 something that we should do here. Try this to unmute. Yes? Please speak. Can you hear me now? Very good. Okay, thank you. Okay, go ahead, Ming. Okay, thank you. So dear friends. So hello, I'm Min Ma from Chihua University. I'm honored to give a talk online. I noticed that I'm the very first one. I'm going to talk about online talk for this workshop. Very lucky. And I'm a testing person. And I've left to set the organizers for the very kind invitation. And all the contents I'm going to talk today haven't been published. So I also noted that I'm the last one. So one before lunch. So I'll try to make it quick and sorry for the delay. So let's start. So the idea of my talk is about friction between different solid and it's titled as transversency and temperature dependence for the sleep loss of water on supportive graphene and FTPS. Sorry to interrupt you. We could not see your presentation actually. Sorry, which one? Can you see me now? Can you see the presentation? I'm sharing my student can you see it? So I can continue right? Can you see my screen? Hello. Yes, we can see your screen. Okay. Okay. So first of all, those of you who is not familiar with this one. So I'm going to give a very short introduction about the sleep loss. So as shown in this figure. So this figure is a psychometric window for the velocity profile. When the liquid is just lying on a solid surface. And it shows three typical states, no sleep, partial sleep and perfect sleep. So when we talk about the partial sleep, it means that the velocity of the liquid next to solid surface does not equal to the velocity of solid. And this is termed as a sleep. And in fact, about 200 years ago, neighbor already gave a definition of the sleep loss for Newtonian equations. Because we are talking about the frictions and the relation between sleep and friction is very straightforward. You may just think about this force balance between the friction between solid and surface and the friction within the liquid. And then we found that, and we can easily find that the sleep loss is equal to the ratio between the liquid viscosity and the friction coefficient. So that it will say that the sleep loss considerably describes the friction at the solid liquid interface. And because we are using the continuum mechanics, and the first of all, we need to know the applicable range. And this is based on the following assumption, which is called continuum assumptions. And this assumption says that for given system, if the characteristic time of momentum diffusion is larger than the characteristic time of the molecular motion, then we are safe. So for water, this critical length will be about one nanometer. And generally speaking, if we are looking at a broader scale, we found that for a simple surface, in terms of simple surface, so we compare to those surface with structure. And the water on those simple surface, the sleep loss will be between 0.1 nanometer to 10 nanometers. So we are talking about things happened, of the phenomenon that happened on nanoscale. And because this is a nanoscale, so it mainly has applications in the following small scale operators. For example, the micro applications, the transport across membrane and oil explorations, and also cheap cooling. And so you can see that in different fields, it all shows great applications. And because sleep loss is very important, there are already many studies about this topic, especially for water on graphene-related surface, because it shows very interesting phenomenon. And for example, in this paper published on Nature, about six years ago, people found a sleep loss of about 60 nanometers when water flowing through graphite nanochannels. And later, when water flowing through graphene nanochannels, the sleep loss reduced to 16 nanometers. And later, a French group, and they measured the dependence of the sleep loss on the radius of the criminal tubes, and they found a very nice decrease when the radius of the tubes increases. And also, not surprisingly, 10 years ago, people measured the sleep loss of water on graphene surface, and with an average sleep loss of about a few nanometers. Although there are many studies about this topic, but surprisingly, we found that there is, that is the dependence of sleep loss for water on the types of supporting substrates and thickness of covenants layers. And this is very important, because we know that in practical applications, these graphene layers, or fuel layer graphene, must be supported by certain substrates. And usually, we are interested in fuel layer graphene because it shows exotic behaviors, and so this is why we are interested in this topic. And to this end, we start our own experiment. So the method we use is a very traditional one. It's called the colloid-prote FM, and the figure A is the schematic of the system. So we have an FM tip, and there is a micro sphere attached on the tip, and the whole system is immersed in the liquid, and then there is a substrate, and there is a fuel layer graphene. So we approach the sphere to the surface and the retraction, and we record the force and the velocity, and then we can get figure B. And the figure B is the y-axis is the force exerted on the tip, and the axis is the separation between the micro sphere and the surface. This can be calculated by integrating the velocity. This is raw data. And further on, we do one more step. We convert it to the axis, and the axis remains separation, but the y-axis will be the ratio between the velocity, the vertical velocity, and the force exerted on the FM tip. And then surprisingly, so what we find will be that if you do the linear fitting for approaching the, for the approaching stage, and then do, you do extrapolate to the x-axis, and this one, this intersection will be the sequence. This is straightforward because the y-axis is to the left of the equation, and when this is equal to zero, so because LS must be positive, and is what we are interested in, so H must be negative, and this is the intersection. And details can be found in these references. And before we show the marrying results, we want to elaborate more about the characterizations because doing experiments is very important to make sure the system you are marrying is what we are thinking. So this is figure A is the surface of the macro sphere. So we are using the inverse scan AFM, and this is a typical surface morphology of the sphere. So we can see that within the scale of few hundred nanometers, the surface of the sphere is very smooth. It's about less than 1 nanometers. And also, the two supporting substrates we are using is silica and OTS, and so we measure the contact angle and make sure that the y being hydrophilic and y being hydrophobic, and this also the values agree with existing reports. And the most important surface is the fuel air graphene and to this end, so we measured, as shown in figure C, the morphology as well as the chemistry of the surface with