Shape-Anisotropic Diblock Copolymer Particles with Varied Internal

Subscriber access provided by TULANE UNIVERSITY

Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Shape-Anisotropic Diblock Copolymer Particles with Varied Internal Structures Min Ren, Zhen Geng, Ke Wang, Yi Yang, Zhengping Tan, Jiangping Xu, Lianbin Zhang, Lixiong Zhang, and Jintao Zhu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b04147 • Publication Date (Web): 08 Feb 2019 Downloaded from http://pubs.acs.org on February 10, 2019

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 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 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.

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 27 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

Shape-Anisotropic Diblock Copolymer Particles with Varied Internal Structures Min Ren†, #, Zhen Geng†, #, Ke Wang†, Yi Yang†, Zhengping Tan†, Jiangping Xu†,*, Lianbin Zhang†, Lixiong Zhang‡, and Jintao Zhu†,* †Key

Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education,

School of Chemistry and Chemical Engineering and State Key Laboratory of Materials Processing and Mold Technology, Huazhong University of Science and Technology, Wuhan 430074, China ‡State

Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University,

Nanjing 210009, China # These

authors contributed equally to this work.

Corresponding Authors: [email protected] (J. X.) [email protected] (J. Z.)

1

ACS Paragon Plus Environment

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 27

Abstract: Anisotropic polymer particles have promising applications in various fields, whereas their preparation usually suffers from tedious procedures. Here, we introduce a facile strategy to fabricate novel shape-anisotropic particles with varied internal structures via self-assembly of block copolymers (BCPs) with perfluorooctane (PFO) as liquid template in emulsion droplets. By increasing the volume ratio of PFO to polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) or decreasing the initial concentration of the BCPs, the self-assembled polymer particles change from spherical core-shell structures to anisotropic particles. Moreover, the anisotropic shape and internal structure of the polymer particles, including cone-like particles with alternative PS and P4VP lamellas, crescent-shaped particles with cylindrical P4VP domains, and plate-like particles with spherical P4VP domains, can be obtained by changing block ratio, molecular weight, or adding hydrogen bonding agent. Based on the in-situ optical microscopy investigation on the morphology evolution of emulsion droplet, we conclude that both kinetic and thermodynamic factors during emulsion evolution determine the formation of shape-anisotropic polymeric particles with controllable internal structures.

Keywords: Block copolymers; Anisotropic particles; Self-assembly; Confinement; Emulsions

2


Page 3 of 27 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 Polymeric particles have attracted much attention due to their potential applications in photonics,1 biomedicine,2, 3 nanoreactors,4 catalysis5 and other fileds.6-8 Generally, the particle shape and internal structure can significantly influence their properties and functional behavior. For example, amphiphilic Janus particles have larger adsorption energy to an oil-water interface compared to its homogeneous counterpart and thus can be used as particle surfactants for stabilizing emulsions.9 The shape of particle plays a dominant role in phagocytosis, where target shape at initial contact point determines whether cells will proceed with phagocytosis or simply spread on the particle.10 The particle shape will also influence targeting ability, for example, cylindrical micelles as long-circulating vehicles can effectively deliver the anticancer drug paclitaxel and shrink tumors in mice compared to spherical micelles.11 As a new class of colloidal materials, shape-anisotropic particles with broken centrosymmetry provide not only varied morphologies but sometimes advanced properties over the isotropic spherical counterparts.9, 12 Thus, it is desired to control shape and internal structures of the polymer particles. Till now, many approaches, such as photolithography,13 non-wetting template molding,14 stretching of spherical particles,15 phase separation in emulsion droplets,16-18 microfluidics and others,19-22 have been introduced for the synthesis of shape-anisotropic particles. Among these methods, microfluidic techniques are especially attractive, which enable the production of highly uniform microparticles and provide a variety of methods for engineering the microparticle shape, compartment, and microstructure.9, 23-25

19,

Yet, the droplet-based microfluidics essentially suffer from low-throughput preparation and

particle size limitations due to the relatively large emulsion droplets. It remains a great challenge to

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 27

fabricate polymer particles with controllable anisotropic shape and internal structure, particularly in the size range of 100 nm to 1 m. It has been reported that confined assembly of block copolymers (BCPs) in emulsion droplets is an effective approach to fabricate nanoparticles (NPs) with various shapes and internal structures. The structures can be well controlled by varying polymer composition, confinement strength, and boundary interaction.26-39 Nevertheless, as nature tends to form spherical particles in order to minimize surface energy, the preparation of anisotropic NPs through emulsion approach is still challenging. Recently, an effective strategy was described for the fabrication of non-spherical NPs by using a mixture of surfactants that selectively interact with each BCP domain or by introducing a hydrogen-bonding agent into BCPs matrix to change the interfacial interactions between the BCP particles and the surrounding aqueous solution.27,

36, 37, 40

When the surfactants establish a nearly

neutral interface which has non-selective or minimal preferential interactions with the two blocks, the internal structure of the particle will strongly affect its shape in order to minimize the free energy. Yet, only several non-spherical NPs, including ellipsoid-shaped and convex lens-shaped particles, have been fabricated based on the design of a surfactant-BCP pair to date.27, 34, 37 When multiple incompatible compounds are introduced into single emulsion droplets, macrophase separation will occur spontaneously until reaching the final thermodynamic equilibrium state. By this means, a variety of polymeric particles with unique morphologies can be fabricated, such as patchy spheres, Janus-like particles, core-shell and multi-compartmental particles.23, 25, 41-45 For example, the macrophase separation of a high-boiling non-solvent (HBNS, e.g., long-chain alkanes) in emulsion droplets containing a low-boiling good solvent (LBGS, e.g., chloroform) and a polymer has been developed for fabricating polymer capsules.45-47 Recently, PS-b-P4VP BCP 4


