Structural Transformation of Diblock Copolymer ... - ACS Publications

Subscriber access provided by CMU Libraries - http://library.cmich.edu

Article

Structural Transformation of Diblock Copolymer/Homopolymer Assembles by Tuning Cylindrical Confinement and Interfacial Interactions Jiangping Xu, Ke Wang, Ruijing Liang, Yi Yang, Huamin Zhou, Xiaolin Xie, and Jintao Zhu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b03146 • Publication Date (Web): 22 Oct 2015 Downloaded from http://pubs.acs.org on November 1, 2015

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

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

Page 1 of 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

Structural Transformation of Diblock Copolymer/Homopolymer Assembles by Tuning Cylindrical Confinement and Interfacial Interactions Jiangping Xu,1, 2 Ke Wang,1 Ruijing Liang,1 Yi Yang,1 Huamin Zhou,2 Xiaolin Xie,1 JintaoZhu1, *

1

State Key Laboratory of Materials Processing and Mold Technology, School of Chemistry and

Chemical Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China 2

School of Materials Science and Engineering, HUST, Wuhan 430074, China

*Corresponding author, E-mail:[email protected](J. Z.) Tel: 86-27-87793240; Fax: 86-27-87543632

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

ABSTRACT: In this study, we report the controllable structural transformation of block copolymer/homopolymer binary blends in cylindrical nanopores. Polystyrene-b-poly(4-vinyl pyridine)/homopolystyrene (SVP/hPS) nanorods (NRs) can be fabricatedby pouring the polymers into anodic aluminum oxide (AAO) channel, and isolated by selective removal of the AAO membrane. In this two dimensional (2D) confinement, SVP self-assemble into NRs with concentric lamellar structure, and the internal structure can be tailored with the addition of hPS. We show that weight fraction and molecular weight of hPS, and the diameter of the channels can significantly affect the internal structure of the NRs. Moreover, mesoporous materials with tunable pore shape, size, and packing style can be prepared by selective solvent swelling of the structured NRs. In addition, these NRs can transform into spherical structures through solvent-absorption annealing, triggering the conversion from 2D to 3D confinement. More importantly, the transformation dynamics can be tuned by varying the preference property of surfactant to the polymers. It is proved that the shape and internal structure of the polymer particles are dominated by the interfacial interactions governed by the surfactants. KEYWORDS: Block copolymer, Homopolymer, Confined assembly, Structural transformation, Interfacial interaction

2


Page 2 of 27

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

1. INTRODUCTION Shaping the morphology of polymeric particles is critical for their applications in drug delivery, photonic crystal, electronic ink, and other fields, because the property of the particle materials is mainly dominated by their shape, internal structure, and surface topology.1-7 Template directed approaches have been employed to fabricate polymeric particles with controllable shape and structure.8-9 Confined assembly of block copolymers (BCPs) in a limited space has proved to be a facile and robust strategy to tailor assembly structures.10-15 _ENREF_10Generally, the shape and surface property of the assemblies can be tuned by manipulating the property of template wall, while the internal structure is dependent on the confining strength and the interfacial interaction. Soft templates, such as emulsion droplet, have been developed to shape the particle morphology. Due to the deformable wall and tunable interfacial interactions, the shape and internal structure of the particles can be readily tailored. While inside of the hard template, such as anodic aluminum oxide (AAO) channel and inverse-opal cavity, the particle shape is severely restricted by the walls, which makes it inconvenient to alter the particle shape. Thus, thermal annealing has been introduced to shape the polymeric nanorods (NRs) in AAO template. Chen and coworkers reported that the NRs would transform to spheres upon thermal annealing, which was driven by Rayleigh instability. Core-shell particles, short NRs, peapod-like complexes, and multicomponent particles were obtained through this route.16-20 Yet, most of their work are focused on homopolymer particles, thus no obvious nanostructures can be observed inside the particles. In order to fabricate particles with hierarchical internal structures, BCPs can be introduced into the confined assembly. Jin et al. reported the solvent swelling of BCP rods to spheres. The composition of BCPs and solvent property had great influence on the final structure of the particles.21-22 Recently, Zhu et al. described solvent

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

annealing approach to shape BCP tubes to spheres.23 Particles with various structures, which were dominated by the block ratio of the copolymer, were fabricated. These solvent treatment approaches offer new opportunities to construct the bridge between 2D and 3D confinement of BCPs. It is well know that there are three main factors affecting the confining behavior of BCPs: 1) Interactions among blocks (χN, where χ is the Flory-Huggins parameter, N is the degree of polymerization);24-27 2) Interfacial interaction between polymer and the boundary;14,

28

3)

Commensurability (D/L0) between confining size (D) and periodicity dimension of copolymer (L0).10, 12, 29

These factors dominate the shape and internal structure of the particles during their formation

process under confinement. In addition, the morphology can be tuned by solvent/thermal annealing after the formation of the particles. The annealing strategy can reshape the morphology of the particles. Previous work about the transformation of rods to spheres mainly focused on the effects of the interactions among blocks (including polymer property,17-18,

