Self-organized polymer nanocomposite inverse opal films with combined optical properties

Inverse opal films with unique optical properties have potential as photonic crystal materials and have stimulated wide interest in recent years. Herein, iridescent hybrid polystyrene/nanoparticle macroporous films have been prepared by using the breath‐figure method. The honeycomb‐patterned thin films were prepared by casting gold nanoparticle‐doped polystyrene solutions in chloroform at high relative humidity. Highly ordered hexagonal arrays of monodisperse pores with an average diameter of 880 nm are obtained. To account for the observed features, a microscopic phase separation of gold nanoparticles is proposed to occur in the breath‐figure formation. That is, individual gold nanoparticles adsorb at the solution/water interface and effectively stabilize condensed water droplets on the solution surface in a hexagonal array. Alternatively, at high nanoparticle concentrations the combination of breath‐figure formation and nanoparticle phase separation leads to hierarchical structures with spherical aggregates under a honeycomb monolayer. The films show large features in both the visible and NIR regions that are attributed to a combination of nanoparticle and ordered‐array absorptions. Organic ligand‐stabilized CdSe/CdS quantum dots or Fe₃O₄ nanoparticles may be loaded into the honeycomb structure to further modify the films. These results demonstrate new methods for the fabrication and functionalization of inverse opal films with potential applications in photonic and microelectronic materials.     

(110)‐Oriented ZIF‐8 Thin Films on ITO with Controllable Thickness

(110)‐oriented zeolitic imidazolate framework (ZIF)‐8 thin films with controllable thickness are successfully deposited on indium tin oxide (ITO) electrodes at room temperature. The method applied uses 3‐aminopropyltriethoxysilane (APTES) in the form of self‐assembled monolayers (SAMs), followed by a subsequent adoption of the layer‐by‐layer (LBL) method. The crystallographic preferential orientation (CPO) index shows that the ZIF‐8 thin films are (110)‐oriented. A possible mechanism for the growth of the (110)‐oriented ZIF‐8 thin films on 3‐aminopropyltriethoxysilane modified ITO is proposed. The observed cross‐sectional scanning electron microscopy (SEM) images and photoluminescent (PL) spectra of the ZIF‐8 thin films indicate that the thickness of the ZIF‐8 layers is proportional to the number of growth cycles. The extension of such a SAM method for the fabrication of ZIF‐8 thin films as described herein should be applicable in other ZIF materials, and the as‐prepared ZIF‐8 thin films on ITO may be explored for photoelectrochemical applications.     

Photochromism of novel molybdate/alkylamine composite thin films.

Novel inorganic/organic composite films of molybdates with photochromic properties have been prepared by self-assembly using alkylammonium ions as a supramolecular template. Both 1-hexadecylammonium/polyoxomolybdate (C16-Mo) and 1-octadecylammonium/polyoxomolybdate (C18-Mo) composite films have been successfully fabricated. The elemental analysis and thermal gravimetric analysis show that the main product in the C16-Mo film was (C16H33NH3)4Mo8O26. The X-ray diffraction (XRD) results indicate that the composite films were lamellar in nature. The IR, Raman and X-ray photoelectron spectroscopy (XPS) results show that the polyoxomolybdate anions present as MoO6 octahedra and that the Mo species exists as Mo6+ in the freshly prepared films. The alkyl chains in the 1-hexadecylammonium chains were linear and the alkyl groups are an all-trans configuration. Upon UV irradiation of the C16-Mo films, some Mo6+ was reduced to Mo5+, some -NH3+ became -NH2 with a concomitant increase in the concentration of -OH groups on the molybdate moieties, and the films were colored. Thus, the photochromism of the films involves the reduction of Mo6+ to Mo5+, coupled with a proton transfer from 1-hexadecylammonium ions to an oxygen atom at the Mo site. In contrast to thin films of transition-metal oxides, which all show photochromism in the blue region of the electromagnetic spectrum, these composite films show photochromism in the violet region with the greatest absorbance change at 472 nm.     