Page 5 of 27 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

capsules with tunable shell structures have been prepared by using HBNS (e.g., hexadecane (HD) or perfluorooctane (PFO)) as liquid core through the emulsion solvent evaporation strategy.46 As the evaporation of LBGS, macrophase separation (between HBNS and BCPs) and microphase separation (between the two blocks) occur in emulsion droplets. Interestingly, due to the continuously increased viscosity of the BCP solutions along with evaporation of organic solvent, the macrophase separation process can be kinetically trapped.48, 49 Therefore, the morphology of the polymer particles fabricated in emulsion droplets are determined by both thermodynamic and kinetic factors. Thus, appropriate control of these factors during emulsion evolution may offer good opportunities for preparing shape-anisotropic polymeric particles with tunable internal structures via macrophase separation and anisotropic self-assembly under confinement. Herein, we demonstrate the preparation of novel shape-anisotropic particles with internal structure via self-assembly of BCPs with PFO as liquid template in emulsion droplets (Scheme 1). Formation of shape-anisotropic BCP particles includes generation of emulsion droplets by membrane-extrusion emulsification and phase separation induced by solvent evaporation, in which macrophase separation of the blends and microphase separation of the BCPs simultaneously exist. The self-assembled structure of the particles is readily adjustable by simply altering emulsion compositions. The anisotropic shape and internal structure can be changed by altering block ratio, molecular weight, and using additives. In addition, the evolution of emulsion droplets and formation process of the polymer particles during solvent evaporation were investigated through optical microscope, and the results are helpful for deeply understanding the formation mechanism of the shape-anisotropic particles. These findings may inspire the design and preparation of polymer particles with tunable shape and internal structures for the applications of catalysis and drug delivery. 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

Page 6 of 27

Scheme 1. Schematic illustration showing the preparation of BCP particles through confined assembly of PS-b-P4VP with liquid core as template in emulsion droplets.

EXPERIMENTAL SECTION Materials The diblock copolymers PS9.8K-b-P4VP10K (the subscripts are Mn of each block, Mw/Mn = 1.08), PS22K-b-P4VP21.6K (Mw/Mn = 1.15), PS51K-b-P4VP18K (Mw/Mn = 1.15), and PS110K-b-P4VP107K (Mw/Mn = 1.15) were purchased from Polymer Source, Inc., Canada. The perfluorooctane (PFO, purity 99%) were supplied by Aladdin. Poly (vinyl alcohol) (PVA, Mw: 13K-23K g mol-1, 87-89% hydrolyzed), and 3-n-pentadecylphenol (PDP, purity ≥ 90 %, recrystallized twice from hexane before use) were purchased from Aldrich. The water-in-oil emulsifier, Abil EM 90, was supplied by Evonik Industry. Preparation of BCP Particles Emulsion-solvent evaporation method was applied to prepare BCP particles. Typically, PS-b-P4VP and PFO were separately dissolved in chloroform (concentration: 10 mg/mL for BCPs, 35 mg/mL for PFO). Then, the polymer solution was blended with PFO solution at various volume ratios (7:3, 4:6, 3:7, and 2:8). Notably, additional Abil EM 90 is needed to stabilize the PFO droplet in the core 6


Page 7 of 27 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

during the evaporation (concentration of Abil EM 90 in the mixed solution is 3 mg/mL).46 Then, 0.1 mL of the mixed solution was emulsified with 1.0 mL aqueous solution of PVA (3 mg/mL) through a hand-driven membrane-extrusion emulsification device. The emulsion was collected in a 10 mL open vial including 1.0 mL PVA aqueous solution to allow the slow evaporation of chloroform for 3 days at 30 °C. Finally, the particles were washed with deionized water (DI water) and separated by centrifugation (14 000 rpm, 6 min) to remove the surfactants. Characterization The shape and internal structures of BCP particles were investigated by FEI TecnaiG2 20 transmission electron microscope (TEM) operated at an accelerating voltage of 200 kV. Before TEM characterization, iodine vapor was employed to selectively stain P4VP domains of polymer particles for 2 h at 30 °C. The shape and surface morphology of the polymer particles was characterized by Sirion 200 scanning electron microscope (SEM). The samples were prepared by dropping polymer particle suspension onto a silicon wafer at room temperature. After drying, the samples were coated with gold for SEM characterization. The evolution of the emulsion droplets during solvent evaporation was monitored by optical microscope (Olympus, IX71).

