Your value is nonsense - random noise on noise. Zeta potential is the holistic property of particles in a liquid medium. You can have no ZP value for a pure liquid - unless of course your product is significantly contaminated with particulate matter. Check out your zeta potential instrument with an appropriate standard.

Your value is nonsense - random noise on noise. Zeta potential is the holistic property of particles in a liquid medium. You can have no ZP value for a pure liquid - unless of course your product is significantly contaminated with particulate matter. Check out your zeta potential instrument with an appropriate standard.

Thank you sir..

yes, the pure water has no zeta-potential, even the dust "particles" in water do not exibit electrokinetic potential, my colleague Alan Rawle is absolutely right- the instrument is wrong in your case

zeta potential is an intrinsic property of particles when they are dispersed in a polar solvent. There is no physical sense of the existence of zeta potential of pure water. See the eleletric double layer theory.

What do you mean writing " What is the zeta potential value of deionised or distilled water?" Water has no potential, surface charge and potential is a property of particles. The result can be completely normal, and the values can be even greater. Distilled water is not perfectly pure water. What is the nature of the particles, their size and water conductivity? Problems with measurement can only be in high-resistance water, which does not come into contact with air.

If you got such a potential without bringing anything into the water, then it might be dust from the laboratory, not a perfectly clean cuvette or random air bubbles. If your device allows you to measure the concentration and particle size, you need to analyze these quantities.

@ Nataliya

Dear Madam,

My nanoparticle (carbon nanodots) surface is functionalized with plenty of amine groups. So I expected positive zeta potential. However, I ended up with negative zeta potential of about -1.7 mV. I wondered about the result and I just took water alone without any nanoparticle in it. I got about -30 mV! The water is fresh triply distilled water and I took utmost care to avoid any dust contamination while collecting the distilled water from the receiver. I red in an article that the presence of nanobubbles and dust particles in water will show negative zeta potential (I have attached the article herewith). I don't think the interference of any dust particle. The zeta potential cuvette is a newly taken one (disposable capillary cuvette). I suspect some invisible nanobubbles (provided the instrument is correctly working) as I am injecting my sample to the cuvette with the aid of a plastic syringe (air may be mixed with the sample but I couldn't see any visible air bubble). Else there should be some problem with the instrument. (The instrument is newly bought one form HORIBA, Model: nanopartica ZS-100). I don't know whether I can get good results if I use dip cell. I don't have enough expertise to resolve this issue.

I request your valuable suggestions.

Thank You.

Hello.

Sorry, at present I am very busy and cannot read the attached paper. Therefore I quickly looked through the abstract. In my previous comments I also wrote about the bubbles.

In every case, the terminology of your question was wrong.

This is not the question about the zeta potential value of water, but air/water interface. Really gas bubbles are charged and most probably your messsured just the potential of the bubbles. According to different papers the potential of the bubbles can be from -10 mV to -250 mV. However, in pure water it can be close to your values. The charge is related with the negatively charged groups HCO3as a result of dissolution of carbon-dioxide gas.

Dependingly on the configuration the system SZ-100 can be used as a particle size analyzer. Could you measure the concentration and size of your objects in pure water? If you have such data, probably I will help you with solution of this problem.

Regards,

Nataliya

I absolutely agree with the comments of Dr. Mishchuk.

Dear Ramanan,

Prof. Nataliya Mishchuk nicely explained you possible reasons of the observed value of the zeta potential of 'something' present in water. I personally would incline towards presence of nano-bubbles dispersed in water. I suggest you purchase a standard sample to check validity of your instrument and don't mind about this problem you you are going to investigate typical colloidal sysyems.

Good luck!!

Emil Chibowski

Few cents more: measured value of the zeta potential is a function of surface properties and electrolyte i.e. material + adsorption + surface reactions. pH and ionic strengths (concentration for single component systems) are two major parameters that can be controlled in the experiment.

Check pH and conductivity of your water. Usually good distilled water is equivalent to 10-6 normal (NaCl equivalent) and DI (demineralized) up to 10-4..10-5 normal.

Additional possible issue is your surface modification process. Excess of the modifying agent may result in multi-layer adsorption and formation of sandwich-like structures with blocked functional groups. I'd recommend to compare zeta potential for particles with different degree of functionalization.

