酸性条件下Laponite的分散及凝胶化行为研究

发布时间：2018-02-28 06:17

本文关键词： Laponite 纳米复合水凝胶分散化学分解凝胶化　出处：《新疆大学》2017年硕士论文　论文类型：学位论文

【摘要】：锂藻土(Laponite),一类人工合成粘土,可作为无机交联剂广泛应用于制备纳米复合(NC)水凝胶以提高水凝胶的机械强度。由于Laponite在水中可剥离分散成直径为25 nm,厚度为1 nm的片层颗粒,其表面带有大量的负电荷边缘带有少量的正电荷。因此,当在Laponite分散液中引入离子型单体或者改变分散液的pH和离子强度时,片层颗粒会因静电吸引形成“卡片屋”结构,从而形成弱凝胶,导致体系不均匀,严重影响所合成的水凝胶的光学性能和力学性能。本课题组在前期工作中发现离子型单体2-丙烯酰胺-2-甲基丙磺酸(AMPS)在一定程度上可以促进Laponite的分散,但是对于分散体系的稳定性及分散机理尚未清楚。因此,在本论文的工作中探讨了不同AMPS含量下Laponite分散液的稳定性及分散机理。结果表明:当AMPS含量小于2.0 wt%时,由于范德华力的吸引和静电排斥减弱导致Laponite颗粒发生了聚集。当AMPS含量大于2.0 wt%时,由于Laponite颗粒在酸性环境下发生化学分解而导致原有的聚集或凝胶化现象逐渐消失。而且分散液老化7天后,不同AMPS浓度下的分散液将呈现出不同的流变学行为,当AMPS的含量大于6 wt%时,分散液从假塑性流体转变为牛顿流体。Laponite在低AMPS浓度下分散稳定性主要受电解质效应和AMPS官能团取向的影响,在高AMPS浓度下分散主要受AMPS的酸性影响。由于Laponite在酸性环境中易发生化学分解,因此进一步探讨了不同酸对Laponite的分散及化学稳定性的影响。结果表明:同一H+浓度下,分散Laponite所选用的酸由强酸变至弱酸时,分散液达到稳定所需的外加H+浓度增加;而用同种酸分散时,Laponite结构破坏的度程随着H+浓度的增加而增大。放置时间对Laponite在酸溶液中的分散稳定性及化学稳定也有很大影响。当H+浓度小于0.4 mol/L时,分散液在放置前后pH变化较大,主要是由于Laponite结构在H+的作用下片层边缘释放出的OH-影响所致,而且受Laponite分解后释放的Mg2+影响,分散液的状态也发生改变。随着时间的延长,强酸对Laponite结构破坏程度变化不大,而弱酸对Laponite结构的破坏程度变化较大,且两者中Laponite结构破坏程度逐渐接近。在前两章工作的基础上,通过在不同酸性的Laponite分散液中同时引入聚乙烯醇(PVA)及丙烯酰胺(AM),制备了新型的NC水凝胶,并探讨了不同分解程度下的Laponite作为交联剂时对所制备的凝胶结构形貌,凝胶化时间的影响,以及温度对成胶状况的影响。结果表明:随着体系中酸含量的增加,体系中的无定型硅产物及金属离子增多时,凝胶三维网络结构更加密集,孔洞变小。当体系在弱酸条件下成胶,Laponite发生聚集,凝胶化时间较长;随着酸性增强,体系中Laponite分解后生成的硅产物及无机金属离子促进凝胶的形成,凝胶化时间减少,凝胶速率增大,水凝胶的强度增加。但当酸增加到一定程度后,凝胶化时间延长,凝胶速率开始下降,而且高温导致水凝胶的强度下降。
[Abstract]:Laponite (Laponite), a kind of synthetic clay can be used as inorganic crosslinking agent widely used in preparation of nano composite (NC) hydrogel in order to improve the mechanical strength of the hydrogel. Because the Laponite in the water can be stripped dispersed into a diameter of 25 nm and the thickness of sheet particles of 1 nm, with a negative charge on the surface of the edge a large number of positively charged amount. Therefore, when the introduction of ionic monomers or change the dispersion liquid in Laponite dispersion of pH and ionic strength, lamellar particles due to electrostatic attraction to form a "house of cards" structure, so as to form weak gel, cause the system is not uniform, optical properties and mechanical properties of serious influence the synthesis of hydrogels. The research group found that ionic monomer 2- acrylamide -2- methyl propane sulfonic acid (AMPS) in previous work in a certain extent can improve the dispersion of Laponite, but the stability of dispersion and dispersion machine Science is not clear. Therefore, in this thesis discusses the stability and dispersion mechanism of different AMPS content under Laponite dispersion. The results show that when the AMPS content is less than 2 wt%, the van Edward force attraction and electrostatic repulsion leads to weakening of Laponite particle aggregation. When the AMPS content is greater than 2 wt%, aggregation the original or gelation phenomenon gradually disappear due to the Laponite particles in the acidic environment of chemical decomposition. And the dispersion of aging after 7 days, the dispersion under different AMPS concentrations will exhibit different rheological behavior, when the content of AMPS is more than 6 wt%, the dispersion from pseudoplastic fluid into the influence of Newton.Laponite fluid at low AMPS concentration dispersion stability is mainly affected by the electrolyte effect and AMPS functional orientation, dispersion of acidic AMPS was mainly affected by the high concentration of AMPS. The Laponite in acidic environment Easy chemical decomposition, thus further explore the effects of different acid on Laponite dispersion and chemical stability. The results showed that the same concentration of H+, the dispersion of Laponite acid from acid to weak acid, dispersion is required to achieve stable with the increase of H+ concentration; and with the same acid dispersion, of Laponite damage increases with the increase of H+ concentration. The time also has a great influence on the stability and chemical stability and dispersion of Laponite in acid solution. When the concentration of H+ is less than 0.4 mol/L, the dispersion in the placement of pH changes before and after large, is mainly caused by the OH- effect of Laponite structure under edge layers released in H+ the role of, and affected by Mg2+ release after the Laponite decomposition, dispersion state changes. With the extension of time, strong extent of damage to small changes in the Laponite structure, and the structure of Laponite acid Change the destructiveness, and both in Laponite damage gradually close. Based on the work of the two chapter, through the Laponite in different acidic dispersion while introducing polyvinyl alcohol solution (PVA) and acrylamide (AM), NC new hydrogels were prepared, and discuss the different degree of decomposition under Laponite as the cross-linking agent on the gel structure and morphology of the prepared, affect the gelation time, and effect of temperature on the gelling conditions. The results showed that with the increase of acid content in the system, amorphous silicon products and metal ions increased much more intensive gel system, three-dimensional network structure, while smaller pores. In the system under the condition of weak acid gel, Laponite aggregation, gelation time longer; with the increased acidity, gel formation of silicon products and inorganic metal ions Laponite decomposition generated after the promotion system, the gelation time decreased, When the gel speed increased, the strength of hydrogel increased, but when the acid increased to a certain extent, the gel time prolonged, the gel rate began to decline, and the high temperature led to the decrease of the strength of hydrogel.

【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O648.17

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