Study on the Compatibilizing Effect of Janus Particles on Liquid

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX

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Study on the Compatibilizing Effect of Janus Particles on Liquid Isoprene Rubber/Epoxy Resin Composite Materials Wenqin Xu,† Jiawen Chen,† Shuning Chen,†,‡ Qinhui Chen,*,† Jinhuo Lin,† and Haiqing Liu† †

College of Chemical and Material Science, Fujian Normal University, Fuzhou, Fujian 350007, People’s Republic of China CAS Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China

‡

ABSTRACT: Janus hybrid particles (MPS-SiO2@PDVB-DM, JPs) were successively fabricated by grafting dodecyl mercaptan (DM) onto polydivinylbenzene (PDVB) lobe and 3-(trimethoxysilyl)propyl methacrylate (MPS) chains onto SiO2 lobe in the case of SiO2@PDVB Janus particles as the template. Moreover, MPS-SiO2@PDVB-DM Janus particles were used as the compatibilizer of immiscible polymer blends of liquid isoprene rubber (LIR) and epoxy resin (ER). The modified Janus particles were embedded in the interface of LIR and ER, which could improve the compatibility of LIR and ER, mitigating the macrophase separation in the blends. Besides, the compatibilizing effect of MPS-SiO2@PDVB-DM depends not only on the Janus molecular structure but also on the blending process and the curing agent of ER.

1. INTRODUCTION

property of Janus particles, they can be anchored in the interface of composite materials. Consequently, the researchers have prepared Janus particles used as compatibilizers in blending polymers with poor compatibility. Muller18,19 et al. prepared symmetrical ball-like Janus particles with polystyrene (PS) at one side and poly (methyl methacrylate) (PMMA) at the other side and used them as the compatibilizer of PS/ PMMA and poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/ poly(styrene-co-acrylonitrile) (SAN). The study showed that Janus particles could improve the compatibility of PS and PMMA. Even under high shear, the particles could still be anchored in the interface of two phases because of the amphiphilicity of Janus particles. Hengti Wang20,21 synthesized the Janus particles of poly(styrene-co-glycidyl methacrylate)graf t-poly(methyl methacrylate) (RGCs) and used them as the

Polymer blending is a common, economic route to develop new materials with expected properties. Nevertheless, blending polymers may be separated on the micrometer scale limited by the different interfacial tension of polymers,1−4 which can cause the desired properties of blending materials to be worse than the expected ones. To solve blending polymers’ phase separation, the use of compatibilizer is a very common means. These compatibilizers embedding in the two-phase interface can decrease the interfacial tension, increase the interfacial adhesion, and thereby improve the performance of the final products. There are many typical compatibilizers such as block graft copolymers5,6 and nanoparticles.7−9 Among them, nanoparticles due to their distinctive performance10 are very suitable for solving the problem of interfacial tension. In these compatibilized nanoparticles, anisotropic Janus particles have special effects due to their asymmetric chemical structure.11−13 Janus particles have two different components compartmentalized onto the same surface.14−17 Because of the amphiphilic © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

August 31, 2017 November 1, 2017 November 7, 2017 November 7, 2017 DOI: 10.1021/acs.iecr.7b03200 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

