Name: hydrogels and their water absorption
Uploaded: 2023-04-30T07:06:34.000Z
Duration: 8 min 33 s
Channel: JoVE

预凝胶溶液在1000 µL离心管中配制；所用材料、在聚合反应中的作用及添加量见表1。
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>材料</td>
			<td>用途</td>
			<td>结构</td>
			<td>摩尔百分比</td>
		</tr>
		<tr>
			<td>2,2-二甲氧基-2-苯基-乙酰苯（DMPAP）</td>
			<td>自由基引发剂（光引发剂）</td>
			<td><img alt="苯甲酸苄酯合成反应式，有机化学结构式。" src="/files/ftp_upload/10486/10486eq5.jpg" data-altupdatedat="1761830439000" data-alt="方程式 5"> </td>
			<td>0.0012</td>
		</tr>
		<tr>
			<td>2-羟乙基甲基丙烯酸酯
			
			（HEMA）
			</td>
			<td>聚合物主链</td>
			<td><img alt="乳酸乙酯分子化学结构图；有机化合物分子式。" src="/files/ftp_upload/10486/10486eq6.jpg" data-altupdatedat="1761830439000" data-alt="方程式 6"> </td>
			<td>21.2121</td>
		</tr>
		<tr>
			<td>四乙二醇二甲基丙烯酸酯（TEGDMA）</td>
			<td>交联剂</td>
			<td><img alt="己二酸衍生物化学结构图；有机化合物，己二酸分子结构示意图。" src="/files/ftp_upload/10486/10486eq7.jpg" style="opacity: 0.9;" data-altupdatedat="1761830439000" data-alt="方程式 7"> </td>
			<td>3.0303</td>
		</tr>
		<tr>
			<td>乙二醇
			
