Spontaneous ordering in polymeric nematic liquids and solids

Polymers can spontaneously orientationally order when rod-like elements form the main chain or are pendant as side chains from the backbone. There exists strong coupling between chains and nematic order. Thus unlike simple rod liquids where the molecules remain undistorted on ordering, these molecules become elongated or flattened. Shape change is at the heart of polymer properties and new character enters the liquid crystal problem. Characteristic ordering of both main and side chain nematic melts, and the concomitant shape response will be discussed. Polymer networks (elastomers) exhibit rubber elasticity, that is resistance to macroscopic shape change reflecting the loss of freedom of chains distorted by applied stress. On the other hand spontaneous microscopic shape changes resulting from nematic ordering, bring with them the spontaneous macroscopic shape changes seen in experiments on nematic monodomain elastomers. The anisotropy of chain shape at chemical crosslinking is permanently recorded. Conversely there are stress-nematic effects unknown in simple nematics.

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Internal constraints and arrested relaxation in main-chain nematic elastomers

Nature Communications ◽

10.1038/s41467-021-21036-3 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Takuya Ohzono ◽

Kaoru Katoh ◽

Hiroyuki Minamikawa ◽

Mohand O. Saed ◽

Eugene M. Terentjev

Keyword(s):

Mechanical Properties ◽

Main Chain ◽

Polymer Networks ◽

Nematic Order ◽

Nematic Elastomers ◽

Nematic Director ◽

Highly Nonlinear ◽

Nonlinear Mechanical ◽

Liquid Crystal Elastomers ◽

Memory Applications

AbstractNematic liquid crystal elastomers (N-LCE) exhibit intriguing mechanical properties, such as reversible actuation and soft elasticity, which manifests as a wide plateau of low nearly-constant stress upon stretching. N-LCE also have a characteristically slow stress relaxation, which sometimes prevents their shape recovery. To understand how the inherent nematic order retards and arrests the equilibration, here we examine hysteretic stress-strain characteristics in a series of specifically designed main-chain N-LCE, investigating both macroscopic mechanical properties and the microscopic nematic director distribution under applied strains. The hysteretic features are attributed to the dynamics of thermodynamically unfavoured hairpins, the sharp folds on anisotropic polymer strands, the creation and transition of which are restricted by the nematic order. These findings provide a new avenue for tuning the hysteretic nature of N-LCE at both macro- and microscopic levels via different designs of polymer networks, toward materials with highly nonlinear mechanical properties and shape-memory applications.

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Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts

Science Advances ◽

10.1126/sciadv.aay5349 ◽

2020 ◽

Vol 6 (13) ◽

pp. eaay5349 ◽

Cited By ~ 2

Author(s):

James T. Waters ◽

Shucong Li ◽

Yuxing Yao ◽

Michael M. Lerch ◽

Michael Aizenberg ◽

...

Keyword(s):

Liquid Crystalline ◽

Incident Light ◽

Side Chain ◽

Chiral Structure ◽

Left Handed ◽

Complex Modes ◽

Nematic Director ◽

Macroscopic Shape ◽

Shape Changes ◽

Director Orientation

Photoresponsive liquid crystalline elastomers (LCEs) constitute ideal actuators for soft robots because their light-induced macroscopic shape changes can be harnessed to perform specific articulated motions. Conventional LCEs, however, do not typically exhibit complex modes of bending and twisting necessary to perform sophisticated maneuvers. Here, we model LCE microposts encompassing side-chain mesogens oriented along a magnetically programmed nematic director, and azobenzene cross-linkers, which determine the deformations of illuminated posts. On altering the nematic director orientation from vertical to horizontal, the post’s bending respectively changes from light-seeking to light-avoiding. Moreover, both modeling and subsequent experiments show that with the director tilted at 45°, the initially achiral post reversibly twists into a right- or left-handed chiral structure, controlled by the angle of incident light. We exploit this photoinduced chirality to design “chimera” posts (encompassing two regions with distinct director orientations) that exhibit simultaneous bending and twisting, mimicking motions exhibited by the human musculoskeletal system.

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Effect of Nematic Order Coupling on the Phase Diagrams of Side-Chain Polymer Gels with Liquid Crystal Solvent

e-Polymers ◽

10.1515/epoly.2006.6.1.878 ◽

2006 ◽

Vol 6 (1) ◽

Author(s):

Richard Vendamme ◽

Ulrich Maschke

Keyword(s):

Phase Diagram ◽

Polymer Network ◽

Polymer Networks ◽

Polymer Gels ◽

Side Chain ◽

Miscibility Gap ◽

Polymer Backbone ◽

Chain Polymer ◽

Nematic Order ◽

Solvent Lead

AbstractWe have explored the influence of nematic order coupling on the swelling and phase diagram of polymer networks in nematogenic low molar weight LC solvent, in view of the increasing importance of such systems in advanced optical devices. Firstly, one isotropic polyacrylate network and one nematic sidechain polyacrylate network is prepared. Immersing these two networks in nematic LC solvent lead to the formation of well-defined polymer gels with LC solvents and allow us to establish the phase diagram of these relatively new materials in the concentration-temperature frame. Results were critically analysed as a function of temperature and network nature (isotropic or nematic). We demonstrate that in the case of gel made from an isotropic polymer network, the LC solvents fails to form a nematic phase inside the gel due to the lack of anisotropic coupling. Moreover, in that case the gel shrinks below TNI Solvent because of a strong “entropic” incompatibility between the isotropic flexible coils and the LC nematogens. However, the situation is drastically different in the case of LC side-chain network due to a strong coupling of the nematic order between the mesogens of the solvents and those of the polymer backbone. In that case, tremendous distortions appear in the phase-diagram, in which we especially emphasize the apparition of a stable nematic gel phase and a miscibility gap between TNI Solvent and TNI Gel. Finally, results are critically examined and compared to the few studies found in the literature.

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Faculty Opinions recommendation of Main chain and side chain dynamics of oxidized flavodoxin from Cyanobacterium anabaena.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1002693.29208 ◽

2001 ◽

Author(s):

Vincent Rotello

Keyword(s):

Main Chain ◽

Side Chain ◽

Chain Dynamics ◽

Cyanobacterium Anabaena ◽

Side Chain Dynamics

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Substrate Scope for Human Histone Lysine Acetyltransferase KAT8

International Journal of Molecular Sciences ◽

10.3390/ijms22020846 ◽

2021 ◽

Vol 22 (2) ◽

pp. 846

Author(s):

Giordano Proietti ◽

Yali Wang ◽

Chiara Punzo ◽

Jasmin Mecinović

Keyword(s):

Main Chain ◽

Coenzyme A ◽

Side Chain ◽

Histone H4 ◽

Chemical Probes ◽

Acetyl Coenzyme A ◽

Acetyl Coenzyme ◽

Histone Lysine ◽

Lysine Acetyltransferase

Biomedically important histone lysine acetyltransferase KAT8 catalyses the acetyl coenzyme A-dependent acetylation of lysine on histone and other proteins. Here, we explore the ability of human KAT8 to catalyse the acetylation of histone H4 peptides possessing lysine and its analogues at position 16 (H4K16). Our synthetic and enzymatic studies on chemically and structurally diverse lysine mimics demonstrate that KAT8 also has a capacity to acetylate selected lysine analogues that possess subtle changes on the side chain and main chain. Overall, this work highlights that KAT8 has a broader substrate scope beyond natural lysine, and contributes to the design of new chemical probes targeting KAT8 and other members of the histone lysine acetyltransferase (KAT) family.

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