Webinar: The Importance of Moisture in Pharmaceuticals and Food Materials by Surface Energy

Thank you Zen, for your introduction. And welcome everybody to today's webinar. The topic today is the importance of moisture in pharmaceuticals and food materials, utilizing surface area and activation energy of diffusion studies. So in the presentation today, I'm going to go over an introduction of two techniques, IGC SCA and dbs. And then I will go on to talk about the methods we carry, experimental methods we carried out, and some results. So first I'm going to talk about IGC sca. So this is inverse gas chromatography surface energy analyzer. So the IGC system was first developed in the 1950s and it uses vapor molecules to analyze material. Since then, surface Measurement system has improved this model and introduced surface energy analyzer. So it was specifically designed to determine the surface energy and heterogeneity of samples. And from this we can obtain different parameters such as adsorption, isotherms, heat absorption, glass transition temperature, solubility parameters, and a few others as well. So comparing to our traditional analytical gas chromatography, this is where we have unknown mixture of gas vapours in a known column. And by interacting with the column, we can separate out the vapours and obtain different retention time for each for each vapour injected. However, in the case of inverse gas chromatography, the technique that we're looking at, we have our column packed of our sample of interest and we're injecting known molecules. And from the interaction with our molecules and our sample, we obtain different retention times. From there we can analyze the peaks and obtain different physical chemical properties. So when we're looking at analyzing a material, there's a few things that we can possibly answer by using different techniques. So what does material look like? For this we can use spanning electron microscopy and other microscopy methods. And we can also maybe understand what the material is made out of using techniques such as xrd, EDS and eels. And on this side, we're looking at atoms in the center and in the bulk of the material, which are surrounded by other atoms. And on the other side, if we want to understand factors that affect how a material interacts, this is where IGC can come in. And in this technique we can understand the interaction of other materials with the sample. We're able to quantify the ability of the surface to react. We're focusing more on the IGCSE side group in this SCA technique in this presentation. So on the right hand side is an IGC SCA system. As you can see, there's a door in the middle and two drawers that open up so Each drawer occupied by six different reservoirs. And this is where you put your gas vapors and your solvents that you wish to use for analysis. Typically we have some non polar and polar probes we introduce into the system. And this is very useful, especially when analyzing surface energy. We need a mixture of both to obtain dispersive surface and specific surface energy. Each system has a carrier gas of either helium or nitrogen. And in the middle we have our columns. So we have a two column oven system. So our packed column goes in position one and another one in position two. And it's surrounded by a column oven. And the column oven can go from 20 degrees to 150 degrees. In the system you can also measure background humidity. So in this case one of the probes will have to be water. You can introduce humidity onto a surface and analyze its properties based on this change in surface. We use a flame ionization detector to detect all our solvents. And this is particularly useful in obtaining very accurate readings of organic vapours. Of course we have safety features such as hydrogen leak and organic vapour leak detectors.

Also.

