I just wanted to express my deepest gratitude for your incredible contributions to the field of electrochemistry. Your work has been enlightening and inspiring, and it has significantly advanced our understanding and application of this important scientific discipline. Thank you for sharing your knowledge with the world.
This is nice explanation. Some may find it easier to understand the potential definitions by turning things around. Rather than starting with the surface potential and then considering how the potential falls off as one moves away from the surface, instead start with the (arbitrary) definition of zero potential at infinity. From there, consider bringing a positive test change towards the surface. Moving through the neutral bulk, we are far from the positively charged surface and do little work. As we approach closer, we do more and more work causing the total work done (q*V) to rise. The value when we reach the surface is the surface potential. The values as we cross various critical points along the way define other values, such as the zeta potential. I came here searching for an understanding of the definition of the slipping plane. I hope sharing my (hopefully correct!) way of thinking about the electrostatics will be helpful to someone else. It is entirely consistent with what was presented, but is just another way to think about it that some may prefer.
Thank you. I agree with your approach! Somewhere in one of the other videos I use a similar idea to explain the relationship between potential and charge.
Hi, why the potential of the inner slipping plane is defined as the zeta potential, not the outer plane of the slipping plane? If it is the inner plane, then what make it different than the stern potential? I though the zeta potential is the potential at the outer slipping plane. Dr. John Miller please address my confusion, thank you .
Thank you for your comment. I don't mention the Stern layer so I don't understand your remark. I intentionally avoid any jargon associated with a specific model of the diffuse double layer (e.g., Gouy-Chapman) and, instead, describe the qualitative features.
Dear John, thank you for this great video. How does instrument know what the charge of the particle is during zeta potential measurements? I cant find any relationship between the sign of the charge on the particle and the sign of the zeta potential that the instrument reports.
Hi - thank you for watching. The sign of the zeta potential indicates the sign of the electrical potential at the slipping plane relative to the bulk. This isn't necessarily the same as the potential at the true surface of the particle. Although it is generally okay to use the zeta potential to give a fair indicator of the surface potential/charge, it is important to understand the nature of the particle-liquid interface. For example, a charged particle with an adsorbed layer of a nonionic polymer will yield a zeta potential lower than that of the same particle without the polymer.
Thank you for your comment. I don't mention the Stern layer so I don't understand your remark. I intentionally avoid any jargon associated with a specific model of the diffuse double layer (e.g., Gouy-Chapman) and, instead, describe the qualitative features.
Enlighten Scientific the diffuse layer is when the charges become even. It is also called the “outer diffuse region” since the first layer where you only have the immobilized negative charges is know as inner molecular layer.
@@patrickdamacet6085 My description is consistent with yours though I have never heard the term "inner molecular layer". Do you have a reference that defines this? As I say, I deliberately don't get into the specifics of a given model since the classic models don't apply in many situations (e.g., porous particles, fixed charged networks, conductive surfaces) and even the concept of zeta potential becomes invalid.
@@patrickdamacet6085 You are incorrect. The charges are "even" in the bulk solution. The diffuse layer always has non-equal concentrations of ions and counterions - it has to. The concentration differential is greatest near the particle and tends to zero infinitely far away. Where does the term "inner molecular layer" come from? I have never seen this in any definitive works on electrokinetics (notably Hunter). For a simple electrolyte solution, there are no molecules, just atomic ions. I've seen "inner Helmholtz plane" which is related to the immobile bound ions and the "outer Helmoltz plane" which is related to the distance of nearest approach of hydrated ions (for GC-type models).
Dear John, thank you very much for sharing this fantastic presentation. I have read all the comments but I have still two doubts about what you said. 1. The paper you recommended (Delgado et al., 2007) describes that "The potential at the plane where slip with respect to bulk solution is postulated to occur is identified as the electrokinetic or zeta potential,ζ". Instead you locate the zeta potential between the rigid layer associate with the particle and the diffuse layer of ions. There is something I am missing. 2. In the previous video, you define de EDL as the sum of the rigid layer and the diffuse layer of ions. However, in the plots you define the EDL as that represented by the length 1/k which does not take into account the rigid layer. I would really appreciate any help to understand. Thank you very much.
