The Sauerbrey model describes the linear relationship between frequency shifts and mass changes for thin films. For a detailed description of the Sauerbrey model, see here.
The simple answer is: as soon as D is larger than zero. Theoretically, as soon as there is any viscoelastic behavior in the adsorbed layers, the mass will not couple 100% to the oscillatory motion of the crystal, and the true mass will be under-estimated if only the Sauerbrey equation is being used. Putting it the opposite way: as soon as you are able to obtain a stable fit to your data set, it is never wrong to model it… Practically though, it is obvious that small values of D still hold for as a rigid film, especially if the D/f ratio still is very small (for instance, 1:30 or above).
Viscoelastic behavior of polymers and other materials are often simulated using elastic springs and viscous dashpots. The Maxwell model is the simplest model for a more liquid-like viscoelastic soft matter material and it consists of a spring and dashpot in series. The Voigt model is the simplest model for a more rigid viscoelastic soft matter material and it consists of a spring and dashpot in parallel.
A detailed description, including the equations, of the implemented models can be found in "M.V.Voinova, M.Rodahl, M.Jonson and B.Kasemo "Viscoelastic Acoustic Response of Layered Polymer Films at Fluid-Solid Interfaces: Continuum Mechanics Approach", Physica Scripta 59 (1999) 391-396
Yes, you can model either the density OR the viscosity of a Newtonian fluid. It is not possible through modeling to separate the density and viscosity of a Newtonian fluid. You need to know either one or the other. The frequency and dissipation response going from vacuum to such a fluid depends only on the density x viscosity product. So you need to fix one of the parameters in order to get the other.
It is not possible by modeling to separate viscosity and density of a Newtonian fluid. The frequency and dissipation response going from vacuum to such a fluid depends only on the viscosity*density product. You need one of the parameters in order to get the other.
Under the tab 'Parameters' you can choose to fit the parameters, or to use them as fixed values in order to help determining other fitted parameters. By double-clicking on each parameter, you move them between the two alternative categories.
If you want to model the thickness of a layer, it is recommended to have the density of that layer fixed in the model, since the two parameters are connected to each other (high density/small thickness is equal to low density/large thickness, for a certain amount of mass) and the software will have a problem to find one single solution.
Normally, the parameters "thickness", "viscosity" and "shear modulus" are chosen as parameters to fit. The density is then assumed to be the same during the whole measurement. The input values for the parameters to fit are set as an interval, with 'maximum guess' and 'minimum guess' values inserted in the table.
The values for the fixed parameters need to be rather accurate - the easiest way to find out how exact they need to be, is to play around with the values and observe the fluctuations of the model output.
The extended model has been introduced since there was a demand from many customers to be able to test the frequency dependence of the viscoelastic parameters. In the extended model, possible frequency dependence has been introduced but only in the simplest way, i.e. a linear dependence. So strictly speaking, this model is only valid when the film you are modeling has linear frequency dependence from the viscoelastic parameters. The more the frequency dependence deviates from a linear relationship, the less the extended viscoelastic model will apply for that particular system.
Checking “L1” when modeling a two-layer system (or any multilayer), means that QTools will treat the film as one homogeneous film, finding an average value for each parameter (viscosity, shear modulus and density) for the whole film. The modeled thickness will be the total thickness for the whole film. Checking both “L1” and “L2” means that QTools will try to find a solution with two regions having different properties, with “L1” being the innermost layer. The more distinct the interface is (i.e. the larger the difference is between the two layers), the better is the chance to find a good fit. A good way to investigate a two-layer system is to build it sequentially during an on-going measurement, so that you can model the first layer (first part of the measurement) separately, using only “L1”. When this is done, set all modeled “L1” parameters as “fixed parameters”, then include “L2” and model the properties of the second layer. This approach assumes that the properties of the first layer do not change when introducing the second one.
The thickness of a L1 modeling would be the same as the total thickness of a L1+L2 modeling, if the viscoelastic properties of the two layers are close to each other. In case of e.g. a rigid layer and a soft layer and different densities the L1 modeling will find viscoelastic output parameters that are an average between the two layers. In such case the total thickness might be slightly different from the one obtained using a two layer model.
