Sulfur sol preparation and its ζ-potential determination
I. Objectives of the experiment
1, to master the method of determining the sol potential with JS94G+ microelectrophoresis instrument;
2, to explore the conditions of sulfur sol preparation by replacing solvents, and the determination of ζ-potential of sulfur sol;
3, to explore the influence of electrolytes, surfactants and their concentrations on the ζ-potential of sulfur sol;
3, to explore the influence of electrolytes, surfactants and their concentrations on the Zata-potential of sulfur sol. The effects of electrolytes, surfactants and their concentrations on the ζ-potential and dispersion stability of sulfur sols.
The experimental principle
The solubility of sulfur in water is very small, while it has a certain solubility in ethanol. If the appropriate amount of sulfur ethanol solution is added to water, the solute sulfur will be precipitated in the form of molecular aggregates, these tiny particles are uniformly dispersed in water, which can form a more stable sulfur sol[1]. This method of preparing sols is known as the solvent replacement method. Since sulfur is hydrophobic, the sol is a liquid-repellent sol.
In the above-prepared sulfur sol, sulfur microparticles can reduce their own free energy and that of the sol by undergoing surface adsorption due to their high specific surface energy and surface activity
. Nonpolar, hydrophobic monomeric sulfur tends to preferentially adsorb ethanol molecules in aqueous solutions containing small amounts of ethanol. The mode of adsorption in which the energy of the system may be lowered more is that the sulfur microparticles adsorb the hydrophobic ethyl group at one end of the ethanol molecule in solution; while the hydrophilic hydroxyl group at the other end of the ethanol molecule tends to form a hydrogen bond with the neighboring water molecule. Obviously, through this way, can significantly reduce the energy of the sol system, so that the original hydrophobic sulfur particles can be uniformly dispersed with the water to form a more stable sulfur sol. For this reason, ethanol can be called the stabilizer of the sol.
The sulfur sol formed above is a negatively charged sol. The possible reasons for the electrification of sulfur particles are: sulfur
Sulfur microparticles due to Brownian motion, and the dielectric constant of water molecules with a large sustained friction and polarity induced; sulfur particles adsorbed on the surface of the dissociation of substances; sulfur particles adsorbed on the surface of the ions or dipole molecules.
If an appropriate amount of surfactant is added to the sulfur sol, due to the significant lipophilicity and
hydrophilicity of the surface-active ions, it is easier to adsorb on the surface of the sulfur particles, thus affecting the interfacial electrical properties and dispersion stability of the sol. If it is changed to add electrolyte in the sulfur sol, it will also affect the interfacial electrical properties and dispersion stability of the sol. In addition, the addition of some high-valent counter ions (such as Fe3 + ions, etc.), can occur on the surface of the gel particles characteristic adsorption, and can even change the electrical properties of the sulfur sol, and make it happen irregular aggregation and sedimentation. Surfactant and electrolyte on the sol dispersion stability of the impact of dual nature: adding the right amount of surfactant or electrolyte, can improve the stability of the sol; add too much, it will destroy the stability of the sol.
Often the absolute value of the colloidal ζ-potential can be used to measure the dispersion stability of the sol. For rely on electrostatic
stabilized hydrophobic colloid, there is a critical ζc potential, when the absolute value of the colloid's ζ potential is less than ζc, the colloid's stability is poor, prone to agglomeration and sedimentation. The ζc value of most colloids is around 25-30mV. The relationship between the concentration of stabilizer and the ζ potential of the sol can be obtained by determining the ζ potential of sulfur sols containing different concentrations of electrolytes or surfactants. From these results, the appropriate concentration of stabilizer required for the preparation of stable sulfur sol can be determined, the adsorption on the surface of sulfur particles and the effect of stabilizer concentration on the dispersion stability of the sol can be analyzed and explored, and more knowledge about the interfacial electrical properties of sulfur sol can be obtained.
Three, instruments and reagents
1, instruments
JS94G + micro-electrophoresis instrument (Shanghai Zhongchen Digital Technology Equipment Co., Ltd. manufacturing, East China Normal University supervision)
Ultrasonic instrument (JL-60, Shanghai Jieli Science and Technology Co., Ltd.); super thermostat (Shanghai Experimental Instrument Factory);
8 50mL beakers; 1 pipette (1 mL, 2mL); 2 measuring cylinders (25mL); a number of glass droppers; mirror paper.
2. Reagents
Sulfur powder (C.P.), anhydrous ethanol (A.R.), KCl (C.P.), MgCl2 (C.P.), FeCl3 (C.P.),
Sodium dodecylbenzenesulphonate, hexadecyltrimethylammonium bromide, all of A.R grade.
3, solution
Preparation of 0.1M NaCl , MgCl2, FeCl3 solution; 1.0g/L cetyltrimethylammonium bromide solution; 1.0g/L sodium dodecylbenzenesulfonate solution.