Hi Raffaella - thanks for your questions. Regarding 1., at a high level, my description and Delgado et al's are consistent. The EDL comprises a rigid layer (particle) and diffuse layer. Think of it like an electrical capacitor but where one plate is diffuse. The zeta potential is - by definition - the location that delineates motion of the particle and any bound materials from the bulk liquid. At a most simplistic level, this is the same as delineating between the particle and the surrounding diffuse layer of ions. Regarding 2. and following on from 1., the definition of zeta potential (as the electrokinetic potential) is chosen so as to be of experimental value. i.e., it is the potential that we can access somehow through experimentation such as electrophoresis, electroosmosis, streaming potential or sedimentation potential. There's nothing inherently "magical" about it - it's just represents an experimentally-accessible estimate of the potential near the surface. Because electrokinetic experiments relate to the potential at this location, they tell us nothing about the nature of the interface at regions closer to the true particle surface. Hence, it is appropriate to find some way to characterize the concentration profile of ions in the region of the diffuse part of the double layer up to the location of the zeta potential, rather than the true particle surface. As with many properties that decay exponentially with distance, it is convenient to use a parameter that indicates the distance at which the property is 1/e of its starting value. In our case, the starting value is the ionic composition at the slipping plane.
I really got confused when it comes to the definition of surface charge. Is it the overall charge created by the first (and fixed) layer of ions adsorbed on the surface (i.e. the stern layer), or the charge of the solid surface that makes ions adsorbed on the surface? The prior definition means that in you explanation the surface charge is negative, while the later means that the surface charge is positive.
Sorry I confused you :) Surface charge refers to the charge without anything adsorbed. For example, silica particles develop charge because of dissociation of OH groups on the surface. The surface charge means all of the O- groups. Of course, H+ ions will be in solution. Some will be attracted back to the particle and adsorb (not necessarily where the -ve charges are) and some will remain in solution. The adsorbed ones will screen the surface charge, thereby reducing the potential. The ions in solution will form the diffuse part of the double layer. Addition of extra electrolyte may cause more (counter)ions to adsorb, lowering the potential even further.
@@johnmiller0000 Don't worry, it is mostly not because of your explanation. I still got some insight from you video, so thank you. However, we all working in this field should be more careful with the definition of terms. My field is chemical engineering, but I have to study colloid science for my research. I found that surprisingly different sources will say different things about these two: surface charge (I asked you) and the structure of the double layer. If you search for explanations or textbooks, you will find many who said that the surface charge is the charge due to the adsorption of ions, as opposed to what you said. Of course, there are also those who explain it the same way like you did. Regarding the double layer, it is even more confusing. Many scientific articles from reputable journals will give you different picture of the double layer. For example, here you define the slipping plane as the line (or border) between the fixed ion layer (Stern layer) and the diffuse layer. In some papers or books you will find that it is between the diffuse layer and the bulk liquid, while some said it is between outer Helmholtz layer and diffuse layer. I googled "double layer slipping plane" and found figures of different schemes. This is so frustrating.
I agree with the confusing range of explanations. I try to cut through all that and keep it simple enough to get the physical basis across. Descriptions of the double layer etc are just theories and the terminology is quite subjective. I made a point of explaining how potential relates to charge - that's something that is rarely explained.
@@johnmiller0000 Yes, you're right. I really appreciate your effort in this video. Moreover, you are willing to discuss this detail with me, so thanks again. :)
@@leinadatidumarp Yes I thought I was in the same situation.Looking for more information but just getting more and more confused.Seems that there isn't a common agreement about these definitions.
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I just wanted to express my deepest gratitude for your incredible contributions to the field of electrochemistry. Your work has been enlightening and inspiring, and it has significantly advanced our understanding and application of this important scientific discipline. Thank you for sharing your knowledge with the world.
