Self-assembling Behavior of Amphiphilic Copolymer Containing Cross-linked Hydrophilic Block in Ethan

CHEM. RES. CHINESE UAvailableonlineatwww.sciencedirect.com2007,23(1),101-104Article ID1005-040(2007)1-101404Science DirectSelf-assembling Behavior of Amphiphilic Copolymer ContainingCross-linked Hydrophilic Block in EthanolWANG Ying, ZHANG Jun-hu, WANG Zhan-hua, ZHANG KaiWANG Zheng, YU Wen-zhi and YANG BaiKey Lab for Supramolecular Structure and Materials of Ministry of Education, College of ChemistryJilin University, Changchun 130012, P.R. ChinaReceived Apr. 3, 2006The self-assembly behavior of the amphiphilic block copolymer poly( methyl methacrylate)-block-poly( lead dimmethacrylate)(PMMA-b-PLDMA)with cross-linked hydrophilic block( PLDMA) in ethanol was investigated. The re-sults show that the size and morphology of the resulting micelle or micellar aggregates are ascribed to the content ofethanol and the nature of the solvent mixture. PbS nanoparticles were formed in the micelle by in situ reaction withH,S gas. The morphology and size of the self-assembly objects were investigated usin(SEM)and transmission electron microscopy(TEM)Keywords Cross-linking: Ethanol; PbS nanoparticles; Self-assemblIntroductionnol. Compared with the traditional dialysis method, theIt is well known that amphiphilic block copolymers experimental procedure was simplified, and also thecan self-assemble in block-selective solvent to form preparation of the micelle was done using a friendly solcore-shell micelle or colloidal size aggregates1). Pbs nanoparticles wereUsually the micelle are prepared via traditional dialysis polymer micelle in ethanol by bubbling H,S into thenethod[68. Besides micellization of amphiphilic block micellarcopolymers in block-selective solvents, another method Experimentalhas also been proposed to prepare micellar aggregates 1 Chemicalsbonding or electrostatic interactionalin common solvents through noncovalent hydrogenThe block copolymer poly( methyl methacrylateTo avoid the block-poly lead dimethacrylate )( PMMA-b-PLDMA)oxic organic solvents(i. e, DMF and dioxane) which was synthesized by two-step ATRP in DMF according toare currently used in the preparation of crew-cut aggre- the method from ref [18][M, ( PMMA)=2. 1 x10gates, few groups of researchers attempted to prepare M(PMMA-b-PLDMA)rm alcelle in alcohols4-l63. To our knowledge, only a ethanol were analytical chemical reagents and werefew methods for the direct preparation of steady micelle used as received without further purificationin ethanol are known. The hybrid systems constituting 2 Characterizationelf-assembled amphiphilic block copolymers and semiField emission scanning electron microscopyconductor nanoparticles are important in modern materi (SEM) was carried out on a JEOL JSM-6700F micro-al science; therefore, many groups have obtained the scope at 3 kv. The samples were prepared by droppingsemiconductor/copolymer composite nanoparticles in the micellar solution on a clean silicon wafer at firstqueous solution. In the present study, the self-as- then volatilizing the solution at room temperature, andsembly of the block copolymer PMMA-b-PLDMA was finally sputtering a thin gold layer about 3 nm thickcarried out using cross-linked PLDMA block in ethanol using a Hitachi E-1010 ion sputter machine. A JEOL-through selective volatilization of chloroform from the 8100 electron microscope operated at 200 kv was usedcopolymer solution. After the chloroform was complete- for transmission electron microscopy(TEM). The samly volatilized, the steady micelle was prepared in etha- plesmicellar solution on中国煤化工Suppored by the National Natural Science Foundation of ChinaCNMHG and the PrograChangjiang Scholars and Innovative Research Team in Universities( No. IRT04Z2)To whom correspondence should be addressedail; byangchem@ jluu. cnCHEM. RES. CHINESE UVol 23a copper grid coated with thin carbon film. After a few lar solutionminutes, the excess solution was removed with a strip Results and Discussionof filter paper, and the sample was dried in airThe self-assembly behavior of an amphiphilic3 Procedureblock copolymer in water has been extensively studiedThe PMMA-b-PLDMA block copolymers were first in the past decades; however, only a few studies exdissolved in common solvent, chloroform( CHCl,), and plain the self-assembly behavior of block copolymer inthen the solution was filtered through membrane filter ethanol 4. The self-assembly behavior of PMMA-bwith a nominal pore size of 0. 45 um resulting that the PLDMA in ethanol have been investigated in this sturaw copolymer solution had an initial concentration of dy. The volumes of ethanol added to a series of 2 mLof1%(mass fraction). Subsequently, the given volume raw copolymer solutions were gradually increased stepof ethanol was added in drops to a series of 2.0 mL of by step from 2 mL to 20 mL. The formation of the aggreraw copolymer solutions with stirring, and then the so- gates, as indicated by the appearance of turbidity in thelutions were exposed to air. Because of the difference polymer solution, typically occurred when the ethanolin the volatilization rates between chloroform and etha- content reached the critical ethanol content(CEC, canol,CHCl, was first separated from the resulting mi- 8. 