8532 DOI: 10.1021/la8031094 Langmuir 2009, 25(15), 8532–8537Published on Web 12/24/2008

pubs.acs.org/Langmuir

© 2009 American Chemical Society

Self-Assembled Liquid-Crystal Gels in an Emulsion†

Xia Tong,‡ Jong Won Chung,§ Soo Young Park,§ and Yue Zhao*,‡

‡D�epartement de Chimie, Universit�e de Sherbrooke, Sherbrooke, Qu�ebec, Canada J1K 2R1, and §School ofMaterials Science and Engineering, ENG445, Seoul National University, San 56-1, Shillim-dong, Kwanak-ku,

Seoul 151-744, Korea

Received September 22, 2008. Revised Manuscript Received November 8, 2008

Self-assembled liquid-crystal (LC) gels in an emulsion (i.e., LC gel droplets dispersed in aqueous solution) wereprepared and investigated for the first time. The aggregation of gelator molecules confined in the LC droplets results inthe formation of circular and highly folded nanoscale fibers, in contrast to the extended ones formed in the bulk LC gel.Another manifestation of the confinement effect is that the electrooptical behavior (switching times and contrast) ofsingle LC gel droplets is largely determined by the droplet size. By bridging LC gels and LC emulsions, this studyintroduces a new hybrid LC system and offers new possibilities of exploring functional LC materials.

Introduction

In recent years, more and more research effort onliquid crystals (LCs) has been directed to exploring their usein new materials aimed at applications other than liquid-crystaldisplays (LCDs). Among them, the LC-in-water emulsion(i.e., with LC droplets dispersed in aqueous solution) hasreceived increasing attention.1-4 Though it has long been estab-lished that nematic LCs confined in small spherical cavitiescan display a rich variety of configurations determined by anumber of factors such as the nature of LC molecular an-choring at the interface,5,6 most studies have been conductedin relation to polymer-dispersed liquid crystals (PDLC) whereLC droplets are dispersed in a polymer matrix.3,7,8 Some recentwork on the LC-in-water emulsion has shown potential. Mostnotably, Fernandez-Nieves et al. prepared a monodispersenematic LC emulsion and obtained optically and geometricallyanisotropic solid particles through photopolymerizationthat locked in the LC orientation inside the droplets; opticaltweezing was used to rotate such particles, suggesting their usein microfluidic applications.1 Keeping in mind the exploitationof the large interface in LC emulsions for possible sensingapplications, Abbott and co-workers succeeded in assembling apolyelectrolyte multilayer film at the droplet-water interfaceand showed that the transition of LC configurations insidethe droplets could be sensitive to the adsorption of asurfactant (analyte).2

On another front, self-assembled LC gels, first reported byKato’s group,9 are another emerging LC system of interest.9-20

They are characterized in the LC by the presence of a smallnumber of nanoscale fibrous aggregates formed by a gelator. Theinteraction of the nanofibers with the LC host can impartinteresting properties to this type of LC material. These includebistable nematic LC states11 and scattering-based electroopticalswitching,12,16 to name a few examples. Using gelators containingazobenzene chromophores in their structures, patterning13 anddiffraction gratings17 can also be obtained fromLCgels as a resultof the trans-cis photoisomerization of azobenzene. Self-as-sembled LC gels are usually prepared by dissolving a gelator inan LC host at elevated temperature (in the isotropic phase) andthen cooling the mixture to induce the aggregation of gelatormolecules. Generally, gelator molecules have structures promot-ing highly specific intermolecular interactions (hydrogen bondinginmost cases) that favor preferential 1Dgrowthor crystallization.This often results in nanoscale fibrous aggregates whose networkcan gel the LC either in the isotropic or nematic phase dependingon the clearing (nematic-to-isotropic phase transition) tempera-ture of the LC.

In this article, we report the first study on a self-assembled LCgel in an emulsion (i.e., a new hybrid material of the above-citedtwo types of LC systems). First, it is of fundamental interest toknowwhether gelation can occur inside the spherical LC cavities,under confinement, resulting in LC gel droplets dispersed inaqueous solution. Second, should fibrous aggregates be formed,the question can be raised as to how they can affect the LCdirector configuration and the electro-optical behavior of thedroplets. For bulkLCgels, gelation is indicated by the loss of flowof the LC/gelator mixture on cooling. Obviously, this indication

† Part of the Gels and Fibrillar Networks: Molecular and Polymer Gels andMaterials with Self-Assembled Fibrillar Networks special issue.