In our IGC SCA system we can measure a different range and variety of samples. So here at the bottom you can see a few examples. We have carbon fibre, cotton, hair granules, powder and so on. So it's very diverse and we can actually analyze a lot of different types of samples. The system has two softwares. One is a control software. So this is directly linked to, to our IGC SCA system. And this is where we start to make our experiments and program them into our system. We also have an analysis software and this is where you analyze your peaks so you obtain retention times where you automatically calculate different properties and, and as you can see from a few of the tabs at the top, there's a few different things that we can do with the sca. So we can measure surface energy, isotherms and bet surface area. So we can do a different range of different types of analysis. And it's important to know that there's, it's an automatic analysis so it doesn't require much input from yourselves. And we can also generate reports also for each different method and each different measurement. So before starting a experiment first what we need to do is pack a column of interest. And then we need to select different probes. So we can select with regards to maybe a surface energy experiment, non polar probes which are useful for the dispersive interactions and some polar probes for the specific interactions. We can then choose how to inject them. So we can inject them at very small concentrations, at infinite dilution and also at larger concentrations. And from the interaction of the sample we will obtain different retention times. And from this we can analyze these peaks and obtain different physical chemical properties. So to pack a column is fairly simple with respect to our standard GC column. Our columns which I use is cyanized column and effectively what you will do first is add some cylonized glass wall and put into the column your sample and again plug the top with some more glass wall. This just ensures that none of our sample goes into the system during the experiment. We have different column sizes. We have 2, 3, 4 millimeter columns and these are for maybe the 2 and 3 is usually for powders and granules. And 4 millimeter columns are for fibres and fibres and things like paper that you wish to kind of chop up and put into your column. The 10 millimeter column requires a specific oven size, but a 10 millimeter column is useful for carrying out experiments with whole samples. So let's say a whole tablet or a block of wood. So it's quite useful that something that you don't wish to break up further, we also have a YouTube clip showing you how to pack a column. It's fairly straightforward if you're interested in that also. So there's a few benefits of using igcsea. First is the two column position oven design. So effectively what you can do is we can run the column sequentially and automatically. We can have up to 10 methods onto our software, so we can run them automatically. There's no need for any outgassing facilities. So in our system we can do in situ column conditioning. So in this case we don't need any third party outsourcing facilities. Next to our system, column packing is relatively straightforward. And because we're injecting vapor, we're injecting vapor molecules. Our injectable amounts are very precise and we can inject a wide range of different concentrations. And our injections are all automatic. And with regards to our results, we have excellent reproducibility, especially in the case of surface energy. So one of the things that we can do with the ICSCA is to analyze our BT specific surface area. So in this case, what we have as an example is our reference CRM aluminium sample. And here we have 500 milligrams. And if you look here we have our reported value and our value obtained from igcse. So in this case we've injected octane molecules into the system to calculate the isotherm and bet. So this is the corresponding isotherm. It is in the bet range and this is our corresponding bet plot. And as you can see that there's a good agreement between the reported value and our value obtained by the igcsea. So I'm going to briefly introduce the DBS system. This is dynamic vapor absorption. So to analyze materials there's a few ways different types of probes you can use to analyze. We can use energy as a probe. So in this case an example would be spectroscopy such as light spectroscopy or x rays and lasers. This is useful to obtain any analytical and structural information. We can also use heat as a probe and for this example is a calorimetry. In our case with regards to the GBS we use molecules as a probe. So this is more looking at sorption techniques and more thermodynamical, chemical and structural information can be obtained using this method. So really what we do is we introduce a particular vapour molecules into our material and they can either absorb on the surface or on can be absorbed into the bulk. So this process is the process of sorption. We can also measure desorption. So when these molecules leave our sample. So with regards to molecules being adsorbed, we're looking at molecules on the surface. These gives rise to physiosorption and chemo sorption interactions. With regards to molecules being absorbed into the bulk, this is more bulk sorption and we can understand how these molecules have interacted in the bulk and in the lattice structure. So with adsorption we have two types of interactions. We have pithy sorption and these are weak interactions. And the molecules are not chemically bound to the surface. And this can give rise to reversible absorption. And there's a few properties that can be obtained from this and these are structural properties, for example surface area and pore size. We can also understand chemical interactions e.g. hydrophobicity and surface heterogeneity. We can also understand thermodynamic properties such as heat absorption and free energy. We also can have chem absorption. So in this case the probe molecules usually have stronger interactions and they're more covalently bound to the surface. So this can as a result cause reversible or irreversible absorption. And a few properties attributed to this is active surface area or titrate acid based sites. So next we're looking at more bulk sorption. So this is the absorption properties and this in this case molecules tend to penetrate into the surface and this penetration is often diffusion limited. So this can correlate to a reversible or an irreversible absorption. And again we have a few properties that we can obtain from this kind of bulk absorption. We have structural properties so we can have a look at the glass transition temperature, crystallization and eliquescence. We can also understand total sorption capacity and solubility of T parameters. And because it is a