基于法向热传导的垂直取向液晶高分子薄膜研究

Up to now, most of liquid crystalline polymeric (LCP) materials, especially liquid crystalline elastomers (LCEs) are usually prepared by homogeneous alignments; however, homeotropic aligned LCP materials lack of attentions and research interests, because these materials do not have a clear application background, in contrary to that homogeneous aligned LCEs can be potentially used as artificial muscles and actuators. Herein, we propose to prepare some homeotropic aligned LCP films. By taking advantage of the anisotropic property of liquid crystals and using a variety of homeotropic alignment methods, we try to force the polymer backbones to stretch along the normal directions of the corresponding films, in order to enhance the thermal conductivities in the normal directions. We hope these novel materials would take place of the traditional thermal conductive filler/polymer composites with poor mechanical properties, and expand the field of application for homeotropic aligned LCP materials. The research objectives and main contents include: 1) Design and synthesize acrylate and thiol-ene liquid crystalline monomers. 2) Apply electric fields, magnetic fields and surface anchoring effects, align the monomers homeotropically, and perform in situ photo-polymerization/photo-crosslinking, to prepare three types (side-chain side-on, main-chain end-on, discotic) of homeotropic aligned LCP films. 3) The thermal conductivity λ in film normal direction is expected to be higher than 2.0 W.K-1.m-1. Through studying the physical and thermal properties of these materials, we would like to get a conclusion and judgment of the feasibility of homeotropic aligned LCP films being novel non-filler type thermal conductive polymeric materials.

目前绝大多数以液晶弹性体为代表的液晶高分子材料普遍采取水平配向，而针对垂直取向液晶高分子材料的研究工作非常少，其根本原因在于它缺乏一个明确的应用背景做支撑，如人造肌肉、起动器等。本项目拟借助液晶的各向异性，采取多种配向手段，使高分子主链沿薄膜的法向有序排列，显著提高该方向上的导热性能，争取替代机械性能较差的传统填充型导热高分子复合材料，拓展垂直取向液晶高分子材料的功能化应用领域。主要的研究内容和目标为：1）设计并合成丙烯酸酯类、硫-烯类光敏性液晶单体；2）利用电场、磁场、配向膜/剂等配向方法，使液晶单体垂直排列，原位光聚合/交联，分别制备三类（侧链腰接型、主链尾接型、盘状）垂直取向液晶高分子薄膜；3）期望制备的垂直取向液晶高分子薄膜的法向热导率λ> 2.0 W.K-1.m-1，通过对材料的一系列物理表征和导热性能研究，初步验证垂直取向液晶高分子薄膜作为非填充型导热聚合物材料的应用前景。

随着电子元器件工作频率的急剧增加，器件内部产生的热量已经成为影响电子设备功能及寿命的严重威胁。因此，如何提高电子设备的散热能力，尤其是开发具有各向异性导热性能的新型聚合物材料已成为重要的研究课题。本项目借助液晶的各向异性，采取电场配向手段和紫外光照原位聚合技术，使液晶高分子主链沿薄膜的法向有序排列，研制了一类新型高导热垂直取向主链型含二苯并乙炔核的液晶高分子薄膜材料，其法向热导率λ⊥高达3.56 W.K-1.m-1，各向异性常数（法向/面向热导率）λ⊥/λ∥ 达到15.0，超过原设定技术指标要求，也是目前见于文献报道的基于液晶高分子材料的最高法向热导性能。该垂直取向液晶高分子薄膜材料，有望成为新一代非填充式导热薄膜材料，用于电子元器件的包装和散热，在民用和国防领域都有很好的应用前景。通过该研究计划的资助，课题负责人在Nature Communications、Journal of the American Chemical Society等国际高水平杂志上发表通讯作者SCI论文24篇；以第一发明人身份申请国家发明专利11项，目前3项专利已获得授权。