The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature,...The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature, was studied. Therod-coil copolymers, which have the same PS length but different PMPCS length, were synthesized by 2,2,6,6-tetramethyl-I-piperidinyloxy (TEMPO) mediated living free radical polymerization. The influence of the rod length on the self-assemblymorphology was studied by transmission electron microscopy (TEM). At a concentration of 2.0 mg/mL, those copolymerswith relatively shorter PMPCS length (copolymers 1 and 2) form individual spherical micelles; those with relatively longerPMPCS length (copolymer 3 and 4) form 'pearl chains' coexisting with individual spherical micelles; the ones with longestPMPCS length form 'pearl chains' coexisting with occasionally formed nanofibers. The diameter of all the morphologieswas controlled by the rod length. This gives us a way to govern the self-assembly morphology by altering the length of oneblock in the block copolymer.展开更多
Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization.During the polymerization process,the molecular weight distri...Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ^1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.展开更多
The synthesis of rod-coil diblock copolymers was achieved for the first time by TEMPO-mediated 'living' free radical polymerization of styrene and 2,5-bis [(4-methoxyphenyl)oxycarbonyl] styrene(MPCS). The blo...The synthesis of rod-coil diblock copolymers was achieved for the first time by TEMPO-mediated 'living' free radical polymerization of styrene and 2,5-bis [(4-methoxyphenyl)oxycarbonyl] styrene(MPCS). The block architecture of the two diblock copolymers thus prepared, MPCS-b-St(5400/2400) and MPCS-b-St(10800/8700), was confirmed by GPC, DSC studies and the formation of multimolecular micelles. (Author abstract) 10 Refs.展开更多
The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections (regu- lar triangles, squares, and ellipses) is investigated using a simulated annealing technique. In th...The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections (regu- lar triangles, squares, and ellipses) is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel's cross section. In the case of triangle-shaped cross sections, stacked parallel lamel- lae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end- to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels.展开更多
The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dep...The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dependence of the wall-block interaction and the distance between walls(confinement degree) has been systematically studied,and the effect of repulsive interactions between different monomers is also discussed.It is interesting that multiple novel morphological transitions are observed by changing these factors,and various multilayered sandwich structures are formed in the mixture.Furthermore,the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed.From the simulation,we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer.Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists.This model system can also give a simple way to realize orientational order transition in soft materials through confinement.展开更多
Systematic comparison between computer simulation results and those predicted by Scheutjens-Fleer (SF) self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on...Systematic comparison between computer simulation results and those predicted by Scheutjens-Fleer (SF) self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on attractive surface. It is shown that although SF is a mean-field theory, it can qualitatively describe the adsorption phenomena of diblock copolymers. However, systematic discrepancy between the theory and simulation still exists. The approximations inherited in the mean-field theory such as random mixing inside a layer and the allowance of direct back folding may be responsible to those deviations.展开更多
The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory. In the simulation study, a rich variety of novel morphologie...The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory. In the simulation study, a rich variety of novel morphologies are observed by variations in the strength of the surface field for the diblock copolymers. Different surface-field-induced effects are examined for the diblock copolymers in the arrays with distinct preferential surfaces. It is observed that the majority-block preferential surfaces have more obvious induced effects than those of minority-block preferential surfaces. The strong surface fields exhibit different behaviours from those observed in the weak surface fields, by which the morphologies possess cylindrical symmetries. Results from this research deepen the knowledge of surface-induced effects in a confinement system, which may aid the fabrication of polymer-based na^omaterials.展开更多
The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulation...The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulations. The induction of diversified patterned surfaces on phase separation of symmetric diblock copolymer films in snapshots, density profiles and concentration diagrams of the simulated systems are presented. The phase separations can be controlled by the patterned surfaces. In the meantime, the mean-square end-to-end distance of the confined polymer chains < R(2)> is also discussed. Surface-induced phase separation for diblock copolymers can help us to create novel and controlled nanostructured materials.展开更多
