Cargille™ Refractive Index Liquids
Liquids with high refractive indices: Those above 1.63
Taken from materials supplied by Cargille Laboratories, Inc.
We present technical information not just for the Cargille fluids that are
in the official SPI product line, but for other Cargille fluids as well.
Naturally should a customer require any of these other Cargille fluids,
just let us
know, since we can supply all of these products.
Most water based liquids have refractive indices between 1.33 and 1.45.
Most organic based liquids have refractive indices between 1.45 and 1.55.
Liquids above 1.63 are rare. Generally. fpr Cargille Optical Liquids above
1.63, the higher the refractive index the less desirable the liquid's other
properties.
Cargille Optical Liquids with Refractive Indices Above 1.63
Series A 1.632 to 1.640 Code 40BN 1.631 to 1.656
Series B 1.642 to 1.700 Code BNDN 1.657 to 1.700
Series M 1.705 to 1.800 Code 50BN 1.631 to 1.656
Series H, EH, FH, and GH 1.81 to 2.31 Code EC31 1.631 to 1.640
Gem Refractometer Liquid 1.81
Meltmount Adhesives 1.662, 1.68, and 1.704
Toxicity
The liquid with the highest refractive index and relatively low toxicity is
Laser Liquid Code 5763, n = 1.630. All Cargille Optical Liquids between
1. 63 and 1.800 and the Gem Refractometer Liquid (n = 1.81) are of moderate
toxicity.
Series H, EH, FH, and GH (n = 1.81 to 2.31) are arsenic based and highly
toxic. They contain various solids dissolved in arsenic tribromide, a
compound that is slightly volatile and therefore an inhalation hazard that
requires proper ventilation. Within Series H. EH, FH, and GH, the higher
refractive index, the lower the arsenic tribromide content, making the
higher refractive index materials less of an inhalation hazard than those
with lower refractive index.
Color and Transmittance
Cargille Optical Liquids above refractive index 1.63 range in color from
slightly yellow to very dark red. Liquids between 1.63 and 1.78 are similar
in color. They are light yellow. Cargille Optical Liquids above 1.78 tend
to be darker. Note that above 1.78, the higher the liquid's refractive
index, the darker the color and the more light it absorbs below 5000Å. An
exception is the Gem Refractometer Liquid which has a refractive index of
1. 81 but in darkness is similar to Series M, 1.780. Series H, EH, FH,
and GH, because of their dark color, are usually used in thin layers such
as under the cover glass of a microscope slide. This is the primary way
they are used by microscopists.
Crystallization
Cargille Optical Liquids with refractive indices above 1.735 have dissolved
solids which may come out of solution if kept for a long time below 20° C.
The solids are dissolved in a slightly volatile base. If left open to the
air, they will deposit crystals as the base evaporates. The evaporation
causes the refractive index to rise. When subjected to either cold or
evaporation, Series M, between 1.780 and 1.800 and the Gem Refractometer
Liquid develop crystals more quickly than do the rest of the liquids with
dissolved solids (these being M Series 1.740 to 1.775, Series B and Code
BNDN 1.700, and Series H, EH, FH, and GH). Immersion Liquid Code EC31 can
precipitate an oxide powder especially if in a thin layer that is exposed
to air for a month or longer.
Compatibility and Reactivity
Series H, EH, FH, and GH will fume in moist air. They are chemically very
aggressive. They react with all plastics, metals and elastomers tested
except for phenolic, polyethylene, polypropylene, and fluorosilicone rubber.
They will attack lead glass. The remainder of the Cargille liquids above
1.63 are much less aggressive with the lower of the refractive indices
being generally the least reactive. All (except Code EC31) contain
halogens that may become free and tarnish or corrode some metals. For a
detailed list of compatible and incompatible materials, consult the Typical
Characteristics Sheet for the specific fluid.
