Co-reporter:Faqiang Liu;Tongjie Sun;Hongdong Zhang;Feng Qiu
Soft Matter (2005-Present) 2017 vol. 13(Issue 44) pp:8250-8263
Publication Date(Web):2017/11/15
DOI:10.1039/C7SM01892D
We employ a rod–coil multiblock molecular chain model to investigate chain folding behavior, which is a significant characteristic in semicrystalline polymers, by using the method of self-consistent field theory (SCFT). Polymer chains with different conformations in crystalline and amorphous regions are described by rigid rod chains and flexible Gaussian chains, respectively. At present, we concentrate on the thermodynamic behaviors of polymer semi-crystals after the formation of the initial lamellar crystals. A new mechanism for lamellar thickening is proposed to realize that the end of lamellar thickening depends on the crystallinity degree. In other words, it is impossible for lamellae to develop into extended-chain crystals by means of lamellar thickening if crystallinity is limited to a certain degree. We further discuss the competition between crystalline and amorphous regions and its influence on crystallization behaviors, such as the formation of double lamellae, chain tilt, the anomalies and adjacent re-entry. The synergistic influences of the driving force of crystallization, interfacial energy and crystallinity degree on chain folding behavior are also investigated when the density anomalies in amorphous regions are excluded. Our model demonstrates advantages in accurately describing the mesoscopic layered structures of semicrystalline polymers based upon a microscopic chain model and provides at least a semi-quantitative thermodynamic picture for chain folding.
Co-reporter:Cangyi Chen, Tiancai Zhang, Lei Zhu, Bin Zhao, Ping Tang, and Feng Qiu
ACS Macro Letters 2016 Volume 5(Issue 6) pp:718
Publication Date(Web):May 26, 2016
DOI:10.1021/acsmacrolett.6b00176
Hierarchical superstructures assembled by binary mixed homopolymer-grafted nanoparticles are investigated by using a self-consistent field theory (SCFT). Our results demonstrate that grafting mixed homopolymer brushes provides an effective way to program the spatial lattice arrangement of the nanoparticles. For the polymer-grafted nanoparticles with specific interaction parameter and total grafting density, the unusual non-close-packed simple cubic (SC) crystal lattice is obtained at small spherical core/polymer size ratios (R/() < 1). As the size ratio increases to > 1, the nanoparticle arrangement transforms into a body-centered cubic (BCC) crystal lattice. Meanwhile, some unconventional microphases are formed in the polymer matrix, such as the tetragonal cylinder and simple cubic sphere phases. Furthermore, the two-dimensional (2D) model calculations reveal that the binary hairy nanoparticles prefer to arrange into the lattice in a way they can maintain the free energy-minimizing morphology as an isolated particle. Our findings suggest a possible strategy to design hierarchical nanomaterials composed of unique inorganic/organic hybrid superstructures.
Co-reporter:Rui Li;JingJing Si
Polymers for Advanced Technologies 2016 Volume 27( Issue 5) pp:615-622
Publication Date(Web):
DOI:10.1002/pat.3728
Small molecular surfactant (SMS), used as antistatic agent of polymers, is prone to the wash-out effects thus reducing its lifetime. To address this issue, the sustained-release antistatic agent is prepared by encapsulating SMS (HDC-102 or HDC-193) into mesoporous silica nanoparticles such as MCM-41 and is used to modify the antistatic properties of polystyrene (PS). The water-resistant test is used to evaluate the sustained-release effect, and the results showed that the HDC-102/MCM-41/PS composite retains favorable antistatic properties with the Rs of 6.2 × 1011 after five times washing, while the HDC-102/PS loses antistatic properties after twice washing. The contact angle measurement demonstrates that the sustained-release effect is affected by the characteristics of SMS. Moreover, the coefficient of thermal expansion of SMS/PS composites is decreased, and the thermal decomposition temperature is increased with incorporation of MCM-41. This approach may be used in polymer systems with the other small molecular additives to prolong their lifetime. Copyright © 2015 John Wiley & Sons, Ltd.
