Flexible or Robust Amorphous Photonic Crystals from Network

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Flexible or Robust Amorphous Photonic Crystals from NetworkForming Block Copolymers for Sensing Solvent Vapors Cheng-Sian Wu, Po-Yu Tsai, Teng-Yi Wang, En-Li Lin, Yen-Chang Huang, and Yeo-Wan Chiang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b00326 • Publication Date (Web): 08 Mar 2018 Downloaded from http://pubs.acs.org on March 8, 2018

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Analytical Chemistry

Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors

Cheng-Sian Wu, Po-Yu Tsai, Teng-Yi Wang, En-Li Lin, Yen-Chang Huang, Yeo-Wan Chiang*

Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan

Fax: (+886) 7-5252000 ext 4081 E-mail: [email protected]

1

ACS Paragon Plus Environment

Analytical Chemistry 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

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Abstract Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene-block-poly(methyl

methacrylate)

(PS-PMMA)

block

copolymers.

Kinetically-controlled microphase separation combining with synergistic weak incompatibility gives rise to short-range-order network microstructures, exhibiting noniridescent optical properties. Solubility-dependent solvatochromism with distinct responses to various organic solvent vapors is observed in the network-forming APC film. By taking advantage of photodegradation of the PMMA block, nanoporous network-forming films were prepared for subsequent template synthesis of robust SiO2- and TiO2-based APC films through sol-gel reaction. Consequently, refractive index contrast of the APC film was able to manipulated, resulting in intensely enhanced reflectivity and increased response rate for detecting solvent vapor. With the integration of self-assembly and photolithography approaches, flexible and robust network-forming APC films with well-defined photopatterned textures are carried out. This can provide a novel means for the design of photopatterned organic or inorganic APC films for sensing solvent vapors.

2


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Table of Contents Graphic

Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors Cheng-Sian Wu, Po-Yu Tsai, Teng-Yi Wang, En-Li Lin, Yen-Chang Huang, Yeo-Wan Chiang*

3



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Introduction Amorphous photonic crystals (APCs) from living organisms have been drawn much attention due to the specific optical properties of isotropic photonic bandgap (PBG) or pseudogap.1-5 Recently, bioinspired macaw-feather-like short-range-order interconnected morphology was intensely investigated due to its angle-independent reflectance wavelength in visible wavelength range. Although full bandgap of conventional photonic crystals can also shows the angle-independent reflectance wavelength, the fabrication of full-bandgap materials requires high-refractive-index contrast and is very difficult to achieve, especially for 3D structures. Unlike conventional

long-range-order

short-range-order

(not

photonic

completely

crystals

random)

(PCs),

microstructures

APCs exhibit

featuring unique

angle-independent or noniridescent coloration. This gives uniform structural coloration and is promising in a variety of novel applications such as random lasing, display, sensor, and energy fields.6-9 The top-down photolithography method, which can easily prepare long-range-order patterns, has limitations on the fabrication of the short-range-order APCs. Accordingly, the APCs from bottom-up self-assembly are intensely exploited such as controlled packing of colloidal particles,10-13 phase separation of polymers,14 and microstructural replication from living creatures. Among them, the macaw-feather-like interconnected network microstructure plays a 4


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critical role to reach complete PBG in contrast to the isolated microstructure.15,16 However, human-made APCs are rarely reported due to the difficulty in preparation of short-range-order microstructures (not completely disorder) with the length scale corresponding to visible wavelength. Therefore, the self-assembled microstructures of living creatures such as macaw feathers frequently provide the fine templates for the fabrication of the network-structured APCs by backfilling and replication.17-22 Because of the restriction on acquiring these templates from nature, manufacturing large-area human-made APCs with macaw-feather-like interconnected network microstructures is still a great challenge. Thomas and coworkers had prepared high-Mw polystyrene-block-poly(2-vinyl pyridine) (PS-P2VP) and polystyrene-block-polyisoprene (PS-PI) BCP films with long-range-order lamellar microstructures.23-25 By solvent annealing, highly-aligned lamellar microstructures parallel to substrate could be successfully obtained. Owing to insufficient lattice size, the visible reflectance wavelength could be achieved through stretching the block chains by brush copolymers or introducing external additives.26-29 The reflectance wavelength in the parallel lamellar microstructures are strongly angle dependent. This expresses the result that the reflectance wavelength decreases with the increase of the viewing angle away from the lamellar normal, namely, angle-dependent or iridescent coloration. For the lamellar microstructure, it is unease 5



to

serve

as

a

template

for

subsequent

Page 6 of 40

infiltration

or

backfilling

of

high-refractive-index materials due to the collapse of the lamellar microstructure after removing one of layered microdomains and subsequent calcination. Therefore, 3D microstructures such as double gyroid and amorphous network microstructure are the good candidates for further modifying the refractive index contrast and reaching high thermal resistance. However, owing to the limitation of synthesis, gyroid- and network-forming photonic crystals featuring visible reflectance wavelength are rarely to be obtained. Urbas and coworkers in 2002 proposed a gyroid photonic crystal having near-UV reflectance wavelength at 327 nm using an ultra-high-Mw PS-PI BCP.30 Recently, our group proposed an unique method, i.e., trapping of structural coloration, to trap visible structural coloration of a solvated gyroid-structured photonic crystal in solid state.31 However, investigation about the fabrication of angle-independent APCs from self-assembly of BCPs is not proposed. As a result, the fabrication of human-made noniridescent network-forming photonic crystals is emerging for further demonstration of the advanced noniridescent optical properties for applications. In this study, we developed a facile technique to fabricate visible-wavelength APCs

having

microstructures

macaw-feather-like from

the

short-range-order

interconnected

self-assembly

of

6


the

network high-Mw

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polystyrene-block-poly(methyl

methacrylate)

(PS-PMMA)

BCP.

