Amphiphilic azo polymer spheres, colloidal monolayers, and photoinduced chromophore orientation

In this work, azobenzene-containing colloidal spheres have been fabricated and used to construct photoresponsive monolayers. The colloidal spheres were prepared from an amphiphilic azobenzene-containing random copolymer through hydrophobic aggregation of the polymer chains, which was induced by adding the selective solvent (H2O) into a THF solution of the polymer. The size and size distribution of the spheres depended on the initial concentration of the azo polymer in THF and the H2O/THF ratio. Adjusting those factors and optimizing other preparation conditions, uniform colloidal spheres could be obtained. Monolayers composed of hexagonally close-packed colloidal spheres were prepared by the capillary-force-driven method. The colloidal monolayers showed obvious dichroism after laser irradiation due to the photoinduced azo-chromophore orientation occurred in the spheres. The orientation order parameter was related to the irradiation time and estimated to be 0.09 at the photostationary state. The colloidal spheres and their monolayers can potentially be used as building blocks or media for reversible optical data storage, photo-switching, sensors, and other photo-driven devices.     

木质素基偶氮聚合物胶体球的制备

利用造纸废液中的碱木素(AL)合成了木质素基偶氮聚合物(AL-azo-COOEt), 并研究其自组装胶体化过程. 木质素偶氮聚合物的成功合成通过核磁共振氢谱(¹H NMR)、紫外-可见(UV-Vis)光谱、傅里叶变换红外(FTIR)光谱和元素分析等表征方法得到证实. 激光光散射(LLS)监测了AL-azo-COOEt的胶体化过程, 自组装形成的胶体球利用透射电镜(TEM)、扫描电镜(SEM)、X射线光电子能谱仪(XPS)和元素分析等进行表征. 结果表明,木质素偶氮聚合物通过疏水聚集作用可以形成规整的实心胶体球, 且为内部较疏水外部较亲水性质的结构. 木质素偶氮聚合物胶体球可以包载疏水性药物阿霉素(DOX), 且其缓释性能可以通过缓冲溶液的pH值来调控.     

Formation of ordered mesoporous films from in situ structure inversion of azo polymer colloidal arrays

This work shows that mesoporous polymeric films with spherical and elliptical pores can be obtained by in situ structure inversion of the azo polymer colloid arrays through selective interaction with solvent. The epoxy-based azo polymer contained both the pseudo-stilbene-type azo chromophores and the hydrophilic carboxyl groups. The colloidal spheres of the azo polymer were prepared by gradual hydrophobic aggregation of the polymeric chains in THF-H2O media, induced by a steady increase in the water content. Ordered 2D arrays of the hexagonally close-packed colloidal spheres were obtained by the vertical deposition method. After the solvent (THF) annealing, the ordered 2D arrays were directly transformed to mesoporous films through the sphere-pore inversion. Under the same condition, the 2D arrays composed of the ellipsoidal colloids, which were obtained by the irradiation of a polarized Ar+ laser beam on the colloidal sphere arrays, could be transformed to films with ordered elliptical pores. To our knowledge, this is the first example to demonstrate that mesoporous structures can be directly formed from the colloidal arrays of a homopolymer through structure inversion. This observation can shed new light on the nature of self-assembly processes and provide a feasible approach to fabricate mesoporous structures without the infiltration-removal step. By exploring the photoresponsive properties of the materials, mesoporous film with special pore structure and properties can be expected.     

Photoinduced deformation of amphiphilic azo polymer colloidal spheres

Photoinduced shape deformation of colloidal spheres made of an amphiphilic azo polymer has been demonstrated in this work. The polymer contains the donor-and-acceptor-type azobenzene chromophores and can form uniform colloidal spheres by dropwise adding water into its THF solution. When the colloidal spheres obtained were exposed to the interfering p-polarized Ar+ laser beams (150 mW/cm2), the colloidal spheres changed to prolates (i.e., "rugby-balls"), "spindles", and finally "rods", depending on the irradiation times. The elongated direction of the spheres was observed to be the same as the polarization direction of the laser beam. The average major-to-minor ratio of the ellipsoids could be easily adjusted by controlling the irradiation time. The deformation effect observed in this work can offer a new way to prepare nonspherical colloids from colloidal spheres and will shed new light on the correlation between the photodriven shape deformation and photoinduced surface relief gratings for the same type of polymers.     