Glueindustry Co. Ltd. 2,2′-Azobis (2-methylpropionitrile) (AIBN) (98%, Aladdin) was recrystallized before use. 3(Trimethoxysilyl) propyl methacrylate (MPS), dicumyl peroxide (DCP), anhydrous ethanol, 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenyl sulfone (DDS) were purchased from Sinopharm Chemical Reagent. Dodecyl mercaptan (DM) and triallyl isocyanurate (TAIC) were purchased from Aladdin. 2.2. Synthesis of the Janus Particles of SiO2@PDVB. The Janus particles of SiO2@PDVB were prepared according to the method reported in the literature.36 2.3. Synthesis of the Janus Particles of SiO2@PDVBDM. About 0.5 g of SiO2@PDVB was dispersed in xylene in a flask under ultrasonic. Next, 0.01 g of AIBN and 10 g of DM were added into the suspension of SiO2@PDVB. The flask was transferred into a water bath of 70 °C and stood there for 48 h under stirring at the atmosphere of nitrogen. After polymerization, the product was centrifuged and washed with acetone several times. The Janus particles of SiO2@PDVB-DM were obtained after freeze-drying. 2.4. Synthesis of the Janus Particles of MPS-SiO2@ PDVB-DM. About 0.45 g of SiO2@PDVB-DM was dispersed in 20 mL of xylene in a flask under ultrasonic, and then 1.5 mL of MPS was added into the suspension of SiO2@PDVB-DM. The flask was transferred into a water bath of 70 °C and stood there for 18 h under stirring. After reaction, the product was centrifuged and washed with anhydrous ethanol several times. The Janus particles of MPS-SiO2@PDVB-DM were obtained after freeze-drying. 2.5. Preparation of LIR/ER Composite Materials. First, 5 wt % of DCP and 5 wt % of TAIC were added to the mixture of LIR/ER (20/80, w/w) in the presence of certain contents of MPS-SiO2@PDVB-DM Janus particles. The mixture was stirred at different speeds of 300, 600, or 900 r/min for 1, 2, or 3 h at a temperature of 100 °C. Next, the cross-linking agent of ER that is DDM (25 wt % to ER) or DDS (30 wt % to ER) was added into the previous mixture. After being stirred for 3 min, the mixture was poured into a mold. The mold was put into an oven of 120 °C for 2 h and then heated to 160 °C and maintained for 2 h. After the mold was cooled to room temperature, the composite material of ER/LIR was gained. The pristine ER sample as a control was obtained using the same method with the curing agent of DDM stirred for 3 h at a speed of 900 r/min. 2.6. Characterization. FT-IR spectra of the unmodified and modified Janus particles were recorded on Nicolet-5700 FTIR spectrometer (Thermo Nicolet, U.S.) using KBr pellets. The morphology of Janus particles and the brittle fracture surfaces of polymer blends were observed with a JSM-7500F scanning electron microscope (SEM, JEOL, Tokyo, Japan) after the scanned surfaces were vacuum-sputtered with platinum at an accelerating voltage of 15 kV. The surface chemical composition of unmodified and modified Janus particles was tested by Oxford energy-dispersive X-ray (EDS) linked-up with a SEM at an accelerating voltage of 20 kV. Impact performance of composite materials was tested with an impact strength tester (ZBC1251, Kedaotest, Hebei, China) according to GBT 2567-2008 with the method of a simple support beam. The specimens were molded in the form of rectangular strips with the dimensions of 80 mm × 10 mm × 4 mm. Each result was collected as an average value of five samples.

