Co-reporter:Fuguang Tang, Peite Bao, and Zhaohui Su
Analytical Chemistry 2016 Volume 88(Issue 9) pp:4926
Publication Date(Web):April 14, 2016
DOI:10.1021/acs.analchem.6b00798
In this paper, compositions of nanodomains in a commercial high-impact polypropylene (HIPP) were investigated by an atomic force microscopy-infrared (AFM-IR) technique. An AFM-IR quantitative analysis method was established for the first time, which was then employed to analyze the polyethylene content in the nanoscopic domains of the rubber particles dispersed in the polypropylene matrix. It was found that the polyethylene content in the matrix was close to zero and was high in the rubbery intermediate layers, both as expected. However, the major component of the rigid cores of the rubber particles was found to be polypropylene rather than polyethylene, contrary to what was previously believed. The finding provides new insight into the complicated structure of HIPPs, and the AFM-IR quantitative method reported here offers a useful tool for assessing compositions of nanoscopic domains in complex polymeric systems.
Co-reporter:Jingjing Wei, David A. Hoagland, Guangyu Zhang, and Zhaohui Su
Macromolecules 2016 Volume 49(Issue 5) pp:1790-1797
Publication Date(Web):February 19, 2016
DOI:10.1021/acs.macromol.5b02151
When exposed to divalent counterion solutions, polyelectrolyte multilayer (PEM) films of poly(diallyldimethylammonium chloride) and sodium poly(styrenesulfonate) (NaPSS) prepared in the presence of monovalent salt, or equilibrated with such a salt, are physically cross-linked by divalent counterion incorporation, altering PEM properties significantly. The rapid cross-linking was monitored by the quartz crystal microbalance with dissipation (QCM-D) method, which finds PEM deswelling and rigidification after exposures to a low concentration of Cu(NO3)2; at higher concentration, deswelling is countered by increased PEM uptake of the salt, which disrupts polyelectrolyte–polyelectrolyte ion pairs. Divalent ion incorporation into PEMs has the character of ion exchange, and incorporated divalent ions are quickly and completely removed when presented with monovalent salt solution but not with water. While counterion cross-linking extends across the bulk of the PEM, the fraction of exchanged counterions remains low. Entropically driven binding of divalent ions to NaPSS in solution was studied for Cu(NO3)2 and other divalent nitrate salts by isothermal titration microcalorimetry and dynamic light scattering to support the QCM-D conclusions.
Co-reporter:Longbiao Li;Guangyu Zhang ; Zhaohui Su
Angewandte Chemie International Edition 2016 Volume 55( Issue 31) pp:9093-9096
Publication Date(Web):
DOI:10.1002/anie.201604671
Abstract
While of immense scientific interest, superhydrophilic surfaces are usually difficult to prepare, and preparation methods are typically substrate specific. Herein, a one-step coating method is described that can endow superhydrophilicity to a variety of substrates, both inorganic and organic, using the coordination complexes of natural phytic acid and FeIII ions. Coating deposition occurs in minutes, and coatings are ultrathin, colorless, and transparent. Superhydrophilicity is attributed, in part, to the high density of phosphonic acid groups. The ease, rapidness, and mildness of the assembly process, which is also cost-effective and environmental-friendly, points towards potential applications, such as self-cleaning, oil/water separation, antifogging.
Co-reporter:Longbiao Li;Guangyu Zhang ; Zhaohui Su
Angewandte Chemie 2016 Volume 128( Issue 31) pp:9239-9242
Publication Date(Web):
DOI:10.1002/ange.201604671
Abstract
While of immense scientific interest, superhydrophilic surfaces are usually difficult to prepare, and preparation methods are typically substrate specific. Herein, a one-step coating method is described that can endow superhydrophilicity to a variety of substrates, both inorganic and organic, using the coordination complexes of natural phytic acid and FeIII ions. Coating deposition occurs in minutes, and coatings are ultrathin, colorless, and transparent. Superhydrophilicity is attributed, in part, to the high density of phosphonic acid groups. The ease, rapidness, and mildness of the assembly process, which is also cost-effective and environmental-friendly, points towards potential applications, such as self-cleaning, oil/water separation, antifogging.
