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Morphology and high-performance of in-situ self-assemble epoxy resin with side aliphatic dangling chains
Materials Letters 166 (2016) 150–153
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Morphology and high-performance of in-situ self-assemble epoxy resin with side aliphatic dangling chains Tao Yang, Rui Wang, Xuqi Hou, Jue Cheng n, Junying Zhang n Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 16 September 2015 Received in revised form 14 December 2015 Accepted 15 December 2015 Available online 17 December 2015
A series of epoxy resins containing side aliphatic pendant chains (abbreviated as EPC-04, EPC-08, EPC-12 and EPC-18) were prepared by the reaction between the diglycidyl ether of bisphenol F (DGEBF) and the single-ended fatty amine with a chain length ranging from C4 to C18. Studies on the film morphology and the physical performance demonstrate that the cured EPC-04, EPC-08, EPC-12 and EPC-18 composites possess excellent mechanical and thermal properties, which are originated from the micro-, submicroand nano-structured phases distributed in the epoxy matrix. In addition, by adjusting the lengths of the dangling aliphatic chains, the mechanical properties of the cured resins can be tuned in different scales. Consequently, by prolonging the pendant chain length to C18, the cured resin exhibits a striking tensile strength of 90.65 MPa, an elongation of 6.1% and a modulus of 2.55 GPa. & 2015 Elsevier B.V. All rights reserved.
Keywords: Epoxy resin Microphase separation Microstructure Nanoparticles Dangling chain
1. Introduction Epoxy polymers have been recognized as the high-performance thermosetting polymers because of their excellent engineering properties. However, the highly crosslinked structure induced severer brittleness dramatically limits the applications of epoxy polymers [1,2]. To improve the toughness of epoxy polymers, one effective solution is to introduce the nano- and micro-structured phases by incorporating the block copolymers (BCPs) into epoxy systems [3–5]. For example, amphiphilic BCPs can form specific nanostructures in the uncured epoxy polymer, which were proven to significantly enhance the toughness [5,6]. The corresponding toughening mechanisms were ascribed as: the cavitation of the particles and subsequent void growth, or a combination of cavitation, shear yielding and crack tip blunting, crack bridging and viscoelastic energy dissipation [4]. However, the miscibility of the BCPs and the epoxy precursor has been considered to be an important factor determining the final toughness [6]. Meanwhile, the epoxy polymers incorporated with BCPs always show slightly reduced modulus and glass transition temperatures [7]. Inspired by this idea, we tried to bring aliphatic pendant chains into epoxy matrix. Due to the incompatibility of the aliphatic chain and backbone of epoxy resin which contains benzene ring, the epoxy resins we designed may possess the unique film n
Corresponding authors. E-mail addresses: [email protected] (J. Cheng), [email protected] (J. Zhang). http://dx.doi.org/10.1016/j.matlet.2015.12.066 0167-577X/& 2015 Elsevier B.V. All rights reserved.
morphology of phase separation in micro- or nano-scale. In addition, the “dangling chains” with different chain lengths would also facilitate the self-assemble into a more uniform and controllable micro- or nano-structures. The chemical bonds between the aliphatic chain and backbone insured the microscopic miscibility of the “dangling chains” and the epoxy matrix. In this work, EPC-04, EPC-08, EPC-12 and EPC-18 systems were prepared via the reaction between the DGEBF and the singleended fatty amine. The microstructure and the fracture surface were monitored by the atomic force microscope (AFM) and scanning electron microscope (SEM) measurements, respectively. Moreover, the effect of chain lengths of “dangling chains” on mechanical and thermal properties was investigated, and the toughening mechanism was further proposed.