			（EG）
			</td>
			<td>溶剂</td>
			<td><img alt="乙二醇化学结构图；有机化合物分子，HO-CH2-CH2-OH。" src="/files/ftp_upload/10486/10486eq8.jpg" data-altupdatedat="1761830439000" data-alt="方程式 8"></td>
			<td>75.7576</td>
		</tr>
	</tbody>
</table>
表1. 水凝胶预凝胶组分、其在水凝胶自由基聚合中的作用、化学二维聚合物结构以及添加到预凝胶溶液中的用量。
合成
<ol>
	<li>开始水凝胶合成之前，使用两片玻璃载片和三片厚度为520微米的聚烯烃片材作为间隔物组装一个合成模具；该装置通过文件夹夹固定，如图6所示。将大片玻璃载片错开几毫米，以形成一个通道，便于将预凝胶溶液用移液枪注入模具中。</li>
	<li>开始水凝胶合成前，准备一个1000µl离心管、表1中列出的化学品、配有洁净吸头的微量移液器以及固化模具（图6）。所有操作均应在通风橱内进行，并穿戴适当的个人防护装备（PPE），包括护目镜或安全眼镜、实验服和防护手套。</li>
</ol>
<img alt="使用长尾夹演示简单物理杠杆原理，说明静态平衡概念。" src="/files/ftp_upload/10486/10486fig6.jpg" data-altupdatedat="1761830439000" data-alt="图6"> 
图6：水凝胶合成模具，由两片玻璃载片、三条520微米厚的聚烯烃片材作为间隔物，并用大型长尾夹固定而成。
<ol start="3">
	<li>首先向试管中加入0.0012摩尔百分比的2,2-二甲氧基-2-苯基苯乙酮（DMPAP），该物质为固体光引发剂（一种由光引发的自由基引发剂）。</li>
	<li>使用新的移液枪头，依次向试管中加入21.2121摩尔百分比的甲基丙烯酸-2-羟乙酯（HEMA），即主链分子，以及3.0303摩尔百分比的四乙二醇二甲基丙烯酸酯（TEGDMA），即交联分子。在自由基存在下，TEGDMA将通过连接聚合物链形成网络聚合物，从而实现HEMA链的化学交联。</li>
	<li>使用涡旋振荡器混合溶液，直至获得均匀的溶液。</li>
	<li>称取0.25克溴甲酚紫，用75.7576摩尔百分比的乙二醇（EG）冲洗并加入溶液中，EG作为溶剂。该色素仅用于观察目的（否则水凝胶为透明状态），而EG作为溶剂可溶解引发自由基的引发剂，并保持水凝胶的柔韧性。</li>
	<li>再次使用涡旋振荡器混合溶液，直至色素完全溶解且溶液均匀。</li>
	<li>使用微量移液器，将移液器枪头对准大尺寸玻璃载片的偏移边缘，将预凝胶溶液均匀注入模具中心。</li>
	<li>将模具置于紫外光手电筒（Warson SK66）下方5厘米处，照射1分钟。紫外光会断裂引发剂分子中的化学键，使其转化为自由基，进而攻击聚合物和交联剂分子。当完全形成网络结构后，水凝胶应呈现类似橡胶的固体状态，具有果冻般的质地。</li>
	<li>将模具从光源处取出，拆卸模具组件，并将水凝胶从玻璃载片上取下。</li>
	<li>用去离子水冲洗水凝胶的两面，以去除产物中任何未反应的化学物质和寡聚物。</li>
	<li>为表征不同紫外光照射时间对交联程度和溶胀能力的影响，可重复本实验步骤，仅改变第九步的处理时间。在本表征实验中，溶液分别接受1分钟、1.5分钟和5分钟的紫外光照射，共制备三种水凝胶样品。</li>
</ol>
表征
通过干燥、水合然后再干燥聚合物，可以计算水凝胶的溶胀度。
<ol>
	<li>将制备好的水凝胶放入含有异丙醇等醇类的容器中，确保其完全浸没。静置4-8小时，使醇完全置换水凝胶中的乙二醇。</li>
	<li>将水凝胶从醇中取出，在空气中放置约30分钟使其自然干燥。由于醇的挥发速度比水或溶剂更快，有助于水凝胶保持其结构。</li>
	<li>称量干燥后的水凝胶。</li>
	<li>将水凝胶浸入去离子水中至少30分钟，直至其完全溶胀。取出水凝胶，轻轻擦干表面，然后称重。</li>
	<li>使用公式计算溶胀度：<img alt="溶胀百分比公式，%swelling=(ws-wd)/wd x100，方程分析，材料科学" src="/files/ftp_upload/10486/10486eq9v2.jpg" style="opacity: 0.9;" data-altupdatedat="1761830439000" data-alt="Equation 9">，其中 <img alt="ΣFx=0 方程，静力平衡，公式，教学示意图" src="/files/ftp_upload/10486/10486eq10.jpg" data-altupdatedat="1761830439000" data-alt="Equation 10"> 为溶胀后聚合物的重量，<img alt="扭矩符号方程，表示为 W_d" src="/files/ftp_upload/10486/10486eq11.jpg" data-altupdatedat="1761830439000" data-alt="Equation 11"> 为干燥聚合物的重量。</li>
</ol>

水凝胶合成是一种制备交联聚合物材料的技术，这类材料能够响应液体、紫外光、pH值或多种其他刺激而发生溶胀。通过液体溶液混合进行合成具有操作简便、易于形成水凝胶的优点，但最终产物通常纯度较低，且倾向于含有分子量较低的聚合物。该特定实验步骤虽然简单，但涉及的化学试剂具有毒性和易燃性，因此必须格外小心并采取充分的预防措施。通过此方法制备的水凝胶在药物递送、传感器以及吸水性卫生用品等多种应用中具有重要用途。
水凝胶被广泛应用于多种消费品、医疗器械和传感器中。医院用垫、女性卫生巾和婴儿尿布等消费品含有聚丙烯酸钠，这是最常见的高吸水性聚合物之一。该水凝胶在液体存在下可膨胀至其自身重量的300至800倍，使制造商能够减少材料使用量，生产出更轻薄且佩戴舒适的产品。
此外，软性隐形眼镜由硅水凝胶制成，这种材料允许氧气轻松透过并到达角膜，佩戴起来比硬性隐形眼镜更舒适。水凝胶也常用于药物递送系统，因为其交联网络结构能够将药物储存在三维网络中，并缓慢释放到体内。
水凝胶还可根据盐度、pH值或其他信...