diffusion limited interaction, we have can also understand the kinetics, so diffusion coefficients and looking at maybe drying kinetics. So we can also have absorption into the lattice structure. So in this case we can it's possible to have a look at solvate formation. This can be irreversible and or reversible. So the associated properties with regards to this is the stoichiometric hydrate or solvate properties and understanding the channels and the solvate channels in the system. And again we can also have some kinetic properties measured as well. So here we have an example of what's happening in the dvs. So a DVS is a gravimetric technique. It's continuously measuring the mass of your sample. So in the system we have a balance. We have a reference plan and we have a sample. So our reference plan stays empty and our sample pan has the sample that we're wishing to measure. And what we do is we introduce some molecules, in this case water molecules, into the system. And as a result this is what we obtain. So we have a few parameters. We have temperature, time and weight. So here in the purple is our experimental method. So here we are increasing let's say each step by 10% relative humidity. And what we before going on to the next step we have to reach a level of equilibrium. So once this is reached we'll go on to the next step and so on. So this in this case it's looking at the sorption properties and the reverse phase we can also look at the desorption properties when the molecules are leaving the system. So in this case we've mirrored our absorption and decreasing in the same manner. Our red line is our experimental data. So at the beginning we may have a drying period where we want to actually dry our sample. So no, we have no kind of adsorbent on the surface which may was maybe a few differences in our results. So it's best to dry the system initially. And again we have our sorption profile and our desorption profile. So all this time our DBS is measuring the weight of the sample at each time. So the DBS can be compared to a more static method, a jar method. And in this Case, what you would need to do is have a separate jar for each different relative humidity that you'd like to measure. However, in our system we just have one instrument which can handle all different levels of relative humidity. In the jar method, we have very slow equilibrium to be achieved. This is only using Brownian motion. However, in our system, we can have a gas flow of up to 200ml per minute, and with this we can obtain fast equilibrium. So as a result of this, our experimental time can be considerably shortened. So with regards to the static jar method, to obtain a single data point, it can take weeks or even months. In our case, the whole experiment can take less than a day. There's also differences in the amount of mass that we can use. So, so the jar method we need up to from 1 to 100 grams of the sample. But in our case we have sensitive balances, so we can use very little sample from 1 to 10 milligrams of sample. Also with the jar method, you need to remove the sample each time and weighing it each time to obtain data points. And of course in this case you have a risk of contamination or sample loss. And in this case it can take a very long time just to get one single data point. However, in our case, the sample is measured constantly and range throughout the experiment with no contamination or loss of sample. For this reason, we can have very short experimental times. With the DAR method, we are only able to obtain information about the absorption curve and it's not possible to actually measure any desorption characteristics. However, in the dvs, we can measure absorption and desorption and obtain more information, especially with regards to the hysteresis gap between the isotherms and this between the absorption curves. And we can understand maybe the kinetics and morphology changes much more better with this system. So this is a schematic of one of our DBS instruments. You have a sample pan and a reference pan, and these will be these two here. We also have both pans attached to a micro balance. We have two mass flow controllers. So we have air, dry air and nitrogen. And we also have our probe mass flow controller also. So in this case it's a water reservoir. So these can be flowed through our system. So what you do is we take these, take our sample and place it into the sample pan. And from here we can actually attach a preheater that would be underneath this space here. So we can attach a preheater and we can preheat our sample prior to any experiments. So in the case study, we're looking at how moisture can affect the properties of some materials and what can be the effect of too little or too much moisture in a complex organic material. So in the case of some food samples we have, for example potato crisps and introducing humidity can lose their crispiness and it kind of decreases the the glass transition temperature of the crisp. With regards to crystalline pharmaceuticals, hydrates can become very dehydrated and thermodynamic stability is compromised at low relative humidities. Similarly with proteins at low rh, they can actually denature and lose their biological activity. With regards to freeze dried powders, they can transform into liquids and maybe form amorphous solids and deliquescents forming solutions. With regards to free flowing powders, when you introduce humidity, what can happen is it can turn into kind of rigid solid cakes and the amorphous solid can crystallize and have high moisture content. With dry powders such as aerosols bringing increased humidity, they tend not to disperse and particles would adhere to each other, making them quite poor in their behavior. So now I'm going to have a look at our case study. So in this case study we are looking at using IGC to determine the surface area and DVS for some sorption measurements. So moisture has a large impact on the mechanical, physical and chemical properties of materials. The drying process can be found in key production stages such as crystallization, wet milling, granulation, and this can improve stability and prevent deterioration of drug compounds. It can be useful to prepare a granule for tablets and formulation and is very useful to understand if the product will be good for easy transportation. Introducing humidity can have physical chemical stability effects and it may convert some samples into amorphous samples or they may become chemically labile. As mentioned before, it can also affect flowability because water can actually cause condensation inside the bulk of the material and forms inter particle liquid bridges affecting the flow behavior of some powders. So in this case study we're looking at starch samples. Starch samples we're looking at are starch samples that have been gelatinized. So