Clemens Liedel

On the alignment of a cylindrical block copolymer: a time-resolved and 3-dimensional SFM study

In a combined quasi in situscanning force microscopy study we close trace the alignment process of thin polymer films of poly(styrene)-b-poly(2-vinylpyridine)-b-poly(tert-butyl methacrylate) triblock terpolymer exposed to a high electric in-plane field and solvent vapor. Our experiments show that in this triblock terpolymer a perforated lamella structure forms the basis for the core–shell cylindrical structure. Further we observe a hexagonal superstructure during the alignment process that occurs with solvent vapor annealing in the presence of a high electric field (6–15 V μm−1). The electric field induced reorientation includes a rupture-and-growth mechanism and the rotation of the hexagonal lattice. We reconstruct the 3D-structure of the aligned microdomains with quasi in situSFM nanotomography. The gained 3D reconstructions lead to a detailed understanding of the polymer film behavior in the border region between perforated lamella and the cylindrical phase. Combining time-resolved SFM datasets with 3D reconstructions, we present a model for the rearrangement of the polymer cylinders on the basis of a hexagonally perforated lamella. One-dimensionally aligned core–shell cylinders could form the basis for electrically isolated nanowires once the cylinder core is metalized.

Electric-Field-Induced Alignment of Block Copolymer/Nanoparticle Blends

External electric fields readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-field-induced alignment of a lamellae-forming polystyrene-block-poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-field-assisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such films under benign experimental conditions.

Piezoelectric Properties of Non-Polar Block Copolymers

Most polymers are typical dielectric materials, but recent research in our group has shown that nanostructured block copolymer morphologies exhibit new and unexpected electroactive behavior. We present herein the fi rst study of converse piezoelectric properties in non-crystalline polymer systems, consisting of non-polar monomers, and evaluate its evolution with temperature to yield detailed information on electric fi eld‐ polymer interaction on a molecular level. The observed properties should hold generally and suggest that block copolymers may provide a valuable new route to piezoelectric materials. So far, mostly inorganic, perovskite structured ceramics, many of them titanate derivatives such as lead zirconate titanate (PZT), dominate the fi eld of commercial piezoelectric applications. Nanogenerators, fi eld-effect transistors, strain, and optoelectronic sensors are only few of many applications for this interesting class of materials. [ 1 , 2 ] Whilst the piezoelectric properties of many of these crystals and ceramics are well

Green Imidazolium Ionics–From Truly Sustainable Reagents to Highly Functional Ionic Liquids

We report the synthesis of task-specific imidazolium ionic compounds and ionic liquids with key functionalities of organic molecules from electro-, polymer-, and coordination chemistry. Such products are highly functional and potentially suitable for technology applications even though they are formed without elaborate reactions and from cheap and potentially green reagents. We further demonstrate the versatility of the used synthetic approach by introducing different functional and green counterions to the formed ionic liquids directly during the synthesis or after metathesis reactions. The influence of different cation structures and different anions on the thermal and electrochemical properties of the resulting ionic liquids is discussed. Our goal is to make progress towards economically competitive and sustainable task-specific ionic liquids.

Ultrafast Self-Assembly of Sub-10 nm Block Copolymer Nanostructures by Solvent-Free High-Temperature Laser Annealing

Laser spike annealing was applied to PS-b-PDMS diblock copolymers to induce short-time (millisecond time scale), high-temperature (300 to 700 °C) microphase segregation and directed self-assembly of sub-10 nm features. Conditions were identified that enabled uniform microphase separation in the time frame of tens of milliseconds. Microphase ordering improved with increased temperature and annealing time, whereas phase separation contrast was lost for very short annealing times at high temperature. PMMA brush underlayers aided ordering under otherwise identical laser annealing conditions. Good long-range order for sub-10 nm cylinder morphology was achieved using graphoepitaxy coupled with a 20 ms dwell laser spike anneal above 440 °C.

Reversible Switching of Block Copolymer Nanopatterns by Orthogonal Electric Fields

It is demonstrated that the orientation of striped patterns can be reversibly switched between two perpendicular in-plane orientations upon exposure to electric fields. The results on thin films of symmetric polystyrene-block-poly(2-vinyl pyridine) polymer in the intermediate segregation regime disclose two types of reorientation mechanisms from perpendicular to parallel relative to the electric field orientation. Domains orient via grain rotation and via formation of defects such as stretched undulations and temporal phase transitions. The contribution of additional fields to the structural evolution is also addressed to elucidate the generality of the observed phenomena. In particular solvent effects are considered. This study reveals the stabilization of the meta-stable in-plane oriented lamella due to sequential swelling and quenching of the film. Further, the reorientation behavior of lamella domains blended with selective nanoparticles is addressed, which affect the interfacial tensions of the blocks and hence introduce another internal field to the studied system. Switching the orientation of aligned block copolymer patterns between two orthogonal directions may open new applications of nanomaterials as switchable electric nanowires or optical gratings.

Composition inversion to form calcium carbonate mixtures

Composition inversion takes place in equimolar solid mixtures of sodium or ammonium carbonate and calcium chloride with respect to the combination of anions and cations leading to the corresponding chloride and calcite in complete conversion. The transformation takes place spontaneously under a variety of different situations, even in a powdery mixture resting under ambient conditions. Powder X-ray diffraction data and scanning electron microscopy micrographs are presented to describe the course of the reaction and to characterize the reaction products. The incomplete reaction in the interspace between two compressed tablets of pure starting materials leads to an electric potential due to the presence of uncompensated charges.

Recent Developments in In Situ SFM of Block Copolymers: 3D Volume Structures and Dynamics

This chapter uses various research examples to illustrate how recent developments in scanning force microscopy (SFM) allow a detailed understanding of complex soft matter structures. The central focus lies in the introduction to the technical working principle of quasi in situ SFM (QIS-SFM) which is supported by selected applications for the analysis of dynamic and structural behavior of block copolymer films under solvent vapor annealing in the presence of a high electric field. We demonstrated that the internal film structure can be reconstructed tomographically with high depth resolution by a combination of topography and phase imaging after successive surface erosion via low-pressure plasma treatment. The QIS-SFM has a large potential, which goes significantly beyond the problems and systems reported here.

More sustainable energy storage: lignin based electrodes with glyoxal crosslinking

Lignin is a promising material to be used in sustainable energy storage devices. It may act as an active component due to hydroquinone motifs or as a binder in electrodes. While usually it is blended or modified with unsustainable chemicals, we investigate crosslinking with glyoxal as a new route to obtain more benign electrodes. For combining the advantages of high charge (lignin as an active material) and electrode stability (lignin as a binder), we chose a two-step process in which we first form lignin–carbon composites and subsequently crosslink lignin on the carbon. We discuss crosslinking of the material as well as influences on charge storage. Final electrodes benefit from combined faradaic and non-faradaic charge storage and reach a capacity of 80 mA h g−1 at a discharge rate of 0.2 A g−1.