纳米复合水凝胶的独特拉伸现象及其功能响应性的研究
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摘要
本工作的主要目的是以锂藻土Laponite XLS作为交联剂,通过功能性单体在Laponite XLS分散液中原位聚合得到纳米复合水凝胶(nanocomposite hydrogel,NC gel),探讨其具有优异力学性能的本质及制备出具有环境响应性的NC凝胶。研究工作的基本思路是:通过重复拉伸及迟滞性测试,观察NC凝胶的拉伸现象,并通过时间追踪确定NC凝胶的可恢复性的时间依赖性;通过偏光显微镜、XRD测试,及小应变下的动态粘弹性测试,揭示锂藻土Laponite与高分子的相互作用和交联网络的结构,从而明确NC凝胶具有优异力学性能的本质。在此基础上,筛选出合适的功能性单体与亲水性的N-异丙基丙烯酰胺(NIPAm)在Laponite的分散液中原位共聚,控制、优化反应工艺条件,制备具有优异力学性能的环境响应性NC凝胶。本工作的主要内容和结果如下:
1.以溶胶型的锂藻土Laponite XLS为交联剂, NIPAm为单体,合成了具有超拉伸性的NC凝胶。重复拉伸及迟滞性实验发现NC凝胶在拉伸过程中出现应力硬化现象,并随锂藻土含量的增加更加明显;通过对不同交联剂含量的NC凝胶做时间追踪回复性测试,发现低粘土含量的NC凝胶能够得到更快的恢复;为了揭示NC凝胶具有可回复性的本质,对拉伸前后的NC凝胶进行偏光显微镜以及XRD观测对比,证实了拉伸过程中NC凝胶分子链会发生取向,这表明NC凝胶的超大拉伸应力可能与此相关。而对PNIPAm溶液及(PNIPAm + Laponite XLS)混合溶液的小应变下的动态粘弹性测试则证实了NC凝胶超大拉伸率及可回复性的原因:NC凝胶在拉伸过程中可能出现部分分子链的拉脱,而在经过一段时间恢复之后,大分子链能够重新粘附到锂藻土Laponite XLS片层上。
2.以溶胶型的锂藻土Laponite XLS为交联剂,采用阳离子型单体甲基丙烯酸N,N-二甲胺基乙酯(DMAEMA)与NIPAm在Laponite XLS分散液中原位自由基聚合,合成了具有明显温度及pH双响应性的阳离子型NIPAm/DMAEMA/Laponite纳米复合水凝胶,并考察了阳离子型单体DMAEMA对Laponite XLS分散液稳定性的影响及NIPAm/DMAEMA/Laponite纳米复合水凝胶的力学性能、透明度和温度、pH响应性。DMAEMA的加入导致分散液的Zeta电位绝对值降低,稳定性下降。从而导致合成的共聚NC凝胶结构不均匀,凝胶呈现半透明,并且随着共聚NC凝胶中阳离子型单体DMAEMA含量的增加,透明度下降。这种结构的不均一性导致共聚得到的NC凝胶其拉伸强度和断裂伸长率有所下降,但是仍然具有优异的拉伸性能,拉伸强度大于120kPa,断裂伸长率大于790%。对该NC凝胶根据小应变下的平衡剪切模量Ge计算得到不同组成的NC凝胶的有效网链密度较低,当交联剂含量高达6w/v%时,其NC凝胶的有效网链密度为0.739 mol/m~3,远远小于化学交联凝胶有效网链密度的4.1 mol/m3(约为单体含量的2.7mol%)。结果表明:NC凝胶的超拉伸性来源于其较低的网链密度。该双响应水凝胶在温度为35°C时有明显的温度敏感性;在pH<4的介质中溶胀,在pH>4的介质中收缩,当pH在4-6之间发生体积突变。
In this thesis, stimuli-responsive nanocomposite hydrogels (NC gel) with ultrahigh tensibility were synthesized by in-situ copolymerization of functional monomers in the aqueous suspension of hectorite clay Laponite XLS and Laponite was used as the cross-linker. And the internal reason of the amazing mechanical properties was also investigated. First, the special elongation phenomenon was investigated by the method of the repeated elongation and the hysteresis experiments, and we confirmed the recovery of the NC gels by time-tracking; through the tests of Polarizing microscope and XRD, and the results of the Dynamic moduli also proved it, the interaction and the network between the Laponite XLS and the polymer were assumed to be the reason of the amazing mechanical ability of the NC gels. On the basis, we chose suitable ionic monomers and prepared ionic NC gels with ultrahigh tensibility by in-situ copolymerization of functional monomers and N-isopropylacrylamide (NIPAm) in the aqueous suspension of Laponite XLS. The main contents and the results of the work are as follows:
