Biomedical Engineering Reference
In-Depth Information
The instrument has the performance of a conventional SEM but has the additional advantage
that practically any material can be examined in its natural state. The samples were freeze-
fractured in freon and immediately placed in the ESEM. Relative humidity in the ESEM
chamber (100%) was maintained using a Peltier stage. Such conditions were applied to
minimize solvent loss and condensation, and control etching of the sample. Images were
obtained within less than 5 minutes
of the sample reaching the chamber. The ESEM images
were recorded multiple times and on multiple samples in order to ensure reproducibility.
R
ESULTS AND
D
ISCUSSION
Cryo ESEM images of the two phase W-SC(6 wt%)-SA(0.29 wt%)-DSS system, and
single phase W-SC(6 wt%)-DSS system shows no significant difference in their structure
(Figure 1). In the both cases the main structural element visualized by ESEM is a network
created jointly by SC and DSS. A small difference between these two images consists only in
the presence of thickening for two phase W- SC(6 wt%)-SA(0,29 wt%)-DSS system. Figure 2
presents photography's of semidilute two phase W-SC(1.6 wt%)-SA(0.29 wt %)-DSS
systems without particles (Fig 2 a ) and with 3 um particles (Figure 2 b), as well as
microphotography's of the same system containing 3 um particles (Figure 2 c), and its SC
enriched phase (Figure 2 d). One can see that addition of 0.5 wt% micro particles to demixed
SC-SA system leads to their complete localization in SC enriched continuous phase. The
same results were obtained for the same two phase system containing smaller (0.21 um and
0.91 um) and larger (5 um) particles; all the particles were distributed into the SC enriched
phase. Use of the positively charged aliphatic amino latex (3 um) gave also the same results
(data are not presented). Obviously charged micro spheres shows significant affinity to the SC
enriched phase of the system, the main component of which, SC is polyampholyte containing
negatively and positively charged functional groups. To visualize the structure of SC enriched
phase containing particles, the samples were freezed, gold-coated, and studied by cryo ESEM.
Figure 1. Typical ESEM images of the single-phase W-SC(6 wt %) -DSS (a) and two -phase W-SC(6
wt%)-SA(0.29 wt %) -DSS systems (b). DSS/SC weight ratio, q=0.14.
As is shown in Figure 3 all the particles distributed into SC enriched phase are
incorporated in the SC-DSS network independently from their sizes, but the final structure of
SC enriched phase is strongly determined by the sizes of the particles. Small particles with the
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