Claudia Haensch

Extended dissolution studies of cellulose in imidazolium based ionic liquids

Ionic liquids (ILs) have become advantageous solvents for the dissolution and homogeneous processing of cellulose in recent years. However, despite significant efforts, only a few ILs are known for their capability to efficiently dissolve cellulose. In order to overcome this limitation, we screened a wide range of potentially suitable ILs. From our studies, some remarkable results were obtained, for example, an odd–even effect was found for different alkyl side-chain lengths of the imidazolium chlorides which could not be observed for the bromides. Furthermore, 1-ethyl-3-methylimidazolium diethyl phosphate was found to be best suitable for the dissolution of cellulose; dissolution under microwave irradiation resulted in almost no color change. No degradation of cellulose could be observed. In addition, 1-ethyl-3-methylimidazolium diethyl phosphate has a low melting point which makes the viscosity of the cellulose solution lower and, thus, easier to handle.

Reversible supramolecular functionalization of surfaces: terpyridine ligands as versatile building blocks for noncovalent architectures.

We report on the reversible and selective functionalization of surfaces by utilizing supramolecular building blocks. The reversible formation of terpyridine bis-complexes, based on a terpyridine ligand-functionalized monolayer, is used as a versatile supramolecular binding motif. Thereby, click chemistry was applied to covalently bind an acetylene functionalized Fe(II) bis-complex onto azide-terminated self-assembled monolayers. By decomplexation of the formed supramolecular complex, the ligand modified monolayer could be obtained. These monolayers were subsequently used for additional complexation reactions, resulting in the reversible functionalization of the substrates. The proper choice of the coordinating transition metal ions allows the tuning of the binding strength, as well as the physicochemical properties of the formed complexes and thus an engineering of the surface properties.

Chemical surface reactions by click chemistry: coumarin dye modification of 11-bromoundecyltrichlorosilane monolayers

The functionalization of surfaces and the ability to tailor their properties with desired physico-chemical functions is an important field of research with a broad spectrum of applications. These applications range from the modification of wetting properties, over the alteration of optical properties, to the fabrication of molecular electronic devices. In each of these fields, it is of specific importance to be able to control the quality of the layers with high precision. The present study demonstrates an approach that utilizes the 1,3-dipolar cycloaddition of terminal acetylenes to prepare triazole-terminated monolayers on different substrates. The characterization of the precursor monolayers, the optimization of the chemical surface reactions as well as the clicking of a fluorescent dye molecule on such azide-terminated monolayers was carried out. A coumarin 343 derivative was utilized to discuss the aspects of the functionalization approach. Based on this approach, a number of potential surface reactions, facilitated via the acetylene-substituted functional molecules, for a broad range of applications is at hand, thus leading to numerous possibilities where surface modifications are concerned. These modifications can be applied on non-structured surfaces of silicon or glass or can be used on structured surfaces. Various possibilities are discussed.

Fast Surface Modification by Microwave Assisted Click Reactions on Silicon Substrates

Microwave irradiation has been used for the chemical modification of functional monolayers on silicon surfaces. The thermal and chemical stability of these layers was tested under microwave irradiation to investigate the possibility to use this alternative heating process for the surface functionalization of self-assembled monolayers. The quality and morphology of the monolayers before and after microwave irradiation was analyzed by surface-sensitive techniques, such as Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and contact angle measurements. As a model reaction, the 1,3-dipolar cycloaddition of organic azides and terminal acetylenes was tested for the chemical modification of functional azide monolayers. Low and high molar mass compounds modified with an acetylene group were successfully clicked onto the surfaces as confirmed by FTIR spectroscopy and AFM investigations. It could be verified that the reaction can be performed in reaction times of 5 min, and a comparison to conventional heating mechanisms allowed us to conclude that the elevated reaction temperatures result in the fast reaction process.

Orthogonal functionalization of silicon substrates using self-assembled monolayers.

A fabrication process for multifunctional surfaces is designed leading to five different functional moieties (amine, thiol, carboxylic acid, fluoro, and methyl) being present on a single structured surface. The multifunctional surface is created by combining UV-ozone patterning, electro-oxidative lithography, the local deposition of self-assembled monolayers (SAMs), and surface modification schemes. Besides the characterization with conventional surface-sensitive techniques, the nature of the locally functionalized regions is demonstrated by self-assembly of three different probe nanomaterials (Si nanoparticles, Au nanoparticles, and hydroxyl functionalized micelles). A versatile fabrication approach for complex surfaces with addressable functionalities can be created, and it was possible to integrate five different functionalized areas on one substrate.

Combination of Different Chemical Surface Reactions for the Fabrication of Chemically Versatile Building Blocks onto Silicon Surfaces

The use of nucleophilic displacement reactions on bromine-terminated monolayers is presented to create new functional moieties onto silicon surfaces. Functional amines were used as suitable nucleophiles to introduce versatile building blocks onto self-assembled monolayers to perform further surface chemistry toward the fabrication of surfaces with designed properties by combining compatible chemical routes. These modified substrates were analyzed by suitable surface sensitive techniques. Furthermore, the functional monolayers were used for different postmodification reactions. For example, functional amines facilitated with acetylene groups were applied in the click chemistry approach. The use of amino-functionalized terpyridine units leads to the construction of supramolecular systems, where the choice of the metal monocomplex for the complexation is important for the tuning of the surface properties.

'Clicking' on the nanoscale: 1,3-dipolar cycloaddition of terminal acetylenes on azide functionalized, nanometric surface templates with nanometer resolution

Electro-oxidative lithography is used as a tool to create chemical nanostructures on an n-octadecyltrichlorosilane (OTS) monolayer self-assembled on silicon. The use of a bromine precursor molecule, which is exclusively assembled on these chemical templates, can be used to further functionalize the nanostructures by the site-selective generation of azide functions and performing the highly effective 1,3-dipolar cycloaddition reaction with acetylene functionalized molecules. The versatility of this reaction scheme provides the potential to integrate a large variety of functional molecules, to tailor the surface properties of the nanostructures or to anchor molecular building blocks or particles in confined, pre-defined surface areas. The results demonstrated in the present study introduce a conceivable route towards the functionalization of chemically active surface templates with high fidelity and reliability. It is demonstrated that surface features with a lateral resolution of 50 nm functionalized with propargyl alcohol can be fabricated.