1. NC gels with ultrahigh tensibility were synthesized through in-situ polymerization of NIPAm with hectorite clays of Laponite XLS. The stress hardening became more apparently with more Laponite XLS while the repeated elongation and the hysteresis; the NC gels with lower Laponite XLS recovered more quickly; by comparing the results of the Polarizing microscope and XRD before and after elongation, it was concluded the NC gels can be oriented to make the NC gels hard while the elongation. After the Dynamic moduli under the small strain was tested on the PNIPAm and (PNIPAm + Laponite XLS) solution, we found the reason for high tensibility of the NC gels maybe the process of peel-off and adhere back to between the polymer and the clay platetes.
2. Positively chargeable nanocomposite hydrogels (NC gels) with temperature and pH responsed were synthesized by in-situ copolymerization of N-isopropylacrylamide (NIPAm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in an aqueous suspension of hectorite clay Laponite XLS. The stability of the Laponite suspension containing DMAEMA was monitored and the mechanical property, transmittance and dual response of the NC gels were also investigated. The addition of DMAEM decreased the absolute value of the zeta potential to make the half-transparent of the NC gels. The nonuniformity of the structure made the NC gels weaker, however, still with ultrahigh tensibility. The stress was bigger than 120 kPa and the strain also exceeded 790 %. The effective network chain density of the NC gel determined from equilibrium shear modulus was 0.739 mol/m3 of the NC gels with 6 w/v% Laponite, which was evidently lower than that of the chemically cross-linked hydrogel (about 4.1 mol/m3). The present results reveal that the high deformability of these NC gels comes from their low effective network chain density. The NC gels showed obvious volume phase transition at 35oC or pH=4.
1.以溶胶型的锂藻土Laponite XLS为交联剂, NIPAm为单体,合成了具有超拉伸性的NC凝胶。重复拉伸及迟滞性实验发现NC凝胶在拉伸过程中出现应力硬化现象,并随锂藻土含量的增加更加明显;通过对不同交联剂含量的NC凝胶做时间追踪回复性测试,发现低粘土含量的NC凝胶能够得到更快的恢复;为了揭示NC凝胶具有可回复性的本质,对拉伸前后的NC凝胶进行偏光显微镜以及XRD观测对比,证实了拉伸过程中NC凝胶分子链会发生取向,这表明NC凝胶的超大拉伸应力可能与此相关。而对PNIPAm溶液及(PNIPAm + Laponite XLS)混合溶液的小应变下的动态粘弹性测试则证实了NC凝胶超大拉伸率及可回复性的原因:NC凝胶在拉伸过程中可能出现部分分子链的拉脱,而在经过一段时间恢复之后,大分子链能够重新粘附到锂藻土Laponite XLS片层上。
2.以溶胶型的锂藻土Laponite XLS为交联剂,采用阳离子型单体甲基丙烯酸N,N-二甲胺基乙酯(DMAEMA)与NIPAm在Laponite XLS分散液中原位自由基聚合,合成了具有明显温度及pH双响应性的阳离子型NIPAm/DMAEMA/Laponite纳米复合水凝胶,并考察了阳离子型单体DMAEMA对Laponite XLS分散液稳定性的影响及NIPAm/DMAEMA/Laponite纳米复合水凝胶的力学性能、透明度和温度、pH响应性。DMAEMA的加入导致分散液的Zeta电位绝对值降低,稳定性下降。从而导致合成的共聚NC凝胶结构不均匀,凝胶呈现半透明,并且随着共聚NC凝胶中阳离子型单体DMAEMA含量的增加,透明度下降。这种结构的不均一性导致共聚得到的NC凝胶其拉伸强度和断裂伸长率有所下降,但是仍然具有优异的拉伸性能,拉伸强度大于120kPa,断裂伸长率大于790%。对该NC凝胶根据小应变下的平衡剪切模量Ge计算得到不同组成的NC凝胶的有效网链密度较低,当交联剂含量高达6w/v%时,其NC凝胶的有效网链密度为0.739 mol/m~3,远远小于化学交联凝胶有效网链密度的4.1 mol/m3(约为单体含量的2.7mol%)。结果表明:NC凝胶的超拉伸性来源于其较低的网链密度。该双响应水凝胶在温度为35°C时有明显的温度敏感性;在pH<4的介质中溶胀,在pH>4的介质中收缩,当pH在4-6之间发生体积突变。
