Shape and Color Switchable Block Copolymer Particles by

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Shape and Color Switchable Block Copolymer Particles by Temperature and pH Dual-Responses Junhyuk Lee, Kang Hee Ku, Chan Ho Park, Young Jun Lee, Hongseok Yun, and Bumjoon J. Kim ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b09276 • Publication Date (Web): 11 Mar 2019 Downloaded from http://pubs.acs.org on March 11, 2019

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Shape and Color Switchable Block Copolymer Particles by Temperature and pH Dual-Responses Junhyuk Lee, Kang Hee Ku, Chan Ho Park, Young Jun Lee, Hongseok Yun and Bumjoon J. Kim* Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea

*E-mail: [email protected] (B. J. K.)

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Abstract Herein, we report a simple and robust strategy for preparing dual-responsive shapeswitchable block copolymer (BCP) particles, which respond to subtle temperature and pH changes near physiological conditions (i.e. human body temperature and neutral pH). The shape transition of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCP particles between lens and football shape occurs in very narrow temperature and pH ranges: no temperaturebased transition for pH 6.0, 40-50 °C for pH 6.5, and 25-35 °C for pH 7.0. To achieve these shape

transitions,

temperature/pH-responsive

polymer

surfactants

of

poly(N-(2-

(diethylamino)ethyl)acrylamide-r-N-isopropylacrylamide) (poly(DEAEAM-r-NIPAM)) are designed to induce dramatic changes in relative solubility and their location in response to temperature and pH changes near physiological conditions. In addition, the BCP particles exhibit reversible shape-transforming behavior according to orthogonal temperature and pH changes. Colorimetric measurements of temperature and pH changes are enabled by shapetransforming properties combined with selective positioning of dyes, suggesting promising potential for these particles in clinical and biomedical applications.

Keywords: responsive particle, block copolymer particle, temperature/pH dual-responsiveness, shape-changing particle, color-changing particle


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Detecting physiological signals (i.e., pH 7.0 and human body temperature) with high sensitivity is essential for clinical and biomedical applications.1,

2

In particular, direct

visualization of physiological response signals has been a long-thought goal for the development of tumor indicator and drug delivery systems targeting tumor sites.3-5 In order to achieve high-sensitivity detection of responsive signals, significant efforts have been made to utilize stimuli-responsive polymers.6-12 Tremendously increasing interest in this method is attributed to the following aspects: i) conformational engineering of polymer chains enables delicate adjustment of the response range on demand, and ii) introduction of dye molecules or fluorescent groups into responsive polymers allows converting conformational transitions of polymer chains into an optical signal. However, despite those efforts, the development of precise detection systems under physiological conditions is still very challenging, due to the synthetic challenges of certain polymers,13,

14

the slow insoluble-to-soluble transition of

polymer chains,15, 16 and deactivation of polymer functionality with exposure to physiological fluids.17-19 Dynamic shape-switching particles that respond to external stimuli have attracted significant attention as a promising platform because various functionalities of these types of particles, such as their rheological behavior,20, 21 capillary interactions,22, 23 as well as optical properties such as light-matter interactions,24 can be precisely tuned depending on their shape. Recently, soft and deformable block copolymer (BCP)-containing droplets have been reported as an effective approach to prepare non-spherical shaped particles.25-39 The self-assembly of BCPs confined in droplets allows for systematic design of overall shape and nanostructure by engineering the bending/stretching of polymer chains and their interfacial dynamics. For example, pH-driven stretching and shrinking of football-shaped particles were demonstrated by employing BCPs composed of pH-responsive P2VP blocks (i.e., polystyrene-bpolyisoprene-b-poly(2-vinylpyridine) (PS-b-PI-b-P2VP), and PS-b-P2VP.40-42 More recently,


