Co-reporter:Jordana K. Palacios, Agnieszka Tercjak, Guoming Liu, Dujin Wang, Junpeng Zhao, Nikos Hadjichristidis, and Alejandro J. Müller
Macromolecules September 26, 2017 Volume 50(Issue 18) pp:7268-7268
Publication Date(Web):September 6, 2017
DOI:10.1021/acs.macromol.7b01576
Triple crystalline triblock terpolymers are materials with remarkable semicrystalline superstructures. In this work, we report for first time the alternating triple lamellar morphology that self-assembles inside spherulites of a triblock terpolymer composed of poly(ethylene oxide) (PEO), poly(ε-caprolactone) (PCL), and poly(l-lactide) (PLLA). The morphology of the PEO-b-PCL-b-PLLA triblock terpolymer is compared to an analogous PCL-b-PLLA diblock copolymer. Both diblock and triblock form a single phase in the melt. Two crystallization protocols were employed to create particular crystalline morphologies. In both cases, the isothermal crystallization of the PLA block is induced first (at 81 °C, a temperature above the melting points of both PCL and PEO blocks) and PLLA spherulites form a template, whereupon cooling the other two blocks can crystallize within the PLLA interlamellar spaces. WAXS analysis demonstrated the double crystalline and triple crystalline nature of the materials. The lamellar structure was evaluated by AFM observations and SAXS measurements. Moreover, theoretical SAXS curves of one-dimensional structural models were calculated. AFM micrographs of the triblock terpolymer evidenced the three different lamellae of PLLA, PCL and PEO that coexist together within the same spherulite. Three different lamellar thickness were determined, and their dimensions suggested that all blocks crystallized in chain-folded conformations. The evolution of the triple lamellar morphology during heating of tricrystalline samples was followed by in situ synchrotron SAXS measurements. The theoretical analysis of the SAXS curves of the triblock terpolymer allowed us to propose a stacking morphological model, in which a particular trilayer structure exists, where one lamella of PCL or one lamella of PEO is inserted randomly between two adjacent PLLA lamellae.
Co-reporter:Guangyu Shi, Guoming Liu, Cui Su, Haiming Chen, Yu Chen, Yunlan Su, Alejandro J. Müller, and Dujin Wang
Macromolecules November 28, 2017 Volume 50(Issue 22) pp:9015-9015
Publication Date(Web):November 15, 2017
DOI:10.1021/acs.macromol.7b02284
The crystallization of poly(ε-caprolactone) (PCL) and isotactic polypropylene (iPP) infiltrated in nanoporous anodic alumina oxide (AAO) templates was reexamined to demonstrate the importance of obtaining polymer-free, clean AAO surfaces on the nucleation, size dependence of crystallization temperature (Tc), and texture. The AAO pore diameters cover a broad range from 400 to 20 nm. When the AAO templates were completely free of any residual polymer on their surfaces, differential scanning calorimetry (DSC) experiments exhibited a single crystallization peak for all the samples with different AAO pore sizes. A drastic decrease in Tc with density of domains indicated a transition from heterogeneous to homogeneous/surface nucleation. A regular decrease of Tc with pore size was observed in the low Tc regime, as a result of the volume dependence of nucleation events. The chain alignment of the two polymers infiltrated in AAO was studied by two-dimensional wide-angle X-ray scattering (WAXS). By comparing the experimental and simulated WAXS patterns, the orientation modes of the polymers were identified and compared with previous studies.
Co-reporter:Yongai Yin, Guoming Liu, Yan Song, Xiuqin Zhang, Sicco de Vos, Ruyin Wang, Cornelis A.P. Joziasse, Dujin Wang
European Polymer Journal 2016 Volume 82() pp:46-56
Publication Date(Web):September 2016
DOI:10.1016/j.eurpolymj.2016.05.033
•SC formation in PLLA/PDLA was investigated by in-situ WAXS and SAXS.•Formation of SC depended strongly on annealing temperature.•A new concept of “diffusion zone” was proposed to explain the results.The formation of stereocomplex (SC) in enantiomeric poly(lactide)s via recrystallization of homocrystals was investigated by using simultaneous wide-angle and small-angle X-ray scattering. When the symmetric blend of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) was heated from the glassy state at a slow heating rate (5 °C/min), predominant homocrystals were formed during heating (cold crystallization). Melting of homocrystals and crystallization of stereocomplex occurred almost simultaneously. In this case, the diffusion of PLLA and PDLA chains played an important role in determining the maximum attainable SC crystallinity. The crystallization behavior during annealing at different temperatures (185 °C, 195 °C and 225 °C) and subsequent cooling was further investigated to understand the effectiveness of annealing on the formation of stereocomplex. The stereocomplex content was unchanged during annealing at 185 °C and kept constant during cooling to room temperature. The SC crystallinity increased slightly during annealing at 195 °C and subsequently cooling. On the other hand, the content of SC increased during annealing at 225 °C and increased remarkably during cooling. A possible mechanism considering the diffusion of PLLA and PDLA chains was proposed.
