Surface dilatational rheological study of the trans–cis isomerisation of copolymers with trifluoromethoxy substituted metacrylate monolayers
Surface dilatational rheological study of the trans–cis isomerisation of copolymers with trifluoromethoxy substituted metacrylate monolayers
复制标题
DOI：
10.1016/s0927-7757(00)00464-7
复制
发表时间：
2000-12
期刊：
影响因子：
--
通讯作者：
R. Wüstneck;D. Prescher;S. Katholy;G. Knochenhauer;L. Brehmer
中科院分区：
文献类型：
--
作者：
R. Wüstneck;D. Prescher;S. Katholy;G. Knochenhauer;L. Brehmer
用π/A等温线、布鲁斯特角显微镜（BAM）和表面流变学参数表征了光致变色三氟甲氧基取代甲基丙烯酸酯共聚物在空气/水界面上的光诱导反-顺异构化。使用适当的照射朗缪尔薄膜的两种异构体可以分别表征。BAM图像证实了两种异构体的均匀结构，仅反射率不同。最大反式和顺式构象的膜的表面构象行为和π/A等温线差别很大。最大反式构象的单分子膜在压缩时表现出增加的表面摩擦弹性和粘度。所得的表面流变行为是粘弹性的，具有高的粘度。表面压力增加到50 mN m− 1，然后开始稳定。具有最大顺式含量的单层的表面压力在较低的表面覆盖度下开始增加，并在很宽的表面覆盖度范围内超过反式构象膜的值，但在35 mN m−1时趋于稳定。从0.45 nm 2/重复单元开始，单层变得高度可压缩。结果被解释为增加的最小平均表面需求的共聚物偶氮苯侧基的顺式异构体和折叠的单层随着表面压力的增加。
Spread monolayers of a photochromic trifluoromethoxy substituted metacrylate copolymer were characterised by π/A isotherms, Brewster angle microscopy (BAM) and surface dilatational rheological parameters for light induced trans–cis isomerisation at the air/water interface. Using appropriate irradiation Langmuir films of the two isomers can be characterised almost separately. The BAM images confirm a homogeneous structure for the two isomers, differing only in reflectivity. The surface dilatational behaviour and the π/A isotherms of the films of maximum trans and cis conformation differ strongly. The monolayer of maximum trans conformation exhibit increasing surface dilatational elasticity and viscosity when the monolayer is compressed. The resulting surface rheological behaviour is viscoelastic with a high dilatational viscosity. The surface pressure increases up to 50 mN m−1before it starts to level off. The surface pressure of a monolayer with maximum cis content starts to increase at lower surface coverage and exceeds the values of the trans conformer film over a wide range of surface coverage, but it levels off at 35 mN m−1. Starting from 0.45 nm2per repeated unit the monolayer becomes highly compressible. The results are explained by an increase of the minimum average surface demand of the copolymer azobenzene side-groups for the cis isomer and a folding of the monolayer with increasing surface pressure.