Unlike

the

formation of long-range-order microstructures from strongly incompatible BCPs, short-range-order

network

microstructures

were

obtained

using

the

weakly-incompatible PS-PMMA BCP. The network-structured PS-PMMA thin film exhibited solvent-sensitive angle-independent reflectivity due to the change of chain stretching level dominated by polymer-solvent interaction. Taking advantage of the photodegradation of the PMMA block allows us to fabricate robust SiO2- and TiO2-based APC film having different refractive index contrast by template synthesis of sol-gel method. Under the exposure of solvent vapors, the TiO2-based APC film having high refractive index contrast exhibited rapid color change, being potential for sensing applications. The large-area APC thin film with a well-defined photopatterned texture by masking and photolithography was also demonstrated.

7



Experimental Section Materials and Sample Preparation. A high-Mw PS-PMMA BCP was used as received from Polymer Source, Inc. (Dorval, Canada). The number-average molecular weights of PS and PMMA block chains are 550 and 340 kg mol-1, respectively. The volume fraction of the PS was calculated as 0.65 by which the densities of PS and PMMA are 1.05 and 1.18 g cm-3, respectively. BCP thin films were spin-cast on wafer substrates at a rate of 1500 rpm at room temperature. Nanoporous Inorganic Network Microstructures. The nanoporous PS template was immersed into the SiO2 precursor solution consisting of a mixture of tetraethyl orthosilicate, HCl (0.1 M) and methanol with the weight ratio of TEOS to HCl to methanol = 10g:1g:25g at 25 °C for 3 h. The solvated template was then dried under vacuum for 2 h and subsequently calcined at 550°C for 12 h, giving the nanoporous SiO2-network microstructures. Similary, a TiO2 precursor solution (TiCl4) with pH = 2 (4g) was first mixed with anhydrous methanol (10g). The nanoporous PS template was immersed in the previous mixture at 0 °C for 2 h and the solvated template was then dried under vacuum for 2 h. Two-stage calcination process was conducted including first annealing at 440°C for 1 h under nitrogen and subsequent annealing at 500°C for 2 h at atmosphere. This can give the nanoporous TiO2-network microstructures. 8


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Transmission Electron Microscopy (TEM). To explore the cross-sectional microstructure, the film was first embedded by epoxy resin. The epoxy-embedded film was microsectioned at room temperature using a Reichert ultracut microtome equipped with a diamond knife. The microsectioned slices were then stained by RuO4 for 30 min. Morphological observation was conducted by a JEOL JEM-2100 TEM at an accelerating voltage of 200 kV. After staining by RuO4, PMMA is bright and PS is dark under TEM observation. Reflectivity Measurements. Reflectivity spectra were measured by an optical microscope (ESPA N-800M) equipped with a fiber-optic spectrometer (B&W Tek

i-trometer). An Ag mirror is used as 100% reflectivity of standard in microscopic spectroscopy. The in-situ reflectivity measurements were conducted with a customized quartz chamber in the presence of various solvent vapors.

9



Results and Discussion Flexible PS-PMMA APC Films Featuring Network Microstructures. The high-Mw PS-PMMA films were prepared on wafer substrates by spin casting. In Figure 1a, the cross-sectional micrograph of transmission electron microscope (TEM) displayed an oriented and stretched double gyroid morphology featuring interconnected microstructures with curved interfaces in the as-spun film from a good solvent, 1, 1, 2-trichloroethane (TCE), in accordance with the solubility data (δPS = 9.1, δPMMA = 9.5 and δTCE = 9.5 cal0.5cm-1.5). With RuO4 staining, the PS region appears dark and the PMMA region is bright. In contrast to the well-order lamellar morphology in bulk state (Figure S1), the distorted gyroid morphology with many defects was observed in the as-spun thin film due to insufficient time for the self-ordering process of the high-Mw block chains (film drying time is about 3 min for spin casting). Notably, the corresponding fast Fourier transform (FFT) pattern revealed the anisotropic arc texture along meridian direction (i.e., substrate normal) (inset of Figure 1a). This indicates that the as-spun lamellar morphology still exhibits the preferred orientation parallel to the substrate surface, which is attributed to thin-film confinement effect.32 The ultraviolet-visible (UV-Vis) spectra revealed the corresponding reflectivity at 406 nm. Also, a blue shift of the reflectivity to shorter-wavelength range could be obtained with the increase of the angle (θ) 10


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enclosed by the incident probe beam and the substrate normal (Figure 1c). This is attributed to the preferred parallel orientation of the lamellar microstructure. Consequently, the as-spun lamella-forming PS-PMMA film displayed the angle-dependent and iridescent coloration of conventional PCs. After fuming by TCE vapor at 60°C for 6 h, we found that the previous lamellae transformed into interconnected network microstructures (Figure 1b). A nearly ring texture without high-order signals was obtained in the two-dimensional ultra-small angle-X-ray scattering (USAXS) pattern (inset of Figure 1b). Also, only a broad reflection peak was found in the one-dimensional USAXS profile (Figure S2), indicating that the network microstructure exhibits the isotropic orientation and short-range order. As calculated, the network microstructure possesses a statistical length of 129 nm. In addition, the reflectivity spectra of the network-structured thin film reveal the unchanged peak position of the reflectance wavelength at 410 nm despite the variation of the θ value, namely, noniridescent or angle-independent reflectivity (Figure 1d). This is due to the isotropic orientation of the short-range-order network microstructures similar to the channel-type spongy keratin structures found in macaw blue feather bards. Here, the term of pseudogap wavelength is used to describe the bandgap property of the APC due to the incapability of defining the direction of incident light with respect to an isotropic 11



