Interfacial tension, polymer surface properties

A temperature of 140°C is shown in Table 12.2 because all of the polymers must be above their glass transitions if amorphous, and above their melting temperatures if senucrystalline for the determination of interfacial tensions and related properties. Values of surface tension sometimes listed for glassy or semicrystalfine polymers are usually extrapolated from the melt. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Interfacial properties cannot be described without identifying the contacting medium. Interfacial properties of a polymer solid are dependent on the conditions under which the surface is equilibrated. The surface configuration of a polymer is a function of the contacting phase of polymer/contacting phase interface. In this context, the conventional sense of surface property (interface with air) is dependent on the history of the surface and the humidity of air. The surface dynamic change occurs when the interfacial equilibrium is broken and is driven by the interfacial tension in the new environment. 

IGC can be used to determine various properties of the stationary phase, such as the transition temperatures, polymer—polymer interaction parameters, acid-base characteristics, solubility parameters, crystallinity, surface tension, and surface area. IGC can also be used to determine properties of the vapor-solid system, such as adsorption properties, heat of adsorption, interaction parameters, interfacial energy, and diffusion coefficients. The advantages of IGC are simplicity and speed of data collection, accuracy and precision of the data, relatively low capital investment, and dependability and low operating cost of the equipment. 

The determination of the conformational and segregation properties of polymer brushes, created by diblock copolymers, has triggered their application to more complex problems. Diblock copolymers have been used to increase adhesion [277] or to eliminate the interfacial tension [256] between immiscible polymers. They may also modify the surface induced mode [116] and the bulk mode [278] of the spinodal decomposition observed in homopolymer blends. 

Finally, it is highly desirable to improve the ability to calculate the properties of surfaces and interfaces involving polymers by means of fully atomistic simulations. Such simulations can, potentially, account for much finer details of the chemical structure of a surface than can be expected from simulations on a coarser scale. It is, currently, difficult to obtain quantitatively accurate surface tensions and interfacial tensions for polymers (perhaps with the exception of flexible, saturated hydrocarbon polymers) from atomistic simulations, because of the limitations on the accessible time and length scales [49-51]. It is already possible, however, to obtain very useful qualitative insights as well as predictions of relative trends for problems as complex as the strength and the molecular mechanisms of adhesion of crosslinked epoxy resins [52], Gradual improvements towards quantitative accuracy can also be anticipated in the future. 

Dynamic properties of interfaces have attracted attention for many years because they help in understanding the behaviour of polymer, surfactant or mixed adsorption layers.6 In particular, interfacial rheology (dilational properties) is crucial for many technological processes (emulsions, flotation, foaming, etc).1 The present work deals with the adsorption of MeC at the air-water interface. Because of its amphiphilic character MeC is able to adsorb at the liquid interface thus lowering the surface tension. Our aim is to quantify how surface active this polymer is, and to determine the rheological properties of the layer. A qualitative and quantitative evaluation of the adsorption process and the dilata-tional surface properties have been realised by dynamic interface tension measurements using a drop tensiometer and an axisymmetric drop shape analysis. 

This chapter summarizes the potential of surface segregation in order to vary the surface chemical composition based on thermodynamical parameters. As a result, materials containing at least two constituents, one being of higher surface energy than the other will evolve towards a state where the interfacial tension is minimized. Minimization of the surface energy requires overcoming entropic forces and drives the movement of one of the components towards the material surface. So that, in principle, and as has been reviewed in this chapter one can tailor the surface properties of a polymer film. 

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