On the influence of surfactants on the adsorption of polysaccharide-based polymers on cotton studied by means of fluorescence spectroscopy.

In this study, we examined the influence of surfactants on the adsorption of polymers on cotton fibers. The extent of polymer adsorption on cotton was determined directly by means of fluorescence spectroscopy using fluorescently labeled polymers. The investigation of polymer adsorption in the presence of different types of surfactants and for a large range of differently structured polymers allows us to obtain a rather general picture of this important issue. Systematic relationships between the presence of surfactant and the type of polymer can be deduced but cannot be cast in simple terms such as electrostatic interaction but instead depend on the detailed interaction between the surfactant and polymer both in solution and adsorbed on the cotton surface. A particularly complex situation arises for the case of oppositely charged surfactant and polymer because of the possibility of precipitate formation. The study of such complex systems not only is of scientific interest but also is of great commercial interest because both polymers and surfactants are parts of detergent formulations and cotton is one of the most abundantly used materials for fabrics.

Adsorption isotherms of cellulose-based polymers onto cotton fibers determined by means of a direct method of fluorescence spectroscopy.

We present a novel method for the measurement of polymer adsorption on fibers by employing fluorescently labeled polymers. The method itself can be used for any compound that either shows fluorescence or can be labeled with a fluorescent dye, which renders it ubiquitously applicable for adsorption studies. The main advantage of the method is that the choice of adsorbent is not limited to flat surfaces, thereby allowing the investigation of fibrous and porous systems. As an example of high interest for application we determined the adsorption isotherms of various polysaccharide-based polymers with different charges and different substituents on cotton fibers. These experiments show that the extent of adsorption depends not only on the charge conditions but also very much on the specific interactions between the polymer and fiber. For instance, the cationic hydroxyethyl cellulose can become bound to an extent similar to that of the anionic alginate, while the anionic carboxymethyl cellulose of similar charge density adsorbs much less under these conditions. This shows that the adsorption of polymers depends subtly on the details of the interaction between the polymer and fiber but can be determined with good precision with our direct fluorescence method.

The influence of polymers, surfactants and salt on the fine structure of cotton revealed by SANS.

Cotton is the most abundantly employed material for the production of fabrics. Therefore it is very interesting to know the influence of compounds commonly in contact with cotton during the washing process, on its mesoscopic structure. Small angle neutron scattering (SANS) is able to monitor structural changes in the range of 1 to a few 100 nm, making it a powerful tool to observe such changes. For that purpose we studied the change of fibre structure if exposed to low concentrations of polymer or surfactant, as they are relevant in the washing process. An interesting observation is that for the effectively available surface of cotton fibres their nanometric structure appears to be the central aspect. However, this local structure is only little affected by the presence of anionic surfactant. The same applies to a variety of polymers and only for the addition of a cationically modified cellulose a substantial increase of the thickness of the locally present rod-like structures by ~30% is observed.

Mechanism of formation of DNA-cationic vesicle complexes.

Cationic vesicles and DNA form complexes that are promising gene delivery systems. Despite the increasing number of publications on their morphology and structure, the mechanism leading to their formation is not yet understood due to a lack of kinetic data. In the present study the kinetics of the interaction between DNA and cationic vesicles were followed using stopped-flow turbidity and small-angle neutron scattering techniques. The neutron real-time experiments were performed on a high-flux diffractometer, the D22 at the ILL, using a stopped-flow set-up. Extruded mixed vesicles of dimethyldioctadecylammonium bromide (DODAB) with various amounts of dioleoylphosphatidylethanolamine (DOPE) were investigated at 25 degrees C. The results show that the transition from unilamellar vesicles to a multilamellar structure upon DNA addition occurs in three steps. The first step, on the millisecond time scale, is currently not accessible to neutron scattering but was observed by stopped-flow turbidity and fluorescence experiments. The second step, on a time scale of seconds, corresponds to the formation of an intermediate with a locally cylindrical structure. As time progresses this unstable intermediate evolves to a multilamellar structure, on a time scale of minutes. An understanding of the mechanisms behind the DNA-cationic vesicle complex formation event will allow the production of more homogeneous, efficient delivery systems in pharmaceutically acceptable forms.