Co-reporter:Cangyi Chen, Ping Tang, Feng Qiu, and An-Chang Shi
The Journal of Physical Chemistry B 2016 Volume 120(Issue 24) pp:5553-5563
Publication Date(Web):May 31, 2016
DOI:10.1021/acs.jpcb.6b03005
The conformation of homodendrimers and amphiphilic dendrimers in various solvents is studied using classical density functional theory (DFT), in which the excluded-volume effects are treated explicitly. For homodendrimers in an athermal solvent, DFT results predict a remarkable fold-back behavior for the outer generation of segments, supporting the dense-core model. A coil-to-globule transition is observed for homodendrimers in a poor solvent. The size of the dendrimers, characterized by the radius of gyration, ⟨Rg⟩, is found to follow the scaling relationship, ⟨Rg⟩ ∼ Nν, where N is the total number of segments of the dendrimers. For amphiphilic dendrimers, DFT results show that chemical modification in the outermost generation is an effective method to drive the ends toward the periphery of the dendrimers. In particular, a conformation with a hollow interior structure could be formed for amphiphilic dendrimers with longer end spacers in a selective solvent. The resulting unimolecular micelles with a hollow core and dense shell could serve as a unique candidate for encapsulation applications, such as sustained-drug-release nanocontainers.
Co-reporter:Shili Xing;Yuliang Yang
Journal of Applied Polymer Science 2015 Volume 132( Issue 2) pp:
Publication Date(Web):
DOI:10.1002/app.41240
ABSTRACT
Poly(styrene-co-maleic anhydride) (SMA) ionomers were synthesized and designed as a new kind of nucleation agent according to the crystallization theory for improving the crystallization of poly(ethylene terephthalate) (PET). The crystallization behavior of PET with the addition of nucleation agents was investigated by differential scanning calorimetry, polarized-light microscope, and X-ray diffraction (XRD). Avrami equation and Hoffman–Lauritzen theory are adopted for analyzing isothermal and non-isothermal crystallization kinetics, respectively. The results show that the addition of 1 wt % SMA ionomers effectively accelerates the crystallization rate and reduces the fold surface free energy of PET at high temperature regions. PLM results also indicated that the crystals impinge on each other, thus decreasing the spherulite size for PET/SMA ionomers samples compared with PET. XRD measurement revealed that the introduction of SMA ionomers does not change the crystal structure but indeed accelerates the crystallinity of PET. The results clearly demonstrate that our synthesized SMA ionomers are an efficient nucleating agent for PET. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41240.
Co-reporter:Shili Xing;Rui Li
Macromolecular Chemistry and Physics 2015 Volume 216( Issue 3) pp:301-313
Publication Date(Web):
DOI:10.1002/macp.201400444
Co-reporter:Nan Ji, Ping Tang, and Feng Qiu and An-Chang Shi
Macromolecules 2015 Volume 48(Issue 23) pp:8681-8693
Publication Date(Web):November 19, 2015
DOI:10.1021/acs.macromol.5b02023
The kinetic pathways connecting the lamellar and gyroid phases in weakly segregated block copolymers are examined by combining the string method and the self-consistent mean-field theory for polymers. In particular, phase transition from arbitrarily oriented lamellae to gyroid is studied. The results reveal that initially the lamella will evolve into a metastable structure via a nucleation and growth mechanism, and then a secondary nucleation of the gyroid occurs in the metastable phase. The observed metastable structures include the perforated lamellae (PL), the O70 phase, and the tetragonally perforated layers (TPLabc). Nucleation and growth is the dominant mechanism, and prior phase transition passed by HPLabc, which is a long-lived metastable structure, has the minimal energy barrier.
Co-reporter:Jie Gao, Ping Tang and Yuliang Yang
Soft Matter 2013 vol. 9(Issue 1) pp:69-81
Publication Date(Web):12 Oct 2012
DOI:10.1039/C2SM26758F
We investigate the self-assembly of coil–semiflexible block copolymers in 2D positional space by using self-consistent field theory (SCFT) based on the wormlike chain model for the semiflexible block and the Gaussian chain model for the coil block. A highly accurate and efficient operator splitting pseudospectral algorithm is adopted to cope with the computational intricacy of solving modified diffusion equations for the propagators of wormlike chains. Within the framework of anisotropic Maier–Saupe orientational interactions and isotropic Flory–Huggins interactions, the phase diagram including isotropic, smectic-C, and further appended non-lamella structures is constructed for the coil–semiflexible block copolymers in the region of coil volume fractions from 0.6 to 0.8. Hexagonal packed pucks and rhombic pucks formed by the semiflexible block with major orientation perpendicular to their nearest neighbors in the latter are discovered at relatively high coil fractions and strong orientational interactions. We also study the influence of chain rigidity on the phase behavior of coil–semiflexible block copolymers.
