Semisoft Colloidal Crystals in Ionic Liquids - Langmuir (ACS

Subscriber access provided by EAST TENNESSEE STATE UNIV

Article

Semisoft Colloidal Crystals in Ionic Liquids Yun Huang, Akisato Takata, Yoshinobu Tsujii, and Kohji Ohno Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01449 • Publication Date (Web): 26 Jun 2017 Downloaded from http://pubs.acs.org on June 27, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Semisoft Colloidal Crystals in Ionic Liquids Yun Huang,1 Akisato Takata,1 Yoshinobu Tsujii,1 and Kohji Ohno1,*

1

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

* To whom correspondence should be addressed. E-mail: [email protected]

KEYWORDS: Colloidal crystal, Ionic liquid, Polymer brush, Living radical polymerization

ACS Paragon Plus Environment

1

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 31

ABSTRACT: We here introduce a technique for the direct formation of semisoft colloidal crystals of hybrid particles in non-volatile ionic liquid solvents. The hybrid particles are comprised of a silica core and a densely grafted polymer brush shell, which were synthesized by surface-initiated living radical polymerization. A phase transition of the suspensions from a disordered fluid to a crystallized system was observed within a narrow concentration range. Confocal laser scanning microscopy observation and UV-VIS spectrometry confirmed the highly ordered structure of the hybrid particles in ionic liquids. The effect of the hybrid particle structure on the photonic band-gap of the colloidal crystals was investigated, and the band-gaps varied by changing graft chain lengths. Additionally, the colloidal crystal suspensions were successfully immobilized in ionic liquids.


2

Page 3 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

INTRODUCTION

Surface-initiated living radical polymerization (SI-LRP) has been employed to prepare various solid surfaces such as flat substrates,1-18 particles of varied materials,19-43 and porous structures,

44-46

among others, graphene nanosheets,47-50 polystyrene nanorods,51 cellulose

nanocrystals.52 With extraordinary controllability over the molecular weight and distribution of the graft polymers, as well as their capability of affording an exceptionally high graft density,53-56 our group has successfully applied SI-LRP techniques to the surface of silica particles (SiPs) to achieve perfectly dispersive, monodisperse SiPs grafted with a polymer brush of high grafting density.19 Utilizing the excellent dispersity and high uniformity of these hybrid particles, two- and three-dimensional ordered particle arrays have been successfully fabricated.20-24 Such Semisoft colloidal crystals represent a new type of crystal, with long-range repulsive (non-interpenetrating) interactions between the highly swollen brush layers and the high graft density providing the driving force for crystallization.21-24, 57-62 Notably, the hybrid particle shell in the colloidal crystal can be functionalized with vinyl groups via the SI-LRP technique, and cross-linking between the polymer chains on different particles gives rise to immobilized colloidal crystals.26 Our group also successfully modified iron oxide particle surfaces with a well-defined polymer brush shell via the SI-LRP technique. The resultant rod-shape particles were very dispersible and amenable for application as liquid crystals and transparent films of highly oriented hybrid rods.63, 64 In general, the polymer brush layer on the particles serves two functions. First, the layer plays a crucial role by providing excellent self-assembly dispersibility; second, the polymer brush can be tailored to provide the self-assemblies with versatility for use in different solvents.

As the three-dimensional periodic structure of colloidal particles, colloidal crystals induce


3

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 31

Bragg scattering of visible light that can be exploited in applications such as photonic materials, optical filters, sensors, and non-bleachable color materials.65-70 However, especially for colloidal crystals in solution system, their use in real-world applications has been somewhat limited because their fragile structures can be easily destroyed by mechanical vibration, solvent evaporation, and impurities. For this reason, immobilizing colloidal crystals in polymer gels has been explored.71-74 As noted, our group has successfully introduced vinyl groups into the polymer brush layer and immobilized semisoft colloidal crystals.26 Still, such approaches do not adequately address the solvent evaporation problem, which profoundly affects the colloidal crystal structures, especially during long-time storage. To this end, using a non-volatile solvent would be ideal to form a colloidal crystal with a constant concentration, and it would also broaden the potential applications of the material.

Ionic liquids (ILs) are molten salts that typically consist of organic cations and organic or inorganic anions; notably, they are liquids at room temperature. Their special properties of non-volatility, excellent thermal stability, non-flammability, and negligible vapor pressure make ILs ideal candidate solvents for both particles75-79 and colloidal crystals.80,81 Sawada et al. successfully developed a stepwise process to immobilize hard colloidal crystals in a polymer gel via UV irradiation and then solvent-exchanged from water to an ionic liquid using a soaking process. However, in addition to the time-consuming processes of ion-exchanging for crystal formation and soaking for solvent-exchange, immobilization of the colloidal crystal also required deoxygenation of the colloidal crystal suspension with the monomer and cross-linker, as well as photo radial initiator reacted by UV light followed by injection of the suspension into a capillary cell.80,81 Clearly, it would be advantageous to both generate and immobilize colloidal crystals directly in a


4

Page 5 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

non-volatile solvent like an ionic liquid without the need for soaking or other laborious steps.

In this work, hybrid particles with a silica core (diameter 130 nm) and a shell of concentrated poly(methyl methacrylate) grafts will be used to produce colloidal crystals in ILs. The phase diagram of the resultant colloidal crystals will compare with previously reported semisoft colloidal crystals.21,23 Further, the photonic band-gaps (i.e., the light forbidden region) of the colloidal crystals and the correlation between their structures and band-gaps will be investigated and discussed. Finally, immobilization of the colloidal crystals in the ILs will be examined.

