Homopolymer surface tension

Theories of Homopolymer Surface Tension. More rigorous expressions for predicting polymer surface tension have been derived from equations of state for polymers. Corresponding states principles have been employed to derive expressions for surface tensions in terms of characteristic equation of state parameters and the associated reduced temperature, pressure, and volume. One proposed expression is of the form (14)... 

Polarity of Vinyl Acrylic Latex and Surfactant Adsorption Contact angle measurements, dispersion and polar contribution to latex film surface tension and polarity of polymer calculated according to the method of Kaelble (10) of the three latex films are whown in Table V. It is seen that the polarity of the latex film decreases with increase in butyl acrylate content of the vinyl acrylic co-polymer. The polarity of the 70/30 (VA/BA) latex is very similar to that of the polybutyl acrylate homopolymer estimated to be about 0.21 (1). ... 

The monomers chosen for these investigations are shown in Table I. They were selected so that a range of properties changed depending on the pair selected for the synthesis of these semi-1-IPNs (34). Factors of particular interest were the water solubility of the monomers, which could influence the locus of polymerisation and the relative hydrophilicities of the homopolymers as indexed by critical surface tension. In a semi-l-IPN the first-formed polymer is a network, but the second-formed polymer is linear. 

Microphase separation and domain formation in block copolymers, which are the result of incompatibility of block chains, have been studied extensively (1,2). In addition to being incompatible, block chains in a copolymer generally have different thermal transition temperatures. The surface tensions of molten block chains also differ. When a crystalline block chain is incorporated into a block copolymer, it is expected that crystallization of the crystalline block chain causes considerable change in resultant morphology. Surface properties of a block copolymer and of its blend with a homopolymer should also be modified by the surface tension difference between block chains and the homopolymer. Since these factors determine the morphological features of a block copolymer both in bulk and at surface, a unified study of morphology, crystallization, and surface activity of any block copolymer is important to our understanding of its physical properties. 

Surface tensions of both the ST copolymers in homopolymers and the PS-PTHF homopolymer blend were measured in argon by the pendant drop method described by Roe (5). 

Surface tension vs. temperature for PS and PTHF are shown in Figure 15. The data of Gains and Bender (17) on PS surface tensions (yGps) agree well with ours. However, our value for the surface tension of PTHF (yoPthf) is about 4.5 dynes/cm higher than Roe s value (18). The reason for this discrepancy is not clear. The y0i thf is always smaller than the yoPS by Ay = 3 dynes/cm, which is much smaller than the surface tension difference between the blocks of PS and polydimethylsiloxane. The time-dependent surface tensions of four blends (ST-PS, ST-PTHF, PS-PTHF, and PTHF-PS) were measured. To prepare the blends, the block or homopolymers were added in small amounts (0.3-1 wt %) to the homo-PS or PTHF. The mixture was completely dissolved in benzene, the solutions were quickly frozen by a dry ice-acetone mixture, and the samples were freeze dried. 

From these results, it is concluded that for the ST-PS blend, both the surface tension difference and the incompatibility between PTHF block and homo-PS assist in the adsorption of the PTHF block, which has lower surface tension than molten homo-PS. On the contrary, it is clear that incompatibility alone is not sufficient to force the PS block chain to the surface of the ST-PTHF blend against the increase of surface free energy. Therefore, quite an important conclusion has been reached from these studies, that is, an AB block copolymer, in which the surface tension difference between the two blocks AY = 7a - 7b is as small as 3 dynes/cm, is still sufficiently surface active when it is added in low concentration to a homopolymer corresponding to block A as long as yA > yB. 

More extensive investigations have been performed on HDPE/PP blends by Martuscelli et al. [1980] and Bartczak and Galeski [1986]. From the isothermal crystallization experiments, it was found that the rate of crystallization of the HDPE matrix was markedly reduced upon addition of small amounts of PP (10 wt%). The authors attributed this phenomenon to the increased melt-viscosity of the sample caused by the presence of solidified PP domains. Moreover, Plesek and Malac [1986] have calculated from the surface tensions of the homopolymers at T, that PP crystallization will not cause the nucleation of the HDPE phase, while in the reverse case HDPE crystals will induce the nucleation of PP. 

The quantities yi and y2 refer to the surface tensions of the corresponding homopolymers, and )/ =kBTIa acts as a reference surface tension. Originally, this equation was applied to the surface tension of miscible polymers with A = 1 [Belton and Evens, 1945 Kammer, 1994]. We want to discuss two limiting cases of Eq. (8.42) ... 

Owing to the large difference in surface tensions of the two constituting homopolymers, SAN copolymers are situated closer to limiting case I than to n. The least-squares procedure yields... 

Three classes might characterize the variation of y with copolymer composition. First, a linear change in surface tension with composition is observed for EVOH. This occurs when there is no difference in composition between the bulk and surface regions. Second, deviations from constancy of y occur when the surface tensions of parent polymers are about equal. This behavior can be seen in EVAc copolymers. Different area coverings of the constituting segments cause this effect. Third, y values of the corresponding homopolymers are sufficiently different, as in SAN here the surface tension varies nonlinearly with copolymer composition, as in polymer blends. 

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