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short-range-order microstructure, distinct from the term of bandgap wavelength utilized in the typical PC. Owing to the isotropic optical media, the pseudogaps in APCs exhibit angle-independent or noniridescent features, namely, evenly isotropic reflection in all directions. The pseudogap wavelength of the APC can be calculated by Equation (1):

θ 2dn cos = λ (1) 2 where λ is the pseudogap wavelength or the reflectance peak wavelength; d is the statistical length of the microstructure; neff is the effective refractive index; θ is the angle enclosed by incident beam and the film normal. The value of neff,s of the solid-state PS-PMMA BCP can be estimated by the Bruggeman effective medium model:33,34

(1 − ϕ )

,

!,

+ ϕ

# ,

# !,

=0

(2)

where φi and ni are the volume fraction and refractive index of the i component, respectively. Based on the data of nPS=1.592, nPMMA=1.491 at 580 nm and φPS =0.65, the value of neff,s is calculated as 1.556. With the incident light source parallel to the film normal and d=129 nm, the reflectance peak wavelength λ can be calculated as 402 nm which is similar to the observed peak wavelength at 410 nm in Figure 1d. Consequently, the APC film having bioinspired network microstructures could be fabricated from self-assembly of the high-Mw PS-PMMA BCP. Different from the 12


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long-range-order PCs fabricated from strongly incompatible high-Mw BCPs such as polystyrene-block-polyisoprene (PS-PI) (Flory Huggins interaction parameter, χPS/PI, is 0.15 at 25°C)35 and polystyrene-block-poly(2-vinyl pyridine) (PS-P2VP) (χPS/P2VP= 0.18 at 25°C),36 we suggest that weak incompatibility, i.e., samll value of interaction parameter (χ), between the PS and PMMA blocks (χPS/PMMA= 0.04 at 25°C)37 is effective in the formation of the short-range-order network microstructure. Although high N (degree of polymerization) value in a high-Mw BCP largely increases the overall segregation strength, i.e., χN value, the kinetic reason due to N usually gives rise to the non-equilibrium or metastable phase-separated microstructure in the self-assembly of high-Mw BCPs.38-40 In addition, the long-range-order lamellar microstructure was unobserved in the high-Mw PS-PMMA films after annealing with various solvent vapors (Figure S3) even though the lamellar morphology is the equilibrium morphology in bulk state. In contrast, long-range-order microstructures can easily achieved in the high-Mw PS-PI25 or high-Mw PS-P2VP23 films by using extremely low-vapor-pressure solvent for spin casting or by solvent annealing, respectively. Also, short-range-order network microstructures are hardly observed and cannot be further stabilized after thermal or solvent annealing in the high-Mw PS-PI and PS-P2VP BCPs due to the strong incompatibility (i.e., large χ value) between the constituted

blocks.

Although

the

disorder

network-like

13


morphology

(not


short-range-order

network)

might

be

obtained

Page 14 of 40

via

spin

casting

from

a

high-vapor-pressure solvent such as dichloromethane, the completely random morphology could only give serious incoherent scattering rather than constructive interference. Furthermore, the Mw,PS and Mw,PMMA in the high-Mw PS-PMMA BCP are much higher than the critical entangled molecular weights of the PS (Me,PS~19500 g/mol) and PMMA (Me,PMMA~20000 g/mol), respectively. Therefore, the severe entangled PS-PMMA BCP chains lead to prolonged relaxation time, τ, which is proportional to the third power of the degree of polymerization, τ~N3. Because of the large value of τ, the network microstructure might be stabilized kinetically. This can be confirmed by further increasing the solvent annealing time up to 24 h. As shown in Figure S4, we still obtained short-range-order network microstructure rather than long-range-order lamellar microstructure. This indicates that this short-range-order network microstructure is relatively stable in the high-Mw PS-PMMA film at a sufficient condition.

14


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Figure 1. Cross-sectional TEM micrographs of the PS-PMMA films (a) spin-cast from TCE (5wt%) and (b) followed by TCE annealing at 60°C for 6 h. The insets reveal the two-dimensional FFT and USAXS patterns for (a) and (b), respectively. (c) and (d) are the reflectivity spectra of (a) and (b) measured with different angles enclosed by the incident beam and the film normal.

Solvatochromism by Solvent Quality. Also, the flexible network-forming PS-PMMA film exhibited solvatochromic behavior by chloroform vapor (Figure 2a). To explore the stimuli-sensitive behavior, the network-forming PS-PMMA film was placed into a customized disk-shaped quartz chamber containing saturated chloroform vapor. When exposed to the chloroform vapor, an optical microscope equipped with a 15



UV-Vis spectrometer was employed to in-situ measure the reflectance wavelength change with elapsed time. During the fuming process, a significant bathochromic shift (i.e., red shift to longer-wavelength range) of the reflectance wavelength from the initial value of 410 nm to a maximum value of 660 nm was obtained due to the solvent–driven swelling of the network microdomain (Figure 2b). In contrast, a hypsochromic shift (i.e., blue shift) to shorter-wavelength range of the reflectance wavelength was obtained as chloroform vapor gradually evaporates, resulted from the deswelling of the network microdomain. The reflectance wavelength finally returned to the initial wavelength position after the complete evaporation of chloroform, indicating the reversible solvatochromism of the PS-PMMA APC film. The decrease of the reflectance intensity during swelling results from the decrease of refractive index difference with the increase of the solvent contents in the APC thin film (Figure S5). In Figure S6, after several cycles of solvatochromism, the dried APC film still displayed the unchanged network microstructure, indicating the fine stability of the network morphology due to severe chain entanglement. Figure 3 shows a series of optical photographs taken under various viewing angles for the PS-PMMA APC film exposed under saturated chloroform vapor. As shown, the red coloration exhibited the angle-independent feature for the solvated PS-PMMA film upon swelling in the chloroform vapor (Supplementary Movie S1). 16


