Reactive Nanoparticles Compatibilized Immiscible Polymer Blends

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Reactive Nanoparticles Compatibilized Immiscible Polymer Blends: Synthesis of Reactive SiO2 with Long Poly(methyl methacrylate) Chains and the in Situ Formation of Janus SiO2 Nanoparticles Anchored Exclusively at the Interface Hengti Wang,†,‡,§ Zhiang Fu,† Xuewen Zhao,† Yongjin Li,*,† and Jingye Li‡

ACS Appl. Mater. Interfaces 2017.9:14358-14370. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 09/03/18. For personal use only.

†

College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal University, No. 16 Xuelin Rd., Hangzhou, Zhejiang 310036, P. R. China ‡ Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, P. R. China § University of Chinese Academy of Sciences, Beijing, 100049, P. R. China S Supporting Information *

ABSTRACT: The exclusive location of compatibilizers at the interface of immiscible binary polymer blends to bridge the neighboring phases is the most important issue for fabricating desirable materials with synergistic properties. However, the positional stability of the compatibilizers at the interface remains a challenge in both scientific and technical points of view due to the intrinsic flexibility of compatibilizer molecules against aggressive processing conditions. Herein, taking the typical immiscible poly vinylidene fluoride (PVDF)/polylactic acid (PLLA) blend as an example, we demonstrate a novel approach, termed as the interfacial nanoparticle compatibilization (IPC) mechanism, to overcome the challenges by packing nanoparticles thermodynamically at the interface through melt reactive blending. Specifically, we have first synthesized nanosilica with both reactive epoxide groups and long poly(methyl methacrylate) (PMMA) tails, called reactive PMMA-graf t-SiO2 (Epoxy-MSiO2), and then incorporated the Epoxy-MSiO2 into the PVDF/PLLA (50/50, w/w) blends by melt blending. PLLA was in situ grafted onto SiO2 by the reaction of the carboxylic acid groups with epoxide groups on the surface of SiO2. Therefore, the reacted SiO2 particles were exclusively located at the interface by the formation of the Janus-faced silica hybrid nanoparticles (JSNp) with pregrafted PMMA tails entangled with PVDF molecular chains in the PVDF phase and the in situ grafted PLLA chains embedded in the PLLA phase. Such JSNp with a distinct hemisphere, functioning as compatibilizer, can not only suppress coalescence of PVDF domains by its steric repulsion but also enhance interfacial adhesion via the selective interactions with the corresponding miscible phase. The interfacial location of JSNp is very stable even under the severe shear field and annealing in the melt. This IPC mechanism paves a new possibility to use the various types of nanoparticles as both effective compatibilizers and functional fillers for immiscible polymer blends. KEYWORDS: reactive blending, Janus SiO2 particles, interfacial nanoparticle compatibilization, in situ reaction, immiscible polymer blends “compatibilizer”.11,12 Such copolymers, either premade or in situ formed during blending, will prefer to span the interface: they could take on the role as macromolecular surfactants to reduce interfacial tensions, suppress particle coalescence, enhance interfacial adhesion, and eventually achieve a finer phase morphology.13−16 Extensive research in past decades has confirmed that the copolymer formed in situ by reactive blending can facilitate a much better phase dispersion and thus render higher compatibilizing efficiency than the premade one.17,18 For

1. INTRODUCTION Polymer blending1−3 provides a practical and efficient strategy to fabricate desirable materials with synergistic properties which cannot be obtained by homopolymers. Nevertheless, most of the polymer pairs are thermodynamically immiscible due to the intrinsic low mixing entropy, leading to the morphology coarsening and finally the deterioration of mechanical performances by the inherent propensity.4−6 Thus, the compatibility of polymer components becomes a key issue to manipulate both the micromorphology and physical properties of blends, which relies largely on the interface between phases.7−10 One of the classic approaches to strengthen the interface is the incorporation of a specific surface-active copolymer called the © 2017 American Chemical Society

Received: February 5, 2017 Accepted: April 4, 2017 Published: April 5, 2017 14358

DOI: 10.1021/acsami.7b01728 ACS Appl. Mater. Interfaces 2017, 9, 14358−14370

Research Article

ACS Applied Materials & Interfaces

adhesion but also enhances the interfacial stability against the mechanical shear and the thermal annealing due to the rigid nanoparticle core. A new type reactive-hybrid nanoparticle compatibilizer with both long molecular tails and reactive groups is then conceived. The pregrafted long molecular tails and the in situ grafted polymer chains shall adjust their configuration by interacting selectively with the miscible components of a blend, and the nanoparticles with Janus-corona selectively located at the interface were in situ formed. Thus, a remarkably enhanced interfacial adhesion could be achieved. In this work, we have first synthesized reactive nanosilica (Epoxy-MSiO2) with both reactive epoxy groups and PMMA chains via the “attaching onto” approach. The reactive nanosilica is then incorporated into well-characterized immiscible poly vinylidene fluoride (PVDF)/polylactic acid (PLLA) blends4,8,14,15 through melt blending. The compatibilization effects of the Epoxy-MSiO2 are carefully characterized. It is found that the in situ formation of interfacial Janus-shell during blending could promote a stronger interaction between the PMMA (PLLA) hemisphere and its corresponding PVDF (PLLA) phase via molecular entanglements. Meanwhile, such nanoparticles exhibit an ordered arrangement at the PVDF/ PLLA interface. We consider that the IPC mechanism might be of importance in emulsifying polymer alloys and could even achieve more advanced nanocomposites for industrial purposes.