EXPERIMENTAL SECTION

Materials. Ethyl bromoisobutyrate (2-(EiB)Br, 98%) was obtained from the Tokyo Chemical Industry, Tokyo, Japan. 4,4’-Dinonyl-2,2’-bipyridine (dNbipy,97%), copper(I) chloride (Cu(I)Cl, 99.9%), dibutyl(IV) dilaurate (DBTDL, 90%), hydroquinone monomethyl ether (MEHQ, 99%), anhydrous methyl ethyl ketone (MEK, 99%), Irgacure 907, and methanol (MeOH, 99.5%) were purchased from Wako Pure Chemicals, Osaka, Japan. Methyl methacrylate (MMA, 99%), 2-hydroxyethyl methacrylate (HEMA, extra pure), 1,2-dichloroethane (99.5%), chlorobenzene (99%), and o-dichlorobenzene (99%) were obtained from Nacalai Tesque Inc., Osaka, Japan, and MMA was purified by flash chromatography over activated neutral alumina. Silica particles (SiPs) (SEAHOSTER KE-E10, 20 wt% suspension of SiPs in ethylene glycol) were obtained from Nippon Shokubai Co., Ltd., Osaka, Japan. The mean diameter of the SiPs was 130 nm, with a relative standard deviation of 10 %, as measured by transmission electron microscopy. 2-Isocyanatoethyl methacrylate (MOI) was kindly donated by Showa Denko K.K., Tokyo, Japan. The hybrid particles (PMMA-SiP) were synthesized by surface-initiated atom transfer radical polymerization of MMA, as reported previously.19 The characteristics of the PMMA-SiPs used in this work are summarized


5

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

in

Table

1.

The

ionic

liquids

bis(trifluoromethylsulfonyl)imide

N,

Page 6 of 31

N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium

(DEME-TFSI)

and

1-butyl-3-methylimidazolium

bis(trifluoromethylsulfonyl)imide (BMI-TFSI) were purchased from Toyo Gosei Co., Ltd., Osaka, Japan. All other reagents were used as received from commercial sources.

Measurements. Gel permeation chromatographic (GPC) analysis was performed at 40 °C using a Shodex GPC-101 high-speed liquid chromatography system (Showa Denko K.K.) equipped with a guard column (Shodex GPC KF-G), two 30 cm mixed columns (Shodex GPC KF-806L, exclusion limit = 2 × 107), and a differential refractometer (Shodex RI-101). Tetrahydrofuran (THF) was used as the eluent at a flow rate of 0.8 mL/min. Poly(methyl methacrylate) (PMMA) standards were used to calibrate the GPC system. Proton nuclear magnetic resonance (1H NMR) spectra were obtained on a JEOL/AL300 spectrometer (300 MHz, JEOL, Tokyo, Japan). Thermal gravimetric analyses (TGA) were performed on a Shimadzu TGA-50 (Shimadzu, Kyoto, Japan) under a nitrogen atmosphere.

Preparation of the PMMA-SiP Suspensions for Colloidal Crystal Formation. A two-step process was used to prepare the PMMA-SiP suspensions in the ILs. As reported previously,21, 23-25 PMMA-SiPs were first dispersed in mixed solvents to match both their refractive indices (n) and densities (ρ). Sample P1 was dispersed in a mixture of 1,2-dibromoethane/chloroform with a volume composition of 12/88 (Table 1). Similarly, additional samples were prepared in appropriate solvent mixtures to match their n and ρ values in the present study. Next, the concentrations of the PMMA-SiP suspensions were estimated once the colloidal crystals formed, and the solvent mixtures were exchanged to an ionic liquid (DEME-TFSI or BMI-TFSI, see below) with the same volume fraction by evaporation. The volume fractions of the PMMA-SiP suspensions are shown in Table 1.


6

Page 7 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Table 1. Characteristics of silica particles grafted with a concentrated PMMA brusha Sample code

a

Mwb

Mw/Mnc

Graft density (chains/nm2)

d

n

ρe (g/mL)

Volume fractionf (%)

P1

28,900

1.18

0.35

1.45

1.66

24.6

P2

40,300

1.15

0.39

1.46

1.59

15.9

P3

36,700

1.13

0.40

1.46

1.58

16.7

P4

25,500

1.24

0.33

1.45

1.69

19.1

P5

8,400

1.27

0.32

1.44

1.82

33.0

P6g

---

1.46

1.56

23.5

---

---

The diameter of the silica particle core was 130 nm. b Weight-average molecular weight of

the PMMA grafts. c Dispersity index (PDI) of the PMMA grafts. d Refractive index and e density of PMMA-SiPs were calculated via the weight fraction of PMMA in the hybrid particle and literature values of the bulk refractive indices n and densities ρ of PMMA and SiP.

f

Volume fraction of

PMMA-SiP estimated from the crystal suspension in the solvent mixture. g PMMA-SiP previously reported with a SiP core (diameter of 130 nm) and a block copolymer shell with a PMMA first layer (Mn = 23,000 Mw/Mn = 1.17) and a P(MMA-co-HEMA) second layer (Mn = 14,900 Mw/Mn = 1.28). Immobilization of Semi-Soft Colloidal Crystals in Ionic Liquids. As seen in Table 1, sample P6 particles grafted with a vinyl-group-carrying polymer brush, which were prepared following our previous report,26 were dispersed in the DEME-TFSI ionic liquid with the same volume fraction as the crystallization concentration in the solvent mixture. Subsequently, 0.3 wt% of the vinyl-group-carrying free polymer (Mn = 200,000; Mw/Mn = 1.25) was added to the suspension in the ionic liquid and left to stand at room temperature to initiate the colloidal crystal formation. The suspensions were then poured into glass tubes charged with dried Irgacure® 907 (0.1 wt% with respect to the suspension) and left in the dark to continue the colloidal crystal formation process. Finally, the samples were irradiated under UV light for 3 h with an optical filter (>300 nm


7

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 31

of the wavelength).

Confocal Laser Scanning Microscopic (CLSM) Measurements of the PMMA-SiP Suspensions. A PMMA-SiP suspension was placed into a glass cell (inner diameter = 0.8 cm; height = 1.5 cm) with a coverslip bottom. Observations were made on an inverted-type CLSM (LSM 5 PASCAL, Carl Zeiss, Germany) with a 458 nm wavelength Ar laser and a 63× objective (Plan Apochromat, Carl Zeiss) in reflection mode.

UV-VIS Spectrometric Analysis of the PMMA-SiP Suspensions. A PMMA-SiP suspension in the BMI-TFSI ionic liquid was sandwiched between a pair of slide glasses with a silicon spacer (thickness = 100 µm) in the middle. A square-shaped hole (1×1 cm) was cut in the center of the spacer to retain the suspension. The complete cell was then fixed by two clips on each side. After 1 h, the suspension in the cell was analyzed by a UV-VIS spectrophotometer (UV-3600, Shimadzu, Japan) in the wavelength range between 400 nm and 800 nm.