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Thickness dependence of the films during fuming can be determined from the in-situ reflectivity spectra in Figure 2b. The swelling process of the PS-PMMA APC film in various solvents is one dimensional along the film normal, due to the confinement effect along in-plane directions. Based on the calculated results of neff,s the discrepancy is insignificant between the Bruggeman effective medium model (1.556) and the linear relationship model (1.557) (see supporting information). Also, it becomes much more complicated to describe the relationship among λ, d and neff using the Bruggeman effective medium model for the APC film swollen by solvent vapor. Therefore, a linear relationship model for the calculation of neff was proposed. The effective refractive index of the gel-state PS-PMMA BCP film (neff,g) during solvent fuming could be thus expressed by Equation (3): neff,g ≈ nBCPφBCP + nsφs =1.556φBCP+1.443(1-φBCP) = 1.556(d0/d) +1.443(1- d0/d) (3) where d0 and d is the statistical length of the network microstructure before and during fuming, respectively; φBCP and φs are the volume fraction of the BCP and chloroform solvent (φBCP + φs=1), respectively. With this simplification, a concise relationship (Equation 4) between the reflectance wavelength and statistical length of the microstructure during fuming could be formulated by combining Equations (3) and (1) with d0 =130 nm, nBCP=1.556 and ns=1.443. λ = 29.38 + 2.886d

(4)

17



With the known reflectance wavelength in Figure 2b, the corresponding statistical length of the microstructure (d), swelling ratio (α) and film thickness during fuming can be calculated (Table 1). In Figure S7, the reflectance wavelength varied with the film thickness during fuming can be thus obtained, showing linear relationship. We also found that the maximum reflectance wavelength was strongly dependent upon the solvent quality (Figure 4). Table 2 summarizes the maximum peak positions of the APC film exposed under various solvent vapors. As shown, no shift of the reflectance wavelength at 410 nm is obtained in the presence of cyclohexane vapor, i.e., a poor solvent for both PS and PMMA in accordance with the large difference in the values of solubility parameters of PS, PMMA and cyclohexane (δPS = 9.1, δPMMA = 9.5 and δcyclohexane = 8.2 cal0.5cm-1.5).41 When the APC film was exposed in the PS-selective solvent vapor, toluene (δtoluene = 8.9 cal0.5cm-1.5), the reflectance wavelength reaches the maximum wavelength of 582 nm. In contrast, when exposed under benzene vapor (δbenzene = 9.1 cal0.5cm-1.5), the large red shift of the reflectance wavelength to 700 nm is obtained. However, when exposed under chloroform vapor (δchloroform = 9.2 cal0.5cm-1.5), the peak maximum slightly decreases to 660 nm. Because of high vapor pressure of chloroform (196.7 mmHg at 25 °C), the decrease of the maximum wavelength is due to the reduced segregation strength by screen effect of chloroform vapor.42 When using a PMMA-selective solvent such as 18


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acetone (δacetone = 9.7 cal0.5cm-1.5) for fuming, we observed the smaller red shift of the maximum wavelength at 473 nm. Owing to the severe entanglement of the high-Mw PS-PMMA chains, the APC film after several tests of solvatochromism would not give rise to the morphological change. This can be confirmed by the cross-sectional TEM micrographs exhibiting the preserved short-range-order network microstructures after 10-cycle solvatochromic treatments with various solvent vapors (Figure S8). As a result, the maximum solvatochromic reflectance wavelength of the PS-PMMA ACP film is strongly affected by the solvent/polymer solubility and the vapor pressure of the solvent.

Figure 2. (a) Swelling and deswelling photographs of the PS-PMMA APC film exposed in chloroform vapor. (b) In-situ reflectivity spectra measured during the fuming process with chloroform vapor. 19



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Figure 3. A series of optical photographs taken at various viewing angles for the solvated PS-PMMA APC film exposed under saturated chloroform vapor. (a) 0°, (b) 10°, (c) 30° and (d) 40°. Table 1. Parameters during fuming process with chloroform vapor.

a

d(nm)b

αc

Film thickness (µm)

φBCP

410

130

1

3.1d

1

463

150

1.15

3.57

0.87

509

166

1.28

3.95

0.79

576

189

1.45

4.51

0.69

660

219

1.68

5.20

0.59

Measured by Figure 2b.

b c

λ (nm)a

Calculated by Equation (4).

Swelling ratio = d/do

d

Measured by Figure 1b.

Figure 4. The reflectivity spectra of the maximum reflectance wavelengths of the network-forming PS-PMMA APC film in the presence of various solvent vapors. 20


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Table 2. Maximum reflectance wavelengths varied with various solvents. λmax(nm)a

δ(cal/cm3)1/2b

Vs (mmHg)c

nd

cyclohexane

410

8.2

97.5

1.426

toluene

582

8.9

28.4

1.497

benzene

700

9.1

95.3

1.501

chloroform

660

9.2

196.5

1.443

acetone

473

9.7

229.6

1.357

Solvent

a

Determined by UV-Vis spectra.

b c

Solubility parameter.

Vapor pressure at 25°C.

d

Refractive index.