compatibilizer for immiscible poly(L-lactide) (PLLA)/poly(vinylidene fluoride) (PVDF) blends. The study showed that RGCs were able to effectively improve the miscibility of polymer blends. Previous studies show that Janus can increase the interfacial adhesion and improve the mechanical properties of the composite materials. However, the existing research mainly focuses on the compatibilization of Janus particles on thermoplastic resins. Herein, Janus particles are used as the compatibilizers of thermosetting resins of epoxy resin. Epoxy resin (ER) is widely used in cast materials, impregnated materials, laminated materials, adhesives, and coatings.22,23 ER has good dielectric properties, small curing shrinkage, high hardness, and so on. However, epoxy resin is poor in impact resistance due to its highly cross-linked threedimensional network structure, which restricts its application.24 The incorporation of liquid rubber,25 block copolymer,26 inorganic particles,27 and core−shell particles28 is a wellknown pathway to improve mechanical properties, and in particular toughness, of epoxy resins. Although epoxy resin toughened by reactive rubber modifiers is accompanied by the sacrifice of strength and thermal properties, it can still satisfy the requirement of high impact strength for epoxy resin. Blending some rubber phase with ER is a commonly used toughening strategy. The majority of used rubbers are polar, as nitrile rubber,29−31 polysulfide rubber,32,33 and silicone rubber,34 which limit the choice of rubber used as toughened material. Liquid isoprene rubber (LIR) is a kind of nonpolar rubber. Because the link structure is the same as nature rubber, LIR is environmentally friendly. However, LIR has poor compatibility with epoxy resin, which means a weak interface adhesive force between LIR and ER. The bonding of the interface between rubber and epoxy resin plays a very important role in toughening epoxy resin.35 If rubber and epoxy resin interface bonding is too weak, that is, poor interfacial compatibility, this will lead to the increased average phase domain size of rubber particles, the macrophase separation of polymer blends, which results in a decrease in the mechanical properties of composite materials. Therefore, it is key issue to solve the incompatibility between LIR and ER. Herein, the Janus particles of SiO2@PDVB were modified and added in the LIR/ER blends to improve their compatibilization. Because one lobe of Janus particle of SiO2@PDVB was silicon dioxide with hydroxyl groups, the silane coupling agent γ-methacryloxypropyltrimethoxysilane (MPS) was used to react with hydroxyl groups to be compatible with the ER. At the end of poly (divinylbenzene), the carbon−carbon double bond was reacted with dodecanethiol (DM) to improve the compatibility between PDVB lobe and LIR. The distribution and the orientation of MPSSiO2@PDVB-DM in LIR/ER blends were investigated. The effects of the dosage of MPS-SiO2@PDVB-DM on the LIR/ER phase behavior, glass transition temperature, and mechanical properties were studied. Besides, the effects of blending variables, including stirring speed, curing time, and curing agent type, on the MPS-SiO2@PDVB-DM/LIR/ER system were also discussed.

2. EXPERIMENTAL SECTION 2.1. Materials. Liquid isoprene rubber (LIR, LIR-50, Mw is 47 000−55 000 and PDI is 1.1−1.3) was purchased from Masini Elasyomer (Shenzhen) Co. Ltd. Bisphenol a epoxy resin (ER, E-44, epoxy value is 0.44) was purchased from Wuhuigang B

DOI: 10.1021/acs.iecr.7b03200 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Scheme 1. Synthesis Diagram of MPS-SiO2@PDVB-DM Janus Particles

3. RESULTS AND DISCUSSION 3.1. Morphology and Chemical Composition of MPSSiO2@PDVB-DM. As is shown in Scheme 1, the hybrid Janus particles were synthesized by sequential grafting DM and MPS chains onto each lobe of the Janus particles of SiO2@PDVB. First, the double bond at the PDVB lobe underwent a free radical grafting reaction with dodecanethiol initiated by AIBN, and as such dodecyl mercaptan was grafted onto the PDVB lobe. The silane coupling agent of MPS reacted with the hydroxyl groups on the SiO2 lobe, so MPS was grafted onto the SiO2 lobe. The morphologies of SiO2@PDVB and MPS-SiO2@PDVBDM were investigated, as shown in Figure 1. Unmodified Figure 2. FT-IR spectra of (a) SiO2@PDVB and (b) MPS-SiO2@ PDVB-DM.

cm−1 is assigned to the vibration of −OH, 2900 cm−1 is the vibration absorption peak of methylene, 1724 cm−1 is ascribed to the absorbance of −CO, 1600 cm−1 is the characteristic peak of asymmetric stretching vibration of CC double bonds on PDVB lobe, and 904 cm−1 is the stretching vibration peak of Si−OH on SiO2 lobe. For MPS-SiO2@PDVB-DM, the absorption intensity of carbonyl groups almost does not change. However, the absorption intensity of methylene groups at 2900 cm−1 is enhanced, and that of CC double bond at 1602 cm−1 is weakened. This is attributed to the polymerization of the residual CC double bond in PDVB lobe with DM. Meanwhile, the peak at 904 cm−1 is weakened, which is due to the reaction between MPS and the hydroxyl groups of SiO2 lobe. Table 1 shows the EDS results of SiO2@PDVB Janus particles and MPS-SiO2@PDVB-DDM Janus particles. There is a sulfur element on the PDVB-DM lobe of MPS-SiO2@PDVBDM Janus particles, while there is none on the SiO2@PDVB

Figure 1. SEM images of (a) SiO2@PDVB and (b) MPS-SiO2@ PDVB-DM.