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our group reported the use of thermo-responsive poly(N-isopropylacrylamide) surfactants, which show dramatic solubility changes in response to temperature, to demonstrate temperature-driven shape transformation of BCP particles.43 However, to the best of our knowledge, pH and temperature dual-responsive shape-switchable particles, which respond near physiological conditions (i.e., pH 7.0 and human body temperature), have not yet been demonstrated. Furthermore, the potential of shape-switching particles for use as an optical sensor to detect local temperature and pH changes remains unexplored. In this work, we demonstrate temperature and pH dual-responsive shape-switchable polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCP particles (i.e., convex lens and striped football) near pH 7.0 and 35 °C by adopting temperature/pH dual responsive polymeric surfactants. To satisfy the facile adjustment of the response range and precise location control of surfactants within the emulsion, which is driven by pH and temperature changes, a random copolymer of N-(2-(diethylamino)ethyl)acrylamide (DEAEAM) and N-isopropylacrylamide (NIPAM) (poly(DEAEAM-r-NIPAM)) was utilized as a responsive polymeric surfactant. Poly(DEAEAM-r-NIPAM) with an optimized ratio of DEAEAM to NIPAM produced a dramatic solubility change in the pH range from 6.0 to 7.0 and temperature range from 30 to 40 °C, thereby yielding a change in the particle shape between football and lens according to subtle temperature and pH changes near a neutral pH and human body temperature. In addition, the reversible shape transformation of BCP particles was carried out through solvent-adsorption annealing with orthogonal changes of temperature and pH. Moreover, selective incorporation of fluorescent dyes into the BCP particles enabled detection of particle shape changes by colorimetric response, thus allowing for colorimetric monitoring of pH and temperature.


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Results/Discussion A series of BCP particles were produced from solvent-evaporative emulsion droplets containing PS27k-b-P4VP7k (number-average molecular weight (Mn) of PS = 27 kg mol-1, Mn of P4VP = 7 kg mol-1, dispersity (Ð) = 1.15) and poly(DEAEAM-r-NIPAM)5k copolymers (Figure 1a). First, PS-b-P4VP was dissolved in chloroform to be 1 wt% solution. To induce pH/temperature-driven shape transitions, a poly(DEAEAM-r-NIPAM) copolymer was added to the PS-b-P4VP solution with a feed volume fraction (𝜙poly(DEAEAM-r-NIPAM), Feed) of 0.36. Then, the mixture was emulsiﬁed using a homogenizer in a pH buffer solution containing 0.1 wt% cetyltrimethylammonium bromide (CTAB), followed by slow evaporation of chloroform at different temperatures. Temperature (from 20 to 55 °C) and pH (from 6.0 to 7.0) were independently controlled in order to examine the change of resulting particle shape at different temperature and pH conditions. To achieve the transition of particle shape under physiological condition (i.e., pH 7.0 and 37 °C), poly(DEAEAM-r-NIPAM) surfactants were designed in the following aspects. First, poly(DEAEAM) is composed of both thermoresponsive and pH-responsive groups, where a large solubility change is observed in the range of pH 8.5 to 9.5 and in the temperature range of 25 to 50 °C.44 In addition, incorporation of the NIPAM monomer allows the decrease of the transition pH values of poly(DEAEAM-r-NIPAM) without any disruption of the temperature responsive properties.45,

46

Therefore, it is expected that the transition pH can be adjusted to

physiological conditions by optimizing the composition ratio. A series of poly(DEAEAM-rNIPAM) copolymers with different NIPAM fractions ranging from 0 to 48 mol % were synthesized for determining the optimum ratio of NIPAM to DEAEAM (Table S1). In addition, the Mn of the poly(DEAEAM-r-NIPAM) copolymers was carefully controlled to have small value (4-5 kg mol-1), which ensures successful incorporation into P4VP domain. The poly(DEAEAM-r-NIPAM) copolymers with higher fractions of NIPAM exhibited solubility


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transitions at lower pH values due to the intrinsic hydrophobicity of the thermo-responsive NIPAM monomer (Figure S1). In this study going forward, the copolymer containing 48 mol % of NIPAM (P48) was used to explore the effects of pH and temperature on particle shape because the cloud point of P48 changed from 42 to 29 °C when the pH was changed from 6.0 to 7.0, representing conditions near the physiological conditions of interest.

Figure 1. (a) Chemical structure of polymers used in our experiments and schematic illustration to produce shape-transforming PS27k-b-P4VP7k particles using temperature and pH dual-responsive poly(DEAEAM-r-NIPAM) surfactants; (b) TEM images of PS-b-P4VP particles formed in different buffer solutions (pH 6.0, 6.5 and 7.0) under different temperature conditions (20, 35 and 50 °C). The P4VP domains are stained with iodine vapor; SEM images of representatives of (c) lens-shaped particles and (d) football-shaped particles.