*Corresponding author. E-mail: yue.zhao@usherbrooke.ca.(1) Fernandez-Nieves, A.; Cristobal, G.; Garces-Chavez, V.; Spalding, G. C.;

Dholakia, K.; Weitz, D. A. Adv. Mater. 2005, 17, 680.(2) Tjipto, E.; Cadwell, K. D.; Quinn, J. F.; Johnston, A. P. R.; Abbott, N. L.;

Caruso, F. Nano Lett. 2006, 6, 2243.(3) Tixier, T.; Heppenstall-butler,M.; Terentjev, E.M.Langmuir 2006, 22, 2365.(4) Woltman, S.; Jay, G.; Crawford, G. P. Nat. Mater. 2007, 6, 929.(5) Drzaic, P. S. J. Appl. Phys. 1986, 60, 2142.(6) Erdmann, J. H.; Zumer, S.; Doane, J. W. Phys. Rev. Lett. 1990, 64, 1907.(7) Cairns, D. R.; Sibulkin,M.; Crawford,G. P.Appl. Phys. Lett. 2001, 78, 2643.(8) Liquid Crystals in Complex Geometries Formed by Polymers and Porous

Networks; Crawford, Gp. P., Zumer, S., Eds.; Taylor & Francis: London,1996.(9) Mizoshita, N.; Hanabusa, K.; Kato, T. Adv. Mater. 1999, 11, 392.(10) Kato, T.;Mizoshita, N.; Kishimoto, K.Angew. Chem., Int. Ed. 2006, 45, 38.(11) Mizoshita, N.; Suzuki, Y.; Hanabusa, Y.; Kato, T. Adv. Mater. 2005, 17,

692.

(12) Suzuki, Y.; Mizoshita, N.; Hanabusa, K.; Kato, T. J. Mater.Chem. 2003,13, 2870.

(13) Moriyama, M.; Mizoshita, N.; Yokota, T.; Kishimoto, K.; Kato, T. Adv.Mater. 2003, 15, 1335.

(14) Guan, L.; Zhao, Y. Chem. Mater. 2000, 12, 3667.(15) Guan, L.; Zhao, Y. J. Mater. Chem. 2001, 11, 1339.(16) Tong, X.; Zhao, Y. J. Mater. Chem. 2003, 13, 1491.(17) Tong, X.; Zhao, Y. Adv. Mater. 2003, 15, 1431.(18) Tong, X.; Zhao, Y. J. Am. Chem. Soc. 2007, 129, 6372.(19) Janssen, R. H. C.; Stumpflen, V.; Broer, D. J.; Bastiaansen, C. W.;

Tervoort, T. A.; Smith, P. J. Appl. Phys. 2000, 88, 161.(20) Tolksdorf, C.; Zentel, R. Adv. Mater. 2001, 13, 1307.

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cannot be utilized for an emulsion. Toovercome this difficulty,weused a special gelator, 1-cyano-trans-1,2-bis(3

0,5

0-bis-trifluoro-

methyl-biphenyl)ethylene (CN-TFMBE). This gelator displaysaggregation-induced enhanced emission (AIEE) by being highlyfluorescent in the solid (aggregated) states but virtually nonfluor-escent in the solubilized state.21 Previous studies found thatCN-TFMBE is able to gel organic solvents22 and LCs23 whileforming highly fluorescent fibrous aggregates as a result of theπ-π stacking interactions of the aromatic cores and the interac-tions induced by CF3 units. The use of this peculiar propertymakes it possible to confirm the formation of fibrous aggregatesinside emulsified LC droplets in aqueous solution. As will beshown, compared to the bulk LC gel, the LC gel in an emulsionexhibits different electrooptical behavior. Moreover, the gelationoccurred inside the LC droplets under the confinement results inthe formation of circular and highly folded fibrous aggregates, incontrast to the extended fibers formed in the bulkLC. BybridgingLC gels and LC emulsions, this study demonstrates a new type ofhybrid LC system and thus opens the door to exploring newfunctional LC materials.