RESULTS AND DISCUSSION

Preparation of the PMMA-SiP Suspensions for Colloidal Crystal Formation. In this work, the ionic liquids DEME-TFSI and BMI-TFSI were chosen as solvents for the PMMA-SiP suspensions.82,83 Although both ILs were initially selected to investigate the formation and phase diagram of semisoft colloidal crystals, lower viscosity of BMI-TFSI relative to DEME-TFSI resulted in a faster rate of crystallite sedimentation in the former IL. Thus, the results reported herein primarily utilize the BMI-TFSI ionic liquid, as described below. Since the colloidal crystal formation process is challenging because of the narrow concentration range required for


8

Page 9 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

crystallization, a two-step process was established.

First, colloidal crystal suspensions were prepared in solvent mixtures to match both the refractive index and density of the hybrid particles, as previously reported.21, 23 The concentrations of the hybrid particles (i.e., PMMA-SiPs) were measured once tiny iridescent flecks were observed after the onset of the experiments. Identical amounts (i.e., volume fractions) of the solvent mixture were replaced with BMI-TFSI (or DEME-TFSI) to prepare the particle suspensions within a narrow concentration range. Note that colloidal crystals can also be formed using a dilution process from a concentrated ionic liquid PMMA-SiP suspension; however a gradual process is crucial because of the narrow concentration window required for crystal formation, as shown below (cf. Figures 1 and 2).


9

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 31

Figure 1. Photographs of sample P1 suspensions (cf. Table 1) in the ionic liquid BMI-TFSI illuminated from behind by white light two months after sample preparation. The weight-average molecular weight of the PMMA grafts is 28,900, and the SiP core diameter is 130 nm. Note that the samples possess different PMMA-SiP volume fractions φ, increasing from 0.229 (leftmost) to 0.251 (rightmost). In samples 2–4, Bragg-diffracting crystalline and (random) fluid phases coexist, with the volume fraction of the crystalline phase decreasing with decreasing φ.

Suspensions of the hybrid particles P1 in BMI-TFSI with different volume fractions (φ = 0.229 − 0.251) were placed in Pyrex glass cells (10 × 1 × 40 mm). The suspensions were then thermostated in an oil bath at 50 °C for 2 months. Photographs were taken from a series of samples illuminated with a white light from behind, with the hybrid particle concentration increasing from sample 1 to sample 5 (Figure 1). As seen, a slightly turbid suspension was observed for sample 1 as a result of Tyndall scattering of the colloidal suspension. Meanwhile, iridescent flecks were observed in samples 2−5, indicating the occurrence of Bragg-reflection from single crystals in BMI-TFSI. The color difference between the flecks is likely caused by different single crystal orientations.23The crystallites in sample 5 filled the entire volume of the suspension without sedimentation over 2 months. In contrast, crystallites precipitated from the suspensions in samples 2,


10

Page 11 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

3, and 4 over time. During the experiment, gradual separation between the crystalline phase with the iridescent flecks sediment and the fluid phase with the slightly turbid supernatant occurred, causing the formation of a distinct boundary in the suspensions. This phase separation in BMI-TFSI is similar to that in solvent mixtures reported previously21,

23

and can be interpreted by the

Kirkwood-Alder transition.84-85 The sedimentation of the crystalline phase occurred because the average density of the hybrid particles was set slightly larger than that of BMI-TFSI (ρBMI-TFSI: 1.44 g/mL) (Table 1). Thus, the density of the crystalline phase was slightly larger than that of the fluid phase.

Figure 2 shows the phase diagram of the suspensions in BMI-TFSI, which was generated using the data from Figure 1 by measuring the volume ratio between the crystalline and fluid phases. In the coexisting region of the crystalline and fluid phases, the plot shows a linear relationship between the volume fraction of the crystalline phases and the particle concentrations. By extrapolating the concentration from 0 % to 100 % crystal, the freezing (φf) and melting (φm) volume fractions were determined to be 0.233 and 0.249, respectively. The φ values are the sum of the volume fractions of the silica core and the grafted PMMA chains, and lie between the typical values of a soft colloidal crystal (0.01) and a hard colloidal crystal (0.545).21, 23 the relative width of the coexisting regime, (φm – φf)/φf = 0.069, is smaller than the value 0.103 for hard crystal systems, indicating a difference in their equilibrium characteristics.


11

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 31

Figure 2. Phase diagram showing the volume fraction of crystal as a function of the particle Figure 3. Photographs of the P2 suspension in the ionic liquid BMI-TFSI. The volume fraction of PMMA-SiP suspension (data from Fig. 1). By extrapolating the linear line weight-average molecular weight of the PMMA grafts is 40,300, and the diameter of the SiP core observed for(a) thePhotograph coexisting of region to 0 % and 100 suspension % crystal, the (φf)illuminated and meltingfrom (φm) is 130 nm. the colloidal crystal in afreezing Pyrex cell volume fractions of the crystal were determined to be 0.233 and 0.249, respectively. behind by white light. (b) Confocal laser scanning microscopic image of P2 colloidal crystal suspension. Observations were performed using an Ar laser of 488nm wavelength and a 63× objective in reflection mode. The mean nearest-neighbor interparticle distance is 290 nm.

The sedimentation of crystallites was also examined using the ionic liquid DEME-TFSI. However, the sedimentation of crystallites formed in this ionic liquid progressed negligibly over 2 months, which was likely caused by the higher viscosity of DEME-TFSI relative to BMI-TFSI, as noted previously. Nevertheless, the mechanism of colloidal crystal formation in these two ILs is not likely to differ since they possess similar chemical and physical properties and contain the same particles.

