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Biomedical subjects

Wilhelm T S Huck

Publications and source records attributed to Wilhelm T S Huck.

At least 19 recordsLinked to original sources
PubMed2007

Probing the responsive behavior of polyelectrolyte brushes using electrochemical impedance spectroscopy.

Cyclic voltammetry and impedance spectroscopy were employed to probe the responsive properties of polyelectrolyte brushes. Poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes over 100 nm thick on gold substrates were synthesized via surface-initiated atom-transfer radical polymerization and quaternized with methane iodide to obtain cationic brushes (Q-PDMAEMA). Q-PDMAEMA brushes respond to electrolytes by exhibiting swollen and collapsed states. Swollen brushes allow good permeability of electroactive probes, while collapsed states block electron transport. Electrolytes have different impacts on the electrochemical properties of Q-PDMAEMA. Some salts (NaNO3) cause brush collapse due to charge screening, while others such as those with more hydrophobic anions (ClO4-, PF6-, and Tf2N-) induce brush collapse because of solubility changes. The collapsed brushes exhibit intrinsically different resistance as probed with impedance. Charged screened brushes retain good permeability to electroactive probes. Strongly coordinating hydrophobic anions lead to insoluble brushes, resulting in a high resistance. These results show that electrochemical impedance spectroscopy is a powerful technique to probe the properties and structure of polyelectrolyte brushes.

Journal Article↗
PubMed2006

Multicomponent polymer brushes.

This article describes a general synthetic route to laterally distinctive multicomponent polymer brushes on gold. The procedure involves repeated surface patterning using microcontact printing (muCP) of initiator-terminated thiols without backfilling with inert thiols and surface-initiated atomic transfer radical polymerization steps. In between brush growth, the remaining initiator moieties are deactivated to avoid reinitiation on existing brushes. Optical and fluorescence microscopy, atomic force microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy have been used to characterize every step of this procedure. We found that brushes can be grown from initiator-modified surfaces that contain bare gold areas and that these areas remain available for further patterning using muCP. To demonstrate the flexibility of this approach, surfaces containing four different polymer brushes in patterns ranging from 2 x 4 microm lines to 20 x 20 microm squares were fabricated. The range of chemical functionalities incorporated includes cationic and anionic polyelectrolytes, as well as thermally responsive polymers.

Journal Article↗
PubMed2006

Polyelectrolyte brushes as efficient ultrathin platforms for site-selective copper electroless deposition.

Ion-exchange in surface-initiated polyelectrolyte brushes provides a versatile route to the formation of catalytically active surfaces for electroless deposition of Cu. The advantage of this procedure is the covalent anchoring of the catalyst support layer, eliminating delamination of the metal film, even when deposited onto PDMS substrates. Furthermore, by tuning the concentration of PdCl4(2-) ions in the brushes, the rate of deposition and hence the thickness of the overall film can be controlled easily.

Journal Article↗
PubMed2006

Topography printing to locally control wettability.

This paper reports a new patterning method, which utilizes NaOH to facilitate the irreversible binding between the PDMS stamp and substrates and subsequent cohesive mechanical failure to transfer the PDMS patterns. Our method shows high substrate tolerance and can be used to "print" various PDMS geometries on a wide range of surfaces, including Si100, glass, gold, polymers, and patterned SU8 photoresist. Using this technique, we are able to locally change the wettability of substrate surfaces by printing well-defined PDMS architectures on the patterned SU8 photoresist. It is possible to generate differential wetting and dewetting properties in microchannels and in the PDMS printed area, respectively.

Adsorption↗
PubMed2006

Highly reversible and multi-stage cantilever actuation driven by polyelectrolyte brushes.

Microcantilever bending can be reversibly driven by conformational changes of phosphate containing polyelectrolyte brushes when exposed to different pH or salt solutions. The deflection of the cantilevers allows a detailed analysis of the properties of polymer brushes, while these systems are also a first step toward polymer-based nanoactuators.

Journal Article↗
PubMed2006

Thermal and UV shape shifting of surface topography.

The confinement of LCE materials into surface monodomains via micropatterning leads to the formation of reversible, shape-shifting surface patterns. The individual features are liquid crystalline monodomains, and by switching to an isotropic state using light or heat, the features switch between imprinted circular features and anisotropic liquid crystalline features.

Journal Article↗
PubMed2006

Enhancement of charge-transport characteristics in polymeric films using polymer brushes.

We show that charge-transporting polymer chains in the brush conformation can be synthesized from a variety of substrates of interest, displaying a high degree of stretching and showing up to a 3 orders of magnitude increase in current density normal to the substrate as compared with a spin-coated film. These nanostructured polymeric films may prove to be suitable for electronic devices based on molecular semiconductors as current fabrication techniques often provide little control over film structure.

Journal Article↗
PubMed2005

Effects of nanoconfinement on the morphology and reactivity of organic materials.

When organic materials are placed in environments which physically confine the materials at the nanometre scale, interfacial effects and confinement-induced loss of entropy can significantly alter materials' properties such as the glass transition temperature as well as the nanoscale morphology as compared to a "free" system. In block copolymers, nanoconfinement leads to a range of unusual self-organized nanoscale morphologies. In this article, attempts to induce nanoconfinement effects in new polymer systems as well as at interfaces will be highlighted and some possible future implications for organic synthesis and biology will be discussed.

Journal Article↗
PubMed2005

Shape-memory nanoparticles from inherently non-spherical polymer colloids.

Samples of polymeric materials generally have no intrinsic shape; rather their macroscopic form is determined by external forces such as surface tension and memory of shear (for example, during extrusion, moulding or embossing). Hence, in the molten state, the thermodynamically most stable form for polymer (nano)particles is spherical. Here, we present the first example of polymer nanoparticles that have an intrinsic non-spherical shape. We observe the formation of high-aspect-ratio ellipsoidal polymer nanoparticles, of controlled diameter, made from main-chain liquid crystalline polymers using a mini-emulsion technique. The ellipsoidal shape is shown to be an equilibrium (reversible) characteristic and a direct result of the material shape memory when a liquid crystal nanoparticle is in its monodomain form.

Colloids↗
PubMed2005

Self-organization of nanocrystals in polymer brushes. Application in heterojunction photovoltaic diodes.

We present a new approach to achieving order in molecular semiconductors via alignment of polymer chains using surface-initiated polymerization. Polyacrylate brushes grown from transparent conducting electrodes, with triarylamine side groups as hole-transporting components, show characteristics of high mobilities for hole transport. Solution processing a second component with favorable enthalpic interactions can form a composite with mesoscale order and be exploited for heterojunction diodes. We find substantial uptake of CdSe nanocrystals (with diameter in the range 2.5-2.8 nm), and such composites show photovoltaic quantum efficiencies of up to 50%.

Journal Article↗