Microscale Property Control on Polymer films by Utilizing Interfering Laser Heating

在这个研究项目中，我们将注意力集中在使用干涉红外辐射进行微尺度性能控制。第一步，通过干涉红外激光的照射将注塑聚合物条带表层的双折射控制为“图案”。通过实验检验了双折射图案的可控性，结果表明：（1）干涉红外辐射可以在表层上“记录”明显的双折射图案，其间距小于70μm；（2）可记录双折射图案的最小间距受到成型条件的影响，例如熔体温度和速度、模具壁温度和辐射强度。为了研究聚合物熔体中图案可记录性和温度分布之间的关系，在干涉红外激光照射条件下对熔体内的传热进行了数值估计。结果表明，（3）表层内的温度分布与聚合物条上记录的双折射图案很好地对应，并且（4）聚合物内的热扩散阻碍了双折射图案的记录，特别是当图案间距变窄时。应用所获得的基本发现，第二步是通过使用干涉红外辐射来控制聚合物薄膜中的分子取向。通过使用干涉IR照射，与注塑成型相同的方式也在膜上记录了双折射图案，但表明可以记录明显双折射图案的膜的照射条件比注塑成型更严格。这是因为薄膜受到周围环境的冷却比注射成型弱，而且薄膜的厚度太薄，一般无法吸收照射的红外能量；它们都会导致薄膜内“平坦”的温度分布。

In this research project, we focused attention to the microscale property control by using an interfering IR radiation. As the first step, birefringence in skin-layers of an injection-molded polymer strip was controlled as a "pattern" by irradiation of interfered IR laser. Controllability of the birefringence pattern was experimentally examined, and the results showed that (1) an evident birefringence pattern, spacing of which is less than 70 μm, can be "recorded" on the skin-layer by the interfered IR irradiation, and that (2) the minimum spacing of the recordable birefringence pattern is influenced by the molding conditions, such as melt temperature and velocity, mold wall temperature, and radiation intensity. In order to investigate the relation between the pattern recordability and temperature distributions in the polymer melt, heat transfer within the melt was numerically estimated under the interfered IR laser irradiation condition. The results showed that (3) the temperature distributions within the skin-layer correspond well with the birefringence pattern recorded on the polymer strip, and that (4) thermal diffusion within the polymer obstructs the recording of birefringence pattern especially when the pattern spacing becomes narrower. Applying the basic findings obtained, molecular orientation in a polymer film was controlled by using the interfered IR irradiation as the second step. The birefringence pattern was recorded also on the film as same manner as the injection-moldings by using the interfered IR irradiation, but it was shown that the irradiation condition for the film where the evident birefringence pattern can be recorded is more rigid than for the injection-molding. This is explained by the fact that cooling of the film by the surroundings is weaker than that of the injection-molding, and that the thickness of film is too thin to absorb irradiated IR energy in general; both of them result in "flat" temperature distribution within the film.