An official website of the United States government
Abstract Liquid crystalline elastomers (LCEs) that retain the cholesteric phase (CLCEs) are soft, polymeric materials that retain periodic structure and exhibit a selective reflection. While prior studies have examined thermochromism in CLCEs, the association of temperature change and reflection wavelength shift has been limited to 1.4 nm °C−1. Here, CLCEs with intra‐mesogenic supramolecular bonds are prepared to enhance tunability as well triple the rate (e.g., 4.8 nm °C−1). Specifically, these materials incorporate liquid crystalline monomers based on dimerized oxy‐benzoic acid (OBA) derivatives. Increasing the concentration of the OBA comonomers increases the magnitude of red‐shifting thermochromism of the selective reflection. At and above a threshold concentration, the selective reflection in the CLCEs can disappear upon heating, analogous to on‐off “switching.” Further, the introduction of the supramolecular bonds within the CLCE enable mechanical programming and enhanced one‐time tunable thermochromism via a one‐way shape memory process. Accordingly, this research could enable functional use in low temperature sensitive optical elements, fail‐safe thermal indicators for food packaging, and smart window coatings.
more »
« less
Should I stay or should I flow? An exploration of phase‐separated metallosupramolecular liquid crystal polymers
Abstract Dynamic liquid crystalline polymers (dLCPs) incorporate both liquid crystalline mesogens and dynamic bonds into a single polymeric material. These dual functionalities impart order‐dependent thermo‐responsive mechano‐optical properties and enhanced reprocessability/programmability enabling their use as soft actuators, adaptive adhesives, and damping materials. While many previous works studying dynamic LCPs utilize dynamic covalent bonds, metallosupramolecular bonds provide a modular platform where a series of materials can be accessed from a single polymeric feedstock through the variation of the metal ion used. A series of dLCPs were prepared by the addition of metal salts to a telechelic 2,6‐bisbenzimidazolylpyridine (Bip) ligand endcapped LCP to form metallosupramolecular liquid crystal polymers (MSLCPs). The resulting MSLCPs were found to phase separate into hard and soft phases which aids in their mechanical robustness. Variations of the metal salts used to access these materials allowed for control of the thermomechanical, viscoelastic, and adhesive properties with relaxations that can be tailored independently of the mesogenic transition. This work demonstrates that by accessing phase separation through the incorporation of metallosupramolecular moieties, highly processable yet robust MSLCP materials can be realized. This class of materials opens the door to LCPs with bulk flow behavior that can also be utilized as multi‐level adhesives.
more »
« less
- PAR ID:
- 10614861
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 31
- Issue:
- 25
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Supramolecular polymer networks exhibit unique and tunable thermodynamic and dynamic properties that are attractive for a wide array of applications, such as adhesives, rheology modifiers, and compatibilizers. Coherent states (CS) field theories have emerged as a powerful approach for describing the possibly infinite reaction products that result from associating polymers. Up to this point, CS theories have focused on relatively simple polymer architectures. In this work, we develop an extension of the CS framework to study polymers with reversible bonds distributed along the polymer backbone, opening a broad array of new materials that can be studied with theoretical methods. We use this framework to discern the role of reactive site placement on sol–gel phase behavior, including the prediction of a microstructured gel phase that has not been reported for neutral polymer gels. Our results highlight the subtleties of thermodynamics in supramolecular polymers and the necessity for theories that capture them.more » « less
-
Abstract Dynamic liquid crystal elastomers (LCEs) are a class of polymer networks characterized by the inclusion of both liquid crystalline monomers and dynamic covalent bonds. The unique properties realized through the combination of these moieties has produced a plethora of stimuli‐responsive materials to address a range of emerging technologies. While previous works have studied the incorporation of different dynamic bonds in LCEs, few (if any) have studied the effect of the specific placement of the dynamic bonds within an LCE network. A series of dynamic LCE networks were synthesized using a generalizable approach that employs a tandem thiol‐ene/yne chemistry which allows the location of the dynamic disulfide bond to be varied while maintaining similar network characteristics. When probing these systems in the LC regime, the thermomechanical properties were found to be largely similar. It is not until elevated temperatures (160–180 °C) that differences in the relaxation activation energies of these systems begin to materialize based solely on differences in placement of the dynamic bond throughout the network. This work demonstrates that through intentional dynamic bond placement, stress relaxation times can be tuned without affecting the LCE character. This insight can help optimize future dynamic LCE designs and achieve shorter processing times.more » « less
-
Pluripotency, which is defined as a system not fixed as to its developmental potentialities, is typically associated with biology and stem cells. Inspired by this concept, we report synthetic polymers that act as a single “pluripotent” feedstock and can be differentiated into a range of materials that exhibit different mechanical properties, from hard and brittle to soft and extensible. To achieve this, we have exploited dynamic covalent networks that contain labile, dynamic thia-Michael bonds, whose extent of bonding can be thermally modulated and retained through tempering, akin to the process used in metallurgy. In addition, we show that the shape memory behavior of these materials can be tailored through tempering and that these materials can be patterned to spatially control mechanical properties.more » « less
-
Metal-ion-containing soft materials include metallogels, metal-organic frameworks, and coordination polymers. These materials show commercial value in catalysis, hydrogen storage, and electronics. Metal-containing soft materials reported to date are structurally weak, falling short of a Young’s modulus typical of engineering-grade materials. We report herein that inclusion of an antisolvent in metal-thiolate metallogel synthesis results in a colloidal sol, where the colloids comprise amorphous metal-organic complexes. Upon desolvation, the colloids coalesce to form a solid phase that is both gel like and glass like. This solid phase is structurally amorphous, comprises continuous networks similar to organic polymers, and has stiffness observed in polymeric materials with extended structure, yet contains a superstoichiometric amount of metal relative to organic ligand. The solid phase is therefore a rigid, amorphous metal-rich (RAMETRIC) material. Highlighting the rigidity, the Young’s modulus of the gel-phase material is 1,000× greater than metallogels comprised of the same constituent building blocks.more » « less