Experimental Section

Figure 1 shows the chemical structures of the CN-TFMBEgelator and the nematic LC, E7 (purchased from Merck) havingTni≈ 68 �C in the pure state. The typical procedure for preparingan LC gel emulsion is detailed as follows. Weighed E7 andCN-TFMBE (2 wt% with respect to the LC) were first dissolvedin THF, after removal of the solvent (drying at 40 �C in a vacuumoven), an LC gel was formed at room temperature. Then, the as-prepared LC gel was heated to 140 �C to melt all aggregates ofCN-TFMBE to obtain a homogeneous LC/gelator mixture. Thismixture was then cooled to about 65 �C, at which temperature noaggregation of CN-TFMBE took place while E7 was still in theisotropic state. The warmed LC/gelator mixture was added to anaqueous solution of 2 wt % sodium dodecyl sulfate (SDS) undervigorous stirring at room temperature (the LC/gelator mixturewas 4% by volume with respect to the aqueous solution). After-ward, the emulsion was diluted by the addition of the samevolume of an aqueous solution of 4% poly(vinyl alcohol)(PVA), with PVA acting as a steric stabilizer to prevent thecoalescence of the LC droplets and as a thickening agent toincrease the viscosity of the emulsion. To prepare a film of anLC emulsion used for characterization, a drop of the solutionwascast on a glass plate and sandwiched between two plates in somecases. PVA (molar mass ∼22000, from BDH) and SDS (purity>99%, from Fluka) were used as received.

We tested various conditions for the preparation of the LC gelemulsion. The procedure described above gave rise to the bestdispersion of LC gel droplets in water. Prior to being added to

water at room temperature, the LC gel needed to be in thehomogeneous isotropic phase to be easily dispersible understirring. However, when water was also heated to the sametemperature (65 �C), part of the gelator was extracted from thesolution, probably because of its different solubility in water ascompared to that of the LC. Therefore, with the procedure thatwas used, the aggregation of the gelator took place upon coolingof the LC/gelator mixture in water while the solution wassubjected to the vigorous stirring required for the dispersion; theaggregation process was basically completed after the emulsionwas obtained. Observations on the LC gel emulsion were madewithin 1 day after the preparation, and the actual delay time hadlittle effect on the results. Because of the preparation procedure,wewere unable to investigate the kinetics of gelation inside theLCdroplets.

The LC gel emulsions were observed using an optical micro-scope (Leitz DMR-P) both in bright field and under crossedpolarizers. The microscope was also used to carry out theelectrooptical measurements on single LC gel droplets by repla-cing the digital camera for photomicrographs with a high-speedphotodetector (Melles Griot) that is connected to a digitaloscilloscope (Tektronix, TDS 420A).The change in transmittanceof the LC gel droplets could thus be measured in response to anelectric field (1000 Hz ac field) provided by a high-voltage wave-form generator (SWF6000, Circuit Test). More details on themeasurements on single LC droplets will be given later.A fluorescence microscope (Leica DMRX) was used to observethe formation of fluorescent fibrous aggregates of CN-TFMBEinside the LC droplets. It was equipped with filters for 450-490 nm excitation and emission detection at >510 nm. Thesteady-state fluorescence emission spectra of LC gel emulsionswere recorded using a fluorescence spectrophotometer (VarianCary Eclipse) equipped with a single-cell Peltier for controlled-temperature measurements. Finally, fibrous aggregates formedinside the LC droplets and, for comparison, in the bulk LC wereexamined on a Hitachi S-4700 emission gun scanning electronmicroscope (SEM). In the case of LC gel emulsion, the samplethat was used was prepared by first evaporating water at roomtemperature for 2 days, followed by the slow extraction of E7 inhexane. For the bulk LC gel, only the extraction of LC wasrequired.

Results and Discussion

The formation of LC droplets dispersed in aqueous solution(most diameters are in the range of 2-5 μm) and the aggregationof gelator molecules inside the droplets were revealed by opticaland fluorescence microscopy (images in Supporting Informa-tion). The fluorescence emission from the droplets indicates thatCN-TFMBE molecules are in an aggregated state inside the LCcavities. As will be shown later, the presence of a network offluorescent fibrous aggregates inside the LC droplets is visibleunder the fluorescence microscope. Considering the fact thatCN-TFMBE can gel bulk LCs upon aggregation,23 the observeddroplets should be gelled E7. From the microscopy images, it canbe noticed that fluorescent micrographs apparently show fewer

Figure 1. Chemical structures of the gelator (CN-TFMBE) and nematic liquid crystal (E7).

(21) An, B.-K.; Kwon, S.-K.; Jung, S.-D.; Park, S. Y. J. Am. Chem. Soc. 2002,124, 14410.(22) An, B.-K.; Lee, D.-S.; Lee, J.-S.; Park, Y.-S.; Song, Y.-S.; Park, S. Y. J. Am.

