Supporting Information
Effect of Magnetization on Gel Structure and
Protein Electrophoresis in Polyacrylamide Hydrogel
Nanocomposites
Jeffery W. Thompson†, Holly A. Stretz*†, Pedro E. Arce†, Hongsheng Gao†† Harry Ploehn††and
Jibao He†††
† Tennessee Technological University, Cookeville, Tennessee 38501
†† University of South Carolina, Columbia, South Carolina 29208
†††
Tulane University, New Orleans, Louisiana 70161
*Corresponding author. Email: HStretz@tntech.edu Phone: 931-372-3495 Fax: 931-372 6352
6 pages of Supporting Information include a comparison of size distributions for the water
suspensions of sodium montmorillonite (by atomic force microscopy or AFM) showing
individual platelets, distribution of platelet thicknesses and distribution of platelet aspect ratios
for nearly 1500 particles. Additional information presented includes three Kratky plots for the
small angle x-ray scattering (SAXS) data showing linear fits for the control, filled and
magnetized-filled composite hydrogels.
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Figure S1. Atomic force microscopy image (left) showing individual MMT platelets. Crosssection analysis of one platelet (green line in left image) yields the height profile (right),
indicating a platelet thickness of 1.23 nm.
2
0.25
N = 1468
Mean = 1.29 nm
Median = 1.20 nm
Frequency
0.2
0.15
0.1
0.05
0
0.6
1.1
1.6
2.1
2.6
3.1
3.6
MMT Mean Platelet Thickness (nm)
more
Figure S2. Histogram of mean platelet thicknesses based on N=1468 particles from 39 different
AFM images. The inset shows a part of one AFM image showing mostly single platelets; the
arrows point to two particles that are probably unexfoliated stacks containing two platelets.
Discussion: For every individual “particle” in each AFM image, we can measure the vertical
dimension relative to the background at every point on each particle. The average value of the
vertical dimension is the mean thickness of that particle. Based on the typical lateral dimensions
seen in the AFM images (10’s to 100’s of nm) and the median thickness of 1.20 nm, these
particles are clearly platelets. The median thickness of 1.20 nm is consistent with the expected
thickness of hydrated MMT platelets.
About 83% of the particles seen in the AFM images have mean thicknesses between 0.9
nm and 1.5 nm: these are pristine single platelets. If one defines exfoliation as the production of
pristine single platelets, we would say that this sample is 83% exfoliated. About 15% of the
particles have mean thicknesses between 1.6 and 2.5 nm. Typically, these are single platelets
with all or part of a second platelet on top (see inset of Figure S2). Even pristine single platelets
are often observed to have small fragments somewhere on their top surface. If the second
platelet fragment is large, it may cover most of the surface of the first platelet underneath. This
can be called a “duplex” stack (two platelets). Strictly speaking, these platelets are not
exfoliated. However, we can say that 98% of the MMT in this sample are exfoliated into single
platelets or duplex stacks. We do not see a significant incidence of duplex stacks that appear to
be created due to the random deposition of one pristine single platelet overlapping part of
another single platelet.
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0.18
0.16
N = 1468
Mean = 159
Median = 142
0.14
Frequency
0.12
0.1
0.08
0.06
0.04
0.02
0
20
80
140 200 260 320 380
MMT Platelet Aspect Ratio
440
500
Figure S3. Histogram of MMT platelet aspect ratio based on N=1468 particles from 39 different
AFM images.
Discussion: For every individual particle in each AFM image, image analysis gives us the lateral
area in nm2. We compute a characteristic lateral length for that particle as the square root of the
measured area. The particle’s aspect ratio equals the characteristic lateral length divided by the
mean thickness of that individual particle. In this way, we can measure the exact aspect ratio of
every particle in an AFM image. The distribution of aspect ratios of many particles are shown in
the histogram of Figure S3.
4
Figure S4. Kratky plot for control PAAm gel. The linear fit has a correlation coefficient (R2) of
0.916.
5
Figure S5. Kratky plot for filled PAAm/MMT. The linear fit has a correlation coefficients (R2)
of 0.917.
Figure S6. Kratky plot for magnetized-filled PAAm/MMT gel. The linear fit has a correlation
coefficient (R2) of 0.964.
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Figure S7. Overlay of intensity versus distance for carbonic anhydrase (far right peak) and
ovum serum albumin (middle peak) after electrophoresis through magnetized-filled hydrogel of
PAAm/MMT,  = 2.25 x 10-4. The reproducibility of the result is evident.
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