Co-reporter:Yan Song, Xiuqin Zhang, Yongai Yin, Chunbo Zhang, Sicco de Vos, Ruyin Wang, Cornelis A.P. Joziasse, Guoming Liu, Dujin Wang
European Polymer Journal 2016 Volume 75() pp:93-103
Publication Date(Web):February 2016
DOI:10.1016/j.eurpolymj.2015.12.001
•The crystallization behavior of 1:1 PLLA/PDLA mixture under shear was investigated.•The nucleation density and crystallization rate increased with shear rate.•The phase content of SC increased with shear rate.•The α content displayed a bell-shaped curve with increasing shear rate.The isothermal crystallization behavior of a 1:1 poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) mixture under pulsed shear was investigated by in-situ polarized light optical microscopy (POM) and wide angle X-ray scattering (WAXS). The effects of shear rate and temperature were studied. The results showed that application of shear flow increased the nucleation density, crystallization rate and degree of orientation for both stereocomplex crystals (SC) and α crystals. Interestingly, when the crystallization temperature was below the melting temperature of α crystals, the phase content of SC increased with shear rate, while the α content displayed a bell-shaped curve with regard to shear rate. The structure formation in this system was closely related to the shear-induced nucleation, phase mixing and chain mobility.
Co-reporter:Chunbo Zhang;Qianhong Jiang;Ying Zhao;Dujin Wang
Journal of Applied Polymer Science 2016 Volume 133( Issue 5) pp:
Publication Date(Web):
DOI:10.1002/app.42930
ABSTRACT
Propylene-based propylene–ethylene random copolymer (PPR) has been widely used in the production of hot-water pipes. To further improve its toughness and thermal resistance, β-nucleating agents (β-NAs) are frequently incorporated. In this study, PPR containing 5.6 mol % ethylene units was modified by two kinds of β-NAs, that is, calcium pimelate and N,N′-dicyclohexylterephthalamide. The notched Izod impact strength of PPR increased with the addition of the β-NAs. Drastically different toughening effects were found between the two β-NAs. The structure of PPR with and without a β-NA was investigated by calorimetry, X-ray diffraction, and thermomechanical analysis. The results indicated that the relative fraction of β crystals (kβ) in the injection-molded specimens was determined by the type and content of β-NA. The relationship between kβ and the impact toughness was summarized. A critical value for kβ (0.68) was identified for the brittle–ductile transition of PPR. PPR with β-NA having a kβ greater than 0.68 displayed a higher impact strength than the other mixtures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42930.
Co-reporter:Pan Sun;Dong Lv;Xia Dong;Jingshen Wu;Dujin Wang
Journal of Applied Polymer Science 2016 Volume 133( Issue 13) pp:
Publication Date(Web):
DOI:10.1002/app.43249
ABSTRACT
This work investigated the effect of silane modification of halloysite nanotubes (HNTs) on the mechanical properties of epoxy/HNTs nanocomposites. Three kinds of silane coupling agents, including 3-(2-aminoethyl)-aminopropyltrimethoxysilane (AEAPS), (3-glycidyloxypropyl)-trimethoxysilane (GPTMS), and octyltriethoxysilane (OTES), were employed. It was shown that the modified HNTs exhibited a better dispersion in the epoxy matrix compared with pristine one. Because of strong interfacial interaction between AEAPS modified HNTs and the epoxy matrix, the nanocomposites exhibited the highest glass transition temperature and modulus among all the samples. On the other hand, AEAPS and GPTMS modified HNTs/epoxy nanocomposites showed enhanced tensile strength and toughness. The toughing mechanisms were identified by the SEM micrographs of the fracture surfaces of the different kinds of samples. In this study, simultaneous enhancement of strength, toughness, and thermal stability of epoxy by the modified HNTs provides a novel approach to produce high-performance thermosets. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43249.
