to establish and maintain such an interfacial layer. Liquids of surface tension values less than the critical surface tension iy ) of the membrane material are capable of completely "wetting" the polymer. It may be possible therefore, to select membrane materials capable of accomplishing specific separations by their ability to be wet by one solution component but not by the other. For this reason Yc membrane materials is important. By employing the standard techniques of Zisman (43), the critical surface tension for PSF and CA were determined to be 43.0 and 36.5 dynes/cm, respectively. This data indicates that PSF is more readily wet by a larger number of liquids than is CA. Similar measurements for the various sulfonated polysulfones are underway. 

The viscosity or resistance to flow increases as the number of repeat units increases, but physical properties, such as surface tension and density, remain about the same after a DP of about 25. The liquid surface tension is lower than the critical surface tension of wetting, resulting in the polymer spreading over its own absorbed films. The forces of attraction between polysiloxane films are low resulting in the formation of porous films that allow oxygen and nitrogen to readily pass though, but not water. Thus, semipermeable membranes, films, have been developed that allow divers to breath air under water for short periods. 

In contrast to water-soluble polymers, such as polyacrylamide, which has a relatively high critical surface tension (35 dyne/cm), water-repellent polymers, such as the silicones and ptfe, have relatively low critical surface tensions (24 and 19 dyne/cm, respectively). The presence of hydroxyl groups in polymers, such as polyvinyl alcohol and polyacrylic acid which tend to... 

With values in the range of about 10-18 mN m 1 perfluorinated liquids have the lowest surface tensions among the known organic liquids, and will completely wet any solid surface. Increasing amounts of hydrogen in the molecule increase the surface tension. Fluorinated solid surfaces, e.g. fluoropolymers, possess very low critical surface tensions yc, which relates to their antistick and low frictional properties, whereas hydrocarbon polymers have substantially higher values (PTFE yc = 16.0 mN m-1 PE yc = 31.0 mN m-1).7... 

The effects of fluorination on solid-surface free energies parallel the liquid trends Perfluonnated polymers have the lowest critical surface tensions, which directly relate to their antislick properties [19], but substitution of fluorine by hydrogen or by the more polarizable chlonne atom markedly raises their surface free energy. 

The high values for the trifiuoropropyl group are surprising but correspond with the liquid surface tension of polytrifluoropropylmethylsiloxane [13], although not in line with its critical surface tension and solid surface tension. The low values for the longer fluoroalkyl groups are comparable to the lowest surface tension fluoropolymers and correspond well with the values for related preformed fluorosilicone polymers [14-15]. 

The wetting properties of polyacetylene have been studied by Schonhom et al. 380) who measured a critical surface tension of 51 mN m 1, considerably higher than for other hydrocarbon polymers. This value was attributed to oxidation of the surface as no change was observed on further oxidation. Treatment of polyacetylene with aqueous potassium permanganate renders it hydrophilic, reduces the contact angle for water from 72° to 10° and renders the structure more water-permeable 381)... 

Allcock and Smith118 have prepared a series of poly(organophosphazenes) containing siloxane grafts and/or trifluoroethoxy side groups (31-34). Polymers 31 and 32 had critical surface tensions of 16-17 rn N rn 1 and surface layers which were enriched in fluorine. In the case of 32, silicone was not observed at the surface. Polymer 33 had a critical... 

Table 3.4 gives an overview of critical surface tension values of different polymer surfaces [10]. From these data it is obvious that polytetrafluoro ethylene surfaces can only be wetted by specific surfactants with a very low surface tension, e.g. fluoro surfactants. 

Table 3.4 Critical surface tension of polymer solids [10] ...

The critical surface tension value for most inorganic solids is in the hundreds or thousands of dynes per centimeter. For polymers and organic liquids, it is at least an order of magnitude lower. Critical surface tension is an important concept that leads to a better understanding of wetting and adhesion. 

Critical Oxygen Index (COI), 853 Critical size, 704-705 Critical spherical nucleus, 710, 711 Critical strain, 867, 868 Critical stress energy factor, 474 Critical surface tension of wetting, 232 Critical temperature, 655 Cross-linked polymers, 29 Cross-linking, 148 Cross model, 731 Cross polarisation, 376, 377 Crystallinity, 728, 732, 815 Crystallites/Crystallisation, 690, 725 of rigid macromolecules, 739 Cyclical chain length, 782... 

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