INFLUENCES OF STRUCTURE AND PREPARATION CONDITIONS ON SIZE AND PHOTORESPONSIVE PROPERTIES OF AMPHIPHILIC AZO POLYMER COLLOIDAL SPHERES
INFLUENCES OF STRUCTURE AND PREPARATION CONDITIONS ON SIZE AND PHOTORESPONSIVE PROPERTIES OF AMPHIPHILIC AZO POLYMER COLLOIDAL SPHERES
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结构和制备条件对两亲性偶氮聚合物胶体球尺寸和光响应性能的影响
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
Tian Feng
中科院分区：
文献类型：
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作者：
Wang Xiaogong;Li Nan;Tian Feng
合成了具有不同偶氮发色团和功能化度（DF）的两亲性偶氮聚合物，并在选择性溶剂中通过疏水聚集法制备了聚合物的胶体球。以一定的搅拌速率向THF溶液中加入所需量的水，以获得胶体球的悬浮液。当水含量达到约70 vol%时，在悬浮液中加入过量的水来“淬灭”形成的结构。得到的胶体球悬浮液经四氢呋喃完全挥发后密封，用DLS和紫外-可见光谱对其进行表征。采用DLS/SLS-5022F激光散射仪对胶体球的大小和分布进行了测量。测量前，样品经0.45 μm Millipore滤光片澄清以去除粉尘，所有DLS测量均以90°散射角进行。采用紫外可见光谱法，通过测量光稳定状态下的反-顺光异构速率和异构度等参数，研究了偶氮发色团在胶体形成过程中的结构变化。在光响应实验中，用365 nm紫外光源照射样品，在38 cm距离处的光强为7000 mV/cm~2，在5 cm距离处的光强为21000 mV/cm~2。在我们的实验中，样品距离紫外线15cm，环境温度为30℃。研究了分子结构和制备条件对胶体球尺寸和光响应性能的影响。结果表明，官能团类型、DF以及制备条件（聚合物初始浓度、加水速率等）对胶体球的尺寸和光响应性能有显著影响。胶体球的大小随DF和初始浓度的增加而增大，随加水速率的增加而减小。聚{2-[4-（4-乙氧基苯基偶氮）苯氧基]丙烯酸乙酯-共丙烯酸}（PEAPE）胶体的光致异构化率高于聚{2-[4-（4-氰基苯基偶氮）苯氧基]丙烯酸乙酯-丙烯酸}（PCNPE）胶体。DF越大，PEAPE胶体的光异构化速率越慢。胶体的光致异构化速率随初始浓度的增加和水加入速率的降低而降低。从热力学和动力学的角度讨论了影响的可能机理。认为胶体球的形成是由动态条件控制的自组装过程。在初始浓度高、滴水速率慢的条件下，当水含量高于临界水含量（CWC）时，大多数疏水链形成的致密岩心上倾向于聚集更多聚合物链。此外，由于加水速度慢，聚合物链有机会重新排列形成稳定紧凑的结构。另一方面，随着加水速率的增加，附着在核上的聚合链在完全调整构象之前就被迅速“冻结”了。同时，它们可以形成新的不致密的核，从而削弱连续聚集的可能性。结果表明，形成的聚集体结构松散，光致异构化速率较快。
Amphiphilic azo polymers with different azo chromophores and degree of functionalization(DF) were synthesized,and colloidal spheres of the polymers were prepared by gradual hydrophobic aggregation in selective solvents.To obtain suspensions of colloidal spheres,the required amounts of water were added into the THF solutions at a certain stirring rate.As the water content reached ca.70 vol%,an excess of water was added into the suspensions to "quench" the formed structures.The obtained suspensions of colloidal spheres were sealed after THF was completely volatilized and were characterized by DLS and UV-Vis spectroscopy.The size and size-distribution of colloidal spheres were measured by using a DLS/SLS-5022F laser light scattering apparatus.Before the measurement,the sample was clarified by a 0.45 μm Millipore filter to remove dust,and all the DLS measurements were carried out with 90° scattering angle.UV-Vis spectroscopy was used to study the azo chromophore structure variation in the colloid formation process by measuring the parameters such as the trans-to-cis photoisomerization rate and the isomerization degree at the photostationary state.In the photoresponse experiments,the sample was irradiated by a 365 nm UV light source,and the light intensity was 7000 mV/cm~2 at a distance of 38 cm and 21000 mV/cm~2 at a distance of 5 cm,respectively.In our experiment,the sample was 15 cm away from the UV light,and the temperature of the environment was 30℃.The influences of molecular structure and preparation conditions on the size and photoresponsive properties of the colloidal spheres were studied in some detail.The result shows that the functional group type and DF as well as the preparation conditions(initial polymer concentration,the rate of water addition,etc.) have significant effects on the size and photoresponsive properties of the colloidal spheres.The size of colloidal spheres increases with the increase of DF and initial concentration,but decreases with the increase of the rate of water addition.The photoinduced isomerization rate of poly{2-[4-(4-ethoxyphenylazo)phenoxy]ethyl acrylate-co-acrylic acid}(PEAPE) colloids is higher than that of poly{2-[4-(4-cyanophenylazo)phenoxy]ethyl acrylateco-acrylic acid}(PCNPE) colloids.The PEAPE colloids with higher DF show a slower photoisomerization rate.The photoinduced isomerization rate of the colloids decreases with the increase of initial concentration and the decrease of the rate of water addition.The possible mechanism for the influence is also discussed based on thermodynamics and kinetics consideration.It is believed that the colloidal spheres form through a self-assembling process controlled by the dynamic conditions.For high initial concentration and slow water dropping rate,more polymer chains tend to aggregate on the compact cores formed from the most hydrophobic chains as the water content is above the critical water content(CWC).Moreover,the polymeric chains had chance to rearrange themselves to form stable and compact structures due to the slow rate of water addition.On the other hand,as the rate of water addition increased,the polymeric chains attached to the cores were quickly "frozen" before they could completely adjust their conformations.Also,they could form new less compact cores so as to weaken the continuous aggregation probability.As a result,the formed aggregates had loose structures,and the photoinduced isomerization rate was relatively fast.