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Porous polymers have received much attention in recent years because of their light quality,high strength,good permeability and easy-revisable.Various fabrication methods of porous polymers have been used in which ice templating is a process which can prepare porous materials with complex structures and fine microstructures.This method has been widely used to prepare porous polymers but it still has many problems,such as poor homogeneity of pore distribution and pore connectivity.To solve these problems,it is necessary to understand the morphology of ice crystal growth in the solidification process of polymer solution.In situ observation of directional solidification is adopted in this paper to study the morphology evolution during directional solidification of polyvinyl alcohol (PVA) aqueous solution with different concentrations and molecular weights under different pulling speeds.The experimental results show that the primary dendrite spacing of PVA aqueous solution decreases with the increase of pulling speed at low concentration (1 wt%,2.5 wt%).However,increasing PVA concentration does not result in significant change in primary dendrite spacing.The primary dendrite spacing varies with pulling speed whereas the dendritic primary arm tends to shrink with increasing velocity.The effects of PVA concentration and pulling speed on morphology are partly because of diffusion instability from the classical solidification theory.When the concentration of solution is 5 wt%,there is little change of primary dendrite spacing with the velocity,which is due to the suppressed diffusion instability by high concentration of the polymer solution and large viscosity.When the concentration of solution increases to 10 wt%,ice crystal morphology is seaweed-like,where the PVA molecules are enriched and crosslinked ahead the ice crystal,leading to the continuous bifurcation of the dendrites.For the solidification morphologies of the aqueous solutions with different PVA molecular weights,the primary dendrite spacing of PVA aqueous solution decreases with the increase of pulling speed at low molecular weight (Mw=24000).Increasing PVA molecular weight does not result in significant change in primary dendrite spacing.At the low PVA molecular weight,the interface shows cell morphology.With the increase of PVA molecular weight,the large chain length leads to the stronger interaction among them and suppressing their diffusion. The corresponding constitutional undercooling is strengthened,thereby promoting the interfacial instability and dendrite formation.From the classical solidification morphology formation mechanism it may be concluded that the solidification morphology of PVA aqueous solution is determined by the competition between the two different mechanisms,i.e., interface instability induced by diffusion of PVA molecule and the local phase separation from the crosslinking of PVA polymer chains.
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Keywords:
- directional solidification /
- ice-templating /
- polyvinyl alcohol /
- microstructure
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[1] Liu Q, Tang Z, Ou B, Zhou Z 2014 Mater. Chem. Phys. 144 213
[2] Nemoto J, Uraki Y, Kishimoto T, Sano Y, Funada R, Obata N, Yabu H, Tanaka M, Shimomura M 2005 Bioresour. Technol. 96 1955
[3] Adiga S P, Jin C, Curtiss L A, Monteriro-Riviere N A, Narayan R J 2009 Wires. Nanomed. Nanobi. 1 568
[4] Colombo P 2006 Philos. Trans. R. Soc. London Ser. A 364 109
[5] Karimi A, Wan M A W D 2015 Polym. Compos. 38 1135
[6] Colosi C, Costantini M, Barbetta A, Pecci R, Bedini R, Dentini M 2012 Langmuir 29 82
[7] Holloway J L, Lowman A M, Palmese G R 2013 Soft Matter 9 826
[8] Li X, Kanjwal M A, Lin L, Chronakis L S 2013 Colloids Surf. B 103 182
[9] Jiang X R, Guan J, Chen X, Shao Z Z 2010 Acta Chim. Sin. 68 1909 (in Chinese)[江霞蓉, 管娟, 陈新, 邵正中 2010 化学学报 68 1909]
[10] Deville S 2008 Adv. Eng. Mater. 10 155
[11] Deville S, Saiz E, Nalla R K, Tomsia A P 2006 Science 311 515
[12] Deville S 2010 Materials 3 1913
[13] Fukasawa T, Deng Z Y, Ando M, Ohji T, Goto Y 2001 J. Mater. Sci. 36 2523
[14] Delattre B, Bai H, Ritchie R O, Coninck J D, Tomsia A P 2013 ACS Appl. Mater. Inter. 6 159
[15] Kim S S, Seo I S, Yeum J H, Ji B C, Kim J H, Kwak J W, Yoon W S, Noh S K, Lyoo W S 2004 J. Appl. Polym. Sci. 92 1426
[16] Ren L, Zeng Y P, Jiang D 2009 Ceram. Int. 35 1267
[17] Zhang H, Hussain I, Brust M, Butler M F, Rannard S P, Cooper A I 2005 Nat. Mater. 4 787
[18] Zhang H, Cooper A I 2007 Adv. Mater. 19 1529
[19] Gutirrez M C, Garca-Carvajal Z Y, Jobbgy M, Rubio F, Yuste L, Rojo F, Ferrer M L, Monte F D 2007 Adv. Funct. Mat. 17 3505
[20] Wu X, Liu Y, Li X, Wen P, Zhang Y, Long Y, Wang X, Guo Y, Xing F, Gao J 2010 Acta Biomater. 6 1167
[21] Qian L, Zhang H 2011 J. Chem. Technol. Biotechnol. 86 172
[22] Wang L L, Wang X B, Wang H Y, Lin X, Huang W D 2012 Acta Phys. Sin. 61 148104 (in Chinese)[王理林, 王贤斌, 王红艳, 林鑫, 黄卫东 2012 61 148104]
[23] Yu H L, Lin X, Li J J, Wang L L, Huang W D 2013 Acta Metall. Sin. 49 58 (in Chinese)[宇红雷, 林鑫, 李俊杰, 王理林, 黄卫东 2013 金属学报 49 58]
[24] You J, Wang L, Wang Z, Li J, Wang J 2015 Rev. Sci. Instrum. 86 084901
[25] Wang X B, Lin X, Wang L L, Bai B B, Wang M, Huang W D 2013 Acta Phys. Sin. 62 108103 (in Chinese)[王贤斌, 林鑫, 王理林, 白贝贝, 王猛, 黄卫东 2013 62 108103]
[26] Zhang L, Zhao J, Zhu J, He C, Wang H 2012 Soft Matter 40 10447
[27] He H 2012 Ph. D. Dissertation (Chongqing:Chongqing University) (in Chinese)[何洪 2012 博士学位论文 (重庆:重庆大学)]
[28] Doi M 2013 Soft Matter Physics (New York:Oxford University Press) p145
[29] Utter B, Ragnarsson R, Bodenschatz E 2001 Phys. Rev. E 72 011601
[30] Li J J, Wang J C, Xu Q, Yang G C 2007 Acta Phys. Sin. 56 1514 (in Chinese)[李俊杰, 王锦程, 许泉, 杨根仓 2007 56 1514]
[31] Gao H W, Yang R J, He J Y, et al. 2010 Acta Polym. Sin. 5 542 (in Chinese)[高瀚文, 杨荣杰, 何吉宇, 等 2010 高分子学报 5 542]
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