Shape-Morphing Chromonic Liquid Crystal Hydrogels. Supporting information

Transcription

1 Shape-Morphing Chromonic Liquid Crystal Hydrogels Ruvini S. Kularatne, Hyun Kim, Manasvini Ammanamanchi, Heather N. Hayenga, and Taylor H. Ware* Supporting information

2 Contents 1. Materials Synthetic procedures... 3 Scheme 1: Synthetic scheme for the synthesis of PDI-DA monomer... 3 Scheme 2: Synthetic scheme for the synthesis of chiral PDI monomer General experimental details HNMR spectra of the synthesized compounds UV-Vis measurements of the monomer and the chromonic polymer thin films Phase diagram of PDI-DA/ NIPAM mixture Determination of the alignment of the chromonic hydrogel and the PDI-DA monomer Determination of the mechanical anisotropy of the chromonic hydrogel Deformations of the twisted chromonic hydrogel Phase diagram of PDI-DA/ NIPAM / Chiral PDI-DA mixture Chiral chromonic hydrogel... 16

3 1. Materials Perylene-3,4,9,10-tetracarboxylic dianhydride (PDA), N,N-dimethylethylendiamine, 2-bromoethanol, methacrylic anhydride, K 2S 2O 8, and (S)-(-)-2-aminomethyl-1-ethylpyrrolidine were purchased from Sigma Aldrich and used without further purification. The solvents DMF, THF, and MeOH were purchased from Fisher Chemicals and were used as purchased. NMR measurements: All the synthesized compounds were characterized using Bruker Avance 500 MHz spectrometer at room temperature. The spectra were recorded in CDCl 3 or in D 2O. The data were reported in ppm on the scale relative to trimethylsilane (TMS) as the internal standard. multiplicity (br= broad, s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet) 2. Synthetic procedures Synthesis of dimethacrylate functionalized perylene diimide (PDI-DA) Scheme 1: Synthetic scheme for the synthesis of PDI-DA monomer Synthesis of PDI-1 Perylene-3,4,9,10-tetracarboxylic dianhydride (2.50 g, mol), and N,N-dimethylethylendiamine (2.786 ml, mol) were added to a round bottom flask and dissolved in DMF (25.0 ml). The reaction mixture was refluxed for 12 hrs at 130 C. The reaction mixture was cooled to room temperature and was quenched in cold THF (300 ml). At which time, a brown color compound precipitated. The precipitate was filtered under vacuum, washed with cold THF (3 100 ml) and dried under vacuum to obtain a brown solid (PDI-1). (3.78 g, 95%) 1 H NMR (500MHz, CDCl 3, ): 8.67 (dd, 8H), 4.35 (t, 4H), 2.68 (t, 4H), 1.53 (s, 12H) Synthesis of PDI-2 A suspension of PDI-1 (2.00 g, mol) in 2-bromoethanol (2.65 ml, mol) was refluxed for 12 hrs at 100 C. The reaction mixture was cooled to room temperature and was poured in to cold THF (300