Co-reporter:Guang Yang, Ping Tang, and Yuliang Yang
Macromolecules 2012 Volume 45(Issue 8) pp:3590-3603
Publication Date(Web):April 2, 2012
DOI:10.1021/ma2027879
We investigate the isotropic–anisotropic phase transitions and the conformation of combined main-chain/side-chain liquid crystal polymers (MCSCLCPs) by numerically solving semiflexible chain self-consistent field theory (SCFT) equations with the pseudospectral method. Two kinds of interactions are involved: the global coupling between backbone segments, between the backbone and side groups, and between the side mesogens and the local coupling between the polymer backbone and its attached side groups. When the hinges are flexible, both global and local effects prefer parallel alignments of backbone and side groups, forming only prolate uniaxial nematic phase NPIII. When the hinges are relatively stiff, the competition between the global interaction preferring parallel orientations of the system and the perpendicular tendency of the two components due to the comb architecture results in rich phases with various orientation modes, including uniaxial prolate phases NPI, NPII, and oblate phase NO and biaxial phases NBI, NBII, and NBIII. The new phases NO and NBIII have not yet been reported by the previous theoretical results. We conclude that the occurrence of the biaxial phases results from not only the perpendicular toplogical structures between the oriented main chain and side groups but also the bending feature of the wormlike chain backbone, another necessary condition for NBI and NBII.
Co-reporter:Wendi Song, Ping Tang, Feng Qiu, Yuliang Yang and An-Chang Shi
Soft Matter 2011 vol. 7(Issue 3) pp:929-938
Publication Date(Web):25 Nov 2010
DOI:10.1039/C0SM00841A
The phase behavior of semiflexible-coil diblock copolymer melts is studied by solving the self-consistent field theory (SCFT) equations of wormlike chains. Significant improvement of numerical accuracy and stability is achieved by a hybrid numerical implementation of SCFT, in which the space-dependent functions are treated using a spectral method and the orientation-dependent functions are discretized on a unit sphere (3D Euclidean space) with an icosahedron triangular mesh. The angular Laplacian is solved in real-space using a finite volume algorithm. Phase diagrams of the model system are constructed from SCFT. Phase transitions between various smectic phases such as monolayer and bilayer smectic-A, monolayer and bilayer smectic-C, as well as folded smectic phases, are predicted. In particular, the stability of the monolayer and bilayer smectic phases is associated with the competition between interfacial energy and coil-stretching entropy, which strongly depends on the interplay between orientational interaction and microphase separation and the topological disparity between the semiflexible and coil blocks.
Co-reporter:Jie Gao, Wendi Song, Ping Tang and Yuliang Yang
Soft Matter 2011 vol. 7(Issue 11) pp:5208-5216
Publication Date(Web):02 Apr 2011
DOI:10.1039/C1SM05142C
The phase behavior of rod-coil diblock copolymers is investigated in a two-dimensional positional space by using self-consistent field theory (SCFT) based on wormlike chain model. The segment orientation is defined on a unit spherical surface in three-dimensional space with an icosahedron triangular mesh and a finite volume algorithm is borrowed to numerically solve the Laplacian on the sphere. By taking advantage of 2D space calculation, the phase diagram including isotropic, nematic, smectic-A, smectic-C and further appended non-lamellar structures is constructed for the rod-coil diblock copolymers within the framework of Onsager excluded-volume interactions, in which microphase separation and liquid crystalline behavior are driven only by the entropy. Similar to our previous 1D space calculations, although smectic structures occupy large region in the phase diagram, tetragonal packed arrays of ellipse like domains in our 2D space simulations is observed at relatively high coil fractions and strong orientational interactions. We also reexamine the stability of zigzag and confirm it as a thermodynamically metastable structure of rod-coil copolymers in terms of the SCFT free energy.