instance, Inoue and co-workers successfully improved compatibility of the polyamide 6 (PA 6)/polyethylene (PE) blend with maleic anhydride grafted PE (PE-MAH) by reactive blending and suggested that the in situ formed copolymers exhibited a much better emulsifying efficiency.19 Macosko and co-workers20 indicated that an ethylene-glycidyl methacrylate-methyl acrylate terpolymer (PEGMMA) was the highly efficient emulsifying agent for the polylactide (PLA)/polypropylene (PP) blend through coupling to the end group of PLA during the mixing process. However, the actual reactive compatibilizing process is confronted with crucial challenges. Due to the inherent flexibility of copolymers, such compatibilizers would be “pulled-out” or “pulled-in” readily from the interface under aggressive flow conditions to form micelles.21−24 The inevitable migration of the in situ formed copolymer reduces the compatibilizing efficiency.25−27 It is indeed still urgent and challenging to pursue new types of compatibilizers and to increase the interfaciallocalization stability of emulsifier between polymers. On the other hand, inorganic nanofillers, concurrently, are gaining attention to improve the interfacial miscibility of particular blends.28−30 Owing to their high specific area and fine scale, nanofillers such as graphene oxide (GO),31,32 clay, 3 3 − 3 5 carbon black (CB), 3 6 carbon nanotubes (CNTs),37−39 nanosilica,40−46 and fullerene47 exhibit great potential to accommodate at the polymer−polymer interface with appropriate wetting parameters.48−50 In addition, such interfacial nanofillers show a better seclusion capacity and stability than copolymer species even against intense shear field because of their inherent rigidity.40−43,51,52 Improvement of compatibility depends mainly on the shape, size, and surface modification of nanofillers or the external processing field. Trifkovic et al.48 previously determined the compatibilizing effect of nanoclays in polyethylene (PE)/poly(ethylene oxide) (PEO) blends. The nanoclay platelets preferentially jammed the interface by thermodynamic force and supplied complete inhibition of phase coarsening with only 1 wt % loadings. Recently, Schmalz and co-workers38,53 used “patchy” CTNs as efficient emulsifier for poly styrene (PS)/poly(methyl methacrylate) (PMMA) blends. A significant decrease of PMMAdomain size was achieved with increasing patchy CNTs content, which was attributed to the selective swelling of CNTs toward the respective phase at the PMMA−PS interface. Recently, Cassagnau and co-workers54,55 systematically investigated the influence of nanofiller shapes on the phase structures of polymer blends. On the basis of the rheological behaviors, they pointed out that the surface functionality of nanoparticles takes a critical role on morphological refinement in polymer blends. However, the potential feasibility of nanoparticles compatibilizing remains largely explored. One major reason is the deficiency on the thermal dynamic compatibilization. The location of nanoparticles at the interface is mostly kinetically controlled. Besides, since the main effect of nanoparticles is to prevent coalescence of polymer domains, rather than enhancing interfacial adhesion by molecular entanglements, it is challenging to compatibilize blends sufficiently at the molecular level without sacrificing mechanical properties. Moreover, this strategy seems laborious and system specific, making it relatively too expensive to be scaled up. We considered that interfacial nanoparticle compatibilization (IPC) should be feasible to compatibilize immiscible polymer blends once the surface of the nanoparticles can entangle with binary components separately. The thermodynamic compatibilization by the nanoparticles not only improves the interfacial

2. EXPERIMENTAL SECTION 2.1. Materials. Methyl methacrylate (MMA, Shanghai Sinopharm Co., China, polymer grade) was washed with 5 wt % NaOH solution to remove moisture and then distilled with CaH2 under reduced pressure. 4,4′-Azobis (4-cyanovaleric acid) (ACVA, Acros Co., Belgium, analytical pure) was recrystallized from methanol before use. Tetrahydrofuran (THF, Shanghai Lingfeng Co., China, analytical pure) was refluxed over sodium/benzophenone complex and then distilled under high vacuum. Nanosilica with mean size of 20 nm/110 nm (Carbot bluestar Co., China) was dried in vacuum at 200 °C for 12 h before use. All other reagents were purchased from Aldrich and used as received. All reactions were carried out under nitrogen condition unless otherwise stated. The PVDF (Mn = 1.05 × 105 g/mol, Mw/Mn = 2.0) and PLLA (Mn = 8.93 × 104 g/mol, Mw/Mn = 1.77) used were purchased from Kureha and Nature Works, respectively. 2.2. Synthesis of Reactive Nanoparticles. 2.2.1. General Procedure for Telomerization for Carboxyl Ended Poly(methyl methacrylate) (PMMA-COOH). PMMA-COOH was synthesized according to our previous work.8 In a typical reaction, MMA (20 g, 0.2 mol), ACVA (0.56 g, 0.002 mol), Thio (Thioglycolic acid, 0.41 g, 0.0045 mol), and THF (100 mL) were added into a flask. The mixture was stirred at 60 °C for 4 h. The solution was then dissolved in acetone, precipitated into excess petroleum ether and distilled water, filtered and dried in vacuum to afford 11.2 g (yield: 55%) of white powder. GPC: Mn = 4600 g/mol, Mw/Mn = 2.4. 1H NMR (500 MHz, CDCl3, δ): 3.58 (s, 3H, −OCH3), 3.32−3.25 (t, 2H, −CH2S), 2.03−1.81 (m, 2H, −CH2), 1.2−0.83 (t, 3H, −CH3); FTIR (KBr): 3438 cm−1, 2995 cm−1, 1746 cm−1, 1470m−1, 1443 cm−1, 1395 cm−1, 1260 cm−1, 1230 cm−1, 1185 cm−1, 1145 cm−1, 755 cm−1. 2.2.2. General Procedure for Exterior Functionalization of SiO2 with Epoxy Groups (Epoxy-SiO2). Epoxy-SiO2 was prepared similar to the method demonstrated in ref 56. SiO2 (6 g) was first dissolved into 250 mL of toluene, and the mixture was ultrasonicated for 15 min. 3Glycidoxypropyl trimethoxysilane (GPTS, 3.5 g) was then added dropwise to the suspension. The reaction mixture was transferred into a flask and refluxed at 110 °C for 10 h under nitrogen. The resulting material was centrifuged and washed thoroughly with toluene or ethanol to remove the unreacted GPTS. The washing procedure was repeated three times, respectively, and Epoxy-SiO2 was dried under vacuum at 65 °C for 25 h. 14359


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ACS Applied Materials & Interfaces Scheme 1. Illustrative Synthesis of Epoxy-MSiO2 through “Attaching onto” Method

