Muller M, Albano EV, Binder K
Institut fur Physik, WA 331, Johannes Gutenberg Universitat, D-55099 Mainz, Germany and INIFTA, Universidad de La Plata, C.C. 16 Sus. 4, 1900 La Plata, Argentina.
Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 2000 Oct;62(4 Pt B):5281-95. doi: 10.1103/physreve.62.5281.
We study the phase behavior of a symmetric binary polymer blend that is confined in a thin film. The film surfaces interact with the monomers via short-range potentials. We calculate the phase behavior within the self-consistent field theory of Gaussian chains. Over a wide range of parameters we find strong first-order wetting transitions for the semi-infinite system, and the interplay between the wetting/prewetting behavior and the phase diagram in confined geometry is investigated. Antisymmetric boundaries, where one surface attracts the A component with the same strength as the opposite surface attracts the B component, are applied. The phase transition does not occur close to the bulk critical temperature but in the vicinity of the wetting transition. For very thin films or weak surface fields one finds a single critical point at straight phi(c)=1 / 2. For thicker films or stronger surface fields the phase diagram exhibits two critical points and two concomitant coexistence regions. Only below a triple point there is a single two-phase coexistence region. When we increase the film thickness the two coexistence regions become the prewetting lines of the semi-infinite system, while the triple temperature converges toward the wetting transition temperature from above. The behavior close to the tricritical point, which separates phase diagrams with one and two critical points, is studied in the framework of a Ginzburg-Landau ansatz. Two-dimensional profiles of the interface between the laterally coexisting phases are calculated, and the interfacial and line tensions analyzed. The effect of fluctuations and corrections to the self-consistent field theory are discussed.
我们研究了限制在薄膜中的对称二元聚合物共混物的相行为。薄膜表面通过短程势与单体相互作用。我们在高斯链的自洽场理论框架内计算相行为。在广泛的参数范围内，我们发现半无限系统存在强烈的一级润湿转变，并研究了受限几何结构中润湿/预润湿行为与相图之间的相互作用。应用了反对称边界，即一个表面吸引A组分的强度与相对表面吸引B组分的强度相同。相变不是发生在本体临界温度附近，而是在润湿转变附近。对于非常薄的薄膜或弱表面场，在φ(c)=1 / 2处会出现一个单一的临界点。对于较厚的薄膜或较强的表面场，相图会出现两个临界点和两个伴随的共存区域。只有在三相点以下才存在一个单一的两相共存区域。当我们增加薄膜厚度时，两个共存区域会变成半无限系统的预润湿线，而三相温度则从上方趋近于润湿转变温度。在金兹堡-朗道假设的框架内研究了接近三临界点的行为，三临界点将具有一个和两个临界点的相图分开。计算了横向共存相之间界面的二维轮廓，并分析了界面张力和线张力。讨论了涨落和对自洽场理论的修正的影响。
