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首页> 外文会议>Croucher ASI on nano science and technology >Distinguishing Spinodal and Nucleation Phase Separation in Dewetting Polymer Films
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Distinguishing Spinodal and Nucleation Phase Separation in Dewetting Polymer Films

机译：区分纺丝膜和成核相分离在脱水聚合物膜中

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It is a common experience that liquid films on non-wetting surfaces may dewet and break up into liquid droplets. Despite of its ordinariness, the physics of this phenomenon is not fully understood. Specifically, it cannot be resolved whether these thin films rupture by a spinodal mechanism or heterogeneous nucleation. According to Cahn (1965), if the second derivative of a system's free energy as a function of the order parameter is less than zero (i.e. G"(h) < 0), the system is unstable against spinodal decomposition. Under this circumstance, spontaneous fluctuations in the system order parameter may grow exponentially with time (Cahn, 1965). In particular, the fluctuation mode with wavevector, q, equals q_m = [G"(h)/γ]~(1/2) will grow the fastest, resulting in a characteristic wavevector = q_m in the morphology incurred in the initial stage of phase separation, though in the later stage coarsening of the morphology may occur (Chaikin and Lubensky, 1995) whereupon the characteristic wavevector will shift to smaller q. In apolar liquid films on a substrate, if the film thickness is less than ～100 nm, the free energy is mainly due to non-retarded van der Waals interactions (deGenees, 1985) so is of the form -A/12πh~2 per unit area, where A is the Hamaker constant and h, i.e. the system order parameter, is the film thickness. It follows that those liquid films with A < 0 are unstable against spinodal decomposition. From the foregoing, spinodal rupturing proceeds by exponential growth of the amplitude of the surface undulations in these films and the initial phase-separated state is a distribution of ridges and valleys before the dewetting film ripens into liquid beads. However, if G"h) is positive, the spinodal process will be suppressed. Nonetheless, so long as G'(h) is negative, the film will still undergo phase separation though by heterogeneous nucleation.
机译：它是非润湿表面上的液体膜可以脱绒和分解成液滴的共同体验。尽管其司法性，但这种现象的物理学尚未完全明白。具体地，不能解决这些薄膜是否通过旋光机构或异质成核破裂。根据CAHN（1965），如果系统的自由能的第二导数作为订单参数的函数小于零（即G“（H）<0），则系统对旋转晶膜分解不稳定。在这种情况下，系统订单参数中的自发波动可能随时间呈指数（CAHN，1965）。特别地，具有波浪传感器，Q的波动模式等于Q_M = [G“（H）/γ]〜（1/2）将生长最快，导致特征波动= Q_M在相分离的初始阶段产生的形态，尽管在后期的形态粗化中可能发生（Chaikin和Lubensky，1995），但是特征波动器将移位到较小的Q。在基板上的甲状腺液体膜中，如果膜厚度小于〜100nm，则自由能主要是由于非延迟的范德华相互作用（脱烯，1985）所以形式-a /12πh〜2单位区域，其中A是Hamaker常数和H，即系统订单参数，是膜厚度。因此，具有<0的那些液体薄膜对旋尖分解不稳定。从前述内容中，通过这些薄膜中的表面起伏的幅度的指数增长进行旋转性破裂，并且初始相位分离状态是在脱模膜成熟成液体珠前之前的脊和谷的分布。然而，如果G“H）是阳性的，则将抑制旋尖过程。尽管如此，只要G'（H）为负，薄膜仍将通过异质成核来进行相分离。

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