Co-reporter:Wendi Song, Ping Tang, Feng Qiu, Yuliang Yang, and An-Chang Shi
The Journal of Physical Chemistry B 2011 Volume 115(Issue 26) pp:8390-8400
Publication Date(Web):June 6, 2011
DOI:10.1021/jp201972n
The phase behavior of binary blends of rod–coil diblock copolymers and coil or rod homopolymers is studied by the self-consistent field theory (SCFT). The rod blocks are modeled as wormlike chains and the corresponding SCFT equations are solved using a hybrid method, in which the orientation-dependent functions are discretized on a unit sphere, while the positional space-dependent functions are treated using a spectral method. Phase diagrams of the blends are constructed as a function of the homopolymer volume fraction and phase segregation strength. It is discovered that the phase behavior of the system depends on the flexibility of the homopolymers. The addition of coil-homopolymers stabilizes the smectic phases. Low-molecular weight coil-homopolymers tend to mix with the coil-blocks, whereas high-molecular weight coil-homopolymers are mostly localized at the center of the coil-domains. On the other hand, the addition of rod-homopolymers strongly affects the orientation ordering of the system, leading to transitions between monolayer smectic-C, monolayer smectic-A and bilayer smectic-A phases.
Co-reporter:Guang Yang, Ping Tang, Yuliang Yang, and Qiang Wang
The Journal of Physical Chemistry B 2010 Volume 114(Issue 46) pp:14897-14906
Publication Date(Web):November 3, 2010
DOI:10.1021/jp107997b
We employ the self-consistent field theory (SCFT) incorporating Maier−Saupe orientational interactions between rods to investigate the self-assembly of rod−coil diblock copolymers (RC DBC) in bulk and especially confined into two flat surfaces in 2D space. A unit vector defined on a spherical surface for describing the orientation of rigid blocks in 3D Euclidean space is discretized with an icosahedron triangular mesh to numerically integrate over rod orientation, which is confirmed to have numerical accuracy and stability higher than that of the normal Gaussian quadrature. For the hockey puck-shaped phases in bulk, geometrical confinement, i.e., the film thickness, plays an important role in the self-assembled structures’ transitions for the neutral walls. However, for the lamellar phase (monolayer smectic-C) in bulk, the perpendicular lamellae are always stable, less dependent on the film thicknesses because they can relax to the bulk spacing with less-paid coil-stretching in thin films. In particular, a very thin rod layer near the surfaces is formed even in a very thin film. When the walls prefer rods, parallel lamellae are obtained, strongly dependent on the competition between the degree of the surface fields and film geometrical confinement, and the effect of surface field on lamellar structure as a function of film thickness is investigated. Our simulation results provide a guide to understanding the self-assembly of the rod−coil films with desirable application prospects in the fabrication of organic light emitting devices.
Co-reporter:Guang Yang, Ping Tang, Yuliang Yang and Joao T. Cabral
The Journal of Physical Chemistry B 2009 Volume 113(Issue 43) pp:14052-14061
Publication Date(Web):October 8, 2009
DOI:10.1021/jp9033613
Motivated by recent experiments of copolymer patterning by nanoimprinting, we investigate microphase separation and morphology for symmetric AB diblock copolymers with lamellar structure in bulk, confined between a flat bottom surface and a square-wave top surface by using the self-consistent field theory (SCFT). The efficient and high-order accurate pseudospectral method is adopted to numerically solve the SCFT equations in irregularly shaped domains with the help of the “masking” technique by embedding the confined domains of arbitrary shape within a larger rectangular computational cell. Our simulations reveal that the inverted T-style and trapezoid structures occurring in the relatively strong and weak surface fields, respectively, are following our topographically patterned surface. For neutral walls, when the thickness of the lower section is commensurate with the lamellae period of bulk block copolymers, the topographically patterned surface in this work leads to parallel lamellae, and completely parallel lamellae are favored when both the width and height of the upper section are equal to the lamellae bulk period. Furthermore, the prevalent structures are the parallel lamellae in the upper section combined with the perpendicular lamellae in the lower section. When the walls repel one of the block species, parallel lamellae occur in a wide range of film thicknesses compared to the case of neutral walls. To our knowledge, some new structures, however, such as square and partial square structures and reversed-T and trapezoid structures, have not been reported before under parallel surface confinement. In general, the required structures can be obtained by choosing the proper degree of spatial confinement, characterized by variations of the ratio of film thicknesses to bulk repeat period, and the block−substrate interactions. Moreover, we show that the confinement width of the lower section (or the period of the square wave) plays a critical role in microstructure formation. These findings provide a guide to designing novel microstructures involving symmetric diblock copolymers via topographically patterned surfaces and surface fields, relevant to nanoimprinting.
