Silicic acid, lithium magnesium sodium salt

Nanomaterial Zeta potential

Administrative data

Endpoint:

nanomaterial Zeta potential

Type of information:

experimental study

Adequacy of study:

key study

Study period:

January 2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2013

Report date:

2013

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: Colloidal Dynamics Zeta Probe with auto titrator

Version / remarks:

The Colloidal Dynamics Zeta Probe instrument uses an acoustic method to determine zeta potential and can tolerate a variety of dispersions in terms of concentration, clarity and particle size, provided they are liquid or flowing during measurement. Strongly gelled systems cannot be measured. The instrument is fitted with an auto titrator to automatically perform zeta vs. pH sweeps and also allows the possibility of titrating with any other additive in solution form. Sample sizes range from a minimum of 30 mL to 300 mL maximum. The instrument was also supplied with a jacketed vessel for variable temperature experiments.

Deviations:

not applicable

Principles of method if other than guideline:

There is no guideline for this test

GLP compliance:

no

Other quality assurance:

other: ISO9001

Type of method:

other: acoustic

Details on methods and data evaluation:

The stability of colloidal dispersions can be determined by the measurement of the zeta potential at the surface of the particles in an aqueous or organic solvent. Zeta potentials > +/- 30 mV indicate stable dispersions of colloidal particles that are repelling each other whereas between +/- 30 mV indicates instability/attraction. The iso-electric point (IEP) is the pH at which zeta potential = 0 mV. The Colloidal Dynamics Zeta Probe instrument uses an acoustic method to determine zeta potential and can tolerate a variety of dispersions in terms of concentration, clarity and particle size, provided they are liquid or flowing during measurement.

Test material

Test material information

Constituent 1

Reference substance name:

Silicic acid, lithium magnesium sodium salt

EC Number:

258-476-2

EC Name:

Silicic acid, lithium magnesium sodium salt

Cas Number:

53320-86-8

Molecular formula:

Na0.7[Li0.3Mg5.5Si8O20(OH)4]

IUPAC Name:

magnesium(2+) lithium(1+) sodium bis(oxosilanebis(olate))

Specific details on test material used for the study:

Identification: Laponite Type 2 – silicic acid, lithium sodium magnesium salt, CAS#53320-86-8, EC#258-476-2

Description: White powder

Batch Number 09-3286-2 (Type 2)

Date Manufactured: Type 2 - 27th October 2009

Data gathering

Instruments:

• Colloidal Dynamics Zeta Probe with auto titrator
• Overhead mixer i.e. Heidolph fitted with Cowels blade
• Other high-shear mixers e.g. Silverson, Dispermat.

Calibration:

The instrument was calibrated as required by the manufacturer.

Reproducibility:

Three samples of the same batch were analysed. The results gave better than 0.5% deviation from the mean value

Results and discussion

Zeta potential

Key result

Zeta potential:

ca. -61 mV

St. dev.:

0.1 mV

pH:

9.65

Medium:

The test material was prepared at 0.5%w/w (dried weight) concentration in demineralised water (conductivity of <2μS/cm confirmed).
The dispersion was mixed for 1 hour using an overhead stirrer with a cowles blade attachment. The dispersion is referred to as the stock dispersion.
The stock dispersion was analysed for its zeta potential and its zeta potential over a range of pH’s (pH 4-12) after 24 hours hydration.
For the purpose of this work a one litre sample of the stock dispersion was prepared, sufficient sample for each preparation and analysis.
The stock dispersion was allowed to hydrate in a 25°C incubator for 24 hours. Subsequently, 250g of the Laponite® dispersion is analysed with a single point zeta potential using the methodology detailed by the manufacturer for this instrument.
The substance would be in nano form after this preparation method.

Any other information on results incl. tables

	Laponite T2 09-3286-2
Target pH	pH measured	Zeta potential (mV)
4	3.67	-30.59
5	4.53	-33.08
6	5.98	-41.59
7	6.94	-47.81
8	7.99	-53.09
9	9.71	-60.35
10	9.86	-59.81
11	10.99	-53.20
12	12.02	-32.30

Applicant's summary and conclusion

Conclusions:

The results show that in a 0.5%w/w (dry weight) dispersion, Type 2 Laponite® is stable in a solution of demineralised water owing to its zeta potential of -61.0 mV at its natural pH of 9.65. Changing the pH of the system decreases the zeta potential in the acid direction, presumably neutralising a portion of the negatively charged faces. The pH was not lowered past pH 4 due to the dissociation of Laponite® previously reported. Increasing from the natural pH of the dispersion, the zeta potential appears to decrease, potentially due to the increased Na+ cations brought in by the addition of base which can cause instability through partial gelation.
In conclusion, the results confirm that Laponite® and Type 2 is a stable colloidal dispersions at 0.5%w/w (dry weight). The negative zeta potentials at the naturalpH show that the clay particles are negatively charged as would be expected.
An isoelectric point was not reached by changing the pH. This is due to the major contribution of the overall particle surface charge made by the negative faces of the clay platelets which dominate any effects from the addition of acid or base.