Mechanistic study of the anchoring behavior of liquid crystals supported on metal salts and their orientational responses to dimethyl methylphosphonate
Mechanistic study of the anchoring behavior of liquid crystals supported on metal salts and their orientational responses to dimethyl methylphosphonate
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DOI：
10.1021/jp0470391
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发表时间：
2004-12-30
影响因子：
3.3
通讯作者：
Abbott, NL
中科院分区：
文献类型：
--
作者：
Yang, KL;Cadwell, K;Abbott, NL
本文研究了4 '-戊基-4-联苯腈（5CB）在不同高氯酸盐负载下的液晶膜的取向行为及其对甲基膦酸二甲酯（DMMP）的取向响应。发现高氯酸盐负载的5CB由具有高电子亲合势的金属离子组成（> 15.64eV）的金属离子，如Cu 2+、Zn 2+、Cd 2+、Ni 2+、Co2+、La 3+、Al 3+、Eu 3+和Fe 3+，呈现垂面取向，而5CB负载在具有低电子亲和性的金属离子的盐上，包括Mn 2+、Mg 2+、Ag+、Cs+和Na+，呈现平面或倾斜的取向。通过偏振调制红外反射-吸收光谱（PM-IRRAS）支持5CB的腈基通过其与金属离子的配位在确定LC的取向行为中的作用。一个新的腈伸缩峰测量与Cu 2+，Ni 2+，和Cd 2+（导致垂面锚定），但不与Ag+，Na+，和Mg 2+（导致倾斜或平面取向的5CB）。当暴露于100 ppb的DMMP时，负载在Al 3+、Eu 3+和Cu 2+的高氯酸盐上的5CB经历了垂直到平面的锚定转变，而负载在其他金属离子上的5CB对DMMP没有显示出可测量的取向响应。这些结果，当结合起来，支持的观点，5CB DMMP对金属高氯酸盐的取向反应的结果从竞争性结合的5CB和DMMP的金属盐的阳离子。
This paper reports an investigation of the orientational behavior of films of nematic liquid crystal (LC) 4'-pentyl-4-biphenyl-carbonitrile (5CB) supported on a variety of metal perchlorate salts and their orientational response to dimethyl methylphosphonate (DMMP). It is found that 5CB supported on perchlorate salts comprised of metal ions with high electron affinities (> 15.64 eV), such as Cu2+, Zn2+, Cd2+, Ni2+, Co2+, La3+, Al3+, Eu3+, and Fe3+, assumes a homeotropic orientation whereas 5CB supported on salts of metal ions with low electron affinities, including Mn2+, Mg2+, Ag+, Cs+, and Na+, assumes a planar or tilted orientation. The role of the nitrile group of 5CB in determining the orientational behavior of the LC via its coordination with the metal ions is supported by polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). A new nitrile stretching peak is measured with Cu2+, Ni2+, and Cd2+ (which cause homeotropic anchoring) but not with Ag+, Na+, and Mg2+ (which cause tilted or planar orientations of 5CB). Upon exposure to 100 ppb of DMMP, the 5CB supported on the perchlorate salts of Al3+, Eu3+, and Cu2+ undergoes a homeotropic-to-planar anchoring transition while 5CB supported on the other metal ions shows no measurable orientational response to DMMP. These results, when combined, support the view that the orientational response of 5CB to DMMP on metal perchlorate salts results from a competitive binding of 5CB and DMMP to the cations of the metal salts.