30-31

block ratio,21 and solvent

property32) on the structure of the final particles. To the best of our knowledge, there is no work focusing on the effect of interfacial interaction on the transformation of BCPs rods to spherical particles. During the annealing process, the polymer chains have been endowed with mobility, which is prerequisite for the structural rearrangement. The interfacial interactions (attractive or repulsive) will affect the arrangement of polymer segments. In our previous study, we’ve proved that the interfacial interaction dominated the morphology of the particles upon solvent annealing.29, 33 Here we focus on the influence of surfactants on the shape and internal structure of the particles during the transformation of BCPs NRs to nanospheres. We first fabricate polystyrene-b-poly(4-vinyl pyridine)/homopolystyrene (SVP/hPS) NRs based on AAO template approach. In this 2D confined

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

space, SVP can self-assemble concentric lamellar structures, and introduction of hPS can systemically tune the internal structure of the NRs. We demonstrate that the weight fraction and molecular weight of hPS, and the diameter of the template can significantly affect the structure of the NRs. Moreover, the structured NRs can be selectively swollen in ethanol to get mesoporous materials with tunable pore shape, size and packing style. Furthermore, these NRs will transform into spheres by solvent-absorption annealing in different surfactants solution, triggering the conversion from 2D to 3D confinement. We have proved that the transformation dynamics, and the shape/internal structure of the spheres are dominated by the interfacial preference of the polymer particles.

2. EXPERIMENT SECTION 2.1 Materials: Diblock copolymer PS9.8K-b-P4VP10K (SVP-10, the subscripts are the Mn of the blocks, Mw/Mn = 1.08), PS22K-b-P4VP22K (SVP-22, Mw/Mn = 1.15), homopolymer hPS2.8K (Mw/Mn = 1.09), hPS21K (Mw/Mn = 1.04), and hPS876K (Mw/Mn = 1.19) were purchased from Polymer Source, Inc., Canada. Poly(vinyl alcohol) (PVA, average Mw: 13K−23K g mol-1, 87−89% hydrolyzed) and cetyltrimethylammonium bromide (CTAB, purity ≥ 99%) was purchased from Aldrich. AAO templates (Figure S1 in supporting information) with channel diameter (D) of 61 nm and 96 nm were purchased from Puyuan Nanotech, Co., Ltd., China, while that with channel size of 210 nm were purchased from Whatman, Inc. All of the materials were used as received without further purification. 2.2 Fabrication of SVP/hPS NRs: SVP and hPS were first dissolved in chloroform at a concentration of 5 mg/mL, respectively, and then mixed at varied weight fraction of hPS (φhPS = mhPS/(mhPS+mSVP)). The AAO membrane was immersed in 0.08 mL of the mixed solution. 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

Chloroform was allowed to slowly evaporate and the polymers would enter the pores. Subsequently, saturated chloroform vapor was introduced to anneal the samples for 24 h at 30 °C. Finally, the AAO membrane was removed using 5 wt % sodium hydroxide aqueous solution. Isolated SVP/hPS NRs were obtained by ultrasonication and dispersed in water. 2.3 Formation of Mesporous Materials by Swelling the SVP/hPS NRs: The isolated SVP/hPS NRs were collected by centrifugation at 12 000 rpm for 5 min. Then, 0.5 mL of ethanol was added to redisperse the NRs under ultrasonication. After that, the suspension was gently stirred in water bath of 25 °C for 24 h to complete the swelling process. 2.4 Conversion from 2D to 3D Confinement by Solvent-Absorption Annealing of SVP/hPS NRs: Solvent-absorption annealing strategy29, 33-34_ENREF_22 was employed to reshape the SVP/hPS NRs to spheres. Thus, the 2D confinement was transformed to 3D confinement. Typically, the NRs were firstly dispersed in water or surfactant aqueous solution (e.g., PVA or CTAB). Then, 0.5 mL of the suspension was added in an open small vial (5 mL) and placed inside a large vial (25 mL) containing 1.0 mL of chloroform. After that, the large vial was sealed and kept still in water bath at 30 °C for a certain period. Subsequently, the inner small vial was taken out to release the absorbed chloroform. Finally, the particles were separated by centrifugation (14 000 rpm, 6 min). 2.5 Characterization: The structures of the polymer particles were investigated using FEI Tecnai G2 20 TEM operated at an accelerated voltage of 200 kV. Before TEM characterization, P4VP domains were selectively stained with iodine vapor at 30°C for 2 h.

