Co-reporter:Lin Xu, Ashutosh Sharma, Sang Woo Joo, Hui Liu, and Tongfei Shi
Langmuir 2014 Volume 30(Issue 49) pp:14808-14816
Publication Date(Web):2017-2-22
DOI:10.1021/la503319w
We investigate the control of pattern size and kinetics in spontaneous dewetting of thin polymer films (polystyrene) that are stable to thermal annealing by annealing in a poor solvent (acetone)/nonsolvent (ethanol or n-hexane) liquid mixture. Dewetting occurs by the formation and growth of circular holes that coalesce to form droplets. The influence of the nature and the volume fraction of the nonsolvents on the contact angle of polymer droplets, number density of holes, and the kinetics of holes formation and growth is studied. Addition of ethanol greatly increases the hole density and slows down the kinetics substantially, while affecting only a small change in wettability. n-Hexane addition shows an interesting nonmonotonic response in decreasing the hole density and contact angle in the volume fraction range of 0–0.3 but an opposite effect beyond that. Although the two nonsolvents chosen cannot by themselves induce dewetting, their relative affinity for the solid substrate vis-à-vis acetone can strongly influence the observed dewetting scenarios that are not understood by the existing theoretical considerations. n-Hexane, for example, has great affinity for silicon substrate. In addition to the changes in wettability, viscosity, and film interfacial tension engendered by the nonsolvents, the possibility of the formation of adsorbed liquid layers at the substrate–polymer interface, which can modify the interfacial friction and slippage, needs to be considered.
Co-reporter:Xiaozheng Duan, Ran Zhang, Yunqi Li, Tongfei Shi, Lijia An, and Qingrong Huang
The Journal of Physical Chemistry B 2013 Volume 117(Issue 4) pp:989-1002
Publication Date(Web):January 4, 2013
DOI:10.1021/jp310017j
Monte Carlo simulations are employed to investigate the adsorption of a flexible linear cationic polyelectrolyte onto a fluid mixed membrane containing neutral (phosphatidyl-choline, PC), multivalent (phosphatidylinositol, PIP2), and monovalent (phosphatidylserine, PS) anionic lipids. We systematically study the effect of chain length and charge density of the polyelectrolyte, the solution ionic strength, as well as the membrane compositions on the conformational and interfacial properties of the model system. In particular, we explore (i) the adsorption/desorption limit, (ii) the interfacial structure variations of the adsorbing polyelectrolyte and the lipid membrane, and (iii) the overcharging of the membrane. Polyelectrolyte adsorbs on the membrane when anionic lipid demixing entropy loss and polyelectrolyte flexibility loss due to adsorption are dominated by electrostatic attraction between polyelectrolyte and anionic lipids on the membrane. Polyelectrolytes with longer chain length and higher charge density can adsorb on the membrane with increased anionic lipid density under a higher critical ionic concentration. Below the critical ionic concentration, the adsorption extent increases with the charge density and chain length of the polyelectrolyte and decreases with the ionic strength of the solution. The diffusing anionic lipids prohibit the polyelectrolyte chain from forming too long tails. The adsorbing polyelectrolyte with long chain length and high charge density can overcharge a membrane with low charge density, and conversely, the membrane charge inversion forces the polyelectrolyte chain to form extended loops and tails in the solution.
Co-reporter:Ran Zhang, Xiaozheng Duan, Tongfei Shi, Hongfei Li, Lijia An, and Qingrong Huang
Macromolecules 2012 Volume 45(Issue 15) pp:6201-6209
Publication Date(Web):July 27, 2012
DOI:10.1021/ma300663p
The gelation behavior of polypeptide–polyelectrolyte–polypeptide in solution is investigated by Monte Carlo techniques. It is found that different hydrogen bonding styles, parallel and antiparallel, provide a major influence on the sol–gel transition and the chain conformation. The antiparallel hydrogen bonding style favors the bridge conformation, while loop conformation has less structural limitation with parallel bonding. However, in the parallel style, polyelectrolyte blocks are aligned in the same side of β-sheets, which induces more steric constrains and the electrostatic repulsion. Consequently, compared with the parallel bonding style, the sol–gel transition of antiparallel style occurs at lower hydrogen bonding energy and the dihedral angle θ of antiparallel β-sheets is a little higher. The increase of charging fraction of polyelectrolyte blocks prompts the sol–gel transition of both bonding styles but causes an impact on the number of hydrogen bond and the dihedral angle, indicating a decrease in the structure integrity.
