Model of laser-driven mass transport in thin films of dye-functionalized polymers
Model of laser-driven mass transport in thin films of dye-functionalized polymers
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DOI：
10.1063/1.476701
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发表时间：
1998-07-22
影响因子：
4.4
通讯作者：
Natansohn, AL
中科院分区：
文献类型：
--
作者：
Barrett, CJ;Rochon, PL;Natansohn, AL
基于牛顿流体动力学关系，建立了一个描述含可异构偶氮苯生色团的聚合物薄膜中激光诱导质量输运的模型，在该模型中，表面轮廓衍射光栅可以用相干光的干涉图样刻出。粘性流体的层流的Navier-Stokes方程的开发与在膜中的压力梯度的压力梯度的膜中的速度分量，通过定义的边界层条件。这种一般层流模型适用于通过各种机制形成表面光栅。考虑到异构化驱动的自由体积膨胀产生内部压力梯度的机制，开发了一个特定的模型来描述由激光诱导的大体积发色团的异构化导致的聚合物流动。这就产生了一个表达式的表面光栅的时间演变的性质，可以改变实验，如那些照射光，铭文的几何形状，和散装聚合物，其中包括没有任意的拟合参数或积分常数。在一般的模型中，光栅铭文的速率被预测为直接随铭文激光的强度而变化，在纠缠极限以下与聚合物的分子量成反比，并且与膜的初始厚度的三次方成比例。考虑到异构化压力机制，该模型预测的速率光栅铭文进一步变化的自由体积的染料分子的诱导几何变换的要求，和铭文激光的偏振状态。从该模型的预测进行了测试，对实验结果，以改变这些参数，并被证明是在良好的协议。(C)1998年美国物理学会。
Based on Newtonian fluid dynamic relations, a model is constructed to describe laser-induced mass transport in thin films of polymers containing isomerizable azobenzene chromophores, in which surface profile diffraction gratings can be inscribed with an interference pattern of coherent light. The Navier-Stokes equations for laminar flow of a viscous fluid are developed to relate velocity components in the film to pressure gradients in the polymer film, by definition of boundary layer conditions. This general laminar flow model is applicable to the formation of surface gratings through a variety of mechanisms. Considering the mechanism of an isomerization-driven free volume expansion to produce internal pressure gradients, a specific model is developed to describe polymer flow resulting from laser-induced isomerization of the bulky chromophores. This yields an expression relating the time evolution of the surface gratings to properties which could be varied experimentally, such as those of the irradiating light, inscription geometry, and bulk polymer, which incorporates no arbitrary fitting parameters or integration constants. In the general model, the rate of grating inscription is predicted to vary directly with the intensity of the inscription laser, to vary inversely with the molecular weight of the polymer below the limit of entanglement, and to scale with the third power of the initial thickness of the film. Considering an isomerization pressure mechanism, the model predicts the rate of grating inscription to further vary with the free volume requirements of the induced geometric transformation of the dye molecules, and the polarization state of the inscription laser. Predictions from the model were tested against the results of experiments to vary these parameters, and are shown to be in good agreement. (C) 1998 American Institute of Physics.