optical and AFM and RMA. And with all this together, it shows that within the range of 20 by 20 micrometers, the RMS roughness is very small, and also we found no detectable effects. So now coming to our marrying results. So figure A shows the slip length versus the approaching velocity for different substrates. That means, so the graphene in different layers either on silica or OTS. So despite all the details, we find that the slip length is, in fact, this is, they are all vertical lengths, so that means the horizontal length, sorry, so that means the slip length is independent of the velocities. And also we measure the slip length for bare silica and bare OTS, and so our marrying results are in good agreement with existing reports. And now come into one of our most important results, as shown in figure B here. So in figure B, the X axis is the number of layers, all we can call it thickness of graphene, and the Y axis will be the slip length. And here the blue one is for those system where the OTS is covered by filial graphene, and for the red one is the silica covered by filial graphene. So first of all, what we see is that for OTS, the slip length gradually decreases and somehow saturates with a number of layers, larger than three, and also for the silica, the slip length increases and saturates to the same value. And this value, we measure it, and we found that this slip length is the same, and also it agrees with existing data reported for slip lengths of water on HOPG, but here we are making sure, we are sure that the surface is very smooth and is of a single crystalline. So by noticing this, sorry, and the dependence of slip lengths on the thickness of graphene layers, and here we term it as translucency, and maybe one, several papers already come into a mind, come to your mind, which is the whiting translucency. We will talk about it later. And the first question will be that is this translucency caused by the changes in roughness. So in order to answer this question, so we took very careful and intensive measurement on the roughness of the surface, and as here we show some of the key measurement, and from figure A to figure C, it shows the morphology of the graphene with one layer to layer or three layer supported on silica. First, just by eyes, because we are using the same legend. So just by eyes, you will see that there are negligible qualitative difference. And if you do the quantitative estimations and showing figure D here, we will notice that the X axis is a thickness of layers. And the Y axis are RMS or peak to valley values. They all of them, they does not change with the number of layers. And this is in direct contrast to the slip loss. And also, if you do the Fourier transformations of either of these morphologies, you will find that the peak period is the main period is larger than five micrometers. With the corresponding magnitude less than one nanometers and existing theoretical studies already shows that such small roughness will not introduce errors in the environment. So as a conclusion, so we can say that the slip loss translucency is not caused by the change in roughness. So, since roughness is not caused, so what are the possible reasons. And to this end, we noticed that about 10 years ago there are many studies about wetting translucency for water on filiography, and that was founded due to the addition energy. And to this end, we follow their concept. If we can assume that the interaction between liquid and solid additives and the friction follow the Green Cooper relation, then we can relate the slip loss to the addition energy. And also, if we further assume that the density of water along the z direction follow the Boltzmann distributions, then we can calculate this quantity here. And here, this figure shows our results, calculation results. So here, again, the x-axis is thickness, y-axis is the slip loss. And the black data is from our experiment, and the red data is from our theory. And I want to emphasize here that we only have one fitting parameter here, which is kappa, and one and only one fitting parameters. So, we can see that this good agreement shows that the translucency of slip loss shares the same mechanisms as that of contact angle, which is due to the translucency of addition energy, which is very good because we got a reasonable explanation for our observations. But then another question is that, is slip loss decided by the contact angle only? Because here it seems that it shares the same mechanism for the translucency. And to this end, we notice that when you consider the slip loss, its dependence on temperature, you find something very interesting. So figure A is a theoretical study shows that for hydrophobic surface, the slip loss decreases as the temperature increases, and for hydrophilic, it increases. However, later, another theoretical studies found just the opposite directions, where slip loss increases for hydrophobic surface. And what is more interesting is that later, recently, a paper published another scale already, also shows that sometimes if you're considering also this is a theoretical paper, considering the slip loss for water on hydrophilic and hydrophobic surface, they can show the same trend. So what all this study shows that is there is the temperature dependence of slip loss is controversial and without any explanations. And to understand this, first of all, we also carried our own environment, and this is our results. So we found that for water slip on two layer graphene supported by Celica, the slip loss always decreases, doesn't matter of the velocities. And, but meanwhile, we also noticed that existing literature reported that the contact angle is independent of temperature when the temperature is below in the boiling point, which is the case for our systems. So that means the dependence of slip loss and contact angle on temperature should share different mechanisms. So in other words, the sequence does not depend on the contact angle only. And in order to understand this, so because cyclones and temperatures are independent, so we used energy barrier. So, and here, we are very familiar with this theory proposed by Lideric Bacay, and he was able to link this slip loss to the energy barrier for the water molecule sliding on the solid surface. And this is very nice one. And the further we notice, if you use the theory from my notion, which is half a decade ago, you can further relate the energy barrier to the following quantum quantities. And with all these tedious calculations, in the end, you will be able to derive suction equation. This equation shows that the slip loss is proportional to this ratio, which is a pre coefficient. And what is the most important is that all these five quantities in this part, they can be calculated separately and independently. And with all this, in this figure, we compare our experimental value, the black dots, to our theoretical predictions with only