Dynamic Contact Angle Analyzer Tutorial
Contents
1. detailed instruction in the hardware set up manual Sample Compartment Set up By setting up the DCA it can be seen that there might be one two or three diamond shape loops in the DCA based upon the DCA model For DCA 312 which has one loop the loop will be the place for putting the sample holder and sample For DCA 315 there are two loops The one on the left is for the sample holder and sample and the one on the right is for counterweighs There are three loops in DCA 322 named as loop A loop B and loop C start from left to right Loop C is always used for counterweighs and loops A and B are for samples When the DCA is set up its sample compartment will look like the following picture Picture shows the in line stirrup and sample and counterweights Page 2 Thermo Cahn DCA Tutorial Balance Counterweighing In the balance of the DCA 315 and DCA 322 there is a counter weight side which is the loop at the far right hand side loop C The counter weight side is used to counter balance the sample s weight so that the maximum weighing sensitivity and weighing range is obtained Please refer to the instruction manual for further detailed information about the balance specifications For DCA 322 it is necessary to note that there are two sample loops loop A and loop B Before performing the counterweighing please make sure that the active method selects the correct loop of operation Itis also worthy to mention that the r2. file e Perform the experiments Important The calibration of the DCA system should be performed AFTER the method file has been loaded or created It is also recommended to ensure that the weight readings are correct that you check them by using the DCA Record or DCA Weight function prior to running the experiments Page 4 Thermo Cahn DCA Tutorial Making a DCA Run Contact Angle When collecting the contact angle data from the Wilhelmy equation Fx g y x PR x cos0 it can be seen that cos0 can only be obtained if the other parameters are known or measured Therefore in the method it s necessary to enter g y and dimension of the solid probe correctly Under this sampling technique both advancing and receding contact angles are measured Typically three different methods are utilized The first method performs experiments with one cycle multiple experimental steps and one loop a set of advancing and receding steps The second method has one cycle with multiple loops The third method consists of multiple cycles and loops The recommended steps for these three methods are listed as follows pamend Mace Lace agp OM Loop default method Multiple Loops Loops Recommended Set Speed Same as the Single different cycles which Experimental Tare Balance Cycle and Single Loop can be a combination Steps Detect ZDOI method but with more of the previous two Advance than one methods Dwell optional advance recede loops
3. is also necessary to know the density of the liquid Interfacial Tension Similar to the Surface Tension technique both the Wilhelmy plate and Du Nouy ring can be used as the solid probe to measure the interfacial tension between two liquids a light liquid on top of a heavier liquid Itis required that the solid probe pass only once between the interface of the two liquids typically from the heavier to the lighter liquid The experimental steps however are more complicated than those of a surface tension measurement We recommend you use two beakers for the experiment and use the following experimental procedure x Wait for Operator Press the OK button once Immerse the solid probe totally inside Ready the operator finishes the the light liquid beaker 1 by using the step s in the right column manual stage height adjustment 4 Wait for Operator Press the OK button once Remove the solid probe have it Ready the operator finishes the cleaned and reinstalled Remove step s in the right column beaker 1 and replace with beaker 2 containing the heavier liquid underneath the solid probe al Advance make sure that the solid probe breaks the surface of the heavier liquid so that the Wilhelmy plate is partially or the Du Nouy ring is completely immersed 7 Wait for Operator Press the OK button once Pour the light liquid slowly into beaker Ready the operator finishes the 2 Make sure there is enough light step s in the r
4. testing At the mean time it may be necessary to expose a very short piece of single fiber sample about 2 to 4 mm in order to gain rigidity During the data collection it s recommended to use a slow stage moving speed Powder Sample Wettability of powder samples are often needed for various industries In order to quantitatively obtain the wettability the contact angle experiments should be performed However as you know already DCA is utilizing the Wilhelmy plate technique which requires a plate Therefore for powder samples sample preparation needs to be performed prior to the experiments Generally speaking there are three different ways to measure the wettability of powder samples 1 Press the powder into pellet and then treat it as a disc or cut it into rectangle shape and treat it as a plate However the pressing procedure can easily introduce unknown factor to the surface properties of the powder sample Therefore this technique is not commonly practiced or recommended 2 Using double side tape or a rectangle shape substrate coated with spray glue coat the powder onto its surface It will then be treated as a plate However during the preparation it s necessary to make sure that the tape or substrate is totally and uniformly coated with powder and powder particles have to be small enough so that there is no tape or substrate exposed This technique has been commonly practice and proved to be very easy and fairly