2.2.3. General Procedure for Grafting PMMA-COOH Chains onto the Exterior Surface of E-SiO2 by “Grafting onto” Method (EpoxyMSiO2). Epoxy-MSiO2 was synthesized by grafting PMMA-COOH onto Epoxy-SiO2 through ring-opening reaction in the presence of alkali catalyst. A typical procedure is as follows: Epoxy-SiO2 (2 g) was first dissolved into 80 mL of xylene and ultrasonicated for 5 min. Then, the solution containing PMMA-COOH (Mn = 4600 g/mol, 1 g, 0.25 mmol), N,N′-dimethyllaurylamine (amine, 0.0061 g, 0.045 mmol), and an extra 20 mL of xylene was added dropwise into the suspension, and the mixture was transferred into a flask and refluxed at 140 °C for 25 h. The resultant suspension was centrifuged and washed extensively with ultrasonication in toluene, THF, and acetone, respectively. Finally, the product was dried in vacuum at 65 °C for 25 h to afford 2.3 g (yield: 76%) of white powder. 2.2.4. General Procedure for Grafting PLLA Chains onto the Exterior Surface of Epoxy-MSiO2 by “Grafting onto” Method (PMMArandom-PLLA)-g-SiO2, LM-SiO2)). The LM-SiO2 was synthesized by the ring-opening reaction of carboxyl-terminated PLLA with the epoxy groups of Epoxy-MSiO2. In a typical procedure, Epoxy-MSiO2 (5g) and PLLA (45g) were premixed and added into the batch mixer (Haake Polylab QC) with a rotation speed of 50 rpm at 190 °C for 10 min. The resultant sample was dissolved into chloroform and centrifuged. This procedure was repeated at least three times to completely remove the unreacted PLLA chains. The resulting LM-MSiO2 was dried under vacuum at 65 °C for 25 h. 2.3. Incorporation of Nanoparticles into PVDF/PLLA (50/50, w/w) Blends. The PVDF/PLLA (50/50, w/w) blends with various contents of SiO2, Epoxy-SiO2, or Epoxy-MSiO2 were fabricated by melt blending directly in a Haake Polylab QC mixer at 190 °C. These blends were prepared by mixing under the screw speed of 50 rpm for 10 min. The resulted blends were then compression molded at 200 °C under 10 MPa pressure for 6 min and quenched into liquid nitrogen. The obtained sheet with a thickness of 0.5 mm was applied directly in the subsequent characterization. 2.4. Characterization. The number-averaged molecular weight (Mn) and polydispersity (Mw/Mn) of PMMA-COOH were determined by gel permeation chromatography (GPC). GPC was performed with an Optical T-rEX detector using two MZ-Gel SDplus 10 μm bead-sized columns (10E3 and 10E5 Å) in THF eluent with a flow rate of 1 mL/ min at 35 °C. Linear polystyrene standards from 2000 to 106 g/mol were applied for calibration. The GPC retention diagrams were analyzed via ASTRA 6 software from Wyatt Technology. Fourier transform infrared resonance (FT-IR) was carried out with a VERTEX 70 V (Bruker, Germany) spectrometer. The samples were ginned and tableted with KBr, and then, such KBr plates were scanned from 4000 to 400 cm−1 at a resolution of 2 cm−1 with a minimum of 64 scans. 1 H Nuclear magnetic resonance (1H NMR) and 29Si NMR measurements were performed on a Bruker Avance 500 spectrometer with CDCl3 as solvent. The operating frequency was 500 MHz. X-ray photoelectron spectroscopy (XPS) analysis was carried out using a Kratos Axis Ultra instrument with monochromatic Al Kα X-ray

source. Wide scan was investigated in the range of 1300−0 eV, and the narrow scans were measured for the O 1s, C 1s, and Si 2p regions. The thermogravimetric analysis (TGA) was carried out on a TGAQ500 (TA Instrument) in nitrogen atmosphere at a heating rate of 10 °C/min from 30 to 650 °C. The graft density of Epoxy-MSiO2 (σEpoxy‑MSiO2) was calculated by the following equation:42

σEpoxy‐MSiO2 =

(1 − fSiO )NAρSiO d 2

2

6fSiO M n 2

(1)

where f SiO2 was the weight fraction of SiO2 in Epoxy-SiO2/Epoxy-MSiO2 determined by TGA measurement; NA was the Avogadro’s number; ρSiO2 was the density of SiO2; d was the average diameter of SiO2; Mn was the overall number-average molecular weight of polymer chains. Field emission scanning electron microscopy (FE-SEM, Hitachi S4800) was performed to observe the morphologies of PVDF/PLLA blends at an accelerating voltage of 5.0 kV. The specimens were fractured by immersing in liquid nitrogen for 5 min and then spur-coated by gold. Besides, the number-average diameter of PVDF domains (dn) was calculated according to the following eq 2:

dn =

∑i Nd i i ∑i Ni

(2)

Here, N was the number and d was the diameter of PVDF domain with i ≥ 300. Transmission electron microscopy (TEM, Hitachi HT-7700) was carried out to observe the distribution of nanoparticles in PVDF/PLLA blends at an accelerating voltage of 100 kV. The specimen was first ultramicrotomed to a section with the thickness of 80 nm and then stained with ruthenium tetroxide (RuO4) for 4 h at room temperature. Thus, the PVDF domains could be selectively stained and turned gray in TEM observations. Dynamic mechanical analysis (DMA) was carried out using DMA Q800 (TA Instrument) under nitrogen atmosphere. The specimens were punched into a rectangle shape, 8 mm × 6.3 mm × 0.5 mm, and tested with a heating rate of 10 °C/min from −50 to 180 °C with the amplitude of 4 μm and the frequency of 5 Hz.

3. RESULTS 3.1. Preparation and Characterization of Epoxy-MSiO2. 3.1.1. Synthesis of Epoxy-MSiO2: Functionalization of SiO2. As illustrated in Scheme 1, the reactive SiO2 with long PMMA chains (Epoxy-MSiO2) was synthesized by sequential immobilization of reactive epoxide groups and PMMA chains onto the exterior surface of SiO2 using silane coupling agent and PMMACOOH, respectively. Such Epoxy-MSiO2 could take on the role of compatibilizer in immiscible polymer blends by reactive melt blending. The SiO2 particles with an average diameter of 16 nm were used as model nanoparticles. First, the pristine SiO2 was 14360


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ACS Applied Materials & Interfaces Table 1. Molecular Parameter of PMMA-COOH and the Hybrid Nanoparticles

XPS results of nanoparticlesf sample

Mna (g/mol)

Pa

PMMA-COOH SiO2 Epoxy-SiO2 Epoxy-MSiO2 LSiO2g LEpoxy-SiO2g LEpoxy-MSiO2g

4600

2.4

4600

2.4

4600

2.4

db (nm)

Tdc (°C)

f Sio2c (%)

σRSMd (nm−2)

398.8 16.5 ± 3.1 17.4 ± 2.8 18.3 ± 3.5 110 ± 36 115 ± 35 120 ± 37

405.1 403.7 428.8 403.7

Tge (°C)

O 1s (atomic %)

Si 2p (atomic %) C 1s (atomic %)