Robust APC Films with Distinct Refractive Index Contrasts. With a degradable BCP template, a robust inorganic 3D structure such as a double gyroid microstructure could be prepared by sol-gel synthesis, followed by calcination.43-46 In contrsat to previous flexible APC films, robust APC films could be accomplished by template synthesis of inorganic ceramic materials using this photodegradable PS-PMMA BCP (Figure 5a). After exposed to UV irradiation of 254 nm (3 mWcm-2) for 30 min, the exposed network-forming PS-PMMA film was then immersed into acetic acid to remove the decomposed PMMA block chains. In Figure 5b, the cross-sectional micrograph by field emission scanning electron microscope (FESEM) revealed the porous PS-network microstructure. In addition, the porous PS-network film exhibited much stronger reflectivity than the intrinsic PS-PMMA film prior to etching (Figure 6). This is attributed to the enlarged refractive index contrast defined as the ratio of 21



the refractive index of the high-n material to that of the low-n material (nPS/nAir ~ 1.592 > nPS/nPMMA ~ 1.068). To fabricate robust APC films, the porous PS template was immersed into a SiO2 or TiO2 precursor solution. After subsequently calcination, robust porous inorganic APC films were obtained. The top- and side-view FESEM micrographs clearly revealed the successful replication of the network microstructures in the SiO2-based APC film (Figure 5c). This self-supporting network further confirms the high interconnectivity of the short-range-order network microstructure. The reflectivity spectrum of the SiO2-based APC film showed weak reflectivity (Figure 6) due to the reduced refractive index contrast (nSiO2/nAir ~ 1.45) as compared with nPS/nAir(~ 1.592). High-refractive-index materials such as TiO2 (nTiO2 ~ 2.5) have been considered as one of the promising materials to open up photonic bandgaps. The FESEM micrograph showed that well-defined porous TiO2-network microstructures could be obtained after calcination (Figure 5d). The corresponding wide-angle X-ray diffraction profile reveals the characteristic reflections of the anatase phase for this TiO2-network microstructure (Figure S9). The corresponding reflectivity profile revealed that an intense and broad reflectance band was observed due to high refractive index contrast (nTiO2/nAir ~ 2.5). Notably, except for refractive index contrast, the reflectance wavelength is also determined by the change of the fill fraction at different stages. As reported by Thomas and coworkers,47,48 the decreased 22


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fill fraction of a high-refractive-index component results in the decrease of the width of the photonic gap at a constant dielectric contrast. Here, the major composition is PS possessing the volume fraction of 0.65 in the porous PS (PS/air) film. In contrast, in the TiO2/air film, the major composition is TiO2 having the volume fraction of 0.35. Although the decrease of the fill fraction in the TiO2/air film after calcination may give rise to the decrease of the width of the photonic gap, the increase of the refractive index contrast could inversely extend the width of the photonic gap. Accordingly, the photonic properties of the APC films were also affected by the competition between the effects of the fill fraction and the refractive index contrast. As a result, the reflectivity of the APC film could be manipulated by alternating the refractive index contrast and the fill fraction through degradation or replacement of the PMMA microdomain. Notably, the strongly scattering background ranging from visible to near infrared region was observed in the TiO2-network APC film (Figure 6). As reported,49 the strongly scattering background might be due to the formation of defects after calcination and high Fresnel loss. As shown in Figure S10, the low-magnitude FESEM micrograph revealed large-area TiO2 network microstructures with few defects in the TiO2-based APC film after calcination. Accordingly, the strongly scattering background in the near IR region should not be mainly attributed to the formation of defects after calcination. We suggest that this might be attributed 23



to the high Fresnel loss. As calculated, the Fresnel loss would be 18% for a dielectric material with the refractive index of 2.5. In addition, TiO2 possesses a strongly wavelength-dependent refractive index, for instance, 2.9 at 400 nm and 2.5 at 900 nm. The trend of the wavelength-dependent refractive index of TiO2 exhibits the similar inclination of the reflectance profile of TiO2-based APC film in Figure 6. In Figure 7, when the TiO2-based APC film was exposed under benzene vapor, the red-shifting structurally colour change form blue to green was clearly observed (Supplementary Movie S2). The red-shifting reflectance wavelength for the TiO2/air film exposed under benzene vapor is mainly due to the increase of the effective refractive index by diffusion of benzene vapor into the pores. In contrast to nAir =1 of the air pores in the TiO2/air film prior to fuming, the existence of benzene vapor (nbenzene=1.501) in the pores could increase the effective refractive index of the TiO2/air/benzene film, resulting in red-shifting reflectance wavelength. When the lid was removed, the green hue rapidly turned back to the initial blue color (Supplementary Movie S3). This indicates that the robust TiO2-based APC film possesses high sensitivity with the change of the effective reflective index, being promising for sensing solvent vapors.

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Figure 5. (a) Schematic illustration for backfilling and replicating of inorganic materials in the network-forming PS-PMMA APC film. FESEM micrographs of the (b) porous PS-network, (c) porous SiO2-network and (d) porous TiO2-network APC films.

Figure 6. Corresponding reflectivity spectra of the various porous network-forming APC films.

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Figure 7. Optical photographs of the TiO2-network APC film under benzene vapor and (b) at atmosphere.

Photopatternable APC Films. As illustrated in Figure S11, the network-forming PS-PMMA film was first covered with a copper grid for masking. After exposure under UV lamp of 254 nm for 0.5 h and removal of exposed PMMA by acetic acid, the porous PS-network microstructure was obtained in the exposed region of the film. In Figure 8a, the photopatterned APC film exhibited the well-defined grid shape in the presence of chloroform vapor. The unexposed region revealed the identical reflectance coloration to the previous APC film without UV irradiation, whereas the exposed region exhibited no visible reflectance coloration. This is attributed to the collapse of the porous PS-network microstructures by the chloroform vapor (Figure S11). This could be verified by the rapid disappearance of the reflectivity in the initial stage of the fuming process (Figure 8b). After photodegradation of the PMMA microdoamins in this grid-shaped topographic film again, the photopatterned TiO2-based APC film could be carried out by subsequent template synthesis and calcination (Figure 8c). Consequently, this might provide an efficient way to fabricate 26


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large-area flexible or robust APC films with desired photopatterned textures.