This is nice explanation. Some may find it easier to understand the potential definitions by turning things around. Rather than starting with the surface potential and then considering how the potential falls off as one moves away from the surface, instead start with the (arbitrary) definition of zero potential at infinity. From there, consider bringing a positive test change towards the surface. Moving through the neutral bulk, we are far from the positively charged surface and do little work. As we approach closer, we do more and more work causing the total work done (q*V) to rise. The value when we reach the surface is the surface potential. The values as we cross various critical points along the way define other values, such as the zeta potential. I came here searching for an understanding of the definition of the slipping plane. I hope sharing my (hopefully correct!) way of thinking about the electrostatics will be helpful to someone else. It is entirely consistent with what was presented, but is just another way to think about it that some may prefer.
Thank you. I agree with your approach! Somewhere in one of the other videos I use a similar idea to explain the relationship between potential and charge.
Hi, why the potential of the inner slipping plane is defined as the zeta potential, not the outer plane of the slipping plane? If it is the inner plane, then what make it different than the stern potential? I though the zeta potential is the potential at the outer slipping plane. Dr. John Miller please address my confusion, thank you .
I think you are right, I watched and read several doc about zeta potential and normally the zeta potential is the outer plane of the slipping plane
The video is misleading - it confuses the stern layer with the slipping layer! 1:27
Thank you for your comment. I don't mention the Stern layer so I don't understand your remark. I intentionally avoid any jargon associated with a specific model of the diffuse double layer (e.g., Gouy-Chapman) and, instead, describe the qualitative features.
Dear John, thank you for this great video. How does instrument know what the charge of the particle is during zeta potential measurements? I cant find any relationship between the sign of the charge on the particle and the sign of the zeta potential that the instrument reports.
Hi - thank you for watching.
The sign of the zeta potential indicates the sign of the electrical potential at the slipping plane relative to the bulk. This isn't necessarily the same as the potential at the true surface of the particle. Although it is generally okay to use the zeta potential to give a fair indicator of the surface potential/charge, it is important to understand the nature of the particle-liquid interface. For example, a charged particle with an adsorbed layer of a nonionic polymer will yield a zeta potential lower than that of the same particle without the polymer.
the diffuse region shouldn't include the stern layer. this is a mistake in your explanation.
Thank you for your comment. I don't mention the Stern layer so I don't understand your remark. I intentionally avoid any jargon associated with a specific model of the diffuse double layer (e.g., Gouy-Chapman) and, instead, describe the qualitative features.
Enlighten Scientific the diffuse layer is when the charges become even. It is also called the “outer diffuse region” since the first layer where you only have the immobilized negative charges is know as inner molecular layer.
@@patrickdamacet6085 My description is consistent with yours though I have never heard the term "inner molecular layer". Do you have a reference that defines this? As I say, I deliberately don't get into the specifics of a given model since the classic models don't apply in many situations (e.g., porous particles, fixed charged networks, conductive surfaces) and even the concept of zeta potential becomes invalid.
@@patrickdamacet6085 You are incorrect. The charges are "even" in the bulk solution. The diffuse layer always has non-equal concentrations of ions and counterions - it has to. The concentration differential is greatest near the particle and tends to zero infinitely far away. Where does the term "inner molecular layer" come from? I have never seen this in any definitive works on electrokinetics (notably Hunter). For a simple electrolyte solution, there are no molecules, just atomic ions. I've seen "inner Helmholtz plane" which is related to the immobile bound ions and the "outer Helmoltz plane" which is related to the distance of nearest approach of hydrated ions (for GC-type models).
Thank you! Where have you been all these while when i was confused in class?
Dear John, thank you very much for sharing this fantastic presentation. I have read all the comments but I have still two doubts about what you said.
1. The paper you recommended (Delgado et al., 2007) describes that "The potential at the plane where slip with respect to bulk solution is postulated to occur is identified as the electrokinetic or zeta potential,ζ". Instead you locate the zeta potential between the rigid layer associate with the particle and the diffuse layer of ions. There is something I am missing.