91.5 99.0 95.2 74.5 99.1 91.4 63.0

0.78 0.27

139.9

9.7 3.1

138.9

72.9 68.0 59.1 67.9 59.7 46.7

22.3 19.3 13. 8 29.4 24.0 16.3

4.8 12.7 27.1 2.7 16.3 37.0

Determined by GPC plots using THF as eluent and linear PS as calibration at 35 °C (Mn: number-averaged molecular weight of PMMA chains; P: polydispersity (Mw/Mn) of PMMA chains). bMeasured from TEM images (d: number-averaged diameter of nanoparticles). cMeasured from the TGA curves of purified specimen (Td: the TGA temperature with maximum loss rate; f SiO2: inorganic content; forg.: organic content). dCalculated by eq 1 on the basis of TGA data (σEpoxy‑SiO2: graft density of PMMA chains). eDetermined from DSC results (Tg: glass transition temperature of PMMA chains). fCalculated from XPS spectrum. gLSiO2, LEpoxy-SiO2, and LEpoxy-MSiO2 referred to the nanoparticles with larger size (dSiO2 ≈ 110 nm). a

Figure 1. (a) FT-IR spectra and (b) 1H NMR spectra of the representative products: (I) SiO2, (II) Epoxy-SiO2, (III) Epoxy-MSiO2, (IV) GPTS, and (V) PMMA-COOH.

of Si−OH of Epoxy-SiO2 became weaker after modification (step I), accompanied by the new absorption peaks at 1370, 1460, and 2810−3000 cm−1 attributed to the stretching vibration of −CH from GPTS. This implied the occurrence of reaction between silica hydroxyl of pristine SiO2 and methoxyl of GTPS. Subsequently, a new peak at 1730 cm−1 derived from carbonyl groups of PMMA segments appeared in Epoxy-MSiO2 (sample III). Since the unreacted PMMA-COOH was removed by extensive washing with organic solvents, the spectrum of EpoxyMSiO2 indicated that the long PMMA chains were successfully grafted onto the exterior of Epoxy-SiO2 via the ring-opening reaction (step III). However, the intensity of the epoxide characteristic peak is too low to be observed before and after modification of SiO2. 1H NMR (Figure 1b) demonstrated the appearance of epoxide (2.96 ppm, 2.89 ppm) and methoxyl (3.63 ppm) groups for Epoxy-MSiO2, providing the direct evidence of the reactive epoxy groups after the grafting reaction. Figure 2 showed the XPS spectrum of pristine SiO2 and modified SiO2 nanoparticles. The major peak of all samples with the binding energy (BE) of 532.6 eV was assigned to O 1s element signal while the minor bands of 155.1 and 103.9 eV corresponded to Si 2s and Si 2p signals, respectively, which could be attributed to the existence of SiO2 core. As demonstrated in Figure 2a,b, the intensity of O 1s, Si 2s, and Si 2p was significantly reduced with the functionalization. Besides, a new peak at the BE of 285.3 eV assigned to C element signal was observed for both Epoxy-SiO2 and Epoxy-MSiO2 samples. The C 1s peak of EpoxyMSiO2 turned much stronger than that of Epoxy-SiO2 (details

functionalized with epoxide groups by chemical modification using 3-glycidoxy-propyltrimethoxylsilane (GPTS) to yield reactive SiO2 (Epoxy-SiO2) (step I). At the same time, PMMA-COOH with finely tuned molecular weight was synthesized by telomerization of MMA using ACVA as initiator and Thio as chain transfer agent (Scheme S-1, Table S-1, and Figures S-1 to S-3) (step II). Epoxy-SiO2 was then modified by adding a small amount of PMMA-COOH (step III) to synthesize Epoxy-MSiO2. Long PMMA chains were rooted readily on the surface of SiO2 with a covalent bond, which was attributed to the efficient nucleophilic cycloaddition reaction between epoxide groups of Epoxy-SiO2 and carboxyl groups of PMMA-COOH in the presence of alkali catalyst (N,N′-dimethyl laurylamine). Larger hybrid nanoparticles could be achieved through the same synthetic routes, using a pristine SiO2 with the diameter of 110 nm. Detailed information on the products was listed in Table 1. It should be noted that all reactions above were conducted under extremely mild conditions (moisture and atmosphere pressure), making it a reproducible preparation of hybrid nanoparticles for industrial production. 3.1.2. Characterization of Epoxy-MSiO2. Figure 1a shows the FTIR spectra of pristine SiO2, Epoxy-SiO2, and Epoxy-MSiO2. The intense bands at 817 and 1080 cm−1, which were assigned to the asymmetric bending vibration of Si−OH and asymmetric stretching vibration of Si−O−Si, respectively, were observed in pristine SiO2 (sample I), Epoxy-SiO2 (sample II), and EpoxyMSiO2 (sample III), confirming the existence of SiO2 core in the hybrid nanoparticles. Compared with the pristine SiO2, the peak 14361


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Figure 2. XPS spectra of SiO2, Epoxy-SiO2, and Epoxy-MSiO2: (a) the survey scan spectrum; (b) the C 1s (c) the O 1s, and (d) the Si 2p core-level spectrum; (e) the C 1s and (f) Si 2p spectrum parameters for Epoxy-MSiO2.

corroborated that PMMA long chains had been positively covalently bonded onto the exterior surface of SiO2. Further characterizations such as 29Si NMR (Figure S-6), TGA (Figure S-7), TEM (Figure S-8,) and DSC (Figure S-9) were performed and listed in Table 1. From TEM data, the finely improved dispersion and gradually formed gray corona for both nanoparticles (d = 16 nm/110 nm) were clearly observed, after being modified with epoxide groups and PMMA long chains successively. On the basis of the TGA data, the grafting density (σEpoxy‑MSiO2) was calculated to be 0.27 chain/nm2 for EpoxyMSiO2 (f SiO2 = 74.5 wt %) and 3.1 chains/nm2 for LEpoxyMSiO2 (f SiO2 = 63.0 wt %), respectively, which was in agreement with the previous study42,58 in which the nanoparticles containing higher surface area were conducive to the accommodation of more grafts. In addition, an obvious elevation of Tg of PMMA chains (Tg, Epoxy‑SiO2 = 139.9 °C, Tg, PMMA‑COOH = 91.5 °C) was acquired from the DSC technique. It was directly