Four, experimental content
1, practice JS94G + microelectrophoresis instrument test operation
Bentonite water dispersion system ζ potential determination: in a beaker containing 20 mL of concentration of 10-3 mol - L-1 KCl solution, add a little bentonite. The beaker was placed in an ultrasonic instrument and oscillated for 2-3 minutes to make the bentonite uniformly dispersed. The ζ-potential of the bentonite dispersion system was determined by practicing the test operation of the JS94G+ microelectrophoresis instrument according to the operating instructions of the instrument and the tips in the appendix. The main mineral component of bentonite is montmorillonite, dispersed in aqueous solution has a more stable ζ potential.
2, the preparation of sulfur sol and its ζ potential determination
Take an appropriate amount of sulfur powder into a small beaker, add a certain amount of anhydrous ethanol stirring, dissolution, sulfur powder is still a small amount of remaining. The beaker was placed in a thermostatic bath at 60 ℃ for about 15 min, and then the beaker was oscillated several times, and after the solution was clarified, the ethanol clear solution of sulfur was sucked up with a burette, and 5, 10, 15, 20, 25 and 30 drops were added to the beaker of distilled water each containing 18 mL, and then the beaker was added with water and fixed to 20 mL, and then the beaker was oscillated so that the colloid dispersed homogeneously. The ζ-potential of each sulfur sol was determined on a microelectrophoresis apparatus, and the amount of sulfur ethanol solution required to be added to the sol with the largest absolute value of ζ-potential was determined x (drops).
(Note: 20 drops of ethanol solution of sulfur were taken for the following experiments.)
3. Determination of the ζ-potential of a sulfur sol containing an electrolyte
Take NaCl, MgCl2, and FeCl3 at concentrations of 5 × 10-5, 1.0 × 10-4, 5.0 × 10-4, 1.0 × 10-3, 5.0 × 10-3, 0.01 mol -
L-1 ( 1.0×10-5, 5×10-5, 1.0×10-4, 5.0×10-4, 1.0×10-3, 5.0×10-3) solutions of 15 mL each were put into different beakers, and then 20 drops of ethanol solution of sulfur were added, respectively, and the volume was fixed to 20 mL with water, and the colloids were oscillated so as to be evenly dispersed. The ζ-potential of each sol was determined.
4. Determination of ζ-potential of sulfur sol containing surfactant
(1) Take 15mL of cetyltrimethylammonium bromide (CTAB) with the concentration of 0.001, 0.01, 0.05, 0.20, and 1.0g/L into different beakers, then add 20 drops of ethanol solution of sulfur, add distilled water to 20mL, and then shaking. Make the colloid dispersed evenly. The ζ-potential of each sol was determined.
(Note: the ζ-potential of the sulfur sols changed from negative to positive with the increase of CTAB concentration.)
(2) Take 15 mL of sodium dodecylbenzene sulfonate (SDBS) solution with concentrations of 0.001, 0.01, 0.05, 0.20 and 1.0 g/L into different beakers, then add 20 drops of ethanol solution of sulfur respectively, add distilled water and fix the volume to 20 mL, and oscillate the beaker to make the colloid dispersed evenly. The ζ-potential of each sol was determined.
V. Data processing and discussion of results
The experimentally determined concentration-ζ potential data were required to be tabulated and plotted (ζ potential-concentration) respectively, and the obtained experimental results were discussed.
1. ζ-potential of bentonite water-dispersed system.
2, ζ-potential of each sulfur sol formed by dropwise addition of different amounts of sulfur ethanol solution. Analyze the adsorption on the surface of the sulfur gel particles to show why the absolute value of the ζ potential of the sol is the largest when x drops of sulfur ethanol solution are added.
3. ζ-potential of each sulfur solute with different concentrations of NaCl, MgCl2 and FeCl3 solutions as stabilizers. Summarize the relationship between the concentration of each electrolyte and the ζ-potential of the sol, compare their differences, and analyze the reasons for the differences.
4. ζ-potential of each sulfur sol with different concentrations of surfactant solutions as stabilizers. Summarize the relationship between the concentration of each surfactant and the ζ-potential of the sol, compare their differences, and analyze the reasons for the differences and the adsorption on the surface of the sulfur particles.
VI. Reflective questions
1. Why is the ζ potential of the sulfur sol prepared by adding different amounts of sulfur ethanol solution is different?
2, try the Stern model of diffuse bilayer, discuss the reason why the sulfur sols prepared under different conditions are charged.
3, Try to analyze the adsorption on the surface of each sulfur sol-gel prepared in this experiment.
4. Discuss the effect of the concentration of Fe3+ ions on the surface adsorption of sulphur colloids and on the ζ-potential of the colloids.Is it
possible for Fe3+ ions to form surface sulphides with sulphur? Try to design simple experiments that can demonstrate this fact.
5. Sulfur sol has a certain bactericidal effect. If it is used as a fungicide, how should a suitable surfactant be selected as a stabilizer and its concentration determined? What tests need to be done for the trial design?