3. RESULTS AND DISCUSSION The 2D confined assembly of diblock copolymer in nanochannels has been investigated via experimental10,

12, 35

and simulative approaches.13-14,

26

Several factors, including the interfacial

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

interaction and the confining strength are proved to severely affect the assembly behavior, resulting in unconventional structures. Here we focus on the effect of homopolymer on the phase separation of diblock copolymers under 2D confinement, which is seldom reported in experiment.36 3.1 Effect of hPS Weight Fraction (φ) and Pore Diameter (D) In the wet-brush regime (r < 1, where r = Mn(hPS)/Mn(PS block)), hPS2.8K (r= 0.13) is added to SVP-22 matrix. In this case, hPS2.8K can penetrate into the brushes formed by PS blocks of SVP-22, inducing phase transformation.37-41 Figure 1 shows the TEM images of the NRs obtained by changing φ and D. When D = 61 nm, neat SVP-22 will form NRs with concentric lamellar structure (Figure 1a) due to the symmetry of the two blocks. Increasing φ to 14.3 wt % will change P4VP phase from lamellae to cylinder (Figure 1b). Further increasing φ to 50 wt %, spherical P4VP domains in continuous PS domain can be observed (Figure 1d and Figure S2-S3). Such spheres originate from the fragmentation of the P4VP cylinders (Figure 1c, φ = 20 wt %). Interestingly, the spheres stack in a zig-zag manner. In this case, D/L0 equals to 1.68, indicating that the incommensurability between D and L0limits the spheres packing along the radial direction of the channel.42 When D is increased to 96 nm, similar morphological evolution is observed as the increase of φ (Figure 1e-h and Figure S2d-f). An obvious difference is that more P4VP spheres pack along the short axis of the NRs. Due to the increase of the channel size (D/L0 = 2.58), the confining strength is weakened. Thus, more repeated periods can be involved. There are three spheres in one layer aligning along the long axis of the NR, indicating that they are not closely packing because of the frustration induced by confinement (Figure S4). Further increasing D to 210 nm, lamellae will transform to cylinder, then to spheres, as the increase of φ (Figure 1i-l). However, the P4VP

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

cylindrical domains are not parallel to the NRs like which in the narrow channels (Figure 1b and 1f). Interestingly, helices with a string of spheres in the center are formed, which are shown in Figure 1k and Figure S5. When φ = 14.3 wt %, intermediate structures of the transformation from lamellae to helix can be observed (Figure 1j). Based on the above results, we can conclude that the lamellae first transforms to perforated lamellae, then to single helix, and finally to helices with a linear chain of spheres, as the increase of hPS in the blend. At φ = 50 wt %, the P4VP spheres stack hexagonally (Figure 1l), similar to the sphere packing without confinement. As D/L0 = 5.27, the confining effect is markedly weakened. The packing of the spheres is almost not affected by the incommensurability between D and L0.42

Figure 1. Representative TEM images of SVP-22/hPS2.8K NRs with various structures by tuning the AAO template channel diameter and weight fraction of hPS. All of the samples are stained by I2 vapor before TEM investigation. Insets in (a, b, d, h, and k) are the cartoons showing the internal 8


Page 8 of 27

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

structures of the NRs. 3.2 Effect of the Molecular Weight of hPS The molecular weight of hPS has significant influence on the phase structure of the NRs. SVP-22/hPS21K (r = 0.95) NRs with various structures are obtained by tuning φ and D (Figure 2 and Figure S6 in Supporting Information). From Figure 2a-d (D = 61 nm), we can see the transformation from lamellae to sphere, indicating that homopolymer with molecular weight similar to that of BCP brush will form wet-brush.43 On the other hand, some hPS domains can also be observed in the NRs when φ > 20 wt % (indicated by arrows in Figure 2c-d), implying that macro-phase separation also takes place. Similar results are observed at D = 96 nm (Figure S6). Further increasing D to 210 nm (Figure 2e-h), lamellar, cylindrical, and spherical P4VP domains coexist as the increase of φ. Pure hPS domains can also be observed (Figure 2h). Partial hPS21K chains penetrate into BCP domains to trigger the morphological transformation, while partial of them segregate to form pure hPS domains. Thus, it has been proved that both micro- and macro-phase separation (both wet- and dry-brush regimes) exist between SVP-22 and hPS21Kin the NRs. The competition between them at different length scale will cause unprecedented internal structures.

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

Figure 2.TEM images showing the SVP-22/hPS21KNRs with various internal structures.Arrows indicate the macro-phase separation. All of the samples are stained by I2 vapor before TEM investigation. The macro-phase separation can be enhanced by increasing the molecular weight of hPS. When hPS876K (r = 40) is added to SVP-22, obvious macro-phase separation, which is independent with φ, appears between them (Figure 3 and Figure S7). However, the micro-phase separation of SVP-22 is not affected with the addition of hPS876K. SVP-22 self-assembles into lamellar structures, while hPS876Kchains segregate to the pure hPS domains (Figure 3). Therefore, no hPS876K chain penetrates into BCP brush, and no obvious phase transformation can be observed in SVP-22 domains. As stated above, under 2D confinement, hPS with r < 1 will penetrate into the BCP brush to induce the phase transformation. Yet, hPS with r > 1 will lead to macro-phase separation and the micro-phase separation of BCP is not affected by hPS. Those hPS with r ~ 1 will cause the competition between microphase and macrophase separation, especially at high weight fraction of hPS. The coexistence of the different length scale phase separation will enrich the assembled structures.The limited space of the channel will guide the distribution of hPS, especially in dry-brush 10


Page 10 of 27

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

regime, avoiding the further condensation of hPS to large scale domains. This is important for the preparation of particles with hierarchical structure by annealing the NRs obtained under 2D confinement (details will be shown in Section 3.4).