The mechanism for the self-assembly of hollow micelles from rod-coil diblock copolymers is proposed. In a coilselective solvent, the diblock copolymers self-assemble into a layered structure. It is assumed that the ri...The mechanism for the self-assembly of hollow micelles from rod-coil diblock copolymers is proposed. In a coilselective solvent, the diblock copolymers self-assemble into a layered structure. It is assumed that the rigid rods form an elastic shell whose properties are dictated by a bending energy. For a hollow micelle, the coils outside the micelle form a brush, while the coils inside the micelle can be in two different states, a brush or an adsorption layer, corresponding to symmetric or asymmetric configurations, respectively. The total energy density of a hollow micelle is calculated by combining the interfacial energy, elastic bending energy and the stretching energy of the brushes. For the asymmetric configuration with a polymer brush on one side, the competition between the elastic bending energy and the brush stretching energy leads to a finite spontaneous curvature, stabilizing hollow spherical micelles. Comparison of the free energy density for different geometries demonstrates that transitions for the different geometry micelles are controlled by the degree of polymerization of the coils and the length of the rods. These results are in agreement with the experimental results.展开更多
Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles ...Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.展开更多
Well-defined P4VP-b-PBLG diblock polymer composed of poly (4-vinylpyridine) (P4VP) and poly (γ-benzyl-L-glutamate) (PBLG) was synthesized by click reaction with alkyne- and azide-functionalized homopolymers. Besides,...Well-defined P4VP-b-PBLG diblock polymer composed of poly (4-vinylpyridine) (P4VP) and poly (γ-benzyl-L-glutamate) (PBLG) was synthesized by click reaction with alkyne- and azide-functionalized homopolymers. Besides, P4VP blocks were synthesized by copper-mediated atom transfer radical polymerization (ATRP) with a chlorine-containing alkyne bifunctional initiator, and the azido-terminated PBLG homopolymers were synthesized by ring-opening polymerization (ROP) of γ-benzyl-L-glutamate with an amine-containing azide initiator. In addition, the synthesized P4VP-b-PBLG with different block ratios has been characterized by proton nuclear magnetic resonance (1H NMR), Gel permeation chromatograph (GPC) and fourier transform infrated spectroscopy (FT-IR). Then, the self-assembly behaviors of P4VP-b-PBLG have been studied by changing parameters like dripping speed and block ratio. The morphologies of self-assembly of spherical, disk-like and ellipsoid-like shape particles have been observed and analyzed by scanning electron microscopy (SEM). These results have provided guidelines for the design of macromolecular self-assembly.展开更多
Well - defined diblock copolymers Of styrene (St ) and ethylene oxide (EO )have been prepared by sequential living anionic polymerization of the twocomonomers in THF. Diphenyl methyl potassium has been used as initiat...Well - defined diblock copolymers Of styrene (St ) and ethylene oxide (EO )have been prepared by sequential living anionic polymerization of the twocomonomers in THF. Diphenyl methyl potassium has been used as initiator. Theblock copolymers were characterized in detail by methods Of size exclusion chromatography (SEC ) , 1H - Nab, FT - IR, dynamic mechanical analysis(Daal ) and WAXD.展开更多
Aiming at the difficult problem of solving the conformation statistics of complex polymers, this study presents a novel and concise conformation statistics theoretical approach based on Monte Carlo and Neural Network ...Aiming at the difficult problem of solving the conformation statistics of complex polymers, this study presents a novel and concise conformation statistics theoretical approach based on Monte Carlo and Neural Network method. This method offers a new research idea for investigating the conformation statistics of complex polymers, characterized by its simplicity and practicality. It can be applied to more complex topological structure, more higher degree of freedom polymer systems with higher dimensions, theory research on dynamic self-consistent field theory and polymer field theory, as well as the analysis of scattering experimental data. The conformation statistics of complex polymers determine the structure and response properties of the system. Using the new method proposed in this study, taking the semiflexible ring diblock copolymer as an example, Monte Carlo simulation is used to sample this ring conformation to construct the dataset of polymer. The structure factor describing conformation statistics are expressed as continuous functions of structure parameters by neural network supervised learning. This is the innovation of this work. As an application, the structure factors represented by neural networks were introduced into the random phase approximation theory to study the microphase separation of semiflexible ring diblock copolymers. The influence of the ring's topological properties on the phase transition behavior was pointed out.展开更多
The controlled free radical polymerization of styrene and isoprene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125 'C were performed. The obtained poly...The controlled free radical polymerization of styrene and isoprene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125 'C were performed. The obtained polyisoprene and polystyrene homopolymers served as macroinitiators for block copolymerization of isoprene and styrene to synthesize poly- (styrene-b-isoprene) and poly(isoprene-b-styrene) diblock copolymers. Diblock copolymers with well-defined structures as well as controlled and narrow molecular weight distribution were obtained from the lower-mass polystyrene and polyisoprene homopolymers. These copolymers were found to be active as macroinitiators in the synthesis of the poly(styrene-b-isoprene-b-styrene) and poly(isoprene-b-styrene-b-isoprene) triblock copolymers. 1H-NMR spectroscopy and gel permeation chromatography (GPC) were used for the investigation of polymer structure, molecular weight and polydispersity (PD).展开更多