Co-reporter:Haiming Chen, Guoming Liu, Yunpeng Qin, Alejandro J. Müller, Jianhui Hou, and Dujin Wang
Macromolecules 2016 Volume 49(Issue 22) pp:8653-8660
Publication Date(Web):November 10, 2016
DOI:10.1021/acs.macromol.6b02218
The structural transitions in solution-cast film of poly[5,5′-bis(2-butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT) copolymer have been systematically studied by a combination of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), in situ Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, and in situ wide-angle X-ray scattering (WAXS). The glass transition temperature of the main chain as well as the melting and crystallization temperatures of the polymer were determined as 10, 238, and 221 °C, respectively. The out-of-plane deformation vibration of PDCBT Cβ–H groups in FTIR has been manifestly assigned for the first time. A broad endothermic peak between 30 and 120 °C was observed during DSC heating process and was attributed to the enthalpic relaxation of the twist glass transition, which resulted in a small negative effect on the power conversion efficiency (PCE) of solar cells. A reorganization process in the crystalline region was observed in WAXS upon heating, including the increase of grain size along the a-axis.
Co-reporter:Pan Sun, Guoming Liu, Dong Lv, Xia Dong, Jingshen Wu and Dujin Wang
RSC Advances 2015 vol. 5(Issue 65) pp:52916-52925
Publication Date(Web):01 Jun 2015
DOI:10.1039/C5RA04444H
The present work reports a novel modification methodology for halloysite nanotubes (HNTs) that includes two successive steps, i.e., activation by piranha solution and silanization reaction. A commercial silane coupling agent, 3-aminopropyltriethoxysilane (APS), was selected to modify the surface of HNTs. The presence of APS moieties on the HNT surface was characterized by the combination of Fourier transform infrared (FTIR) spectroscopy, thermogravimetry (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen sorption. For the coupling reaction, the effect of reaction time, temperature, rehydration and APS concentration on the course of silanization degree was carefully investigated. The mechanism and the grafted product structure of the reaction between activated HNTs and APS were revealed through 29Si solid-state NMR spectroscopy and XPS analysis. The result shows that piranha solution is an effective activation agent for silanization of HNTs. A higher reaction temperature (120 °C) contributed to a higher grafted amount compared with a lower temperature (70 °C). Moisture led to a higher degree of silanization. The grafted amount increased with APS concentration and leveled off at about 1%. Further increase in the APS concentration only led to a drastic decrease in grafting yield. The grafting reaction was confirmed by the presence of tridentate (T3) and bidentate (T2) bonded Si in 29Si NMR. Free terminal amino groups and protonated amine groups were identified in modified HNTs by XPS.
Co-reporter:Chunbo Zhang, Guoming Liu, Qianhong Jiang, Jian Yang, Ying Zhao and Dujin Wang
RSC Advances 2015 vol. 5(Issue 55) pp:44610-44617
Publication Date(Web):11 May 2015
DOI:10.1039/C5RA04952K
Copolymerization for making propylene-based random copolymers is an important strategy to broaden the applications of polypropylene, such as propylene random copolymer with β-nucleating agent as hot water pipes. In the present work, a β-nucleated propylene–ethylene random copolymer (P–E copolymer) containing a low content of ethylene (5.6 mol%) was subjected to uniaxial stretching at 30 and 100 °C. The structural evolution during deformation was investigated by in situ X-ray scattering using synchrotron radiation. An interesting temperature dependence of the deformation feature of β-crystal was observed. The β-crystal in the sample transformed to mesophase at 30 °C and to α-crystal at 100 °C. Molecular chains in β-crystal stretched at 30 °C was identified to be perpendicular to the stretching direction, while they tended to be parallel to the direction at 100 °C. On the other hand, cavitation was observed in β-nucleated P–E copolymer when stretched at 30 °C. As the tensile temperature reached 100 °C, no cavities could be detected. A deformation model of the β-nucleated P–E copolymer combining crystal transition, cavitation and orientation depending on the drawing temperature was described.
Co-reporter:Yu Guan, Guoming Liu, Guqiao Ding, Tieying Yang, Alejandro J. Müller, and Dujin Wang
Macromolecules 2015 Volume 48(Issue 8) pp:2526-2533
Publication Date(Web):April 15, 2015
DOI:10.1021/acs.macromol.5b00108
The crystallization behavior of poly(l-lactic acid) (PLLA) infiltrated in anodic alumina oxide templates (AAO) was investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). During heating from the glassy state, the crystallization of infiltrated PLLA was unexpectedly enhanced as compared with bulk PLLA. The cold crystallization temperature of infiltrated PLLA from the glassy state was much lower than that of bulk PLLA. The half-crystallization time (t1/2) of infiltrated PLLA at 75 °C decreased with the diameter of AAO nanopores. The glass transition temperature of PLLA was not influenced by the geometrical confinement. The enhanced crystallization from the glassy state was explained by surface-induced nucleation of AAO walls on PLLA. Our results provide the first observation of enhanced cold crystallization of polymers in confined geometry.