水凝胶合成

来源：Amber N. Barron、Ashlea Patterson 和 <a href="https://www.jove.com/author/Taylor+D._Sparks">Taylor D. Sparks</a>，犹他大学材料科学与工程系，美国犹他州盐湖城
水凝胶是一类通过相对简单的工艺和通常廉价的材料制备而成的交联聚合物，具有广泛的适用性。它们可通过溶液形成，包含由单体试剂构成的聚合物主链、使聚合物具有反应活性的引发剂，以及将聚合物链交联在一起的交联剂。这类材料的一个重要特性是能在水中溶胀，且可通过调节使其对盐度、pH值或其他信号的响应进一步增强溶胀性能。作为最终产品，水凝胶可用于水相或干燥环境中，具备柔韧性、高吸水性、透明性和隔热性等多种有用特性。它们常用于液体吸收、传感器、消费品以及药物递送系统。

最终水凝胶单体如图7所示，合成的水凝胶如图8所示。1分钟样品的溶胀度约为136%，1.5分钟样品为387%，5分钟样品为81%。这些结果表明了交联程度（即网络连接的密集程度）与溶胀能力之间的关系。聚合物分子之间形成的交联越多，对聚合物链产生的弹性约束力就越强，从而抑制其扩张程度，使其无法像交联程度较低的水凝胶那样充分膨胀。
<img alt="聚合物结构示意图；显示化学键和官能团的聚乳酸单体。" class="xfigimg" src="/files/ftp_upload/10486/10486fig7.jpg" data-altupdatedat="1761830439000" data-alt="图7"> 
图7：由光引发剂DMPAP、HEMA主链、...

来源：Amber N. Barron、Ashlea Patterson 和 Taylor D. Sparks，美国犹他大学材料科学与工程系，盐湖城，...

