Erratum to 'How to develop globular proteins into adhesives'.
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Journal Article↗
Biomedical subjects
G Frens
Publications and source records attributed to G Frens.
How to develop globular proteins into adhesives.
To make globular proteins suitable for application in adhesives, the specific bonds and interactions which shape their structure have to broken. Only then, a layer of relatively large, flexible and interwoven polymer chains, which are firmly attached to the solid surface by adsorption, can be created. Such a network layer is essential to save the adhesive bond under an applied force, because it can distribute the concentration of stresses generated at the interface into the bulk. Unfolding and swelling of a protein can be achieved by changing the solvent quality. For the globular whey protein beta-lactoglobulin, the optimal conditions for unfolding and swelling is found with 98% formic acid as a solvent. In formic acid, beta-lactoglobulin looses its amphoteric character (it is protonated, probably for approximately 20%). In addition, formic acid is less polar than water and thus a better solvent for the apolar parts of the protein. The swelling and unfolding behaviour of beta-lactoglobulin is studied by viscosity and CD-spectroscopy measurements. For the interpretation of the results we apply the Kuhn formalism that the conformation of a protein can be described in terms of a statistical chain which consists of segments of an average persistence length P. The statistical segment length P, which varies with the experimental conditions, is directly related to the adsorption energy required for a strong adhesion between coil and surface. It determines the depletion energy kT P(-2) m(-2) which must be overcome by specific attraction between side groups of the protein chain and the surface. For beta-lactoglobulin in 98% formic acid, we find a P value of approximately 2.2 nm, pointing at a relatively flexible chain. The minimum net adsorption energy kT P(-2) is then approximately 1 mJ m(-2), a relatively small value to be exceeded. Preliminary results of destructive adhesion tests on beech wood lap-shear joints reveal promising tensile strengths of approximately 2.9+/-1.1 N mm(-2), indeed.
Adhesives↗
Marginal Regeneration and the Marangoni Effect.
On the basis of experimental observations described earlier, we have proposed that marginal regeneration is caused by surface tension gradients at the borders of mobile foam films. Marginal regeneration is the rate-determining mechanism in the drainage of such films, and, as such, a determining factor in the persistence (or long-term stability) of foams. Marangoni flows are caused by surface tension gradients, and these set off the exchange of thicker for thin film elements along the borders, while the total film area remains the same. In this paper we present simulations of the drainage of liquid in a vertical soap film, and show that it is realistic to expect large surface tension gradients along the lower border of the film under the conditions which lead to marginal regeneration. Copyright 1999 Academic Press.
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Marginal Regeneration in Thin Vertical Liquid Films.
Marginal regeneration is the rate-determining drainage mechanism in mobile vertical liquid films stabilized with surfactants. Mysels, Frankel, and Shinoda explained this process from (thermal) thickness fluctuations, like capillary waves. The Laplace underpressure in the Plateau border would exert a larger force on a thick, rather than on a thinner film element. This force unbalance would make film elements of different thicknesses move in opposite directions so that they are exchanged at the border. However, experiments and simulations prove that marginal regeneration cannot be the result of thickness fluctuations. Our alternative view is, that marginal regeneration is due to surface tension gradients between the film and its borders. Drainage of film elements into the lower Plateau border causes a local excess of surfactant, and thereby local differences in surface tension. This causes film elements to flow and generates the thickness differences between the absorbed and emerging film elements. The rates of the Marangoni flows reflect the surface dilational properties. This Marangoni effect is a consequence of the compression of the film surface when a film element flows into the lower Plateau border. Marginal regeneration is then a mechanism which returns the surfactant back into the film. Copyright 1998 Academic Press.
Journal Article↗