Chem. Soc. 2004, 126, 10232.(23) Tong, X.; Zhao, Y.; An, B.-K.; Park, S. Y. Adv. Funct. Mater. 2006, 16,

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LC droplets than in the optical micrographs, which seems to becaused by the varying focusing distances for the droplets locatedin different layers of the emulsion solution. However, it cannot beruled out that no aggregation occurred in someLCdroplets underthe preparation conditions; those droplets were invisible underthe fluorescence microscope.

To determine the stability of the fluorescent aggregates ofthe gelator inside the LC droplets, various-temperature fluores-cence emission spectra of the LC gel emulsion were recorded(λex= 380 nm). As can be seen from the spectra in Figure 2, withincreasing temperature, the fluorescence intensity decreases, sug-gesting some thermally induced dissolution of gelator moleculesin the LC host. However, the fluorescence emission remains evenat 80 �C, which is above Tni = 68 �C of E7. This observationindicates that fibrous aggregates are present in the droplets of E7in the isotropic phase, which likely gives rise to an isotropic gel.Although there were no further increases in temperature so as toavoid the evaporation of water, the results indicate that theaggregates inside the LC droplets have a melting temperature of>80 �C. This is no surprise considering the melting temperatureof∼130 �C for the aggregates formed in bulkE7 (measured on theoptical microscope). Upon subsequent cooling of the LC gelemulsion, the fluorescence intensity is only partially recovered,which can be seen from the spectrum recorded with the solutioncooled to 25 �C. This suggests some irreversible structural ormorphological changes of the aggregates during the thermaltreatment, whereas the chromophore gelator could also undergopartial trans-cis isomerization caused and modulated by theambient light and/or a thermal effect.24

In a normal LC emulsion (without gelation inside the droplet),the LC configuration is determined by the anchoring of LCmolecules at the aqueous interface. In an LC gel emulsion, thephysical network formed by the fibrous aggregates should inter-act strongly with LC molecules and thus alter the LC directoralignment. This indeed was observed on a polarizing opticalmicroscope by comparing LC droplets with and without theCN-TFMBE gelator (polarizing photomicrographs in Support-ing Information). For the LC emulsion without gelator, perpen-dicular anchoring of LC molecules at the interface results in thenoticeable radial configuration for the LC droplets. By contrast,for the LC gel emulsion prepared under the same conditions, the

radial configuration is no longer observable; only birefringent LCdroplets could be recognized. It is no surprise that the fibrousaggregates inside the droplet disrupt the LC director alignment.

Wewere able tomeasure the change in optical transmittance inresponse to an electric field for single LC gel droplets of variousdiameters. The results have revealed the effect of droplet sizeon the electrooptical behavior of the LC gel. For this experiment,the initial LC gel emulsion was diluted (by a factor of 20) in anaqueous solution of 20 wt % PVA. The use of this highconcentration of PVA was necessary to increase the viscosity ofthe emulsion so that a film with stable (immobilized) LC geldroplets could be obtained and sandwiched between two indiumtin oxide (ITO)-coated glass slides. This was essential for singleLC gel droplet electrooptical measurements. To prepare the film,a drop of the emulsion was cast on an ITO-coated glass slide and,after partial evaporation ofwater, a second slidewas put on top tosandwich the LC gel emulsion film between the electrodes (thefilmhad a thickness of about 66μmand a surface area of about 25mm2). By placing the sample on the object stage of the opticalmicroscope under crossed polarizers and using an appropriatemagnification objective, a single LC droplet could be selected andpositioned in the frame of the photomicrograph. Because onlyone birefringent LC droplet was viewed by the polarizing micro-scope, with the surrounding material being isotropic, the changein transmittance upon application of a voltage came from theelectric field-induced reorientation of LC molecules inside thesingle droplet. Moreover, it should be emphasized that LC geldroplets of varying diameters were selected from the sameemulsion film, ensuring that they were subjected to the sameeffective electric field strength, and the comparison of theirelectrooptical response is straightforward. Before discussing theresults of the electrooptical measurements realized on single LCgel droplets of various sizes ranging from 12 to 55 μm in diameter(large droplets were selected to facilitate the single-droplet mea-surement), Figure 3 shows their polarizing photomicrographs inthe field-off and field-on states (ac field, 1000 Hz, 5.3 V/μm, peakto peak) as well as their images recorded with the fluorescencemicroscope. Interesting observations can be made. First, underthe same applied field strength, as the droplet size decreases, theremaining birefringence of the droplet is more prominent, in-dicating a more difficult field-induced reorientation of LC mole-cules inside the cavity. This behavior might be explained by anincreasing confinement effect upon reducing the droplet size.Second, a similar network of fluorescent fibrous aggregates ofCN-TFMBE is visible inside all of the LC gel droplets, suggestingthat the basic aggregation process of gelator molecules remainsthe same under the increasingly severe confinement.

