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Growth Rates
Pure sorbitol
2.5 hours at 40°C
17 hours at RT
2 hours at 35°C
Linear Birefringence
Figure 4a. Figure 4c.
CV
CV
Figure 4b. Figure 4d.
Figure 3a. Figure 3b.
Linear Dichroism Image
Distorted Growth
At Elevated Temperature
CV
Figure 4b.
Diameter (Millimeters
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
Figure 3c. Linear
Birefringence Magnitude
Growth rates are influenced by temperature,
molecular structure, and thickness of sample.
With increased temperature there is loss of order
in the assembly process as indicated by Figure
4b above; additionally the optical properties are
changed indicated by 3b, a linear dichroism
image. In the case of D-sorbitol spherulites, the
birefringence is strongly dependent on the
growth temperature. The bright section in Figure
3a has higher birefringence, quantified by the
corresponding Metripol image in Figure 3c.
Growth rates of MGO and CV are plotted in
Figure 3d which shows significant variance
based not only on temperature, but also dye
inclusion. Nucleation could not be initiated
above 50° C, though slides that were previously
nucleated showed even faster growth at 50° and
above. Ongoing studies are being conducted to
quantify these growth rates.
Spherulite Growth (µm/hr) at 45°C
Malachite
Green
Oxalate
Malachite
Green
Oxalate
Crystal
Violet
Crystal
Violet
m1y = 0.0014x + 0.0629
R 2 = 0.9603
m2y = 0.0019x + 0.0418
R 2 = 0.9956
c1y= 0.0022x + 0.2124
R 2 = 0.9962
c2y = 0.0024x + 0.0237
R 2 = 0.9473
84 µm/hr
132 µm/hr
144 µm/hr
114 µm/hr
MGO
Metripol has elucidated the slow direction
for light propagation through the spherulites as
indicated in Figures 4a and 4b above. The
magnitude of birefringence can also be measured
as seen in Figures 4c and 4d and Table 2. The
direction with the highest refractive index is
oriented radially in the polycrystalline mass
illustrated by the green line in the images 4a
and4b. Work is ongoing to correlate the
refractive index anisotropy to the molecular
structure of the material.
Conclusions
Using the self assembly of crystal growth
we have demonstrated an anisotropic
chromophore alignment without the use of
poling techniques. Two orthogonal orientations
are possible with differing chromophores.
Birefringence can also be manipulated based on
the chromophore structure. Growth rates are
easily altered with changes in temperature and
dye structure. Further studies will investigate the
extent to which dyes are aligned in a polar
manner, as well as testing these materials for
their potential as EO devices.
References
Yu, L. 2003 Cryst. Growth Des. 3, 967-971
Wood, E.A. 1977 Crystals and Light, Dover
Publications, New York
Kaminsky, W. 1996 JSTOR 452, 195
Kaminsky, W. 2000 J. Microscopy 198, 1-9
0.05
0
0 20 40 60 80 100 120
Time (Minutes)
Figure 3d. Pure sorbitol spherulites grow at
69.4+ 2.8 µm/hr at 40.5° C.
48 CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004