SiO2@PDVB Janus particles are snowman-like with a rough surface. The head is SiO2 lobe with an average size of 203.3 ± 49.3 nm, and the body is PDVB lobe with an average diameter of 375.1 ± 60.5 nm. The modified MPS-SiO2 @PDVB-DM Janus particles maintain snowman like. The axial length through head and body is 623 ± 61 nm, which increases by 44.6 nm as compared to the unmodified Janus particles. FTIR spectra of SiO2@PDVB and MPS-SiO2@PDVB-DM Janus particles are shown in Figure 2. For SiO2@PDVB, 3439 C


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is pushed away from ER when the MPS-SiO2@PDVB-DM Janus particles are dispersed in the mixture of LIR/ER. The attraction and the repulsion on MPS-SiO2@PDVB-DM impel the Janus particles to move forward directionally in company. When MPS-SiO2@PDVB-DM Janus particles move to the LIR/ER interface, the PDVB-DM lobe is attracted by LIR and pushed away from ER. Consequently, the PDVB-DM lobe is accelerated into the LIR domains. The MPS-SiO2@PDVB-DM Janus particles are arranged directionally between the interface of ER and LIR automatically, which might increase the interfacial adhesion of LIR/ER. Table 2 is the glass transition temperature (Tg) of LIR/ER composite materials. Tg is an important parameter to measure

Table 1. EDS Results of SiO2@PDVB and MPS-SiO2@ PDVB-DM sample SiO2@ PDVB MPSSiO2@ PDVBDM

lobe

C (mol/%)

O (mol/%)

PDVB SiO2 PDVB SiO2

61.02 55.40 57.82 48.54

38.98 7.11 34.69 7.17

Si (mol/%)

S (mol/%)

37.49 1.09 44.29

Janus particles, which proves that the carbon−carbon double bond on the PDVB lobe reacts with the dodecanethiol. 3.2. Compatibilization of MPS-SiO2@PDVB-DM in LIR/ ER. Figure 3 shows SEM images of LIR/ER composite

Table 2. Tg of ER/LIR Composite Materials samples

Tg (°C) of ER

Tg (°C) of LIR

ER/LIR without Janus particles ER/LIR with 3% of Janus particles

160.5 154.8

−71.2 −59.3

the compatibility of blends. Tg of every phase is close to each other if two phases possess good compatibility. Tg values of ER/LIR composite materials in the absence of MPS-SiO2@ PDVB-DM are 160.5 and −71.2 °C corresponding to ER and LIR. In the presence of MPS-SiO2@PDVB-DM, Tg of ER decreases to 154.8 °C and Tg of LIR rises to −59.3 °C. The Tg difference between ER and LIR decreases by 16.6 °C, which indicates that the compatibility between LIR and ER improves. The effect of the dosage of MPS-SiO2@PDVB-DM Janus particles on the compatibility of LIR/ER composite materials is investigated and shown in Figure 4. The average LIR phase domain diameter and the distribution of LIR domain diameter with different Janus particles addition are illustrated in Figures 5 and 6. It is 11.83 μm without MPS-SiO2@PDVB-DM Janus particles, and LIR domain size distributes in the broad range of 6−24 μm. As the solubility parameters of LIR and ER are significantly different, when LIR is dispersed in the ER matrix under the action of shearing force, LIR forms microspheres droplet to reduce interfacial tension. After the shear force was removed, the LIR micro phases dispersed in the ER matrix are in an unstable state and reunite into larger microspheres spontaneously, resulting in forming a large LIR phase domain. The phase domain size of LIR decreases to 9.57 μm, and most are in the 6−18 μm range once 1% of MPS-SiO2@PDVB-DM Janus particles are added into the LIR/ER blends. This is due to MPS-SiO2@PDVB-DM Janus particles enhancing the interfacial adhesion between LIR and ER, preventing the dispersion of LIR from forming a larger microphase. However, 1% of MPS-SiO2@PDVB-DM Janus particles achored between the LIR/ER interfaces is not enough to hinder the LIR emulsion droplets from gathering into a larger microphase. When the dosage of MPS-SiO2@PDVB-DM Janus particles is added up to 3%, 5%, the average domain size of LIR dispersed phase is reduced to 7.94, 6.11 μm, respectively, and concentrated in 3− 15 μm. The phase domain size of LIR decreases significantly, which is 3.98 μm, and most of the LIR domains’ diameter is located at 3−9 μm when 7% of Janus particles was loaded. At this condition, the domain size of LIR dispersed phase is more uniform than the less dosage of Janus particles. This reason is that the increase of MPS-SiO2@PDVB-DM Janus particles prevents the rubber emulsion droplets from gathering into a large phase during cross-linking.