Temperature Coefficient of Refractive Index
A liquid's temperature coefficient of refractive index can be expressed as
the change in refractive index per °C. It is always negative so that as
temperature increases, refractive index decreases. Liquid temperature
coefficients are usually so much higher than for solids that the user must
know the temperature of a liquid to know its refractive index. With solids,
temperature is less critical. It is sometimes advantageous to adjust the
refractive index of a liquid by adjusting the temperature. Optical liquids
with refractive indices less than 1.63 tend to have temperature coefficients
of -0.0003 to -0.0004. Temperature coefficients for liquids with refractive
indices above 1.63 and up to 1.70 tend to be about -0.0005. Series M
liquids have temperature coefficients of about -0.0007. When you consider
the liquids of Series H, EH, FH and GH the higher the refractive index the
lower the temperature coefficient. Series H begins with a liquid having
a refractive index of 1.81 and a temperature coefficient of -0.0009. Series
GH 2.31 has a temperature coefficient of -0.0002.
Series FH and GH
These Series are called "melts" because they are solids or soft solids at
room temperature and must be heated to a liquid state. As heated liquids,
they can be applied to heated surfaces. Cooled to 25° C, they will have
the refractive index printed on their label. At 25° C, they are only fair
adhesives. Series FH melts are too soft to hold anything rigidly. Series
GH melts are more rigid but have only fair adhesion. Series GH melts of
2.29 and higher are brittle.
Meltmount Adhesives
Meltmounts at room temperature, 25° C, appear to be solid but they are
really highly viscous liquids. When heated they become thinner until at
about 70° C they become quite fluid, at which point they can be placed
between two flat surfaces such as glass cover slip and slide. The bonded
system will then have the refractive index stated on the Meltmount's label.
When reheated, the two surfaces can then be separated.
Viscosity
Viscosity decreases with increasing temperature. Here we will consider
viscosity at 25° C. Viscosity can be measured in cSt (centistoke) with water
being 1 cSt, motor oil (30W) being 225 cSt, and molasses being 2500 cSt.
Immersion Liquids Code EC31 are fairly viscous with refractive index 1.630
being 1259 cSt and 1.640 being 2463 cSt. The remainder of Cargille Optical
Liquids with refractive indices above 1.63 and 1.80 have low viscosities of
between 2 and 10 cSt. This excludes Meltmounts which can be considered
solids. Series H and EH liquids become more viscous with increases
refractive indices. Series H 1.81 is 0.4 cSt, Series H 2.00 is 84 cSt,
and Series EH 2.11 is 8496 cSt. Series FH are soft solids, and Series GH
are solids. Gem Refractometer Liquid is 2 cSt.
Fluorescence
Cargille Optical Liquids 1.705 and higher absorb 3560Å excitation radiation
and do not visibly fluoresce. Cargille Optical Liquids above 1.63 and
1.700 do transmit some light at 3560Å. although very little is transmitted
by liquids above n=1.66, and all do visibly fluoresce. Immersion Liquid
Code 50BN and Immersion Liquid Code EC31 fluoresce much less than the other
liquids above 1.63, but up to 1.700.
Density
Water has a density at 25° C of 1.0 gram/cc. Cargille Optical Liquids with
refractive indices above 1.63 and up to 1.700 have densities of 1.3 to 1.7
grams/cc. Above n=1.700, the liquids are quite dense, on the order of 3
grams/cc.
Odor
At room temperature (approximately 25° C), all Cargille Optical Liquids with
refractive index above 1.63 have an unpleasant odor to some degree. The
perceived degree of unpleasantness varies, of course, from person to person.
Meltmount has a mild odor only when melted. Immersion Liquid Code EC31 has a
mild fruity odor that is not objectionable to most people. The odor of
Series A and Series B 1.632 to 1.700, for most people, is not objectionable
but for some, there is great objection. Series M and Gem Refractometer
Liquid have a fairly strong and unpleasant odor. The series H and EH have
a moderate odor which should be avoided because it comes from toxic arsenic
tribromide. Series FH and GH do not have much of an odor unless melted
and the odor then is from a toxic vapor and should not be inhaled. For that
reason we recommend that it is essential that work with these odorous
materials be done in a properly working fume hood of some sort, or some
other form of adequate ventilation.
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Monday December 01, 2008
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