17 research outputs found
Simulations of Solid-on-Solid Models of Spreading of Viscous Droplets
We have studied the dynamics of spreading of viscous non-volatile fluids on
surfaces by MC simulations of SOS models. We have concentrated on the complete
wetting regime, with surface diffusion barriers neglected for simplicity.
First, we have performed simulations for the standard SOS model. Formation of a
single precursor layer, and a density profile with a spherical cap shaped
center surrounded by Gaussian tails can be reproduced with this model.
Dynamical layering (DL), however, only occurs with a very strongly attractive
van der Waals type of substrate potential. To more realistically describe the
spreading of viscous liquid droplets, we introduce a modified SOS model. In the
new model, tendency for DL and the effect of the surface potential are in part
embedded into the dynamics of the model. This allows a relatively simple
description of the spreading under different conditions, with a temperature
like parameter which strongly influences the droplet morphologies. Both rounded
droplet shapes and DL can easily be reproduced with the model. Furthermore, the
precursor width increases proportional to the square root of time, in
accordance with experimental observations. PACS: 68.10.Gw, 05.70.Ln, 61.20.Ja.Comment: to appear in Physica A (1994), standard LaTex, 20 page
Dynamics of Spreading of Chainlike Molecules with Asymmetric Surface Interactions
In this work we study the spreading dynamics of tiny liquid droplets on solid
surfaces in the case where the ends of the molecules feel different
interactions with respect to the surface. We consider a simple model of dimers
and short chainlike molecules that cannot form chemical bonds with the surface.
We use constant temperature Molecular Dynamics techniques to examine in detail
the microscopic structure of the time dependent precursor film. We find that in
some cases it can exhibit a high degree of local order that can persist even
for flexible chains. Our model also reproduces the experimentally observed
early and late-time spreading regimes where the radius of the film grows
proportional to the square root of time. The ratios of the associated transport
coefficients are in good overall agreement with experiments. Our density
profiles are also in good agreement with measurements on the spreading of
molecules on hydrophobic surfaces.Comment: 12 pages, LaTeX with APS macros, 21 figures available by contacting
[email protected], to appear in Phys. Rev.
Maize flour parameters that are related to the consumer perceived quality of ‘broa’ specialty bread
Relating microstructure, sensory and instrumental texture of processed oat
This study is a part of a larger project aiming to produce new, healthy, and tasty food ingredients from oat. Germination and different heating processes can be used to improve the texture and flavour of cereals. In this study effects of germination and wet and dry heating on the microstructure, instrumental structure and sensory properties of two oat varieties were assessed. The microstructure of native, germinated, autoclaved and extruded grains of the hulled cv. Veli and hull-less cv. Lisbeth was examined by light microscopy, the texture was measured by determining the milling energy and hardness of the grains and sensory characteristics were evaluated with descriptive sensory profile analysis. In cv. Veli the cells of the starchy endosperm were smaller than in cv. Lisbeth and ß-glucan was concentrated in the subaleurone layer. In cv. Lisbeth ß-glucan was evenly distributed in the starchy endosperm. The grains of cv. Lisbeth were more extensively modified in the germination process than the grains of cv. Veli, otherwise the effects of processing on the grains of the two cultivars were similar. Germination caused cell wall degradation, autoclaving and extrusion cooking caused starch gelatinization. Autoclaving resulted in the hardest perceived texture in oat. Gelatinization of starch appeared to contribute more to the hardness of oat groats than the cell wall structure. Of the instrumental methods used in this study the milling energy measurement appeared to be the most useful method for the analysis of the effects of processing on grain structure.
The effect of enzymatic treatment on blackcurrant (<i>Ribes nigrum</i>) juice flavour and its stability
Effect of extrusion processing on lipid stability of rye bran
The aim of this study was to investigate under which processing conditions the extrusion of rye bran could produce a material with a long shelf life in terms of lipid chemistry and possibilities to link lipid stability with physical properties of the extrudates. In addition to water content (13-30%) and temperature (80-140°C) as variables during extrusion, the effect of rye bran particle size (633 and 15 µm) was studied. Stability of lipids was measured by volatile compounds and the loss of tocopherols and tocotrienols. Of the studied process parameters, the water content had a significant effect both on the physical properties and on lipid stability. Low water content (13 or 16%) in the extrusion of coarse or fine bran led to the highest expansion and porosity and the most stable lipids during storage. The improved oxidative stability when processed at low water contents in extrusion was connected with a higher formation of Maillard reaction products, which could have acted as antioxidants. In spite of the loss of tocols during grinding, the lipids in the fine rye bran extrudates were at least as stable as the lipids in the coarse rye bran extrudates when processed at low water content. However, the high furfural content in the fine rye bran extrudate at 13 % indicated that Maillard reaction was extensive which could lead to undesirable flavour. Thus, the overall best performance was obtained when the coarse rye bran was processed at the lowest water content