水凝胶是一类多功能的交联聚合物，通常使用成本较低的材料通过相对简单的工艺制备而成。它们广泛应用于液体吸收剂、传感器、消费品以及药物递送系统。水凝胶可通过溶液法形成，其中引发剂使单体分子活化，进而聚合形成聚合物主链，随后交联剂将聚合物链连接在一起。这类材料的一个重要特性是在水中会发生溶胀。此外，这种溶胀行为还可通过调节盐浓度、pH值或其他刺激信号进一步优化。水凝胶既可在水相环境中使用，也可在干燥条件下应用，具有柔韧性、高吸水性、透明性和热绝缘性等多种优良性能。本视频将演示水凝胶的合成及其表征方法。水凝胶能够吸收其自身重量数百倍的水。当水进入交联的聚合物网络时，会溶解聚合物主链上的亲水性、离子性或同时具有这两种特性的基团。水分子比被溶解的基团更大，因此它们存在于网络内部会导致水凝胶发生溶胀。而连接聚合物主链的交联结构则防止其溶解或破裂。水凝胶合成是一种制备这类交联聚合物材料的技术。该过程虽然简单，但涉及的化学物质具有毒性和易燃性，因此必须格外小心并采取预防措施。利用预凝胶组分，可通过自由基聚合方法制备水凝胶。其中一种方法以DMPAP作为自由基引发剂开始。DMPAP 中的碳-碳键在紫外光作用下发生断裂，使每个碳原子上形成一个未成对的、高反应活性的电子，即自由基。这些自由基与 HEMA 中的碳-碳双键发生反应，形成一个末端带有自由基的链式增长结构。从主链上延伸出的羟基在水中具有溶解性，导致交联网络在有水存在时发生溶胀。自由基还会与交联剂 TEGDMA 分子中的两个碳-碳双键发生反应，从而将主链相互连接起来。当自由基被完全消耗或反应结束后，水凝胶的合成即告完成。可通过将聚合物干燥、水化后再干燥的方法来评估其溶胀性能。在下一节中，我们将利用这种自由基聚合方法合成并表征水凝胶。开始水凝胶合成之前，需准备好所需的材料和化学品。先前组装的合成模具中的玻璃载玻片相互错开几毫米，以形成一个通道，便于将预凝胶溶液用移液枪加入模具中。所有操作均应在通风橱内进行，并佩戴适当的个人防护装备，因为该过程涉及有毒且易燃的化学品。首先，向1000微升的离心管中加入0.0012 mol%的DMPAP。接着，每次使用新的移液枪头，依次向离心管中加入21.2121 mol%的HEMA，然后加入3.0303 mol%的TEGDMA。使用涡旋振荡器混合溶液，直至形成均匀的溶液。取少量颜料BCP沾于刮刀上，再用75.7576 mol%的溶剂乙二醇冲洗刮刀，将颜料加入上述溶液中。使用涡旋仪混合溶液，直至色素完全溶解且溶液均匀。该色素用于使透明水凝胶可见，而溶剂则用于溶解自由基引发剂并保持水凝胶的柔韧性。使用微量移液器将溶液沿合成模具的偏移边缘注入模具中。将预凝胶溶液均匀地注入模具中心。将装有溶液的模具置于紫外光手电筒下方5厘米处，照射1分钟。将模具从光源处取出，拆卸模具以从玻璃载片上取出水凝胶。完全交联后，水凝胶应呈现类似橡胶的固体状态，具有类似果冻的质地。用去离子水冲洗水凝胶的两面，以去除产物中未反应的化学物质和聚合物。分别采用1.5分钟和5分钟的紫外光照射时间重复该步骤，共制备三种水凝胶。将制备好的水凝胶浸入盛有异丙醇的容器中，放置1至2小时。异丙醇将置换水凝胶中的乙二醇，使水凝胶在保持其结构的同时快速干燥。将水凝胶从酒精中取出，在空气中干燥约30分钟。称量并记录每块干燥水凝胶的质量。将水凝胶浸入去离子水中，直至完全溶胀。将水凝胶从水中取出，轻轻擦干表面。称量并记录溶胀后水凝胶的质量。利用溶胀后水凝胶的质量Ws与干燥水凝胶的质量Wd，计算溶胀度。结果显示，一分钟样品的溶胀度约为136%，1.5分钟样品为387%，五分钟样品为81%。这些结果表明，在最长的紫外光照射时间下，溶胀程度较低。随着紫外光照射时间增加，聚合物分子间形成更多的交联结构，从而对聚合物链产生更强的弹性约束力。因此，交联程度较高的水凝胶比交联程度较低的水凝胶膨胀更小。了解了水凝胶的合成与表征方法后，让我们来看看它们在日常产品中的应用。医院用垫、女性卫生巾和婴儿尿布等消费品中均含有一种最常见的高吸水性聚合物。这种水凝胶可吸收高达其自身重量800倍的液体，使制造商能够生产出轻薄且舒适的用品。本视频中合成的水凝胶则被用作草坪洒水器中的传感器。该传感器与土壤接触，在草坪浇水过程中吸水溶胀，直至触发洒水器关闭机制。您刚刚观看了 JoVE 关于水凝胶合成的简介。现在您应该了解水凝胶的合成与表征方法。感谢观看。

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Hydrogel Synthesis

hydrogels and their water absorption

Hydrogels are cross-linked polymers that can absorb water and swell. They are made with relatively simple procedures and inexpensive materials, which makes them useful for many school-level chemistry and materials science topics.