I support the comments of prof. Takhistov. My previous answer concerned only the water/air interface. As for data for nanodots, it is natural that their zeta potential strongly depends on the characteristics of the solution, the surface state of the particles, including the roughness of their surface, shape, structure of adsorbed molecules or ions, pH of solution, etc. (The same can be said about the bubbles.)This is especially important for nanoscale particles in the distilled water, when the thickness of the double layer is much larger than their size. In this case, the thickness of the double electrical layer depends strongly on the electrical conductivity of the solution. Its incorrect accounting can lead to an underestimation of the value of the electrokinetic potential. Note also that an important role can by played by hydrophobicity of the surface, the effect of which has not yet been taken into account in existing devices.

The negative value of zeta potential in all cases is attributed to the negatively charged ions adsorbed on particles or the negative zeta potential value indicates a negative charge on particle surface.

My research I have used Zeta potential analyser, Malvern Zetasizer (Nano-Z, U.K).

I also agree with the comments of Dr. Mishchuk.

In my opinion, measuring the mobility of a bubble according to the method used in the work The ζ-Potential of Gas Bubbles bubbles in a rotating fluid is accompanied by a number of additional factors, which can strongly affect the obtained results. Therefore it is easier to measure the sedimentation potential many bubbles or even better to apply an electric field to the bubble floating in a vertical tube, providing a downwardly directed electrophoresis, so that the bubble stops. The calculations in this case are sufficiently simple and the results will be considerably more exact. However, it seems that we have moved away from the main question :-)) So, I repeat the question from my previous comment: Could you measure the concentration and size of your objects in pure water which leads to the value -30 mV? Best wishes, Nataliya

May be our paper, where we discuss how to interprete zeta potential of a hydrophobic surface, including liquid-gas interface, could be of some help Article Electrohydrodynamics Near Hydrophobic Surfaces

Hello Ramanan,

FYI, I am the inventor of Phase Analysis Light Scattering (PALS) which is the technique used in most of today's light scattering instruments for measuring electrophoretic mobility and zeta potential.

Without additional information from you, I would consider the fact that commercial instruments are designed to be "simple" for the user. In fact, users have become so used to the "just walk up, insert sample and press a button" idea that they, through no fault of their own, do not understand the technique, its limitations, and a given manufacturer's implementation. Your instrument isn't necessarily wrong - it might be you are trying to measure something it simply cannot. You cannot blame a hammer for not drilling a round hole!

In your case, -1.7mV is meaningless without seeing the experimental data. By that, I don't mean the number printed on a report, but graphs of the distribution and/or phase analysis functions etc. Also, any indicators of signal strength etc. Perhaps you simply do not have enough particles in your nanodot samples to give enough signal, or the particles are too small to be meaningfully measured (the diffusion dominates) - I know of some instruments whose graphical reports would have you believe you can measure zeta potential on particles as small as 0.1nm.

A simple test to see if you have any/enough particles is to look at a laser beam passing through the sample. You may be able to do this with the instrument itself. If not, you could use a laser pointer. If you see a beam within the liquid then you can be confident you have colloidal particles. If you see nothing then you have no particles and the instrument will analyze noise or, depending on the manufacturer, the software may warn you that the signal is too low. You may also see bright specks floating around - these would likely be "dust" - how instruments handle this varies significantly.

You mention using the capillary cell. Personally, I don't see the value in it other than for avoid cross-contamination. For most practical purpose, the dip cell is the preferred option. It requires a much lower voltage to operate which avoids many of the issues associated with capillary tubes that the dip cell was originally invented to overcome. If your particles really have such a small zeta potential then a voltage so high would have to be applied using the capillary cell so as to cause a host of measurement problems.

There are many other factors that affect the measurement. The important is the belief that all the user needs to do is press Go.

Hope this helps,

John.

we should not forget that the original question was about water as 1 phase system, not about zetapotential of a dispersed phase in water. So the corresponding answer is that of Alan.

there are many paper about this .

Please consider the explanation of Dr. Miller who is inventor of PALS. He is completely right. If in the water there are no particles, as well as gas nano-bubbles, the observed residual zeta potential is a meaningless.

deionise and "deaerate" the water.