For the 1st two samples we used poled PVDF films. Using thesefilms we prepared bi and multilayer films. The aluminium film on one side ofthe film has been removed by etching. The films were glued together in thereverse dipole moment direction using two component glue.For the 2nd two samples we used P (VDF-TrFE) 56/44 mol% and P(VDF-TrFE) 70/30 mol% composite granulate.
From these composite granulate, weprepared films by using hot press. These films are unpoled. Films were gluedtogether using two component glue. S1: Sample one consists of two PVDF films, each film thickness is 9µm.
Thesetwo films glued together in the reverse dipole moment direction using twocomponent glue. Total thickness of the films is 21µm S2: Sample two consists of three PVDF films, each film thickness is 9µm.These three films glued together in the reverse dipole moment direction usingtwo component glue.
Total thickness of the films is 30µm S3: Sample three consists of two P(VDF-TrFE) films with different molarand weight ratios one side is P(VDF-TrFE) 56/44 mol%, 10µm and the other sideP(VDF-TrFE) 70/30 mol%, 10µm. These two films glued together using twocomponent glue. Total thickness of the films is 23µm S4: Sample three consists of two P (VDF-TrFE) films with different molarand weight ratios one side is P (VDF-TrFE) 56/44 mol%, 10µm and the other sideP(VDF-TrFE) 70/30 mol%, 10µm.
These two films glued together using twocomponent glue. Total thickness of the films is 25µm S5: Sample three consists of two P (VDF-TrFE) films with different molarand weight ratios one side is P (VDF-TrFE) 56/44 mol%, 13µm and the other sideP(VDF-TrFE) 70/30 mol%, 13µm. These two films glued together using twocomponent glue. Total thickness of the films is 30µmS6: Sample three consists of two P (VDF-TrFE) films with different molarand weight ratios one side is P (VDF-TrFE) 56/44 mol%, 15µm and the other sideP (VDF-TrFE) 70/30 mol%, 15µm.
These two films glued together using twocomponent glue. Total thickness of the films is 33µm3.1 Hot Press:The film maker and its cooling system are packed in a protective plasticcase. The contents of the case are as follows:-1 Film Maker, comprising top platen, bottom platen and guiding ring1 Cooling ChamberA set of spacer rings as listed below. These are engraved to denotenominal thickness to be produced:-Spacer rings ThicknessA 15µmB 25µmC 50µmD 150µmE 250µmF 500µm 1 Pack of 200 AI foil discs1 Stainless steel forceps20 SpecacardsHeated platens with 20° – 300°C temperature Controller 220-240V, 50Hz INSTALLATION AND OPERATION 1. Connect the cooling system to a cold water supply and drain via theinlet/outlet ports on the rear of the unit.
2. Assemble the Specac Heated Platens on the press according to theinstructions supplied and set to the required pressing temperature 180degreecentigrade. 3.
Select the spacer ring for the required thickness and locate the ringon the bottom platen of the film maker around the central raised polishedsurface.4. Place the guiding ring around the spacer.5. Place one aluminium foil disc on the bottom platen of the film makerlocating it inside the spacer ring. If a reduction in spectroscopicinterference fringes is sought, this disc should be placed matt surfaceuppermost.
Conversely if fringes are required, for example to measurethickness, place the shiny surface uppermost.6. Place the sample to be pressed on the foil disc and locate the topplaten of the film maker (polished surface facing down) on top of the sampleusing the guiding ring for location. The handle of the top platen should belocated between the guiding pins on the bottom platen.
7. Locate the assembled film maker centrally between the heated platenson the press so that the top platen makes contact with the film maker. Allowapprox 5 minutes for the film maker to reach the required temperature. Ifrequired a thermocouple may be inserted into a drilled hole in either the topplaten or guiding ring. As the sample softens the top bolster of the press maybe screwed down further.8. Tighten the locking nut on the press and pump until the required load(4 tons) is reached.
Allow the film maker to remain under load for 3-4 minutesthen release.9. Transfer the film maker to the cooling unit.
10. The film maker may be removed from the cooling unit after 3-5minutes depending on original temperature and water flow rate. Close the lid ofthe cooling unit between Operations to allow self-cooling.
11. Disassemble the film maker by lifting the top platen. This shouldcome away easily.
For emergency use a release lever is provided on theright-hand side of the bottom platen.12. The pressed film will be removed with the top platen together withthe foil disc.
Use the forceps provided to remove the foil disc and then thesample.13. The sample may be mounted in a Specacard (P/N 3800 or 3810) or amagnetic film holder (P/N 3820) for spectroscopic analysis.NOTES ON TOLERANCEThe spacer rings have manufacturing tolerances such that the samplethickness tolerances are +/- 3µm for rings A and B and +/- 10µm for all otherrings.
This refers to the absolute thickness produced; once a pressing cyclehas been established reproducibility will be greater than this tolerance.Spacer rings A and B are engraved with a series of one to four dots. Toachieve the stated tolerance it is essential that the number of dots matchesthe number engraved adjacent to the polished surface on the bottom platen. Ifreplacement rings or bottom platen are required please specify this number ofdots.Both the bottom and top polished surfaces are removable from the platensby releasing the three locating screws in each case.
