Biomedical Engineering Reference
In-Depth Information
It has been shown that there is typically a saturation surface coverage of protein of 1-3
mg/m2, and the particles in the protein solution then act not as charged bare latices but as
sterically stabilized protein-coated particles. However, in the presence of interacting
polysaccharides like dextran sulfate, the adsorbed layer structure is more complex.
This type of the structure was detected close to periphery of the particles, far from the
center. From the producer information we know that just amino groups of the latex placed at
the periphery of the particles.
These
groups has a greater freedom to rotate, therefore in a free
unbound state they does not oriented along the line from the center of the particle to
periphery. Thus, their orientation shown in Figure 3 (d,e) may be the result of interaction and
incorporation of the particles into the SC-DSS network.The second type of the structure
include weakly oriented structural elements, and it placed in the central part of the particles. It
is important to note that incorporation of 3 um particles into the SC enriched phase are not
exceptional phenomenon which is observed only in the presence of DSS in W
-
SC-SA system.
The use of the same particles in the SC enriched phase containing 0.06 wt% lambda
carrageenan instead of DSS leads to the same result (Figure 4).
Figure 4. ESEM images of SC enriched phase W-SC(1.6wt%)-SA(0.29wt%)-lambda carrageenan
systems in the presence of 0.5% 3 um carboxylate modified sulfonate latex. Lambda carrageenan/SC
weight ratio, q=0.06.
Since the size of the charged particles has a strong effect on the structure of W- SC-SA-
DSS system, the important question is arise; whether the presence of low-volume fractions of
nano- and microparticles effect the phase separation?
In order to quantify the effect of the particles on phase equilibrium in semi diluted
demixed SC-SA system, the isothermal phase diagrams of the system were determined at
25
o
C in the presence of 0.21 um, 0.9 um, 3.0 um and 5.0 um particles, plotted in the classical
triangular representation (Figure 5, curves 2, 3), and compared with that obtained in the
absence of particles (Fig 5, curve 1). The phase separation in all cases has a segregative
character with preferential concentrating of SC and SA in different phases. The degree of
compatibility was valuated by comparison position of the binodal line, the critical, and
threshold points. The phase diagram of the demixed system, without particles is characterized
by a low total concentration of biopolymers at the critical and threshold points (C
t
cr
= 10.6
g/L, C
t
*= 6.2 g/L), and a relatively strong asymmetry (
K
s
=4.9). The presence of small
particles with the sizes 0.21 um and 0.91 um do not effect appreciably on the position of the
binodal line, and the critical and threshold points. We did not observe any difference in
thermodynamic behavior of these systems, at least at concentration particles in the mixtures
studied (0.5 %). In the contrast to small particles, the presence of 3 um CML sulfonate or
sulfate particles in the system affects the phase separation, significantly increasing the
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