Growth of bubbles on a solid surface in response to a pressure reduction
Li, J. ; Chen, H. ; Zhou, W. ; Wu, B. ; Stoyanov, S.D. ; Pelan, E.G. - \ 2014
Langmuir 30 (2014)15. - ISSN 0743-7463 - p. 4223 - 4228.
contact angles - drop size - dynamics - water - nanobubbles - cavitation - interface - line
A diffusion-controlled method is presented to study the growth of bubbles on a solid surface. The bubbles are nucleated spontaneously on a hydrophobic smooth surface in response to a sudden pressure reduction and then grow with an expanding contact line. The evolution of the bubbles in the early stage is found to grow with a constant bubble radius and a decreasing contact angle, while the bubbles continue their growth with a constant contact angle and an increasing bubble radius after the contact angle reaches its equilibrium value. A total variation of about 60° of the contact angle is observed during the growth of the bubbles with the size scale of 10–100 µm in radius. The growing process is described by the diffusion theory with the validation of the growth constant.
Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects
Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2014
Journal of Colloid and Interface Science 430 (2014). - ISSN 0021-9797 - p. 69 - 77.
in-water emulsions - protein-exposed hydrophobicity - beta-lactoglobulin - drop size - adsorption - flocculation - interface - stabilization - ph - dependence
This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil–water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths > 30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0–R1), the other variants (R1.5–R2.5) were stable against flocculation ¿ 200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0–R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil–water interface, leading to a shift to the protein-rich regime.
Protein Concentration and Protein-Exposed Hydrophobicity as Dominant Parameters Determining the Flocculation of Protein-Stabilized Oil-in-Water Emulsions
Delahaije, R.J.B.M. ; Wierenga, P.A. ; Nieuwenhuijzen, N.H. van; Giuseppin, M.L.F. ; Gruppen, H. - \ 2013
Langmuir 29 (2013)37. - ISSN 0743-7463 - p. 11567 - 11574.
diffusing wave spectroscopy - beta-lactoglobulin - coalescence stability - disjoining pressure - drop size - adsorption - films - ph - interfaces - ovalbumin
DLVO theory is often considered to be applicable to the description of flocculation of protein-stabilized oil-in-water emulsions. To test this, emulsions made with different globular proteins (ß-lactoglobulin, ovalbumin, patatin, and two variants of ovalbumin) were compared under different conditions (pH and electrolyte concentration). As expected, flocculation was observed under conditions in which the zeta potential is decreased (around the isoelectric point and at high ionic strength). However, the extent of flocculation at higher ionic strength (>50 mM NaCl) decreased with increasing protein-exposed hydrophobicity. A higher exposed hydrophobicity resulted in a higher zeta potential of the emulsion droplets and consequently increased stability against flocculation. Furthermore, the addition of excess protein strongly increased the stability against salt-induced flocculation, which is not described by DLVO theory. In the protein-poor regime, emulsions showed flocculation at high ionic strength (>100 mM NaCl), whereas emulsions were stable against flocculation if excess protein was present. This research shows that the exposed hydrophobicity of the proteins and the presence of excess protein affect the flocculation behavior.
Microcapsule production by an hybrid colloidosome-layer-by-layer technique
Rossier Miranda, F.J. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2012
Food Hydrocolloids 27 (2012)1. - ISSN 0268-005X - p. 119 - 125.
polyelectrolyte multilayer microcapsules - protein adsorption - responsive colloidosomes - stabilized emulsions - beta-lactoglobulin - hollow spheres - drop size - particles - emulsification - fabrication
Although many different methods for microencapsulation are known only some of them had been applied at industrial scale, due to complexity, lack of mechanical strength of the resulting capsules, and the costs related to their production. One of such methods is the electrostatic layer-by-layer (LbL) adsorption, which produce shells from oppositely charged polymers. The thickness of those shells can be tuned with nanometric precision, but to build enough strength for practical applications requires the adsorption of an impractical number of layers. We present here a method to produce strong microcapsules combining the assembly of a protein/pectin shell via electrostatic LbL adsorption with the adsorption of bigger charged colloidal particles. Those colloidal particles do not need any pretreatment to modify their wettability, as would be the case for a standard colloidosome route. In this way strong encapsulates with porous walls are obtained, which can be used as easy to load scaffolds. The pores in the walls can be closed through subsequent adsorption of more layers of protein and pectin. Since the assembly scheme occurs at pH 3.5 we expect the produced microcapsules to act as an effective delivery system in food products, protecting their contents from the acidity of the stomach and dissolving later at the small intestine. The proteins and pectins used as basic building blocks are food-grade and inexpensive.