Simulated annealing study of diblock copolymer thin films confined between two homogeneous surfaces.

Thin films of symmetric diblock copolymers confined between two parallel surfaces have been systematically investigated by means of simulated annealing on a simple cubic lattice. The study was carried out for systems with different film thicknesses and surface-polymer interactions. Very regular equilibrium morphologies of lamella are formed in almost all cases. The dependence of lamellar orientations, total energy, chain-conformation entropy, and free energy of the confined films on the film thickness and the strength of surface-polymer interactions has been studied systematically. The influence of packing frustration on morphology is observed and the mechanisms of lamellar orientations are investigated.     

金属有机骨架薄膜材料的三阶非线性光学性能研究进展

金属有机骨架(MOFs)材料因其可设计的结构以及灵活可控的配位模式,在三阶非线性光学(NLO)领域引起了广泛的关注。与液体分散状态相比,MOFs在固体状态下的三阶NLO性能更为重要,这不仅可以深入了解MOFs本身所固有的光学性能,还有助于实现MOFs在光学器件中的实际应用。然而,由于散射的存在和透光率的限制,单独的MOFs材料难以直接实现固体状态下的三阶NLO性能研究,将MOFs制备成具有较好光学透过性的薄膜是研究其NLO性能最为可行的一种策略。MOFs薄膜不仅很好地继承了MOFs所固有的三阶NLO性能,而且还结合了薄膜的高透光率以及灵活的机械性能。基于此,本文分析总结了MOFs薄膜的制备方法及其NLO性能研究方面的相关工作,并根据目前MOFs薄膜在三阶NLO性能方面的研究现状对其未来发展予以了展望。     

金属有机骨架薄膜材料的三阶非线性光学性能研究进展

金属有机骨架(MOFs)材料因其可设计的结构以及灵活可控的配位模式,在三阶非线性光学(NLO)领域引起了广泛的关注。与液体分散状态相比,MOFs在固体状态下的三阶NLO性能更为重要,这不仅可以深入了解MOFs本身所固有的光学性能,还有助于实现MOFs在光学器件中的实际应用。然而,由于散射的存在和透光率的限制,单独的MOFs材料难以直接实现固体状态下的三阶NLO性能研究,将MOFs制备成具有较好光学透过性的薄膜是研究其NLO性能最为可行的一种策略。MOFs薄膜不仅很好地继承了MOFs所固有的三阶NLO性能,而且还结合了薄膜的高透光率以及灵活的机械性能。基于此,本文分析总结了MOFs薄膜的制备方法及其NLO性能研究方面的相关工作,并根据目前MOFs薄膜在三阶NLO性能方面的研究现状对其未来发展予以了展望。     

Progressive transition from resonant to diffuse reflection in anisotropic colloidal films

The synthesis and characterization of highly ordered three‐dimensional photonic crystals have been the subjects of intense study over the past two decades due to the unique ability of these structures to control light at the nanoscale. Building on that work in recent years, increasing interest is now focused on the unique optical properties of disordered and quasi‐ordered photonic structures. We present a study of the effects of shape anisotropy and disorder on the specular reflection properties of polymer‐based colloidal films comprised of rod‐shaped subunits of varying aspect ratio. We characterize the specular reflectance properties of these films as a function of their increasing levels of disorder, demonstrating progressive transition from resonant reflection to diffuse reflection. The onset of the diffuse reflection is governed by particle size. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys. 2014 , 52, 611–617     

From cloudy to transparent: chain rearrangement in hydrogen-bonded layer-by-layer assembled films.

