Jürgen Reiners

Aqueous polyurethane dispersions

This review describes basic chemistry, preparation process, and physical properties of aqueous polyurethane disperisons and the derived films, along with the methods of post treatment to modify the properties. Basic way to render a polyurethane water dispersible without external emulsifier has been described. Regarding the methods of preparation, four major processes are described and compared. Methods to improve the relatively poor water and solvent resistance of aqueous polyurethane dispersions which is introduced by the hydrophilicity and linear structure of polyurethane have been discussed with an emphasis on acrylate incorporations.

Silicon-Modified Carbohydrate Surfactants V: The Wetting Behaviour of Low-Molecular-Weight Siloxane, Carbosilane, Silane and Polysilane Precursors on Low-Energy Surfaces

The surface tensions, wetting tensions, contact angles and solid/liquid interfacial tensions of defined siloxanes as well as those of analogous carbosilanes, polysilanes and neopentyl substituted silanes were determined. The wetting experiments were carried out on a glass plate coated with perfluoroalkyl methacrylate (FC 722®). The siloxanes possess the lowest surface tensions. Due to the presence of oxygen atoms in the siloxane backbone, a donor–acceptor portion (γ+/−lv) of the surface tension of about 1–2 mN/m was determined. The solid/liquid interfacial tension also contains a donor–acceptor portion (γ+/−sl). Its value is almost identical to that of γ+/−lv. The γ+/−sl differences between individual molecules of the same surface tension are responsible for contact angle differences of up to 4°.

Silicon-modified carbohydrate surfactants. IV. The impact of substructures on the wetting behaviour of siloxanyl-modified carbohydrate surfactants on low-energy surfaces

The siloxanyl-modified carbohydrate surfactants investigated consist of the four structural elements: (1) siloxanyl moiety; (2) spacer; (3) carbohydrate unit; and (4) modifying element. By static surface tension (γ lv σ) and wetting tension (γ sv - γ sb α) measurements the contact angles of aqueous surfactant solutions above the critical micelle formation concentration (cmc) on nonpolar perfluorinated surfaces (FEP® plate) were determined. Although the siloxanyl units were found to have a high capacity to level out the interfacial properties, both surface tension and wetting tension react independently to defined changes in the chemical structure of the surfactant molecules. The results of spreading experiments on polypropylene show good correlation with the dependences found by wetting measurements.

Silicon-Modified Carbohydrate Surfactants I: Synthesis of Siloxanyl Moieties Containing Straight-chained Glycosides and Amides

New siloxanyl-modified carbohydrate surfactants of the amide and glycoside type have been synthesized by coupling between defined as well as higher-molecular-weight siloxanes and carbohydrate structures via spacers of different lengths and hydrophilic power. Linear and branched monohydrogen di-, tri-, tetra- and penta-siloxanes and polyhydrogen siloxanes as well as mono- and di-saccharide lactone structures have been found to be good starting materials for the synthesis of amides, often in quantitative yield, whereas glycosides had to be prepared in low-yield multistep sequences including protection/deprotection steps. Selected strategies were applied to polysiloxanes yielding quantitatively a broad variety of carbohydrate-modified comb-like structures. The new substances were characterized by means of 13 C NMR spectroscopy, GC, capillary GC, GC-MS coupling and elemental analysis.

Silicon‐Modified Carbohydrate Surfactants II: Siloxanyl Moieties Containing Branched Structures

Branched siloxanyl-modified carbohydrate surfactants have been synthesized by coupling mono-, di- and poly-functional siloxanes to carbohydrate units either via a branched spacer or by attaching a separate modifying element to a straight-chained structure. Hydrophilic as well as extremely hydrophobic elements have been incorporated successfully. Siloxanyl-modified carbohydrates bearing a secondary amino function were alkylated in regioselective reactions by different epoxides ranging from glycidol- to siloxanyl-modified allyl glycidyl ether derivatives. Alternatively, carbohydrate-modified piperazinyl structures yielded cyclic subunits after alkylation. Structures bearing two identical hydrophilic groups are accessible by alkylation of carbohydrate-modified bisamides. The derivatives synthesized were characterized by means of GC, NMR and elemental analysis.