CLSM Observations. Figure 3 shows CLSM images of the P2 sample suspension at the melting fraction (φm = 0.249) in BMI-TFSI after the sample was placed in a glass cell (inner diameter = 0.8 cm; height = 1.5 cm) with a coverslip bottom. As shown in Figure 3b, the presence


12

Page 13 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

of a two-dimensional ordered array is evident as bright spots in the CLSM image of sample P2. A high degree of positional order of the silica cores and a constant interparticle distance are observed. The PMMA brushes surrounding the silica cores are invisible under CLSM because of their much lower reflectivity. Compared with the CLSM image reported in our previous studies,82,83 where a solvent mixture was used to match refractive indices between the solvent and PMMA-SiPs, a blurry and lower contrast CLSM image was obtained in the present study, which is caused by a close interparticle distance and strong light-scattering resulting from the large difference in refractive indices between BMI-TFSI and the PMMA-SiPs.

On the basis of Figure 3b, the Ddis was measured to be 290 nm. According to our previous work of semisoft colloidal crystals,21 this distance can be also calculated from the melting fraction

φm of the crystal via the equation Ddis,cal = 21/6(Vp/φm)1/3, where Vp is the PMMA-SiP particle volume in nm3. The calculated mean nearest-neighbor center-to-center distance (Ddis,cal) using this equation is 272 nm for sample P2, which is reasonably consistent with the Ddis measured from the CLSM image (Figure 3b). These Ddis and Ddis,cal values are much larger than the 166 nm distance calculated on the basis of the “compact core-shell model” and are approximately 88 % as large as the 331 nm distance calculated on the basis of the “fully stretched core-shell model”.21, 23 The former model consists of a silica core and a PMMA shell with bulk density, whereas the latter model consists of a silica core and a PMMA shell whose size is equal to that of the PMMA chains stretched radially in all trans conformations. The interparticle distance value indicates that the PMMA chains were not compact but highly stretched chains that radiated from the silica core surface. Additionally, the mean nearest-neighbor center-to-center distance values indicate good solubility of the PMMA brushes in BMI-TFSI and the presence of an excluded-volume repulsion


13

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 31

effect between the graft chains. Finally, the results also show similarities to those on colloidal crystals in a solvent mixture reported in our previous study.21, 23, 24 Therefore, the polymer brushes on the silica core surface appear to be playing the same role as those in the previously reported semisoft colloidal crystals. Thus, combined with the phase diagram results presented above, we can also categorize the colloidal crystals formed in the ILs in this study as semisoft colloidal crystals. Further, since a non-volatile solvent is applied in the present system, the results reported here are significant for applications requiring the development of semisoft colloidal crystals with constant concentration for long-term storage.

UV-VIS Spectrometry. As is well known, photonic properties of colloidal crystals are strongly influenced by their structures. In this work, UV-VIS spectrometry was utilized to confirm the highly-ordered structure of the hybrid particles in ILs (Figure 4). According to Bragg’s law, the peak positions (i.e., band-gaps or light forbidden areas) can be estimated from the interparticle distance, according to the following equations for a closed-packed structure.86

2 1 d =( ) 2D 3

λ = 2nd sin θ


14

Page 15 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

where n is the refractive index of whole system, λ is the wavelength of light, d is the interlayer distance, and θ is the angle between the incident light and the scattering planes. As measured from the CLSM image shown in Figure 3, sample P2 has a mean nearest-neighbor center-to-center distance (Ddis) of 290 nm, which corresponds to a calculated λ value of 700 nm. Correspondingly, only one sharp peak (photonic band-gap) for sample P2 was observed at 693 nm (Figure 4), which indicates a homogeneous ordered structure of hybrid particles in BMI-TFSI. It is noteworthy that the interparticle distances of sample P2 observed under CLSM and UV-VIS spectroscopy agree well with each other, which also confirm a homogeneous crystal structure in the ionic liquid. Figure 4 also shows that the peaks are shifted to a short wavelength region as the molecular weight of the polymer chains decrease. That is, the band-gaps of the colloidal crystals varied as a function of the interparticle distance via grafting polymer chains with different lengths (i.e., molecular weights).

Figure 4. UV-VIS spectra of the PMMA-SiP suspensions. Measurements were performed from a wavelength of 800 nm to 350 nm. The black, red, dark yellow, and blue lines show the spectra of suspension of P2, P3, P4, and P5 suspensions with graft polymer weight-average molecular weights of 40,300, 36,700, 25,500, and 8,400, respectively.


15

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 31

However, it was difficult to obtain sharp CLSM images for samples other than P2 because of their closer interparticle distances and strong background signals from light-scattering resulting from their lower graft chain molecular weights.

Immobilization of Semisoft Colloidal Crystals in Ionic Liquids. As mentioned above, immobilized semisoft colloidal crystal structures in solvent mixtures26 are difficult to preserve because of the evaporation of volatile solvents. In this work, which took advantage of ionic liquids and a reported previously immobilization technique for semisoft colloidal crystals,26 we first immobilized the colloidal crystal in ILs as a permanently fixed crystal structure. DEME-TFSI and 0.3 wt% of the vinyl-group-holding free polymer were used here to fix the PMMA-SiP colloidal crystal.26 Tiny iridescent flecks within sample P6 were observed at a 23.5 % volume fraction of the suspension after 1 h following the onset of the experiment (Figure 5a). The suspension was then irradiated under UV light with the prescribed amount of free polymer and photo-radical initiator, which formed a solid-like gel. Figure 5b shows the resulting material to be well fixed even when the glass tube was inverted, and the iridescent flecks indicate a successful colloidal crystal immobilization in the ionic liquid.


16

Page 17 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 5. Photographs of semisoft colloidal crystals in glass tubes illuminated from behind by white light showing the presence of tiny iridescent flecks. (a) Semisoft colloidal crystal before UV irradiation. (b) Semisoft colloidal crystal after UV irradiation.