in this case we are looking at partially gelatinized samples and completely modified starch samples, native start samples and pre gelatinized samples. We want to understand their effectability humidity with regards to the surface area as well as the diffusion kinetics. So for the IGC SCA method, experimental method, we carried out the experiment at 30 degrees and keeping the concentration in the range of the BET range. And we want to compare 0% relative humidity and 50% relative humidity. So in this case just comparing A few properties of BET surfacer with the traditional volumetric and the IGC SCA and dbs, the DVS is quite similar to the nitrogen absorption technique in the range of its capability to calculate BET surface area. So we have from about 1 meter squared per gram to over 100 meters squared per gram. In the case of IGCSEA, we can actually obtain BET surface area of very small surface area materials, so below 1 meter squared per gram. So this is very useful for products like drug products or fibers or hair expenses. The difference between our two instruments compared to the nitrogen absorption technique is the experimental temperatures. Especially so with nitrogen technique, we need to be under vacuum and also very low temperatures. However, with regards to the DVs and IGC SCA, we can actually have it at ambient temperatures or even high temperatures also. And in case of the DVs, if need be, we can also introduce vacuum to the system. For the nitrogen absorption technique, of course you need nitrogen. However, the GVS and IGCSEA we can use other vapours, a range of different types of vapours. So like I mentioned, the nitrogen absorption technique carries out BET surface area analysis for quite higher surface area material. And if you wish to analyze materials below 0.5, you need to use Krypton. In this case, we might find that because of these kind of extreme conditions of vacuum and low temperatures, it may completely dry out pharmaceuticals or it may even break fragile crystals. However, in our IDC and DBS experiments, we can actually carry out our experiments at ambient room temperatures and we can use the various different probes. So you can use any N alkanes, even cyclohexane, as long as the isotherm conforms to a type 2 and type 4 isotherm, then we can analyze and obtain the BT surface areas. So with regards to our DBS experiments, we carried out experiments with regards to watersorption and in this case we use the DVS resolution and we carried out experiments at 25, 50 and 70 degrees Celsius using 200 milliliter per minute of dry air. We also dried our samples for 10 hours and we used relative humidity steps from 0 from 0% to 95%, 10% step increments. So I'm just going to show you the results for our BET surface area. So in this case we have our partially gelatinized starch sample and at 0% relative humidity. And the probe we've used is ethanol at 30 degrees Celsius. So we obtained a BT value of 2 meters squared per gram. So, so then we introduce humidity in this case 50% humidity, water starts to compete for. We have water starting to compete for the sites which are blocked. And in this case, what's interesting is that as humidity increases, the measured bet surface area also increases. So at 0% we have 2 meters squared per gram, and at 50% we have 5 meters squared per gram. And this trend can be observed for all our other different types of starch materials. Increasing humidity results in an increase of surface area. So the table kind of summarizes the different surface area of the material. And we can see that the samples increased subs area of increase in blended humidity. This can be attributed to the swelling of the starch. So also what's quite interesting here is that in the table, the ncs, which hasn't been gelatinized, and the, sorry, the modified ncs, which has been completely gelatinized, has a very high surface area and also high surface area at both 0% and 50% RH. And the fully treated modified NCS is high even at 0%. And after exposure to water as a result of swelling, the surface area increases even more. And this could be attributed to. This could be attributed to moisture acting as a plasticizer, which causes a reduction of the TG in these samples. So in this table here, we are looking at the activation energy and the diffusion coefficients and the relative humidity and temperature increases the diffusion coefficient. So because we have now an increased surface area with regards to our relative humidity, we now have an increased diffusion coefficient. And this could be followed by the swelling of the porous structure from a more firmer structure. So at high temperatures, there is sufficient thermal energy to overcome the activation energy barrier. So now the atoms and molecules are now very free to move in and out of the system. This can actually result into a lower uptake of moisture. So this is one of the DBS plots obtained. So in this case, we're looking at a mass plot of starch at different temperatures. We have 25, 50 and 70 degrees. And it's showing the percentage change of mass of the water molecules soaked in the powder solid over time. So what you can see here is actually at 25 degrees, we have a higher uptake compared to higher temperatures, 50 degrees and 70 degrees. And this is because, like we saw before, the diffusion coefficients are relatively higher at higher temperatures. So atoms are freely moving in and out of the system so that actually the sample can't retain as much moisture and water. And this is why we have relatively low uptake of water in these samples. So here we have three different plots. So we have different temperatures, we have all four samples 25 degrees Celsius, 50 degrees Celsius and 70 degrees Celsius. And we can see that actually the graph shapes actually change with regards to increasing of temperature. And like I mentioned before, before going to the next step, we have to reach a certain amount of equilibrium here. So in this case equilibrium takes a longer time to reach at 25 degrees. But when you start increasing the temperature at 50 degrees and 70 degrees, this equilibrium is reached much faster and the kinetics are much faster at these two temperatures. So just to conclude, the BT surface area was used measured used IGCSEA and this was carried at a 0% ability humidity at 50% relative humidity. And we saw there's an increase of surface area with increased humidity and this could be attributed to swelling of the sample. With regards to the dbs, we carried out watersorption method for different temperatures and we could understand the diffusion kinetics much better. And because of these diffusion kinetics we can understand why there was a lower uptake of moisture of these samples. So, thank you for listening to my presentations and if you have any questions, please do let me know.