Co-reporter:Ran Zhang, Tongfei Shi, Lijia An, and Qingrong Huang
Macromolecules 2012 Volume 45(Issue 1) pp:555-562
Publication Date(Web):December 22, 2011
DOI:10.1021/ma201872e
Using Monte Carlo simulation techniques, we focus on the physical gelation behavior and conformation change under the existence of additional monovalent salt, which provides screening to the electrostatic interaction of charged telechelic polyelectrolyte chains and causes new balance between hydrophobic interaction of end groups and electrostatic interaction originated from the polyelectrolyte blocks. For the electrostatic interaction dominated system, the screening effects will decrease the electrostatic repulsion between small sized clusters and enable the further aggregation of TP chains, resulting in prompting the sol–gel transition progress; for the short-range attraction dominated system, the screening effects present a complicated phenomenon, which includes the prompting effect at the beginning of sol–gel transition and a hindering effect when the gelation progress is close to an end.
Co-reporter:Jichun You, Yonggui Liao, Yongfeng Men, Tongfei Shi, Lijia An, and Xiuhong Li
Macromolecules 2011 Volume 44(Issue 13) pp:5318-5325
Publication Date(Web):June 10, 2011
DOI:10.1021/ma200082m
Using in situ atomic force microscopy (AFM) and grazing incidence ultrasmall-angle X-ray scattering (GIUSAX), the composition dependence of phase separation, dewetting, and interplay between them in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] ultrathin films (∼1Rg, radius of gyration) on silicon oxide substrate was investigated. It was found that phase behaviors depended crucially on the composition in blend. First, dewetting morphologies in SAN50 and SAN70 were still under the control of Uq0/E, which was introduced in our previous work [ Polymer 2009, 50, 4456] to distinguish different dewetting pathways. Here, Uq0 and E described the initial amplitude of the surface undulation and original thickness of film, respectively; second, composition produced significant influences on its gradient in composition fluctuation, resulting in the accelerated (or suppressed) dewetting; last, this kind of acceleration or suppression affected the following interplay between phase separation and dewetting so much. Using two samples of “dewetting/wetting–phase separation” and “wetting–dewetting/phase separation” with different components, we discussed the interplay mechanism of them in detail. In conclusion, our results indicate that dewetting, phase separation, and the following interplay between them are sensitive to composition in blend. Furthermore, composition gradient plays an important role in them.
Co-reporter:Lin Xu, Günter Reiter, Tongfei Shi and Lijia An
Langmuir 2010 Volume 26(Issue 10) pp:7270-7276
Publication Date(Web):February 9, 2010
DOI:10.1021/la904420d
We investigated the dependence of the dewetting velocity of a thin, low-viscosity polystyrene (PS) top film on a poly(methyl methacrylate) (PMMA) double layer consisting of a low-viscosity underlayer of thickness hL coated with a high-viscosity middle layer of thickness hM. The addition of the liquid underlayer generated complex nonmonotonic behavior of the dewetting velocity as a function of increasing hM. In particular, we observed an acceleration of dewetting for an intermediate range of hM. This phenomenon has been interpreted by a combination deformation of the middle elastic layer and a concurrent change in the contact angle. On one hand, deformation led to the formation of a trench that dissipated energy during its movement through the liquid underlayer and thus caused a slowing down of dewetting. However, with an increase in the thickness of the elastic middle layer, the size of the trench decreased and its influence on the dewetting velocity also decreased. On the other hand, the deformation of the elastic layer also led to an increase in the contact angle. This increase in the driving capillary forces caused an increase in the dewetting velocity.