CONCLUSIONS

Monodisperse polymer-brush-grafted silica particles were suspended in the BMI-TFSI and DEME-TFSI ionic liquids and formed colloidal crystals within a certain concentration range. A phase transition from a disordered fluid to a fully crystallized system with a narrow fluid/crystal coexisting regime was observed with BMI-TFSI as the ionic liquid. The phase diagram reveals a coexisting regime width in the same range as that previously reported for semisoft colloidal crystals, which differs from those for hard and soft colloidal crystals. Combining these results with the interparticle distance from the CLSM image, we conclude that the colloidal crystals form successfully in non-volatile IL solvents with the same driving force as the semisoft colloidal crystals in solvent mixture, that is, long-range repulsive interactions between highly swollen polymer chains. Because of this success, investigating the correlation between the interparticle distance (or crystal structure) and photonic properties becomes increasingly important for the applications. We also


17

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 31

found that the graft chain molecular weight on the silica particle surfaces can control the location of the photonic band-gaps as the interparticle distance changes. The success of immobilizing colloidal crystals in ionic liquids provided a colloidal crystal tolerant against mechanical vibration and solvent evaporation, which represents a step forward in broadening the scope of these materials for widespread application.

ACKNOWLEDGMENT

This work was partly supported by a Grant-in-Aid for Scientific Research (Grant-in-Aid 15H03866) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. We thank JNC Corporation for their kind donation of triethoxysilane.


18

Page 19 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

REFERENCES

1. Jeon, H.; Schmidt, R.; Barton, J. E.; Hwang, D. J.; Gamble, L. J.; Castner, D. G.; Grigoropoulos, C. P.; Healy, K. E., Chemical Patterning of Ultrathin Polymer Films by Direct-Write Multiphoton Lithography. J. Am. Chem. Soc. 2011, 133 (16), 6138-6141.

2. Turan, E.; Caykara, T., A Facile Route to End-Functionalized Poly(N-isopropylacrylamide) Brushes Synthesized by Surface-initiated SET-LRP. React. Funct. Polym. 2011, 71 (11), 1089-1095.

3. Ohno, K.; Kayama, Y.; Ladmiral, V.; Fukuda, T.; Tsujii, Y., A Versatile Method of Initiator Fixation for Surface-Initiated Living Radical Polymerization on Polymeric Substrates. Macromolecules 2010, 43 (13), 5569-5574.

4. Idota, N.; Nagase, K.; Tanaka, K.; Okano, T.; Annaka, M., Stereoregulation of Thermoresponsive Polymer Brushes by Surface-Initiated Living Radical Polymerization and the Effect of Tacticity on Surface Wettability. Langmuir 2010, 26 (23), 17781-4.

5. Ding, S.; Floyd, J. A.; Walters, K. B., Comparison of Surface Confined ATRP and SET-LRP Syntheses for a Series of Amino (meth)acrylate Polymer Brushes on Silicon Substrates. J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (23), 6552-6560.

6. Sakata, H.; Kobayashi, M.; Otsuka, H.; Takahara, A., Tribological Properties of Poly(methyl methacrylate) Brushes Prepared by Surface-Initiated Atom Transfer Radical Polymerization. Polym. J. 2005, 37 (10), 767-775.

7. Yoshikawa, C.; Goto, A.; Tsujii, Y.; Fukuda, T.; Yamamoto, K.; Kishida, A., Fabrication of


19

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 31

High-Density Polymer Brush on Polymer Substrate by Surface-Initiated Living Radical Polymerization. Macromolecules 2005, 38, 4604-4610.

8. Lindqvist, J.; Malmström, E., Surface Modification of Natural Substrates by Atom Transfer Radical Polymerization. J. Appl. Polym. Sci. 2006, 100 (5), 4155-4162.

9. Kim, J.; Huang,W.; Miller, M. D.; Baker, G. L.; Bruening, M. L., Kinetics of Surface-Initiated Atom Transfer Radical Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 386-394.

10. Li, L.; Nakaji-Hirabayashi, T.; Kitano, H.; Ohno, K.; Kishioka, T.; Usui, Y., Gradation of Proteins and Cells Attached to the Surface of Bio-Inert Zwitterionic Polymer Brush. Colloids Surf. B. Biointerfaces 2016, 144, 180-7.

11. Huang, Z.; Feng, C.; Guo, H.; Huang, X., Direct Functionalization of Poly(vinyl chloride) by Photo-Mediated ATRP without a Deoxygenation Procedure. Polym. Chem. 2016, 7 (17), 3034-3045.

12. Fukazawa, K.; Nakao, A.; Maeda, M.; Ishihara, K., Photoreactive Initiator for Surface-Initiated ATRP on Versatile Polymeric Substrates. ACS Appl. Mater. Interfaces 2016, 8 (38), 24994-8.

13. Friis, J. E.; Brons, K.; Salmi, Z.; Shimizu, K.; Subbiahdoss, G.; Holm, A. H.; Santos, O.; Pedersen, S. U.; Meyer, R. L.; Daasbjerg, K.; Iruthayaraj, J., Hydrophilic Polymer Brush Layers on Stainless Steel Using Multilayered ATRP Initiator Layer. ACS Appl. Mater. Interfaces 2016, 8 (44), 30616-30627.

14. Du, T.; Li, B.; Wang, X.; Yu, B.; Pei, X.; Huck, W. T.; Zhou, F., Bio-Inspired Renewable Surface-Initiated Polymerization from Permanently Embedded Initiators. Angew. Chem. Int. Ed.


20

Page 21 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

2016, 55 (13), 4260-4.

15. Zhang, T.; Chen, T.; Amin, I.; Jordan, R., ATRP with a Light Switch: Photoinduced ATRP Using a Household Fluorescent Lamp. Polym. Chem. 2014, 5 (16), 4790-4796.

16. Li, B.; Yu, B.; Zhou, F., Spatial Control Over Brush Growth Through Sunlight-Induced Atom Transfer Radical Polymerization Using Dye-Sensitized TiO2 as a Photocatalyst. Macromol. Rapid Commun. 2014, 35 (14), 1287-92.

17. Xu, F. J.; Kang, E. T.; Neoh, K. G., UV-Induced Coupling of 4-Vinylbenzyl Chloride via Surface-Initiated ATRP. Macromolecules 2005, 38, 1573-1580.

18. Yu, W. H.; Kang, E. T.; Neoh, K. G., Controlled Grafting of Comb Copolymer Brushes on Poly(tetrafluoroethylene) Films by Surface-Initiated Living Radical Polymerizations. Langmuir

2005, 21, 450-456.