shown in Tables 1 and S-2), suggesting that the PMMA-chain corona around SiO2 was thick enough to shield most signals of SiO2 core from XPS instrument.56,57 On the other hand, the O 1s signal of Epoxy-MSiO2 had a decreased BE, as compared with SiO2 and Epoxy-SiO2 (Figure 2c). This indicated that the electron cloud density was changed due to the grafting reaction of PMMA long chains. To further identify the molecular structure in the Epoxy-MSiO2 nanoparticles, peak-differentiation-imitating analysis was carried out, as shown in Figure 2e,f. C 1s peak was clearly divided into three peak components with the BE of 288.6, 286.2, and 284.7 eV, corresponding to carboxyl carbon (CO), methyl side ether carbon (C−O), and carbon− carbon/hydrogen carbon (C−C/H) (Tables S-3 and S-4, Figure S-4), respectively. In addition, the high resolution of Si 2p spectra was consistent with two silica environments owning to BE at 103.8 and 102.9 eV, which was assigned to O−Si−O and O−Si− C species (Table S-5, Figure S-5). These facts further 14362


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Scheme 2. Chemical Equation of the in Situ Ring-Opening Reaction between Epoxy Groups of Epoxy-SiO2 and Carboxyl Groups of PLLA during Melt Blending

Figure 3. (a, b) FT-IR spectra and (c, d) thermogravimetric curves of the representative product: (I) original Epoxy-MSiO2, (II) PMMA-COOH, (III) LM-SiO2, and (IV) neat PLLA.

MSiO2 is a key factor for the following reaction with the PLLA molecular chains so that Epoxy-MSiO2 enhances the interfacial interaction between polymer components during the reactive compatibilizing process. As demonstrated in our previous study,4,8,15,17 an in situ coupling reaction between epoxide and carboxyl groups could be envisaged during melt blending, facilitating the compatibilizing efficiency of immiscible polymer pairs. In this section, the reaction between PLLA and EpoxyMSiO2 was first conducted, under the same melt processing condition, to verify the feasibility of this methodology applied to

related to the immobilization effect of PMMA onto the solid inorganic core. The mobility of PMMA chains was confined, and the free volume decreased significantly. Similar results (Figures S-10 and S-11) were obtained for the nanoparticles with larger inorganic core (dSiO2 = 110 nm). These facts above indicated that the “step-by-step” modifications of SiO2 took place and the reactive epoxide groups as well as long PMMA chains have been successfully attached onto the surface of SiO2. 3.1.3. Estimation of Reactivity of Epoxy-MSiO2: In Situ Coupling Reaction during Blending. The reactivity of Epoxy14363


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ACS Applied Materials & Interfaces reactive compatibilization. As shown in Scheme 2, a cycloaddition reaction between the remaining epoxide groups of Epoxy-MSiO2 and terminating carboxyl groups of PLLA occurred. Double long chains grafted nanoparticles containing both pregrafted PMMA tails and in situ grafted PLLA chains were obtained. Note that the grafting of both PMMA and PLLA is random and the analysis in the real compatibilization will be discussed in the following section. The reactants after the melt blending, termed as LM-SiO2 (PMMA-random-PLLA)-g-SiO2), were separated from the mixture with unreacted PLLA components by repeated suspension (chloroform), centrifugation, and decanting of the supernatant. The obtained LM-SiO2 was verified by the FT-IR in Figure 3a. Compared with Epoxy-MSiO2, the spectra of LM-SiO2 presented a shoulder peak around 1730 cm−1, assigned to the characteristic peak of carboxyl groups. The selected band in Figure 3a was enlarged in Figure 3b. The peak could be curve-fitted with two band segments with the wavenumber at 1723 cm−1 (PMMA) and 1757 cm−1 (PLLA), indicating that both PLLA grafts and PMMA tails were presented on the surface of SiO2 nanoparticles. The ratio of I1757/I1723 (intensity of peak) could be applied to verify the weight composition of PLLA and PMMA. On the basis of the normalized curves (Figure S-12), the weight composition of PLLA tails was estimated to be 51.3 wt %. The presence of PLLA grafts was also verified by TGA, evident from the significantly reduced weight loss ( f LM‑SiO2 = 61.9 wt %, f Epoxy‑MSiO2 = 75.2 wt %) and broadened differential peaks as shown in Figure 3c,d. Moreover, the appearance of Tg around 58.4 °C (attributed to PLLA chains) was observed from DSC, consistent with the previous results (Figure S-13). Thereby, Epoxy-MSiO2 particles show high reactivity after grafting with PMMA and can be further melt grafted by PLLA molecular chains. In the following section, Epoxy-MSiO2 would be utilized as a new type interfacial compatibilizer in the wellcharacterized immiscible PVDF/PLLA (50/50, w/w) blends by reactive melt blending. 3.2. Reactive Compatibilization of Epoxy-MSiO2 for PVDF/PLLA Blends. 3.2.1. Localization of SiO2 and EpoxySiO2. To allow a meaningful appraisal of the performance of Epoxy-MSiO2, i.e., a beadlike emulsifier, the PVDF/PLLA (50/ 50, w/w) blends with pristine SiO2 and Epoxy-SiO2 were investigated for comparison. First, 1 wt % of SiO2 was incorporated into the 50/50 blend by melt compounding to estimate the selective dispersion of pristine SiO2. As shown in Figure 4a1, the blend displayed a typical feature of sea-island morphology with a broad distribution of PVDF-domain size (8.9 ± 9.6 μm), indicating a strong incompatibility and high interfacial tension between PVDF and PLLA phases. The enlarged SEM micrographs (Figure 4a2) demonstrated that the SiO2 nanoparticles were aggregated and located almost entirely in the PLLA matrix with little interfacial accommodation. Similar results were obtained for PVDF/PLLA blends with LSiO2 (Figure S-14). The surface modification of pristine SiO2 from OH groups into epoxide groups does not change the location of the nanoparticles in the blend. As shown in Figure 4b1,b2, all the Epoxy-SiO2 particles are selectively located in the PLLA phase and PLLA/PVDF blends show almost the same phase structure with incorporation of pristine SiO2 or Epoxy-SiO2. The selective location of SiO2 and Epoxy-SiO2 within the PLLA matrix was further confirmed to be stable against kinetic interruptions such as shear fields and high temperature annealing. It could be concluded that the thermodynamic

Figure 4. SEM images of PVDF/PLLA (50/50, w/w) blends with 1 wt % of (a) SiO2 and (b) Epoxy-SiO2.

