D Daan Wouters

Tuning solution polymer properties by binary water–ethanol solvent mixtures

The solubility of polymers can be significantly altered by the use of solvent mixtures. The solvent composition also effects the self-assembly properties of amphiphilic copolymers. In addition, water-ethanol mixtures are known to exhibit abnormal physicochemical properties due to the presence of hydration shells around the ethanol molecules, while at the same time both solvents have very low toxicity. However, the solution properties of amphiphilic copolymers in water-ethanol mixtures have been scarcely studied. Here we show that the solution polymer properties of amphiphilic copoly(2-oxazoline)s can be significantly altered in binary water-ethanol mixtures resulting in increased solubility, tuneable lower critical solution temperatures as well as polymer-solvent combinations with both a LCST followed by an UCST and improved dispersion stability. Surprisingly, it was found that polymers insoluble in both ethanol and water could be dissolved in water-ethanol mixtures, opening the way to novel formulations for drug delivery or personal care applications. Our results represent a straightforward method for tuning solution polymer properties without the synthetic efforts that are generally required to change the copolymer composition and properties.

Local probe oxidation of self-assembled monolayers: templates for the assembly of functional nanostructures.

The local oxidation of self-assembled monolayers with a scanning probe is a promising method for the generation of structures with chemical functionalities on the nanometer scale. This technique, which takes advantage of the chemical stability and versatility of self-assembled monolayers and the ability to pattern these monolayers by scanning-probe-based oxidation methods, enables the hierarchical assembly of complex structures in a controlled manner. Surface modification can be followed by the assembly of a further functional monolayer and/or additional surface-modification reactions in the targeted, sequential construction of functional device features.

Constructive Nanolithography and Nanochemistry: Local Probe Oxidation and Chemical Modification

The possibility to prepare and use submicrometer-sized patterns in successive functionalization reactions with quaternary ammonium salts and (functional) chlorosilanes, as well as cationic gold nanoparticles, is presented. Submicrometer-sized structures were prepared by local probe oxidation of octadecyl trichlorosilane functionalized silicon wafers. By this method, patterns were oxidized with 40-nm resolution, which can be used in local surface functionalization reactions. The principle of subsequent functionalization, either with additional quaternary ammonium salts or by a polymer grafting reaction, has been demonstrated.

Local probe oxidation of self-assembled monolayers on hydrogen-terminated silicon

Local probe oxidation experiments by conductive AFM have been performed on a hexadecyl monolayer and a N-hydroxysuccinimide (NHS)-ester-functionalized undecyl (NHS-UA) monolayer assembled on hydrogen-terminated (i.e., unoxidized) silicon. The oxidation conditions for the mild oxidation of the top terminal groups of monolayers and the deep oxidation of the underlying silicon into silicon oxide were investigated. The results show that the bias threshold for the AFM tip-induced oxidation of the top groups of monolayers on oxide-free silicon can be reduced by 2 V for the methyl-terminated hexadecyl monolayer and even by 3.5 V for the active NHS-ester-terminated undecyl monolayer, in comparison to a methyl-terminated octadecyl trichlorosilane (OTS) monolayer on oxidized silicon. Upon such local mild oxidation, the active NHS ester group of the NHS-UA monolayer is selectively cleaved off to generate carboxyl-containing monolayer nanopatterns, opening further possibilities for subsequent patterned multifunctionalization.

Block copolymer libraries: modular versatility of the macromolecular Lego® system

The synthesis and characterization of a new 4 x 4 library of block copolymers based on polystyrene and poly(ethylene oxide) connected by an asymmetrical octahedral bis(terpyridine) ruthenium complex at the block junction are described, while initial studies on the thin film morphology of the components of the library are presented by the use of Atomic Force Microscopy, demonstrating the impact of a library approach to derive structure-property relationships.

Micellar dye shuttle between water and an ionic liquid

The reversible transfer of poly(2-ethyl-2-oxazoline)-block-poly(2-nonyl-2-oxazoline) nanocarriers comprising encapsulated dyes is demonstrated between water and an ionic liquid. This dye transfer concept is shown to be applicable for loading and delivery of dye molecules as well as to provide a protective environment for the encapsulated dye.

Amphiphilic brushes from metallo-supramolecular block copolymers

A novel strategy to control the formation of amphiphilic brushes from metallo-supramolecular block copolymers is described. The investigated copolymer consists of a polystyrene block linked to a poly(ethylene oxide) one via a charged bis-terpyridine ruthenium(II) complex (PS-[Ru]-PEO). The initial hexafluorophosphate counterions associated to the complex have been exchanged for poly(styrenesulfonate) anions (PSS). In DMF, flexible amphiphilic brushes are observed in which PS-[Ru]-PEO chains decorate the PSS main-chain. These structures have been further transferred into pure water, resulting in the collapse of the PS chains into hydrophobic cores. Spherical or worm-like micelles have been observed in water, depending on the length of the PSS chain.

Sequential oxidation and functionalization of nanostructures: the site-specific controlled assembly of different sized particles on a surface

In this contribution the formation of nanostructures consisting of two differently sized nanoparticles is reported which is a crucial step towards the directed preparation of functional devices as the presented technique not only allows for the use of a wide range of materials but also combines site-specificity with the possibility to sequentially construct architectures consisting of multiple components without affecting previously deposited structures.

Large-scale local probe oxidation of OTS monolayers

A broad variety of functional structures with nanometer dimensions can be produced by combining the local probe oxidation of octadecyl trichlorosilane (OTS) self-assembled monolayers on silicon and suitable chemical modification and self-assembly methods. However, local probe-based patterning methods are inherently slow and, due to the small areas that are addressed, spectroscopic characterization is difficult. Here we report on the possibility of creating large-scale surface patterns by electro-oxidation using both an automated oxidation setup and conductive parallel cantilever arrays. This enables large-scale surface pattering while retaining the high resolution and freedom of (sequential) pattern formation, which would be lost if macroscopic patterned stamps were applied as electrodes.

Morphological transition during the thermal deprotection of poly(isobornyl acrylate)-b-poly(1-ethoxyethyl acrylate)

A set of poly(isobornyl acrylate)--poly(1-ethoxyethyl acrylate) polymers has been prepared by atom transfer radical polymerization. The 1-ethoxyethyl protecting group can be removed by a mild thermal treatment yielding the poly(acrylic acid) segment. The thin film morphological behavior of selected block copolymers was studied for as well as deprotected block copolymers using atomic force microscopy (AFM). Low-temperature thermal treatment yielded strongly phase-separated cylindrical features whereas treatment at temperatures above the glass transition temperature of the individual polymer blocks resulted in the initial generation of a similar phase contrast followed by a decrease in phase contrast caused by selective surface enrichment of the more hydrophobic poly(isobornyl acrylate) segment.