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The shape transformation of BCP particles by pH and temperature was investigated varying the pH of the buffer solution used in the emulsion process from 6.0 to 6.5 and 7.0, and the temperature from 20 to 35 and 50°C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images in Figures 1b-d show a dramatic difference in shape and structure of PS-b-P4VP BCP particles from lens-shaped particles having cylinders to striped football-shaped particles. As the particles were formed at pH 6.0, only lens-shaped particles were observed, regardless of the temperature conditions used (Figure 1b). The resulting particles showed hexagonally arrayed dark P4VP domains, indicating the formation of regularly-ordered standing-up cylinders inside the particles. By contrast, the BCP particles produced at pH 6.5 and 7.0 showed morphological difference between lens- and footballshaped particles according to the temperature conditions used. When the pH was 6.5, lensshaped particles were produced at 20 and 35 °C, whereas football-shaped particles, with axially stacked lamellae, started to appear at 50 °C. On the other hand, in pH 7 conditions, the critical temperature for causing a transition from lens-shaped to football-shaped particles was changed: for example, lens particles were produced at 20 °C, whereas football-shaped particles were obtained at 35 and 50 °C. To highlight the facile tunability of pH-and temperatureresponsiveness, the shape and morphological differences of BCP particles prepared with a P48 surfactant at various temperature and pH conditions were investigated (Figure S2). The shape transitions of the BCP particles between lens and football shape occurred within very narrow temperature and pH ranges: 25-35 °C at pH 7.0, 40-50 °C at pH 6.5, and no transition occurred in the studied temperature range at pH 6.0. Representative low-magnification SEM images (Figures 1c and d) and TEM images (Figure S3) confirmed that the morphological transition from football to lens shapes consistently occurred for all the particles in the batch at different temperatures and pH conditions. The football and lens-shaped particles had the average volumes of 0.052 ± 0.041 μm3 for football-shaped particles and 0.054 ± 0.047 μm3 for lens-


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shaped particles, respectively (Figure S3). The size distributions of the particles in this size range did not affect the efficiency of their morphological transition. Formation of non-spherical BCP particles such as lens- and football-shaped particles can be understood by segregation of P48 to the interface between the P4VP and water on the particle surface during particle formation.40 Since CTAB and P48 have selective interactions to the PS and P4VP blocks, respectively, a mixture of CTAB and P48 neutralizes the surface preference of the PS and P4VP blocks with the surrounding aqueous medium.26, 41, 47 Such neutral interfaces lead to exposure of both PS and P4VP blocks at the particle surface to have perpendicular BCP orientation. Once the perpendicular BCP orientation to surrounding is achieved, BCP particles can be deformed to non-spherical shapes to relieve large entropic penalty associated with bending/stretching of the polymer chains.48-50 Consequently, perpendicularly-oriented lamellae or cylinders are first formed near the surface of the particle, and the BCP ordering is propagated to the center of the particle, resulting in the production of the striped football- or lens-shaped particles. While the BCP particles retained a nearly neutral surface regardless of pH and temperature conditions, a difference of overall shape between lens and football was observed in response to pH and temperature. Therefore, the driving force inducing the shape transition is suggested to be the change of volume fraction, in response with pH and temperature changes, of BCP and P48 in the particles.


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Figure 2. (a) Volume fraction of P48 (𝜙P48) in the BCP particle according to temperature and pH conditions. (b) Schematic illustration of the equilibrium morphologies corresponding to the 𝜙P48 in the BCP particle. To gain deeper insights into the effect of P48 on the temperature/pH-dependent shape differences of BCP particles, the volume fraction of P48 (𝜙P48) in the BCP particles was characterized by 1H NMR, after removal of excess surfacant. Figure 2a summarizes the volume fractions of P48 and PS27k-b-P4VP7k within the BCP particles. In the case of BCP particles prepared at pH 6.5 and 7, a sharp increase of ϕP48 at a critical temperature (40-45 °C for pH 6.5 and 30-35 °C for pH 7) was observed. For example, ϕP48 increased from 2 vol% (which was significantly lower than the feed volume fraction (ϕP48, feed = 36 vol %)) to 31 vol % for pH 6.5. By contrast, ϕP48 in the BCP particles prepared at pH 6 was constant at 2-3 vol % regardless of temperature. The pH and temperature-dependence of 𝜙P48 in the BCP particles was further investigated by measuring the chloroform/water partition coefficient (log Kpc) of P48, as summarized in Table S2. The value of log Kpc, which is defined by [P48 in chloroform]/[P48 in DI water], was measured from the shake-flask method under various pH and temperature conditions.51 At pH 6.5 and 7, a dramatic increase of log Kpc was observed as temperature