Figure 3. TEM images of the SVP-22/hPS876K (φ = 50 wt %) NRs.Both micro- and macro-phase separation can be observed. Red dash lines show the interfaces between SVP-22 and hPS. Arrows indicate the hPS876K domains in the NRs. 3.3 Mesoporous NRs with Tunable Pore Shape The P4VP domains of SVP/hPS NRs can be selectively swollen by ethanol while the PS domains keep unchanged.44 The volume of P4VP domains increases as the swelling of the P4VP chains, resulting in squeezing the PS matrix. Thus, the glassy PS matrix is forced to reconstruct to accommodate the increased volume of P4VP domains. After removal of ethanol, mesoporous materials with tunable pore shape are obtained due to the collapse of the P4VP chains.45-47 The shape of the mesopores is dependent on the phase structure of P4VP domain. Figure 4 shows the TEM images of the mesoporous NRs obtained by swelling the NRs shown in Figure 1 in ethanol at 25 °C for 24 h. The pore shape is controlled by tailoring the weight fraction of hPS2.8K and the channel diameter. Mesoporous NRs with various shapes, including lamellar, cylindrical, ellipsoidal, helical, and spherical pores, are thus easily obtained. Wang et al. has reported the swelling-deswelling method to fabricate mesoporous materials with tunable pore shape.44, 47 Yet, the pore shape was 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

dependent on the block ratio of copolymer, and various BCPs with varied block ratio are need when varying pore shape. Here, only one kind of BCP is used to reshape the pores for our strategy, without bothering the tedious synthesis of BCPs with varied block ratio. Another advantage of our strategy is that the mesopores can form at room temperature. As demonstrated in the literature,44 no obvious mesopores could be obtained when swelling the SVP NRs in ethanol at room temperature, because the swelling solvent could hardly penetrate through the solid PS layer in this case. An elevation of temperature could trigger the mesopore formation. However, in our case, the short chain hPS2.8K can act as compatibilizer to soften the PS matrix and to increase the penetrability of the PS layer. Thus, ethanol can easily enter the P4VP domains to swell them and the PS matrix can rapidly reconstruct, resulting in the formation of the mesopores after evaporation of ethanol at room temperature. As a result, our strategy is a convenient and effective way to construct structured and mesoporous materials.

Figure 4. TEM images of mesoporous NRs with tunable pore shapes obtained by swelling SVP-22/hPS2.8K NRs in Figure 1. As shown in Figure 1d and h, the packing of spherical P4VP domains is significantly affected 12


Page 12 of 27

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

by the channel size. After carefully checking of the NRs with different diameters, we’ve found several packing styles of the P4VP spherical domains, as shown in Figure 5a-d. The packing of the spheres changes from linear (Figure 5a, D/L0 = 1.10) to zig-zag (Figure 5b, D/L0 = 1.68), then to three-sphere layer (Figure 5c, D/L0 = 2.58), and finally to double-sphere layer (Figure 5d, D/L0 = 2.83), as the NR diameter is increased from 52 nm to 134 nm. The spheres tend to stack hexagonally in bulk. However, in a limited space, the packing is constrained and complex structures appear.48

Figure 5. TEM images of various SVP-22/hPS2.8K NRs obtained at φ = 50 wt %. (a)-(d) NRs with different sphere packing styles, e.g., linear chain, zig-zag, three-sphere layer, and double-sphere layer, respectively. The mesoporous NRs are obtained by swelling in ethanol at (e)-(h) 25 °C and (i)-(l) 40 °C for 24 h. Insets in (a-c) are the cartoons showing the packing of P4VP spheres in the NRs. The packing of P4VP spherical domains can be precisely tailored by altering the channel