The phase behaviours of diblock copolymers under cylindrical confinement are studied in two-dimensional space by using the self-consistent field theory. Several phase parameters are adjusted to investigate the cylindr...The phase behaviours of diblock copolymers under cylindrical confinement are studied in two-dimensional space by using the self-consistent field theory. Several phase parameters are adjusted to investigate the cylindrical-confinement-induced phase behaviours of diblock copolymers. A series of lamella-cylinder mixture phases, such as the mixture of broken-lamellae and cylinders and the mixture of square-lamellae and cylinders, are observed by varying the phase parameters, in which the behaviours of these mixture phases are discussed in the corresponding phase diagrams. Furthermore, the free energies of these mixture phases are investigated to illustrate their evolution processes. Our results are compared with the available observations from the experiments and simulations respectively, and they are in good agreement and provide an insight into the phase behaviours under cylindrical confinement.展开更多
Four new rod-coil diblock molecules, which had well-defined para-phenylene oligomers (PPP, from biphenyl to quinquephenyl) as rigid segments and poly(ethylene oxide) (PEO, M-w ca. 750) as flexible segments, were synth...Four new rod-coil diblock molecules, which had well-defined para-phenylene oligomers (PPP, from biphenyl to quinquephenyl) as rigid segments and poly(ethylene oxide) (PEO, M-w ca. 750) as flexible segments, were synthesized. The chemical structure and the number of repeating unit in PEO coil and PPP rod were characterized by H-1-NMR and MALDI-TOF mass spectrometry. The diblock oligomers showed good solubility in common organic solvents and aggregated in water as characterized by a blue shift in UV-vis absorption spectra, a red shift in emission spectra, quenching of the fluorescence and formation of the microfibrilla and fractal-like structures. The formation of different supramolecular structures meant that this effort might lead to commercial important highly organized functional materials.展开更多
The diblock copolymers intercalated layered silicate was prepared via a melt dispersion technique. Then the effect of intercalated hybrid as filler on acrylonitrile- butadiene-styrene resin was characterized by X-ray ...The diblock copolymers intercalated layered silicate was prepared via a melt dispersion technique. Then the effect of intercalated hybrid as filler on acrylonitrile- butadiene-styrene resin was characterized by X-ray diffraction, transmission electron microscopy, stress-strain measurements in elongation.展开更多
By mechanism-transformation (anionic --> cationic) poly(styrene-6-2-ethyl-2-oxazoline) diblock copolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene block capped with e...By mechanism-transformation (anionic --> cationic) poly(styrene-6-2-ethyl-2-oxazoline) diblock copolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene block capped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of 2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as H-1-NMR, IR, DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distribution.展开更多
Block copolymers are a class of soft matter that self-assemble to form ordered morphologies on the scale of nanome- ters, making them ideal materials for various applications. These applications directly depend on the...Block copolymers are a class of soft matter that self-assemble to form ordered morphologies on the scale of nanome- ters, making them ideal materials for various applications. These applications directly depend on the shape and size of the self-assembled morphologies, and hence, a high degree of control over the self-assembly is desired. Grafting block copolymer chains onto a substrate to form copolymer brushes is a versatile method to fabricate functional surfaces. Such surfaces demonstrate a response to their environment, i.e., they change their surface topography in response to different external conditions. Furthermore, such surfaces may possess nanoscale patterns, which are important for some applica- tions; however, such patterns may not form with spun-cast films under the same condition. In this review, we summarize the recent progress of the self-assembly of block copolymers grafted onto a flat substrate. We mainly concentrate on the self-assembled morphologies of end-grafted AB dibloek eopolymers, junction p0int-grafted AB diblock copolymers (i.e., Y-shaped brushes), and end-grafted ABA triblock copolymers. Special emphasis is placed on theoretical and simulation progress.展开更多
Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and sy...Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration (RMSGR) and end-end distance (RMSED) increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.展开更多
基金The financial support of the National Natural Science Foundation of China (Grants. 29992590-4 and 20134010)
文摘The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature, was studied. Therod-coil copolymers, which have the same PS length but different PMPCS length, were synthesized by 2,2,6,6-tetramethyl-I-piperidinyloxy (TEMPO) mediated living free radical polymerization. The influence of the rod length on the self-assemblymorphology was studied by transmission electron microscopy (TEM). At a concentration of 2.0 mg/mL, those copolymerswith relatively shorter PMPCS length (copolymers 1 and 2) form individual spherical micelles; those with relatively longerPMPCS length (copolymer 3 and 4) form 'pearl chains' coexisting with individual spherical micelles; the ones with longestPMPCS length form 'pearl chains' coexisting with occasionally formed nanofibers. The diameter of all the morphologieswas controlled by the rod length. This gives us a way to govern the self-assembly morphology by altering the length of oneblock in the block copolymer.
