Ph.D. degree: TU Dortmund, Germany, 2008
Studies: Chemistry, TU Dortmund, Germany, 2001-2005
Rheological Characterization of Proteins at Interfaces
Proteins are used in a multitude of applications and industries. Often, those applications require storage of proteins in aqueous solution. While this seems to be a trivial statement, the implications are that proteins are mobile and can accumulate at interfaces where they are prone to destabilize. Thus, it poses a challenge especially if solutions need to be stored and to remain active for a longer period of time.
The strong adsorption of proteins at interfaces is due to their amphiphilic nature and also simply because of their colloidal dimensions. The accumulation of protein molecules at interfaces give rise to coherent interfacial films, which exhibit relatively strong rheological moduli.
The rheology of proteins at interfaces is frequently studied by dilatational techniques, mainly with the oscillating drop method. This approach is especially suited for the investigation of the role of proteins in emulsion systems. On the other hand, in dilatational rheology, the effects of the surface tension of the adsorbed film cannot be easily differentiated from structural changes at the interface. This, and simple technical reasons like maintaining a stable drop over an extended period of time makes the pendant drop technique unsuited for the investigation of protein stability.
Interfacial shear rheology makes it possible not only to measure the adsorption but also to simultaneously monitor structural changes within interfacial films. Only recently, techniques sensitive enough for providing dynamic interfacial shear moduli were developed. The oscillating rod rheometer is an extremely sensitive tool and is especially suited for the investigation insoluble lipid films as a function of surface pressure. In our work, we used a TA instruments AR G2 rheometer, which was equipped with a Pt/Ir Du Noüy Ring and a custom built 2D Couette cell.
Self-Assembly of Nanoparticles at Fluid Interfaces
The self-assembly of nanoparticles leads to the formation of ordered structures on a meso- or macroscopic scale and thus combines the advantages of large scale structures with the special properties of the nanoscale. In this respect it is of foremost interest to investigate new ways for the preparation of self-assembled and at the same time durable nano-structured materials like cohesive thin films.
During our studies of the biomimetic formation of calcium carbonate thin films we found a new method for the preparation of cohesive thin films at the liquid-liquid interface, which consist of a mixture of a surfactant (e.g. stearic acid) and nanoparticles (e.g. Silica Ludox beads). Although the mechanism of film formation is unknown to us at present, this system presents a straight-forward approach which can be studied by means of interfacial rheology and methods of colloid and interface sciences.
Maas, M., Ooi, C. C., Fuller, G. G. “Thin Film Formation of Silica Nanoparticle/Lipid Composite Films at the Fluid-Fluid Interface.” Langmuir 2010.
Paulus, M., Degen, P., Schmacke, S., Maas, M., Kahner, R., Struth, B., Tolan, M. & Rehage, H. “In situ observation of maghemite nanoparticle adsorption at the water/gas interface.” The European Physical Journal – Special Topics, 167, 133-136, 2009.
Degen, P., Paulus, M., Maas, M., Kahner, R., Schmacke, S., Struth, B., Tolan, M. & Rehage, H. “In Situ Observation of g-Fe 2 O 3 Nanoparticle Adsorption under different Monolayers at the Air/Water Interface.” Langmuir 24 , 12958-12962, 2008.
Maas, M., Degen, P., Rehage, H., Nebel, H. & Epple, M. “Biomimetic formation of iron-containing organic/inorganic composite thin films.” Published online first by Colloids and Surfaces A, DOI: 10.1016/j.colsurfa.2009.04.049 .
Maas, M., Rehage, H., Nebel, H. & Epple, M. “Detailed study of closed calcium carbonate films at the oil/water interface.” Langmuir 25, 2258-2263, 2008.
Maas, M., Rehage, H., Nebel, H. & Epple, M. “Formation and Structure of Coherent, Ultra-thin Calcium Carbonate Films below Monolayers of Stearic Acid at the Oil/Water Interface.” Progress in Colloid and Polymer Science, Springer, Berlin / Heidelberg, 11-18, 2008
Maas, M., Rehage, H., Nebel, H. & Epple, M. “On the formation of calcium carbonate thin films under Langmuir monolayers of stearic acid.” Colloid and Polymer Sciences, 285, 1301-1311, 2007.