Mixed Alkylsilane Functionalized Surfaces for Simultaneous Wetting and Homeotropic Anchoring of Liquid Crystals
Mixed Alkylsilane Functionalized Surfaces for Simultaneous Wetting and Homeotropic Anchoring of Liquid Crystals
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DOI：
10.1021/am201026r
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发表时间：
2011-11-01
影响因子：
9.5
通讯作者：
Schwartz, Daniel K.
中科院分区：
文献类型：
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作者：
Noonan, Patrick S.;Shavit, Amit;Schwartz, Daniel K.
表面功能化的自组装单层（SAM）形成的混合物的两种烷基硅烷具有不同的链长已被设计为同时提高液晶（LC）的润湿性和促进垂面锚定的LC。大多数化学官能化的表面（例如，长烷基链SAM）具有低的表面能，并导致差的LC润湿性，抑制LC渗透到微结构化表面中，有时导致LC从表面去湿。然而，用十八烷基三乙氧基硅烷（C18）和乙基三乙氧基硅烷（C2）的混合SAM改性的表面表现出非常低的LC接触角，同时提供垂面锚定。椭圆偏振法被用来关联的沉积溶液中的C18的表面覆盖的C18在混合单层的体浓度;这些体和表面浓度被发现是相等的实验不确定性内。发现LC接触角与表面覆盖密度非单调相关，在C18表面覆盖度为0.26 +/-0.08时具有最小值（14.4 +/-0.1度）。在>= 0.11 +/-0.04的C18表面覆盖率下，在观察到LC接触角最小值的情况下，实现了各向异性LC锚定。使用微柱阵列传感器基板证明了这种方法的实际应用，表面改性。当阵列用常规C18 SAM官能化时，LC不渗透阵列并表现出47.4 +/-0.50度的接触角。然而，当用C18/C2混合SAM官能化时，LC材料成功地渗透并润湿相同的微结构化基底，同时仍表现出所需的垂面锚定。
Surfaces functionalized with a self-assembled monolayer (SAM) formed from a mixture of two alkylsilanes with different chain lengths have been designed to simultaneously improve the liquid crystal (LC) wettability and promote homeotropic anchoring of the LC. Most chemically functionalized surfaces (e.g., long alkyl chain SAMs) that promote homeotropic alignment of LC possess low surface energy and result in poor LC wettability, inhibiting LC infiltration into microstructured surfaces and sometimes resulting in LC dewetting from the surface. However, a surface modified with a mixed SAM of octadecyltriethoxysilane (C18) and ethyltriethoxysilane (C2) exhibited very low LC contact angle while providing homeotropic anchoring. Ellipsometry was used to correlate the bulk concentration of C18 in the deposition solution to the surface coverage of C18 in the mixed monolayer; these bulk and surface concentrations were found to be equal within experimental uncertainty. The LC contact angle was found to depend nonmonotically with the surface coverage density, with a minimum (14.4 +/- 0.1 degrees) at a C18 surface coverage of 0.26 +/- 0.08. Homeotropic LC anchoring was achieved at a C18 surface coverage of >= 0.11 +/- 0.04, in the regime where a minimum in the LC contact angle was observed. The practical application of this approach to surface modification was demonstrated using a micropillar array sensor substrate. When the array was functionalized with a conventional C18 SAM, the LC did not infiltrate the array and exhibited a contact angle of 47.4 +/- 0.50 degrees. However, the LC material successfully infiltrated and wetted the same microstructured substrate when functionalized with a C18/C2 mixed SAM, while still exhibiting the desired homeotropic anchoring.