Figure 8. (a) Solvatochromic photographs of the photopatterned PS-PMMA APC film in the presence of chloroform vapor. (b) In-situ reflectivity spectra of the UV-exposed region during the fuming process with chloroform vapor. (c) FESEM micrograph of the photopatterned TiO2-based APC film after template synthesis and calcination. The inset shows the TiO2 network microstructures in the framework region.

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Conclusion In summary, the weakly incompatible PS-PMMA film featuring isotropic and short-range-order network microstructures exhibited angle-independent colorations of APCs. Because of the swelling and deswelling of the network microdomains, the flexible PS-PMMA APC film revealed the distinct and reversible solvatochromism in which the solubility-associated maximum reflectance wavelength of the pseudogap is found. The refractive index contrast of the PS-PMMA APC film can be manipulated by degradation of the photodegradable PMMA microdomains or replacement of them by inorganic SiO2 and TiO2 materials. The robust TiO2-based APC film exhibits high sensitive with the change of the refractive index contrast. With the integration of photolithography and self-assembly, the flexible PS-PMMA or robust TiO2-based APC films featuring well-defined photopatterned textures were demonstrated. Consequently, this can provide an efficient means in the design of photopatternable flexible or robust APC films featuring interconnected network microstructures.

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Acknowledgements Authors thank Mr. Hsien-Tsan Lin of Regional Instruments Center at National Sun Yat-Sen University for his help in TEM experiments. Regarding the synchrotron USAXS experiments, we thank Drs. U. S. Jeng and C. J. Su at National Synchrotron Radiation Research Center (Taiwan). Authors are grateful to the Ministry of Science and Technology of the Republic of China (MOST 105-2628-E-110-002-MY3), Taiwan, for the financial support.

Supporting information Calculation of effective refractive index, TEM micrograph of the PS-PMMA bulk sample cast from dichloromethane, USAXS profile of the network-structured PS-PMMA thin film spin-cast from TCE (5wt%) and followed by TCE annealing at 60°C for 6 h, Cross-sectional TEM micrographs of high-Mw PS-PMMA films spin-cast from 1,1,2-trichloroethane (TCE) and subsequently annealed by toluene, benzene TCE, THF and 1,2-dichloroethane at 60oC for 6 h, Cross-sectional TEM micrograph of the PS-PMMA film spin-cast from TCE and followed annealed by TCE at 60°C for 24 h, Effective refractive index of the PS and PMMA varied with solvent composition, Cross-sectional TEM micrograph of the PS-PMMA film after swelling and deswelling treatment by chloroform vapor for 20 cycles, The reflected 29



wavelength varied with the corresponding film thickness during fuming by chloroform vapor, Cross-sectional TEM micrographs of the PS-PMMA films after 10-cycle solvatochromic treatments by cyclohexane, toluene, benzene, chloroform and acetone vapors, Wide-angle X-ray diffraction profile of the porous TiO2-network after calcination, FESEM micrograph of large-area TiO2-network microstructures after sol-gel reaction followed by calcination, Schematic illustration for preparation of the flexible or robust photopatterned APC film, Movie of angle-independent coloration in the solvated PS-PMMA APC film in the presence of chloroform vapor; Movie of red-shifting reflectivity in the TiO2-based APC film during the fuming process with benzene; Movie of blue-shifting reflectivity in the TiO2-based APC film during the evaporation of benzene vapor. These materials are available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected] Notes

The authors declare no competing financial interest.

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Figure captions Figure 1. Cross-sectional TEM micrographs of the PS-PMMA films (a) spin-cast from TCE (5wt%) and (b) followed by TCE annealing at 60°C for 6 h. The insets reveal the two-dimensional FFT and USAXS patterns for (a) and (b), respectively. (c) and (d) are the reflectivity spectra of (a) and (b) measured with different angles enclosed by the incident beam and the film normal. Figure 2. (a) Swelling and deswelling photographs of the PS-PMMA APC film exposed in chloroform vapor. (b) In-situ reflectivity spectra measured during the fuming process with chloroform vapor. Figure 3. A series of optical photographs taken at various viewing angles for the solvated PS-PMMA APC film exposed under saturated chloroform vapor. (a) 0°, (b) 10°, (c) 30° and (d) 40°. Figure 4. The reflectivity spectra of the maximum reflectance wavelengths of the network-forming PS-PMMA APC film in the presence of various solvent vapors. Figure 5. (a) Schematic illustration for backfilling and replicating of inorganic materials in the network-forming PS-PMMA APC film. FESEM micrographs of the (b) porous PS-network, (c) porous SiO2-network and (d) porous TiO2-network APC films.

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Figure 6. Corresponding reflectivity spectra of the various porous network-forming APC films. Figure 7. Optical photographs of the TiO2-network APC film under benzene vapor and (b) at atmosphere. Figure 8. (a) Solvatochromic photographs of the photopatterned PS-PMMA APC film in the presence of chloroform vapor. (b) In-situ reflectivity spectra of the UV-exposed region during the fuming process with chloroform vapor. (c) FESEM micrograph of the photopatterned TiO2-based APC film after template synthesis and calcination. The inset shows the TiO2 network microstructures in the framework region.

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References 1. Prum, R. O.; Torres, R. H.; Williamson, S.; Dyck, J. Coherent light scattering by blue feather barbs. Nature 1998, 396, 28–29. 2. Dufresne, E. R.; Noh, H.; Saranathan, V.; Mochrie, S. G. J.; Cao, H.; Prum, R. O. Self-assembly of amorphous biophotonic nanostructures by phase separation. Soft

Matter 2009, 5, 1792–1795. 3. Takeoka, Y. Angle-independent structural coloured amorphous arrays. J. Mater.

