Performing Refractive Index Measurement of Liquids with the BeNano 180 Zeta Max

This application note presents refractive index measurements for various liquid samples using the BeNano 180 Zeta Max, a nanoparticle size and zeta potential analyzer developed by Bettersize.

 

Product	BeNano 180 Zeta Max
Industry	Chemicals
Sample	Water and Toluene
Measurement Type	Refractive Index
Measurement Technology	Optical Refraction

 

Jump to a section: 

• Introduction
• Experimental
• Results and Discussion
• Conclusion

 

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Introduction 

 

The refractive index (RI) of the dispersant is a critical factor in dynamic light scattering (DLS), static light scattering (SLS), and electrophoretic light scattering (ELS) measurements. For commonly used dispersants, RI values are readily available in reference sources such as the CRC Handbook of Chemistry and Physics. In aqueous systems containing salts, the RI of pure water is often sufficient without significantly affecting measurement accuracy. However, for uncommon dispersants or mixtures of water and organic solvents, precise RI measurements are essential for ensuring reliable light scattering results. Typically, a 1% deviation in RI can lead to a 2% variation in particle size results obtained through DLS.

 

This application note presents refractive index measurements for various liquid samples using the BeNano 180 Zeta Max, a nanoparticle size and zeta potential analyzer developed by Bettersize.

 

 

 

The BeNano 180 Zeta Max determines the refractive index of liquids using transmission optics and the principles of refraction. The measurement process involves two liquid samples with known refractive indices. The sample is placed in a wedge-shaped cuvette, and as the laser passes through, it refracts. A CMOS detector positioned at 0° captures the location of the refracted light spot.

 

 

By measuring the light spot positions of two reference samples with known refractive indices (n1 and n2) with the nanoparticle size and zeta potential analyzer -  BeNano 180 Zeta Max, a calibration curve is plotted, showing the relationship between liquid refractive index and light spot position. This curve demonstrates strong linearity within the refractive index range of 1.20 to 1.60. The light spot position of an unknown sample is then measured, and its refractive index is determined using the calibration curve.

Experimental 

Sample	Refractive Index @ 25°C (Measured by Abbe Refractometer)
Water	1.3326
Toluene	1.4928

 

In this study, water and toluene were utilized as reference samples for calibration before measurement. The analyzed samples included acetone, ethanol, 30% DMSO in water, 50% DMSO in water, 70% DMSO in water, and pure DMSO.

 

Results and Discussion 

 

 

 

As illustrated in Figure 3, the results exhibit a strong linear correlation within the refractive index (RI) range of 1.20 to 1.60, suggesting that the extrapolated curve remains applicable for a broad spectrum of liquid samples.

 

A comparison between the RI values measured by the BeNano and the nominal values obtained using an Abbe refractometer revealed minimal deviation. Absolute deviations did not exceed 0.001, while relative deviations remained below 0.1%, confirming the accuracy of the measurement.

 

Conclusion 

 

 

The BeNano 180 Zeta Max delivers highly precise refractive index (RI) measurements, with absolute deviations below 0.001 and relative deviations under 0.1% compared to nominal values. These results validate its reliability and accuracy in characterizing dispersants for light scattering applications, especially in cases involving mixed or less common solvents where RI data may be limited.

 

About the Authors

	Zhibin Guo Application Manager @ Bettersize Instruments
	Dr. Ning Chief Product Officer @ Bettersize Instruments

 

BeNano 180 Zeta Max Advanced Nanoparticle Size & Zeta Potential Analyzer Particle size measurement via sedimentation technology Refractive index measurement Particle concentration measurement   Learn more