Thank you very much Sabiya for that informative presentation. We are now open for questions, so if you have questions, please use the chat box or unmute your microphone. So I have here one from Millie. Can the samples be remeasured? How much consistence or disparities? If the sample has been measured again or multiple times, do I need to worry about the irreversible adsorption that damaged my samples?

Well, with regards to the samples that do swell to obtain consistent results, it would be better to have a fresh sample each time because once you run your humidity experiments, you've already introduced humidity onto your surface and at this point we've already made changes to the surface. So in this case it's probably best to use a fresh sample if you want to test reproducibility. And in our systems we have excellent reproducibility lower than 1%.

Just to follow up Sebiya, how much sample do we need for IGC or DBS experiment?

So with the IGCSE it's dependent on the BT surface area of your samples. So if you have a relatively high surface area material, such as activated carbon, you'd want to use very small amounts of material, so about 10 milligrams. However, if you have samples with very small BT surface area, you want to use quite high masses, so around 100 milligrams. And for the DBS we also use around 10 milligrams. However, if we have maybe a sample which is more hydrophobic, we may want to increase the mass. And also if we have a relatively higher uptake and equilibrium is not reached very well, then we might want to lower the mass. So it is sample dependent, but it's around between 10 and 100 milligrams.

All right, thank you. I hope we answered that. Millie, another question from Bruce. Pharma stability temperatures are typically 25 degrees to 40 degrees. Can you comment on the change of a devious isotherm on excipients over this temperature range? If I generate an isotherm at 25 degrees Celsius, is it likely representative at 40 degrees.

Changes? Oh, sorry, one second.

If I may clarify on that. Sabiha, I think.

Yes sir, carry on. Majid.

Bruce is talking about glass transition temperature and the effect of humidity. Of course the humidity changes and vice versa, as you increase the humidity, glass transition temperature changes. So you'd have to take into account the glass transition and the changes that might occur as a result of change in temperature and humidity. In fact, if you do the experiment, the same humidity experiment at different temperatures, you can plot a map of the stability of the material where changes of both temperature and humidity can predict the stability of your material.

Okay, thank you. I hope that answered Bruce. Okay, another question from Ilham. Thank you for your presentation. According to the last slide, the temperature was more important factor than the type of material since the graphs were almost identical in each temperature category. So what about the RH percentage? Does higher percentage, does higher RH cause any effect like the saturation and affecting the sorption isotherm? What about the rate of introducing RH to the material?

So yes, that's correct. So with, in these, in this case for the starch samples, when you increase the temperature we have the different graphs and with these, with the same, with all four, we have kind of similar plots. So in this case when you increase, when at each stage of relative humidity equilibrium is reached much quicker. So the kinetics are much, much faster in this case. And so if you do maybe change the different steps you will probably obtain kind of, if you go from, in this case we're going from steps of increments of 10% so you'd get a plot like this. But if you were to jump from 10 to 30 and then 50, you would expect the same kind of trend but at different stages. And you can also have different experiments such as ramping experiments. So you can go directly from 0% relative humidity to say 50% relative humidity in the space of Half an hour. So there's also different types of relative humidity experiments you can do with your samples.

Okay, I have here. Thanks for that. Sabiha. I have here another question from Millie. I have a little difficulty to understand the mechanism behind the increased surface energy. At high rh, would the swelling take more cavity of the sample leading to reduced surface energy?

The experiments we mentioned here are not to do with surface energy, they're to do with surface area. And in this case when we, when we introduce humidity, what we have is because the water interacts with the bulk of the material, causing it to swell, we have an increase of relative humidity. However, in some samples this is not necessarily the case. We can have samples when you introduce relative humidity. If you're doing, let's say ethanol molecule, they're competing with the sites for the water. So really what would happen? You'd have a decrease in surface area and that's more common. However, in this case, our water molecules actually interacted with the bulk of our material causing it to swell and that's. We have a higher beauty surface area.