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

diameter, offering an opportunity to fabricate mesoporous NRs with ordered pores. As shown in Figure 5e-h, mesoporous NRs with packing pores (average diameter: 9.6 nm) are obtained after being swollen in ethanol at 25 °C for 24 h. The stack styles are the same as those of the solid NRs (Figure 5a-d). Moreover, the pore size is proved to be dependent on the temperature of swelling. After swelling the NRs in ethanol at 40 °C for 24 h, the pore diameter of the linear chain is increased to 21.2 nm (Figure 5i-l). Heating plays at least two roles in the mesopore formation process: 1) Heating will increase the swelling degree of P4VP chains, which will further expand the P4VP domains; 2) The segmental mobility of the PS chains will be enhanced by heating and thus the PS matrix will become softer, leading to the rapid reconstruction of the matrix.44 The enlargement of the P4VP domains will crush the PS matrix, and thus the P4VP chains can spread on surface of the NRs. Upon evaporation of ethanol, the PS matrix will become glassy rapidly and retain its altered shape, while the P4VP chains collapse to form open pores (Figure 5j-l). As stated above, we can precisely control the internal structure of the NRs and thus the pore packing of mesoporous assemblies by combining 2D confining assembly and selective swelling. Such structured mesoporous materials can be applied in ultrafiltration, catalysis, drug loading and controlled release, and many other fields. 3.4 Rods to Spheres Transformation: from 2D to 3D Confinement The NRs obtained in AAO template (hard confinement) can transform to spheres (soft confinement) via annealing process. Chen and coworkers have proved that the transformation from rods to spheres is driven by Rayleigh instability.30 Spherical, peapod like and core-shell particles can be obtained by finely tailoring the composition and annealing condition.18, 49 Jin et al. reported the transformation process of BCP rods to spheres during selective solvent swelling.21 Recently, solvent absorption annealing method was applied to reshape BCP tubes to spheres with various structures by Zhu et al. 14


Page 14 of 27

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

The structure of the particles was determined by the composition of copolymer.23 Yet, precisely control of the transformation dynamics, and the shape and internal structure of the resulting spheres by tuning the interfacial interaction has not been reported. As demonstrated in our previous studies, the morphology of the particles can be tuned by altering the surfactants during the annealing process.29, 33 Here, this strategy is employed to control the dynamics of the transformation from rods to spheres.

Figure 6. TEM images show the morphological evolution of the SVP-10 NRs annealed in chloroform vapor in (a)-(c) water, (d)-(f) PVA aqueous solution, and (g)-(i) CTAB aqueous solution. The NRs obtained in AAO template with D = 96 nm are used as the initial state. Insets in (a, c, e-i) 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

are the cartoons showing the internal structures of the polymer particles. The NRs with lamellar structure from SVP-10 are used as the initial state (Figure 6a). The outermost layer of the NRs is proved to be P4VP phase, due to the attractive interaction between P4VP block and the template wall.47 After being annealed in water for 10 min, strings of spheres can be observed (Figure 6b), which are the intermediate structures of the transformation driven by Rayleigh instability.23 The NRs transform to onion-like spherical particles after 2 h annealing (Figure 6c). The outermost layer of the onion is P4VP based on the I2 staining result, as water has preference to P4VP block. If the NRs were annealed in PVA aqueous solution, which creates a nearly neutral interface for both PS and P4VP blocks,33 pupa-like particles were obtained (Figure 6d-f). The NRs first transform to onion-like particles (Figure 6d), then to bud-like particles (Figure 6e). Then, pupa-like ellipsoids with alternating PS and P4VP layers appear after being annealed for 2 h (Figure 6f). Moreover, reverse onion-like particles with PS at the outermost layer (Figure 6i) are formed when the NRs are annealed in CTAB, which preferentially wets PS block. During the transformation process, the NRs first breakup to onion-like particles, then to pupa-like particles (Figure 6g), then to reverse bud-like particles (Figure 6h), and finally to reverse onion-like particles (Figure 6i). To the best of our knowledge, this is the first observation of the inversion process between onion- and inverse onion-like particles, in which the bud-like and pupa-like particles are the intermediate states. In the transformation process, the property of the surfactant dominates the internal structure of the particles. The absorption of good solvent enhances the mobility of the polymer chains. The block, which is attractive to the surfactant, will immigrate to the surface of the particle. The other block will be forced to rearrange to be accordant to the chain distribution on the surface. Thus, the internal structure can be altered by the tuning interfacial interaction. More interestingly, the shape of the 16


Page 16 of 27

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

particles varies as the change of the internal structure of the particles because of the deformable interface under soft confinement. On the contrary, under hard confinement (AAO membrane channels), the shape of the NRs is dominated by the wall, and their internal structure is hard to be engineered through this route. In summary, the shape and internal structure of the particles can be well controlled by tuning the property of surfactants, which dominates the interfacial preference. Thus, the 2D to 3D confinement transformation is realized conventionally. Moreover, the dynamics of the morphological evolutioncan also be readily controlled. The transformation of SVP-22/hPS blended NRs to spheres is also studied. Particles with hierarchicalstructures can be obtained. As shown in Figure 7a and 7b, where the SVP-22/hPS2.8K NRs is used as the initial state (φ = 14.3 wt % and 50 wt %, respectively), particles with cylindrical and spherical P4VP domains are observed. The internal structures under 3D confinement are similar to that under 2D confinement (Figure 1f and 1h). When SVP-22/hPS21K NRs are annealed in water for 2 h, particles with cylindrical (Figure 7c, φ = 14.3 wt %) and spherical (Figure 7d, φ = 50 wt %) P4VP domains are obtained. As demonstrated above, the macrophase and microphase separations coexist in the blend of SVP-22/hPS21K, inducing unprecedented phase structures in the NRs (Figure 2). Actually, the macrophase separation is also observed under 3D confinement. The homogeneous hPS21K spheres are observed in Figure 7c and 7d (indicated by arrows). In SVP-22/hPS876K blend, only macrophase appears between SVP-22 and hPS876K (Figure 3). Such inhomogeneous NRs are annealed to produce Janus particles with one hemisphere of SVP-22 and another of hPS876K (Figure 7e-f and Figure S8). The onion-like structure of SVP-22 hemisphere is not affected by the addition of hPS876K. Interestingly, the particle shape under 3D confinement is connected with the internal structure due to the soft boundary. For example, the particles with cylindrical P4VP domains (Figure