RESULTS AND DISCUSSION Effect of BCP to PFO Ratio on the Particle Morphology The composition of emulsion plays an important role in determining particle topology. Here, diblock copolymer PS-b-P4VP and immiscible PFO were employed as oil phase, and PVA aqueous solution as continuous phase for stabilizing emulsion. After complete removal of chloroform in the droplets, structured PS-b-P4VP particles were formed. We found that the ratio of BCP to PFO in the emulsion 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 27

droplets significantly influenced the particle morphology. Figure 1 shows an evident transition of the morphology of PS9.8K-b-P4VP10K particles with different volume ratio of BCP/PFO (r, represents the volume ratio of BCP solution to PFO solution). The gray and dark domains correspond to PS and P4VP domains in the TEM images, due to selective staining of P4VP with iodine vapor. Core-shell capsules were observed when r = 7:3 (Figure 1a). Clearly, the PFO liquid core is encapsulated by the structured BCP shell. Decreasing r to 6:4, we obtained a mixture of frustum-like particles and pupa-like particles with one dimple, as shown in Figure S1 in Supporting Information. When r = 4:6, frustum-like particles were observed (Figure 1b and Figure S2a). Further decreasing r to 3:7, cone-like particles were formed (Figure1c, e and Figure S2b). Bowl-like BCP particles could be found at r = 2:8 (Figure 1d). As stated above, when BCPs are the majority in the final particles, i.e., r = 7:3, there are enough BCPs to encapsulate PFO liquid core within each emulsion droplet, resulting in isotropic core-shell particles (Figure 1a). However, as the increase of PFO (r decreases), there are too few BCPs to fully encapsulate the PFO core, resulting in a dramatic morphology transition from core-shell particles to anisotropic particles. In addition, an alternative PS and P4VP lamellar structure was preserved for all of the above four kinds of PS9.8K-b-P4VP10K particles without shape dependence, which is consistent with the structure of its bulk system.50 The thickness of PS lamellar (~23 nm) and P4VP lamellar (~19 nm) are basically the same due to similar volume fraction of PS (51.8%) and P4VP (48.2%). Interestingly, it seems that there is only one domain contacting with PFO for core-shell particles, but both PS and P4VP domains can contact with PFO for frustum-like or cone-like particles. Since the water-in-oil surfactants (EM 90) locate at the PFO/BCP interface, the PS/P4VP chains will not directly contact with PFO. When the PFO droplets locate in the center of emulsion 8


Page 9 of 27 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

droplets, only one block can contact with the interface for minimizing interfacial energy, leading to the formation of concentric lamellar structure. However, when the PFO droplets are excluded out of the emulsion droplets, the surfactants in aqueous phase can also stabilize the PFO droplets, further decreasing their interfacial tensions. Both the PS and P4VP chains can contact with the oil/water interface. Since the surfactant (PVA) in water has similar affinities to PS and P4VP, pupa-like particles can thus be obtained.31 In this case, partial PS and P4VP chains can contact with PFO. Notably, PFO droplets can’t be found in Figure 1b-d even though PFO is non-volatile. Presumably, the centrifugation during the wash process may detach the PFO droplet from the BCP particles due to strong shear force exerted by centrifugation. As a control experiment, we dropped the same batch of particle suspension before centrifugation onto the copper grid for TEM investigation. In this case, we could see a hemi-spherical droplet, which is believed to be PFO droplet, attaching to BCP particles (Figure 1f). The TEM images of plate-like and crescent-like particles before centrifugation treatment (which will be further discussed in Section 3.2) also show that PFO droplet attaches BCP particle after chloroform evaporation (Figure S3 in Supporting Information). These results indicate that the macrophase separation occurs between PFO and BCPs during solvent evaporation, and implies that PFO can be removed together with surfactant through centrifugation.

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 27

Figure 1. TEM images of the PS9.8K-b-P4VP10K particles obtained by using PFO as the liquid core template. The particles with varied shapes and structures were synthesized by decreasing volume ratio of BCP to PFO (r): (a) r = 7:3, core-shell capsules; (b) r = 4:6, frustum-like particles; (c) r = 3:7, cone-like particles; (d) r = 2:8, bowl-like particles. The P4VP domains look dark due to I2 vapor staining. The insets in the upper right of (a), (b), and (c) are cartoons showing structures of the particles. Green and red regions represent P4VP and PS domains, respectively. (e) SEM image of PS9.8K-b-P4VP10K particle at r = 3:7. (f) TEM image of PS9.8K-b-P4VP10K particle formed at r = 3:7 before centrifugation. The red arrow indicates the position of PFO droplet. Moreover, we found that by altering the initial concentration of BCP (Cinitial) while fixing the volume ratio of BCP solution and PFO solution, the morphology of particles could also be changed (Figure 2). In this case, with fixed r = 7:3, varying the Cinitial only changes the BCP component while the PFO component in oil phase remains unchanged. Core-shell capsules with alternative PS and P4VP domains were obtained when Cinitial = 10 mg/mL (Figure 2a). Decreasing Cinitial to 8 mg/mL, the core-shell capsules and frustum of cone-shaped particles with lamellar structure coexisted (Figure 2b). When Cinitial = 6 mg/mL, frustum-shaped particles were obtained (Figure 2c), while Cinitial = 5 mg/mL, cone-like particles were formed (Figure 2d). Obviously, when Cinitial = 8 mg/mL, part of the particles changed from core-shell to frustum-shaped particles. The concentration of BCP in the initial emulsion droplets was 5.6 mg/mL, which was regarded as the critical point for morphology transition. The change of BCP initial concentration (from 10 mg/mL to 8 mg/mL) will 10


Page 11 of 27 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

not significantly affect the spreading parameters and particle size. However, viscosity of the BCPs within a single droplet is highly related to BCPs concentration. Therefore, we can conclude that both the volume fraction of PFO and concentration (viscosity) of BCP play important roles in the particle morphology. We will further discuss these factors in Section 3.4.