Co-reporter:Wendi Song, Ping Tang, Hongdong Zhang, Yuliang Yang and An-Chang Shi
Macromolecules 2009 Volume 42(Issue 16) pp:6300-6309
Publication Date(Web):July 24, 2009
DOI:10.1021/ma9007412
A new real-space numerical implementation of the self-consistent field theory for semiflexible polymers is developed. Specifically, a finite volume algorithm on a unit sphere with an icosahedron triangular mesh is employed to describe the orientation degree of freedom of the wormlike chains. The validity of the new method is analyzed by comparing with results from the spectral method. As a concrete example, the new numerical method is applied to the self-assembly of rod−coil diblock copolymers within the framework of Onsager excluded-volume interaction. A variety of liquid crystalline phases such as disordered isotropic, nematic, and smectic phases have been obtained. In particular, the new method provides a particularly convenient method for studying the smectic-C phase. A phase diagram is constructed for the rod−coil diblock copolymers, which is in agreement with previous theoretical and experimental results.
Co-reporter:Wenchi Han, Ping Tang, Xuan Li, Feng Qiu, Hongdong Zhang and Yuliang Yang
The Journal of Physical Chemistry B 2008 Volume 112(Issue 44) pp:13738-13748
Publication Date(Web):October 11, 2008
DOI:10.1021/jp801675z
Microphase separation and morphology of star ABC triblock copolymers confined between two identical parallel walls (symmetric wetting or dewetting) are investigated with self-consistent field theory (SCFT) combined with the “masking” technique to describe the geometric confinement of the films. In particular, we examine the morphology of confined near-symmetric star triblock copolymers under symmetric and asymmetric interactions as a function of the film thickness and the surface field. Under the interplay between the degree of spatial confinement, characterized by the ratio of the film thickness to bulk period, and surface field, the confined star ABC triblock copolymers are found to exhibit a rich phase behavior. In the parameter space we have explored, the thin film morphologies are described by four primary classes including cylinders, perforated lamellae, lamellae, and other complex hybrid structures. Some of them involve novel structures, such as spheres in a continuous matrix and cylinders with alternating helices structure, which are observed to be stable with suitable film thickness and surface field. In particular, complex hybrid network structures in thin films of bulk cylinder-forming star triblock copolymers are found when the natural domain period is not commensurate with the film thickness. Furthermore, a strong surface field is found to be more significant than the spatial confinement on changing the morphology of star triblock copolymers in bulk. These findings provide a guide to designing novel microstructures involving star triblock copolymers via geometric confinement and surface fields.
Co-reporter:Shili Xing, Rui Li, Jingjing Si, Ping Tang
Journal of Industrial and Engineering Chemistry (25 June 2016) Volume 38() pp:167-174
Publication Date(Web):25 June 2016
DOI:10.1016/j.jiec.2016.04.020
The poly(styrene-alt-maleic anhydride)/organic montmorillonite (SMA/OMMT) nanocomposites are obtained through in situ polymerization of styrene and maleic anhydride. The OMMT is exfoliated into small platelets and dispersed well in SMA copolymers, which is thus easily made into ionomers/OMMT (IM) nanocomposites. The IMs are employed as nucleating agents for poly(ethylene terephthalate) (PET) and the crystallization behavior is investigated by DSC isothermally and non-isothermally, respectively. The crystallization rate of PET is significantly accelerated and melt-crystallization temperature is increased with the addition of IMs which acted as heterogeneous nucleating agent due to good miscibility between anhydride and PET, and large interfaces provided by exfoliated OMMT.Download high-res image (95KB)Download full-size image