Figure 4 compares the change in transmittance as a function ofapplied voltage (ac field, 1000 Hz, peak to peak) for LC geldroplets of different sizes and, for comparison, the bulk LC gel.The bulk LC gel was prepared under the same conditions (2%CN-TFMBE in E7) except for being dispersed into droplets inwater, and it was used to fill a 50 μm-gap ITO-coated cell for theelectrooptical measurements. In all cases, the LC reorientationalong the electric field direction gives rise to a drop in thetransmittance. However, as compared to the bulk LC gel, theLC gel droplets have a higher threshold voltage and a lowerapparent optical contrast (transmittance at field off is greater thanthat at 5.3 V/μm), and the effect of droplet size on electroopticalbehavior is also clear: the threshold voltage increases and theoptical transmittance decreaseswith decreasing size of the droplet.Moreover, in contrast to the bulk LC gel, the electric-field-inducedreorientation inside the droplets develops gradually with the risein voltage (the apparent shoulderlike change around 1.5 V/μm for

Figure 2. Steady-state fluorescence emission spectra (λex =380 nm) of a self-assembled liquid crystal (LC) gel emulsionrecorded upon heating from 25 to 80 �C and then cooling to 20 �C.

(24) Gulino, A.; Lupo, F.; Condorelli, G. G.; Fragala, M. E.; Amato, M. E.;Scarlata, G. J. Mater. Chem. 2008, 18, 5011.

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the 55 μm droplet may be caused by data scattering related toexperimental uncertainty).

The electrooptical switching of theLCgel droplets is repeatableand similar to that of the bulk LC. Several cycles of transmittance

change upon application (field on) and removal (field off) of avoltage (5.3 V/μm) results in no deterioration of the switchingperformance (an example of themeasurement is given in Support-ing Information). However, a close inspection reveals that theirswitching times are different and that the droplet size affects theswitching times. Figure 5 shows (a) the decrease in transmittanceupon application of an electric field of 5.3 V/μm and (b) therecovery of transmittance after turning off the field for the bulkLC gel and the LC gel droplets of different sizes; the calculatedswitching-on and switching-off times, defined as the time requiredfor a transmittance change of between 10 and 90% of the initialand final levels, respectively, are indicated in parenthesis. On onehand, the comparison among the LC gel droplets shows that theswitching-on time increases with decreasing droplet size, whereasthe opposite trend is observed for the switching-off time. As thesize of the LC gel droplet decreases, the increasing confinementrenders the reorientation of LCmolecules under the voltagemoredifficult to develop, which is also revealed by the decreasingcontrast as alreadymentioned above. Apparently, when the field-induced reorientation is more difficult, the opposite processwould be easier upon removal of the field, resulting in a fasterrelaxation of LC molecules returning to the initial state. On theother hand, the switching behavior of the bulk LC gel seems to bequite different from that of the LC gel droplets. Although the

Figure 3. Photomicrographs for LC gel droplets of various diameters: (a) polarizing photomicrographs in the field-off state, (b) polarizingphotomicrographs under a voltage (ac field, 1000 Hz, 5.3 V/μm, peak to peak), and (c) fluorescence images showing the presence of fibrousaggregates.

Figure 4. Change in optical transmittance vs applied voltage forthe bulk LC gel and single LC gel droplets of different sizes.

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switching-on time is of the same order of magnitude as for thedroplets with a diameter of 30 μmor larger, the switching-off timeis significantly longer than for all of the droplets.

The likely reason for the difference in electrooptical behaviorbetween the bulk LC gel and the LC gel droplets may be theconfinement effect that is absent for the former and present for thelatter. Likewise, the differences among the LC gel droplets ofvarious sizes also point to the confinement effect. However, thesituation is complicated by the presence of fibrous aggregates inthe LCgel droplets.Generally speaking, confinement refers to theeffect arising from the curvature of the spherical cavity on the LCdirector and thus is mainly determined by the size of the LCdroplet, regardless of the fibers inside, but at the same time, thepresence of fibers obviously disrupts the LCdirector and creates alarge interface between LC and the fibers, which can also affectthe reorientation of LC molecules in response to an electric field.Therefore, for LC gel droplets, the confinement effect is coupledto both the distortion of the LC director by the fibers and theeffect of fiber/LC interfacial interaction.More studies are neededto understand the coupling and interplay of the confinementeffect and the effect arising from the presence of fibrous aggre-gates. Another point is worth mentioning. The electroopticalbehavior of LC gel droplets (higher threshold voltage and lowercontrast) suggests that they have limited potential for display-type

applications, but sensing with LC gels in an emulsion may be ofinterest to explore in future work because the adsorption of ananalyte at the LC gel droplet/water interface may cause a changein the electrooptical signal.