Figure 3. SEM images of the brittle fracture surface of LIR/ER composite materials (a) in the absence of MPS-SiO2@PDVB-DM and (b) in the presence of 5% of MPS-SiO2@PDVB-DM.

materials. In the absence of MPS-SiO2@PDVB-DM, the phase interface between LIR domains and ER matrix is very distinct because of their poor compatibility. In contrast, in the presence of MPS-SiO2@PDVB-DM, the range of LIR domains is reduced from 11.83 to 6.11 μm. The silane coupling agent of MPS in one lobe of MPS-SiO2@PDVB-DM is compatible with ER. On the other hand, DM contains sulfur element and can act on the cross-linking of LIR, so it is obvious that the other lobe of Janus particles is compatible with LIR. During stirring, the Janus particles of MPS-SiO2@PDVB-DM are anchored between the interface of ER and LIR. The diagram of the orientation of MPS-SiO2@PDVB-DM Janus particles in the blends of LIR/ER during preparation is shown in Scheme 2. Because ER is polar and LIR is nonpolar, the MPS-SiO2 lobe is attracted by ER and the PDVB-DM lobe Scheme 2. Diagram of the Orientation of MPS-SiO2@PDVBDM Janus Particles in the LIR/ER Blends

D


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Figure 4. SEM images of the brittle fracture surface of LIR/ER composite materials with (a) 1%, (b) 3%, (c) 5%, and (d) 7% of MPS-SiO2@PDVBDM.

Figure 6. Distribution of LIR domain sizes with different Janus particle addition. Figure 5. Average phase domain size of LIR.

Figure 8 shows the effect of stirring time on the compatibilization of 3% of MPS-SiO2@PDVB-DDM Janus particles. When the stirring time is 1 h, it can be observed that the LIR dispersed phase is easy to pull out when the LIR/ER is hit after frozen. Because the stirring time is too short, it is not enough for MPS-SiO2@PDVB-DM Janus particles to move to the LIR/ER interface. As a result, there are few MPS-SiO2@ PDVB-DM Janus particles distributed at the LIR and ER interfaces, and the interface adhesion between LIR and ER is weak. MPS-SiO2@PDVB-DM Janus particles can be embedded in the LIR/ER interface completely when the stirring time is 2 h, but the distribution of the LIR phase is not uniform in the ER matrix. When the stirring time is 3 h (Figure 7c), the rubber phase is dispersed in the ER matrix uniformly. The LIR dispersed phase is apt to coagulate if DDS is used as the curing agent of ER (Figure 9). The reactivity of DDS is

3.3. Influential Factors of the Compatibilization of MPS-SiO2@PDVB-DM Janus Particles. Figure 7 shows the effect of stirring speed on the compatibilization of 3% of MPSSiO2@PDVB-DM Janus particles. When the stirring speed is 300 r/min, the LIR dispersed phase in ER matrix is of large size because of the small shear force. After the shear force was removed, the adjoining LIR dispersed phases are attracted and integrated to each other. Thus, the LIR phase is not sphere-like scattered in the ER matrix, but a relatively continuous state. As the speed is 600 r/min, the shape of LIR dispersed phase is spherical. However, the LIR dispersed phase is still apt to gathering within a region. When the stirring speed is 900 r/min, the phase domain size and the distribution of LIR dispersed phase become uniform. E


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Figure 10. Impact strength of LIR/ER composite materials.