A hydrogel starts with a polymer backbone built from monomer reagents. An initiator makes the polymer reactive, and a crosslinking species connects the chains together. This network gives the material its final structure.

Water absorption is one of the key features of hydrogels. Their swelling can also be tuned by salinity, pH, or other signals. That control helps explain why hydrogels can be designed for different uses.

Hydrogels may be used in either aqueous or dry environments. They can offer flexibility, high absorbance, transparency, and thermal insulation. Common applications include liquid absorbance, sensors, consumer products, and drug delivery.

Hydrogels and Their Water Absorption

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electroplating of thin films

Fast Metal Coating Without a Vacuum

Electroplating is a way to add a thin metal coating to a surface using electric current. In this process, dissolved metal cations are reduced and form a film on an electrode. The method is also called electrodeposition. This page also compares electroplating with other thin film deposition methods. Chemical vapor deposition, or CVD, uses a gas-phase precursor. Spin coating spreads a liquid precursor by spinning it outward. Dip coating is similar, but the substrate is fully submerged instead of...

analysis of thermal expansion via dilatometry

analysis-of-thermal-expansion-via-dilatometry

Using Dilatometry to Measure Heating Effects

Dilatometry measures how a material changes in size as temperature changes. It can track changes in length, area, shape, or volume. The method is used to calculate thermal expansion, which is the expansion of a substance when it is heated. Thermal expansion matters when choosing materials for systems that face changing temperatures. Some materials need high thermal expansion, such as the liquid in a thermometer, because the change helps detect temperature shifts. Other uses need materials with...

electrochemical impedance spectroscopy

Why AC Signals Matter in Impedance

Electrical impedance describes how a circuit element resists the flow of electricity. It is a more general measure than electrical resistance, especially when a circuit is not simple enough to be described by resistance alone. Resistance is the ability of a circuit element to resist current. It is defined by Ohm's law, which relates voltage and current. That relationship works well for ideal resistors, but many real circuit elements are more complex. When an alternating current, or AC, is...

ceramic-matrix composite materials and their bending properties

ceramic-matrix-composite-materials-and-their-bending-properties

Bone-Inspired Ceramic Composites in Bending

Bone helps show how ceramic-matrix composites work. In this material system, the ceramic part gives compressive strength, while the polymer fiber reinforcement adds tensile and flexural strength. By changing the amounts of ceramic and polymer, engineers can make materials for specific uses. This idea matters in biomedical engineering, where replacing or copying bone after disease or traumatic injury is an important goal. For this study, plaster of Paris, a calcium sulfate compound, is used to...

nanocrystalline alloys and nano-grain size stability

nanocrystalline-alloys-and-nano-grain-size-stability

Keeping Nanocrystalline Alloy Grains Small

Nanocrystalline alloys are metals with grain sizes smaller than 100 nm. These tiny grains can give the material enhanced physical and mechanical properties. That is why nanocrystalline alloys are used or studied for semiconductor devices, biosensors, and aerospace parts. A major challenge is making dense bulk materials from these alloys. To reach close to 100% density, the material must be processed with elevated temperature and pressure. But as temperature and pressure rise, the small grains...

hydrogel synthesis

Hydrogels are cross-linked polymers that can absorb water and swell. They are made with relatively simple procedures and inexpensive materials, which makes them useful for many school-level chemistry and materials science topics. A hydrogel starts with a polymer backbone built from monomer reagents. An initiator makes the polymer reactive, and a crosslinking species connects the chains together. This network gives the material its final structure. Water absorption is one of the key features...

materials engineering

该系列采用尖端材料分析和表征方法，并介绍了一系列用于新技术和应用的先进材料和工艺。

Explore how hydrogels are made from cross-linked polymers and why they swell in water. Learn their properties and common uses in sensors, absorbent products, and drug delivery.

Hydrogels and Their Water Absorption

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