Co-reporter:Jichun You, Yonggui Liao, Yongfeng Men, Tongfei Shi, and Lijia An
Langmuir 2010 Volume 26(Issue 18) pp:14530-14534
Publication Date(Web):August 20, 2010
DOI:10.1021/la102680b
Film thickness dependence of complex behaviors coupled by phase separation and dewetting in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on silicon oxide substrate at 175 °C was investigated by grazing incidence ultrasmall-angle X-ray scattering (GIUSAX) and in situ atomic force microscopy (AFM). It was found that the dewetting pathway was under the control of the parameter Uq0/E, which described the initial amplitude of the surface undulation and original thickness of film, respectively. Furthermore, our results showed that interplay between phase separation and dewetting depended crucially on film thickness. Three mechanisms including dewetting−phase separation/wetting, dewetting/wetting−phase separation, and phase separation/wetting−pseudodewetting were discussed in detail. In conclusion, it is relative rates of phase separation and dewetting that dominate the interplay between them.
Co-reporter:Ying-ying Pan;Xi-fei Yu;Tong-fei Shi 石彤非
Chinese Journal of Polymer Science 2010 Volume 28( Issue 3) pp:347-355
Publication Date(Web):2010/05/01
DOI:10.1007/s10118-010-9025-x
A series of H-shaped (PS)2PEG(PS)2 block copolymers with different PS chain lengths were prepared. The influence of different confinements active on the crystallization and self-nucleation (SN) behavior of the PEG blocks was investigated by differential scanning calorimetry (DSC). When the content of the crystalline block was high, a classical SN behavior was obtained. The block copolymer with PEG content of 49% (by weight) showed a classical SN behavior with a narrow self-nucleation domain and had bimodal crystallization exotherms. When the PEG dispersed as separated microdomains in the block copolymer, the self-nucleation domain disappeared and only annealing was observed.
Co-reporter:Ran Zhang, Tongfei Shi, Lijia An, Zhaoyan Sun and Zhen Tong
The Journal of Physical Chemistry B 2010 Volume 114(Issue 10) pp:3449-3456
Publication Date(Web):February 22, 2010
DOI:10.1021/jp9092404
A special kind of associating polyelectrolytes, telechelic polyelectrolytes, composed of a flexible linear polyelectrolyte and short hydrophobic blocks at both ends, is investigated by means of Monte Carlo simulations in aqueous media. It is found that the interplay between hydrophobic attraction and the long-range electrostatic interaction as well as the counterion distribution exerts a major influence on the chain conformations (two basic conformations: loop and nonloop), association behavior (loop association contributes to loop conformation; free, dangling, and bridge chains contribute to nonloop conformations), and the forming of clusters. At a concentration close to the overlapping concentration ϕ*, the clusters are found to be further connected by bridge chains under strong hydrophobic interaction, forming a 3D network. In addition, increasing Coulombic interaction strength is in favor of the formation of a gel network. With increasing Coulombic interaction strength, first chains tend to extend and then tend to collapse due to the screening originating from the counterion condensation layer.
Co-reporter:Jianhui Song, Tongfei Shi, Jizhong Chen, and Lijia An
The Journal of Physical Chemistry B 2010 Volume 114(Issue 49) pp:16318-16328
Publication Date(Web):November 17, 2010
DOI:10.1021/jp102863w
Self-assembly of symmetric ABC three-arm star copolymers confined in cylindrical nanopores is investigated by means of a lattice Monte Carlo simulation method. The dependence of morphologies on the degree of confinement and preference of pore surface is studied systematically. For the symmetric ABC three-arm star copolymers which form polygonal cylinder structures with periodic spacing L0 in bulk, various novel structures are observed inside the nanopores. In the nanopores with a neutral surface, we find a minimum diameter value (Dmin ≈ L0) under which helical arranged droplets are formed; otherwise, parallel polygonal cylinder structures are identified. By adjusting the preference between component A and the pore surfaces, a number of novel structures such as A cylinder + BC single-strand helix and complex multilayer double helices are identified. Additionally, the confinement-induced morphology transition is interpreted by the frustration parameter D/L0.
