Polymer Structure Characterization-From Nano to Macro Organization. By Richard A. Pethrick.

Patterning of a Surface Immobilized ATRP Initiator with an Inkjet Printer

A new technique for patterning polymer brushes on the micrometer scale has been developed in which an inkjet printer was used to deposit droplets of acid on a surface-immobilized initiator for atom transfer radical polymerization (ATRP). The acid cleaved an ester bond in the ATRP initiator in a saponification reaction. As a result, the ATRP initiator was rendered inactive. To control the degree of defunctionalization, a new initiator containing a weak ester bond was derived from a tertiary alcohol. Comparison to an established ATRP initiator, derived from a primary alcohol, showed that the novel initiator was defunctionalized with a higher efficiency. Control of the reaction time allowed to…

Nanowear on Polymer Films of Different Architecture

In this paper, we describe atomic force microscope (AFM) friction experiments on different polymers. The aim was to analyze the influence of the physical architecture of the polymer on the degree and mode of wear and on the wear mode. Experiments were carried out with (1) linear polystyrene (PS) and cycloolefinic copolymers of ethylene and norbornene, which are stabilized by entanglements, (2) mechanically stretched PS, (3) polyisoprene-b-polystyrene diblock copolymers, with varying composition, (4) brush polymers consisting of a poly(methyl methacrylate) (PMMA) backbone and PS side chains, (5) PMMA and PS brushes grafted from a silicon wafer, (6) plasma-polymerized PS, and (7) chemically c…

Surface Coatings Based on Polysilsesquioxanes: Solution-Processible Smooth Hole-Injection Layers for Optoelectronic Applications

Optoelectronic devices usually consist of a transparent conductive oxide (TCO) as one electrode. Interfacial engineering between the TCO electrode and the overlying organic layers is an important method for tuning device performance. We introduce poly(methylsilsesquioxane)-poly(N,N-di-4-methylphenylamino styrene) (PMSSQ-PTPA) as a potential hole-injection layer forming material. Spin-coating and thermally induced crosslinking resulted in an effective planarization of the anode interface. HOMO level (-5.6 eV) and hole mobility (1 × 10(-6)  cm(2)  · Vs(-1) ) of the film on ITO substrates were measured by cyclovoltammetry and time-of-flight measurement demonstrating the hole injection capabili…

Exciton diffusion controlled quantum efficiency in hybrid dye sensitized solar cells.

Well-ordered and uniform titania nanoparticle arrays were synthesized using diblock copolymers as structure directing agents. High molecular weight copolymers of polystyrene-b-polyethylene oxide and poly(methylmethacrylate)-b-polyethylene oxide were used to control the distance between titania nanoparticles in the range of 20-60 nm. Using these titania nanoparticle arrays and regioregular poly(3-hexylthiophene), models for a dye sensitized photovoltaic cell were assembled, in which the interparticle spacing was systematically varied. In these simplified solar cells, the titania nanocrystals were surrounded by a continuous regioregular poly(3-hexylthiophene) phase. The spacing between the ti…

From Spherical Mesopores to Worm-Shaped Mesopores : Morphology Transition in Titania–Polystyrene-b-poly(ethylene oxide) Composite Films with Increasing Sol–Gel Reaction Time

A morphology transition from spherical mesopores to worm-shaped mesopores within titania block copolymer composite thin films has been observed by varying the sol–gel reaction time from 40 min to 48 h in the four-component templating system of polystyrene-$\mathit{b}$-poly(ethylene oxide) (PS-$\mathit{b}$-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP) with a PS-$\mathit{b}$-PEO mass concentration of 0.25 wt.-%. The impact of the sol–gel reaction time on the local structure, long-range lateral structure, and vertical structure of the as-prepared, calcined, and UV-degraded thin films as well as the structural changes in solution have been systematically investigate…

A modular approach towards functional supramolecular aggregates - subtle structural differences inducing liquid crystallinity.

Herein we report an efficient modular approach to supramolecular functional materials. Hierarchical self-assembly of azopyridine derivatives and hydrogen-bond donors yielded discotic assemblies. Subtle differences in the core units introduced mesomorphic behaviour and fast photo-response of the liquid crystals based on phloroglucinol. The presented results prove the benefits of a modular methodology towards highly responsive materials with tailor-made properties.

Redox active polymers with phenothiazine moieties for nanoscale patterning via conductive scanning force microscopy

Redox active polymers with phenothiazine moieties have been synthesized by Atomic Transfer Radical Polymerization (ATRP). These novel polymers reveal bistable behaviour upon application of a bias potential above the oxidation threshold value. Using conductive Scanning Force Microscopy, two distinguishable conductivity levels were induced on a nanoscale level. These levels were related to a high conducting “On” and a low conducting “Off” state. The “On” state is generated by the oxidation of the phenothiazine side chains to form stable phenothiazine radical cations. The formation and stability of the radical sites was examined by cyclic voltammetry, electron spin resonance and optical spectr…

Functional templates for hybrid materials with orthogonal functionality.

