This is an interesting question. The quick answer is no, as zeta potential is defined as a potential associated with the interfacial charge density (i.e. surface charge between two phases). Soluble polymers do not have an interface and do therefore not have a zeta potential in a conventional sense. They do exhibit electrokinetic mobility given that they have charge.

The complication lies in the relation between charge density and electric potential. In the case of zeta potential, no surrounding fluid is flowing through the particle (i.e. a solid particle), and the zeta potential is related to the two dimensional surface charge density. For polyelectrolytes, the surrounding fluid can flow through (in between) the polyelectrolyte coils. This results in entirely different expressions. For spherical polyelectrolyte globules, this is given by the Hermans – Fujita equation. The interior charge density is related to the so called Donnan potential. In between, there exist theories describing particles consisting of hard cores with soft shells. Hiroyuki Ohshima has published a lot in this field.

An excellent book chapter by Ohshima (Chapter 5) describing this can be found in the book “Interfacial Electrokinetics and Electrophoresis” ed. By A. Delgado, Surfactant Science Series, vol. 106., Marcel Dekker, Inc., New York, Basel, 2002.

Hope this is helpful

Niels

Zeta sizer is the only commercial instrument capable of measuring the size, zeta potential and molecular weight in a single, compact unit.

Yes, polymers can also have charge around them when dispersed in a solvent. Using zeta sizer you can also measure dispersed particles/polymer aggregates of certain size. If your polymer is solubilized as a single molecular entity and not part of an aggregate of certain size, zeta sizer might not give you a value. Zeta potential is measured in zeta sizer by laser doppler velocimetry. That means, the doppler shift observed depends on laser wavelength which is applicable to particle/aggregates of certain size. You can refer to Zeta sizer manual from Malvern.

Zeta Potential, size, size distribution, molecular weight of polymeric molecules could be measure by using Potentiostat (Gamry etc),

Hello Hossein,

Yes polymer molecules do have charge. To know the surface charge you can evaluate it using Zeta Potential measuring instrument (Brook havens) after making the solution in varying pH 2 to 10.

All the Best !!

Are you asking if polymer , by itself can have a charge when not suspended in a liquid system?

To Mr Ankur: yes. I would like to know is there any method to measure the charge of a polymer molecule in solution state?

This is an interesting question. The quick answer is no, as zeta potential is defined as a potential associated with the interfacial charge density (i.e. surface charge between two phases). Soluble polymers do not have an interface and do therefore not have a zeta potential in a conventional sense. They do exhibit electrokinetic mobility given that they have charge.

The complication lies in the relation between charge density and electric potential. In the case of zeta potential, no surrounding fluid is flowing through the particle (i.e. a solid particle), and the zeta potential is related to the two dimensional surface charge density. For polyelectrolytes, the surrounding fluid can flow through (in between) the polyelectrolyte coils. This results in entirely different expressions. For spherical polyelectrolyte globules, this is given by the Hermans – Fujita equation. The interior charge density is related to the so called Donnan potential. In between, there exist theories describing particles consisting of hard cores with soft shells. Hiroyuki Ohshima has published a lot in this field.

An excellent book chapter by Ohshima (Chapter 5) describing this can be found in the book “Interfacial Electrokinetics and Electrophoresis” ed. By A. Delgado, Surfactant Science Series, vol. 106., Marcel Dekker, Inc., New York, Basel, 2002.

Hope this is helpful

Niels

There is considerable problem if we start the questions from preexisting theory, as opposed to asking a question and devise means to solve it. Many proteins like albumin do have a cut off for the interior and behave similar to membranes, which manifests only when you design relevant experiments. Some of these papers indicate several findings not anticipated by existing theory.

CN Madhavarao, Zuben E. Sauna, V. Sitaramam. Solvent interconnectedness permits measurement of proximal as well as distant phase transitions in polymer mixtures by fluorescence Biophysical Chemistry 90, 147-156, 2000

C.N. Madhavarao Z.E.Sauna, A. Srivatsava, and V. Sitaramam. Osmotic perturbations induce differential movements in the core and periphery of proteins, membranes and micelles Biophysical Chemistry 90, 231-246. 2001

Z.E.Sauna, C.N.Madhavarao, V.Sitaramam Large solutes induce structural perturbations in proteins and membranes. Int. J. Biol. Macromolecules, 29,. 5-18. 2001

The quenching of the electrostatic energy, call it by any name, has consequences and can be explored experimentally by quenching it with electrolytes. Whether a system approximates a porous polymer or not is to be determined. There are lots of surprises.

It should be possible to just try to perform an electrophoretic light scattering measurement to determine the electrophoretic mobility. If the molecules scatter sufficient light, then it should be possible to obtain an electrophoretic mobility. To interpret this as a zeta potential may be more challenging (as stated above), however the presence of an overall positive or negative electrophoretic mobility will confirm the presence of "any charge around the molecule". The reverse is not true: if the electrophoretic mobility is close to zero then this might just be the result of an overall net zero charge, i.e. this could cover up charge anisotropy in/on your molecule.

http://www.materials-talks.com/blog/2017/07/27/isoelectric-points-of-nanomaterials-qa/

 Yes polyelectrolytes which are anionic or cationic polymers develop electrical double layers and then zeta potential also. Surface charges of the charged polymers can be determined by titration and the zeta potential by Streaming Induced Potential measurements.(Please see the attached file).

molecules have no interfacial double layer because they have no interface in sense that molecules have different environment than the bulk - there are only individual molecules, see Niels answer. Situation is different if we have agglomerates of or with polyelectrolytes. Possibility to measure electrophoretic mobilities and calculate 'zeta potential' values with assumptions, which do not apply does not proof that they have zeta potential.

Charge density of polyelectrolytes can be determined using a Streaming Current Detector. This method is commonly used to measure the charge density of polycarboxylate ethers. For more detailed information and understanding you can refer to those documents:

https://www.researchgate.net/publication/223328760_Competitive_Adsorption_Between_Superplasticizer_and_Retarder_Molecules_on_Mineral_Binder_Surface

https://www.researchgate.net/publication/256743627_The_Streaming_Current_Detector_A_Quantitative_Model

It would probably answer Hossein’s question who would like to know if there is any method to measure the charge of a polymer molecule in a solution state.

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