Stretching effect of linearly polarized Ar+ laser single-beam on azo polymer colloidal spheres

This work shows that a linearly polarized Ar+ laser single-beam irradiation can cause stretching deformation of azo polymer colloidal spheres along the polarization direction of the laser beam. An epoxy-based polymer, containing 4-amino-4'-carboxyazobenzene at each repeat unit, was used to construct the colloidal spheres. The colloidal spheres were prepared by gradual hydrophobic aggregation of the polymeric chains in a THF/H2O dispersion medium, which was induced by a steady increase in the water content. When the obtained colloidal spheres were exposed to the spatially filtered and collimated Ar+ laser beam (488 nm, 150 mW/cm2), the colloids were stretched along the polarization direction of the laser beam. In the testing period (20 min), the colloids were deformed continuously as the irradiation time increased. When 2D close-packed arrays of the colloidal spheres were irradiated by the polarized laser single-beam, the colloidal spheres were all uniformly stretched along the polarization direction of the laser beam. On the contrary, when the arrays were irradiated by the interfering p-polarized laser beams, only the colloidal spheres in the bright regions of the interference pattern were significantly deformed.     

结构与制备条件对两亲性偶氮聚合物胶体球尺寸和光响应性的影响

合成了3种具有不同官能团或官能化度的双亲性多分散偶氮聚合物.系统研究了它们在选择性溶剂中形成聚合物胶体球时,各种因素对胶体球尺寸和光响应性能的影响规律.结果表明,不仅官能团和官能化度对胶体球的尺寸与光响应性有明显影响,具体的制备条件(如初始浓度、沉淀剂加入速率等)对胶体球尺寸和光响应性能也有重要影响.聚合物胶体球的粒径随官能化度的增加而增大;随初始浓度的增加和沉淀剂加入速率的减小而增大.聚合物PEAPE胶体球的光致异构化速率快于PCNPE胶体球的光致异构化速率.聚合物胶体球的光致异构化速率随官能化度的增加而减小;随初始浓度的增加和沉淀剂加入速率的减小而减小.这些影响表现出了明显的规律性.从双亲性聚合物在选择性溶剂中自组装形成胶体球的热力学与动力学因素出发,讨论了上述现象产生的原因.     

Synthesis of nanometer-scale polymeric structures on surfaces from template assisted admicellar polymerization: a comparative study with protein adsorption

A novel method for the formation of nanometer-scale polymer structures via template assisted admicellar polymerization (TAAP) is described. Admicellar polymerization uses a surfactant layer adsorbed on a surface to localize monomer to the surface prior to polymerization of the monomer. Nanostructures are formed by restricting adsorption to the uncovered sites of an already-templated surface, in this case to the interstitial sites between adsorbed latex spheres. Unlike most other process that form polymer nanostructures, polymer dimensions can be significantly smaller than the interstitial size because of sphere-surfactant interactions. Protein adsorption in the interstitial sites of colloidal arrays was also studied for three different proteins, and the results were compared with those obtained via admicellar polymerization.     

Azo polymer colloidal spheres containing different amounts of functional groups and their photoinduced deformation behavior

In this work, colloidal spheres composed of azo polymers with different chromophore loading densities were prepared, and their photoinduced deformation behavior was studied. The colloids were constructed by using a series of amphiphilic epoxy-based random copolymers containing 4-carboxylazobenzene functional groups with different degrees of functionalization (DFs). The colloidal spheres were fabricated through gradual hydrophobic aggregation of the polymeric chains in tetrahydrofuran-H2O dispersion media, which was induced by gradually adding water into the systems. The colloidal spheres were characterized by using transmission electron microscopy and dynamic light scattering. The photoinduced deformation behavior was studied by irradiating the colloidal spheres with a linearly polarized Ar+ laser beam. Results showed that the critical water content (CWC) for the colloid formation is related to the DF of the polymers, and CWC increases with the increase of DF. The hydrodynamic diameter of the colloidal spheres is also related to the DF of the polymers. When the DF of the polymers increases, the average size of the colloids gradually decreases. The hydrodynamic diameter of the colloidal spheres increases as the water dropping rate decreases. When the dropping rate is below 20 microL/s, the size of the colloidal spheres increases abruptly as the dropping rate further decreases. Upon the linearly polarized Ar+ laser beam irradiation, the colloids composed of polymers with different DFs can all be elongated along the polarization direction of the laser beam. As DF increases, the deformation degree characterized by the axial ratio (l/d) almost linearly increases. These observations can give some insight into the photoinduced deformation mechanism and can be used to construct colloids with different sizes and photoresponsive ability.     

Copper-mediated synthesis of PdI_2 colloidal spheres

A novel copper-mediated solvothermal method was proposed for synthesizing colloidal spheres of a new composition,palladium iodide(PdI2).Typical procedure was designed to involve the introduction of cupric chloride(CuCl2) as weak oxidant.CuCl2 was found to be essential for preventing the easy formation of palladium deposits as well as facilitating the synthesis and assembly.Under the co-effect of CuCl2 and the surfactant of polyvinylpyrrolidone(PVP),neutral PdI2 colloidal spheres with narrow size distributio...     