Modified Capillary Cell for Foam Film Studies Allowing Exchange of the Film-Forming Liquidwie
Wierenga, P.A. ; Basheva, E.S. ; Denkov, N.D. - \ 2009
Langmuir 25 (2009)11. - ISSN 0743-7463 - p. 6035 - 6039.
anionic surfactant solutions - continuous-flow tensiometry - coalescence stability - protein adsorption - ionic-strength - drop size - emulsions - interfaces - forces - ph
Many of the macroscopic properties of foams and emulsions are controlled by the mesoscopic properties of the thin films separating the bubbles or droplets. The properties of these films depend on contributions (1) from the adsorbed surface layers and (2) from the liquid that separates these adsorbed layers. To separate in the experimental studies the effects of these two contributions, we developed a new modified version of the capillary cell for foam film studies (originally developed by Scheludko and Exerowa (Scheludko, A.; Exerowa, D. Kolloid Z. 1959, 165, 148-151), which allows exchange of the film-forming liquid between the air-water surfaces. This modified cell allows one to distinguish between the role of the adsorbed species (e.g., proteins, particles, or long-chain synthetic polymers) and the species present in the film interior (e.g., particles, electrolytes, or surfactants). The film properties that can be studied in this way include film stability, rate of film thinning, and surface forces stabilizing the film. These properties are of significant interest in understanding and controlling the stability of dispersed systems. The experimental procedure and the capabilities of the modified cell are demonstrated in several examples.
Stochastic simulation experiment to assess radar rainfall retrieval uncertainties associated with attenuation and its correction
Uijlenhoet, R. ; Berne, A.D. - \ 2008
Hydrology and Earth System Sciences 12 (2008). - ISSN 1027-5606 - p. 587 - 601.
raindrop size distributions - polarimetric weather radar - gauge data - drop size - vertical profiles - mountainous area - inverse method - band - precipitation - reflectivity
As rainfall constitutes the main source of water for the terrestrial hydrological processes, accurate and reliable measurement and prediction of its spatial and temporal distribution over a wide range of scales is an important goal for hydrology. We investigate the potential of ground-based weather radar to provide such measurements through a theoretical analysis of some of the associated observation uncertainties. A stochastic model of range profiles of raindrop size distributions is employed in a Monte Carlo simulation experiment to investigate the rainfall retrieval uncertainties associated with weather radars operating at X-, C-, and S-band. We focus in particular on the errors and uncertainties associated with rain-induced signal attenuation and its correction for incoherent, non-polarimetric, single-frequency, operational weather radars. The performance of two attenuation correction schemes, the (forward) Hitschfeld-Bordan algorithm and the (backward) Marzoug-Amayenc algorithm, is analyzed for both moderate (assuming a 50 km path length) and intense Mediterranean rainfall (for a 30 km path). A comparison shows that the backward correction algorithm is more stable and accurate than the forward algorithm (with a bias in the order of a few percent for the former, compared to tens of percent for the latter), provided reliable estimates of the total path-integrated attenuation are available. Moreover, the bias and root mean square error associated with each algorithm are quantified as a function of path-averaged rain rate and distance from the radar in order to provide a plausible order of magnitude for the uncertainty in radar-retrieved rain rates for hydrological applications.
Measurement and parameterization of rainfall microstructure
Uijlenhoet, R. ; Sempere Torres, D. - \ 2006
Journal of Hydrology 328 (2006)1-2. - ISSN 0022-1694 - p. 1 - 7.
raindrop size distribution - induced cross-polarization - 2-layer stochastic-model - drop size - kinetic-energy - weather radar - interception - dependence - precipitation - distributions
Several environmental processes, both occurring in the atmosphere and at the land surface, depend fundamentally on the structure of rainfall at the scale of individual raindrops. From a hydrological perspective, rainfall interception by vegetation canopies, soil erosion through raindrop impact, and the backscattering and attenuation of weather radar signals in rainfall are probably the most important of these. Detailed knowledge of the discrete microstructure of rainfall is a conditio sine qua non to understand, quantify, and ultimately predict these processes, even at much larger scales. This is the Preface to the Special Issue on ¿Measurement and Parameterization of Rainfall Microstructure¿, containing articles that have for the most part been presented at sessions organized at the 27th and 28th European Geosciences Union (EGU) General Assemblies in Nice, France, in 2002 and 2003.