equilibrium position of SiO2/Epoxy-SiO2 was supposed to be the PLLA phase, which would be discussed more detail later. 3.2.2. Localization of in Situ Formed Janus Silica Nanoparticles (JSNp): Effect of Particle Size. To further investigate the influence of PMMA grafts on the location of SiO2 as well as the resultant morphology of blends, two kinds of Epoxy-MSiO2 with different SiO2 sizes were utilized and added into the PVDF/ PLLA (50/50, w/w) blends by the same strategy. Interestingly, both Epoxy-MSiO2 and LEpoxy-MSiO2 were found to be jammed exclusively at the PVDF/PLLA interface, which was totally different from the observations of pristine SiO2 and Epoxy-SiO2 above, as shown in Figure 5. We also noticed that the

Figure 5. SEM images of PVDF/PLLA (50/50) blends with fixed contents (1 wt %) of (a) LEpoxy-MSiO2 and (b) Epoxy-MSiO2.

interface turned better adhesion, suggesting the ability of EpoxyMSiO2 to improve interfacial adhesion (Figures S-15 and S-16). Presumably, Epoxy-MSiO2 could modify the morphology when preferentially located at the interface and serve as a true emulsifier for the typical immiscible PVDF/PLLA blends. As compared with the blends containing LEpoxy-MSiO2, PVDF domains of the blends with Epoxy-MSiO2 exhibited more uniform distribution and better dispersion (Figure 5b), signifying more efficient compatibilizing ability of Epoxy-MSiO2. It was in 14364


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ACS Applied Materials & Interfaces agreement with a previous study: Ginzbur et al.59 reported that the very small particles (Rp < Rg, ∼15 nm) could influence the configuration entropy of its exterior polymer chains and functioned as compatibilizer effectively. On the basis of the results, Epoxy-MSiO2 (finer particle) was selected to further investigate the effect of loadings on compatibilization in the next section. 3.2.3. Epoxy-MSiO2 Loading Effects on the Morphologies and Properties of the Blends. To utilize the new concept above and estimate the effect of Epoxy-MSiO2 on compatibilization, five blends of PVDF/PLLA (50/50, w/w) were fabricated by varying Epoxy-MSiO2 loadings from 0 to 5 wt %. In the absence of Epoxy-MSiO2, typical sea-island morphology formed with irregular PVDF domains of 10.1 ± 12.3 μm in PLLA matrix (Figure 6a1). Besides, the PVDF/PLLA interface was clearly

apparent with many cavities (Figure 6a2), indicating poor adhesion between phases, as reported in our previous study.14,15 Upon the addition of Epoxy-MSiO2 into blends, the morphology exhibited a considerable reduction in the domain size, as depicted in Figure 6b1,c1,d1,e1. On the other hand, it should be noticed that all of the nanoparticles were located exclusively at the PVDF/PLLA interface, regardless of Epoxy-MSiO2 content (Figure 6b2,c2,d2,e2). This indicates the thermodynamic compatibilization effects of the functionalized nanoparticles. TEM observation (Figure 7) was performed to get a better overview of the interfacial coverage for nanoparticles. Here, the white phase, gray phase, and black dots referred to PLLA matrix, PVDF domain, and hybrid nanoparticles, respectively. Nanoparticles located selectively at the PVDF/PLLA interface, which was consistent with the SEM micrographs above. It is difficult to distinguish the asymmetric structure of the interfacial nanoparticles since both PLLA and PMMA grafts consist of the same C, H, and O elements. However, an analogous Janus-shell nanoparticle is observed at the PVDF/PLLA interface, as shown in Figure 7d. It provides a direct evidence of the formation of Janus nanoparticles. Figure 8 shows the statistical analysis of PVDF-domain sizes and the thickness of the interfacial layer as a function of the particle loadings. It is seen from Figure 8a that the domain size linearly reduced with the increasing concentration of EpoxyMSiO2 in the blends ranging from 0.5 to 3 wt %. At 3 wt % of Epoxy-MSiO2, the domain diameter decreased by about 5-fold over the corresponding pristine blends to 1.9 ± 0.7 μm. A finer and more uniform PVDF domain was obtained with higher Epoxy-MSiO2 loadings (5 wt %), which was quite different from previous studies20−22 demonstrating that only a fraction (∼3 wt %) of compatibilizer seemed to be enough to saturate the interface. Furthermore, as estimated in Figure 8b, the thickness of interfacial layer, surrounded with silica nanoparticles, increased from 50 nm at 0.5 wt % to 58.0 nm at 1 wt %. Then, the thickness remained constant with further increasing EpoxyMSiO2 loadings (from 3 to 5 wt %). Previous studies have confirmed that the desorption energy of a singular corona particle was three times lower than the Janus one. Due to the combination of rigid SiO2 core and higher desorption energy of Janus-grafted corona, the in situ formed Janus silica nanoparticles (JSNp) (discussed later) were thermodynamically stable at the PVDF/PLLA interface against the shear field and the high processing temperature. Thus, high loading of Epoxy-MSiO2 resulted in the accommodation of the PVDF/PLLA interface with much more interfacial area, facilitating the significant reduction of domain size, which was consistent with the morphology observations. The fact that both the JSNp locates exclusively at the interface and the JSNp thickness stays almost constant indicated the good correlation between the dispersion phase size and the reactive nanoparticles loadings. In other words, higher loading of EpoxyMSiO2 leads to the larger interface area and the smaller domain size. This provides the facile strategy to design the morphology of the JSNp compatibilized immiscible polymer blends by incorporation of various amounts of reactive nanoparticles. The thermodynamic properties were measured as a function of temperature to explore the change of compabilility and storage modulus with the addition of Epoxy-MSiO2 in blends. As illustrated in Figure 9a, with the increase of Epoxy-MSiO2, the glass transition temperatures (Tg) of both PVDF and PLLA shifted toward each other gradually, indicating enhanced miscibility between phases. Details of the parameters were listed

Figure 6. SEM images of PVDF/PLLA (50/50) blends illustrating the change in PVDF-domain size and distribution of nanoparticles with various Epoxy-MSiO2 loadings (wt %): (a) 0, (b) 0.5, (c) 1, (d) 3, and (e) 5. 14365


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Figure 7. TEM images of PVDF/PLLA (50/50) blends demonstrating interfacial encapsulation with various Epoxy-MSiO2 loadings (wt %): (a) 0, (b) 0.5, (c) 1, (d) 3, and (e, f) 5 wt %. The interfacial black dots are the resultant JSNp.