Co-reporter:Mei Su, Lulu Wang, Guangyu Zhang, Yan Huang and Zhaohui Su
RSC Advances 2015 vol. 5(Issue 6) pp:4350-4354
Publication Date(Web):08 Dec 2014
DOI:10.1039/C4RA14157A
In this report, we show that the structure of an amphiphilic block copolymer assembled through the emulsion and solvent evaporation method can be regulated by tuning the interfacial tension with a third solvent. Microspheres were obtained when a poly(ethylene oxide)-block-polystyrene copolymer was self-assembled by emulsification of its chloroform solution in water. Addition of water-miscible tetrahydrofuran or N,N-dimethylformamide into the aqueous phase by 20 vol% was shown to reduce the interfacial tension between chloroform and water significantly, and strings of vesicles became the dominant structure. Addition of ethanol by 15, 50 and 100 vol% was found to produce strings of vesicles, cylinders and microspheres, respectively. Introduction of cyclohexane, a hydrocarbon solvent, into the organic phase of 1,2-dichloroethane increased the interfacial tension with the aqueous phase, and vesicles were observed instead of the strings of spheres obtained previously. The different assembled structures are discussed in terms of interfacial curvature driven by variation in the interfacial tension.
Co-reporter:Bodong Zhang, David A. Hoagland, and Zhaohui Su
The Journal of Physical Chemistry B 2015 Volume 119(Issue 8) pp:3603-3607
Publication Date(Web):February 3, 2015
DOI:10.1021/jp5128354
Uptake of salts by insoluble polyelectrolyte complexes (PECs) leads to plasticization, and here it is shown that ionic liquids (ILs) are more effective plasticizers than simple organic salts such as NaCl. The PEC uptake of IL cation was monitored by solution 1H NMR, and the mechanical impacts of plasticization were tracked by dynamic mechanical analysis (DMA). PECs prepared with polystyrene sulfonate (PSS) and poly(diallyldimethylammonium chloride) (PDDA) under charge stoichiometric conditions were immersed in aqueous solutions of 1-butyl-3-methylimidazolium chloride [BMIM][Cl] to cause IL uptake, which could be controlled by the solution’s IL concentration: higher concentration leads to higher uptake which leads to greater plasticization. The effectiveness of plasticization was assessed through the position and height of a DMA tan(δ) peak ascribed to a glassy-to-rubbery PEC transition. Consistent with greater PEC uptake, isothermal titration calorimetry demonstrated that solution binding by PSS of [BMIM]+ was much stronger than binding of Na+.
Co-reporter:Guangyu Zhang, Meng Li, Bodong Zhang, Yan Huang and Zhaohui Su
Journal of Materials Chemistry A 2014 vol. 2(Issue 37) pp:15284-15287
Publication Date(Web):28 Jul 2014
DOI:10.1039/C4TA03034F
We report a switchable mesh for oil–water separation that allows handling of various oil–water mixtures in one single device. The mesh operates in oil-removing mode to permeate typical oils in oil–water mixtures, and can rapidly switch to water-removing mode to permeate water and separate viscous and sticky oils from the mixture, both with high separation efficiency.