2. Experimental Materials: DGEBF (equivalent epoxy weight 165.3 g/mol). N-butylamine, n-octylamine, n-dodecylamine and octadecylamine (AR) were purchased from Aladdin Industrial Corporation. Hexahydrophthalic anhydride (HHPA) was purchased from the Puyang Huicheng Electronic Materials Co., Ltd. Tris-(dimethylaminomethyl) phenol (DMP-30) was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. Preparation of EPC-04, EPC-08, EPC-12 and EPC-18: DGEBF was mixed with n-butylamine, n-octylamine, n-dodecylamine and octadecylamine (molar ratio of epoxy group and amine group is
T. Yang et al. / Materials Letters 166 (2016) 150–153
10/1, where the subscript refers to the carbon number in amine), respectively. These mixtures were thermally treated at 65 °C for 2 h and 100 °C for 1.5 h to obtain EPC-04, EPC-08, EPC-12 and EPC-18. Preparation of cured epoxy resins: DGEBF (abbreviated as EPC0), EPC-04, EPC-08, EPC-12 and EPC-18 were mixed with HHPA and DMP-30 according to the stoichiometric ratio, and then the mixtures were stirred for 10 min. All the mixtures were pre-cured at 95 °C for 3 h, cured at 125 °C for 4 h and 185 °C for 3 h. Characterization: Tensile experiment, bending experiment and charpy impact test were carried out at room temperature according to Chinese National Standard GB/T 1040.2–2006, Chinese National Standard GB/T 9341–2008 and Chinese National Standard GB/T 1043.1–2008, respectively. Thermal properties were measured by dynamic mechanical analyzer (Q800, TA Instruments). AFM (Nanoscope IIIa peak force tapping atom force microscope, Bruker, Germany) and SEM (HitachiLimited, S-4700) were used to record the morphology of epoxy resins and fracture surface of cured resins, respectively.
3. Results and discussion Fig. 1 shows AFM phase images of the morphologies of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. The morphology of EPC-0 was homogeneous and featureless, as expected for a monophase material. For EPC-04, EPC-08, EPC-12 and EPC-18, bump structures with sizes ranging from 20 to 50 nm and 100 to 250 nm were observed. In addition, micron-sized bump structures were also found in EPC12 and EPC-18. The difference in length of the dangling aliphatic chains was speculated to cause the variations in the size of the bump structures. This kind of micro-, submicro- and nano-sized bump structures were tentatively ascribed to the self-assemble of the side aliphatic pendant chains. The relatively large micron-sized
151
bump structures were found to abound in EPC-18. These various dimensional bump structures were speculated to have significant impact on the toughness of the final materials. Two different toughening mechanisms are demonstrated here. The nano-sized phase-separated bump structures can induce huge interactions between the matrixes and the bump structures due to the quantum-size-effect as traditional inorganic nano-sized particles [8]. These interactions can absorb the additional energy and stop the development of initialized crazes when strain occurs. Submicronsized and micro-sized phase-separated bump structures, which play an important role as rubber particles in toughening epoxy resin networks, as the center of the stress concentration, can form a large amount of initialized crazes. The voids introduced by this submicron-sized and micron-sized bump structures can absorbed energy and stop the development of initialized crazes at the same time when strain occurs [9,10]. The exception was the co-existence of nano-, submicro- and nano-sized bump structures that were observed in systems of EPC-12 and EPC-18 indicating the coexistence of these two different toughening mechanisms. Fig. 2 shows the SEM micrographs of the fracture surfaces. The fracture surface of EPC-0 was relatively smooth. A large amount of river lines were observed in EPC-04 and EPC-08. The fracture surfaces of EPC-12 and EPC-18 were covered with many voids and divided by many block lines. These voids validate the inference we made above. Meanwhile, a mass of river lines are distributed in these “blocks”. All these river lines might be caused by the nanosized bump structures. After zooming in to observe the river lines of EPC-08 and EPC-18 (see Fig. 2b′ and e′), the jagged river line of EPC-18 is observed. According to Derek Hull's viewpoint, the river lines of fracture surfaces can be caused by the excess stored elastic energy that was released by fast crack propagation [11]. Therefore, the crack propagation's paths of these systems are proposed to be different. The plentiful river lines distributed in EPC-04, EPC-08, EPC-
Fig. 1. AFM phase images of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18.