Figure 2. TEM images of PS9.8K-b-P4VP10K particles obtained by using PFO as the liquid core template with varied initial concentration of BCP when r = 7:3. (a) 10 mg/mL, (b) 8 mg/mL, (c) 6 mg/mL, and (d) 5 mg/mL. The red arrows indicate the position of PFO droplet. Effect of Hydrogen Bonding Agent on the Particle Morphology PDP can selectively hydrogen bond to pyridine units on P4VP chains, leading to the formation of PS-b-P4VP(PDP)x (x represents the molar ratio of PDP to 4VP units) comb-like supramolecules.29 The introduction of PDP can adjust the volume fraction of P4VP (fP4VP) and modify the hydrophilicity of P4VP domains. Here we use this supramolecular strategy to control the morphology of the anisotropic particles. Figure 3 shows the morphology evolution of BCP particles as the change of r and x values. When cylinder-forming BCP PS51K-b-P4VP18K (fP4VP =24.3%) was employed at r = 7:3, core-shell capsules were observed (Figure 3a), in which BCPs completely engulf PFO liquid core. In the shell part, the P4VP chains form spherical domains in PS matrix, which is consistent with self-assembled morphology of neat PS51K-b-P4VP18K confined in emulsion droplet.29 Core-shell capsules and plate-like particles coexist when r = 4:6 (Figure 3b). However, when r = 3:7, plate-shaped particles with hexagonally packed spherical P4VP domains were obtained 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 27

(Figure 3c, Figure S2c and Figure S4a). On the other hand, the addition of PDP to BCPs system induced morphological transition of the particle. When x = 0.2 [P4VP(PDP) volume fraction (fc) increases to 35.9 %], core-shell capsules with cylindrical P4VP(PDP) domains were obtained at r = 7:3, where P4VP(PDP) cylinder is parallel to the spherical PFO core surface (Figure 3d). Decreasing r to 4:6, cylindrical P4VP domains can be found in part of shell due to insufficient polymer (Figure 3e). Interestingly, crescent-shaped particles with cylindrical P4VP domains were generated when r = 3:7 (Figure 3f and Figure S4b). When x = 1.0 (fc = 60.1%), core-shell capsules with lamellar structure were obtained at r = 7:3 (Figure 3g). However, we noted that partial particles cannot keep core-shell structure integrity and were broken into bowl-like structure at r = 3:7 (Figure 3h and i). The P4VP(PDP) domains migrate to particle surface due to higher hydrophilicity of the P4VP(PDP) block. The above results indicate that the shape and internal structure of particles can be controlled by introducing the hydrogen-bond agent.

12


Page 13 of 27 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 3. TEM images of PS51K-b-P4VP18K(PDP)x particles at different volume ratio of BCP/PFO (where x equals to 0, 0.2 and 1.0). The insets in the upper right of (a), (c), (d), (f) and (g) are cartoons showing structures of the particles. Green and red regions represent P4VP and PS domains, respectively. Effect of Molecular Weight on the Particle Morphology Three different PS-b-P4VP BCPs were employed to investigate the effect of molecular weight on the morphology of particles at r = 3:7. As mentioned above, plate-like particles with spherical P4VP domains were obtained when PS51K-b-P4VP18K (P4VP fraction: 26.1 wt%) was used. The microdomain size of P4VP sphere is ~ 35 nm (Figure 4a). When PS22K-b-P4VP21.6K (P4VP fraction: 49.5 wt%) was employed, the spherical P4VP microdomain size increases to ~ 42 nm (Figure 4b), whereas PS110K-b-P4VP107K (P4VP fraction: 49.3 wt%) formed patchy particles with isolated spherical P4VP protuberances of 116 nm (Figure 4c). These results indicate that all the three BCPs 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 27

show spherical P4VP microdomains. Although symmetric BCP (e.g., PS22K-b-P4VP21.6K and PS110K-b-P4VP107K) were employed to prepare structured particles, no lamellar structure could be observed. The reason can be ascribed to the fact that chloroform is slightly selective for PS over P4VP. As the evaporation of chloroform, PS22K-b-P4VP21.6K and PS110K-b-P4VP107K may form spherical micelles with P4VP cores before they coalesce to microparticles.30

Figure 4. TEM images of PS-b-P4VP particles with different P4VP domain sizes formed from BCPs with varied molecular weights: (a) PS51K-b-P4VP18K; (b) PS22K-b-P4VP21.6K; (c) PS110K-b-P4VP107K. The initial volume ratio of BCP/PFO was 3:7 for all samples. The insets in (a), (b) and (c) are the TEM images with high magnification showing the hexagonally stacked P4VP spheres. Proposed Formation Mechanism From a thermodynamic perspective, the morphology of emulsion droplet could be predicted directly by comparing interfacial tensions between different phases, which can be summarized by the spreading coefficient: Si = δjk – (δij + δik)

(1)

where δjk, δik, δjk denote the three interfacial tensions between phases i, j and k correspondingly in emulsion droplet.43,49 The equilibrium morphologies include three possibilities: engulfing, partial-engulfing, and non-engulfing (Scheme 2). In our case, as BCPs have higher affinity with PVA compared to PFO, thus δPFO-BCP is larger than δBCP-PVA, leading to SPFO < 0 according to eq 1. Therefore, there are three possibilities for spreading parameters combination: 14


Page 15 of 27 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

SPFO < 0; SBCP > 0; SPVA < 0

(2)

SPFO < 0; SBCP < 0; SPVA < 0

(3)

SPFO < 0; SBCP < 0; SPVA > 0

(4)

These three equations, eq (2) to eq (4), correspond to core-shell particles, acorn-like particles, and separated particles, respectively. Scheme 2. Three possibilities of microdroplets morphology.