VII, experimental notes
1, to determine the size of the glass burette used: such as ethanol sulfur solution is about 50 drops / mL.
2, the measurement must be used with the same set of electrophoresis cups and electrodes (Pt electrode). Each time you add the colloid sample 0.5mL, slightly tilt the electrophoresis
cup inserted into the electrode to avoid bubbles, and make the liquid level of the colloid on both sides of the electrode in the electrophoresis tube is the same height
3. Determine the sols containing the same kind of stabilizers according to the order of from dilute to concentrated. Before each addition of colloid, the electrophoresis and electrode should be cleaned 3 times.
4.When determining sols containing different stabilizers, the electrophoresis cup should be rinsed with distilled water 3 times each time, and then cleaned 3 times with the sol to be measured.
5. The safety current of the electrophoresis instrument is limited to less than 18mA during the measurement. When measuring the sol containing high concentration of electrolyte, if the particles displayed on the screen keep shaking in one direction, even if the current is below 18mA, the measurement should be stopped immediately to avoid damaging the instrument.
Appendix: Js94+ Microelectrophoresis Instrument Operation Steps
1.Connection
Open the shortcut of "js94g" on the desktop, and then click on the CONNECT option in the OPTION menu after entering the main interface. If OK appears, it indicates that the computer is successfully connected to the instrument; if an error message appears, please check the connection between the computer and the instrument.
2. Focusing and Positioning
Add deionized water to the electrophoresis cup, put in the crosshair, and put it into the sample tank. Tap "Active Image" and click RGB16BIT in OPTION to adjust to grayscale image. Use the adjustment buttons on the instrument to adjust the clear crosshair that appears in the center of the image display area to complete the focusing and positioning work. For each experiment, you only need to focus once just before the beginning of the measurement, and you don't need to focus every time for the following measurement.
3. Sampling operation
Rinse the electrophoresis cup and electrode device several times with deionized water, inject the sample to be measured into the battery cup, insert the Ag electrode, rinse it back and forth, and repeat it twice to make the electrode device fully wetted; (the electrode is better to soak it for a period of time in distilled water beforehand)
Inject the sample into the electrophoresis cup and fill it up to nearly 1/4 of the electrophoresis cup. Tilt the electrophoresis cup and insert the electrode device slowly to avoid air bubbles in the cup; connect the electrode wire, put the electrophoresis cup into the sample tank smoothly and press it to the bottom gently.
4. Screenshot
Click "Active Image" and press "Start". The particles on the image will move left and right with the switching of the electrode, use the buttons on the main page: Q up, A down, Z left, X right, {, } to adjust the contrast, <, > adjust the brightness and so on to adjust the desired picture and picture quality, when there are 3 or more clear points within the range framed by the parallel and vertical red lines, press "Save", the program will capture the image for analysis. The program will intercept the image that can be analyzed.
5, analysis
(1) Press "Analyze Program" to enter the analysis interface.
There are three rectangular areas on the left side of the screen, respectively, for the calibration analysis area #1, #2, #3, and on the right side, there are three areas from top to bottom, the first one is the operation area, the second one is the environment parameter area, and the third one is the calibration data area. The analysis area #1 and #2 are two grayscale images of particle movement, which are the main basis of our analysis. When clicking on the particles with the mouse, the position of the cursor in the calibration data area will have a digital display, indicating the current calibration position. The analysis area #3 is obtained by subtracting #1 and #2 images, and is generally only used as a reference for analysis.
(2) Tap "Start", the system requires the input of a file name.
Press OK to use the default filename search.
(3) Analyze the image
First of all, in the analysis area #1 to determine a particle, the method is to move the mouse to the location of the particle, click to confirm the location of the particle in the calibration data area of the particle OA position will be displayed in the location of the data confirmed. Then, based on the correlation of the particle positions in the two images, the same particle (i.e., the particle in analysis area #1) is identified in analysis area #2, and its position data is displayed after the particle OB in the calibration data area, thus obtaining the first set of data. Next, other particles are identified in analysis area #1, and the second set of data is obtained in the same way. In this way, up to ten sets of data can be obtained. Generally, there are 3 or more groups.
Secondly, press 'continue', the system will call up the second group of images for analysis, the same way to analyze the data obtained, press 'save', the program requires to determine the polarity of the charge of the particles, enter '-' negative sign. ' negative sign.
Finally, press 'confirm', the system automatically calculates the analysis results.
(4) Press OK to launch the analysis calculation subroutine and return to the main interface for the next measurement.
Measure 3 to 5 ξ potential values for one sol sample.
Note: If there is an operation error in the analysis image, you can press the right button of the mouse to cancel the input data one by one and re-input. However, this operation is prone to errors. At this time, you can press 'CANCLE', exit the subroutine, directly press the analysis program to re-enter, and then operate according to the above relevant steps.