Co-reporter:Guangyu Zhang, Xin Zhang, Meng Li, and Zhaohui Su
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 3) pp:1729
Publication Date(Web):January 13, 2014
DOI:10.1021/am404681y
A strategy combining polyelectrolyte multilayer (PEM) deposition and counterion exchange was developed to fabricate wettability gradient surfaces on rough aluminum with wetting characters continuously varied from superoleophilic to superoleophobic. Counterion exchange kinetics was adopted as a means to tailor the surface chemical composition spatially, with the gradient ultimately reflecting position-dependent immersion time during the dipping of substrate in salt solution. Wettability depended on the identity and concentration of the counterion in the outermost PEM layer. Gradients could be erased and rewritten through the exchange of counterions, and the gradient’s wetting character was evaluated by measuring both water and oil contact angles. The surface chemical composition gradient was further investigated by X-ray photoelectron spectroscopy.Keywords: counterion; gradient; polyelectrolyte multilayers; superoleophobicity; surface; wettability;
Co-reporter:Jingjing Wei, Lixia Ren, Chuanbing Tang and Zhaohui Su
Polymer Chemistry 2014 vol. 5(Issue 22) pp:6480-6488
Publication Date(Web):08 Aug 2014
DOI:10.1039/C4PY00918E
Robust fabrication of electroactive multilayer films from a cationic metallocene-containing polymer and their redox-controlled disassembly are presented. Multilayers are assembled from the cationic cobaltocenium polymer (PMCl) and anionic poly(styrene sulfonate) (PSS), and the effect of salt on the assembly process is investigated. Both electrochemical surface plasmon resonance spectroscopy and electrochemical quartz crystal microbalance confirm excellent response properties of the multilayer film to the electric potential. At an appropriate voltage (≤−0.7 V) these multilayer films undergo rapid disassembly due to reduction of the cationic cobaltocenium to neutral cobaltocene in PMCl and disappearance of the electrostatic interactions holding the polymers together. The extent of disassembly is linearly dependent on the time when the voltage is applied, and the film completely disintegrates from the substrate surface in several minutes. Furthermore, the PMCl/PSS film is employed as a switch layer, and upon electric stimulus the disintegration of the switch layer leads to rapid and complete release from the substrate surface of the overlaying poly(diallyldimethylammonium chloride)/PSS multilayer, which is not electro-responsive.
Co-reporter:Mei Su and Zhaohui Su
Macromolecules 2014 Volume 47(Issue 4) pp:1428-1432
Publication Date(Web):February 4, 2014
DOI:10.1021/ma402540w
In this work, a solution of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) block copolymer in an organic solvent was dispersed in water to form an emulsion in the presence of poly(acrylic acid) (PAA), which upon solvent evaporation produced micelles, and the “emulsion and solvent evaporation” process was studied. It was found that PAA interacted with the PEO corona of the micelles to reduce the curvature, transforming the aggregates from cylinders into vesicles when 1,2-dichloroethane was the solvent. However, when a more volatile solvent, dichloromethane, was used instead, cylindrical micelles were obtained. Even from 1,2-dichloroethane, cylinders were the predominant species when the initial solution concentration was higher (i.e., shorter evaporation process) or when PAA with a much higher molecular weight was used. On the basis of these observations, the interplay between the solvent evaporation rate and the mass transport and chain reorganization at the interface is discussed. In addition, some intermediate structures were observed, which provided insight into the assembly process.
Co-reporter:Yuanyuan Han, Yan Guo, Yingfei Chang, Yanhou Geng, and Zhaohui Su
Macromolecules 2014 Volume 47(Issue 11) pp:3708-3712
Publication Date(Web):May 22, 2014
DOI:10.1021/ma5006149
Poly(3-hexylthiophene) (P3HT) is a typical conjugated polymer with rather rigid backbone due to π-conjugation of the thiophene rings. In this work, we grew nanowhiskers of monolayer thickness from P3HTs of different molecular weights, and found that the nanowhisker widths were all ∼16 nm as measured by transmission electron microscopy, independent of the molecular weight and much smaller than the contour lengths of the P3HT chains, indicating the presence of chain folding in the nanowhiskers. Because of the geometry constrain, the chains must fold out of the conjugation plane. An out-of-plane folding model was established based on theoretical calculation results, and its energy was found to be lower than that of the in-plane folding. These results provide new insight into polythiophene crystallization behavior and suggest that conjugated polymers are more flexible than previously perceived.