From the results shown in Figure 1, 3 and Figure S1, we can see that the BCP and PFO phases remain contact, which indicates SPVA is negative. We noted that BCP completely or partially spread over the PFO surface, which implies the interfacial tension between PVA aqueous solution and PFO is greater than that between PVA and BCP, δPFO-BCP > δBCP-PVA. Thus, according to Eq (2), if SBCP > 0, the BCPs would completely spread over the PFO surface to form a core-shell structures; if SBCP < 0, partially engulfing led to acorn-like structures according to Eq (3). In general, the spreading parameter can be controlled by altering surfactant type and concentration. In our system, PVA is employed as surfactant and the concentration is fixed at 3 mg/mL. Thus, changing the volume ratio 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 27

of BCP to PFO will not change the spreading parameter SBCP. We obtained core-shell structures with BCP completely encapsulating PFO at high r value, while anisotropic shapes with partially encapsulated PFO by BCPs at low r value. These results are contradictory in terms of thermodynamics. Nevertheless, the equilibrium morphologies of particles are not necessarily consistent with thermodynamic structure predicted.43, 51 A previous report by Ho et al. demonstrated the final morphology of emulsion droplet was significantly affected by the viscosity of the emulsion phase.48 The dewetting time is determined by the balance of the driving force of interfacial tensions and the viscous force, and it increases as the increase of volume ratio of outer phase to inner phase and the viscosity of the outer phase.49 In our system, the concentration of BCP increases as the evaporation of chloroform, resulting in the increase of viscosity in the emulsion droplets. Therefore, the kinetic factors may affect the final morphology of particles. To understand the experimental results and also explore the mechanism of the formation of anisotropic particles, we took PS51K-b-P4VP18K(PDP)0.2 as an example, to monitor the evolution of emulsion droplets during evaporation at different r values (r = 7:3 and r = 3:7). Figure 5a-e show the formation of PS51K-b-P4VP18K(PDP)0.2 particles at r = 7:3. A few small PFO droplets can be observed inside a droplet at the early stage of evaporation, indicating macrophase separation between BCPs and PFO (Figure 5a). Then, these small PFO droplets gradually coalesce into a large droplet (Figure 5b-d). Although the PFO droplet is immiscible with BCPs, it can still locate at the center of the emulsion droplet. This can be attributed to a significant increase in solution viscosity as the evaporation of chloroform. In this case, BCP is a major component in the solution (r = 7:3). The evaporation of chloroform results in the rapid increase in BCP concentration and thus the solution viscosity. The viscous resistance force hinders the 16


Page 17 of 27 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

movement of PFO to the edge of the emulsion droplet. After completely removal of chloroform, the BCP phase solidifies to trap the PFO droplet, resulting in a core-shell structure (Figure 5e).

Figure 5. Optical microscopy (OM) images showing the evolution of emulsion droplets during chloroform evaporation at different r value. (a-e) r =7:3, (f-j) r =3:7. The BCP used in this case is PS51K-b-P4VP18K(PDP)0.2. The scale bars in the last image of the line apply for the other images in the same lines. The red arrows indicate the position of PFO droplet. In order to confirm that the viscosity plays an important role in determining the morphology of particles, we further monitored the formation of particles at r = 3:7 (Figure 5f-j). Similarly, a few small PFO droplets appear inside a droplet at the early stage of evaporation (Figure 5f). Then, the small PFO droplets coalesce into a large droplet and slowly move to the edge of the emulsion droplet (Figure 5g-h). This phenomenon can be attributed to the interfacial tension-driven dewetting due to the repulsion between PFO and BCPs for a structure with minimum energy.27 In this case (r = 3:7), the BCP is a minor component in the solution. Thus, the increase of viscosity during evaporation is less significant than the previous case (r = 7:3). The emulsion droplet keeps shrinking and further squeezes the PFO out of the emulsion droplet (Figure 5i). Consequently, acorn-like shape particles formed (Figure 5j).

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 27

Therefore, the position of PFO drop in emulsion droplets plays a crucial role in determining the shape of the emulsion droplets, significantly influencing in the formation of shape-anisotropic particles. With less kinetic constraint at relative low r value, interfacial tensions are the major driving force to reach the equilibrium morphology of emulsions. In this case, PFO liquid droplet can direct the self-assembly of BCP into anisotropic particles. However, the evolution of emulsion droplets at high r value is dominated by both the interfacial tensions and the viscosity. As a result, the PFO will experience a resistance to its motion due to higher viscosity, resulting in the formation of core-shell particles. Therefore, we conclude that manipulation of the kinetic and thermodynamic factors during emulsion evolution offers new opportunities for the formation of shape-anisotropic polymeric particles with controllable internal structures.

