High strain actuation liquid crystal elastomers via modulation of mesophase structure
High strain actuation liquid crystal elastomers via modulation of mesophase structure
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DOI：
10.1039/c7sm01380a
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发表时间：
2017-11-04
期刊：
影响因子：
3.4
通讯作者：
Yakacki, Christopher M.
中科院分区：
文献类型：
--
作者：
Saed, Mohand O.;Volpe, Ross H.;Yakacki, Christopher M.
液晶弹性体（LCE）中中间相的控制是利用其独特的刺激响应特性的关键方面。很少有研究直接比较了近晶和非晶主链LCE。传统上认为液晶基元的核和合成路线决定了液晶的相行为。在这项研究中，我们假设在主链LCE系统中的LC相的调谐可以通过改变间隔长度，同时保持相同的液晶元（RM 257）。通过增加沿着间隔基主链（C2至C11）含有2至11个碳的二硫醇烷基间隔基的长度，我们可以将中间相从半晶相调节为近晶相，将半晶相至各向同性转变温度调整为90至140摄氏度，并将平均工作容量从128 kJ m（-3）增加至262 kJ m（-3）。对于C6、C9和C11间隔物，在室温下实现了导致近晶C相的相纳米偏析。在形状切换系统中，这体现在令人印象深刻的700%的致动行程中。在从室温加热时，这些样品转变成均相，随后转变成各向同性相。此外，这种分离沿着聚合物链结晶度发生，这将网络的模量增加一个数量级;然而，结晶速率高度依赖于间隔物长度，并且可以在C11间隔物的5分钟和较短间隔物的24小时之间变化。本研究提出了几种可能性的硫醇-丙烯酸酯反应的热机械和液晶性能的LCE调制，并讨论了其潜在的生物医学应用。
Control of the mesophase in liquid crystalline elastomers (LCEs) is a critical aspect in harnessing their unique stimuli-responsive properties. Few studies have compared nematic and smectic main-chain LCEs in a direct way. Traditionally, it is believed that the mesogen core and synthetic route determines the phase behavior. In this study, we hypothesized that tuning the LC phases in main-chain LCE systems can be achieved by varying the spacer length while maintaining the same mesogen (RM257). By increasing the length of dithiol alkyl spacers containing two to eleven carbons along the spacer backbone (C2 to C11), we can modulate the mesophase from nematic to smectic, tailor the nematic to isotropic transition temperature between 90 and 140 degrees C, and increase the average work capacity from 128 to 262 kJ m(-3). Phase nano-segregation resulting in the smectic C phase is achieved at room temperature for the C6, C9, and C11 spacers. In a shape switching system, this manifests in impressive actuation stroke of 700%. Upon heating from room temperature, these samples transition into the nematic and later, the isotropic phase. Furthermore, this segregation occurs along with polymer chain crystallinity, which increases the modulus of the networks by an order of magnitude; however, the crystallization rate is highly time dependent on the spacer length and can vary between 5 minutes for the C11 spacer and 24 hours for shorter spacers. This study presents several possibilities of a thiol-acrylate reaction in modulation of the thermomechanical and liquid-crystalline properties of LCEs and discusses their potential use for biomedical applications.