You cannot model them all at one time. The approach to model each layer separately would be to group the “L1” and “L2” as one layer – forming a new “L1” layer – and treat layer 3 as the new “L2”, while disregarding the averaged viscoelastic results for the “L1” layer (same idea as describe above, under “How do I work with L1 and L2 modeling?”). The approach requires that the build-up of the multilayer is done sequentially within one measurement data set).
Yes, you can: measure the non-coated crystal first, so that you get a QCM-D baseline before the treatment of the sensor crystal; then, after the external treatment you measure the processes on the treated sensor crystal, as usual. Remember to use the same medium above the sensor crystal in both measurements to be able to compare data. With QSoft401, you then merge the two files by using the “Stitch files” function and model the data in QTools the standard way. With QSoft 301 it is a bit more work: you need to un-offset the data in the first measurement file, which means when you open the QSoft file, you do not accept the “File transcriber” suggestions to offsets and scaling; then copy the baseline from the first measurement and insert it in the beginning of the second, un-offseted, measurement file, to get the right baseline reference in QTools.
Generally experiments are made on a bare sensor and then something is adsorbed to it during the measurement. In these cases you can say that if D is larger than zero and if the overtones are spreading, the film is soft and requires viscoelastic modeling.
In some cases a film is coated on the sensor before the measurement and then something is adsorbed onto that during the measurement. If the initial film is rigid and is not affected (for example degraded or swollen) during the measurement, the statement above is also valid.
But, if you coat the sensor with a film before the measurement which is not rigid and/or which is affected during the measurement (degradation, swelling etc) then the statement above is not valid. The reason that we cannot judge if the film is soft or not from just looking at Δf and ΔD is that f and D are not shown as absolute values but only in relation to the base line (therefore called Δf and ΔD). And since the baseline is the sensor at the beginning of the measurement, and if the properties of this change, we are moving the baseline and then relations will change. It is a bit tricky to explain.
But if we can add the baseline of the bare sensor before coating, to the beginning of the degradation measurement then this would be a solid ground to stand on and in relation to this we can judge if the film is soft or not based on the above statement.
So how do we do this?
Measure the sensor in the instrument with the same buffer as you will use in your experiment. Then coat the sensor and do your measurement. The first measurement could thereafter be stitched to the beginning of the second measurement, so that they are in the same file. Now the measurement will show the bare sensor in fluid, thereafter there will be a jump in f and maybe in D to the coated sensor in fluid and thereafter the degradation.
Note that this is not a standard procedure! There might be some stress in the sensor from mounting so the absolute f and D can differ from time to time. One should try mounting the sensor several times to see if the difference in absolute f and D varies a lot by looking at the absolute values of f and D in the data sheet in QTools. Hopefully it doesn’t differ too much and then you can use this procedure to get the baseline in order to model.
The QCM-D will give the hydrated mass, i.e. the mass of the molecules adsorbed to the surface and the solvent that is trapped in between. There is no means to extract the mass of only the molecules with the QCM-D technique. However, the dissipation may give a hint on the hydration of the formed layer. For example if you have a really, really high dissipation with spreading of overtones you may conclude that the molecules have arranged themselves in an extended and sparse fashion which allows plenty of solvent to be trapped. If the dissipation is low and the spreading of overtones is not so significant the molecules have probably arranged themselves in a more dense and ordered fashion not allowing so much solvent to be trapped. In this case the QCM-D mass will be a closer estimate to the mass of the molecules than the QCM-D mass for the soft layer.
Yes your thickness will vary depending on L1 density value, since they are correlated. You need to state in your experimental section “an estimated L1 density of YYY kg/m3 was used”. You can change the L1 density, the fit should be equally good, but your thickness will change. If you know that your film is 50% hydrated, you can calculate the L1 density: 0.5 x density of the dry layer + 0.5 x density of the bulk solution. But this is something that is almost impossible to know. For hydrated biomaterials the density is close to, however slightly larger than, that for water.
If it is a solid, the elasticity is very high, and the viscosity is very low. Think of the energy losses when sound is transmitted through a material: a good material for sound transfer has low viscosity, and so has quartz almost no viscosity but high elasticity. Maple syrup has high viscosity which means it is not a good material for sound transfer - it dissipates a lot of energy.