CONCLUSIONS In summary, we have demonstrated the preparation of anisotropic polymer particles with controllable structures via three dimensional confined assembly of BCPs using liquid core as template in emulsion droplets. This technique allows us to control the assemblies from symmetrical core-shell to non-spherical structure, simply by adjusting the volume ratio of BCP/PFO or the initial concentration of BCP. Moreover, the non-spherical shape and internal structure of the polymer particles can be changed by altering block ratio, molecular weight, or using additives. We also show that volume ratio of BCP/PFO influences the position of the PFO droplet within the emulsion droplet during solvent evaporation, which play a crucial role in determining the template effect on the self-assembly of BCP. This work not only provides a facile yet robust strategy for the design and fabrication of

18


Page 19 of 27 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

shape-anisotropic BCP particles with various structures, but also presents an understanding of the balance between the kinetic and thermodynamic factors during emulsion droplets evolution.

ASSOCIATED CONTENT Supporting Information Additional TEM and SEM images of the shape anisotropic BCPs particles. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (J. X.) *E-mail: [email protected] (J. Z.)

Notes The authors declare no conflict of interest.

ACKNOWLEDGEMENTS We gratefully acknowledge funding for this work provided by National Natural Science Foundation of China (51525302 and 51473059), Natural Science Foundation of Hubei Scientific Committee (2016CFA001) and Open project of State Key Lab of Materials-Oriented Chemical Engineering (KL 16-04). We thank the HUST Analytical and Testing Center for allowing us to use its facilities.

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 27

REFERENCES 1. Yang, Y.; Kim, H.; Xu, J.; Hwang, M. S.; Tian, D.; Wang, K.; Zhang, L.; Liao, Y.; Park, H. G.; Yi, G. R.; Xie, X.; Zhu, J., Responsive Block Copolymer Photonic Microspheres. Adv. Mater. 2018, 30, 1707344. 2. Otsuka, H.; Nagasaki, Y.; Kataoka, K., PEGylated Nanoparticles for Biological and Pharmaceutical Applications. Adv. Drug Deliv. Rev. 2012, 64, 246-255. 3. Kamaly, N.; Xiao, Z.; Valencia, P. M.; Radovic-Moreno, A. F.; Farokhzad, O. C., Targeted Polymeric Therapeutic Nanoparticles: Design, Development and Clinical Translation. Chem. Soc. Rev. 2012, 41, 2971-3010. 4. Bakshi, M. S., Colloidal Micelles of Block Copolymers as Nanoreactors, Templates for Gold Nanoparticles, and Vehicles for Biomedical Applications. Adv. Colloid Interface Sci. 2014, 213, 1-20. 5. Lu, Z.; Liu, G.; Phillips, H.; Hill, J. M.; Chang, J.; Kydd, R. A., Palladium Nanoparticle Catalyst Prepared in Poly(Acrylic Acid)-Lined Channels of Diblock Copolymer Microspheres. Nano Lett. 2001, 1, 683-687. 6. Pham, H. H.; Gourevich, I.; Oh, J. K.; Jonkman, J. E. N.; Kumacheva, E., A Multidye Nanostructured Material for Optical Data Storage and Security Data Encryption. Adv. Mater. 2004, 16, 516-520.

20


Page 21 of 27 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

7. Wu, M.; Zhu, Y.; Jiang, W., Disassembly of Multicompartment Polymer Micelles in Spatial Sequence Using an Electrostatic Field and Its Application for Release in Chronological Order. Angew. Chem., Int. Ed. 2018, 57, 3578-3582. 8. Liu, W.; Mao, J.; Xue, Y.; Zhao, Z.; Zhang, H.; Ji, X., Nanoparticle Loading Induced Morphological Transitions and Size Fractionation of Coassemblies from PS-b-PAA with Quantum Dots. Langmuir 2016, 32, 7596-76059. 9. Kim, S. H.; Abbaspourrad, A.; Weitz, D. A., Amphiphilic Crescent-Moon-Shaped Microparticles Formed by Selective Adsorption of Colloids. J. Am. Chem. Soc. 2011, 133, 5516-5524. 10. Champion, J. A.; Mitragotri, S., Role of Target Geometry in Phagocytosis. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 4930-4934. 11. Geng, Y.; Dalhaimer, P.; Cai, S.; Tsai, R.; Tewari, M.; Minko, T.; Discher, D. E., Shape Effects of Filaments Versus Spherical Particles in Flow and Drug Delivery. Nat. Nanotechnol. 2007, 2, 249-255. 12. Tu, F.; Lee, D., Shape-Changing and Amphiphilicity-Reversing Janus Particles with pH-Responsive Surfactant Properties. J. Am. Chem. Soc. 2014, 136, 9999-10006. 13. Dendukuri, D.; Pregibon, D. C.; Collins, J.; Hatton, T. A.; Doyle, P. S., Continuous-Flow Lithography for High-Throughput Microparticle Synthesis. Nat. Mater. 2006, 5, 365-369. 14. Rolland, J. P.; Maynor, B. W.; Euliss, L. E.; Exner, A. E.; Denison, G. M.; DeSimone, J. M., Direct Fabrication and Harvesting of Monodisperse, Shape-Specific Nanobiomaterials. J. Am. Chem. Soc. 2005, 127, 10096-10100. 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 27