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increased due to LCST-type phase transitions. For example, the log Kpc of P48 increased from 1.32 ± 0.07 to 3.35 ± 0.18 when the temperature crossed above the critical temperature (40-45 °C for pH 6.5 and 30-35 °C for pH 7). By contrast, at pH 6, the P48 polymer exhibited similar log Kpc values (i.e., 1.36 ± 0.10) regardless of temperature change, which agreed with the trend in ϕP48 of the BCP particles as plotted in Figure 2a. This result is attributed to a fully quaternized diethylamino group in P48 at pH 6, which disrupts a LCST-type phase transition due to the good solubility of P48 in DI water under these conditions.44 Therefore, the temperature/pH-directed positioning of P48 in chloroform-in-water emulsions, which depends on the solubility in each solvent under the given conditions, determines the final P48 volume fraction in the BCP particles, and thereby dictates the resulting shape of the particle. When most of the P48 polymers migrate to the surrounding aqueous media during emulsification (𝜙 P48 =

0.02), the BCP has a cylindrical morphology, producing lens-shaped particles (Figure 2b

lower). In stark contrast, when large amounts of P48 (𝜙P48 = 0.31) remains in the BCP emulsion phase, a preferential segregation of P48 within P4VP domains in the BCP nanostructure is expected due to strong hydrogen bond between the pyridine within the P4VP and amide groups of P48.52 Therefore, blends of PS27k-b-P4VP7k BCP with 31 vol % of P48 lead to two separate domains, one of PS and one of P4VP and P48, each with a volume fraction of ~ 50 %, which corresponds to a lamellar morphology (Figure 2b upper) and the generation of football-shaped particles. It is noteworthy that the temperature range where the particle shape changes from lens to football coincides well with the pH-dependent LCSTs of P48 as observed in Figure S1b.


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Figure 3. TEM images showing the reversible transformation of BCP particle via solventadsorption annealing with adjusting temperature/pH condition. The percentage frequency of each particle morphology was depicted in the bar charts with different colors: football (black), lens (orange) and intermediate (red). The shape transformation of BCP particles in response to the simultaneously changes of temperature and pH was examined, which is important for sensing ability in order to detect different signals of temperature and pH at the same time (Figure 3). To provide the driving force for the movement and rearrangement of polymer chains, which is required for promoting the transformation kinetics of the particle shape, solvent-adsorption annealing was applied using chloroform as a good solvent for both PS-b-P4VP and P48.52-56 The BCP particles prepared at pH 6.5, 40 °C showed the lens shape, as previously shown in Figure 1b. A slight increase of pH conditions from 6.5 to 7.0, while the temperature was constant at 40 °C, produced the transformation of the particle shape from lens to football during the solvent annealing process. The relatively increased solubility of P48 in chloroform at pH 7.0 led to migration of P48 from the aqueous phase to the BCP particle swollen by chloroform. Then, the rearrangement of the BCP and P48 in the particles led to a different ordered nanostructure, producing the football-shaped particles. For the subsequent experiment of tuning the temperature from 40 °C to 30 °C under the constant pH of 7.0, the football-shaped particles


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returned back to lens-shaped particles. Importantly, these transitions between lens-shaped particles and football-shaped particles can occur during many different cycles with excellent reversibility, demonstrating that the shape of these particles are effectively programed using pH and temperature, even near physiological conditions (pH 7.0 and 37 °C). To understand the process of these shape transformations, the structural and morphological evolution of the particles was monitored as a function of annealing time (Figure S4). The football-shaped particle suspensions were subject to chloroform adsorption annealing at pH 6.5 and 40°C for different amounts of time (1, 3, 6, and 12 h). In order to capture the particle morphology in a swollen state, the samples were freeze-dried in vacuum overnight. As the annealing time increased from 0 to 3 h, particles with intermediate structure between the lamellae and cylinders were observed (Figures S4(b, c)). Since the removal of P48 occurs through the surface of the particle, the restructuring of the BCP chains initiated near the particle surface. During the morphological evolution, the BCP particles retained a nearly neutral surrounding conditions. The complete transformation of the particle shape from prolate to oblate ellipsoids occurred with a longer time scale of 12 h (Figure S4e).