Figure 8. (a) Average size of PVDF domains (measured from SEM images) and (b) calculated Epoxy-MSiO2 coating thickness at the PVDF−PLLA interface (measured from TEM images) as a function of the Epoxy-MSiO2 loadings.

Figure 9. (a) Loss tangent and (b) storage modulus as a function of temperature with a frequency of 5 Hz for PVDF/PLLA (50/50, w/w) blends with various concentration of Epoxy-MSiO2, obtained by dynamic thermomechanical analysis (DMA).

blends could be self-supported even above the Tg of PLLA, which was related to the enhancement of interfacial interactions by increasing nanoparticles. Notably, such interfacial jammed nanoparticles were in favor of transferring stress under external

in Table S-6. Besides, the recovery of storage modulus (E′) values in the temperature range of 65−115 °C, corresponding to the cold crystallization of PLLA, increased with the addition of Epoxy-MSiO2. This means that the Epoxy-MSiO2-incorporated 14366


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Scheme 3. Schematic Diagram of the in Situ Formation of the JSNp Originated from the Epoxy-MSiO2 by Reactive Blending and the Proposed Compatibilizing Mechanism of JSNp in Immiscible Polymer Blends

situ formed PLLA tails (long PMMA chains) to interact with PLLA (PVDF) phase for maximizing energetically favorable contacts. On the other hand, the solid silica-core served as stiff nanofiller to improve interfacial stability. Therefore, the interfacial JSNp, which built up a dense layer around PVDF domains, could reinforce interfacial adhesions and effectively facilitate the compatibilization effect. Next, we paid close attention to the thermodynamic theory on the morphology evolution. 4.2. Thermodynamic Prediction of Silica Location with Various Surface Chemistries. Given the significant compatibilization effects by interfacial JSNp, it is desirable to acquire a thermodynamic approach to predict the location of silica nanoparticles with various surface chemistries. Herein, the location of SiO2 in PVDF/PLLA blends can be estimated by evaluating wetting parameter ω using Young’s model60,61,48 (eq 3): γSiO −PVDF − γSiO −PLLA 2 2 ω= γPVDF−PLLA (3)

force due to the improved interfacial interactions between phases (Figure S-17). It should also be noted that the mechanical properties of the blends (both PLLA/PVDF (50/50) and (35/ 65)) increase greatly with the addition of the compatibilizers, as compared to those blends without compatibilizers (Tables S-7 and S-8, Figures S-18 to S-20). For example, the elongation at break and the tensile strength for the compatibilized blend are 10.7% and 56.0 MPa, while those for the uncompatibilized are 5.7% and 43.5 MPa, respectively.

4. DISCUSSION 4.1. Compatibilizing Mechanism of JSNp through Reactive Blending. From the results above, we demonstrate a novel strategy, termed as IPC mechanism, to emulsify the immiscible binary polymer blends by packing nanoparticles thermodynamically and exclusively at the polymer−polymer interface via reactive blending. As shown in Scheme 3, a new kind of reactive hybrid nanoparticle, Epoxy-MSiO2, was synthesized through the “attaching onto” approach first (Section 3.1.1). Such nanoparticle containing both reactive epoxide groups and long PMMA chains on a solid SiO2 core can further react with PLLA during melt compounding (Section 3.1.2). Epoxy-MSiO2 was then employed as interfacial modifier to compatibilize the immiscible PVDF/PLLA blend. Since the SiO2 core preferred to locate in PLLA matrix (Section 3.2.1) by thermodynamic force while the PMMA long tails exhibited better compatibility with PVDF phase, Epoxy-MSiO2 was forced to anchor the interface in the initial stage of melt compounding before the in situ reaction. As the reaction between epoxide groups of Epoxy-MSiO2 and terminated carboxyl groups of PLLA occurred, two kinds of polymers attached randomly to the exterior surface of SiO2 by chemical bonds successively to form heterogeneous polymer corona (Section 3.1.3). Due to the strong immiscibility between PLLA and PMMA grafts, the exterior surface of SiO2 turned into a Janus PMMA/PLLA corona spontaneously across the interface (Figure 7d). We redefine the in situ formed interfacial nanoparticles as Janus silica nanoparticles (JSNp) to distinguish them from original LM-SiO2 with random distribution of PMMA/PLLA grafts. The JSNp featured a solid SiO2 core and equally weighted PMMA/PLLA hemispheres. On the one hand, JSNp stretched its hemispheres, respectively, promoting the in

Here, γ represented the interfacial energy of the interfaces within blends: the SiO2−PVDF interface, the SiO2−PLLA interface, and the PVDF/PLLA interface. Different cases occurred: when ω > 1, SiO2 was expected to be located in the PLLA matrix; when ω < −1, SiO2 preferred to be positioned in the PVDF domains. Only when −1 < ω < 1, SiO2 would be thermodynamically preferred to jam at the PVDF/PLLA interface. Owing to the difficulty in precisely estimating the interfacial energies, they were usually evaluated by the known surface energies of each component using the geometric (eq 4)48,49,62 or harmonic mean equations63,64 (eq 5): γ12 = γ1 + γ2 − 2 γ1dγ2d − 2 γ1pγ2p γ12 = γ1 + γ2 −

4γ1dγ2d γ1d + γ2d

−

(4)

4γ1pγ2p γ1p + γ2p

(5)

Here, γ referred to the surface energy and γ and γ denoted the dispersive and polar contributions of the surface energies of components, respectively (γi = γdi + γpi ). The values of surface energy of each component at processing temperature have been d

