LC Droplets  TBD.
Electro-Active Ionic Elastomers Motivated   by   the   low   voltage   driven   actuation   of   ionic   Electroactive   Polymers   (iEAPs)   [1]   [2],     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).[3]   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. [1]   Y.   Bar-Cohen,   Electroactive   Polyer   Actuators   as   Artficial   Muscles:   Reality,   Potential   and              Challenges, SPIE Press, Bellingham, 2004. [2] O. Kim, S. J. Kim, M. J. Park, Chem. Commun. 2018, 54, 4895. [3] 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 Fibers Airbrushing   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.  [1]   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. [2]    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   [1]   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. [1]   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 Elastomers In   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 Crystal Liquid-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.