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

7a and 7c) are ellipsoidal due to the commensurability between the preferred cylinder stacking and the finite particle size,40, 46 while the particle shape under 2D confinement is severely restricted to be rod-like by the hard boundary. As demonstrated above, we can readily alter the dimension of the confinement of BCPs via solvent-absorption annealing approach, which induce a rod-to-sphere transformation. More importantly, the shape and internal structure of the particles can be easily tailored by tuning the selectivity of the boundary and the composition of the polymers.

Figure 7. TEM images show the particles with hierarchical structures obtained by annealing SVP-22/hPS NRs. The molecular weights of hPS are (a)-(b) 2.8K, (c)-(d) 21K, and (e)-(f) 876K, respectively. The weight fractions of hPS are (a) and (c) 14.3 wt %, (b) and (d)-(f) 50 wt %, respectively. The red dash lines in (e) and (f) indicate the interfaces between SVP-22 and hPS876K. Insets in (a, c, e) are the cartoons showing the internal structures of the polymer particles. 18


Page 18 of 27

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

4. CONCLUSION In summary, the 2D confined assembly of BCP/homopolymer (SVP/hPS) blend is systematically investigated in the present study. The weight ratio and molecular weight of hPS, and the channel diameter of AAO template are proved to play significant role in the phase structure of the assemblies. Particularly, we focus on the packing of spherical P4VP domains in the limited space, which can be well controlled by tuning the pore size. Such structured assemblies can be selectively swollen to mesoporous materials with controllable pore shape. More importantly, the dimension of the confinement can be altered from 2D to 3D through solvent annealing. Thus, particles with hierarchical structures can be fabricated by controlling the transformation dynamics. By tuning the interfacial preference, the shape and internal structure of the particles can be conventionally controlled. This novel strategy is believed to be a facile and effective to design and reshape the polymer particles.

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

ASSOCIATED CONTENT Supporting Information Available: Additional TEM images of the polymer NRs and spherical particles (Figure S1-S8). This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (J. Z.) Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work is funded by National Basic Research Program of China (973 Program, 2012CB821500), National Natural Science Foundation of China (91127046), and China Postdoctoral Science Foundation (2014M552034). We also thank the HUST Analytical and Testing Center for allowing us to use its facilities.

20


Page 20 of 27

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

REFERENCES 1.

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

New Applications. Adv. Mater. 2000, 12, 693-713. 2.

Kim, S.-H.; Hollingsworth, A. D.; Sacanna, S.; Chang, S.-J.; Lee, G.; Pine, D. J.; Yi, G.-R.

Synthesis and Assembly of Colloidal Particles with Sticky Dimples. J. Am. Chem. Soc. 2012, 134, 16115-16118. 3.

Otsuka, H.; Nagasaki, Y.; Kataoka, K. PEGylated Nanoparticles for Biological and

Pharmaceutical Applications. Adv. Drug Delivery Rev. 2003, 55, 403-419. 4.

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. 5.

Ge, J.; Hu, Y.; Zhang, T.; Yin, Y. Superparamagnetic Composite Colloids with Anisotropic

Structures. J. Am. Chem. Soc. 2007, 129, 8974-8975. 6.

Park, J.-G.; Forster, J. D.; Dufresne, E. R. High-Yield Synthesis of Monodisperse

Dumbbell-Shaped Polymer Nanoparticles. J. Am. Chem. Soc. 2010, 132, 5960-5961. 7.

Yin, Y. D.; Lu, Y.; Gates, B.; Xia, Y. N. Template-Assisted Self-Assembly: A Practical Route to

Complex Aggregates of Monodispersed Colloids with Well-Defined Sizes, Shapes, and Structures. J. Am. Chem. Soc. 2001, 123, 8718-8729. 8.

Hulteen, J. C.; Martin, C. R. A General Template-Based Method for the Preparation of

Nanomaterials. J. Mater. Chem. 1997, 7, 1075-1087. 9.

Yang, Z. Z.; Niu, Z. W.; Lu, Y. F.; Hu, Z. B.; Han, C. C. Templated Synthesis of Inorganic

Hollow Spheres with A Tunable Cavity Size onto Core-Shell Gel Particles. Angew. Chem., Int.Ed.