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Fig. 2. SEM micrographs of the fracture surfaces of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. 12 and EPC-18 would predict their excellent mechanical properties, especially for EPC-12 and EPC-18 compared to EPC-04 and EPC-08. Mechanical properties of the cured EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18 were listed in Table 1. After introducing the “dangling chains”, a significant increase was observed in almost all the values of mechanical properties listed here. It is elucidated that all the nano-, submicro- and nano-sized bump structures have significant effect on the toughness of epoxy resins and enhance the mechanical properties drastically. The tensile strength, elongation and tensile modulus increase as increasing the chain length of the “dangling chains”. When the pendant chain length reaches to C18, the tensile strength, elongation and modulus reach to the maximum of 90.65 MPa, 6.1% and 2.55 GPa, respectively. Meanwhile, the bending strength, bending modulus and impact strength of EPC-12 and EPC-18 exhibit a slight difference between each other. Such similarity was also observed between EPC-04 and EPC-08, which however, have a significant decrease in these properties
compared with the parameters of EPC-12 and EPC-18. This phenomenon indicated that the micron-sized bump structures have a more outstanding effect on improving mechanical properties than the submicro-and nano-sized bump structures. In particular, Tg has a significant increase as the introduction of dangling side aliphatic chains and decreases as the increase of the length of dangling chains. This is similar to the trend reported in previous researches [8,12]. Based on the mechanical properties, fracture surface and the morphologies showed in AFM phase images. Fig. 3 shows the formation mechanism of the nano-, submicro- and micro-sized bump structures. The amine group of single-ended fatty amine reacted with the DGEBF at first. The dangling side aliphatic chains existed in synthetic epoxy monomers attracts each other because the main chain in epoxy resin is incompatible with the side aliphatic pendant chains. Over time, the side aliphatic pendant chains gather together to form the aggregations of dangling
Table 1 Mechanical and thermal properties of the cured EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. Systems of cured epoxy resins
Tensile strength (MPa)
Tensile elongation (%)
Tensile modulus (GPa)
Bending strength (MPa)
Bending modulus (GPa)
Impact strength (kJ/m2) Tg (°C)
EPC-0 EPC-04 EPC-08 EPC-12 EPC-18
59.86 81.21 82.63 83.78 90.65
3.97 5.12 5.20 5.21 6.07
2.03 2.33 2.33 2.48 2.55
138.60 144.80 144.72 149.88 149.09
3.59 3.23 3.24 3.91 3.76
12.25 13.89 13.87 18.54 20.93
119.67 141.18 136.44 125.46 121.59
T. Yang et al. / Materials Letters 166 (2016) 150–153
153
Fig. 3. Schematic illustration for the formation of bump structures.
aliphatic chains. Such aggregations become larger and larger as time goes on to form nano-, submicro- and micro-sized bump structures in the end. Meanwhile, the stereo-hindrance effects coming from the chemical bonding limit the “dangling chains” to aggregate into much bigger sizes.
4. Conclusion A series of microphase separation epoxy resins containing side aliphatic pendant chains with different lengths were designed and synthesized. The dangling side aliphatic chains would facilitate the self-assemble into nano-, submicro- and micro-sized bump structures, which were proved to dramatically toughen the cured epoxy resins. When the pendant chain length prolongs to C18, the tensile strength, elongation and modulus reach the maximums of 90.65 MPa, 6.1% and 2.55 GPa, respectively.