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Figure 4. (a, b) TEM images and fluorescence photographs of PS15k-b-P4VP7k particles containing 5 vol % of RB-PS and CM-P4VP prepared with a P48 surfactant at (a) 15 °C and pH 7, and (b) 35 °C and pH 7; (c) reversibility test of the PL behavior of BCP particles: footballshaped particles (red dots) and lens-shaped particles (black dots).

A distinct advantage of the shape-transforming BCP particles is that the reversible change of the periodicity of the BCP self-assembly within the particles can translate to different optical signals depending on the pH/temperature changes,57-60 providing attractive potential for bio-imaging applications. In particular, another advantage of our system is that the PS and P4VP chains allow selective incorporation of two different molecules into each domain.61, 62 To examine the potential of the shape-transforming BCP particles as an optical sensor detecting local temperature and pH changes, a model system of fluorescent dye-incorporated BCP


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particles using rhodamine B (RB) and coumarin (CM) was developed. For selective incorporation of fluorescent dyes into PS and P4VP domains, RB-terminated PS (RB-PS, Mn = 3.1 kg/mol, Ð = 1.08) and CM-terminated P4VP (CM-P4VP, Mn = 3.3 kg/mol, Ð = 1.05) were synthesized.19 Then, RB-PS (5 vol %) and CM-P4VP (5 vol %) were added into PS15k-bP4VP7k BCPs (Ð = 1.18) to effectively modulate Förster resonance energy transfer (FRET) efficiency between RB and CM. We investigated the morphologies of the fluorescent dyecontaining BCP particles by TEM (Figure S5) and SAXS measurements (Figures S6). The TEM images showed that the fluorescent dye-containing BCP particles retained essentially the same morphology transition as the pristine BCP particles. In addition, the SAXS pattern of football-shaped BCP particles showed scattering peaks at positions corresponding to a ratio of 1:2:3, indicating lamellar morphology. By contrast, the scattering pattern of lens-shaped particles was consistent with cylinder structure with scattering peaks at positions corresponding to a ratio of 1:√3. From the primary peak position in SAXS spectra, the sizes of BCP domains were measured to be 12.0 nm and 15.7 nm, for the lens-shaped and football-shaped particles, respectively. According to the change of their shape and nanostructure, the colorimetric response of the BCP particles varied from pale red to blue (Figures 4a and b). Figure S7 shows the PL spectra of the lens and football-shaped BCP particles, exhibiting two emission peaks: one at 450 nm from the CM dye and the other at 600 nm from the RB dye. With the shape transformation from the football to the lens shape, the PL intensity (I) at 450 nm decreased by 35 %, while the intensity at 600 nm increased by 19 %. This result is attributed to the difference in the domain sizes of the BCPs between lens and football-shaped particles, which tuned the FRET efficiency between RB and CM. Also, to examine the general applicability of the color-switching properties, we incorporated different types of fluorescein (FR) and rhodamine 101 (R101) dyes into the BCP particles, where the color response of the particles varied from pale red to yellow (Figure S8).


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For better understanding of the mechanism for the color response of the BCP particle, the average fluorescence lifetimes (τave) of FRET donor (i.e., CM dye) in the BCP particles were measured by using time-resolved fluorescence (TRF) spectroscopy (Figure S9).62, 63 We measured the fluorescence decay of the CM emission from the BCP particles at 450 nm under the irradiation at 370 nm in water. Then, the τave values were obtained by fitting the TRF spectra by a double exponential decay model.64 As shown in Figure S9, the τave of the CM in BCP particles decreased significantly after shape transition from football shape to lens shape, which was attributed to the change of their nanostructure. For the football-shaped particles, the τave value was determined to be 1.53 ns. By contrast, the τave value was decreased to 0.92 ns for the lens-shaped particles, indicating much faster CM emission decay process. The shorter lifetime of the CM emission is due to an increase in the nonradiative decay rate, suggesting promoted FRET from CM to RB. In addition, the value of (τave, football –τave, lens) / τave, football = 0.40 is wellmatched with the value of (ICM,football – ICM,lens) / ICM,football = 0.35. This suggests that the FRET efficiency change caused the shape-dependent fluorescence intensity.19,