The cloudiness of hydrogen-bonded LBL films assembled from polyvinylpyrrolidone (PVPON) and poly(acrylic acid) (PAA) is studied in detail by two approaches: spectroscopy (Fabry-Pérot fringes) and microscopy (AFM). Fabrication parameters such as temperature, molecular weight, pH value, and rinsing time, have notable influences on film cloudiness. The buildup of the PVPON/ PAA film is a two-stage process of adsorption and chain rearrangement. Generally, adsorption is fast, while chain rearrangement is slow. The fast adsorption process traps defects, whereas the relatively slow chain-rearrangement process can not heal the defects in time; therefore; the number of defects continuously increases as LBL assembly proceeds, and a cloudy, heterogeneous film is produced. However, the as-prepared cloudy films become transparent and homogeneous on subsequent annealing in acidic water. UV/Vis spectroscopy and fluid AFM were applied to monitor this transition ex situ and in situ, respectively. It is found that increasing the annealing temperature accelerates the transition from cloudy to transparent, and the transition of the film made from higher molecular weight polymer is slower.     

Effects of dipolar interactions on linear and nonlinear optical properties of multichromophore assemblies: a case study

Interchromophore interactions in flexible multidipolar structures for nonlinear optics were addressed by a combined experimental and theoretical study on two series of one-, two-, and three-chromophore systems in which identical push-pull chromophores are assembled through covalent and flexible linkers in close proximity. The photophysical and nonlinear optical properties (quadratic hyperpolarizability) of the multichromophore systems were investigated and compared to those of the monomeric chromophores. Multimers have larger dipole moments than their monomeric analogues, that is, the dipolar subchromophores self-orientate within the multimeric structures. This effect was found to depend on the intersubchromophore distance in a nontrivial manner, which confirms that molecular engineering of such flexible systems is more complex than in completely geometrically controlled systems. Electric-field-induced second-harmonic generation (EFISHG) measurements in solution revealed increased figures of merit as compared to the monomeric analogue. This effect increases with increasing number and polarity of the individual subchromophores in the nanoassembly and increasing spacing between dipolar subchromophores. Experimental results are interpreted by a theoretical model for interacting polar and polarizable chromophores. The properties of multidipolar assemblies are shown to be related to the relative orientation of chromophores, which is imposed by interchromophore interactions. The supramolecular structure is thus a result of self-organization. The proposed theoretical model was also used to predict the properties of multichromophore structures made up of more polar and polarizable push-pull chromophores, and showed that stronger interchromophore interactions can heavily affect the individual optical responses. This suggests new routes for engineering highly NLO responsive multichromophore systems.     

Self‐assembly of metallo‐supramolecular block copolymers in thin films

The self‐assembly of a metallo‐supramolecular PS‐[Ru]‐PEO block copolymer, where ‐[Ru]‐ is a bis‐2,2′:6′,2″‐terpyridine‐ruthenium(II) complex, in thin films was investigated. Metallo‐supramolecular copolymers exhibit a different behavior as compared to their covalent counterparts. The presence of the charged complex at the junction of the two blocks has a strong impact on the self‐assembly, effecting the orientation of the cylinders and ordering process. Poly(ethylene oxide) cylinders oriented normal to the film surface are obtained directly regardless of the experimental conditions over a wide range of thicknesses. Exposure to polar solvent vapors can be used to improve the lateral ordering of the cylindrical microdomains. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4719–4724, 2008     

Covalently attached self‐assembly of ultrathin films from hydroxy‐containing porphyrin and diazoresin

Ultrathin films from 5,10,15,20‐tetrakis(4‐hydroxyphenyl) porphyrin (HPP) and diazoresin (DR) via a H bonding interaction were fabricated with the self‐assembly technique. Under UV irradiation, the H bonds between the layers will convert to covalent bonds following the decomposition of the diazonium group of DR. The stability of the film against the polar solvent and electrolyte aqueous solution increases a lot because of the formation of the covalent crosslinking structure. Thus, the photoelectric conversion property of DR/HPP film can be measured directly with a normal photoelectric chemical cell with potassium chloride as the electrolyte. The maximum of the anodic photocurrent was measured as 1.7 μ Å for an eight bilayer DR/HPP film deposited on an indium–tin oxide glass electrode. The action spectrum of the photocurrent generation indicated that the HPP contained in the film is responsible for the generation of the observed photocurrent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3103–3108, 2003     

Viscoelastic properties of ultrathin polycarbonate films by liquid dewetting

A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (T_g) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the T_g of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566