References [1] S. Zheng, J. Pascault, R. Williams, Epoxy polymers: new materials and
innovations. J-P Pascault, RJJ Williams, Eds. 2010. [2] A. Salazar, S. Prolongo, J. Rodríguez, The effect of hygrothermal conditions on the fracture toughness of epoxy/poly (styrene-co-allylalcohol) blends, Mater. Lett. 64 (2010) 167–169. [3] S. Wu, Q. Guo, M. Kraska, B. Stü hn, Y.-W. Mai, Toughening epoxy thermosets with block ionomers: the role of phase domain size, Macromolecules 46 (2013) 8190–8202. [4] J. Liu, Z.J. Thompson, H.-J. Sue, F.S. Bates, M.A. Hillmyer, M. Dettloff, et al., Toughening of epoxies with block copolymer micelles of wormlike morphology, Macromolecules 43 (2010) 7238–7243. [5] H. Kishi, Y. Kunimitsu, J. Imade, S. Oshita, Y. Morishita, M. Asada, Nano-phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys, Polymer 52 (2011) 760–768. [6] J. Chen, A.C. Taylor, Epoxy modified with triblock copolymers: morphology, mechanical properties and fracture mechanisms, J. Mater. Sci. 47 (2012) 4546–4560. [7] Y.S. Thio, J. Wu, F.S. Bates, The Role of inclusion size in toughening of epoxy resins by spherical micelles, J. Polym. Sci. B: Polym. Phys. 47 (2009) 1125–1129. [8] D. Quan, A. Ivankovic, Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer, Polymer 66 (2015) 16–28. [9] H. Yahyaie, M. Ebrahimi, H.V. Tahami, E.R. Mafi, Toughening mechanisms of rubber modified thin film epoxy resins, Prog. Org. Coatings 76 (2013) 286–292. [10] G.M. Gladysz, K.K. Chawla, Voids in Materials: From Unavoidable Defects to Designed Cellular Materials, Newnes, Elsevier, 2014. [11] D. Hull, Fractography: Observing, Measuring and Interpreting Fracture Surface Topography, Cambridge University Press, 1999. [12] Y. Liang, R. Pearson, Toughening mechanisms in epoxy–silica nanocomposites (ESNs), Polymer 50 (2009) 4895–4905.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Morphology and high-performance of in-situ self-assemble epoxy resin with side aliphatic dangling chains Tao Yang, Rui Wang, Xuqi Hou, Jue Cheng n, Junying Zhang n Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 16 September 2015 Received in revised form 14 December 2015 Accepted 15 December 2015 Available online 17 December 2015
A series of epoxy resins containing side aliphatic pendant chains (abbreviated as EPC-04, EPC-08, EPC-12 and EPC-18) were prepared by the reaction between the diglycidyl ether of bisphenol F (DGEBF) and the single-ended fatty amine with a chain length ranging from C4 to C18. Studies on the film morphology and the physical performance demonstrate that the cured EPC-04, EPC-08, EPC-12 and EPC-18 composites possess excellent mechanical and thermal properties, which are originated from the micro-, submicroand nano-structured phases distributed in the epoxy matrix. In addition, by adjusting the lengths of the dangling aliphatic chains, the mechanical properties of the cured resins can be tuned in different scales. Consequently, by prolonging the pendant chain length to C18, the cured resin exhibits a striking tensile strength of 90.65 MPa, an elongation of 6.1% and a modulus of 2.55 GPa. & 2015 Elsevier B.V. All rights reserved.