Whereas self-assembled LC gels can be prepared in the form ofspherical droplets dispersed in aqueous solution, it is interesting toknow how the confinement can affect the growth of fibrousaggregates of the gelator. An immediate consequence of theaggregation process occurring inside a small spherical cavity isthat the straight section of a fiber cannot be longer than thediameter of the cavity and a growing long fiber must be folded toaccommodate the geometry of the LC droplet. SEM was used toobserve the fibrous aggregates of CN-TFMBE formed by the LCdroplets. To do this, a drop of the gel emulsionwas cast on a glassslide, dried at room temperature for 2 days to remove water,immersed in hexane to extract the E7 LC host, and dried again inair before the SEM observation. For comparison, a bulk LC gelwas prepared under the same conditions using the same gelatorand nematic LC; SEMobservation was carried out on the fibrousaggregates after the extraction of E7 in hexane. The results areshown in Figure 6. In contrast to the long, extended fibrousaggregates formed in the bulkLC gel, the fibers resulting from theLC gel emulsion are highly folded, and they are also thinner thanthose in the bulkLCgel.Most striking is the formation of circular,

Figure 5. (a) Drop in transmittance upon application of a voltage(5.3 V/μm) and (b) recovery of transmittance upon removal of theelectric field for the bulk LC gel (dotted line) and single LC geldroplets of various sizes. The corresponding switching times areindicated.

Figure 6. SEM images showing the fibrous aggregates of thegelator formed in a bulk LC gel (viewed after the removal of E7)and in LC gel droplets in an emulsion (viewed after the removal ofwater and E7), with the inset being a magnified section of theaggregates.

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ringlike fibrous aggregates whose diameters correspond tothe diameters of the LC gel droplets. The apparent fiber ring isintriguing. Because the fibrous aggregates are homogeneouslydispersed inside the LC gel droplets in the emulsion (Figure 3c),the rings must be formed during the removal of the liquids(water and E7). It seems that in the course of drying, the fibrousaggregates coalesce and somehow move to and accumulate onthe circumference of the droplets. At this point, we do not knowhow to explain this observation. With both the bulk anddroplet LC gels, the fibrous aggregates are a bundle of primaryfibers having a similar thickness (diameter) of about 100 nm, ascan be seen from a magnified section in the inset. This resultsuggests that making LC gels in an emulsion, with aggregationoccurring inside a small spherical cavity under confinement,might provide a way to shape the resulting fibrous aggregates ina circular form.

Conclusions

This work showed for the first time that self-assembled LC gelscould be prepared in the form of micrometer-sized sphericaldroplets dispersed in aqueous solution.The aggregation of gelatormolecules confined in spherical cavities leads to the formation ofcircular and highly folded fibrous aggregates, in contrast to the

extended fibers formed in the bulk LC gel. The confinement alsoaffects the electrooptical behavior, including switching timesand optical contrast, of single LC gel droplets, which is largelydetermined by the droplet size. By building a bridge between LCemulsions and self-assembled LC gels, this study demonstrates anew hybrid LC system and thus offers new possibilities forexploring LC-based functional materials.

Acknowledgment. Y.Z. acknowledges financial supportfrom the Natural Sciences and Engineering Research Councilof Canada (NSERC) and le Fonds Qu�eb�ecois de la Recherchesur la Nature et les Technologies of Qu�ebec (FQRNT).S.Y.P. acknowledges financial support from National Re-search Laboratory Program of Korea. Y.Z. is a member of theFQRNT-funded Center for Self-Assembled Chemical Structures(CSACS).

Supporting Information Available: Optical and fluores-cence microscope images of an LC gel emulsion, polarizingoptical micrographs comparing an LC emulsion with an LCgel emulsion, and electrooptical switching data for a singleliquid-crystal gel droplet. This material is available free ofcharge via the Internet at http://pubs.acs.org.

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