There may be several reasons why it is difficult to find a good fit: - The D-factor is very low (<1), especially in comparison to the frequency shifts. The modeling requires that there is viscoelastic behavior of the adsorbed film. If there is not, the modeling is not applicable and the Sauerbrey function is enough to extract mass and thickness data. Viscoelastic data is not possible to extract, simply because the film is too rigid. - You are trying to model both density and thickness at the same time. When modeling a viscoelastic film, it is generally not possible to separate between these two parameters in much the same way as it is not possible to separate density and viscosity for a Newtonian fluid. You will usually get an equally good fit if you at the same time increase the density by 10% and lower the thickness by 10% (so that the product stays the same).
- The adsorbed films do not fulfill the assumptions made in QTools. A good fit requires that the adsorbed films have a homogeneous density, viscosity and/or shear modulus. If you for instance have fitted your data using a fixed density, it could be worth considering if this parameter is changing during different parts of the measurement. - Your minimum and maximum guesses for the initial search grid are not optimal. Changing the extreme values will give a new set of coordinates, even within the grid, and new solutions to the fitting may be found. - The data set does not include all coating/measurement steps. QTools assumes that the beginning of the measurement reflects the non-coated rigid sensor surface material. If you for instance coat the crystal ex situ with a film and then insert it in the chamber for measurements, you need to have taken a short baseline on the non-coated surface before the coating step as reference, and then combine the two data sets before using QTools. - The fundamental tone is included in the fitting. We do not recommend using the fundamental frequency (5 MHz) when doing liquid measurements since this resonance is much more susceptible to mounting mediated stresses which are aggravated by liquid loading. If the first harmonic is unchecked in the modeling, you will get a better fit.
If you zoom in your QSoft data, they will appear the same way. It is the averaging function in QSoft that does this: if every single data point would be plotted in QSoft, the software would be too slow, i.e. too much processor time would be spent on updating the plots, which would slow down the acquisition speed drastically. So, instead of plotting all points, only one average of them is plotted for each x pixel.
Some of the Windows settings for data table cell color do not show cell contents properly in QTools. The settings should be accessible under Control Panel/ Display/Appearance. Select any of the other "Color Schemes" and you should be able to see the data in the cells.
A reason for unexpected values of modeled viscosity or other parameters when there is nothing adsorbed onto the sensor surface, could be that the measured f and D values are very close to zero. If so, the model may have a problem finding good solutions when fitting. This typically happens in the beginning of an adsorption process, or more precisely, right before anything has been adsorbed. Because of this, the default modeling settings start the fit at the end of the measurement and proceed backwards (this is indicated by the quick-button illustrated by an arrow in the Modeling Center).
The electrical signal strength (voltage) that reaches the instrument decreases as the overtone number goes up. Dampening will decrease the signal strength and when it is low enough, QSoft will lose the overtone.
You cannot really predict Chi-square, since it will be different for different data sets. It is not divided by the number of data points in the data set, which means that if a data set is twice the size as another data set, it will also give twice as large Chi-square for an equally good fit.
Please select your country to view contact information to local sales offices and distributors. Inquiries from countries not listed shall be sent to Q-Sense Headquarters in Sweden.