Should it be necessarythese surfaces may then be returned to Specac for repolishing. Repolishing ofthe bottom surface will obviously affect the thickness produced in subsequentpressings but reproducibility will be maintained. 33.2 Aluminium etching:Aluminium on PVDF film surfaces should be removed because due to smallamount of aluminium on surface of PVDF can deviate the polarization resultsWe need three components to remove aluminiumNAOH solution1 beaker1 tweezerHand gloves Take NAOH solution and pour it in the beaker till half of the beaker. Hold the PVDF film with tweezer and place it in the solution. Using tweezer itself stir the solution continuously until 5 minutes After 5 minutes aluminium layer on PVDF film gets removed. Now we can use this films for our experimentMake sure NAOH solution is pure.
3.3 Electrode deposition:Electrode deposition was done by thermal evaporation of Aluminium. Toget the desired shape of the bottom electrodes, a mask was aligned on top ofthe samples. And To get the desired shape of the top electrodes, a mask wasaligned on bottom of the samples. The mask had initially been designed toproduce single-layer samples. 4 3.4 Poling PVDF:In order for the smart composite structure to generate responses due toan applied load, the PVDF material must be polarized to align the dipolemoments of its crystalline structure.
The crystalline structure of the PVDFfilm will determine the polarization properties of the film. There are fourpossible crystalline forms of the PVDF polymer: the alpha, beta, gamma, anddelta phases 17. Only the beta, gamma, and delta phases can be polarized.However, the alpha phase can also be polarized by applying a large electricfield, which will convert the alpha phase to the delta phase 17. Theprocessing conditions of the PVDF film determine the dominant crystallinephase.
When the PVDF film layers in the composite samples are melted andsolidified, the dominate phase is the alpha crystalline phase 18. Since thealpha phase is the dominate phase upon solidification, an electric field mustbe applied to convert the alpha phase to the delta phase and to align thedipoles for the proposed smart composite structures. Existing research showsthat an electric field of around 125 MV m?1 is required to fully polarize apredominately alpha phase PVDF film 19. However, a higher piezoelectriccoefficient can be attained by polarizing a beta phase film since the betacrystal phase has a greater dipole moment than the delta phase 20. One of themost common means mentioned in the literature to achieve a predominately betaphase PVDF film is to stretch the film mechanically to many times its originallength 21. A second method to transition from an alpha phase film to a betaphase film is to apply a very high electric field on the order of 500 MV m?119. A third method mentioned in the literature to achieve a predominatelybeta phase PVDF film is to cure the film under high pressure 22.
Finally, thecopolymers of PVDF containing trifluoroethylene (TrFE) or tetrafluoroethylenecan be added to the film to encourage the formation of the beta phase 23. 3.4.1. Polarizationset upDuring hot press pvdf film looses small amount of polarization becauseof high temperature. To conduct polarization measurements we need fully polarizedfilm. So we used one method to increase its polarization.For that method we need equipment set up.
The following figure shows theset up to increase polarization in pvdf film.1. Function gernerator2. Oscillator3. Sample holder4. Resistance box5.
Voltage amplifier Figure 5:Polarization set up 1. Connect functiongenerator input wire to voltage amplifier input2. Reistance box inputwire to sample holder input3. Resistance box outputwire to oscillator output4. Amplifier output wireto sample holder output wire Apply voltage is depending on the thickness of the film.Apply voltage until we get hysteresis curve.
After that press sweepon/off button and then press shift and then press rate and then press trigger.Sample will get polarized fully. 3.
5 Annealing:Annealing involves heating a material to above its recrystallizationtemperature, maintaining a suitable temperature, and then cooling. The heattreatment is necessary to increase the crystallinity of ferroelectric copolymerlayers. Annealing process occurs in three stages. For example, sample has toannealed at 110°C. First stage the copolymer gets heated from 30°C temperatureto 110°C in one hour. In the second stage the copolymer must stay for 2 hoursat 110°C. In this stage recrystallization occurs. In the third stage thecopolymer gets cooled from 110°C to 30°C in one hour.
5 Figure 6: Annealing1.6 Soldering:We need: – 1. Pins2. silver3. soldering kit4. two component gluePlace sample on sample holder using two component glueSolder pins on sample holderDraw connections using silver Check connection using resistance measurement4. Measurements4.1Theoretical calculationsFrom LIMM method we will get pyroelectric spectrum and referencespectrum.Pyroelectric spectrum consists fx, Xf, YfFx= frequencyXf= real value of sample front sideYf= imaginary value of sample front side Reference spectrum consists fp, Xp, YpFp= frequencyXp= real value of photo diodeYp= imaginary value of photo diode If Xf, Yf positive If Xf negative, Yf positive If Xf negative, Yf negative If Xf positive, Yf negative If Xp, Yp positive If Xp negative, Yp positive If Xf negative, Yf negative If Xf positive, Yf negative Now we have Zp, ?p, Zf, ?f Corrected values From the corrected values we have to find pyroelectric coefficientPco= pyroelectric coefficient Pco = a – bTo calculate the thickness