Co-reporter:Lin Xu, Xifei Yu, Tongfei Shi and Lijia An
Soft Matter 2009 vol. 5(Issue 10) pp:2109-2116
Publication Date(Web):16 Apr 2009
DOI:10.1039/B818824F
The mechanism of inhibition of polymer film dewetting is investigated by adding a star comb-like polymer, four-arm P(S-ran-VB-g-PMMA), to PS film and PMMA film on different substrates. It is found that the mechanism of inhibition of polymer film dewetting is kinetic in nature, and is related to the miscibility between the additional compound and the polymer film. On addition to the miscible system [four-arm P(S-ran-VB-g-PMMA) and PMMA], the star comb-like polymers can increase the resistant force of dewetting with hole growth and inhibit the dewetting process of the thin polymer film by enrichment in the rim. To the immiscible system [four-arm P(S-ran-VB-g-PMMA) and PS], firstly the four-arm P(S-ran-VB-g-PMMA) enriches the solid substrate and forms nanodroplets in the process of spin-coating, and then PS film dewets on these nanodroplets; however, the star comb-like polymer can inhibit the dewetting of the polymer film only when the contact angle θ of the polymer on the additional four-arm P(S-ran-VB-g-PMMA) is smaller than that of the polymer on the substrate.
Co-reporter:Jichun You, Shanshan Hu, Yonggui Liao, Kaixu Song, Yongfeng Men, Tongfei Shi, Lijia An
Polymer 2009 50(19) pp: 4745-4752
Publication Date(Web):
DOI:10.1016/j.polymer.2009.08.002
Co-reporter:Yonggui Liao;Zhaoyan Sun;Lijia An;Zhaohui Su
Macromolecular Rapid Communications 2006 Volume 27(Issue 5) pp:351-355
Publication Date(Web):16 FEB 2006
DOI:10.1002/marc.200500736
Summary: Dynamics of dewetting and phase separation in ultrathin films (thickness is ca. one radius of gyration, ≈1 Rg) of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) blends on Si substrate has been studied by in situ atomic force microscopy (AFM). In the miscible region, a “spinodal-like” dewetting driven by a composition fluctuation recently predicted by Wensink and Jérôme (Langmuir2002, 18, 413) occurs. In the two-phase region, the dewetting of the whole film is followed by phase separation in the droplets, coupling with the wetting of the substrate by the PMMA extracted by the strong attractive interaction between them.
Co-reporter:Zhihong Nie;Zhaoyan Sun;Lijia An;Zhaohui Su
Macromolecular Theory and Simulations 2005 Volume 14(Issue 8) pp:463-473
Publication Date(Web):28 SEP 2005
DOI:10.1002/mats.200500042
Summary: The behavior of symmetric AnB2nAn triblock copolymer films confined between two hard neutral walls was explored by Monte Carlo simulation. The thicknesses of the films were between ≈1Rg0 and ≈7Rg0, where Rg0 is the unperturbed radius of gyration in the bulk. The confinement leads to a lamellar structure normal to the wall and the order-disorder transition (ODT) temperature was found to be a function of film thickness. When the film thickness (D) was less than a critical value, DC, which is between 3Rg0 and 4Rg0, the ODT temperature (T*ODT) reduced by chain length N (T*ODT/N) decreased with decreasing film thickness. However, T*ODT/N was nearly independent of the film thickness when it was greater than DC. In the case of strong confinement (D < DC), the B block shrinks along the direction perpendicular to the wall and stretches along the direction parallel to the wall with decreasing film thickness, and the volume occupied by the B block shrinks. Under weak confinement conditions (D > DC), the volume of the B block is nearly independent of film thickness. The conformations of the B block in the disordered state are quite different from those in the lamellae. If the film is thick enough, the volume of the B block approaches its value in the unperturbed state, regardless of the morphology. When temperature decreases, the B block stretches in the direction perpendicular to the A/B interface and shrinks in the other two directions. In addition, decreasing the temperature leads to the chains adopting two main extreme conformations, coiling or stretching as much as they can. The scaling behavior of the fraction of bridge chains vs. the temperature obtained in the weak segregation limit was different from that predicted in the strong segregation limit.
Co-reporter:Zhihong Nie;Zhaohui Su;Zhaoyan Sun;Lijia An
Macromolecular Theory and Simulations 2005 Volume 14(Issue 8) pp:
Publication Date(Web):17 OCT 2005
DOI:10.1002/mats.200590014