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

2003, 42, 1943-1945. 10. Shin, K.; Xiang, H. Q.; Moon, S. I.; Kim, T.; McCarthy, T. J.; Russell, T. P. Curving and Frustrating Flatland. Science 2004, 306, 76-76. 11. Yang, R.; Ding, D.; Li, B. Self-Assembly of Symmetric Diblock Copolymer/Homopolymer Blends Confined in Spherical Nanopores. Acta Polym. Sin.2011, 11, 1355-1360. 12. Xiang, H. Q.; Shin, K.; Kim, T.; Moon, S. I.; McCarthy, T. J.; Russell, T. P. Block Copolymers under Cylindrical Confinement. Macromolecules 2004, 37, 5660-5664. 13. He, X. H.; Song, M.; Liang, H. J.; Pan, C. Y. Self-Assembly of the Symmetric Diblock Copolymer in a Confined State: Monte Carlo Simulation. J. Chem. Phys. 2001, 114, 10510-10513. 14. Yu, B.; Sun, P. C.; Chen, T. H.; Jin, Q. H.; Ding, D. T.; Li, B. H.; Shi, A. C. Confinement-Induced Novel Morphologies of Block Copolymers. Phys. Rev. Lett. 2006, 96, 138306. 15. Chen, P.; Liang, H. Nanostructures from Cylinder-Forming Blcok Polymers Self-Assemble under Confined States. Acta Polym. Sin. 2009, 4, 298-308. 16. Tsai, C.-C.; Chen, J.-T. Effect of the Polymer Concentration on the Rayleigh-Instability-Type Transformation in Polymer Thin Films Coated in the Nanopores of Anodic Aluminum Oxide Templates. Langmuir 2015, 31, 2569-2575. 17. Tsai, C.-C.; Chen, J.-T. Rayleigh Instability in Polymer Thin Films Coated in the Nanopores of Anodic Aluminum Oxide Templates. Langmuir 2014, 30, 387-393. 18. Chen, J.-T.; Wei, T.-H.; Chang, C.-W.; Ko, H.-W.; Chu, C.-W.; Chi, M.-H.; Tsai, C.-C. Fabrication of Polymer Nanopeapods in the Nanopores of Anodic Aluminum Oxide Templates Using a Double-Solution Wetting Method. Macromolecules 2014, 47, 5227-5235. 19. Fan, P.-W.; Chen, W.-L.; Lee, T.-H.; Chiu, Y.-J.; Chen, J.-T. Rayleigh-Instability-Driven

22


Page 22 of 27

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

Morphology Transformation by Thermally Annealing Electrospun Polymer Fibers on Substrates. Macromolecules 2012, 45, 5816-5822. 20. Chen, J.-T.; Zhang, M.; Russell, T. P. Instabilities in Nanoporous Media. Nano Lett. 2007, 7, 183-187. 21. Mei, S.; Wang, L.; Feng, X.; Jin, Z. Swelling of Block Copolymer Nanoparticles: A Process Combining Deformation and Phase Separation. Langmuir 2013, 29, 4640-4646. 22. Mei, S.; Feng, X.; Jin, Z. Fabrication of Polymer Nanospheres Based on Rayleigh Instability in Capillary Channels. Macromolecules 2011, 44, 1615-1620. 23. Yan, N.; Sheng, Y.; Liu, H.; Zhu, Y.; Jiang, W. Templated Self-Assembly of Block Copolymers and Morphology Transformation Driven by the Rayleigh Instability. Langmuir 2015, 31, 1660-1669. 24. Higuchi, T.; Motoyoshi, K.; Sugimori, H.; Jinnai, H.; Yabu, H.; Shimomura, M. Phase Transition and Phase Transformation in Block Copolymer Nanoparticles. Macromol. Rapid Commun.2010, 31, 1773-1778. 25. Jin, Z.; Fan, H. Self-assembly of Nanostructured Block Copolymer Nanoparticles. Soft Matter 2014, 10, 9212-9219. 26. Shi, A.-C.; Li, B. Self-Assembly of Diblock Copolymers under Confinement. Soft Matter 2013, 9, 1398-1413. 27. Yabu, H.; Higuchi, T.; Jinnai, H. Frustrated Phases: Polymeric Self-Assemblies in a 3D Confinement. Soft Matter 2014, 10, 2919-2931. 28. Yu, B.; Li, B.; Jin, Q.; Ding, D.; Shi, A.-C. Self-Assembly of Symmetric Diblock Copolymers Confined in Spherical Nanopores. Macromolecules 2007, 40, 9133-9142. 29. Xu, J.; Wang, K.; Li, J.; Zhou, H.; Xie, X.; Zhu, J. ABC Triblock Copolymer Particles with

