Electro-Active Ionic Elastomers Motivated by the low voltage driven actuation of ionic Electroactive Polymers (iEAPs)  , recently we began investigating ionic elastomers. In this talk I will discuss the preparation, physical characterization and electric bending actuation properties of two novel ionic elastomers; ionic polymer electrolyte membranes (iPEM), and ionic liquid crystal elastomers (iLCE). Both materials can be actuated by low frequency AC or DC voltages of less than 1 V. The bending actuation properties of the iPEMs are outperforming most of the well-developed iEAPs, and the not optimized first iLCEs are already comparable to them. Ionic liquid crystal elastomers also exhibit superior features, such as the alignment dependent actuation, which offers the possibility of pre-programed actuation pattern at the level of cross-linking process. Additionally, multiple (thermal, optical and electric) actuations are also possible. We also study issues with compliant electrodes and possible soft robotic applications. Y. Bar-Cohen, Electroactive Polyer Actuators as Artficial Muscles: Reality, Potential and Challenges, SPIE Press, Bellingham, 2004. O. Kim, S. J. Kim, M. J. Park, Chem. Commun. 2018, 54, 4895. C. Feng, C. P. H. Rajapaksha, J. M. Cedillo, C. Piedrahita, J. Cao,V. Kaphle, B. Lussem, T. Kyu, A. I. Jákli, Macromol. Rapid Commun. 2019, 1900299.
Research Interests and Cover Images
Responsive Liquid Crystal/Polymer FibersAirbrushing of a homogeneous LC and polymer solution to make LC/polymer as well electro-spinning and force spinning are techniques via which piezoelectric and responsive fibers are obtained. Quantitative measurements of the optical response of liquid crystal (LC)/polymer composite fiber mats to toluene and acetone vapors have been. Reported Our analyses in comparison with control measurements of pure LC film and polymer fiber mats show that the chemicals can pass through the polymer sheath of the fibers and be absorbed by the LC in the core. This absorption changes the optical properties of the fiber mats which can be used to produce sensitive and reversible detection. The sensitive response at low concentrations of both acetone and toluene demonstrates the feasibility of using these fibers for highly sensitive and specific sensors for volatile organic compound detection. A simple process is demonstrated to clad conventional monofilament fibers with low molecular weight liquid crystals stabilized by an outer polymer sheath. The fibers retain the responsive properties of the LCs in a highly flexible/drapable format. The monofilament core makes these fibers much more rugged with a magnified response to external stimuli when compared to previously reported LC core fibers produced by electrospinning or airbrushing. The microscopic structure and the optical properties of round and flattened fibers are reported.  The sensitivity of the response of individual fibers can be tuned over a broad range by varying the composition of the liquid crystals. Complex fabrics can be easily woven from fibers that respond to different external stimuli, such as temperature variation, chemicals and pressure. The fabrics can be fashioned into garments that can sense and report the state of health or the environment. Yu Guan, Dena Mae Agra-Kooijman, Shaohai Fu, Antal Jákli, and John L. West, “Responsive Liquid-Crystal-Clad Fibers for Advanced Textiles and Wearable Sensors”, Advanced Materials, 1902168 (2019); DOI: 10.1002/adma.201902168
X-Ray Studies on Dimers and Trimers – More Structural Studies Odd-even effects, oscillations in properties of materials comprised of an odd or even number of connected repeating units, are well-known phenomena in materials science. In organic materials, they are usually associated with the number of methylene groups in aliphatic chains. In this work, we unveil multiple signatures of a new odd-even effect in liquid crystals that occurs at the larger scale of molecular moieties that by themselves express liquid crystalline behavior. We demonstrated  that oligomeric liquid crystals, with n=1-4 number of rigid mesogenic segments connected by flexible aliphatic chains with an odd number of methylene groups, produce an odd-even effect in optical anisotropy and the bend elastic constant of the liquid crystal oligomer. This effect is different from the usual odd-even effects with respect to the parity of carbon atoms in an aliphatic chain and can be understood in term of the average molecular shape and the associations between n-mers based on the packing of these shapes. We also show that, although there is no long-range electron density modulation, careful analysis of synchrotron SAXS results can provide important information about the molecular associations in the N and NTB phases that other techniques cannot access. This novel odd-even effect opens a new mode to optimize phase and optical behavior.  Rony Saha, Greta Babakhanova, Zeinab Parsouzi, Mojtaba Rajabi, Prabesh Gyawali, Chris Welch, Georg H. Mehl, James Gleeson, Oleg D. Lavrentovich, Samuel Sprunt and Antal Jákli, “Oligomeric odd-even effect in liquid crystals”, Materials Horizons, published online, June 19. 2019, DOI: 10.1039/C9MH00428A
Liquid Crystal ElastomersIn a recently published report, we fabricated smart assemblies with functional resemblance to gecko toe pads at both the skin and the muscle levels. Integrative soft-lithography was used for micro- texturing of liquid crystal elastomer (LCE) thin films as artificial muscles. LCEs were chosen as they possess features of both rubbers (elasticity) and liquid crystals (responsiveness) with outstanding shape shifting characteristics. Prior to this work, LCEs were used in a variety of forms ranging from simple bending actuators to accordion-like ribbons and sophisticated voxelated 3D structures.
Biological Sensing With Liquid CrystalLiquid-crystal–based biosensors utilize the high sensitivity of liquid-crystal alignment to the presence of amphiphiles adsorbed to one of the liquid-crystal surfaces from water. They offer inexpensive, easy optical detection of biologically relevant molecules such as lipids, proteins, and cells. The techniques use linear or circular polarizers to analyze the alignment of the liquid crystal.