Keywords: Epoxy resin Microphase separation Microstructure Nanoparticles Dangling chain
1. Introduction Epoxy polymers have been recognized as the high-performance thermosetting polymers because of their excellent engineering properties. However, the highly crosslinked structure induced severer brittleness dramatically limits the applications of epoxy polymers [1,2]. To improve the toughness of epoxy polymers, one effective solution is to introduce the nano- and micro-structured phases by incorporating the block copolymers (BCPs) into epoxy systems [3–5]. For example, amphiphilic BCPs can form specific nanostructures in the uncured epoxy polymer, which were proven to significantly enhance the toughness [5,6]. The corresponding toughening mechanisms were ascribed as: the cavitation of the particles and subsequent void growth, or a combination of cavitation, shear yielding and crack tip blunting, crack bridging and viscoelastic energy dissipation [4]. However, the miscibility of the BCPs and the epoxy precursor has been considered to be an important factor determining the final toughness [6]. Meanwhile, the epoxy polymers incorporated with BCPs always show slightly reduced modulus and glass transition temperatures [7]. Inspired by this idea, we tried to bring aliphatic pendant chains into epoxy matrix. Due to the incompatibility of the aliphatic chain and backbone of epoxy resin which contains benzene ring, the epoxy resins we designed may possess the unique film n
Corresponding authors. E-mail addresses: [email protected] (J. Cheng), [email protected] (J. Zhang). http://dx.doi.org/10.1016/j.matlet.2015.12.066 0167-577X/& 2015 Elsevier B.V. All rights reserved.
morphology of phase separation in micro- or nano-scale. In addition, the “dangling chains” with different chain lengths would also facilitate the self-assemble into a more uniform and controllable micro- or nano-structures. The chemical bonds between the aliphatic chain and backbone insured the microscopic miscibility of the “dangling chains” and the epoxy matrix. In this work, EPC-04, EPC-08, EPC-12 and EPC-18 systems were prepared via the reaction between the DGEBF and the singleended fatty amine. The microstructure and the fracture surface were monitored by the atomic force microscope (AFM) and scanning electron microscope (SEM) measurements, respectively. Moreover, the effect of chain lengths of “dangling chains” on mechanical and thermal properties was investigated, and the toughening mechanism was further proposed.
2. Experimental Materials: DGEBF (equivalent epoxy weight 165.3 g/mol). N-butylamine, n-octylamine, n-dodecylamine and octadecylamine (AR) were purchased from Aladdin Industrial Corporation. Hexahydrophthalic anhydride (HHPA) was purchased from the Puyang Huicheng Electronic Materials Co., Ltd. Tris-(dimethylaminomethyl) phenol (DMP-30) was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. Preparation of EPC-04, EPC-08, EPC-12 and EPC-18: DGEBF was mixed with n-butylamine, n-octylamine, n-dodecylamine and octadecylamine (molar ratio of epoxy group and amine group is
T. Yang et al. / Materials Letters 166 (2016) 150–153
10/1, where the subscript refers to the carbon number in amine), respectively. These mixtures were thermally treated at 65 °C for 2 h and 100 °C for 1.5 h to obtain EPC-04, EPC-08, EPC-12 and EPC-18. Preparation of cured epoxy resins: DGEBF (abbreviated as EPC0), EPC-04, EPC-08, EPC-12 and EPC-18 were mixed with HHPA and DMP-30 according to the stoichiometric ratio, and then the mixtures were stirred for 10 min. All the mixtures were pre-cured at 95 °C for 3 h, cured at 125 °C for 4 h and 185 °C for 3 h. Characterization: Tensile experiment, bending experiment and charpy impact test were carried out at room temperature according to Chinese National Standard GB/T 1040.2–2006, Chinese National Standard GB/T 9341–2008 and Chinese National Standard GB/T 1043.1–2008, respectively. Thermal properties were measured by dynamic mechanical analyzer (Q800, TA Instruments). AFM (Nanoscope IIIa peak force tapping atom force microscope, Bruker, Germany) and SEM (HitachiLimited, S-4700) were used to record the morphology of epoxy resins and fracture surface of cured resins, respectively.