19. Ohno, K.; Morinaga, T.; Koh, K.; Tsujii, Y.; Fukuda, T., Synthesis of Monodisperse Silica Particles Coated with Well-Defined, High-Density Polymer Brushes by Surface-Initiated Atom Transfer Radical Polymerization. Macromolecules 2005, 38, 2137-2142.

20. Morinaga, T.; Ohno, K.; Tsujii, Y.; Fukuda, T., Two-Dimensional Ordered Arrays of Monodisperse Silica Particles Grafted with Concentrated Polymer Brushes. Eur. Polym. J. 2007, 43 (1), 243-248.

21. Ohno, K.; Morinaga, T.; Takeno, S.; Tsujii, Y.; Fukuda, T., Suspensions of Silica Particles Grafted with Concentrated Polymer Brush: Effects of Graft Chain Length on Brush Layer Thickness and Colloidal Crystallization. Macromolecules 2007, 40, 9143-9150.


21

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 31

22. Ladmiral, V.; Morinaga, T.; Ohno, K.; Fukuda, T.; Tsujii, Y., Synthesis of Monodisperse Zinc Sulfide Particles Grafted with Concentrated Polystyrene Brush by Surface-Initiated Nitroxide-Mediated Polymerization. Eur. Polym. J. 2009, 45 (10), 2788-2796.

23. Ohno, K.; Morinaga, T.; Takeno, S.; Tsujii, Y.; Fukuda, T., Suspensions of Silica Particles Grafted with Concentrated Polymer Brush: A New Family of Colloidal Crystals. Macromolecules 2006, 39, 1245-1249.

24. Morinaga, T.; Ohno, K.; Tsujii, Y.; Fukuda, T., Structural Analysis of “Semisoft” Colloidal Crystals by Confocal Laser Scanning Microscopy. Macromolecules 2008, 41, 3620-3626.

25. Ohno, K.; Akashi, T.; Huang, Y.; Tsujii, Y., Surface-Initiated Living Radical Polymerization from Narrowly Size-Distributed Silica Nanoparticles of Diameters Less Than 100 nm. Macromolecules 2010, 43 (21), 8805-8812.

26. Huang, Y.; Morinaga, T.; Tai, Y.; Tsujii, Y.; Ohno, K., Immobilization of Semisoft Colloidal Crystals Formed by Polymer-Brush-Afforded Hybrid-Particles. Langmuir 2014, 30 (25), 7304-7312.

27. Wang, W.; Cao, H.; Zhu, G.; Wang, P., A Facile Strategy to Modify TiO2 Nanoparticles via Surface-Initiated ATRP of Styrene. J. Polym. Sci., Part A: Polym. Chem. 2010, 48 (8), 1782-1790.

28. Zhang, H.; Lei, X.; Su, Z.; Liu, P., A Novel Method of Surface-Initiate Atom Transfer Radical Polymerization of Styrene from Silica Nanoparticles for Preparation of Monodispersed Core-Shell Hybrid Nanospheres. J. Polym. Res. 2007, 14 (4), 253-260.


22

Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

29. Jhaveri, S. B.; Koylu, D.; Maschke, D.; Carter, K. R., Synthesis of Polymeric Core–Shell Particles Using Surface-Initiated Living Free-Radical Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2007, 45 (9), 1575-1584.

30. Liu, P.; Su, Z., Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) of n-Butyl Acrylate from Starch Granules. Carbohydr. Polym. 2005, 62 (2), 159-163.

31. Liu, P.; Su, Z., Preparation of Polystyrene Grafted Silica Nanoparticles by Two-Steps UV Induced Reaction. J. Photochem. Photobiol., A 2004, 167 (2-3), 237-240.

32. Qin, L.; He, X. W.; Yuan, X.; Li, W. Y.; Zhang, Y. K., Molecularly Imprinted Beads with Double Thermosensitive Gates for Selective Recognition of Proteins. Anal. Bioanal. Chem. 2011, 399 (10), 3375-85.

33. Wang, K.; Fan, X.; Zhang, X.; Zhang, X.; Chen, Y.; Wei, Y., Red Fluorescent Chitosan Nanoparticles Grafted with Poly(2-methacryloyloxyethyl phosphorylcholine) for Live Cell Imaging. Colloids Surf. B. Biointerfaces 2016, 144, 188-95.

34. Morinaga, T.; Honma, S.; Ishizuka, T.; Kamijo, T.; Sato, T.; Tsujii, Y., Synthesis of Monodisperse Silica Particles Grafted with Concentrated Ionic Liquid-Type Polymer Brushes by Surface-Initiated Atom Transfer Radical Polymerization for Use as a Solid State Polymer Electrolyte. Polymers 2016, 8 (4), 146.

35. Yan, J.; Kristufek, T.; Schmitt, M.; Wang, Z.; Xie, G.; Dang, A.; Hui, C. M.; Pietrasik, J.; Bockstaller, M. R.; Matyjaszewski, K., Matrix-free Particle Brush System with Bimodal Molecular Weight Distribution Prepared by SI-ATRP. Macromolecules 2015, 48 (22),


23

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

8208-8218.

36. Savelli, C.; Salvio, R., Guanidine-Based Polymer Brushes Grafted onto Silica Nanoparticles as Efficient Artificial Phosphodiesterases. Chem. Eur. J. 2015, 21 (15), 5856-63.

37. Vasquez, E. S.; Chu, I. W.; Walters, K. B., Janus Magnetic Nanoparticles with a Bicompartmental Polymer Brush Prepared Using Electrostatic Adsorption to Facilitate Toposelective Surface-Initiated ATRP. Langmuir 2014, 30 (23), 6858-66.

38. Kitayama, Y.; Takeuchi, T., Synthesis of CO2/N2-Triggered Reversible Stability-Controllable Poly(2-(diethylamino)ethyl methacrylate)-Grafted-AuNPs by Surface-Initiated Atom Transfer Radical Polymerization. Langmuir 2014, 30 (42), 12684-9.

39. Arita, T., Coating and Dispersion of Ceramic Nanoparticles by UV-Ozone Etching Assisted Surface-Initiated Living Radical Polymerization. Nanoscale 2010, 2 (10), 2073-6.