5. 0eececceseeeeceees 19 SURFACE ENERGY POLAR OR LEWIS ACID BASE METHOD csseeccccccesceccestsceceesesecceees 20 LIQUID SURFACE TENSION COMPONENTS cccccccccccssesssssceccccccssssssssceccscssssenessesccssssseuneuesesceeseeees 20 WACKING RATE euro E saulo ni ava E EE E EE A unlssseoutecceetace E EE A 20 POWDER OPTION WASHBURN METHOD ccccccccccssesssesccccccccssesssssceccscseessseueesccssssssuueueesseesseees 21 ACCESSORIES FOR DCA iissiscccsscccccesssssccosscccccssscsscsessccoccossccsecoscccucsssctonsessc ccdusnccsssosscccusssscses 21 CME ACCESSORY sintas redes OE ae ida TS Sd DO ceu dia been ide LAS ana DO gd ADS SS LS ca SID Sa ad 21 POWDER ACCESSORY a RE Ela csdsdahcovennlcscaeseched Edo cvcesdelahdepewsteded Ses aaa ds Ualeewadsdehcscanetecwbevsehesost 22 TEMPERATURE MODULE oof 355 205 503 Gseds ence Dus ond bc cultists Set Osteen ius JOE tel dv G8 Av cde cutive e dient 22 TROUBLESHOOTING ivcssssccscccccccccccsccessccsccescscscesecssecessccsecesesscs cesses cused cs cucesdcesesesescesoascdsccessccses 23 COMMUNICATION ices Siceuazs ses a hehe a A Medenadessieciedgbe deca O bas Lad Su a Dt Sc UOL SSL pa 23 Page 1 Thermo Cahn DCA Tutorial STAGE KEPT ON MOVING AT DETECT ZDOI STEP erre eereererereereaa aa aaaaada 23 BALANCE SHOWS ZERO WEIGHT READING ALL THE TIME cssseccccsssecccceccececceeececceeececeeners 24 BALANCE SHOWS 1 5 OR 5 TIMES OF THE ACTUAL WEIGHT 0ssscccceseececceceecccceseccc
6. Bensen burner with blue flame For Platinum plate burning it to dull red after it s cleaned by chemicals is a good sign of good cleaning For glass plate however it s necessary to run it in and out of the flame very quickly for at least 6 times on each side It s also important to visually check the cleaned glass plate to make sure that the surface is not wrapped or bent and the edges of the plate is not dull or deformed With correctly cleaned plate the advancing data line and the receding data line should superimpose and the curve of a surface tension run should be looked like this Page 7 Thermo Cahn DCA Tutorial Read Weight Time until Weight Stable st 31 6578 mN m For the surface tension measurement performed with a Du Nouy ring the data should be looked like the following plot It is necessary to mention that there are two different standards for picking the point for calculating surface tension ASTM and DIN The ASTM standards will use the break point to calculate the surface tension while the DIN standards will use the max pull point to calculate It s our recommendation that the DIN standards should be used st 34 2804 mN m Page 8 Thermo Cahn DCA Tutorial Even though both the Wilhelmy plate and Du Nouy ring can be used for many kinds of liquids we recommend you use the Du Nouy ring method with highly viscose liquids viscosity of 1000 cP or higher However when the Du Nouy ring method is used it
7. Dynamic Contact Angle Analyzer Tutorial Dun Chen Ph D Thermo Cahn Instruments 5225 Verona Road Madison WI 53711 608 327 6779 608 273 6827 fax Dun Chen Thermo com Copyright statement The information in this publication is provided for reference and is believed to be accurate and complete Thermo Cahn Instruments is not liable for errors in this publication or for incidental or consequential damage in connection with the furnishing or use of the information in this publication Thermo Cahn Instruments makes no warranty regarding the material in this publication including but not limited to any implied warranty of fitness or merchantability for any particular use Thermo Cahn Instruments reserves the right to make changes to this publication and to the products described in it without notice All specifications and information concerning products are subject to change without notice Reference in this publication to information or products protected by copyright or patent does not convey any license under the rights of Thermo Cahn Instruments or others Thermo Cahn Instruments assumes no liability arising from infringements of patents or any other rights of third parties This User s Manual is copyrighted 2003 by Thermo Cahn Instruments All rights reserved The information contained in this manual is proprietary and may not be reproduced stored transmitted or transferred in whole or in part in any form without the prior and
8. Recede before the Return to Return to Zero Position Zero Position step The first method is sufficient for most applications The later two are useful for many other applications such as the testing of a sample s cleanliness or the re orientation of the molecules on the sample s surfaces In addition the operator can create special experimental conditions for certain applications Following is an exemplary contact angle run of a piece of polymer against distilled water by using the default single cycle single loop method It can be seen that the advancing and receding traces have a negative slope in them This is caused by the increase of the buoyancy force as the solid enters the liquid deeper The boxes on the advancing and receding parts of the curves show the ranges of data that are used for linear regression to perform line fit and extrapolation to eliminate buoyancy force The final results for advancing and receding are shown in the upper left corner in the order of cos0 0 and regression factor It is necessary to mention that the range of data that are used for calculation can be modified in the software Please refer to the software for operation procedure Page 5 Thermo Cahn DCA Tutorial ee e e eee CA ONE DCD Auto Analysis 1996 350 Advancing 0 383 C 0 9570 Receding 8 54 2 8961 26 35 0 9638 300 250 200 ononmomn 150 es 100 50 Position mm Surface
