Thermo-responsive liquid marbles
Thermo-responsive liquid marbles
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DOI：
10.1038/pj.2013.84
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发表时间：
2014-03
期刊：
影响因子：
2.8
通讯作者：
S. Yusa;M. Morihara;Keita Nakai;S. Fujii;Y. Nakamura;A. Maruyama;Naohiko Shimada
中科院分区：
文献类型：
--
作者：
S. Yusa;M. Morihara;Keita Nakai;S. Fujii;Y. Nakamura;A. Maruyama;Naohiko Shimada
Aussillous和Quéré使用术语“液体大理石”来指代涂覆有微米或纳米级疏水粉末颗粒的不粘液滴。1液滴在液-气界面处被疏水粉末包裹。液体大理石已经使用粉末如石松粉、2二氧化硅、3炭黑、4聚[2-（全氟辛基）丙烯酸乙酯]、5聚四氟乙烯、6聚偏二氟乙烯、7气凝胶、8石墨9等制备。10-12粉末的表面润湿性是制备液体大理石的重要参数。疏水性液体大理石外壳防止液体核心与大理石外壳外部表面之间的直接接触。液体弹珠是球形的，在固体或液体表面上时保持稳定的形状。液体大理石在水表面污染检测、13气体检测14和微反应器中的应用显示出特别的前景。15最近的报告描述了各种刺激响应液体弹珠，其稳定性可由外部刺激控制。例如，通过含有pH响应性聚合物如去质子化的疏水性聚（（2-二甲基氨基）乙基甲基丙烯酸酯）16和聚（2-乙烯基吡啶）（P2 VP）17的颗粒稳定的液体大理石，其可以漂浮在水表面上，在向本体水中加入酸时崩解，因为颗粒表面由于pH响应性聚合物的质子化而变得亲水。Wang等人18报道了使用Fe 3 O 4/SiO2颗粒与含有P2 VP和光酸产生剂的pH响应性嵌段共聚物制备磁和紫外（UV）响应性液体大理石。这些粒子的运动可以通过外部磁场来控制。在UV照射下，光酸发生剂产生的酸，其诱导颗粒表面上的P2 VP链的电离，导致液体大理石的崩解。最近，紫外响应液体大理石制备使用水滴覆盖的光致变色螺吡喃粉末。19这些UV响应性液体大理石在UV照射时崩解，因为疏水性螺吡喃转化为具有甜菜碱结构的亲水性mercury。刺激响应液体弹珠的开发可能会扩大其应用领域。研究新型的刺激响应性液体大理石，包括热响应性液体大理石是一个有趣的课题。在室温下（321 ℃），PNIPAM是亲水性的并且溶于水，由于侧挂的酰胺基团和水分子之间的氢键作用而采用无规卷曲构象。然而，PNIPAM从水相分离时，加热到高于321 ℃的温度，一个较低的临界溶解温度（LCST）。这一发现表明PNIPAM粉末在低于LCST时可能表现出亲水性，而在高于LCST时可能变得疏水。PNIPAM的LCST受添加到水性聚合物中的盐的类型和浓度的影响。
Aussillous and Quéré used the term liquid marbles to refer to non-stick droplets coated with micro-or nano-scale hydrophobic powder particles. 1 A liquid droplet is encapsulated by a hydrophobic powder at the liquid–air interface. Liquid marbles have been prepared using powders such as lycopodium powder, 2 silica, 3 carbon black, 4 poly [2-(perfluorooctyl) ethyl acrylate], 5 polytetrafluoroethylene, 6 polyvinylidene fluoride, 7 aerogels, 8 graphite 9 and others. 10–12 The surface wettability of the powder is an important parameter for the preparation of liquid marbles. The hydrophobic liquid marble shell prevents direct contact between the liquid core and surfaces outside the marble shell. Liquid marbles are spherical and retain a stable shape while on the surface of a solid or liquid. Liquid marbles have shown particular promise for applications in water surface pollution detection, 13 gas detection 14 and microreactors. 15 Recent reports have described various stimulus-responsive liquid marbles with stability that can be controlled by external stimuli. For example, liquid marbles stabilized by particles containing pH-responsive polymers such as deprotonated hydrophobic poly ((2-dimethylamino) ethyl methacrylate) 16 and poly (2-vinylpyridine)(P2VP), 17 which can float on the surface of water, disintegrate upon the addition of acid to the bulk water because the particle surface becomes hydrophilic owing to the protonation of the pH-responsive polymers. Wang et al. 18 reported the preparation of magnet-and ultraviolet (UV)-responsive liquid marbles using Fe3O4/SiO2 particles with a pH-responsive block copolymer containing P2VP and a photo acid generator. The movement of these particles can be controlled by an external magnetic field. Upon UV irradiation, the photo acid generator-generated acid, which induces ionization of the P2VP chains on the particle surface, leads to the disintegration of the liquid marble. Recently, UV-responsive liquid marbles were prepared using a water droplet covered with photochromic spiropyran powder. 19 These UV-responsive liquid marbles disintegrated upon UV irradiation because the hydrophobic spiropyran was transformed into hydrophilic merocyanine, which has a betaine structure. The development of stimulus-responsive liquid marbles may expand their area of application. It is interesting to investigate new stimulus-responsive liquid marbles, including thermally responsive liquid marbles.An aqueous solution of poly (N-isopropylacrylamide)(PNIPAM) undergoes a thermally reversible phase separation. 20 At room temperature (o321C), PNIPAM is hydrophilic and dissolves in water, adopting a random coil conformation because of hydrogen bonding between the pendant amide groups and water molecules. However, PNIPAM separates from the aqueous phase when heated to temperatures higher than 321C, a lower critical solution temperature (LCST). This finding indicates that PNIPAM powder may exhibit hydrophilic properties below the LCST and may become hydrophobic above the LCST. The LCST for PNIPAM is influenced by the type and concentration of salts added to the aqueous