4 ml). The resulting red color precipitate was filtered, washed with cold THF (3 100 ml), and dried under vacuum to obtain PDI-2. (2.12 g, 91%) 1 H NMR (500MHz, D 2O, ): 7.00 (dd, 8H), 4.08 (br, 4H), 3.88 (t, 4H), (br, 4H) 3.53 (t, 4H), (br, 12H) Synthesis of PDI-DA PDI-2 (0.50 g, mol) and 4-dimethylaminopyridine (DMAP) (20 mg) were dissolved in DMF (25.0 ml) and was stirred for 30 mins at room temperature. At which time, methacrylic anhydride (1.80 ml, mol) was added dropwise to the reaction mixture. The reaction mixture was stirred under light protection for 48 hours at room temperature. The resulting precipitate was poured into cold THF (300 ml), and was filtered under vacuum, washed with cold THF (3 100 ml) and dried under vacuum to obtain dark red colored PDI-DA. (0.49 g,70% ) 1 H NMR (500MHz, D 2O, ): 7.00 (dd, 8H), 6.14 (s, 2H), 5.78 (s, 2H), 3.91 (t, 4H), 3.76 (br, 4H), 3.62 (br, 4H) 3.53 (t, 4H), 3.31 (br, 12H), 1,89 (s, 6H) Scheme 2: Synthetic scheme for the synthesis of chiral PDI monomer Synthesis of Chiral PDI: A mixture of (S)-(-)-2-aminomethyl-1-ethylpyrrolidine (2.70 ml, mol) and perylene-3,4:9,10- tetracarboxylic dianhydride (2.54 g, mol) were dissolved in DMSO (50.0 ml) and was stirred at 70 C for 24 hrs. The reaction mixture was filtered and the red color precipitate was washed with cold MeOH (3 100 ml), and was dried under vacuum to obtain the chiral PDI. (3.37 g, 85%) 1 H NMR (500MHz, CDCl 3, ): (d, 4H), (d, 4H), 4.71 (br, 4H), 4.40 (m, 4H), 4.24 (d, 4H), 3,24 (t, 4H), 3.14 (q, 4H), 3.00 (t, 4H), 1.78 (t, 4H), 1.25 (t, 6H) Synthesis of the salt of the Chiral PDI Chiral PDI was completely dissolved in Concentrated HCl. Then the excess HCl was evaporated under reduced pressure. The resulting solid was dried under vacuum for 24 hrs to obtain the salt of the chiral PDI. Synthesis of the polymer network: Microscope glass slides were rubbed once with a fine abrasive pad (3M Trizact TM P400). Glass cells were constructed by placing two rubbed glass slides separated by a 60 µm spacer. The glass slides were glued together by using a thiol-ene mixture (tetrakis(3-mercaptopropionate) and 1,3,5-Triallyl-1,3,5-triazine-

5 2,4,6(1H,3H,5H)-trione) with subsequent curing under 365 nm UV light (250 mw/cm 2 intensity, (OmniCure LX400+, Lumen Dynamics)) for 10 seconds. The reaction mixture was prepared by mixing 20 wt% of PDI-DA, 10 wt% NIPAM and 1 wt% of K 2S 2O 8 with 69 wt% deionized water. The aligned glass cells were filled with the reaction mixture by capillary action and was polymerized under the fluorescent office light (0.07 mw/m -2 intensity) for 30 mins and was post cured at 70 C overnight. The resulting polymer films were washed several times with DI water to remove the unreacted monomers. Patterning of chromonic hydrogels Microscope glass slides were rubbed once with a fine abrasive pad (3M Trizact TM P400). Glass cells were constructed by placing two rubbed glass slides orthogonal to each other and separated by a 30 µm spacer. The glass slides were glued together by using a thiol-ene mixture with subsequent curing under 365 nm UV light (250 mw/cm 2 intensity, (OmniCure LX400+, Lumen Dynamics)) for 10 seconds. The reaction mixture was prepared by mixing 20 wt% of PDI-DA, 10 wt% NIPAM, 1 wt% chiral PDI and 1 wt% of K 2S 2O 8 with 68 wt% deionized water. The aligned glass cells were filled with the reaction mixture by capillary action. The glass cells were placed on the stage of an Olympus BX-51 microscope and a chromium photomask was placed over the transmission source (12 V, 100 W, halogen bulb). The patterned illuminating light was focused on to the sample through a condenser with a numerical aperture of 0.9. The samples were then polymerized through the mask for 1 minute to generate the cross shape. The glass cell was then opened immersed in deionized water to dissolve the unreacted monomer. The cross shape was removed from the glass slide by sonication for 10 seconds. Synthesis of the chiral hydrogels Glass cells were constructed by placing two glass slides separated by a 120 µm spacer. The glass slides were glued together by using a thiol-ene mixture with subsequent curing under UV light for 10 seconds. Reaction mixtures of 14.2 wt % PDI-DA, 14.2 wt% NIPAM and 1wt% K 2S 2O 8, with varying amounts of chiral PDI (7.1 wt%, 8.6 wt%, 9.3 wt% and 14.2 wt%) and deionized water (63.5 wt%, 62.1 wt%, 61.4 wt% and 56.4 wt%, respectively) were prepared. The glass cells were filled with the reaction mixture by capillary action and were polymerized under visible light for 30mins. The resulting polymer films were washed several times with DI water to remove the unreacted monomers. 3. General experimental details UV-Vis measurements: The UV-Vis spectra of the monomer and the polymer thin films were measured using Agilent 8353 UV-Vis. A thin film for the monomer was obtained by the slow evaporation of 20 mg/ml PDI-DA monomer solution in DI water on a glass microscope slide. A thin film of the polymer was obtained by the polymerization of the reaction mixture (20 wt% of PDI-DA, 10 wt% NIPAM and 1 wt% of K 2S 2O 8 with 69 wt% deionized water) in a glass cell and subsequent washing with DI water and drying the polymer film on the glass slide. Polarized Optical microscope (POM) measurements: The optical textures of the PDI-DA monomer at different concentrations were obtained by using POM (Olympus BX-51) coupled with a heating stage (Linkam). The samples were prepared by adding different concentrations of PDI-DA monomer (5 wt%- 25 wt%, in DI water) into 30 µm thick glass cells, and sealing