15. Champion, J. A.; Katare, Y. K.; Mitragotri, S., Making Polymeric Micro- and Nanoparticles of Complex Shapes. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 11901-11904. 16. Min, N. G.; Kim, B.; Lee, T. Y.; Kim, D.; Lee, D. C.; Kim, S. H., Anisotropic Microparticles Created by Phase Separation of Polymer Blends Confined in Monodisperse Emulsion Drops. Langmuir 2015, 31, 937-943. 17. Ku, K. H.; Shin, J. M.; Yun, H.; Yi, G.-R.; Jang, S. G.; Kim, B. J., Multidimensional Design of Anisotropic Polymer Particles from Solvent-Evaporative Emulsion. Adv. Funct. Mater. 2018, 28, 1802961. 18. Shin, J. M.; Kim, M. P.; Yang, H.; Ku, K. H.; Jang, S. G.; Youm, K. H.; Yi, G.-R.; Kim, B. J., Monodipserse Nanostructured Spheres of Block Copolymers and Nanoparticles via Cross-Flow Membrane Emulsification. Chem. Mater. 2015, 27, 6314-6321. 19. Xu, S.; Nie, Z.; Seo, M.; Lewis, P.; Kumacheva, E.; Stone, H. A.; Garstecki, P.; Weibel, D. B.; Gitlin, I.; Whitesides, G. M., Generation of Monodisperse Particles by Using Microfluidics: Control over Size, Shape, and Composition. Angew. Chem., Int. Ed. 2005, 117, 734-738. 20. Guan, S.; Zhang, C.; Wen, W.; Qu, T.; Zheng, X.; Zhao, Y.; Chen, A., Formation of Anisotropic Liquid Crystalline Nanoparticles via Polymerization-Induced Hierarchical Self-Assembly. ACS Macro Lett. 2018, 7, 358-363. 21. Fan, J.-B.; Song, Y.; Liu, H.; Lu, Z.; Zhang, F.; Liu, H.; Meng, J.; Gu, L.; Wang, S.; Jiang, L., A General Strategy to Synthesize Chemically and Topologically Anisotropic Janus Particles. Sci. Adv. 2017, 3, 1603203. 22


Page 23 of 27 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

22. Xu, J.; Wu, Y.; Wang, K.; Shen, L.; Xie, X.; Zhu, J., The Generation of Polymeric Nano-Bowls through 3D Confined Assembly and Disassembly. Soft Matter 2016, 12, 3683-3687. 23. Nisisako, T.; Torii, T., Formation of Biphasic Janus Droplets in a Microfabricated Channel for the Synthesis of Shape-Controlled Polymer Microparticles. Adv. Mater. 2007, 19, 1489-1493. 24. Ekanem, E. E.; Zhang, Z.; Vladisavljevic, G. T., Facile Microfluidic Production of Composite Polymer Core-Shell Microcapsules and Crescent-Shaped Microparticles. J. Colloid Interface Sci. 2017, 498, 387-394. 25. Kim, J. H.; Jeon, T. Y.; Choi, T. M.; Shim, T. S.; Kim, S. H.; Yang, S. M., Droplet Microfluidics for Producing Functional Microparticles. Langmuir 2014, 30, 1473-1488. 26. Chen, P.; Liang, H.; Shi, A.-C., Microstructures of a Cylinder-Forming Diblock Copolymer under Spherical Confinement. Macromolecules 2008, 41, 8938-8943. 27. Jeon, S.-J.; Yi, G.-R.; Yang, S.-M., Cooperative Assembly of Block Copolymers with Deformable Interfaces: Toward Nanostructured Particles. Adv. Mater. 2008, 20, 4103-4108. 28. Arsenault, A. C.; Rider, D. A.; Tétreault, N.; Chen, J. I. L.; Coombs, N.; Ozin, G. A.; Manners, I., Block Copolymers under Periodic, Strong Three-Dimensional Confinement. J. Am. Chem. Soc. 2005, 127, 9954-9955. 29. Deng, R.; Liu, S.; Li, J.; Liao, Y.; Tao, J.; Zhu, J., Mesoporous Block Copolymer Nanoparticles with Tailored Structures by Hydrogen-Bonding-Assisted Self-Assembly. Adv. Mater. 2012, 24, 1889-1893.

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 27

30. Deng, R.; Liang, F.; Qu, X.; Wang, Q.; Zhu, J.; Yang, Z., Diblock Copolymer Based Janus Nanoparticles. Macromolecules 2015, 48, 750-755. 31. Deng, R.; Liang, F.; Li, W.; Yang, Z.; Zhu, J., Reversible Transformation of Nanostructured Polymer Particles. Macromolecules 2013, 46, 7012-7017. 32. Xu, J.; Wang, K.; Li, J.; Zhou, H.; Xie, X.; Zhu, J., ABC Triblock Copolymer Particles with Tunable Shape and Internal Structure through 3D Confined Assembly. Macromolecules 2015, 48, 2628-2636. 33. Lee, J.; Ku, K. H.; Kim, M.; Shin, J. M.; Han, J.; Park, C. H.; Yi, G. R.; Jang, S. G.; Kim, B. J., Stimuli-Responsive, Shape-Transforming Nanostructured Particles. Adv. Mater. 2017, 29, 1700608. 34. Klinger, D.; Wang, C. X.; Connal, L. A.; Audus, D. J.; Jang, S. G.; Kraemer, S.; Killops, K. L.; Fredrickson, G. H.; Kramer, E. J.; Hawker, C. J., A Facile Synthesis of Dynamic, Shape-Changing Polymer Particles. Angew. Chem., Int. Ed. 2014, 53, 7018-7022. 35. Zhang, L. B.; Wang, K.; Zhu, J. T., Research Progress on Confined Assembly of Block Copolymers in China. Acta Polym. Sin. 2017, 8, 1261-1276. 36. Chai, A.-h.; Zhang, L.-X., Microdomain Morphology of Cylinder-Forming Diblock Copolymers under Spherical Shell Confinement. Chinese J. Polym. Sci. 2011, 29, 684. 37. Ku, K. H.; Shin, J. M.; Kim, M. P.; Lee, C. H.; Seo, M. K.; Yi, G. R.; Jang, S. G.; Kim, B. J., Size-Controlled Nanoparticle-Guided Assembly of Block Copolymers for Convex Lens-Shaped Particles. J. Am. Chem. Soc. 2014, 136, 9982-9989. 24