Okay, a follow up question from Elham. Have you considered any RH above the 50%?

So in the experiments we've done, we've done from 0% to 95% RH. So we have done above 50% in this case.

Okay, I hope that answers Ilham, another question from Raksit. Hi Sabiya, thanks for your presentation. Why different kind of starches not showing any difference of moisture uptake event at different temperature? Does it mean they all behave the same? In your previous slide, Starch 1500 has shown some difference compared to other starches. Can you please explain?

I can. I just add that there are differences. If Sebiye, if you could go to the previous slide where you have. Yeah. The one after. Yeah. So as you can see at different temperatures you. For starch 1500 you see differences in uptake. As you go higher in temperature, the uptake decreases and that's expected as at higher temperatures you have higher molecular mobility. So there is more molecules moving in and out of the bulk of the material. And the net effect is that you'll have a lower uptake at higher temperatures. And this you see with the number of different materials, the same effect can be observed with the other samples. Yeah, you're right. The effect is less and the uptakes are more similar at different temperatures. And that's because the material basically hardens after exposure to humidity. These are the more fully gelatinized samples. And basically with the initial gelatinization, the Effect of moisture is taking place and the material has already hardened, and that affects the uptake of the material as well.

All right. Is that answer the question, Rakshit? Okay, probably, yes. Are there any other questions?

Yes, I believe, yes. And thank you for that answer. Majid and Sabya, really nice presentation. But if you go back to one slide that you've shown and further back, if I can ask one more question, follow up question, if I can, one more slide back where you see.

Yeah.

So what, what you analyze and what you derive when you expose the same sample at a different humidity is that the diffusion coefficient of starch is different, different than any other sample.

Well, what we see is here at different relative humidities, we see the differences in the diffusion rate for different samples. So as degree of gelatinization increases, then you see basically similar effects in the diffusion kinetics. And as I said, as the temperature increases, the molecular mobility increases, and then you see diffusion, increased diffusion in and out of the sample. So, yes, obviously you see the differences at higher humidities and also at higher temperatures.

And that's what I wanted to, I expected in the last slide because of diffusion coefficient differences at a different temperature, why that was not materialized when you have the last slide there, think like, you know, effect of temperature shows almost overlapping phenomena. So that was the confusion. But I'll look into much more detail.

And thank you. Yeah, I mean, we can discuss that further offline if you're interested. We have, we have more results, but it's just at the end of the day, it's just the way the material. We have some video images of the material and work is still ongoing to show, to investigate the effects. But actually it shows the material is almost caking, and that is part of the reason.

Okay, well, thank you. We will definitely, I'll definitely look forward to talk to you offline.

Okay, thank you. Thank you.

Okay, thank you, Rakshit. Are there any other questions from our participants?

Hello, this is Bruce again.

Yes, Bruce, please.

And the next slide, go down or down one. So that was actually the question I was asking, and I'm sorry I missed it during the presentation, but it's the impact of temperature on the isothermic. So you run it here at three different temperatures. And my question was in the 25C to 40C range, which is typical in pharmaceutical industry. How much of an impact on the isotherm are we going to see? So it wasn't necessarily about the glass transition, but the change in the mass of water that's absorbed as a function of temperature.

Well, as a function of temperature, it all depends on the nature of the material. But as you say, for pharmaceutical materials, you would mainly work at room temperature.

On stability, we usually measure the isothermic room temperature, 25C. But then if the samples are put up at 30C or 40C for stability testing, then the isotherm would presumably change. But how much of a change is it a significant change? I suppose that's a kind of loaded question, is a significant change.

But.

Yes, it would be. I mean, are you talking about 0% relative humidity and increasing just the temperature or at different humidities?

Yeah, the full isotherm, just as you pictured. Just as we see here at the full isotherm.

Yeah, yeah. Well then you should see a significant effect. And in fact there is a method. What you see here is a step type method where the humidity has increased step by step. Now if you do a ramping method, you'll see the changes. You can, for visualization purposes, you see the effects more clearly. And again again with the ramping rate as well. If you increase the ramping rate, you'll see the effects even better more clearly. But you might not be able to measure the exact RH as accurately as if you do it with a slower ramping rate. So it's quite interesting we have application notes on that which demonstrate to you how the effect of the ramping rate and also the differences between the ramping experiment and the step experiment.