9. Tension To measure the surface tension of liquid there are two different types of solid probes that can be used One is a Wilhelmy Plate made of glass or platinum Another is the Du Nouy ring made of platinum iridium When using a Wilhelmy plate the Wilhelmy equation Fx g y x PR x cos is used again However it s necessary to use standard solid probes which will provide known contact angle values This standard solid probes can be clean glass plate or platinum plate which will give a 0 contact angle or cos0 1 because of the very high surface energies of these two materials when they are clean This turns the Wilhelmy equation into Fxg yx PR Or y Fxg PR Another commonly used surface tension measurement method is using a Du Nouy ring In this method a Platinum Iridium ring is immersed into the testing liquid and pulled out of the surface The force needed to bring the ring out of the liquid is directly related to the surface tension value of the liquid The equation used to calculate the surface tension of the liquid is expressed as follow Y Y xcF Page 6 Thermo Cahn DCA Tutorial Where y is the raw surface tension reading from the measurement and cF is the correction factor which is used to correct for the amount of liquid attached to the bottom of the ring during the pulling process of the experiment Lae 40 04534 1 679 C D R r cF 0 7250 Where C is the mean circumference of the ring D is the d
10. aped solid samples the most common way to obtain its volume is the immersion method This means that the sample is immersed into a liquid and the volume of the solid is measured by either knowing the difference of the volume change of the liquid before and after the immersion or the buoyancy force occurred on the solid after it s immersed in the liquid By following the above logic the solid s volume can be calculated as V Buoyancy Force Liquid s density During the solid volume measurement it s necessary to use a known density liquid and use very thin wire or small volume sample holder to hold the sample Otherwise the experimental steps will be steps that ensure the solid is fully immersed into the liquid The following graph shows a typical run of the solid volume Page 12 Thermo Cahn DCA Tutorial Solid Volume Sample Unknown Operator Unknown Fri Mar 24 12 53 20 2000 0 5 10 15 20 Position mm Solid Volume dcd Auto Analysis Wed Aug 02 08 52 04 2000 Read Weight Time until Weight Stable sv 1 1842 ml Liquid Density The theory of measuring the liquid density is to obtain the buoyancy force of a known volume solid inside the testing liquid By knowing the buoyancy force and the volume of the solid the density can be calculated as Liquid density Buoyancy Force Volume of solid By using the Thermo Cahn supplied liquid density kit which the volume of the solid is known or can be measu
11. atio of the weighs on three loops of DCA 322 loop A loop B loop C is 1 5 1 This means that 100 mg weigh on loops A or loop C creates the same amount of torque as that of 500 mg weigh on loop B By using the DCA Record function of the DCA software the counterweighing procedure is described as follows 1 Make sure that the correct loop is selected in the current loaded method Put on stir ups stir up and in line stir up onto the balance With NO weights on the stir ups tare the balance Start the Record function on the program to monitor the weight as the function of time Put on sample and necessary holder onto the sample loop loop A or B Put on the stirrup on the counter weight side loop C Put on counter weight to make weight reading close to zero Remove sample holder and or sample as needed N SA Re tao NOTE It is necessary to make sure that the maximum sample capacity of the balance is not exceeded during this procedure Following table shows the specifications for the balances in each DCA model DCA 322 DCA 315 A loop B loop Maximum Balance Capacity 1 5g 3 5g 100 g Dynamic Weighing Range 150 mg 750 mg 10g Balance Sensitivity 0 1 ug lug lug Software Operation WinDCA is a Windows based software program used to control the DCA system collect data and perform data analysis It is designed in such a way that the DCA experiments are controlled through experimental steps T
12. cceseececceners 24 BALANCE PERFORMANCE TEST ccccccccccccssessceccccccccssessscsceccccseesuusecscsccsssseeeueusesccscssseuneuseesessseaes 24 VALUES OBTAINED ARE OFF FROM EXPECTED Page 2 Thermo Cahn DCA Tutorial Introduction Understanding the characteristics of a liquid solid interface is important to virtually every manufacturing industry from bio materials and pharmaceuticals to paints and textiles Knowledge of how sheet metal is wetted by different paints for example is as important to the automotive industry as is knowledge of the hydrophicity or water absorption of orally ingested drugs to the pharmaceutical industry Over the past 100 years a number of techniques have been developed to measure these characteristics Methods for determining the wettability of solid surfaces the tensiometry of liquids and the absorption of liquids into solids have given researchers the information they need to more fully understand and control their production process Various techniques have been developed over the last few decades to obtain the surface properties of the liquid and solid These methods include sessile drop goniometer tilted plate Wilhelmy plate capillary rise maximum bubble pressure drop weight ring and pendent drop The parameters that are obtained by those techniques are contact angle between a solid and liquid surface tension of a liquid interfacial tension between two immiscible liquids and surface energy of so
13. ensity of the heavier liquid d is the density of the lighter liquid R is the radius of the ring and r is the radius of the wire of ring When using a Wilhelmy plate two different methods can be used One method has a simple advance and recede cycle where the surface tension value is taken from the receding step Another more accurate and recommended method has a Read Weight Time until Weight Stable step at the ZDOI Zero Depth Of Immersion position which gives the surface tension value A simple advance and recede loop method is used with the Du Nouy ring The following table provides an example of the method steps po WiitheImy Plate DuNouyRing Simpe Recommended default method ___ Experimental Set Speed Set Speed Set Speed Steps Tare Balance Tare Balance Tare Balance Detect ZDOI Detect ZDOI Detect ZDOI Advance Advance Advance Dwell optional Dwell optional Dwell optional Recede Recede to ZDOI Return to Zero Position Return to Zero Read Weight Time until Weight Position Stable Return to Zero Position E The solid probe should be advanced into the liquid deep enough so that the Wilhelmy plate is partially or the Du Nouy ring is completely immersed When using the plate method for measuring the surface tension it s necessary to be sure that the solid probes are cleaned well This can be done by using an oxidizing flame to clean the surface of solid probes for example a propane torch or