基金supported by Major Program of National Natural Science Foundation of China(No. 20836007)National Natural Science Foundation of China(No.20806067).
文摘Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ^1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.
基金This project was supported by the Foundation of Peking University for Young Scientist and the National Natural Science Foundation of China.
文摘The synthesis of rod-coil diblock copolymers was achieved for the first time by TEMPO-mediated 'living' free radical polymerization of styrene and 2,5-bis [(4-methoxyphenyl)oxycarbonyl] styrene(MPCS). The block architecture of the two diblock copolymers thus prepared, MPCS-b-St(5400/2400) and MPCS-b-St(10800/8700), was confirmed by GPC, DSC studies and the formation of multimolecular micelles. (Author abstract) 10 Refs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11204215,51302187,20990234,20925414,21204040,and 91227121)the Natural Science Foundation of Tianjin City,China(Grant Nos.12JCYBJC32500 and 14JCZDJC32100)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT)(Grant No.IRT1257)the 111 Project.A.C.Shi gratefully acknowledges the supports from the Natural Sciences and Engineering Research Council(NSERC)of Canada
文摘The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections (regu- lar triangles, squares, and ellipses) is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel's cross section. In the case of triangle-shaped cross sections, stacked parallel lamel- lae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end- to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels.
基金Project supported by the National Natural Science Foundation of China (Grant No. 20673070)the Natural Science Foundation of Shanxi Province (Grant No. 2007011055)+1 种基金the Natural Science Foundation for Young Scientists of Shanxi Province (Grant No. 2011021008-1)the Soft Science Program of Shanxi Province (Grant No. 2011041015-01)
文摘The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dependence of the wall-block interaction and the distance between walls(confinement degree) has been systematically studied,and the effect of repulsive interactions between different monomers is also discussed.It is interesting that multiple novel morphological transitions are observed by changing these factors,and various multilayered sandwich structures are formed in the mixture.Furthermore,the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed.From the simulation,we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer.Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists.This model system can also give a simple way to realize orientational order transition in soft materials through confinement.
基金Supported by the National Natural Science Foundation of China(No. 20025618)the Doctoral Research Foundation by Ministry of Education of China (No.1999025103) and the Dawn Project of Education Committee of Shanghai.
文摘Systematic comparison between computer simulation results and those predicted by Scheutjens-Fleer (SF) self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on attractive surface. It is shown that although SF is a mean-field theory, it can qualitatively describe the adsorption phenomena of diblock copolymers. However, systematic discrepancy between the theory and simulation still exists. The approximations inherited in the mean-field theory such as random mixing inside a layer and the allowance of direct back folding may be responsible to those deviations.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.20374050,20934004,21074096,50773072,and 90403022)the Outstanding Youth Fund of China (Grant No.20525416)+3 种基金the National Basic Research Program of China(Grant No.2005CB623800)Program for New Century Excellent Talents in University (Grant No.NCET-05-0538)the Natural Science Foundation of Zhejiang Province (Grant Nos.Y4090174 and Y6100033)the Science Technology Development Plan of Wenzhou City,China (Grant No.H20080041)
文摘The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory. In the simulation study, a rich variety of novel morphologies are observed by variations in the strength of the surface field for the diblock copolymers. Different surface-field-induced effects are examined for the diblock copolymers in the arrays with distinct preferential surfaces. It is observed that the majority-block preferential surfaces have more obvious induced effects than those of minority-block preferential surfaces. The strong surface fields exhibit different behaviours from those observed in the weak surface fields, by which the morphologies possess cylindrical symmetries. Results from this research deepen the knowledge of surface-induced effects in a confinement system, which may aid the fabrication of polymer-based na^omaterials.
基金supported by the National Natural Science Foundation of China(Nos.20574052,20774066)the Program for New Century Excellent Talents in Universities(No.NCET-05-0538).