Or could I say you could do an ISO RH experiment so then just pick 50% RH and do 25, 30, 40C and get a fair idea of the expected change.

Exactly. Yeah. That's another way of looking at it. Exactly. That's absolutely right.

Okay, that's good to know.

The only thing is it depends on the type of the instrument as well. We have DBS intrinsic, which ranges in temperature from 20 to 40 degrees. And of course you can do that, you can keep the relative humidity constant and change the temperature. But with the other systems where there is an incubator that's a bit more difficult to do because as you increase the temperature, the balance stability changes and the data becomes noisy. So. So we wouldn't be able to do that experiment with the devious resolution, for example, or devious adventure. But DVS intrinsic would be ideal for that purpose.

I see, I see. We have a resolution. So yeah, you're requiring the whole incubator to increase in temperature and the water bottle to.

That's right, yeah. That wouldn't be really possible because that affects the temperature stability of the balance.

I see. Okay.

If I could ask a question on this curve as well, something I don't quite understand about it. The red curve, the 25 degrees curve is doing what I might expect, which every time you change the humidity, a sudden increase in absorption and then a slow increase to where it's near equilibrium and then you change it again. So you have these scallop shapes going up and then the reverse going down. But in Both the other two curves, in both the other two curves, at 50 and at 70, we have, at least at the start it seems to make sense. There's like a rather rapid climb. But there are a number of places where it seems to. You seem to have allowed it to plateau for some reason. I'm not sure why. So I'm wondering why those plateaus are in there. And I'm even more wondering why those plateaus seem to be going down in a number even very early at like at maybe 500 or 600, one of the, or 700 one of the early parts in the 70 degree curve is clearly dropping. And later on near the summits of both the 50 and the 70, they are clearly dropping. And what is going on there?

That's a good question. I have the same problem or issue trying to understand that myself.

So please, a very good observation, thank you. That's something we were discussing earlier with Sabia. As you increase the temperature, it's due to the evaporative cooling effect. The temperature of the water changes and that affects the basically the concentration generation and then the uptake obviously is affected. So then first to begin with you see an increase and then at each particular step, especially if you go to 70 degrees, this, this effect is more observable, you see a dip in the generation and also if you plot the generation, in fact you see a dip and at the same time you see a dip in the mass uptake as well. So this is due to evaporative cooling, which you can't really do much about it. But my colleagues are working on a heated reservoir at the moment and watch the space. Soon you'll see a heated reservoir which is meant to take this effect away. And this will be a basically pioneer technique as well.

Well, thank you, that is really great explanation, Majid, and thank you for that and thank you for sharing.

Question.

I have one follow up question onto that. Where do you see evaporative cooling more? And where do you see the pronounced.

Effect.

Which, which are the ranges or which, which humidity cycle where you start to see the evaporative cooling effect?

Yeah, it's all to do with the. The reservoir and the head space. We have tried different. We have taken different measures to reduce that. One is by increasing the size of the bottle and then increasing the volume of the liquid in the reservoir. But as you say, there is a particular sort of relative humidity which is towards the higher end of the relative humidity generation. You see more of this effect. And of course, at higher temperatures, at above 50 degrees, again, this effect is more. So we've had when you do the experiments, some of our customers typically do 85 degrees, 85% relative humidity. And that effect is more pronounced at 85 degrees. And like I say, at about 50% relative humidity, you see more of this. And gradually the higher you go there, the more of this slope you see. But again, that's something we could discuss later and I can show you more data and maybe I can share with you a presentation later that shows the generation, how the generation is affected, and you see that effect more pronounced there where the generation is plotted.

Thank you so much.

And this is Bruce again. I'd appreciate seeing that presentation or receiving it by email, whatever.

Okay, I'll get your email addresses from Zen and then forward you the presentation. I'll have to check with my colleague whether at this stage it's not company confidential because we haven't released the data yet. But surely I can send you some slides, some information.

Great, thank you.

Thank you very much. Are there any other questions from our participants? All right, I think that's about it. That concludes our webinar today. If you have any questions later on, you can always email us at scienceurfacemeasurementsystems.com or visit our website at ww.surface measurementsystems.com thank you very much for your time today. Thank you so much to Sabia and to Majit and we hope we will see you, I mean, speak with you again in the following webinars. Thank you. Thank you for your time.

Thank you, everybody.

Bye.

Have a good day.

Thank you. Bye. Bye. Foreign.