5 mL ethanol in this experiment). With the volatili-elle solution. After one day, all the polymer solutions zation of CHCI,, all the solutions turned turbid afterturned milky, indicating the formation of the micelle. one day. The morphologies of the resulting aggregatesFinally, Pbs nanoparticles were synthesized in polymer are shown in Fig.micelle in ethanol through bubbling H,S into the micel,?640mFFig 1 SEM images of the self-assembly morphologies of the block copolymer PMMA-b-PLDMAin 2 mL(A), 4 mL(B),8 mL(C),8.5 mL(D), 10 mL(E), 16 mL(F) ethanolThe results show that when the volume of the distribution of the spheres is broader Fig 1(A)added ethanol differs, the self-assembly spheres with (C)]; when the content of ethanol reaches CEC, thedifferent diameters are formed. When the content of copolymers appropriately begin to self-assemble andethanol is below CEC, the copolymer distributes in the self-adjust to form steady micelle along with the volatil-mixture solvent as molecular block, and then the hy- izaCHC thereby symmetrical spheres cadrophobic block PMMa shrinks to form the core of the中国煤化工 dded ethanolCNMHGCHCI,. This process is similar to the traditional dialy- the micelle attains steady state, in this case the sphesis method but is simple to be operated and facilitates are smaller and adhere to each other Figs 1(E)andthe preparation of micelle in ethanol although the size (F)]. Obviously, the ethanol content plays a key roleNo, 1WANG Ying et al.in regulating the size and morphology of the resulting tion, the solution appeared pellucid and again turnedmicelle, which changes the interaction between the milky after a few minutes. The spheres became morepolymdispersive and smaller asFig. 2(B) with aFurthermore, ca. 10%(mass fraction) water was diameter of ca. 340 nm. By repeating the centrifuga-added to the mixture solution containing 20 mL of raw tion, much smaller spheres were obtained with a diam-eter of ca. 130 nm. These results show that the regulavolatilization of CHCl,. The morphology showedtion of the size and morphology of the resulting micellesized spherical micelle with two different diameters, is also partly ascribed to the nature of the solvent mix640 nm and 250 nm, as seen in Fig. 2(A). Most of ture. The solvent quality for the PMMa chains decrea-the spheres that are similar in size form a similar pearl- ses with the addition of water, which causes annecklace-like structure during the drying process. After increase in the interfacial tensionthe separation of the micellar solution by centrifuga-S(A)B08500mFig 2 SEM images of the micelle in ethanol and water mixture (A), centrifugal at6000 r/min(B), and 6000 r/min again(C)To reduce the total interfacial area, larger spheres tors that alter the above balance, such as the nature ofappear. Through centrifugation, the centrifugal effect the mixed solvent in this experiment, were employed toresulted in the deposition of theregulate the shape and the size of the aggregate.some micelles dispersed in solution, and finally a clear Although there is a need to carry out many experimentssolution was obtained. When the clear solution was al- to accurately control the self-assembly morphologieslowed to stand, it again turned milky because of the re- undoubtedly, the present study proves the effect ofassembly of the residual block copolymer to smaller selective solvent on the self-assembly morphologies ofspheres, which was attributed to the reduction in the the block copolymecontent of the copolymer.The solutions quickly turned black after reactirIn a previous research, the morphology was deter- with H2S gas proving the generation of PbS particlesmined by the force balance among the three contribu- TEM images of the morphologies of the hybrid micelletions to the free energy: core-chain stretching, corona- are shown in Fig 3. By comparing the two images ofchain repulsion, and interfacial tension between the the micelle before and after reacting with H2s, it cancore and the outside solution 9-2. Thereby the fac- be noted that because of the generation of PbS nanoparNUI中国煤化工CNMHG100 nmFig 3 TEM images of the micellar solution( A)and the micellar solution reacted with H, S gas(B)Inset: selected area electron diffraction patten of the PbS nanopartiCHEM. RES. CHINESE UVol 23ticles, the Pb ionic small aggregates( core of reverse [5] Zhang G, Ma J, Wang Y, Chem. J. Chinese Universitiesmicelle )in Fig. 3(A)were replaced by denser[6] Zhang L, Eisenberg A, Science, 1995, 268, 1728nanoparticles in Fig 3(B).The selected area electron [71 LiL.Y, Sun P. C, Yao Y, et al.,Chem. J.Chinese Uni-diffraction pattern( SAED in Fig 3(B)also provesris,2005,26(8),1548the existence of PbS nanoparticles in the micelles[8] Zhang W, Shi L, An Y, et al., Macromolecules, 2004, 37,Conclusions[9 Duan H, Chen D, Jiang M, et al., J. Am. Chem. SocThe self-assembly of the copolymer PMMA-b2001,123,12097PLDMA in ethanol was investigated by SEM and TEM. [10] Duan H, Kuang M, Wang J, et al., J. Phys. Chem. B,The results indicate that the size and the morphology of004,108,550the aggregates can be regulated by altering the volume [il] Zhang Y, Xiang M, Jiang M. et al. Macromolecules, 199730,6084of ethanol and the additive water. The Pbs nanopar- [12] Harada A, Kataoka K, Macromolecules, 2003, 36, 4995cles/ micelle composite materials[13] Tapert H. R, Nishiyama N, Jiang Dtu reaction with H,s gas. By this technique, not onlythe micelle was obtained in ethanol but also the com- [14] Desbaumes L, Eisenberg A, Langmuir, 1999,15,36posite PbS/polymer particles were prepared in ethanol[15] Yuasa M, Oyaizu K, Yamaguchi A, et al.,J.Am.ChemSoc,2004,l26,11128It is expected that this facile technique can be further [16] Zhang W,ShiL,Gao L,et al.,Macromolecules,2005investigated for the fabrication of multifunctional nano-composite particles in friendly solvents[17] Qi L, Coleen H, Antonietti M, Nano Lett., 2001, 1, 61[18] Wang Y, Wang C, Yang B, Chem. J. 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