Janus particles is 5.54 kJ/m2, which is much lower than that of pristine ER whose impact strength is 14.25 kJ/m2. When 1% of MPS-SiO2@PDVB-DM is added, the impact strength is 10.18 kJ/m2, which is much higher than that of LIR/ER blending without Janus particles. When the dosage of MPS-SiO2@ PDVB-DM Janus particles is 3%, the impact strength of LIR/ ER composite materials reaches a maximum of 13.73 kJ/m2, which is close to that of pristine epoxy. At this time, the distribution of the average domain size of LIR is wide. LIR with different domain sizes will play a different role. The nanometer scaled rubbery phase easily cavitates under external stress and promotes the shear yielding of the brittle matrix, and micrometer scaled rubber particles may blunt the crack tip, bridge, and pin the crack line. This mechanism is similar to the literature37 reported as rubber particles’ cavitation and subsequent matrix shear yielding. The toughening effect of LIR on epoxy resin is obvious in the presence of 3% of MPSSiO2@PDVB-DM Janus particles. When 5% of MPS-SiO2@ PDVB-DM Janus particles was added, the impact strength of LIR/ER composite materials decreased to 12.09 kJ/m2. Although the LIR phase domain size decreases at this time, its narrow distribution is bad for ER toughened by LIR. When the amount of MPS-SiO2@PDVB-DM Janus particles is up to 7%, the impact strength of LIR/ER decreases to 7.44 kJ/m2 further for the same reason as when 5% of Janus particles was added. To illustrate the fracture process of LIR/ER with MPSSiO2@PDVB-DM Janus particles, the morphology of the brittle fracture surface of LIR/ER is studied. As is shown in Figure 11a, the crack of the pristine ER is radial, sharp, and its section is smooth, which belongs to typical brittle fracture. The section of LIR and ER blends without any MPS-SiO2@PDVB-DM Janus particles is also smooth. The interface between LIR and ER is clear. Few cracks can be observed. The phase domain size of LIR is quite large, so dispersed phase can not play the role of cavitation. What is worse, large scale of LIR domain can cause stress concentration, resulting in the decline of impact performance; whereas after 1% of MPS-SiO2@PDVB-DM Janus particles was added, the interface adhesion is improved and LIR phase domain size decreases. The Janus particles of MPS-SiO2@PDVB-DM anchored in the interface of ER and LIR can transfer stress. Hence, the cavitated rubber phase acts on subsequent matrix shear yielding when LIR/ER is exposed on an external impact. Consequently, there are some cracks around the LIR phase. The resulting cracks absorb the external impact energy, making the impact properties of the material better than LIR/ER blends without any MPS-SiO2@PDVB-

Figure 7. SEM images of the brittle fracture surface of LIR/ER composite materials at the stirring speeds of (a) 300 r/min, (b) 600 r/ min, and (c) 900 r/min.

Figure 8. SEM images of the brittle fracture surface of LIR/ER composite materials stirred for (a) 1 h and (b) 2 h during preparation.

Figure 9. SEM images of the brittle fracture surface of LIR/ER composite materials cured by DDS with 3% of MPS-SiO2@PDVBDM.

lower than that of DDM. ER still maintains a low viscosity for a long time at 120 °C when using DDS. As a result, the LIR emulsion droplets are pushed away from the ER matrix and result in coagulation in a big phase domain. When the curing agent of ER is DDM (Figure 7c), the cross-linking speed is faster than DDS. The viscosity of ER rises quickly due to the high reactivity of DDM. The migration of LIR emulsion droplets is limited, until they are locked in the ER matrix. So using DDM as the curing agent of ER is beneficial for the LIR phase to be dispersed in the ER matrix perfectly. 3.4. Impact of Properties of LIR/ER Composite Materials with MPS-SiO2@PDVB-DM Janus Particles. MPS-SiO2@PDVB-DM Janus particles can improve the compatibility of ER and LIR. We add LIR to toughen ER, so the impact property is the key index for LIR/ER composite materials. The results are shown in Figure 10. The impact strength of LIR and ER blends without MPS-SiO2@PDVB-DM F