65

To examine the

reversibility of optical behavior during the particle shape transformation, the I600nm/I450nm of the BCP particles were plotted with continuous cycles of different temperature and pH conditions as displayed in Figure 4c. When the shape of the particles was transformed from lens to football, a significant decrease of I600nm/I450nm value was observed from 0.52 to 0.30. In addition, this change was reproducible over repeated solvent annealing cycles. Therefore, the shapetransforming BCP particles provide an excellent platform for facile optical sensing of subtle pH and temperature changes. Furthermore, the extension of this approach to other stimuli such as light and gas may provide shape transforming particles with even more attractive properties.


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Conclusions In summary, shape-transforming, color-changing BCP particles, which can respond to different signals of temperature and pH changes have been developed. As detection of physiological signals with high sensitivity is very important for bio-clinic applications such as tumor indicators and drug delievery systems, we described the applications of these particles for sensing the changes of pH near 7.0 and temperatures near 35 ˚C. The key component of the approach is to design temperature/pH-responsive polymers (P48) as dual responsive surfactants, which exhibit changes in their solubility in water and their position in the BCP particles in a narrow temperature and pH range near 35 ˚C and neutral pH. As a result, the shape of the BCP particles switched from lens to football shape and vice versa in very narrow temperature and pH ranges: no temperature-based transition for pH 6.0, 40-50 °C for pH 6.5, and 25-35 °C for pH 7.0. These shape transformation behaviors of the particles were reversible during the continuous cycles. Importantly, the colorimetric measurements of the pH and temperature responses were successfully demonstrated by selective positioning of light-active motieties into the BCP nanostructures within the particles. Therefore, the shape-transforming, color changing particles can potentially provide a promising platform attractive for the applications of biomedical sensing and clinical systems.


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Methods/Experimental Synthesis of poly(DEAEAM-r-NIPAM): First, DEAEAM was synthesized based on the method described in the literature.66 Detailed synthetic procedure can be found in the Supporting Information. Desired amount of DEAEAM and NIPAM monomers, chain-transfer agent, AIBN, and tetrahydrofuran (THF) were added into a glass ampoule. After degassing process, the polymerization was carried out at 70 °C for 12 h. The resulted product was purified by repeated precipitating into diethyl ether, and poly(DEAEAM-r-NIPAM) was obtained as a translucent pellet after drying under vacuum. Preparation of buffer solutions: A mixture of KH2PO4 and K2HPO4 was used as the phosphate buffer in our system. To achieve the pH range between pH 5.8 and pH 8.0, the amount of each salt was adjusted. The actual pH values of prepared buffer solutions were carefully measured using a Mettler Toledo pH meter with a microelectrode.67 General procedure to prepare PS-b-P4VP BCP particles: A chloroform solution of PS-bP4VP and poly(DEAEAM-r-NIPAM) (10 mg/mL, 0.2 mL) was prepared. (The ratio of PS-bP4VP to poly(DEAEAM-r-NIPAM) was 4:1 wt/wt for PS15k-b-P4VP7k, and 2:1 wt/wt for PS27k-b-P4VP7k, respectively.) Then, the droplets were formed by emulsifying the polymer solution in a buffer solution of CTAB (0.1 wt%) with a homogenizer. Under various temperature conditions, the chloroform was slowly evaporated for 48 hr. Then, repeated centrifugation in deionized water was carried out to remove remaining surfactants.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (B. J. K.)

ACKNOWLEDGMENT This work was supported by the National Research Foundation (NRF) of Korea (2016R1E1A1A02921128). We thank Dr. Ashlee Jahnke for helpful discussions.

ASSOCIATED CONTENT Supporting Information Available: Experimental details and additional characterization data (polymer characteristics, TEM, PL, SAXS and TRF data). This material is available free of charge via the Internet at http://pubs.acs.org.


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Shape and Color Switchable Block Copolymer Particles by Temperature and pH Dual-Responses


Shape and Color Switchable Block Copolymer Particles by

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