3. Results and discussion Fig. 1 shows AFM phase images of the morphologies of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. The morphology of EPC-0 was homogeneous and featureless, as expected for a monophase material. For EPC-04, EPC-08, EPC-12 and EPC-18, bump structures with sizes ranging from 20 to 50 nm and 100 to 250 nm were observed. In addition, micron-sized bump structures were also found in EPC12 and EPC-18. The difference in length of the dangling aliphatic chains was speculated to cause the variations in the size of the bump structures. This kind of micro-, submicro- and nano-sized bump structures were tentatively ascribed to the self-assemble of the side aliphatic pendant chains. The relatively large micron-sized
151
bump structures were found to abound in EPC-18. These various dimensional bump structures were speculated to have significant impact on the toughness of the final materials. Two different toughening mechanisms are demonstrated here. The nano-sized phase-separated bump structures can induce huge interactions between the matrixes and the bump structures due to the quantum-size-effect as traditional inorganic nano-sized particles [8]. These interactions can absorb the additional energy and stop the development of initialized crazes when strain occurs. Submicronsized and micro-sized phase-separated bump structures, which play an important role as rubber particles in toughening epoxy resin networks, as the center of the stress concentration, can form a large amount of initialized crazes. The voids introduced by this submicron-sized and micron-sized bump structures can absorbed energy and stop the development of initialized crazes at the same time when strain occurs [9,10]. The exception was the co-existence of nano-, submicro- and nano-sized bump structures that were observed in systems of EPC-12 and EPC-18 indicating the coexistence of these two different toughening mechanisms. Fig. 2 shows the SEM micrographs of the fracture surfaces. The fracture surface of EPC-0 was relatively smooth. A large amount of river lines were observed in EPC-04 and EPC-08. The fracture surfaces of EPC-12 and EPC-18 were covered with many voids and divided by many block lines. These voids validate the inference we made above. Meanwhile, a mass of river lines are distributed in these “blocks”. All these river lines might be caused by the nanosized bump structures. After zooming in to observe the river lines of EPC-08 and EPC-18 (see Fig. 2b′ and e′), the jagged river line of EPC-18 is observed. According to Derek Hull's viewpoint, the river lines of fracture surfaces can be caused by the excess stored elastic energy that was released by fast crack propagation [11]. Therefore, the crack propagation's paths of these systems are proposed to be different. The plentiful river lines distributed in EPC-04, EPC-08, EPC-
Fig. 1. AFM phase images of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18.
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T. Yang et al. / Materials Letters 166 (2016) 150–153
Fig. 2. SEM micrographs of the fracture surfaces of EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. 12 and EPC-18 would predict their excellent mechanical properties, especially for EPC-12 and EPC-18 compared to EPC-04 and EPC-08. Mechanical properties of the cured EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18 were listed in Table 1. After introducing the “dangling chains”, a significant increase was observed in almost all the values of mechanical properties listed here. It is elucidated that all the nano-, submicro- and nano-sized bump structures have significant effect on the toughness of epoxy resins and enhance the mechanical properties drastically. The tensile strength, elongation and tensile modulus increase as increasing the chain length of the “dangling chains”. When the pendant chain length reaches to C18, the tensile strength, elongation and modulus reach to the maximum of 90.65 MPa, 6.1% and 2.55 GPa, respectively. Meanwhile, the bending strength, bending modulus and impact strength of EPC-12 and EPC-18 exhibit a slight difference between each other. Such similarity was also observed between EPC-04 and EPC-08, which however, have a significant decrease in these properties
compared with the parameters of EPC-12 and EPC-18. This phenomenon indicated that the micron-sized bump structures have a more outstanding effect on improving mechanical properties than the submicro-and nano-sized bump structures. In particular, Tg has a significant increase as the introduction of dangling side aliphatic chains and decreases as the increase of the length of dangling chains. This is similar to the trend reported in previous researches [8,12]. Based on the mechanical properties, fracture surface and the morphologies showed in AFM phase images. Fig. 3 shows the formation mechanism of the nano-, submicro- and micro-sized bump structures. The amine group of single-ended fatty amine reacted with the DGEBF at first. The dangling side aliphatic chains existed in synthetic epoxy monomers attracts each other because the main chain in epoxy resin is incompatible with the side aliphatic pendant chains. Over time, the side aliphatic pendant chains gather together to form the aggregations of dangling
Table 1 Mechanical and thermal properties of the cured EPC-0, EPC-04, EPC-08, EPC-12 and EPC-18. Systems of cured epoxy resins
Tensile strength (MPa)
Tensile elongation (%)
Tensile modulus (GPa)
Bending strength (MPa)
Bending modulus (GPa)
Impact strength (kJ/m2) Tg (°C)
EPC-0 EPC-04 EPC-08 EPC-12 EPC-18
59.86 81.21 82.63 83.78 90.65
3.97 5.12 5.20 5.21 6.07
2.03 2.33 2.33 2.48 2.55
138.60 144.80 144.72 149.88 149.09
3.59 3.23 3.24 3.91 3.76
12.25 13.89 13.87 18.54 20.93
119.67 141.18 136.44 125.46 121.59
T. Yang et al. / Materials Letters 166 (2016) 150–153
153
Fig. 3. Schematic illustration for the formation of bump structures.
