Temperature Dependence of Interfacial Tension of Demixed Polymer Blend Melts: Polystyrene/Poly(dimethylsiloxane)s

Abstract

ABSTRACT:Interfacial tension of polystyrene/poly(dimethylsiloxane) blends with different molecular weights have been measured as a function of temperature by sessile drop method. The results are described as a scaled relation of reduced interfacial tension vs. reduced segregation strength, xix: 1, where x is the segmental interaction parameter and x, is x at the critical temperature. The scaled relation is discussed on the basis of mean-field theory, and a semi-empirical expression has been presented for the scaled relation covering a wide temperature range.KEY WORDS Interfacial Tension / Polymer Blends / Temperature Dependence / Polystyrene / Poly(dimethylsiloxane) / It is theoretically predicted that there are three temperature regions for interfacial tension of polymer melts according to the segregation strength. 1 · 2 In Region I of weak segregation near the critical point, the interfacial tension appears and increases as temperature goes away from the critical point. Region I is specified by x 2/ N, where xis the Flory-Huggins interaction parameter and N is the degree of polymerization. In strong-segregation region, Region II, where 2/N<x<l, the interfacial tension is proportional to Tx 112 , while in Region III of very strong segregation, where x > 1, it is proportional to Tx, with T being the absolute temperature. A region unique to polymeric systems is Region II, where the interfacial tension can increase with increasing temperature even if the polymer blend has the upper critical solution temperature (UCST).In our previous studies, Region I and Region II have been investigated by measuring the temperature dependence of interfacial tension for polystyrene (PS)/ poly(dimethylsiloxane) (PDMS) blends. 3 • 4 It has been demonstrated that the interfacial tension exhibits predicted temperature dependences unique to Region I and Region II, respectively. In this study, adding data of interfacial tension in the intermediate region, we will make a better understanding of the interfacial-tension behavior over the whole temperature region from Region I to Region II by scaled plots.The author has measured coexistence curves of PS/ PDMS mixtures with different molecular weights to evaluate the interaction parameter x as functions of temperature and molecular weight. 5 The value of x is indispensable and will be utilized in data analysis and discussion in the present study. The same series of blend systems are here used to study the intermediate region.Details of the scaling arguments based on the squaregradient theory of mean-field type for the interfacial tension will be made, and a semi-empirical expression will be presented. THEORETICAL CONSIDERATIONS AND A SCALED EXPRESSIONAdopting the square-gradient theory for the free 218 energy of a non-uniform binary system, the interfacial tension y is given by 1 • 2 • 6(1)Here, Af is the excess local free energy per site as a function of concentration ¢ in volume fraction at the position z with the z-axis being perpendicular to the interface, K is the coefficient of square...

Synthesis of Poly(styrene−dimethylsiloxane) Block Copolymers: Influence of the Phase-Separated Morphologies on the Thermal Behaviors

“…Sthün's work suggests a strong dependence of χ on the PS volume fraction φ PS 31 and Mori et al's work a dependence on the polydispersity index giving χ ≈ 106/ T , which is of the same order as existing data . As an illustration, using Sthün's results for φ PS = 0.5, the quench parameter estimated at 100 °C for D51 (see Table ) is roughly 4 times the corresponding styrene/isoprene parameter.…”

“…35 Nevertheless, a rough estimate may be obtained using PS and PDMS solubility parameters, 21 giving χ ≈ 106/T, which is of the same order as existing data. 36 As an illustration, using Sthu ¨n's results for φ PS ) 0.5, 31 the quench parameter estimated at 100 °C for D51 (see Table 4) is roughly 4 times the corresponding styrene/isoprene parameter. Such simple arguments may explain why PS/PDMS block copolymers exhibit such strongly segregated thermal behavior as compared with other block copolymers.…”

Effects of A-B Block Copolymer Additives on Interfacial Tension of A/B Polymer Blends Near the Critical Temperature: Comparison of Mean-Field Calculations with Experiments

“…Although the theory is applicable only to an interface with a very gradual change of the composition at the interface, it is known that the theory provides a reasonably good approximation. [3] Here, the point is to take the orientation of diblock copolymer at the interface into account by introducing a parameter, u, which represents the orientation of block copolymer chains, and is given as a function of position or distance from the interface.…”