14. express written permission of Thermo Cahn Instruments 2003 Thermo Cahn Instruments Part No 099 013022 xx Printed January 2003 Thermo Cahn Instruments 5225 Verona Road Madison WI 53711 Telephone 608 327 6777 Fax 608 273 6827 Service 800 244 6635 Windows and Windows NT are registered trademarks of the Microsoft Corporation Table of Content COPYRIGHT STATEMENE vsdiscscscscccscscdescccsec ccecseseseccscteccessdicsescsediccesssieboccasbestessd cscatetevecsestessss I INT RODU CTTON besisscecccisccccscccassstsssccosscccocsteccassosscscncosesdacdoseccsseosesdcecesscsaccosdsdaeSesecsceeosecdaecesscsecsos 1 HARDWARE iesssdscssscctsesccasdicsecccscoakcssdassccsedsosccasosssecsassosecdsdacssccesdasevevocsoacceseseseevedcosecdseasevevovossoseasos 2 SAMPLE COMPARTMENT SET UP ccccccccccccsssssssscsccccccesssssssesscsscsssssussescceessssssussesccsesseeuauessesceeeesees 2 BALANCE COUNTERWEIGHING a a A a a i s ni 3 SOFTWARE OPERATION scccssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssseees 3 GENERAL NOTE dt E a a EAA t 4 CALBRA TION aa a eh dens a a a a a NG 4 MAKINGA DCA RUN isstesccssccscscscecessusccaccneecaccestecasbeateciccbcaccdeccocedscceoesescaceuscscetersesicdecasedbeadeesecoce 5 CONTACT ANGLE EENAA E AE AE A EE E A 5 SURFACE DENSON ana a a ch chi E a a SUE A a bs E SEO ERE 6 INTERFACIAL TENSION Asuna sete outs aa aa a a alte beans a Meee sala die bebe NS 9 WICKING sussa coimas doa
15. f the needed data the experimental steps are set speed tare balance without solid sample load solid sample read weight time until stable to get the solid weight detect ZDOI advance deep enough to immerse the whole solid sample read weight time until stable to obtain the buoyancy force and return to zero position By performing the above steps a run will look like Page 14 Thermo Cahn DCA Tutorial Solid Density Sample Unknown Operator Unknown Thu Feb 17 08 19 20 2000 Position mm Solid Density dcd Auto Analysis Wed Aug 02 08 51 04 2000 Read Weight Time until Weight Stable sd 8 3213 Denisty g mL 0 5 0 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 Time sec cmc When adding the surfactant into a solvent the threshold concentration at which micellization begins is known as the critical micelle concentration CMC With optional CMC accessory the system will be capable of finding the CMC of surfactant in a solvent A CMC experiment is a series of experiments where a surface tension measurement is performed after making a surfactant concentration change With an understanding of the surface tension measurement steps please refer to the surface tension section it is easy to create the CMC experimental steps by adding the proper dosing related commands There are three modes for dosing linear default fast and manual show the screen capture It is recommended you use the fast mode to optimize the dosing para
16. ght is seen it s caused by the liguid and or solid liquid interaction e Accuracy of weight reading It s necessary to perform calibration with the samples and counterweights hanged on balance loops The amount of calibration should be in the same range of the expected weight change Using the DCA Record function to make sure the accurate weight reading is obtained Values obtained are off from expected When the measured value is not as expected such as the surface tension of distilled water often time there are two possible causes One is related to the accuracy of the balance reading and another is related to the sample It is recommended to check the above two in order DCA is utilizing the Wilhelmy plate theory Therefore all of the measurements and calculation are dependent upon the accuracy of the balance reading By doing the balance performance test mentioned above the balance performance can be checked and corrected When the balance is assured to be performing OK then the problem has to come from the sample side The samples both liquid and solid should then be examined such as the cleanliness of samples cleanliness of containers accuracy of measured solid dimension etc In some cases different liquids or solids should be tried to ensure the correct measurements Page 24 Thermo Cahn DCA Tutorial
17. here are various sampling techniques in the WinDCA program Since each sampling technique serves a different purpose there are different experimental steps involved It is also necessary to understand that the experimental steps are only one part of the WinDCA method For detailed information about this software please refer to the software manual Page 3 Thermo Cahn DCA Tutorial General Note During the deduction of the equation 2 Fx g y x PR x cos0 it is noted that F in the equation represents the interaction force between the liquid and solid at the zero buoyancy point or touching point or Zero Depth Of Immersion ZDOJD point However during the practical data collection it is important to know that the interested solid surface is vertical to the liquid Therefore it s necessary to immerse the solid sample into the liquid deep enough so that the side surfaces of solid sample will interact with the liquid When this is occurring the solid is in the liquid and buoyancy will be measured by the system It is then necessary to do something to correct the buoyancy term in the equation Since the buoyancy is directly proportional to the volume of immersed solid it is then mathematically to fit a line across the collected data in force vs immersed volume or immersion depth so that it can be extrapolated to the ZDOI line The intercept of such fitted line and the ZDOI line then represents zero volume and zero buoyanc