40. Ohno, K.; Koh, K.; Tsujii, Y.; Fukuda, T., Fabrication of Ordered Arrays of Gold Nanoparticles Coated with High-Density Polymer Brushes. Angew. Chem. Int. Ed. 2003, 42 (24), 2751-4.

41. Ryosuke Matsuno, K. Y., Hideyuki Otsuka, Atsushi Takahara, Polystyrene-Grafted Magnetite Nanoparticles Prepared through Surface-Initiated Nitroxyl-Mediated Radical Polymerization. Chem. Mater. 2003, 15, 1-5.

42. Ohno, K.; Koh, K.-m.; Tsujii, Y.; Fukuda, T., Synthesis of Gold Nanoparticles Coated with Well-Defined,

High-Density

Polymer

Brushes

by

Surface-Initiated

Living

Radical

Polymerization. Macromolecules 2002, 35, 8989-8993.

43. Liu, P.; Guo, J., Hg(II) Removal with Polyacrylamide Grafted Crosslinked Poly(vinyl chloride)


24

Page 25 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Beads via Surface-Initiated Controlled/“Living” Radical Polymerization. J. Appl. Polym. Sci.

2006, 102 (4), 3385-3390.

44. Chung, P.-W.; Kumar, R.; Pruski, M.; Lin, V. S. Y., Temperature Responsive Solution Partition of

Organic-Inorganic

Hybrid

Poly(N-isopropylacrylamide)-Coated

Mesoporous

Silica

Nanospheres. Adv. Funct. Mater. 2008, 18 (9), 1390-1398.

45. Yoshikawa, C.; Goto, A.; Ishizuka, N.; Nakanishi, K.; Kishida, A.; Tsujii, Y.; Fukuda, T., Size-Exclusion Effect and Protein Repellency of Concentrated Polymer Brushes Prepared by Surface-Initiated Living Radical Polymerization. Macromol. Symp. 2007, 248 (1), 189-198.

46. Lenarda, M.; Chessa, G.; Moretti, E.; Polizzi, S.; Storaro, L.; Talon, A., Toward the Preparation of a Nanocomposite Material Through Surface Initiated Controlled/“Living” Radical Polymerization of Styrene Inside the Channels of MCM-41 Silica. J. Mater. Sci. 2006, 41 (19), 6305-6312.

47. Chen, X.; Yuan, L.; Yang, P.; Hu, J.; Yang, D., Covalent Polymeric Modification of Graphene Nanosheets via Surface-Initiated Single-Electron-Transfer Living Radical Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2011, 49 (23), 4977-4986.

48. Deng, Y.; Li, Y.; Dai, J.; Lang, M.; Huang, X., Functionalization of Graphene Oxide Towards Thermo-Sensitive Nanocomposites via Moderate in situ SET-LRP. J. Polym. Sci., Part A: Polym. Chem. 2011, 49 (22), 4747-4755.

49. Kumar, A.; Behera, B.; Thakre, G. D.; Ray, S. S., Covalently Grafted Graphene Oxide/Poly(Cn-acrylate) Nanocomposites by Surface-Initiated ATRP: An Efficient Antifriction,


25

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

Antiwear, and Pour-Point-Depressant Lubricating Additive in Oil Media. Ind. Eng. Chem. Res.

2016, 55 (31), 8491-8500.

50. Bansal, A.; Kumar, A.; Kumar, P.; Bojja, S.; Chatterjee, A. K.; Ray, S. S.; Jain, S. L., Visible Light-Induced Surface Initiated Atom Transfer Radical Polymerization of Methyl Methacrylate on Titania/Reduced Graphene Oxide Nanocomposite. RSC Adv. 2015, 5 (27), 21189-21196.

51. Zhang, H.; Ye, W.; Zhou, F., Preparation of Monodispersed and Lipophilic Attapulgite and Polystyrene Nanorods via Surface-Initiated Atom Transfer Radical Polymerization. J. Appl. Polym. Sci. 2011, 122 (5), 2876-2883.

52. Majoinen, J.; Walther, A.; McKee, J. R.; Kontturi, E.; Aseyev, V.; Malho, J. M.; Ruokolainen, J.; Ikkala, O., Polyelectrolyte Brushes Grafted from Cellulose Nanocrystals Using Cu-Mediated Surface-Initiated Controlled Radical Polymerization. Biomacromolecules 2011, 12 (8), 2997-3006.

53. Tsujii, Y.; Ohno, K.; Yamamoto, S.; Goto, A.; Fukuda, T., Structure and Properties of High-Density Polymer Brushes Prepared by Surface-Initiated Living Radical Polymerization. Adv. Polym. Sci. 2006, 197, 1-45.

54. Barbey, R.; Lavanant, L.; Paripovic, D.; Schuwer, N.; Sugnaux, C.; Tugulu, S.; Klok, H.-A., Polymer Brushes via Surface-Initiated Controlled Radical Polymerization Synthesis, Characterization, Properties, and Applications. Chem. Rev. 2009, 109, 5437-5527.

55. Radhakrishnan, B.; Ranjan, R.; Brittain, W. J., Surface Initiated Polymerizations from Silica Nanoparticles. Soft Matter 2006, 2 (5), 386-396.


26

Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

56. Edmonson, S.; Osborne, V. L.; Huck, W. T. S., Polymer Brushes via Surface-Initiated Polymerizations. Chem. Soc. Rev. 2004, 33 (1), 14-22.

57. Hachisu, S.; Kobayashi, Y.; Kose, A., Phase Separation in Monodisperse Latexes. J. Colloid Interface Sci. 1973, 42, 342-348.

58. Kose, A.; Hachisu, S., Kirkwood-Alder Transition in Monodisperse Latexes I. Nonaqueous System. J. Colloid Interface Sci. 1974, 46, 460-469.

59. Pusey, P. N.; Megen, W. V., Phase Behaviour of Concentrated Suspensions of Nearly Hard Colloidal Spheres. Nature (London) 1986, 320, 340-342.

60. Megen, W. V.; Underwood, S. M., Change in Crystallization Mechanism at the Glass Transition of Colloidal Spheres. Nature (London) 1993, 362, 616-618.