6 the glass cells with a thiol-ene mixture to prevent the sample from evaporating. The phase transitions were monitored during the heating process with a heating rate of 1 C/min. The phase diagram of the PDI-DA/NIPAM mixture was constructed by observing the optical textures of the PDI-DA / NIPAM monomer mixture at different concentrations by using POM (Olympus BX-51) coupled with a heating stage (Linkam). Sample mixtures of 20.0 wt % PDI-DA, with varying amounts of NIPAM ( wt%) and deionized water (77.5 wt%, wt%, respectively) were prepared and injected into 30 µm thick glass cells. The glass cells were sealed with a thiol-ene polymerizable mixture to prevent the sample from evaporating. The phase transitions were monitored during the heating process with a heating rate of 1 C/min. The phase diagram of the PDI-DA/NIPAM/Chiral PDI mixture was constructed by observing the optical textures of the PDI-DA / NIPAM/Chiral PDI monomer mixtures at different concentrations by using POM (Olympus BX-51) coupled with a heating stage (Linkam). Sample mixtures of 14.2 wt % PDI-DA, 14.2 wt% NIPAM, with varying amounts of chiral PDI (7.1 wt%, 8.6 wt%, 9.3 wt% and 14.2 wt%) and deionized water (64.5 wt%, 63.1 wt%, 62.4 wt% and 57.4 wt%, respectively) were prepared and injected into 30 µm thick glass cells. The glass cells were sealed with a thiol-ene mixture to prevent the sample from evaporating. The phase transitions were monitored during the heating process with a heating rate of 1 C/min. The alignment of the chromonic monomer and the chromonic gel was characterized by POM images. Sample absorption was determined using POM. PDI-DA and the PDI-DA/NIPAM polymer network were imaged with polarized illumination (analyzer removed) with images taken every 10 over a full rotation. Images were first separated into RGB color channels. The G color channel was then converted to greyscale in ImageJ. The mean grey value was recorded for each image. This method was chosen to enable measurement of dichroism in swollen hydrogels. To determine the dimensional changes of the chromonic hydrogels in solvents, the samples were cut into rectangles with an aspect (length/width) ratio of approximately 2 with the long axis along the nematic director. The samples were placed in a glass chamber and the solvents were added. The swelling of the films was observed on the microscope. The images were analyzed from ImageJ to measure the dimensional changes in each axis. To determine the dimensional changes of the chromonic hydrogels with temperature, first the samples were cut into rectangles with an aspect (length/width) ratio of approximately 2 and the long axis along the nematic director. The samples were placed in a glass chamber filled with DI water. The sample was heated on a heating stage with a heating rate of 1 C/min from room temperature to 50 C and was observed on the microscope. The images were analyzed from ImageJ to measure the dimensional changes in each axis. To determine the pitch in the fingerprint texture of the chiral chromonic hydrogels at different temperatures, samples were placed in a glass chamber filled with DI water. The samples were heated on a heating stage with a heating rate of 1 C/min from room temperature to 45 C and observed in the microscope between crossed polarizers. The images were analyzed from ImageJ to measure the pitch in the finger print texture. Atomic force microscopy measurements:tapping Mode Atomic Force Microscopy (TMAFM) was carried out on the chiral hydrogel on a VEECO-dimension 5000 scanning probe microscope with a hybrid xyz head