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Figure 11. SEM images of the brittle fracture surface of (a) pure ER, (b) pure LIR/ER, (c) 1% MPS-SiO2@PDVB-DM, (d) 3% MPS-SiO2@PDVBDM, (e) 5% MPS-SiO2@PDVB-DM, and (f) 7% MPS-SiO2@PDVB-DM.

DM Janus particles. When the addition of MPS-SiO2@PDVBDM Janus particles increases to 3%, the cross-section becomes rough and the cracks increase, which promotes the composites performance. When 5% of MPS-SiO2@PDVB-DM Janus particles is added, it is embedded in the interface between LIR and ER entirely, which prevents the coagulation of LIR. Although the LIR phase does not coagulate further, it could be observed that the LIR micro phase is concentrated in a certain area nearly instead of being dispersed in ER matrix. The area where the LIR micro phase is concentrated tightly can be regarded as a large-size LIR phase, which becomes the place of stress concentration leading to the decrease of mechanical property. When adding 7% of MPS-SiO2@PDVB-DM Janus particles, this phenomenon of small-size LIR micro phase concentrated tightly is more obvious, resulting in the impact performance decreasing greatly. However, it is obvious that the LIR particles dispersed in ER matrix can promote the shear yielding of the ER that resulted from cavitation and terminate

the crack line. Therefore, the impact property of LIR/ER composites with 7% of MPS-SiO2@PDVB-DM Janus particles is better than pure LIR/ER blending.

4. CONCLUSIONS MPS-SiO2@PDVB-DM Janus particles were successfully prepared by grafting MPS onto SiO2 lobe and DM onto PDVB lobe in the case of SiO2@PDVB as template and used as the compatibilizer of LIR and ER composite materials. The SEM and DSC results showed that MPS-SiO2@PDVB-DM Janus particles were embedded in the interface of LIR and ER phase to enhance the bonding force of LIR/ER and improve the compatibility of LIR and ER. With the increasing amount of MPS-SiO2@PDVB-DM Janus particles, the phase domain size of LIR is decreased and the distribution of LIR domain size concentrates in 3−9 μm. However, the impact properties of LIR/ER composite materials are best when 3% of MPS-SiO2@ PDVB-DM Janus particles are added due to the appropriate G


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phase domain size and phase distribution. On the other hand, the blending process of the LIR/ER composite materials and the different kinds of ER curing agents has a significant effect on the compatibilizing effect of MPS-SiO2@PDVB-DM Janus particles. The results showed that the compatibilizing efficiency is perfect when the composite materials of LIR/ER composite materials are stirred at a speed of 900 r/min for 3 h and the curing agent is DDM.

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AUTHOR INFORMATION

Corresponding Author

*Tel./fax: +86 591 83464353. E-mail: [email protected]. ORCID

Qinhui Chen: 0000-0002-5377-4136 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was subsidized by the National Science Foundation of China (no. 51773038) and the National Science Foundation of Fujian province (no. 2015J01036).

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ABBREVIATIONS SiO2@PDVB = unmodified Janus paritcles JPs, MPS-SiO2@PDVB-DM = modified Janus particles PDVB = polydivinylbenzene DM = dodecyl mercaptan MPS = 3-(trimethoxysilyl)propyl methacrylate LIR = liquid isoprene rubber ER = epoxy resin DCP = dicumyl peroxide DDM = 4,4′-diaminodiphenylmethane DDS = 4,4′-diaminodiphenyl sulfone AIBN = 2,2′-azobis (2-methylpropionitrile)

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REFERENCES

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Study on the Compatibilizing Effect of Janus Particles on Liquid

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