In this thesis, stimuli-responsive nanocomposite hydrogels (NC gel) with ultrahigh tensibility were synthesized by in-situ copolymerization of functional monomers in the aqueous suspension of hectorite clay Laponite XLS and Laponite was used as the cross-linker. And the internal reason of the amazing mechanical properties was also investigated. First, the special elongation phenomenon was investigated by the method of the repeated elongation and the hysteresis experiments, and we confirmed the recovery of the NC gels by time-tracking; through the tests of Polarizing microscope and XRD, and the results of the Dynamic moduli also proved it, the interaction and the network between the Laponite XLS and the polymer were assumed to be the reason of the amazing mechanical ability of the NC gels. On the basis, we chose suitable ionic monomers and prepared ionic NC gels with ultrahigh tensibility by in-situ copolymerization of functional monomers and N-isopropylacrylamide (NIPAm) in the aqueous suspension of Laponite XLS. The main contents and the results of the work are as follows:
1. NC gels with ultrahigh tensibility were synthesized through in-situ polymerization of NIPAm with hectorite clays of Laponite XLS. The stress hardening became more apparently with more Laponite XLS while the repeated elongation and the hysteresis; the NC gels with lower Laponite XLS recovered more quickly; by comparing the results of the Polarizing microscope and XRD before and after elongation, it was concluded the NC gels can be oriented to make the NC gels hard while the elongation. After the Dynamic moduli under the small strain was tested on the PNIPAm and (PNIPAm + Laponite XLS) solution, we found the reason for high tensibility of the NC gels maybe the process of peel-off and adhere back to between the polymer and the clay platetes.
2. Positively chargeable nanocomposite hydrogels (NC gels) with temperature and pH responsed were synthesized by in-situ copolymerization of N-isopropylacrylamide (NIPAm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in an aqueous suspension of hectorite clay Laponite XLS. The stability of the Laponite suspension containing DMAEMA was monitored and the mechanical property, transmittance and dual response of the NC gels were also investigated. The addition of DMAEM decreased the absolute value of the zeta potential to make the half-transparent of the NC gels. The nonuniformity of the structure made the NC gels weaker, however, still with ultrahigh tensibility. The stress was bigger than 120 kPa and the strain also exceeded 790 %. The effective network chain density of the NC gel determined from equilibrium shear modulus was 0.739 mol/m3 of the NC gels with 6 w/v% Laponite, which was evidently lower than that of the chemically cross-linked hydrogel (about 4.1 mol/m3). The present results reveal that the high deformability of these NC gels comes from their low effective network chain density. The NC gels showed obvious volume phase transition at 35oC or pH=4.
引文
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