Biolin Scientific Box 70379 SE-107 24 Stockholm SwedenVisiting address: Klarabergsviadukten 70, House D, floor 8 SE-111 64 Stockholm, Sweden Phone: +46 31 769 7690 Fax: +46 31 69 80 40 E-mail: firstname.lastname@example.orgSupport: email@example.com
Biolin ScientificKlarabergsviadukten 70, House D, floor 8SE-111 64 StockholmSweden
Phone: +46 31 769 7690Fax: +46 31 69 80 40
Nordic sales: firstname.lastname@example.org
International sales: email@example.com
Q-Sense support email: firstname.lastname@example.org
Biolin Scientific, Inc. 514 Progress DriveSuite GLinthicum, MD 21090 USA
Phone: +1 (877) 773-6730Fax: +1 (866) 415-8164
General inquiries: email@example.com
Sales department: firstname.lastname@example.org
Support department: email@example.com
Biolin Scientific AB, Shanghai Representative OfficeRm. 1212-1213, 1101 Pu Dong Road(S)Shanghai 200120China Contacts:Vanilla ChenAaron Li
Phone: +86 21 61659769 / +86 13816317221Fax: +86 21 61659770Email: firstname.lastname@example.org
Supertec SAPiedras No 19301140 Buenos AiresArgentina
Tel: +54 (11)4307-2141Fax: +54(11)4307-8612
Contact Luis Sanchez: email@example.com
Info e-mail: firstname.lastname@example.org
ATA Scientific Pty LtdPO Box 2172Taren PointNSW 2229Australia
Phone: +61 (0)2 9543 0477Fax: +61 (0)2 9543 9459
Information request: email@example.comWebsite: http://www.atascientific.com.au
Emphor FZCOPO BOX - 61232Dubai, UAEwww.emphorlas.biz
Contact:Mr. Harisree Nambiarharisree.firstname.lastname@example.orgTel: +971 4 8830233Fax: +971 4 8830133
LOT-QuantumDesign Belgium and Netherlands
Mr. Stephane Struyvecontact: email@example.comDirect: +32 2 308 43 24
LOT-QuantumDesign GmbHMeenseweg 1428900 IeperBelgium
dpUNION Instrumentacao Analitica e Cientifica Ltda. Rua Monsenhor Basilio Pereira, 50 – Jabaquara ZIP: 04343-090 SAO PAULO - SP - BRAZIL
Phone: 55 11 5079-8411 FAX: 55 11 5079-8411
Sales: firstname.lastname@example.org Support: email@example.com Website: www.dpunion.com.br
CHROMSPEC spol. s r.o.Lhotecka 594252 10 Mnisek Pod BrdyCzech Republicwww.chromspec.cz
Tel: +420-547 246 683-4Fax: +420-547 246 685
Information request: firstname.lastname@example.org
LOT-QuantumDesign FranceZac de la Bonde15 rue du Buisson aux Fraises, Bat CFR-91300 MassyFrance
Contact: Mr Nicholas TcherbakE-mail: email@example.comPhone: +33 1 6919 4949 Fax: +33 1 6919 4930
LOT-QuantumDesign GmbHIm Tiefen See 58DE - 64293 DarmstadtGermany
Dr. Jürgen SchlütterInformation request: E-mail: firstname.lastname@example.orgPhone: +49 (0) 6151/8806-44 Fax: +49 (0) 6151/8966-67
Antisel116 Michalakopoulou Street115 27, Athens, Greece
T: + 30 210 779 5980 F: + 30 210 771 6932
Auro-Science Consulting Kft.Postal address: 1300 Budapest Pf. 234.
Visiting address: 1031 Budapest Drotos u. 1.www.auroscience.hu
Phone: +36-1-2421390Fax: +36-1-2421391
Specialise Instruments Marketing Company305, Kailas Industrial Complex, A-Wing, 3rd FloorBuilding No.2, Parksite Vikhroli(W)Mumbai - 400079 INDIA
Mr. Kamal Sharma, Manager Technical Support:email@example.comWebsite: www.simc.co.in
Particular Sciences Ltd2 Birch HouseRosemount Business ParkBallycoolin Road, Dublin 11 Ireland
Phone: +353 01 820 53 95Fax: +353 01 822 88 13Mr. Gerry PowerMr. Sean Quilty
New-Road Agencies Ltd11 Haamal St.,Afek Business Park,Rosh-Haayin 48092Israelwww.newroad.co.il