Azo polymer microspherical cap array: soft-lithographic fabrication and photoinduced shape deformation behavior

In this work, azo polymer microspherical cap arrays possessing unique photoprocessible properties have been fabricated through a soft-lithographic contact printing approach. In the process, hexagonal polystyrene (PS) colloidal arrays, obtained by the vertical deposition method, were used as masters. Poly(dimethylsiloxane) (PDMS) stamps with aligned hemisphere air voids on the surfaces were obtained by casting the precursor against the colloidal arrays. By using the stamps and a solution of an epoxy-based azo polymer (BP-AZ-CA) as "ink", the microspherical cap arrays were fabricated by pressing the "inked" surfaces against substrates. Uniform 2D arrays of the submicrometer spherical caps could be obtained on the substrates after peeling off the stamps and drying. The characteristic sizes of the arrays depended on some adjustable features, such as the diameters of PS spheres and concentrations of the "inks" used in the process. After exposure to a linearly polarized Ar+ laser single beam, the spherical caps could be stretched along the polarization direction, and the arrays were consequently transformed into ellipsoidal cap arrays. Upon irradiation of interfering p-polarized Ar+ laser beams, only the spherical caps in the bright fringes were deformed by the light irradiation, which resulted in more complicated surface relief patterns. The observation gives another well-defined example of the photoinduced mass migration in the submicrometer scale. The approach can potentially be applied to fabrication of microlens arrays with different converging rate in two directions.     

核/壳乳液聚合工艺中乳化剂的定量研究

以十二烷基硫酸钠(SDS)为乳化剂,采用多步种子乳液聚合方法制备了核/壳结构乳液,研究了乳化剂加入量以及加料速率对核壳乳液聚合的影响,并推导了核及壳乳液聚合阶段所需乳化剂量的计算公式.研究表明,当种子、核、壳乳液聚合阶段单体量分别为12g、50g和50g,种子乳液聚合阶段加入的乳化剂量为0.44g时,控制核、壳乳液聚合阶段乳化剂的加入量分别在0.64～2.07g及0.04～2.12g之间,且预乳化单体的滴加速度低于2.3g/min时,可以防止二次成核及新乳胶粒子的形成,制得粒径分布窄、核/壳结构明显的乳胶粒子.利用透射电镜(TEM)对所制备的核壳结构乳胶粒子的结构形态进行了验证,试验结果与理论预测结果一致.     

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.     

Characterization of nanostructured hollow polymer spheres with small-angle neutron scattering (SANS)

Hollow polymer spheres synthesized from a vesicle-directed polymerization can be dried and redispersed in water using a variety of nonionic ethoxylated alcohol surfactants as stabilizers. The final dispersions consist of both polymer shells and surfactant micelles, which remain together in colloidal suspension for at least several months. Small-angle neutron scattering (SANS) is used to measure the polymer shell thickness (63 A) and core radius (560 A) of the surfactant-stabilized hollow polymer spheres in the presence of surfactant micelles. Characterization by SANS provides information about the surfactant bilayer and polymer shell thicknesses which were previously unattainable.     

偶氮聚合物三角状聚集体的制备及光致形变行为研究

利用滴加沉淀剂法,通过偶氮聚合物BP-AZ-2CA在DMF-H2O体系中自组装得到了碗状的聚集体.利用透射电镜等对聚集体的组装过程及最终形貌等进行了表征.研究表明,通过调节初始聚合物浓度以及制备过程中的滴加水速率,可得到不同尺寸的碗状聚集体.将碗状聚集体置于单束偏振Ar+激光(488nm,110mW/cm2)照射下,所有的碗状聚集体都发生了沿着激光偏振方向的拉伸.碗状聚集体在激光拉伸后仍然维持中空的结构.     

双组分偶氮聚合物胶体球制备及其光致形变行为研究

研究了2种环氧树脂类含4-氨基-4′-硝基偶氮苯和4-氨基-4′-羧基偶氮苯生色团聚合物(BP-AZ-NT、BP-AZ-CA)双组分胶体球的制备和光致形变行为.通过在上述聚合物的四氢呋喃溶液中逐步加水诱导自组装的方法,得到了BP-AZ-CA/BP-AZ-NT双组分胶体球.在上述两种聚合物自组装形成胶体球过程中,较为疏水的BP-AZ-NT分子先发生聚集,而较亲水的BP-AZ-CA则在形成的胶体颗粒表面发生进一步聚集.在胶体球形成过程中,体系的临界水含量(CWC)主要由BP-AZ-NT发生聚集时的水含量决定,双组分胶体球的外层则含较多的BP-AZ-CA分子.比较单组分胶体球与双组分胶体球在线偏振Ar+激光(488nm,100mW/cm2)照射下的形变行为,进一步证实了通过上述方法可以制备BP-AZ-CA和BP-AZ-NT双组份的胶体球;胶体球形变时的初始拉伸速率由胶体球的外层聚合物分子的性质所决定。     