We demonstrate an integrated approach to prepare a nanostructured, multifunctional material with mutually exclusive, orthogonal properties. The hybrid material was obtained within a single step via self-assembly in solution. It consists of TiO(2) as a functional metal oxide and an amphiphilic block copolymer, poly(ethylene oxide)-b-poly(triphenylamine) (PEO-PTPA). Within the materials' synthesis, the block copolymer not only acts as a templating agent but also adds an electronic functionality to the resulting hybrid material. During the synthesis, a variety of self-assembled morphologies, ranging from spheres to wires, can be created. The obtained morphology depends on the weight fraction o…

Hierarchically Structured Titania Films Prepared by Polymer/Colloidal Templating

Hierarchically structured titania films for application in hybrid solar cells are prepared by combining microsphere templating and sol-gel chemistry with an amphiphilic diblock copolymer as a structure-directing agent. The films have a functional structure on three size scales: (1) on the micrometer scale a holelike structure for reduction of light reflection, (2) on an intermediate scale macropores for surface roughening and improved infiltration of a hole transport material, and (3) on a nanometer scale a mesoporous structure for charge generation. Poly(dimethyl siloxane)-block-methyl methacrylate poly(ethylene oxide) (PDMS-b-MA(PEO)) is used as a structure-directing agent for the prepara…

Comparison of Hybrid Blends for Solar Cell Application

In blended hybrid systems distinct micro- or nanostructured materials can be formed by phase separation. Network structures of particles or rods in a polymer matrix can be developed via self-assembly. We use this blending approach to compare active materials for application in solar cell devices. Blends were fabricated from either poly(hexylthiophene) P3HT or poly(triphenylamine) PTPA mixed with nanocrystalline TiO 2 rods. In this manner, we compare two different hole conducting polymers in their performance in photovoltaic devices, while experimental conditions are kept identical. We find that the choice of solvent and photovoltaic characterization conducted in inert atmosphere is of impor…

Template-assisted fabrication of free-standing nanorod arrays of a hole-conducting cross-linked triphenylamine derivative: toward ordered bulk-heterojunction solar cells.

Free-standing nanorod arrays of a thermally cross-linked semiconducting triphenylamine were fabricated on conductive ITO/glass substrates via an anodic aluminum oxide (AAO) template-assisted approach. By using a solution wetting method combined with a subsequent thermal imprinting step to fill the nanoporous structure of the template with a cross-linkable triphenylamine derivative, a polymeric replication of the AAO was obtained after thermal curing and selective removal of the template. To obtain well-aligned and free-standing nanorod arrays, aggregation and collapse of the nanorods were prevented by optimizing their aspect ratio and applying a freeze-drying technique to remove the aqueous…

Crystallization of Vaterite Nanowires by the Cooperative Interaction of Tailor-Made Nucleation Surfaces and Polyelectrolytes

The concepts of template-induced crystallization on self-assembled monolayers (SAMs) and the use of polymer additives are combined into a new strategy, where, through the cooperative interaction of a SAM matrix involved in the nucleation process, poly(acrylic acid), a dissolved polyelectrolyte, and the dissolved ions, hierarchically ordered mineral structures are formed. The adsorption of poly(acrylic acid) to the SAM is monitored using a quartz microbalance. Transmission electron microscopy measurements on samples that are taken from polyacrylate solution in short intervals after the start of the reaction reveals that nanometer-sized particles pre-formed in solution are being attached to t…

Temperature dependence of surface reorganization characteristics of amphiphilic block copolymer in air and in water studied by scanning force microscopy

We have investigated the surface reorganization characteristics of a novel amphiphilic diblock copolymer, poly(acetic acid-2-(2-(4-vinyl-phenoxy)-ethoxy)-ethylester)-block-polystyrene (PAEES-b-PS), in response to varying interfaces from air to water and vice-versa at various temperatures. The surface reorganization characteristics of the block copolymer films was monitored by scanning force microscopy, in order to delineate the kinetically controlled morphological process of surface reorganization of a diblock copolymer, with a particular emphasis on the phase contrast signal which allowed the determination of local composition patterns of PAEES-b-PS at the surface. Upon heating a water-an…

Morphology evolution in mesoporous titania block copolymer composite films with increasing Sol-Gel reaction time

A morphology evolution of thin films of titania from spherical mesopores to worm-shaped mesopores was realized by simply varying the sol–gel reaction time from 46 min to 25 h in the quadruple system consisting of polystyrene–block-poly(ethylene oxide) (PS–b-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP). Imaging techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to investigate the local structure change of the as-prepared, calcined, and UV-degraded composite films. Grazing incidence small angle X-ray scattering (GISAXS) experiments prove that the structure change in local areas is representative of that over the…

CCDC 1455700: Experimental Crystal Structure Determination

Related Article: Michael Pfletscher, Christoph Wölper, Jochen S. Gutmann, Markus Mezger, Michael Giese|2016|Chem.Commun.|52|8549|doi:10.1039/C6CC03966A