Co-reporter:Yongai Yin, Xiuqin Zhang, Yan Song, Sicco de Vos, Ruyin Wang, Cornelis A.P. Joziasse, Guoming Liu, Dujin Wang
Polymer 2015 Volume 65() pp:223-232
Publication Date(Web):18 May 2015
DOI:10.1016/j.polymer.2015.03.061
•The structural evolution during uniaxial stretching of neat and nucleated PLLA above Tg was investigated by in-situ WAXS.•The nucleating effect for PLLA crystallization increased in the following order: PDLA/talc > PDLA > talc.•In step-strain measurements, the effect of nucleating agent on the crystallization of PLLA showed a strain-dependence.This work examined the effect of nucleating agents on the strain-induced crystallization of poly(l-lactide) (PLLA). Talc and poly(d-lactide) (PDLA) were used as the nucleating agents of PLLA. Wide angle X-ray scattering (WAXS) revealed that the original injection molded specimens of nucleated PLLA blends were free of PLLA α crystal. The structural evolution during uniaxial stretching of neat and nucleated PLLA above the glass transition temperature was investigated by in-situ WAXS. It was observed that the nucleating agents significantly accelerated the crystallization of PLLA during stretching. The accelerating effect for the PLLA crystallization during stretching increased in the following order: PDLA/talc > PDLA > talc. In step-strain measurements with a high stretching speed, the effect of nucleating agents on the crystallization of PLLA showed a strain-dependence. The enhancement of crystallization by nucleating agents was remarkable at 200% strain. However, with 500% strain, the strain-induced crystallization was dominant and the effect of nucleating agents on crystallization of PLLA was not obvious. The results were analyzed considering the nucleating effect of nucleating agents on PLLA.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Yan Song, Xiuqin Zhang, Yongai Yin, Sicco de Vos, Ruyin Wang, Cornelis A.P. Joziasse, Guoming Liu, Dujin Wang
Polymer 2015 Volume 72() pp:185-192
Publication Date(Web):18 August 2015
DOI:10.1016/j.polymer.2015.07.023
•The crystallization behavior of PLLA/PDLA equimolar mixture under shear field is investigated by in-situ WAXS.•The nucleation density and final content of stereocomplex are enhanced by shear field.•The final content of α crystal reduced with the increase of stereocomplex content.The non-isothermal crystallization behavior of poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends under shear was investigated by in-situ polarized light optical microscopy (POM) and wide angle X-ray scattering (WAXS). Pulse shear for 5 seconds was applied to the melt during cooling. The effects of shear temperature and shear rate were systematically studied. It was found that the shear field could increase the nucleation density of stereocomplex crystal (SC), and accelerate the overall crystallization rate. The final crystallinity of SC increased to as high as ∼45% with a shear rate of 178 s−1 when the shear temperature was 150 °C. The onset crystallization temperature of α crystals increased by ∼10 °C. The final content of α crystals reduced with the increase of SC content. Multiple factors influence the crystallization of SC and α crystals, including the shear rate, shear temperature and the nucleating/confinement effect of SC on α crystals.
Co-reporter:Chunbo Zhang, Guoming Liu, Yan Song, Ying Zhao, Dujin Wang
Polymer 2014 Volume 55(Issue 26) pp:6915-6923
Publication Date(Web):15 December 2014
DOI:10.1016/j.polymer.2014.10.049
•Structural evolution of initially isotropic β – iPP during uniaxial stretching is investigated by in-situ WAXS and SAXS.•An interesting orientation of β – crystal with molecular chains perpendicular to the tensile direction is identified.•A deformation mechanism of β – iPP based on correlation among crystal transition, orientation and cavitation is proposed.Polymorphism and crystal transition are of great significance for property mediation in polymer materials. Isotactic polypropylene (iPP) with β – crystal has been widely utilized for the preparation of high performance plastics or films. In the present work, the structural evolution of initially isotropic β – nucleated iPP (β – iPP) during uniaxial stretching at different temperatures was investigated by in–situ X – ray scattering using synchrotron radiation. The wide – angle X – ray scattering (WAXS) results confirmed that the β – crystal transformed either to the mesophase at lower temperature (30 °C) or to the α – crystal at higher temperature (60, 100 and 120 °C) during stretching. An interesting orientation of β – crystal with molecular chains perpendicular to the tensile direction was identified. As revealed by small – angle X – ray scattering (SAXS), cavitation took place in β – iPP stretched at temperatures lower than 120 °C. The size and shape of the cavities were observed by scanning electron microscope. A deformation mechanism of β – iPP combining the crystal transition, cavitation and orientation was proposed.
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