Interfacial tension between polymers polymer interfaces

Roe, R. J., Interfacial tension between polymer hquids, J. Colloid Interface Sci., 31, 228-235 (1969). 

An example of adsorption of this kind is the adsorption occurring at the oil-water interface. The driving force for adsorption in this case is the minimization of the interfacial tension between the two interfaces. Typically, random copolymers or block copolymers, in which the monomeric imits are preferentially solvated in either of the two phases, adsorb readily at the interface. In the case of homopolymers, adsorption occurs either if the polymer is soluble in both the phases or if the polymer has functional groups that can reduce the interfacial tension. Thus, both polyCethylene oxide) and poly(methyl methaciylate) readily adsorb at the toluene-water interface. The former is soluble in both the phases while the latter has polar side groups that effectively screen the interactions between toluene and water. However, because of its hydrophobic nature polyst3U ene does not adsorb at the same interface (50). 

Since the interfacial tension between polymers is minor [17] and the adhesion of polymers to a filler differs essentially (Table 12.3), it may be supposed diat the filler localizing between polymer phases by the latter mechanism is most probable. The filler localization at the interface in all blends assigned to the first group according to Table 12.2 is likely to follow the last mentioned scheme. In those blends the local concentration of a filler at the interface is also governed by the equilibrium between the number of particles arriving at the interface and leaving it for a phase. 

From the above discussion it follows that with increasing difference in wetting forces of polymers the equilibrium concentration of CB at the interface must rise when a filler transfers to the interface from the phase of a lesser wetting force and must fall when it comes here from the phase of higher wetting force. Besides, the rise of interfacial tension between polymers must promote the increase in local concentration of CB at the interface when it is redistributed from any phase. 

Roe R J (1969) Interfacial tension between polymer liquids. J Colloid Interface Sci 31 228 235... 

Additives can greatly reduce the interfacial tension between polymers and hence modify the mixing process and the properties of the blend. Block and graft copolymers are the most effective interfacial agents and can be added to the blend or formed during the mixing process by reactions between the base polymers. " There are theoretical treatments of the behavior of block copolymers at the polymer/polymer interface but comparable experimental data is scarce. 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Figure 8.26. Schematic illustration of the interfacial tensions balance at the interface between three liquids. The Neumann s triangle, and the morphologies to appear in the melt-blends of three polymers are also shown. Four morphologies are predicted for dispersions of liquids 1 and 2 in liquid 3 (a) encapsulated hybrid particles (1 in 2), (a ) encapsulated hybrid particles (2 in 1), (b) stuck hybrid particles, (c) isolated particles [Nakamura and Inoue, 1990].

The importance of interfacial tension reduction in polymer blends by CO2 has been addressed by Xue et al. [44] The pendent-drop method was utilized to investigate the interfacial tension between PS/LDPE saturated with SCCO2 and compared to the same system in the absence of CO2. At 200 °C the interfacial tension decreased from 6.62 mN m at 0.1 MPa to 4.69 mN m at CO2 pressure of 9.2 MPa, corresponding to a 30% absolute reduction. This decreased interfacial tension was explained by the presence of dissolved CO2 at the interface of the polymers reducing unfavorable interactions between the two phases and thereby enhancing the miscibility. 

Of the possible emulsifiers, most are what are considered true surfactants, in that they are effective at lowering significantly the interfacial tension between the two hquid phases. Other additives such as polymers and sols function primarily as stabihzers, rather than emulsifiers. Most polymers are not sufficiently effective at lowering interfacial tensions to act in that regard. In addition, because of their molecular size, the adsorption process for polymers is generally very slow relative to the timescale of the emulsification process. The same applies to stabilizing colloids, in which their action requires the wetting of the particles by the two hquid phases to facihtate their location at the interface. The primary function of polymers and sols in emulsions is in the retardation of droplet flocculation and coalescence. 

Theories that describe the reduction of the size of the dispersed phase in the presence of nanoparticles vary, depending on whether the filler is located in the continuous phase, in the dispersed phase, or at the interphase between the two blend components. Compatibilizing effects due to polymer adsorption on the filler surface, as well as reduction in the interfacial tension between the two phases in the presence of the filler, are the generally accepted mechanisms when the fillers are located at the interface [11,13,26]. Ray et al. [11] showed that upon addition of only 0.5 wt% of organically modified clay, the interfacial tension decreased from 5.1 to 3.4 mN/m for a PS/PP blend and from 4.8 to 1.1 mN/m for PS/PP-g-MA, suggesting a possible interfacial activity of the clay that is localized at the interface in similar fashion to classical compatibilizers. 

Quantitative surface and interfacial tension data for polymers are crucial to many aspects of the production and application of elastomers, plastics, textiles, films and coatings, foams, polymer blends, adhesives, and sealants. Although interface is the inclusive term for the region in space where two phases meet, if one of the phases is gaseous it is usually called a surface [1]. Thus we refer here to the surface tension of a polymer in air but to the interfacial tension between a polymer and a condensed phase such as water or another polymer. 

WITH the easy-processing properties in the liquid crystalline phase, main-chain TLCPs have been widely used as high-strength fiber, fiber reinforcement, in situ reinforcement additive, and injection molded articles, etc, [ 1 -4]. The successful applications are quite dependent on the adhesion at interface of the liquid crystalline polymer and the conventional engineering resin, which is indeed affected by surface tension and/or interfacial tension between the two phases [1-2],... 

Often, even immiscible and/or incompatible polymers are also made compatible by addition of a compatibilizer. Compatibilizers are believed to primarily reside at the polymer/polymer interfaces. The compatibilizer can be presynthesized or formed by in situ polymerization. Often the product engineer can make a judicious choice of compatibilizer resulting in improvement of mechanical properties, sometimes with synergistic effects. The compatibilizer is believed to stitch itself across the polymer/polymer interfaces. The addition of a compatibilizer lowers the interfacial tension between the two immiscible phases. The compatibilizer may sometimes be made of block copolymer composed of two different components. One of the block components may be miscible with polymer A, and the block component may be miscible with polymer B. Even if a polymer A and polymer B are immiscible, such a block copolymer would compatibilize the blend of A and B. 

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