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Rudolf Zentel

Publications and source records attributed to Rudolf Zentel.

6 recordsLinked to original sources
PubMed2006

Control of CaCO3 crystallization by demixing of monolayers.

In this paper we describe how to template a demixed monolayer into a spatially patterned inorganic replica. For this purpose a new amphiphilic monomer was synthesized which can be polymerized both in solution and in the monolayer of a Langmuir-Blodgett (LB) trough. Since it inhibits the crystallization of CaCO3, it can be used--in combination with stearic acid (nucleation-promotor)--to control CaCO3 crystals formed under the monolayer. Investigations of the two-component monolayer (Langmuir isotherms and AFM measurements of transferred films) show--in the biphasic region--demixing in solid analogue stearic acid domains and the liquid analogue phase of the monomer. Crystallization of CaCO3 starts under the stearic acid domains whose size varies from less than 100 nm to several tens of micrometers. The addition of poly(acrylic acid) into the subphase hinders the three-dimensional growth of CaCO3 crystals from the monolayer into the solution. Thus, it becomes possible to transfer the pattern of the demixed domains into an inorganic replica of CaCO3.

Acrylic Resins↗
PubMed2006

Integration of self-assembled three-dimensional photonic crystals onto structured silicon wafers.

We report on the fabrication of high-quality opaline photonic crystals from large silica spheres (diameter of 890 nm), self-assembled in hydrophilic trenches of silicon wafers by using a novel technique coined a combination of "lifting and stirring". The achievements reported here comprise a spatial selectivity of opal crystallization without special treatment of the wafer surface, a filling of the trenches up to the top, leading to a spatially uniform film thickness, particularly an absence of cracks within the size of the trenches, and finally a good 3D order of the opal lattice even in trenches with a complex confined geometry, verified using optical measurements. The opal lattice was found to match the pattern precisely in width as well as depth, providing an important step toward applications of opals in integrated optics.

Journal Article↗
PubMed2005

Photochemically and thermally tunable planar defects in colloidal photonic crystals.

We report a bottom-up synthesis of a photochemically and thermally active azobenzene-based polyelectrolyte multilayer (PEM) planar defect embedded in a colloidal photonic crystal (CPC). Both photoisomerization and thermal cycling lead to a precise tuning of an intragap transmitting state induced by the PEM structural defect.

Journal Article↗
PubMed2003

Alpha,omega-functionalized poly-N-isopropylacrylamides: controlling the surface activity for vesicle adsorption by temperature.

The synthesis of alpha,omega-end-functionalized copolymers of N-isopropylacrylamide and N-(3-dimethylaminopropyl)acrylamide was performed. Monomer ratios of 100:0, 96:4, and 81:19 were investigated. The lower critical solution temperature (LCST) of these polymers was determined by cloud-point measurements and by microcalorimetric measurements. The LCST increased from 32 over 37 to 47 degrees C as the hydrophobicity increased with increasing amount of comonomer N-(3-dimethylaminopropyl)acrylamide. The polymers could successfully be adsorbed onto gold surfaces. Finally, vesicle adsorption onto these self-assembled polymer films on flat gold surfaces was investigated as the vesicle solution temperature was varied. It could be observed that vesicle adsorption was hindered as long as the temperature of the vesicle solution was above the LCST of the polymer. As soon as it dropped below the LCST the vesicle adsorption process was initiated.

Journal Article↗
PubMed2003

Semiconductor nanocrystals with multifunctional polymer ligands.

In this letter, we describe the preparation of a versatile polymer ligand, which can be attached to CdSe/ZnS semiconductor nanocrystals via a phase transfer reaction. The ligand is based on a chain of reactive esters, which can, in principle, be substituted by any compound containing amino-functionalities. The polymer/nanocrystal complexes are characterized in terms of structure and photostability.

Journal Article↗