18. ight column liquid to allow the solid probe to be completely immersed in the light liquid after the next step s Return procedures are the same as those of a surface tension measurement For Wilhelmy plate probe use Recede and Return to Zero Position for the simple method or Return to ZDOI Read Weight Time until Weight Stable and Return to Zero Position under the recommended method For Du Nouy ring probe use Return to Zero Position If a Wilhelmy plate is used all of the plate should be immersed in the light liquid Only the ring itself should be immersed in the liquid if a Du Nouy ring is used This is to ensure that the probe returns to the same position once it s pulled out of the heavier liquid and returned to the zero position Page 9 Thermo Cahn DCA Tutorial Steps 1 and 2 can be interchanged Step 2 can even be eliminated from the method but the solid probe must be immersed in the light liquid prior to the start of the data collection It is also suggested that several trial runs be made in order to optimize the experimental conditions and the amount of liquids needed for the experiment The above experimental steps should be used in most cases However when the heavier liquid has a much smaller surface tension than that of the lighter liquid the solid probe should pass through the interface from the lighter liquid to the heavier liquid Under this circumstance the experimental steps for the interfacial tension run is the
19. ique is often applied to low energy non polar solids such as polymers Surface Energy Geometric Mean and Harmonic Mean methods Surface energy or surface tension of a substance Y is often time described to be consisted of two components polar and dispersive oP and expressed as y t7 When two surfaces meet substance i and j the combination result can be expressed as v y f v2 yt yP y 4 Vat OR The term f y yi yP Y9 is then studied by various researchers and two different groups of theories were proposed by different researchers One is called Geometric mean method and was proposed by Girafalco and Good and extended by Fowkes Owens and Wendt and Kaeble In this method it is assumed that the ionization potentials of the two phases are dominated by dipole dipole interactions The equation for calculation is expressed as yL x 1 cos yi yg 27 y8 Due to the assumption it s better utilized to deal with solid surfaces that are polar Since most of the solids have some polarities on their surfaces it is the most often used method Page 19 Thermo Cahn DCA Tutorial Another method is called Harmonic mean method and was proposed by Wu The theory assumed that the polarizabilities of the two phases are equal and assuming that the polar component has the same form as the dispersive component This results in the following equation vs panii yty Y yL x 1 cos 4 This method
20. is often used by many polymer scientists who are dealing with much less polar surfaces and want to know the polarity of the sample However due to the mathematical difficulties in solving for the values it is not as commonly utilized as the Geometric mean method Surface Energy Polar or Lewis Acid Base method Based on the Lewis acid and base theory a different approach other than Geometric Mean and Harmonic Mean methods was proposed by Good van Oss and Chaudhury This method yields the Lifshitz van der Waals component o the Lewis acid y and the Lewis base y components of the solid surface energy The surface energy is expressed as ae E NTT and the equation for interaction between two phases is y x 1 cos 2Ayy yo SRY N Due to the consideration of the bonding between the molecules this method is more applicable for hydrogen bonding systems Since it s still at its early stage the usage of this method is not as wide as the Geometric mean and Harmonic mean method Liquid Surface Tension Components In a solid liquid system the solid surface properties can be studied by using any of the above functions For liquid however the DCA can find out its total surface tension not the polarity or the liquid surface tension components This liquid surface tension components function uses a well characterized non polar solid such as polyethylene or Teflon as the reference to obtain the contact angle value against the liq
21. lid Among all of the techniques that are available the Wilhelmy plate technique provides the most accurate and repeatable measurements In the Wilhelmy plate technique the solid sample is hanged perpendicular to the liquid s surface When the solid is partially immersed in the liquid the equilibrated force can be expressed as F x g F liquid solid interaction F buoyancy Or Fx g yx PR x cos px V 1 Where F is the interaction force between solid and liquid g is the gravitational constant y is the surface tension of the liquid PR is the wetted perimeter of the solid O is the contact angle between the solid and liquid p is the density of the liquid and V is the volume of solid immersed underneath the liquid When the solid is right at the liquid s surface the F buoyancy term p x V equals to zero Then the final equation for calculation will be F x g yx PR x cos 2 Since the equation involves in force measurement with a high precision balance the measurement can then be done with high accuracy and repeatability Page 1 Thermo Cahn DCA Tutorial The Thermo Cahn Dynamic Contact Angle DCA analyzer is an instrument used to measure the surface properties of solid and liquid samples by using the Wilhelmy technique It consists of a highly sensitive balance a moving stage mechanism and a control station Hardware Upon the purchase of a Thermo Cahn DCA system it is necessary to set up the hardware per the