Page 25 of 27 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

38. Wu, Y.; Wang, K.; Tan, H.; Xu, J.; Zhu, J., Emulsion Solvent Evaporation-Induced Self-Assembly of Block Copolymers Containing pH-Sensitive Block. Langmuir 2017, 33, 9889-9896. 39. Wu, Y.; Tan, H.; Yang, Y.; Li, Y.; Xu, J.; Zhang, L.; Zhu, J., Regulating Block Copolymer Assembly Structures in Emulsion Droplets through Metal Ion Coordination. Langmuir 2018, 34, 11495-11502. 40. Xu, J.; Yang, Y.; Wang, K.; Wu, Y.; Zhu, J., Fabrication of Convex Lens-Shaped Polymer Particles by Tuning the Interfacial Interaction. Mater. Chem. Front. 2017, 1, 507-511. 41. Choi, C. H.; Weitz, D. A.; Lee, C. S., One Step Formation of Controllable Complex Emulsions: from Functional Particles to Simultaneous Encapsulation of Hydrophilic and Hydrophobic Agents into Desired Position. Adv. Mater. 2013, 25, 2536-2541. 42. Rosca, I. D.; Watari, F.; Uo, M., Microparticle Formation and Its Mechanism in Single and Double Emulsion Solvent Evaporation. J. Controlled Release 2004, 99, 271-280. 43. Pisani, E.; Fattal, E.; Paris, J.; Ringard, C.; Rosilio, V.; Tsapis, N., Surfactant Dependent Morphology of Polymeric Capsules of Perfluorooctyl Bromide: Influence of Polymer Adsorption at the Dichloromethane-Water Interface. J. Colloid Interface Sci. 2008, 326, 66-71. 44. Shum, H. C.; Zhao, Y. J.; Kim, S. H.; Weitz, D. A., Multicompartment Polymersomes from Double Emulsions. Angew. Chem., Int. Ed. 2011, 50, 1648-1651.

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 27

45. Staff, R. H.; Gallei, M.; Mazurowski, M.; Rehahn, M.; Berger, R.; Landfester, K.; Crespy, D., Patchy Nanocapsules of Poly(vinylferrocene)-Based Block Copolymers for Redox-Responsive Release. ACS Nano 2012, 6, 9042-9049. 46. Xu, J.; Li, J.; Yang, Y.; Wang, K.; Xu, N.; Li, J.; Liang, R.; Shen, L.; Xie, X.; Tao, J.; Zhu, J., Block Copolymer Capsules with Structure-Dependent Release Behavior. Angew. Chem., Int. Ed. 2016, 55, 14633-14637. 47. Pisani, E.; Tsapis, N.; Galaz, B.; Santin, M.; Berti, R.; Taulier, N.; Kurtisovski, E.; Lucidarme, O.; Ourevitch, M.; Doan, B. T.; Beloeil, J. C.; Gillet, B.; Urbach, W.; Bridal, S. L.; Fattal, E., Perfluorooctyl Bromide Polymeric Capsules as Dual Contrast Agents for Ultrasonography and Magnetic Resonance Imaging. Adv. Funct. Mater. 2008, 18, 2963-2971. 48. Kong, T.; Liu, Z.; Song, Y.; Wang, L.; Shum, H. C., Engineering Polymeric Composite Particles by Emulsion-Templating: Thermodynamics Versus Kinetics. Soft Matter 2013, 9, 9780-9784. 49. Kang, Z.; Zhu, P.; Kong, T.; Wang, L., A Dewetting Model for Double-Emulsion Droplets. Micromachines 2016, 7, 196. 50. Darling, S. B., Directing the Self-Assembly of Block Copolymers. Prog. Polym. Sci. 2007, 32, 1152-1204. 51. Sundberg, D. C.; Casassa, A. P.; Pantazopoulos, J.; Muscato, M. R.; Kronberg, B.; Berg, J., Morphology

Development

of

Polymeric

Microparticles

in

Aqueous

Thermodynamic Considerations. J. Appl. Polym. Sci., 1990, 41, 1425-1442.

26


Dispersions.

I.

Page 27 of 27 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 the Table of Contents Use Only: Title: Shape-Anisotropic Diblock Copolymer Particles with Varied Internal Structures Authors: Min Ren, Zhen Geng, Ke Wang, Yi Yang, Zhengping Tan, Jiangping Xu, Lianbin Zhang, Lixiong Zhang, and Jintao Zhu TOC Graph:

27


Shape-Anisotropic Diblock Copolymer Particles with Varied Internal

Recommend Documents