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

Tunable Shape and Internal Structure through 3D Confined Assembly. Macromolecules 2015, 48, 2628-2636. 30. Huang, Y.-C.; Fan, P.-W.; Lee, C.-W.; Chu, C.-W.; Tsai, C.-C.; Chen, J.-T. Transformation of Polymer Nanofibers to Nanospheres Driven by the Rayleigh Instability. ACS Appl. Mater. Interfaces 2013, 5, 3134-3142. 31. Chen, D.; Chen, J.-T.; Glogowski, E.; Emrick, T.; Russell, T. P. Thin Film Instabilities in Blends under Cylindrical Confinement. Macromol. Rapid Commun.2009, 30, 377-383. 32. Feng, X.; Jin, Z. Spontaneous Formation of Nanoscale Polymer Spheres, Capsules, or Rods by Evaporation of Polymer Solutions in Cylindrical Alumina Nanopores. Macromolecules 2009, 42, 569-572. 33. Deng, R.; Liang, F.; Li, W.; Yang, Z.; Zhu, J. Reversible Transformation of Nanostructured Polymer Particles. Macromolecules 2013, 46, 7012-7017. 34. Li, L.; Matsunaga, K.; Zhu, J.; Higuchi, T.; Yabu, H.; Shimomura, M.; Jinnai, H.; Hayward, R. C.; Russell, T. P. Solvent-Driven Evolution of Block Copolymer Morphology under 3D Confinement. Macromolecules 2010, 43, 7807-7812. 35. Dobriyal, P.; Xiang, H.; Kazuyuki, M.; Chen, J.-T.; Jinnai, H.; Russell, T. P. Cylindrically Confined Diblock Copolymers. Macromolecules 2009, 42, 9082-9088. 36. Zhang, L.C.; Sun, M.N.; Pan, J.X.; Wang, B.F.; Zhang, J.J.; Wu, H.S. Copolymer-Homopolymer Mixtures in a Nanopore. Chinese Phys. B 2013, 22, 096401. 37. Matsen, M. W. Phase Behavior of Block Copolymer/Homopolymer Blends. Macromolecules 1995, 28, 5765-5773. 38. Tanaka, H.; Hasegawa, H.; Hashimoto, T. Ordered Structure in Mixtures of a Block Copolymer

24


Page 24 of 27

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

and Homopolymers. 1. Solubilization of Low Molecular Weight Homopolymers. Macromolecules 1991, 24, 240-251. 39. Hashimoto, T.; Tanaka, H.; Hasegawa, H. Ordered Structure in Mixtures of a Block Copolymer and Homopolymers. 2. Effects of Molecular Weights of Homopolymers. Macromolecules 1990, 23, 4378-4386. 40. 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. 41. Yabu, H.; Sato, S.; Higuchi, T.; Jinnai, H.; Shimomura, M. Creating Suprapolymer Assemblies: Nanowires, Nanorings, and Nanospheres Prepared from Symmetric Block-Copolymers Confined in Spherical Particles. J. Mater. Chem. 2012, 22, 7672-7675. 42. Liang, R.; Xu, J.; Deng, R.; Wang, K.; Liu, S.; Li, J.; Zhu, J. Assembly of Polymer-Tethered Gold Nanoparticles under Cylindrical Confinement. ACS Macro Lett.2014, 3, 486-490. 43. Jeon, S.-J.; Yi, G.-R.; Koo, C. M.; Yang, S.-M. Nanostructures inside Colloidal Particles of Block Copolymer/Homopolymer Blends. Macromolecules 2007, 40, 8430-8439. 44. Wang, Y.; Li, F. B. An Emerging Pore-Making Strategy: Confined Swelling-Induced Pore Generation in Block Copolymer Materials. Adv. Mater. 2011, 23, 2134-2148. 45. Deng, R.; Liang, F.; Li, W.; Liu, S.; Liang, R.; Cai, M.; Yang, Z.; Zhu, J. Shaping Functional Nano-Objects by 3D Confined Supramolecular Assembly. Small 2013, 9, 4099-4103. 46. 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. 47. Wang, Y.; Goesele, U.; Steinhart, M. Mesoporous Block Copolymer Nanorods by

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

Swelling-Induced Morphology Reconstruction. Nano Lett. 2008, 8, 3548-3553. 48. Xia, Y. N.; Yin, Y. D.; Lu, Y.; McLellan, J. Template-Assisted Self-Assembly of Spherical Colloids into Complex and Controllable Structures. Adv. Funct. Mater.2003, 13, 907-918. 49. Ko, H.-W.; Chi, M.-H.; Chang, C.-W.; Su, C.-H.; Wei, T.-H.; Tsai, C.-C.; Peng, C.-H.; Chen, J.-T. Fabrication of Multicomponent Polymer Nanostructures Containing PMMA Shells and Encapsulated PS Nanospheres in the Nanopores of Anodic Aluminum Oxide Templates. Macromol. Rapid Commun. 2015, 36, 439-446.

26


Page 26 of 27

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 Table of Contents Use Only: Title: Structural Transformation of Diblock Copolymer/Homopolymer Assemblies by Tuning Cylindrical Confinement and Interfacial Interactions Authors:Jiangping Xu, Ke Wang, Ruijing Liang,Yi Yang, Huamin Zhou, Xiaolin Xie and Jintao Zhu TOC graph:

27


Structural Transformation of Diblock Copolymer ... - ACS Publications

Recommend Documents