Office phone: 972-3-9028787Cell phone: 972-54-2255769Fax: 972-3-9028788
Nordtest s.r.l.Via Liverno 11I-15069 Serravalle Scrivia (AL)Italywww.nordtest.it
Tel. +39-0143-62422Fax +39-0143-65517
Dr. Maurizio Bruni : firstname.lastname@example.org
Dr. Nadia Decarolis: email@example.com
Meiwafosis Co., Ltd.1-14-2 Shinjuku, Shinjuku-ku.Tokyo 160-0022 JAPAN
Telephone: +813-5379-00519-0051Fax: + 813-5379-0811
Contact or requests:Jun Sakaino: firstname.lastname@example.org
Kulim Hi-Tech Sdn BhdA-3-03, Sri HijauanNo. 1, Jalan Bukit Hijau 26/24Section 2640400 Shah Alam, SelangorTelephone : 603 - 5192 5110 Fax : 603 - 5192 0501
Information request: email@example.com / firstname.lastname@example.orgWebsite: http://kulim-kht.blogspot.com
LOT-QuantumDesign PolandSztygarska 12/341 500 Chorzów Poland
Contact: Dr. Agnieszka Kowalczyk E-mail: email@example.comDirect: +48 515 166 893
ParalabTv. do Calvário, 65 Giesta 4420-392 VALBOM GDMPortugal
Phone: 22 466 43 20Fax: 22 466 43 21
SEPADIN SRLStr. Badea Cartan nr 67, Bl 37A, et 3, ap 12 Sector 2, Bucuresti, RomaniaCod postal 020662Phone:+40 - 21211 0795+40 - 21211 9691 Fax: 0040-21-210.39.50www.sepadin.ro
Information request: firstname.lastname@example.org
VALTEX-NT JSC5 Stary Zykovskiy proezd, Suite IV,Moscow 125167,Russiawww.valtex.ru
Tel. +7(495)960-28-37Fax. +7(499)152-23-56
Information request: email@example.com
Naizak Global EngineeringP.O.Box # 57792, Riyadh # 11584Saudi Arabia
Syed Asif IqbalEmail: firstname.lastname@example.org T: +966 1 4161161:Ext. 405 F: +966 1 4633326
Analytical Technologies Pte Ltd50 Ubi Avenue 3#05-08 FrontierSingapore 408866
Tel: +65 6746 8068 Fax: +65 6746 0661
Web site: www.analytical-online.com
CHROMSPEC spol. s r.o.Lhotecka 594252 10 Mnisek Pod BrdyCzech RepublicInformation request: email@example.com
Perovo 30SI-1241 KamnikSlovenia
Telephone: +386 1 830-80-40Fax: +386 1 830-80-70, 830-80-63
E-mail address: firstname.lastname@example.org
Web site: www.mediline.si/eng/index.html
Hucom Systems Inc.6F 1005-7 Yeongtong-dong Yeongtong-gu Suwon-si Gyeonggi-do 443-814 Koreawww.hucom.kr
Phone: 82 31 204 5030Fax: 82 31 204 5090
Information request: email@example.com
Lasing S.AJulián Camarillo 26ES-28037 Madrid, SpainPhone: +34 91 377 5006Fax: +34 91 407 3624Email: firstname.lastname@example.orgWebsite: www.lasing.com
LOT-QuantumDesign SuisseMoulin-du-ChocCH - 1122 Romanel-sur-MorgesSwitzerland
Contact: Mr. Julien DumouchelPhone. +41 21 869 90 33Fax. +41 21 869 9308
Information request: email@example.com
Advantage Scientific Inc.11F06, No. 268, Liancheng Rd Junghe City, TaipeiTaiwan 235www.asi-team.com/intro.htm
Tel: +886 2 82273456Fax: +886 2 82273000Mobile: 86 13764363467
Information request: firstname.lastname@example.org
Terralab Lab. Malz. San. ve Tic. A.S.Cetin Emec Blv. 1328. Sokak No: 14/9A.Övecler Ankara, 06460 TURKEY
Tel: +90 312 472 73 96 / +90 216 327 52 70Fax: +90 312 472 73 98 / +90 216 327 57 02
Contact personsBülent Atamer: email@example.com
Bahadir Bayrak: firstname.lastname@example.org
Biolin ScientificG153000 Manchester Business ParkAviator WayManchesterM22 5TG, England
Direct: +44 (0)7733 893 902 email@example.com
Hängpilsgatan 7SE-426 77 Västra Frölunda Sweden Phone: +46 31 769 7690 Fax: +46 31 69 80 40 E-mail: firstname.lastname@example.org Support: email@example.com