Supplementary Materials
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Direct Visualization of Swollen Microgels via Scanning
Electron Microscopy Using Ionic Liquids
Koji Horigomea, Takeshi Uekic, and Daisuke Suzukia,b*
a
b
Graduate School of Textile Science & Technology, Shinshu University 3-15-1 Tokida, Ueda,
386-8567, Japan
Division of Smart Textiles, Institute for Fiber Engineering, Interdisciplinary Cluster for Cutting
Edge Research, Shinshu University, 3-15-1, Tokida, Ueda, 386-8567 Japan
c
Department of Materials Engineering, School of Engineering, The University of Tokyo,7-3-1
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
* Author to whom correspondence should be addressed. E-mail: d_suzuki@shinshu-u.ac.jp
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Direct visualization of swollen microgels using ionic liquids
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Table of Contents
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1. SI Table 1: Summary of the size of the p2VP microgel.
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2. SI Table 2: Measurements of the weight before or after drying of p2VP microgel dispersion
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and the mixture
3. SI Table 3: Measurements of the weight before or after drying of pNIPAm microgel
dispersion and the mixture
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4. SI Figure 1: SEM images of the dried and IL-swollen p2VP microgels.
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5. SI Figure 2: SEM images of pools of ionic liquid.
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6. SI Figure 3: SEM image of the dried p2VP microgels without sputtering.
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7. SI Figure 4: SEM images of pNIPAm hybrid microgels using [Im][NTf2].
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8. SI Figure 5: TEM image of the dried hybrid microgels.
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9. SI Figure 6: AFM images of dried pNIPAm based microgels and IL-swollen pNIPAm based
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microgels.
10. SI Figure 7: Cross section data of dried and IL-swollen microgels.
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SI Table 1. Measurements of the diameter of the p2VP microgels under various conditions.
Code
Dh [nm]
pH
NaCl concentration [mM]
Dh-pH3
1347
3.3
1
Dh-pH6
234
6.4
1
Dh-pH3-1MNaCl
677
3.1
1000
Ddry
245
-
-
DIL
523
-
-
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SI Table 2. Measurements of the weight before or after drying of p2VP microgel dispersion and
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the mixture. The water content (Z) was calculated by the following equation: Z = Y/X×100 using
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the measurements.
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SI Table 3. Measurements of the weight before or after drying of the poly(NIPAm-co-
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GMA)microgel dispersion and the mixture. The water content (Z) was calculated by the
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following equation: Z = Y/X×100 using the measurements.
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SEM images of the dried and IL-swollen p2VP microgels
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SI Figure 1. SEM image of dried p2VP microgels. (a) A 0.001 wt.% microgel dispersion was
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deposited on a Pt/Pd substrate and dried at 24 °C. (b) A mixture of the microgel dispersion and
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[Im][NTf2] was dried at ~25 °C and observed via SEM without Pt/Pd sputtering. The microgels
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were located near the pools of [Im][NTf2]. In both cases, the sample stage was tilted at 75°. The
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insets show the magnification of a microgel.
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SEM images of pools of ionic liquid.
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SI Figure 2. Scanning electron microscopy (SEM) images of the dried state of a mixture of a
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p2VP microgel dispersion and ionic liquid. 0.5 μL ionic liquid was added to 1 mL dispersion and
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the mixture (10 µL) was dried on a Pt/Pd substrate. (b) and (c) were magnification of the local
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area as shown in (a). (b) Pools of ionic liquid. A white arrow indicates one example indicating a
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pool of ionic liquid. (c) IL-swollen microgels located at near the area of pools
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SEM image of the dried p2VP microgels without sputtering.
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SI Figure 3. Scanning electron microscopy (SEM) image of the dried structure of a p2VP
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microgel dispersion. The sample was observed via SEM without sputtering (i.e., the microgel
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was not coated with a Pt/Pd layer). A white arrow indicates one example indicating artifacts due
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to the accumulation of electrons on the microgel.
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SEM images of pNIPAm based microgels using [Im][NTf2].
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SI Figure 4. Scanning electron microscopy (SEM) images of pNIPAm-based microgels obtained
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using 0.5μL [Im][NTf2]. A mixture of the microgel dispersion and [Im][NTf2] (10 µL) was dried
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at room temperature and then observed via SEM without Pt/Pd sputtering. The sample stage was
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tilted at 75°. The average size was calculated to be 347 nm. The size of the hybrid microgels was
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thus approximately equal to that of the dried state of the microgel when [Im][NTf2] was used for
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this observation (372 nm: Figure 3(a) in the main text). Therefore, to observe swollen microgels
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via this method (as shown in Figure 2 in the main text), selection of the appropriate ionic liquid
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(IL) is required in order to obtain good affinity between the IL and the cross-linked polymer
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network in the microgels. For the pNIPAm hybrid microgels containing Au nanoparticles, the
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water-soluble IL [dema][TfO] was found to be effective.
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TEM image of the dried hybrid microgels.
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SI Figure 5. Transmission electron microscopy image of the dried structure of hybrid microgels.
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The microgel dispersion (1.5 µL) was dried on a carbon-coated copper grid. The average size of
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the Au nanoparticles, determined using ImageJ software, was 26 ± 6.8 nm (N = 30), and was in
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good agreement with the size determined from the FE-SEM observation (Figure 3(b) in the main
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text).
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AFM images of dried pNIPAm based microgels and IL-swollen pNIPAm based microgels.
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SI Figure 6. AFM images (scan size: 10×10 μm2) of (a) dried pNIPAm based microgels and (b)
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the IL-swollen microgels. The measurements data are summarized at the Table. The areas that
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are indicated by white dotted squares show magnification points, and the magnification images
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are shown in SI Figure 7. The pNIPAm microgel dispersion was dried at room temperature, and
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then the samples was dried under reduced pressure. The dried structure was recorded by
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cantilever (SI Figure 6(a)). The diameter (DAFM-dry) and height (hdry) of the dried pNIPAm
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microgels were measured to be 315 nm and 201 nm (N=4), respectively. DAFM-dry is good
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agreement with FE-SEM measurements (DFE-SEM_dry 372 ± 25 nm). In addition, to estimate the
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swelling of the microgels, we tried to record the topography of IL-swollen microgels. First, the
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IL was dissolved in water, and then the microgel dispersion was added to the mixture. Next, the
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mixture was dried on the polystyrene substrate, and then the dried structure was recorded via
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AFM (SI Figure 6(b)). As a result, the diameter (DAFM-IL) and the height (hIL) of IL-swollen
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pNIPAm microgels were measured to be 547 nm and 255 nm (N=4), respectively. DAFM-IL is
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good agreement with FE-SEM measurements (DFE-SEM_IL 555 ± 43 nm). As a result, the swelling
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ratio, φ, of the IL-swollen pNIPAm microgel was calculated to be 3.82.
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Cross section data of dried and IL-swollen microgels.
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SI Figure 7. (a) Cross section data of dried and IL-swollen microgels. Magnifications of AFM
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images of (b) IL-swollen (c) dried microgel. White doted square in SI Figure 6 indicate the
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magnification area.
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