Co-reporter:Chengcan Chu and Zhaohui Su
Langmuir 2014 Volume 30(Issue 50) pp:15345-15350
Publication Date(Web):2017-2-22
DOI:10.1021/la5042019
In this work, bimetallic AuPt alloy nanoparticles were synthesized in situ in polyelectrolyte multilayers (PEMs) via an ion-exchange and coreduction process, in which the PEM support also served to suppress the Au–Pt phase separation, and thus enabled formation of AuPt alloy nanoparticles over a wide composition range. The PEM supported AuPt alloy nanoparticles exhibited higher catalytic activity than Au and Pt monometallic ones for the reduction of 4-nitrophenol by NaBH4, showing synergistic effects between Au and Pt. This work provides a facile approach to in situ synthesis of polymer supported bimetallic nanoparticles of tailored composition for optimum performance in catalysis and other applications.
Co-reporter:Jingjing Wei, Liming Wang, Xin Zhang, Xiaojing Ma, Hui Wang, and Zhaohui Su
Langmuir 2013 Volume 29(Issue 36) pp:11413-11419
Publication Date(Web):August 14, 2013
DOI:10.1021/la401216c
In polyelectrolyte multilayer (PEM) films assembled from poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) via the layer-by-layer deposition technique, the counterions were exchanged with silver ions, which were subsequently reduced in situ to produce silver (Ag) nanoparticles. The Ag nanoparticles embedded in the PEMs were found to undergo an interesting coarsening process over time, through which smaller Ag nanoparticles coalesce into larger ones until reaching an equilibrium. The process was investigated by monitoring the localized surface plasmon resonance of the Ag nanoparticles using UV–vis extinction spectroscopy, and the spectral evolution revealed an increase in nanoparticle size with time, a trend in qualitative agreement with theoretical calculation and further confirmed by transmission electron microscopy. The kinetics of the coarsening process and the size of Ag nanoparticles at equilibrium were found to be affected by the PEM structure as well as the temperature and relative humidity the PEM was exposed to, and coalescence was identified to be the mechanism.
Co-reporter:Yan Guo, Yuanyuan Han, and Zhaohui Su
The Journal of Physical Chemistry B 2013 Volume 117(Issue 47) pp:14842-14848
Publication Date(Web):November 14, 2013
DOI:10.1021/jp405837m
The ordering of poly(3-hexylthiophene) (P3HT) molecules in dilute P3HT/chloroform solutions was accelerated by adding small amounts of concentrated H2SO4. The concentrated H2SO4 stimulates the nucleation of crystals, which controls the overall rate of P3HT crystallization. Dispersed nuclei spur P3HT solution crystallization, and adsorbed nuclei induce P3HT crystallization on substrates. By AFM, the morphology of P3HT nanowhiskers prepared in solution differ from those prepared on substrates, and nanowhisker structure and growth kinetics was further investigated using Raman spectroscopy and UV–vis adsorption spectroscopy. All P3HT nanowhiskers are well-ordered.
Co-reporter:Chengcan Chu, Zhaohui Su
Applied Catalysis A: General (5 May 2016) Volume 517() pp:67-72
Publication Date(Web):5 May 2016
DOI:10.1016/j.apcata.2016.03.002
Co-reporter:Guangyu Zhang, Meng Li, Bodong Zhang, Yan Huang and Zhaohui Su
Journal of Materials Chemistry A 2014 - vol. 2(Issue 37) pp:NaN15287-15287
Publication Date(Web):2014/07/28
DOI:10.1039/C4TA03034F
We report a switchable mesh for oil–water separation that allows handling of various oil–water mixtures in one single device. The mesh operates in oil-removing mode to permeate typical oils in oil–water mixtures, and can rapidly switch to water-removing mode to permeate water and separate viscous and sticky oils from the mixture, both with high separation efficiency.