文摘The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulations. The induction of diversified patterned surfaces on phase separation of symmetric diblock copolymer films in snapshots, density profiles and concentration diagrams of the simulated systems are presented. The phase separations can be controlled by the patterned surfaces. In the meantime, the mean-square end-to-end distance of the confined polymer chains < R(2)> is also discussed. Surface-induced phase separation for diblock copolymers can help us to create novel and controlled nanostructured materials.
文摘The mechanism for the self-assembly of hollow micelles from rod-coil diblock copolymers is proposed. In a coilselective solvent, the diblock copolymers self-assemble into a layered structure. It is assumed that the rigid rods form an elastic shell whose properties are dictated by a bending energy. For a hollow micelle, the coils outside the micelle form a brush, while the coils inside the micelle can be in two different states, a brush or an adsorption layer, corresponding to symmetric or asymmetric configurations, respectively. The total energy density of a hollow micelle is calculated by combining the interfacial energy, elastic bending energy and the stretching energy of the brushes. For the asymmetric configuration with a polymer brush on one side, the competition between the elastic bending energy and the brush stretching energy leads to a finite spontaneous curvature, stabilizing hollow spherical micelles. Comparison of the free energy density for different geometries demonstrates that transitions for the different geometry micelles are controlled by the degree of polymerization of the coils and the length of the rods. These results are in agreement with the experimental results.
文摘Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.
文摘Well-defined P4VP-b-PBLG diblock polymer composed of poly (4-vinylpyridine) (P4VP) and poly (γ-benzyl-L-glutamate) (PBLG) was synthesized by click reaction with alkyne- and azide-functionalized homopolymers. Besides, P4VP blocks were synthesized by copper-mediated atom transfer radical polymerization (ATRP) with a chlorine-containing alkyne bifunctional initiator, and the azido-terminated PBLG homopolymers were synthesized by ring-opening polymerization (ROP) of γ-benzyl-L-glutamate with an amine-containing azide initiator. In addition, the synthesized P4VP-b-PBLG with different block ratios has been characterized by proton nuclear magnetic resonance (1H NMR), Gel permeation chromatograph (GPC) and fourier transform infrated spectroscopy (FT-IR). Then, the self-assembly behaviors of P4VP-b-PBLG have been studied by changing parameters like dripping speed and block ratio. The morphologies of self-assembly of spherical, disk-like and ellipsoid-like shape particles have been observed and analyzed by scanning electron microscopy (SEM). These results have provided guidelines for the design of macromolecular self-assembly.
文摘Well - defined diblock copolymers Of styrene (St ) and ethylene oxide (EO )have been prepared by sequential living anionic polymerization of the twocomonomers in THF. Diphenyl methyl potassium has been used as initiator. Theblock copolymers were characterized in detail by methods Of size exclusion chromatography (SEC ) , 1H - Nab, FT - IR, dynamic mechanical analysis(Daal ) and WAXD.
基金financially supported by the National Natural Science Foundation of China (No. 22173004)。
文摘Aiming at the difficult problem of solving the conformation statistics of complex polymers, this study presents a novel and concise conformation statistics theoretical approach based on Monte Carlo and Neural Network method. This method offers a new research idea for investigating the conformation statistics of complex polymers, characterized by its simplicity and practicality. It can be applied to more complex topological structure, more higher degree of freedom polymer systems with higher dimensions, theory research on dynamic self-consistent field theory and polymer field theory, as well as the analysis of scattering experimental data. The conformation statistics of complex polymers determine the structure and response properties of the system. Using the new method proposed in this study, taking the semiflexible ring diblock copolymer as an example, Monte Carlo simulation is used to sample this ring conformation to construct the dataset of polymer. The structure factor describing conformation statistics are expressed as continuous functions of structure parameters by neural network supervised learning. This is the innovation of this work. As an application, the structure factors represented by neural networks were introduced into the random phase approximation theory to study the microphase separation of semiflexible ring diblock copolymers. The influence of the ring's topological properties on the phase transition behavior was pointed out.
文摘The controlled free radical polymerization of styrene and isoprene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125 'C were performed. The obtained polyisoprene and polystyrene homopolymers served as macroinitiators for block copolymerization of isoprene and styrene to synthesize poly- (styrene-b-isoprene) and poly(isoprene-b-styrene) diblock copolymers. Diblock copolymers with well-defined structures as well as controlled and narrow molecular weight distribution were obtained from the lower-mass polystyrene and polyisoprene homopolymers. These copolymers were found to be active as macroinitiators in the synthesis of the poly(styrene-b-isoprene-b-styrene) and poly(isoprene-b-styrene-b-isoprene) triblock copolymers. 1H-NMR spectroscopy and gel permeation chromatography (GPC) were used for the investigation of polymer structure, molecular weight and polydispersity (PD).