7 equipped with Nano-Scope Software. AFM images were obtained using silicon cantilevers with nominal spring constant of 42 N/m and nominal resonance frequency of 300 khz (OTESPa). Image analysis software Nanoscope 7.30 was used for surface imaging and image analysis. Cantilever oscillation amplitude was equal to ca. 375 mv, and images were acquired at 2 Hz scan frequency. Sample scan area was 25 μm. The AFM studies for the PDI-DA monomer and the chromonic hydrogel were carried out using Bruker Bioscope catalyst. AFM images were obtained using a silicon cantilever with a nominal spring constant of 40 N/m and a nominal resonance frequency of 300 khz (OTESPa). Cantilever oscillation amplitude was equal to ca. 250 mv, and images were acquired at Hz scan frequency. Sample scan area was 500 nm HNMR spectra of the synthesized compounds Figure 1: 1 HNMR spectra of PDI-1

8 Figure 2: 1 HNMR spectra of PDI-2

9 Figure 3: 1 HNMR spectra of PDI-DA

10 Absorbaance (a.u.) Figure 4: 1 HNMR spectra of chiral -PDI 5. UV-Vis measurements of the monomer and the chromonic polymer thin films Wavelength (nm) PDIDA/NIPAM PDIDA 800 Figure 5: UV-Vis absorption spectra of the PDI-DA monomer and PDI-DA/ NIPAM polymer network

11 6. Phase diagram of PDI-DA/ NIPAM mixture Figure 6: Binary phase diagram of PDI-DA/ NIPAM mixture with varying NIPAM and Deionized water concentrations at constant PDI-DA concentration (20 wt%) Note: Due to the extreme sensitivity of the sample to the visible light, the phase diagram was constructed by exposing the samples to the lowest possible intensity of the polarized light.

12 7. Determination of the alignment of the chromonic hydrogel and the PDI-DA monomer Figure 7: AFM image of the PDI-DA/ NIPAM polymer network. Here, the aggregation of the polymer network was observed to be along the rubbing direction

13 Figure 8: Dichroic nature of the a) PID-DA monomer, b) PDI-DA/ NIPAM polymer network in water. Both the PDI-DA monomer and the chromonic hydrogel were kept under a polarized microscope, and images were taken with the polarized illumination at every 10 over a full rotation. For both the monomer and the chromonic hydrogel the brightest image (indicating the lowest absorbance) was observed at 0 and the darkest image (indicating the highest absorbance) was observed at 90.

14 8. Determination of the mechanical anisotropy of the chromonic hydrogel Figure 9: a) POM images indicating the birefringence of the aligned chromonic hydrogel, b) POM images indicating the anisotropic swelling of the chromonic hydrogel by varying the solvent polarity from CHCl 3 to water.

15 Temperature ( C) 9. Deformations of the twisted chromonic hydrogel Figure 10: Chromonic hydrogel with a twisted nematic alignment, a) cut at 0 to the alignment which exhibits simple bending, b) cut at 45 to the alignment which exhibits twisting. 10. Phase diagram of PDI-DA/ NIPAM / Chiral PDI-DA mixture I 8 10 N* + I Figure 11: Binary phase diagram of PDI-DA/ NIPAM/ Chiral PDI mixture with varying Chiral PDI and Deionized water concentrations at constant PDI-DA (14.2 wy%) and NIPAM (14.2 wt%) concentration. Note: Due to the extreme sensitivity of the sample to the visible light, the phase diagram was constructed by exposing the samples to the lowest possible intensity of the polarized light. N* 12 Chiral PDI (wt %) 14

16 11. Chiral chromonic hydrogel Figure 10: Chiral chromonic hydrogels with varying chiral PDI dopant at 25 C and at 45 C

17 Figure 11: AFM height and phase images of the chiral chromonic hydrogel Figure 12: SEM images of the chiral chromonic hydrogel