22. meters once the surface tension measurement steps are optimized After the optimum parameters are obtained the linear or manual dosing method can then be used for a CMC measurement Since the CMC experiment is a series of surface tension measurements at different surfactant concentrations the final CMC curve then looks like Page 15 Thermo Cahn DCA Tutorial MC 0 833291 It s necessary to make sure that there are enough data points before and after the CMC Otherwise the software won t be able to locate the CMC automatically Page 16 Thermo Cahn DCA Tutorial Special Sample Handling and Preparation Thin Film Samples Thick film samples can be easily handled by using a clip However for thin film samples it may not be rigid enough to penetrate into the liquid and no meaningful data will be obtained It s then necessary to use the Thermo Cahn Thin Film sample holder for this purpose In order to make the film piece rigid the Thermo Cahn Thin Film sample holder has a blunt V shape tip to bend the film sample By also cutting the sample short this will enable the sample to penetrate into the liquid and be measured Single Sided Samples When the sample is only coated on one side or one side of the sample is of interest this presents a challenge for DCA technique since during a DCA experiment the wetted solid surface should be the same It s then necessary to prepare the sample in such a way that the in
23. n the same as that of the standard surface tension measurements and only the advancing data will be analyzed by using the manual analysis mode i IT dcd Auto Analysis 1996 it 36 3538 mN m 400 300 200 100 onson 3 _ o 0 2 4 6 8 10 12 14 Position mm Wicking When the amounts of liquid being adsorbed by solid samples porous or powder are of interest you will perform a wicking experiment Under this technique solid samples will be immersed and held just below the liquid s surface and the weight change recorded as a function of time Therefore the experimental steps are Set Speed Tare Balance Detect ZDOI Advance Tare Balance optional but recommended Read Weight Time until Weight Stable Return to Zero Position The motor speed should be set to a high value in order to immerse the solid into the liquid quickly The distance for the advance step should be set to a low value large enough to ensure Page 10 Thermo Cahn DCA Tutorial that solid will be in contact with liquid throughout the run since the liquid level will drop due to adsorption by the solid sample Wicking Your Sample Operator You 1996 DOT es Position mm SS WICKING DCD Auto Analysis 1996 200 250 300 350 400 0 100 200 300 400 500 Time sec Fiber Diameter For fiber samples it s very difficult to measure its diameter since it s usually very small about a few microme
24. onditions 2 When balance is over counter weighed on the sample size or the tare side the balance will be locked into a saturated value all the time This will show no live weight reading during the run The problem can be fixed by performing the balance counter weighing process on page 3 again with the sample and holder Page 23 Thermo Cahn DCA Tutorial Balance shows ZERO weight reading all the time When this occurs it normally means that the system is over counter weighed It happened in Radian DCA 322 the most often In this case please refer the balance counter weighing procedure located on page 3 Balance shows 1 5 or 5 times of the actual weight This happened only in Radian DCA 322 model It s mostly caused by the fact that wrong loop was selected in the method Please check the system configuration of the current method and make sure the correct loop is selected AND used Balance performance test Since the accuracy of the weigh reading is very critical for a DCA measurement it s then necessary to perform the following two tests to verify the correct operation of the DCA balance e Balance stability test 1 Remove every thing from the hang downs of the balance loops Make a run to make sure that the balance is stable all by itself 2 Put samples and counterweights on and make another run without liquid sample Make sure the weight is stable 3 Then put on liquid sample and make another run If unstable wei
25. ore detailed information about this accessory can be obtained from the manual for CMC accessory Powder Accessory As mentioned in the special sample handling techniques one way to measure the wettability of powder samples is to use the Powder accessory This accessory consists of glass tubes with fritted bottom The powder sample will be packed into the tube and wicking experiments will be performed With Washburn technique the contact angle or wettability will then be obtained Further information can be found in the Applications software section Temperature Module As any other physical constants the surface tension of the liquids and solids are highly dependent upon the temperature It s therefore necessary to control and measure the temperature of the experiments The temperature module accessory allows the user to control the temperature of the liquid and its surroundings while the software will record temperature of the liquid More detailed information can be obtained from Thermo Cahn Instruments Page 22 Thermo Cahn DCA Tutorial Troubleshooting Communication When there is an error message about not finding the DCA most commonly seen causes for this communication problem are Wrong RS232 cable is used Wrong power setting is set on the back of DCA Wrong DCA model selected in the method s system configuration Wrong communication port selected in the method s system configuration screen DCA stage is
26. red by using the above solid volume sampling technique the liquid s density can then be measured However it s necessary to be sure that the whole solid with partial support wire is immersed into the liquid Also if the liquid has a higher density than that of the solid it might be necessary to put extra weight on top of the solid to push it into the liquid Typical experimental curves looks as follows Page 13 Thermo Cahn DCA Tutorial Liquid Density Sample Unknown Operator Unknown Fri Mar 24 13 26 47 2000 0 5 10 15 20 Position mm Liquid Density dcd Auto Analysis Wed Aug 02 08 47 51 2000 Read Weight Time until Weight Stable ld 1 1431 Denisty gimL 0 5 10 15 20 25 Time sec Solid Density The density of a material is defined as density weight volume For solid the weight can be measured by a balance The volume can be measured by using the buoyancy force of the solid inside a known density liquid or volume of solid buoyancy force liquid density Therefore the final equation for calculation is Solid Density Liquid Density x Solid Weight Buoyancy Force In the data collection the solid weight will be obtained at the beginning of the run the buoyancy force will then be obtained by immersing the solid into the liquid which the density is known It s necessary to immerse the whole solid into the liquid for accurate measurement To accomplish the necessary steps to collect all o