基金supported by the National Natural Science Foundation of China (Grant Nos. 20574052 and 20774066)the Program for New Century Excellent Talents in University, China (Grant No. NCET-05-0538)the Natural Science Foundation of Zhejiang Province, China (Grant Nos. R404047, Y4090174, and Y405553)
文摘The phase behaviours of diblock copolymers under cylindrical confinement are studied in two-dimensional space by using the self-consistent field theory. Several phase parameters are adjusted to investigate the cylindrical-confinement-induced phase behaviours of diblock copolymers. A series of lamella-cylinder mixture phases, such as the mixture of broken-lamellae and cylinders and the mixture of square-lamellae and cylinders, are observed by varying the phase parameters, in which the behaviours of these mixture phases are discussed in the corresponding phase diagrams. Furthermore, the free energies of these mixture phases are investigated to illustrate their evolution processes. Our results are compared with the available observations from the experiments and simulations respectively, and they are in good agreement and provide an insight into the phase behaviours under cylindrical confinement.
基金This work has been supported by the National Natural Science Foundation of China (Grants 29874003 and 29992590-4), the Research Fund for Doctoral Program of Higher Education (Grant 99000136) and the Teaching and Research Award Fund for Outstanding Young
文摘Four new rod-coil diblock molecules, which had well-defined para-phenylene oligomers (PPP, from biphenyl to quinquephenyl) as rigid segments and poly(ethylene oxide) (PEO, M-w ca. 750) as flexible segments, were synthesized. The chemical structure and the number of repeating unit in PEO coil and PPP rod were characterized by H-1-NMR and MALDI-TOF mass spectrometry. The diblock oligomers showed good solubility in common organic solvents and aggregated in water as characterized by a blue shift in UV-vis absorption spectra, a red shift in emission spectra, quenching of the fluorescence and formation of the microfibrilla and fractal-like structures. The formation of different supramolecular structures meant that this effort might lead to commercial important highly organized functional materials.
基金Chinese Education Ministry Foundation for Nankai University and Tianjin University Joint Academy
文摘The diblock copolymers intercalated layered silicate was prepared via a melt dispersion technique. Then the effect of intercalated hybrid as filler on acrylonitrile- butadiene-styrene resin was characterized by X-ray diffraction, transmission electron microscopy, stress-strain measurements in elongation.
基金Supported by the National Natural Science Foundation of China(Grant no.59503002)and Polymer Physics Laboratory of Changchun Institute of Applied Chemistry,Chinese Academy of Sciences
文摘By mechanism-transformation (anionic --> cationic) poly(styrene-6-2-ethyl-2-oxazoline) diblock copolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene block capped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of 2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as H-1-NMR, IR, DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distribution.
基金supported by the National Natural Science Foundation of China(Grant Nos.20990234,20925414,and 91227121)the Program for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT1257)+1 种基金the Programme of Introducing Talents of Discipline to Universities,Chinaby the Tianhe No.1,China
文摘Block copolymers are a class of soft matter that self-assemble to form ordered morphologies on the scale of nanome- ters, making them ideal materials for various applications. These applications directly depend on the shape and size of the self-assembled morphologies, and hence, a high degree of control over the self-assembly is desired. Grafting block copolymer chains onto a substrate to form copolymer brushes is a versatile method to fabricate functional surfaces. Such surfaces demonstrate a response to their environment, i.e., they change their surface topography in response to different external conditions. Furthermore, such surfaces may possess nanoscale patterns, which are important for some applica- tions; however, such patterns may not form with spun-cast films under the same condition. In this review, we summarize the recent progress of the self-assembly of block copolymers grafted onto a flat substrate. We mainly concentrate on the self-assembled morphologies of end-grafted AB dibloek eopolymers, junction p0int-grafted AB diblock copolymers (i.e., Y-shaped brushes), and end-grafted ABA triblock copolymers. Special emphasis is placed on theoretical and simulation progress.
基金Project supported by the Shanghai Leading Academic Discipline Project(Grant No.S30109)the Research and Development Special Fundation of Excellent Young Teachers of Universities in Shanghai,the Developmental Foundation of Scientific Technology of Shanghai Universitythe Innovation Foundation of Shanghai University
文摘Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length (MSBL) and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration (RMSGR) and end-end distance (RMSED) increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.