One-step fabrication of ZIF-8/polymer composite spheres by a phase inversion method for gas adsorption

This paper reports a phase inversion method for the preparation of macroporous polysulfone (PS) composite spheres through a single orifice spinneret. Surfactant F127 was pre-added in the polymer solution as a surface pore-forming agent, and different amount of zeolitic imidazolate framework-8 (ZIF-8) particles were incorporated to form the ZIF-8/polysulfone (ZIF-8/PS)-composite spheres. ZIF-8 and polymer acted as the adsorbent and binder in the final composite spheres, respectively. The fabrication conditions, such as the types of the surfactant, the amount of the surfactant, and ZIF-8 added in the polymer solution, were investigated. Nitrogen and carbon dioxide sorption analysis indicated the ZIF-8/PS composite spheres had similar properties as the pure ZIF-8 particles, and the active sites of ZIF-8 in the polymer composites were well exposed. The composite spheres exhibited advantages of easy handling and recycling over ZIF-8 particles, and this phase inversion method can be extended to prepare other polymer composite spheres.     

General bottom-up construction of spherical particles by pulsed laser irradiation of colloidal nanoparticles: a case study on CuO

The development of a general method to fabricate spherical semiconductor and metal particles advances their promising electrical, optical, magnetic, plasmonic, thermoelectric, and optoelectric applications. Herein, by using CuO as an example, we systematically demonstrate a general bottom-up laser processing technique for the synthesis of submicrometer semiconductor and metal colloidal spheres, in which the unique selective pulsed heating assures the formation of spherical particles. Importantly, we can easily control the size and phase of resultant colloidal spheres by simply tuning the input laser fluence. The heating-melting-fusion mechanism is proposed to be responsible for the size evolution of the spherical particles. We have systematically investigated the influence of experimental parameters, including laser fluence, laser wavelength, laser irradiation time, dispersing liquid, and starting material concentration on the formation of colloidal spheres. We believe that this facile laser irradiation approach represents a major step not only for the fabrication of colloidal spheres but also in the practical application of laser processing for micro- and nanomaterial synthesis.     

垂直排列法组装胶体晶体的最新进展

光子晶体是一种具有光子带隙的新型功能材料.利用胶体粒子自组装三维光子晶体由于其制备过程比较经济、简单,从而为很多人所关注.目前报道的方法已有多种.其中垂直排列法的简便易行使得其受到了广泛的研究,但另一方面这种方法本身的缺点也限制了它的使用范围.针对这种情况,很多研究机构提出了他们的改进方法.本文简要概述了在这一方面的最新进展,并且在本实验室已能够制备任意单分散、均一尺寸二氧化硅粒子的基础上,采用恒温快速蒸发自组装法得到了高质量的胶体晶体排列.     

Close-packed hemispherical microlens array from two-dimensional ordered polymeric microspheres

This paper describes a facile, reproducible soft-lithography-based method for fabricating hexagonally close-packed microlens arrays by templating the surface of a colloidal monolayer, which is formed by spin-casting monodisperse polystyrene microspheres. The relief structure of colloidal monolayers has successfully generated PDMS elastomers with hexagonal arrays of hemispherical air voids. Closely packed hemispherical microlens arrays were imprinted on ultraviolet-curable photopolymers which are bound on glass substrates. Atomic force microscopy measurements showed that each spherical hole of the PDMS molds is 103 nm deep and the replicated microlens is 95 nm in height with narrow size distribution and good reproducibility. Without a multistep engineering process, this method might provide a reliable route to fabricate embossed thin layers ranging from nanometer to micrometers by controlling the size of polymer microspheres over a centimeter scale area.     

含三氟甲基偶氮生色团环氧树脂类聚合物合成和光致表面自结构研究

利用后重氮偶合反应,将4-(三氟甲基)苯胺的重氮盐与两种具有高苯胺残基密度的环氧树脂类前体聚合物在极性有机溶剂中反应,制备了两种具有高生色团密度的环氧树脂类偶氮聚合物PEP-AZ-CF3和PEP-35AZ-CF3.利用1H-NMR、FTIR、UV-Vis和DSC等分析方法对2种偶氮聚合物结构、热性能及吸收光谱性能进行了分析及表征.研究了在不同波长的激光(488、532及589 nm)照射下,2种偶氮聚合物薄膜光致表面自结构的形成.研究结果表明,入射激光的波长对偶氮聚合物表面自结构现象的形成有明显影响.仅在波长488 nm的偏振激光(线偏振光或圆偏振光)照射下,2种偶氮聚合物薄膜表面能观察到自结构现象.圆偏光比线偏光更有利于诱导表面起伏结构的形成,但形成的表面结构不具备长程取向有序性.聚合物生色团中偶氮键邻位的取代甲基对表面自结构的形成起到阻碍作用.