Chem. 2012, 22, 23299–23309. 4. Yin, H. W.; Dong, B. Q.; Liu, X. H.; Zhan, T. R.; Shi, L.; Zi, J.; Yablonovitch, E. Amorphous diamond-structured photonic crystal in the feather barbs of the scarlet macaw. Proc. Natl. Acad. Sci. USA 2012, 109, 10798–10801. 5. Shi, L.; Zhang, Y.; Dong, B.; Zhan, T.; Liu, X.; Zi, J. Amorphous photonic crystals with only short-range order. Adv. Mater. 2013, 25, 5314–5320. 6. Koo, W. H.; Jeong, S. M.; Araoka, F.; Ishikawa, K.; Nishimura, S.; Toyooka, T. Takezoe, H. Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles. Nat. Photon. 2010, 4, 222–226. 7. Lee, I.; Kim, D.; Kal, J.; Baek, H.; Kwak, D.; Go, D.; Kim, E.; Kang, C.; Chung, J.; Jang, Y.; Ji, S.; Joo, J.; Kang, Y. Quasi-amorphous colloidal structures for electrically tunable full-color photonic pixels with angle-independency. Adv. 33



Page 34 of 40

Mater. 2010, 22, 4973–4977. 8. Noh, H.; Yang, J.; Liew, S. F.; Rooks, M. J.; Solomon, G. S.; Cao, H. Control of lasing in biomimetic structures with short-range order. Phys. Rev. Lett. 2011, 106, 183901. 9. Lee, J.-H.; Koh, C. Y.; Singer, J. P.; Jeon, S.-J.; Maldovan, M.; Stein, O.; Thomas, E. L. Ordered polymer structures for the engineering of photons and phonons. Adv.

Mater. 2014, 26, 532–569. 10. Takeoka, Y.; Honda, M.; Seki, T.; Ishii, M.; Nakamura, H. Structural colored liquid membrane without angle dependence. Appl. Mater. Interfaces 2009, 1, 982– 986. 11. Ueno, K.; Inaba, A.; Sano, Y.; Kondoh, M.; Watanabe, M. A. Soft glassy colloidal array in ionic liquid, which exhibits homogeneous, non-brilliant and angle-independent structural colours. Chem. Commun. 2009, 24, 3603–3605. 12. Forster, J. D.; Noh, H.; Liew, S. F.; Saranathan, V.; Schreck, C. F.; Yang, L.; Park, J.; Prum, R. O.; Mochrie, S. G. J.; O’Hern, C. S.; Cao, H.; Dufresne, E. R. Biomimetic isotropic nanostructures for structural coloration. Adv. Mater. 2010,

22, 2939–2944. 13. Harun-Ur-Rashid, M.; Imran, A. B.; Seki, T.; Ishii, M.; Nakamura, H.; Takeoka, Y.

Angle-independent

structural

color

in

colloidal

34


amorphous

arrays.

Page 35 of 40 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


ChemPhysChem 2010, 11, 579–583. 14. Kumano, N.; Seki, T.; Ishii, M.; Nakamura, H.; Takeoka, Y. Tunable angle-independent structural color from a phase-separated porous gel. Angew.

Chem. Int. Ed. 2011, 50, 4012–4015. 15. Florescu, M.; Torquato, S.; Steinhardt, P. J. Designer disordered materials with large, complete photonic band gaps. Proc. Natl. Acad. Sci. USA 2009, 106, 20658–20663. 16. Liew, S. F.; Yang, J.; Noh, H.; Schreck, C. F.; Dufresne, E. R.; O’Hern, C. S.; Cao, H. Photonic band gaps in three-dimensional network structures with short-range order. Phys. Rev. A 2011, 84, 063818. 17. Prum, R. O.; Torres, R.; Kovach, C.; Williamson, S.; Goodman, S. M. Coherent light scattering by nanostructured collagen arrays in the caruncles of the malagasy asities. J. Expt. Biol. 1999, 202, 3507–3522. 18. Prum, R. O.; Torres, R. Structural Colouration of Avian Skin: Convergent evolution of coherently scattering dermal collagen arrays. J. Exp. Biol. 2003, 206, 2409–2429. 19. Prum, R. O.; Cole, J. A.; Torres, R. H. Blue integumentary structural colours in Dragonflies (Odonata) are not produced by incoherent Tyndall scattering. J. Exp.

Biol. 2004, 207, 3999–4009. 35



20. Kramer, R. M.; Crookes-Goodson, W. J.; Naik, R. R. The Self-organizing properties of squid reflection protein. Nat. Mater. 2007, 6, 533–538. 21. Shi, L.; Yin, H.; Zhang, R.; Liu, X.; Zi, J.; Zhao, D. Macroporous oxide structures with short-range order and bright structural coloration: a replication from parrot feather barbs. J. Mater. Chem. 2010, 20, 90–93. 22. Dong, B. Q.; Zhan, T. R.; Liu, X. H.; Jiang, L. P.; Liu, F.; Hu, X. H.; Zi, J. Optical response of a disordered bicontinuous macroporous structure in the longhorn beetle sphingnotus mirabilis. Phys. Rev. E. 2011, 84, 011915. 23. Kang, Y.; Walish, J. J.; Gorishnyy, T.; Thomas, E. L. Broad-wavelength-range chemically tunable block-copolymer photonic gels. Nat. Mater. 2007, 6, 957–960. 24. Lim, H. S.; Lee, J.-H.; Walish, J. J.; Thomas, E. L. Dynamic swelling of tunable full-color block copolymer photonic gels via counterion exchange. ACS Nano 2012, 6, 8933–8939. 25. Chiang, Y.-W.; Chang, J.-J.; Chou, C.-Y.; Wu, C.-S.; Lin, E.-L.; Thomas, E. L. Stimulus-responsive thin film photonic crystals from rapid self-assembly of block copolymer for photopatterning. Adv. Opt. Mater. 2015, 3, 1517–1523. 26. Sveinbjörnsson, B. R.; Weitekamp, R. A.; Miyake, G. M.; Xia, Y.; Atwater, H. A.; Grubbs, R. H. Rapid Self-Assembly of Brush Block Copolymers to Photonic Crystals. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 14332–14336. 36