27. repeatable However practice is needed for preparing the sample and the powder sample has to be fairly fine 3 Using the Powder accessory mention in the later part the powder is packed into a tube which has a fritted opening at the end Wicking experiments will then be performed on this packed tube and Washburn equation will be applied to obtain the contact angle values This Page 18 Thermo Cahn DCA Tutorial technique can handle powders of any particle size however this technique is fairly time consuming and many experiments have to be performed to optimize the experimental conditions Also for a powder that doesn t wet a certain liquid the experiments can t be carried out Applications Software As a surface analyzer a standard DCA can provide surface related information such as the contact angles between solids and liquids liquid surface tension and liquids interfacial tension However for the surface energy of solid liquid surface tension components and contact angle of porous materials the applications software has to be used The following discusses each of the functions Surface Energy Zisman Plot method The value obtained by using this method is often known as the Critical Surface Tension of the solid The technique was proposed by Zisman and Fox who found a quasi linear relationship between the cosine of the advancing contact angle and the liquid surface tension of a series of liquids This techn
28. rgy Analysis Yesterday and Today CHN 19 8 91 Fox H W and Zisman W A J Colloid Science 1950 5 514 Girafalco L A and Good R J J Phys Chem 1957 61 904 Fowkes F M J Phys Chem 1962 66 382 Owens D K and Wendt R C J Appl Polym Sci 1969 13 1741 Kaele D H J Adhesion 1970 2 66 Wu S J Polym Sci 1971 19 34 van Oss C J Good R J and Chaudhury M K J Colloid Interface Sci 1986 111 378 E W Washburn Physics Review 1921 17 3 273 282 OP AE Boy Accessories for DCA CMC Accessory As a common phenomenon when there is impurity in the liquid its physical properties will change One of the physical properties surface tension will also change For surfactant industries this change is related to the surfactant s concentration There is always a critical concentration that when adding more surfactant the surface tension of the system is not Page 21 Thermo Cahn DCA Tutorial changing or not changing as much This concentration is often time called critical micelle concentration or CMC To obtain the CMC there are many different apparatus based upon different changing physical properties As part of the function of DCA surface tension can be easily measured and therefore the CMC can be obtained by varying the concentration of the surfactant in solvent This is then the purpose of the CMC accessory which will make the CMC measurement automatic M
29. se aca ap ice GOA is dente et he E tes caia ihe eed sag Seid co alls mins dale R 10 FIBER DIAMETER isso fossa sis bee E TUTO ida ca Caes sad sai SD coats EST UE TS aaa TA aT OS N 11 SOLID VOLUMES 23 220 66h da o eee hed alado MOEN ada do Bie EN EN la od do dad dA e dO Sl dd 12 LIQUID DENSI Y acesas E se ticta o cc as tan a isto Se So gi nas DE LES aia US as SA AS LUA coa sai a 6 Said a ao a ad 13 SOLID DENSTEY pes sgiia ir ie tied ESEE EAEE AS SUS dba UA SS ias Dl iia o LE sans Ud ga sedan as stevens 14 CM mare a inertes Caesar atas aa Ls asseio dass na Lusa ASe 15 SPECIAL SAMPLE HANDLING AND PREPARATION ccccccscscscscssscccsssssssevsceceseseves 17 THIN PEM SAMPBUES 323 053 cs8 detec Sexe voesbelencetten dots ielched beth Uocntnedehestewn tends bes ches fal cond Bu a Fiua fada Socios ase 17 SINGLE SIDED SAMPLES nireng arno sedecnstauel sats a aa a a sate sysbegstdavadeds Sagas dual sot voseede 17 SINGLE FIBERS SAMPLE cacosvocued ies cdace Sovdededa de siso s So Ueba Lea cade oct o sai abs sabes E ES assesment aes 18 POWDER SAMPEES so suis tenis st Tron Isin da he cto Denis hate ca des coaedt id aaa extend oie dae aliado 18 APPLICATIONS SOFTWARE fisssscsciscsccteissccciccocscccescssecscansccccsacssecdcaccscececoesecdccucesccsauscecdcauasece 19 SURFACE ENERGY ZISMAN PLOT METHOD ssecccccseececcecesceccaseccceesssccceausecccausceceanesecceaes 19 SURFACE ENERGY GEOMETRIC MEAN AND HARMONIC MEAN METHODS 0
30. still moving back to its zero position Balance is not correctly counterweighed The simplest way to check is to turn off and DCA and exit the WinDCA software Then turn on the DCA with NO weights on the balance Wait for a few seconds and make sure that only one light is on at the front of the DCA panel Now launch the WinDCA software and make sure the communication setting in the current method is correct Select DCA Diagnostics DCA Test to check for the communication If this fails as well please contact Thermo Cahn service department Stage kept on moving at Detect ZDOI step When this happens the stage will keep on moving to its maximum travel distance even though the sample may have been immersed into the liquid There are two possible causes Wrong ZDOI threshold is used in the current method Usually means the current ZDOI threshold is too large Wrong counter weight is used The following steps will allow the user to check the both situations 1 Use Method Edit function to open the method editor On the main editor page click on Experiment setup Now in this dialog locate the field for ZDOI threshold Decease the ZDOI threshold and try the run again NOTE since the ZDOI threshold can be different for different combination of sample size and liquid it s very hard to come up with a good value to use for all of the conditions It s recommended to create different method for different kinds of samples or c