Silicon‐Modified Carbohydrate Surfactants III: Cationic and Anionic Compounds

Ionic siloxanyl-modified carbohydrate surfactants have been synthesized by alkylation/esterification of precursors containing tertiary amino functions. Depending on the reaction strategy, the siloxanyl moiety is part of the alkylating agent or the substrate. Polyhydroxylated tertiary amines can be quaternized by siloxanyl-modified chloroacetic acid esters or epoxysiloxanes in the presence of glacial acetic acid. The esterification of tertiary amines bearing carbohydrate and siloxanyl subunits by cyclic acid anhydrides yields, after neutralization, carboxylate salts. The reaction of hydroxyl groups and sulfamic acid leads to sulfates. The new substances were characterized by means of 13C NMR spectroscopy, gas chromatography, elemental analysis and their solubility profile.

Silicon-modified carbohydrate surfactants. VI: Synthesis of carbosilane, silane, polysilane and non-permethylated siloxane derivatives ; the wetting behaviour of epoxy-modified precursor liquids on non-polar surfaces

The synthesis of carbohydrate surfactants bearing carbosilane, silane, polysilane and non-permethylated siloxane moieties is described. These surfactants consist of three structural elements: (1) a silicon-containing moiety, (2) a spacer and (3) a carbohydrate unit. Additionally two different types of mixed structures have been synthesized: (a) single-chained carbosilane–siloxane surfactants and (b) double-chained combinations of carbo- silanes, silanes and siloxanes. The wetting behaviour of the key intermediates, the allyl glycidyl derivatives, has been investigated by static surface tension (γlv, σ) and wetting tension (γsv−γsl, α) measurements on a non-polar perfluorinated surface (FEP® plate). The contact angles obtained for these pure liquids are not a linear function of the surface tension but depend on the polarity of the substructures.

Silicon-modified carbohydrate surfactants. VIII. Equilibrium wetting of perfluorinated solid surfaces by solutions of surfactants above and below the critical micelle concentration-surfactant distribution between liquid-vapour and solid-liquid interfaces

For selected carbohydrate-modified Silicon surfactants of the siloxane, carbosilane, polysilane and silane type, the concentration dependences of the liquid/vapour and solid/liquid interfacial tensions under equilibrium conditions have been determined. Further, the Lifshitz–van der Waals and donor–acceptor contributions have been calculated. Below the critical micelle concentration (cmc) a steep increase in donor–acceptor contributions to both interfacial tensions was found. The Lifshitz–van der Waals contribution of the liquid/vapour interfacial tension shows a pronounced minimum. Calculations of the concentration-dependent surface coverage suggest that preferential adsorption to one of the interfaces does not take place. Copyright

Silicon‐modified carbohydrate surfactants IX: dynamic wetting of a perfluorinated solid surface by solutions of a siloxane surfactant above and below the critical micelle concentration

The dynamic wetting behaviour on a perfluorinated, low-energy solid has been investigated for a carbohydrate-modified phenylsiloxane surfactant. The surfactant concentration, the rate of interface generation and the [solid/liquid interface area] : [liquid/vapour interface area] ratio were varied systematically. Dynamic data for the liquid/vapour (γ Iv ) and solid/liquid (γ sl ) interfacial tension as well as their Lifshitz-van der Waals and donor-acceptor contributions were determined under strictly controlled conditions. Since γ sl reacts sensitively to variations of the surfactant concentration and the rate of interface generation, the covering of the liquid/nonpolar solid interface is assumed to be a spreading limiting factor. The corresponding γ lv values remain constant and close to those obtained under equilibrium conditions.

Silicon Containing Structures at Interfaces: The Wetting Behavior of Carbohydrate Modified Si Surfactants on Perfluorinated Surfaces and the Modification of Rough Metal Surfaces by Hydrophilic Polysiloxane Networks

Aqueous solutions of certain trisiloxane surfactants wet low energy surfaces (i. e., polypropylene, wax covered leaves). Investigations on the macroscopic spreading velocity, the phase behavior as well as first attempts to visualize slowly spreading drops of pure surfactants did not solve the questions about the structure of rapidly spreading surfactant solution drops and the evolution of the corresponding dynamic energy balance. Therefore, a strategy for the hydrophilic modification of fractal Ir electrodes surfaces for investigating these effects was developed.