Page 36 of 40

Page 37 of 40 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


27. Boyle, B. M.; French, T. A.; Pearson, R. M.; McCarthy, B. G.; Miyake, G. M. Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers. ACS Nano 2017, 11, 3052–3058. 28. Lee, J.-H.; Koh, C. Y.; Singer, J. P.; Jeon, S.-J.; Maldovan, M.; Stein, O.; Thomas, E. L. 25th Anniversary article: ordered polymer structures for the engineering of photons and phonons. Adv. Mater. 2014, 26, 532–569. 29. Noro, A.; Tomita, Y.; Shinohara, Y.; Sageshima, Y.; Walish, J. J.; Matsushita,Y.; Thomas, E. L. Photonic block copolymer films swollen with an ionic liquid.

Macromolecules 2014, 14, 4103–4109. 30. Urbas, A. M.; Maldovan, M.; DeRege, P.; Thomas, E. L. Bicontinuous cubic block copolymer photonic crystals. Adv. Mater. 2002, 14, 1850–1853. 31. Lin, E.-L.; Hsu, W.-L.; Chiang, Y.-W. Trapping structural coloration by a bioinspired gyroid microstructure in solid state. ACS Nano 2018, 12, 485–493. 32. Lee, W.; Yoon, J.; Thomas, E. L.; Lee, H. Dynamic changes in structural color of a lamellar block copolymer photonic gel during solvent evaporation.

Macromolecules 2013, 46, 6528–6532. 33. Jia, Z. Determination of the effective refractive index of porous silicon/polymer composite films. Chin. Opt. Lett. 2005, 3, 608-610.

37



Page 38 of 40

34. Guldin, S.; Inorganic nanoarchitectures by organic self-assembly; Springer Science & Business Media, 2013. 35. Khandpur, A. K.; Forster, S.; Bates, F. S.; Hamley, I. W.; Ryan, A. J.; Bras, W.; Almdal, K.; Mortensen, K. Polyisoprene-polystyrene diblock copolymer phase diagram near the order-disorder transition. Macromolecules 1995, 28, 8796–8806. 36. Dai, K. H.; Kramer, E. J. Determining the temperature-dependent Flory interaction parameter for strongly immiscible polymers from block copolymer segregation measurements. Polymer 1994, 35, 157–161. 37. Russell, T. P.; Hjelm, R. P.; Seeger, J. P. A. Temperature dependence of the interaction

parameter

of

polystyrene

and

poly(methyl

methacrylate).

Macromolecules 1990, 23, 890–893. 38. Xu, T.; Goldbach, J. T.; Misner, M. J.; Kim, S.; Gibaud, A.; Gang, O.; Ocko, B.; Guarini, K. W.; Black, C. T.; Hawker, C. J.; Russell, T. P. Scattering study on the selective solvent swelling induced surface reconstruction. Macromolecules 2004,

37, 2972–2977. 39. Bosworth, J. K.; Paik, M. Y.; Ruiz, R.; Schwartz, E. L.; Huang, J. Q.; Ko, A. W.; Smilgies, D.-M.; Black, C. T.; Ober, C. K. Control of self-assembly of lithographically patternable block copolymer films. ACS Nano 2008, 2, 1396– 1402. 38


Page 39 of 40 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


40. Campbell, I. P.; He, C.; Stoykovich, M. P. Topologically distinct lamellar block copolymer morphologies formed by solvent and thermal annealing. ACS Macro

Lett. 2013, 2, 918−923. 41. Lide, D. R. Handbook of Organic Solvents, CRC Press: FL USA 1994. 42. Chiang, Y.-W.; Chou, C.-Y.; Wu, C.-S.; Lin, E.-L.; Yoon, J.; Thomas, E. L. Large-area block copolymer photonic gel films with solvent-evaporation-induced red- and blue-shift reflective bands. Macromolecules 2015, 48, 4004–4011. 43. Hsueh, H. Y.; Chen, H. Y.; She, M. S.; Chen, C. K.; Ho, R. M.; Gwo, S.; Hasegawa, H.; Thomas, E. L. Inorganic gyroid with exceptionally low refractive index from block copolymer templating. Nano Lett. 2010, 10, 4994–5000. 44. Hsueh, H. Y.; Ho, R. M. Bicontinuous Ceramics with high surface area from block copolymer templates. Langmuir 2012, 28, 8518–8529. 45. Fattakhova-Rohlfing, D.; Zaleska, A.; Bein, T. Three-dimensional titanium dioxide nanomaterials. Chem. Rev. 2014, 114, 9487–9558. 46. Hsueh, H. Y.; Yao, C. T.; Ho, R. M. Well-ordered nanohybrids and nanoporous materials from gyroid block copolymer templates. Chem. Soc. Rev. 2015, 44, 1974–2018. 47. Maldovan, M.; Urbas, A. M.; Yufa, N.; Carter, W. C.; Thomas, E. L. Photonic properties of bicontinuous cubic microphases. Phys. Rev. B 2002, 65, 165123. 39



48. Maldovan, M.; Thomas, E. L. Periodic Materials and Interference Lithography

for Photonics, Phononics and Mechanics; Wiley-VCH: Weinheim, 2008. 49. Mille, C.; Tyrode, E. C.; Corkery, R. W. 3D titania photonic crystals replicated from gyroid structures in butterfly wing scales: approaching full band gaps at visible wavelengths. RSC Adv. 2013, 3, 3109−3117.

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Flexible or Robust Amorphous Photonic Crystals from Network

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