31. terested side of the solid is exposed and will contact liquid To achieve this it is recommended to use double sided tape or apply glue to stick the sample back to back and only expose the interested surface This way the interested side will be exposed to the liquid However since the single sided sample has a certain thickness by using the double side tape or glue won t be able to cover the edges of the sample It s then necessary Page 17 Thermo Cahn DCA Tutorial to prepare a wider sample so as to minimize the contribution of the edges with respect to the overall wetting perimeter of the sample Single Fiber Sample For the DCA 322 single fiber samples are very commonly measured Single fiber samples normally have a diameter ranging from a few microns to about 30 microns Handling fibers this small is very tricky and can be time consuming Mounting the fiber sample to perform DCA experiments is even more difficult The following steps are recommended by Thermo Cahn and have been proven to work very successfully and efficiently 1 Prepare a set of metal wire support The metal wire support should be bent into 7 shape so that one end can be attached to the balance loop and the other straight end will be used to attach the fiber 2 Mounting the single fiber sample onto the metal wire support by using glue or small pieces of tape It s important to make sure the glue or tape won t adsorb the liquid that will be used for
32. ters Even though a microscope can be utilized for this purpose it s very time consuming and the apparatus can be expensive The result obtained from microscopic methods can still be not accurate since the measuring direction and the measuring point are varying among the fibers and within one single fiber For DCA however it s very simple and fast and an accurate averaged diameter can be obtained since the Wilhelmy equation contains the information about the fiber diameter Fx g yx Tx Diameter x cos0 When a very low surface tension liquid is used the contact angle should then be 0 or cos 1 Then the fiber diameter can be obtained as Diameter F x g yx T During the measurement it s necessary to use a liquid with low surface tension such as hexane and acetone This will then ensure the total wetting angle or 0 or cos 1 is obtained Page 11 Thermo Cahn DCA Tutorial The experimental steps are the same as those of the contact angle sampling technique with single cycle single loop Since most of the low surface tension liquids are volatile it s highly possible that the sample or the attachment may absorb the vapor Therefore only the advancing data will be used for calculating the fiber s diameter A typical fiber diameter run is illustrated as follows newfd dcd Auto Analysis Wed Feb 16 15 54 28 2000 Hiber Mean Diameter 0 236744 mm Position mm Solid Volume For irregular sh
33. uid The liquid surface tension components is then calculated by means of both the Geometric mean and Harmonic mean equations Wicking Rate Page 20 Thermo Cahn DCA Tutorial While the wicking experiment provides the weight pick up information for porous or powder samples the wicking rate will provide the information about the rate of the weight pick up The derivative of the wicking curve will be presented Powder Option Washburn method The wettability of porous materials such as paper wood and powder is always important information to obtain However obtaining the wettability information is a challenge DCA utilizes the Washburn theory to calculate the contact angle between the interested solid against a certain liquid The Washburn equation that is utilized in the calculation is as follows 2 t pxyxC where 9 is the contact angle w is the measured weight t is time C is a dimension constant that is related to the porosity and or packing of the solid sample and n y and p are the viscosity surface tension and density of the liquid respectively By using a standard liquid which has low enough surface tension that gives cosO 1 the contact angle between the solid against the interested liquid can then be calculated For detailed information please refer to the Product Note about the DCA Applications Software and the reference papers listed below 1 Thermo Cahn Instruments Inc Product Note Solid Surface Ene
34. y or true force at ZDOI Based upon the above discussion it is then noted that the solid sample should be immersed in the liquid deep enough so that the vertical sides of the solid will interact with the liquid After that the software will allow user to specify a linear region to eliminate the buoyancy term and perform the correct calculation which will be performed automatically by the software CALIBRATION In order to obtain accurate measurements it is always recommended that the DCA system be calibrated regularly There are two parts that need to be calibrated One is the balance and the other is the stage motor The balance calibration ensures that an accurate weight reading will be recorded and the motor calibration guarantees that the correct sample position and motor speed will be attained Since the WinDCA software allows the calibration results to be saved into the same calibration files the following procedure should be used in order to ensure that the correct calibration factors are used e Create a new method file with the correct system configuration or load an existing method file or edit the loaded or created method and save the changed method file e Making sure the balance is correctly counter weighed If not sure please refer to the section about balance counter weighing on page 3 e Calibrate the balance and or the motor of the DCA system Save the new calibration file and update it into the current method
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