Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Soft Matter. 2019 Apr 10;15(15):3111-3121. doi: 10.1039/c8sm02330a.
Gelled lyotropic liquid crystals (LLCs) are highly tunable multi-component materials. By studying a selection of low molecular weight gelators (LMWGs), we find gelators that form self-assembled gels in LLCs without influencing their phase boundaries. We studied the system H2O/NaCl-Genapol LA070 in the presence of (a) the organogelators 12-hydroxyoctadecanoic acid (12-HOA) and 1,3:2,4-dibenzylidene-d-sorbitol (DBS) and (b) the hydrogelators N,N'-dibenzoyl-l-cystine (DBC) and a tris-amido-cyclohexane derivative (HG1). Visual phase studies and oscillation shear frequency sweeps confirmed that 12-HOA acts as co-surfactant (stabilizing the lamellar Lα phase and destabilizing the hexagonal H1 phase), thus preventing gelation. Conversely, DBS was a potent gelator for LLCs, with the phase boundaries un-influenced by the presence of DBS; gelled lamellar Lα, and softly-gelled hexagonal H1 phases are formed. For the hydrogelator DBC, the LLC phase boundaries were only slightly altered, but no gelled LLCs were formed. For the hydrogelator HG1, however, the phase boundaries were unaffected while gelled lamellar Lα and softly-gelled hexagonal H1 phases were formed. Temperature-dependent rheology measurements demonstrated that by changing the DBS or the HG1 concentration, the sol-gel transition temperature of the gelled lamellar Lα phase can be adjusted such that (a) Tsol-gel is below the Lα-isotropic phase transition (DBS, HG1 mass fraction η = 0.0075) and (b) Tsol-gel is above the gelled Lα-isotropic phase transition (DBS, HG1 η = 0.015). This opens the possibility of temporal materials control by addressing phase transitions in different orders. As this system contains oil and water, both the organogelator DBS and the hydrogelator HG1 can gel these LLCs, but this clearly does not apply to all organogelators/hydrogelators. The study indicates that careful optimization of LMWGs is required to avoid interaction with the surfactant layer and to optimize the Tsol-gel value, which is important for the application of LMWGs in gelled LLCs.
胶状溶致液晶（LLC）是一种高度可调的多组分材料。通过研究一系列低分子量凝胶剂（LMWG），我们发现了一些在 LLC 中形成自组装凝胶而不影响其相边界的凝胶剂。我们研究了 H2O/NaCl-Genapol LA070 体系中存在（a）有机凝胶剂 12-羟基硬脂酸（12-HOA）和 1,3:2,4-二亚苄基-d-山梨糖醇（DBS）和（b）水凝胶剂 N,N'-二苯甲酰基-l-胱氨酸（DBC）和一种三酰胺环己烷衍生物（HG1）时的情况。可见的相研究和振荡剪切频率扫描证实，12-HOA 作为共表面活性剂（稳定层状 Lα 相并使六方 H1 相失稳），从而防止凝胶形成。相反，DBS 是 LLC 的有效凝胶剂，其相边界不受 DBS 的影响；形成凝胶层状 Lα 和软凝胶六方 H1 相。对于水凝胶剂 DBC，LLC 相边界仅略有改变，但未形成凝胶 LLC。然而，对于水凝胶剂 HG1，相边界不受影响，同时形成凝胶层状 Lα 和软凝胶六方 H1 相。温度依赖性流变学测量表明，通过改变 DBS 或 HG1 的浓度，可以调节凝胶层状 Lα 相的溶胶-凝胶转变温度，使得（a）Tsol-gel 低于 Lα-各向同性相变（DBS，HG1 质量分数 η=0.0075），（b）Tsol-gel 高于凝胶层状 Lα-各向同性相变（DBS，HG1 η=0.015）。这为通过处理不同顺序的相变来实现临时材料控制开辟了可能性。由于该系统含有油和水，因此有机凝胶剂 DBS 和水凝胶剂 HG1 都可以使这些 LLC 凝胶化，但这显然不适用于所有有机凝胶剂/水凝胶剂。该研究表明，需要仔细优化 LMWG 以避免与表面活性剂层相互作用并优化 Tsol-gel 值，这对于 LMWG 在凝胶 LLC 中的应用很重要。
Zotero 插件