61. Okubo, T., Polymer Colloidal Crystals. Prog. Polym. Sci. 1993, 18, 481-517.

62. Dinsmore, A. D.; Crocker, J. C.; Yodh, A. G., Self-Assembly of Colloidal Crystals. Curr. Opin. Colloid. Interface Sci. 1998, 3 (1), 5-11.

63. Huang, Y.; Sasano, T.; Tsujii, Y.; Ohno, K., Well-Defined Polymer-Brush-Coated Rod-Shaped Particles: Synthesis and Formation of Liquid Crystals. Macromolecules 2016, 49 (22), 8430-8439.

64. Huang, Y.; Ishige, R.; Tsujii, Y.; Ohno, K., Synthesis of Iron Oxide Rods Coated with Polymer Brushes and Control of their Assembly in Thin Films. Langmuir 2015, 31 (3), 1172-9.

65. Xia, Y.; Gates, B.; Yin, Y.; Lu, Y., Monodispersed Colloidal Spheres: Old Materials with New


27

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

Applications. Adv. Mater. 2000, 12, 693-713.

66. Adam, M.; Gaponik, N.; Eychmuller, A.; Erdem, T.; Soran-Erdem, Z.; Demir, H. V., Colloidal Nanocrystals Embedded in Macrocrystals: Methods and Applications. J. Phys. Chem. Lett. 2016, 7, 4117-4123.

67. Ozin, G. A.; Yang, S. M., The Race for the Photonic Chip: Colloidal Crystal Assembly in Silicon Wafers. Adv. Funct. Mater. 2001, 11, 95-104.

68. Zhang, J.; Li, Y.; Zhang, X.; Yang, B., Colloidal Self-Assembly Meets Nanofabrication: From Two-Dimensional Colloidal Crystals to Nanostructure Arrays. Adv. Mater. 2010, 22 (38), 4249-69.

69. Stein, A.; Li, F.; Denny, N. R., Morphological Control in Colloidal Crystal Templating of Inverse Opals, Hierarchical Structures, and Shaped Particles. Chem. Mater. 2008, 20, 649-666.

70. Aguirre, C. I.; Reguera, E.; Stein, A., Tunable Colors in Opals and Inverse Opal Photonic Crystals. Adv. Funct. Mater. 2010, 20 (16), 2565-2578.

71. Holtz, J. H.; Asher, S. A., Polymerizaed Colloidal Crystal Hydrogel Films as Intelligent Chemcial Sensing Materials. Nature (London) 1997, 389, 829-832.

72. Caruso, F., Nanoengineering of Particle Surfaces. Adv. Mater. 2001, 13, 11-22.

73. Furumi, S.; Fudouzi, H.; Miyazaki, H. T.; Sakka, Y., Flexible Polymer Colloidal-Crystal Lasers with a Light-Emitting Planar Defect. Adv. Mater. 2007, 19 (16), 2067-2072.

74. Yoshinaga, K.; Fujiwara, K.; Mouri, E.; Ishii, M.; Nakamura, H., Stepwise Conctrolled


28

Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Immobilization of Colloidal Crystals Formed by Polymer-Grafted Silica Particles. Langmuir

2005, 21, 4471-4477.

75. Dupont, J.; Souza, R. F. d.; Suarez, P. A. Z., Ionic Liquid (Molten Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102, 3667-3692.

76. He, Z.; Alexandridis, P., Nanoparticles in Ionic Liquids: Interactions and Organization. Phys. Chem. Chem. Phys. 2015, 17 (28), 18238-61.

77. Ueno, K.; Fukai, T.; Watanabe, M., Thermosensitive Soft Glassy Colloidal Arrays of Block-Copolymer-Grafted Silica Nanoparticles in an Ionic Liquid. Polym. J. 2015, 48 (3), 289-294.

78. Ueno, K.; Watanabe, M., From Colloidal Stability in Ionic Liquids to Advanced Soft Materials Using Unique Media. Langmuir 2011, 27 (15), 9105-15.

79. Ueno, K.; Sano, Y.; Inaba, A.; Kondoh, M.; Watanabe, M., Soft Glassy Colloidal Arrays in an Ionic Liquid: Colloidal Glass Transition, Ionic Transport, and Structural Color in Relation to Microstructure. J. Phys. Chem. B 2010, 114, 13905-13103.

80. Kanai, T.; Yamamoto, S.; Sawada, T., Swelling of Gel-Immobilized Colloidal Photonic Crystals in Ionic Liquids. Macromolecules 2011, 44 (15), 5865-5867.

81. Furumi, S.; Kanai, T.; Sawada, T., Widely Tunable Lasing in a Colloidal Crystal Gel Film Permanently Stabilized by an Ionic Liquid. Adv. Mater. 2011, 23 (33), 3815-20.

82. Nomura, A.; Ohno, K.; Fukuda, T.; Sato, T.; Tsujii, Y., Lubrication Mechanism of Concentrated Polymer Brushes in Solvents: Effect of Solvent Viscosity. Polym. Chem. 2012, 3 (1), 148-153.


29

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

83. Ueno, K.; Fukai, T.; Nagatsuka, T.; Yasuda, T.; Watanabe, M., Solubility of Poly(methyl methacrylate) in Ionic Liquids in Relation to Solvent Parameters. Langmuir 2014, 30 (11), 3228-35.

84. Hoover, W. G.; Ree, F. H., Melting Transition and Communal Entropy for Hard Spheres. J. Chem. Phys. 1968, 49 (8), 3609-3617.

85. Alder;, B. J.; Hoover, W. G.; Young, D. A., Studies in Molecular Dynamics. V. High-Density Equation of State and Entropy for Hard Disks and Spheres. J. Chem. Phys. 1968, 49 (8), 3688-3696.

86. Rundquist, P. A.; Photinos, P.; Jagannathan, S.; Asher, S. A., Dynamical Bragg Diffraction from Crystalline Colloidal Arrays. J. Chem. Phys. 1989, 91 (8), 4932-4941.


30

Page 31 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

For table of contents use only

Semisoft Colloidal Crystals in Ionic Liquids Yun Huang, Akisato Takata, Yoshinobu Tsujii, and Kohji Ohno*


31

Semisoft Colloidal Crystals in Ionic Liquids - Langmuir (ACS

Recommend Documents