one fitting parameter, which is the pre-coefficient kappa t here. And we can see that somehow we get a reasonable agreement. However, this is good, but also one problem, because here we only found a negative correlation between slip loss and temperature, and I already show that existing theoretical studies show that sometimes it can be positive. So could the positive relation be observed in experiments? And because the indication shows that this somehow has something to do with the wetting properties, so we further measure the dependence of the slip loss for water on FBTS. And this is a hydrophobic surface with a contact angle about 115. And here, if we first found the same decreased tendency for the slip loss versus temperature, but interestingly that if we are using solutions in that water, the solution we use is sodium chloride. And then at smaller concentrations, this is negative, but as a larger concentration, this becomes positive. So this is interesting. And this can be further clearly seen if you plot in this way. The axis is inverse temperature, and the one axis is a logarithm, a non-aliase. And in this case, first of all, you see a very clear trend where they follow linearly dependent, and this is a very strong indication shows that this slip is a read process. Because this is a read process, so we can use the very famous read process theory, and for this theory, generally it tells a very simple thing for our system that is to say for liquid molecule moving along a solid surface, the molecule needs to cross an edge barrier, as shown in this schematic. And with the trivial derivations, you will be able to link the slip loss to these quantities. So in this batch of quantities, so this all has terms that are the partition functions under different conditions, and these four terms that are the system properties. What is important is these two energy barriers, and this E0 will be this barrier, that is the barrier the molecules need to cross over when it slides on the solid surface at 0K. And this E0L is the energy barrier for a single molecule, liquid molecule moving inside bulk liquid at 0K. And with this, we can further rate it in this form, and which seems to be very simple, to be simpler. And with these equations, we can do fitting, right? And so this is the figure we already show, and if we use this equation and fitting to this data set shows a very nice inner dependence, and we can get the value of the difference between the two energy barriers. And with similar derivations, it will be trivial to show that for the friction coefficient between liquid and solid, it is also a rate process, and it follows these relations. And then this is our experimental data, and by doing the fitting, you can extract the values for E0, which is the energy barrier for the water molecule sliding across the solid surface. And with these two, and then you can calculate E0, and E0 is already an tablet value, because it's for bulk liquid. And what we found that is, if we compared with the tablet values and the relative arrow for the estimated E0 is less than 20%. And somehow this is a good indication to show the validity of our theoretical explanations. And so all this just tells one simple thing, which is the monotocity of the dependence for the sequence on temperature is determined just by the difference between two energy barriers. And to understand this theory on molecular scale to provide an atomic picture, we also perform four atomic MD simulations, as shown here. So here you have the silica surface, you have FDTIs, and these are the solutions, so the chloride. And by doing the conducting with an MIT ensemble, we can get the equilibrium configurations, and you can do the statistics. And by doing very nice statistics for the energy barriers, with concentrations being zero, being 0.1 molar and being one molar. And you can estimate the DERTE also from MD simulations and as shown in Figure D here. So in Figure D, the x-axis is a concentration of the solution, so y-axis is the energy barrier is zero. So this is the experiment, and this is directly calculated from our MD simulations. Somehow we got a reasonable agreement between the experiment and MD simulations. We're also relating that the atomic picture we have in mind, which is inspired by the theory you should host. So we can get an overall picture about the dependence of the influence on temperature. So the key, the variable we have is the concentration of the solution. So when the solution of the concentration increases, so first the concentration of dissolved ions on the solid surface increases, and this will increase the energy barrier is zero. And meanwhile, when the concentration increases in our range studies, the viscosity almost remains constant, and this indicates that this E0L almost remains constant. And then that is to say, for this difference, this term is a constant, and this term is increasing as a concentration increases. So the sign of this difference then will gradually changes from positive to negative. And then with the theory we show above this dependence, the monotony will change from minus to positive, a very simple understanding. So with all this, I would like to give a summary of our work. So first, our results provide the first set of experimental reference values for the sequence of water on supported field layer graphene. And second, we found transparency for the sequence of water on supported graphene for the system above. And also, we show that the controversy with the dependence of sleep loss of water on temperature can be understood by the rate process where the difference between two energy barrier is a key. And the last is that the key quantity is zero, because this is a kinetic process and the energy barrier is very important. And this one can be estimated by measuring the dependence of sleep loss on temperature. And in the future, we are interested in the three, four in three aspects. The first is the quantitative relation between energy barrier and concentration of the solution. And second is to apply the method to other systems, all for other, for various solace and solutions. Last, but not least, the two establishing connections to fields such as civil diversity and nano-phoretics. And also, for example, recently, a very, very interesting quantum friction between water and field layer graphene. And with all this, I would like to thank you all for listening and thanks for your patience and welcome any questions. Thank you very much, Ming. Thanks for questions. Please, Mingmar, there are some online questions. Can you see the chatting room? Yes, it's a very fundamental question, so it's a physical meaning. I think you actually explained quite clearly what the slip length was in the very first slide. So I guess whoever it was was distracted at that time. Any further questions? We seem to have no questions, no further questions. I think we thank Professor Ma again and thank you.