Powering smart materials by oscillatory chemical reactions

所有的植物和动物在某种程度上都有适应环境的能力，例如表现出向日性（一些花或叶子的表面跟随阳光的方向）或对热或疼痛有反应。遵循同样的原则，我们更倾向于使用能够感知环境条件并进行相应调整的智能材料，而不是使用适合一系列条件而不是单独适合任何条件的材料。我感兴趣的智能材料是聚合物凝胶，它表现出一种化学-机械反应，即材料介质的化学变化会导致材料所占体积的逐步变化，导致材料膨胀或收缩。这种结构变化可以用来迫使宿主分子脱离凝胶结构（崩溃）或进入凝胶结构（膨胀）。塌陷现象的应用之一是在药物输送系统中，只有在特定的环境条件下才能分配药物分子。另一方面，聚合物凝胶膨胀可用于在介质中封装不需要的反应抑制剂或病原体。智能聚合物凝胶的另一个应用是作为化学机械微阀，其中阀门（凝胶）通过介质的变化被激活。热激活微型阀就是一个例子。加热后凝胶坍塌，阀门打开，而去除热量后凝胶膨胀，阀门关闭。这在微粒径系统的流体流动和混合控制中有直接的应用。智能材料应用的一个基本要素是引起变化发生的刺激因素。本文研究了钯催化的苯乙炔氧化羰基化反应（ppoc）在甲醇中的应用，展望了其多用途性和重要的刺激应用。这是一个非凡的化学系统，当在搅拌间歇式反应器中操作时，pH值和反应热输出表现出明显的振荡。作为一种化学振荡器，它属于非线性化学动力学领域，研究与反应中一种或多种物质浓度的时间周期或近周期变化有关的现象。这类反应中最著名的是别洛乌索夫-扎博廷斯基反应。PCPOC反应是一个高度复杂的振荡系统，是金属配合物催化反应中振荡行为的一个特例。PCPOC反应如此重要的原因有很多：它提供了一种新的、尚未被很好理解的pH振荡器；它代表了由相对简单的试剂在催化系统中以振荡模式合成复杂分子的第一个例子；当在振荡状态下操作该系统时，与在非振荡模式下操作相比，可以实现高水平的产品选择性；除了pH值振荡外，还存在同步振荡热输出；它表现出两个相关的刺激，pH和温度；当与凝胶块耦合时，它可以通过产生振荡力来推进纳米器件。本研究的目的是在实验和理论的协同作用下，研究这种羰基化反应作为刺激物的应用。ppoc反应的预测物理化学模型将被开发，该系统将与pH敏感聚合物、温度响应聚合物和对两者都敏感的材料（即温度和pH响应聚合物复合膜）一起研究：(1)包含智能材料的环境；(2)与包含所述智能材料的环境通信的封闭环境；(3)包含所述智能材料与所述目标环境通信的封闭环境。

All plants and animals have the ability to adapt to the environment to some extent e.g. exhibit heliotropism (some flowers or leaves surfaces follow the direction of sunlight) or react to heat or pain. Following the same principle, instead of using materials designed to suit a range of conditions while not being optimal for any of them individually, we would prefer smart materials that have the ability to sense the conditions in their environment and adjust accordingly. The smart materials I am interested in are polymer gels that show a chemo-mechanical response, i.e. a change in the chemistry of the medium about the material results in a stepwise change in the volume that the material occupies by causing it to swell or collapse. This structural change may be used to force host molecules out of the gel structure (collapsing) or into the gel structure (swelling). One of the applications of the collapsing phenomenon is in drug delivery systems that would dispense drug molecules only under certain environmental conditions. On the other hand polymer gel swelling may be applied for the encapsulation of unwanted reaction inhibitors or pathogens in the media. Another application of smart polymer gels is as chemo-mechanical micro-valves where the valve (gel) is activated by a change in the medium. One example is a heat activated micro-valve. Upon heating the gel collapses and the valve opens while upon removing the heat the gel expands and the valve closes. This has direct application in the control of fluid flow and mixing in micro-size systems.An essential element in the application of smart materials is the stimulus that causes the occurrence of the change. The proposed research investigates the palladium-catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction in methanol envisioning many applications of its versatile nature and importantly application as a stimulus. This is an extraordinary chemical system that exhibits pronounced oscillations in pH and reaction heat output when operated in a stirred batch reactor. As a chemical oscillator it falls into the field of nonlinear chemical dynamics that studies phenomena related to the temporally periodic or nearly periodic variation of the concentrations of one or more species in a reaction. The best known reaction of this type is the Belousov-Zhabotinsky reaction. The PCPOC reaction is an oscillating system of higher complexity and an exceptional example of oscillatory behaviour in reactions catalysed by metal complexes. There are a number of reasons why the PCPOC reaction is of such great importance: it provides a novel and not well understood pH oscillator; it represents the first example of complex molecules synthesised from relatively simple reagents proceeding in a catalytic system in an oscillatory mode; when operating this system in an oscillatory regime high levels of product selectivity may be achieved compared to operating in a non-oscillatory mode; besides oscillations in pH, synchronised oscillatory heat output is present; it exhibits two relevant stimuli, pH and temperature; it may have application in propelling nano devices by generating an oscillating force when coupled with a block of gel.This study is aimed at the cooperative interplay between experimental and theoretical investigation into the application of this carbonylation reaction as a stimulus. Predictive physico-chemical models of the PCPOC reaction will be developed and this system will be researched with pH sensitive polymers, temperature responsive polymers and materials sensitive to both (i.e. temperature and pH responsive polymeric composite membranes) as: (1) an environment containing the smart material; (2) an enclosed environment communicating with the environment containing the smart material and (3) an enclosed environment containing the smart material communicating with the targeted environment.