2. In the previous video, you define de EDL as the sum of the rigid layer and the diffuse layer of ions. However, in the plots you define the EDL as that represented by the length 1/k which does not take into account the rigid layer.
I would really appreciate any help to understand.
Thank you very much.
Hi Raffaella - thanks for your questions.
Regarding 1., at a high level, my description and Delgado et al's are consistent. The EDL comprises a rigid layer (particle) and diffuse layer. Think of it like an electrical capacitor but where one plate is diffuse. The zeta potential is - by definition - the location that delineates motion of the particle and any bound materials from the bulk liquid. At a most simplistic level, this is the same as delineating between the particle and the surrounding diffuse layer of ions.
Regarding 2. and following on from 1., the definition of zeta potential (as the electrokinetic potential) is chosen so as to be of experimental value. i.e., it is the potential that we can access somehow through experimentation such as electrophoresis, electroosmosis, streaming potential or sedimentation potential. There's nothing inherently "magical" about it - it's just represents an experimentally-accessible estimate of the potential near the surface. Because electrokinetic experiments relate to the potential at this location, they tell us nothing about the nature of the interface at regions closer to the true particle surface. Hence, it is appropriate to find some way to characterize the concentration profile of ions in the region of the diffuse part of the double layer up to the location of the zeta potential, rather than the true particle surface. As with many properties that decay exponentially with distance, it is convenient to use a parameter that indicates the distance at which the property is 1/e of its starting value. In our case, the starting value is the ionic composition at the slipping plane.
very good
Pak tolong di jawab, benda apa yang ada kandungan zeta.?
I really got confused when it comes to the definition of surface charge. Is it the overall charge created by the first (and fixed) layer of ions adsorbed on the surface (i.e. the stern layer), or the charge of the solid surface that makes ions adsorbed on the surface?
The prior definition means that in you explanation the surface charge is negative, while the later means that the surface charge is positive.
Sorry I confused you :) Surface charge refers to the charge without anything adsorbed. For example, silica particles develop charge because of dissociation of OH groups on the surface. The surface charge means all of the O- groups. Of course, H+ ions will be in solution. Some will be attracted back to the particle and adsorb (not necessarily where the -ve charges are) and some will remain in solution. The adsorbed ones will screen the surface charge, thereby reducing the potential. The ions in solution will form the diffuse part of the double layer. Addition of extra electrolyte may cause more (counter)ions to adsorb, lowering the potential even further.
@@johnmiller0000 Don't worry, it is mostly not because of your explanation. I still got some insight from you video, so thank you.
However, we all working in this field should be more careful with the definition of terms. My field is chemical engineering, but I have to study colloid science for my research. I found that surprisingly different sources will say different things about these two: surface charge (I asked you) and the structure of the double layer. If you search for explanations or textbooks, you will find many who said that the surface charge is the charge due to the adsorption of ions, as opposed to what you said. Of course, there are also those who explain it the same way like you did. Regarding the double layer, it is even more confusing. Many scientific articles from reputable journals will give you different picture of the double layer. For example, here you define the slipping plane as the line (or border) between the fixed ion layer (Stern layer) and the diffuse layer. In some papers or books you will find that it is between the diffuse layer and the bulk liquid, while some said it is between outer Helmholtz layer and diffuse layer. I googled "double layer slipping plane" and found figures of different schemes. This is so frustrating.
I agree with the confusing range of explanations. I try to cut through all that and keep it simple enough to get the physical basis across. Descriptions of the double layer etc are just theories and the terminology is quite subjective. I made a point of explaining how potential relates to charge - that's something that is rarely explained.
@@johnmiller0000 Yes, you're right. I really appreciate your effort in this video. Moreover, you are willing to discuss this detail with me, so thanks again. :)
@@leinadatidumarp Yes I thought I was in the same situation.Looking for more information but just getting more and more confused.Seems that there isn't a common agreement about these definitions.