aliphatic chains. Such aggregations become larger and larger as time goes on to form nano-, submicro- and micro-sized bump structures in the end. Meanwhile, the stereo-hindrance effects coming from the chemical bonding limit the “dangling chains” to aggregate into much bigger sizes.
4. Conclusion A series of microphase separation epoxy resins containing side aliphatic pendant chains with different lengths were designed and synthesized. The dangling side aliphatic chains would facilitate the self-assemble into nano-, submicro- and micro-sized bump structures, which were proved to dramatically toughen the cured epoxy resins. When the pendant chain length prolongs to C18, the tensile strength, elongation and modulus reach the maximums of 90.65 MPa, 6.1% and 2.55 GPa, respectively.
References [1] S. Zheng, J. Pascault, R. Williams, Epoxy polymers: new materials and
innovations. J-P Pascault, RJJ Williams, Eds. 2010. [2] A. Salazar, S. Prolongo, J. Rodríguez, The effect of hygrothermal conditions on the fracture toughness of epoxy/poly (styrene-co-allylalcohol) blends, Mater. Lett. 64 (2010) 167–169. [3] S. Wu, Q. Guo, M. Kraska, B. Stü hn, Y.-W. Mai, Toughening epoxy thermosets with block ionomers: the role of phase domain size, Macromolecules 46 (2013) 8190–8202. [4] J. Liu, Z.J. Thompson, H.-J. Sue, F.S. Bates, M.A. Hillmyer, M. Dettloff, et al., Toughening of epoxies with block copolymer micelles of wormlike morphology, Macromolecules 43 (2010) 7238–7243. [5] H. Kishi, Y. Kunimitsu, J. Imade, S. Oshita, Y. Morishita, M. Asada, Nano-phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys, Polymer 52 (2011) 760–768. [6] J. Chen, A.C. Taylor, Epoxy modified with triblock copolymers: morphology, mechanical properties and fracture mechanisms, J. Mater. Sci. 47 (2012) 4546–4560. [7] Y.S. Thio, J. Wu, F.S. Bates, The Role of inclusion size in toughening of epoxy resins by spherical micelles, J. Polym. Sci. B: Polym. Phys. 47 (2009) 1125–1129. [8] D. Quan, A. Ivankovic, Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer, Polymer 66 (2015) 16–28. [9] H. Yahyaie, M. Ebrahimi, H.V. Tahami, E.R. Mafi, Toughening mechanisms of rubber modified thin film epoxy resins, Prog. Org. Coatings 76 (2013) 286–292. [10] G.M. Gladysz, K.K. Chawla, Voids in Materials: From Unavoidable Defects to Designed Cellular Materials, Newnes, Elsevier, 2014. [11] D. Hull, Fractography: Observing, Measuring and Interpreting Fracture Surface Topography, Cambridge University Press, 1999. [12] Y. Liang, R. Pearson, Toughening mechanisms in epoxy–silica nanocomposites (ESNs), Polymer 50 (2009) 4895–4905.