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ACS Applied Materials & Interfaces acquired from the literature40,63,65,66 and listed in Tables S-9 and S-10. As shown, the interfacial tensions of PVDF-SiO2 and PLLASiO2 were calculated to be 6.21 and 4.4 mJ m−2 (eq 4) or 11.7 and 8.04 mJ m−2 (eq 5). Thus, Young’s model (eq 3) resulted in a wetting parameter of 9.53 or 8.31, implying that SiO2 should be preferentially positioned in PLLA matrix, which was in agreement with the results above (Figure 4). Also, the surface modification of pristine SiO2 from hydroxyl groups to epoxide groups does not change the location as shown in Figure 4b, which was attributed to the improved affinity between SiO2 and PLLA phase as a result of in situ grafting reaction of PLLA chains onto the surface of SiO2. With the incorporation of both long PMMA chains and epoxide groups onto SiO2, the location differed. Since there are no accurate data available from the literature for the modified SiO2 (Epoxy-MSiO2) with the two polymers, we cannot provide the quantitative γEpoxy‑MSiO2‑Polymer values. However, some qualitative analysis could be performed to provide an evaluation of interfacial tension trends. As calculated in Table S-9, the PVDF−PMMA pair showed the best compatibility (γPVDF−PMMA = 0.025mJ·m−2) among all binary pairs67,68 and seemed totally miscible during blends. Besides, the SiO2−PLLA interfacial energy was less than that of SiO2−PMMA or SiO2−PVDF, which caused the thermodynamic equilibrium of SiO2 in the PLLA phase. Assuming that the kinetic disruptions were negligible, since all blends were prepared simultaneously above the melting point (190 °C) with sufficient time (10 min), nanoparticles were able to achieve equilibrium state. We speculate that, in the initial stage of blending, PMMA grafts were able to adjust their shell structure through selectively stretching toward the PVDF phase, which was beneficial for enthalpically favorable interactions. Meanwhile, the SiO2 core preferred to be located in the PLLA matrix via thermodynamic prediction. Thus, Epoxy-MSiO2 particles were forced to be jammed at the PVDF/PLLA interface since PMMA long tails were linked with SiO2 by chemical bond before the in situ reaction occurred. As the reaction takes place, the second grafts, PLLA chains, were attached randomly onto the exterior of SiO2. In order to maximize the contacts between grafts and blends, the nanoparticles took on Janus-corona configuration, facilitating PMMA tails (PLLA grafts) to interact with PVDF (PLLA phase), respectively. Of note, Müller and coworkers50,51 confirmed that the desorption energy of singular corona particle was three times lower than the Janus one. Therefore, JSNp “arrested” the interface and prevented it from coalescence. Figure 10 shows the SEM images for the compatibilized sample after being statically annealed at 200 °C for 20 min. It is

clear that the phase morphology of the blend was preserved and all nanoparticles were jammed at the PVDF/PLLA interface, as the sample before annealing in Figure 6d, indicating the very stable structure of the compatibilized blends. This is attributed to both the compatibilizing effects of the nanoparticles and the rigid inorganic core. It is considered that the nanoparticles are rheologically difficult to be pulled out of the interface against the annealing and the mechanical shearing, as compared with the traditional block/graft copolymer compatibilizers.

5. CONCLUSION We demonstrated a novel approach, termed as IPC mechanism, to compatibilize the immiscible PVDF/PLLA blends by packing nanoparticles thermodynamically and exclusively at the interface through melt reactive blending. First, the reactive SiO2 with both reactive epoxide groups and PMMA long chains, called EpoxyMSiO2, was synthesized by the “attaching onto” approach. The Epoxy-MSiO2 showed high reactivity and could be covalently grafted with PLLA by in situ ring-opening reaction during blending. Despite the random distribution of grafts, the hybrid nanoparticles spontaneously formed into a Janus PMMA/PLLA corona across the PVDF/PLLA interface due to the specific interactions of the PMMA grafts with PVDF chains and PLLA grafts with PLLA chains. In order to maximize an energetically favorable interaction, the pregrafted PMMA tails and the in situ grafted PLLA chains on the SiO2 core simultaneously adjusted their configuration by interacting selectively toward the miscible components. In addition, the solid nanoparticle core of the final Janus PMMA/PLLA nanoparticles could further take on the role as stiff nanofiller to enhance interfacial stability. The combination of steric repulsion by stiff silica core and strong interfacial affinity originated from selective molecular entanglements promoting the abundant adsorption of nanoparticles to the PVDF/PLLA interface irrespective of the severe processing conditions. The IPC paves a new possibility for the compatibilization of immiscible polymer blends. Moreover, a similar strategy might also be applied for the various types of nanoparticles used as both effective compatibilizer and functional fillers for multiphase polymer materials.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b01728. Additional data for reaction equation of telomerization (Scheme S-1), molecular parameter of PMMA-COOH (Table S-1), XPS parameters of SiO2 (Table S-2), C 1s spectrum for Epoxy-SiO2 (Table S-3), C 1s parameters for Epoxy-MSiO2 (Table S-4), Si 2p parameters for EpoxyMSiO2 (Table S-5), thermal parameters from DMA (Table S-6), mechanical properties of PVDF/PLLA (50/ 50) blends (Table S-7), mechanical properties of PVDF/ PLLA (65/35) blends (Table S-8), surface energy of polymer−particles (Table S-9), particle location in the blends (Table S-10), 1H NMR spectrum of PMMACOOH (Figure S-1), FT-IR spectrum of PMMA-COOH (Figure S-2), GPC curve of PMMA-COOH (Figure S-3), C 1s spectrum of Epoxy-SiO2 (Figure S-4), Si 2p spectrum of Epoxy-MSiO2 (Figure S-5), 29Si NMR spectrum (Figure S-6), TGA curves of SiO2 (Figure S-7), TEM images of SiO2 (Figure S-8), DSC curves of PMMACOOH and Epoxy-MSiO2 (Figure S-9), TGA curves of

Figure 10. SEM images of PVDF/PLLA/Epoxy-MSiO2 (50/50/3) blends illustrating the thermodynamic stability of binary phase morphology after thermal annealing at 200 °C for 20 min with (a) low and (b) high magnification. 14368


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LSiO2 (Figure S-10), TEM images of LSiO2 (Figure S-11), fitted carboxyl spectra of LM-SiO2 from FT-IR (Figure S12), DSC curves of Epoxy-MSiO2 and LM-SiO2 (Figure 13), SEM image of PVDF/PLLA (50/50) blends (Figure S-14), topography images of PVDF/PLLA (50/50) blends (Figure S-15), AFM topography of PVDF/PLLA (50/50) blends (Figure S-16), tensile specimen of PVDF/PLLA (50/50) blends (Figure S-17), tensile curves of PVDF/ PLLA (50/50) blends (Figure S-18), tensile curves of PVDF/PLLA (65/35) blends (Figure S-19), SEM images of PVDF/PLLA (65/35) blends (Figure S-20) (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86 57128867899. Telephone: +86 57128867026 (Y.L.). ORCID

Yongjin Li: 0000-0001-6666-1336 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21674033, 21374027). REFERENCES

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Reactive Nanoparticles Compatibilized Immiscible Polymer Blends

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