1、 South University of Science and Technology of ChinaDepartment of Materials Science and EngineeringComprehensive Experiments of MaterialsLab V: Preparation of mono-disperse polystyrene microspheresObjectivesTo master a basic method for preparation of mono-disperse polystyrene microspheresTo understa

2、nd the functions of the compositions of the dispersion polymerizationTo gain knowledge of the potential applications of the polystyrene microspheres in the fields of optical crystals, biotechniques, and/or electronicsAccording to the purposes of applications and the requirements for various sizes, p

3、olystyrene microspheres can be prepared using different methods or under different conditions. The diameter of polystyrene microspheres prepared by this experimental condition is about two micrometerIntroductionPolystyrene microspheres are typically used in biomedical applications due to their abili

4、ty to facilitate procedures such as cell sorting and immunio precipitation. Lower melting temperature enables polyethylene microspheres to create porous structures in ceramics and other materials. High sphericity of polystyrene microspheres, as well as availability of colored and fluorescent microsp

5、heres, makes them highly desirable for flow visualization and fluid flow analysis, microscopy techniques, health sciences, process troubleshooting and numerous research applications. They are usually prepared by emulsion, dispersion, or suspension polymerizations. Among those techniques, polymer par

6、ticles in 110 m with a narrow particle size distribution can be simply obtained by dispersion polymerization in organic media via a single step.Dispersion polymerization consists of monomer, initiator, and steric stabilizer and all the components should be dissolved in the polymerization medium such

7、 as alcohol. Dispersion polymerization starts in a homogeneous phase, then phase separation occurs when the nuclei precipitate from the medium to give growing particles. Therefore, one of the criteria for choosing the components is solubility in the polymerization medium. Since alcohols such as meth

8、anol and ethanol are most frequently adopted as the medium, alcohol-soluble initiators have been naturally chosen. In dispersion polymerization, the most frequently used initiators include azo-compounds such as an azo-bis-isobutyronitrile (AIBN), peroxide-compounds such as benzoyl peroxide (BPO), an

9、d redox typesandwhere poly (vinyl pyrrolidone) (PVP) or hydroxypropyl cellulose (HPC) is used as the most common steric stabilizer.In this experiment, the polystyrene microspheres size in 2 m will be synthesized by dispersion polymerization with poly(N-vinylpyrrolidone) (PVP) as the dispersant, etha

10、nol as reaction medium and AIBN as the initiator.ExperimentalMaterialsDistilled styrene: 12 ml Poly(vinylpyrrolidone) K30 (PVP, Mw = 40000): 2 g Crystalized AIBN: 120 mg Ethanol：150mL Pure waterApparatusHotplate with magnetic stirring.Oil bath.250 mL three-necked glass flask.Constant pressure funnel

11、.Thermometer (100 ) Ball-condenser with cooling water.Magnetic stirring bar.100 ml graduated cylinder.Centrifuge and centrifuge tubes.ProceduresAdd 2 g of PVP and a stirring bar into the flask. Place the flask with the condenser and the thermostat. And immerse the flask into the oil bath on the top

12、of the hotplate.Add 100 ml of ethanol into the flask.Start stirring and increasing the reaction temperature to 70 oC.Add 120 mg of AIBN after the inside temperature was steady and measured to be around 70 . .Add 12 ml of styrene monomer using an addition funnel within 5 to 10 minutes under stirring

13、(300 rpm).Under stirring, keep the inner temperature at around 70 C for 3 hours (Notice: The temperature may be in a range of 65 70 C, but not higher than 76C).Turn off the hot plate and lift up the flask from the oil bath. After cooling down, put the mixture in 4 centrifuge tubes, centrifuged at 50

14、00 rpm for 10 minutes and dump the supernatant.Re-suspension the precipitate again in 30 mL of 50% ethanol aqueous solution. And centrifuged this mixture again to get the product.Characterized the sizes of the particles using the crystalline phase microscope.Determination of the yieldAdd 0.3-0.5 g o

15、f the product to three accurately weighed empty weighing bottles;Put the weighing bottles in an oven at 60 under vacuum and baked for 0.5 hours; Take out the bottles and then put in a desiccator; Weigh them and calculate the yield after they cool down.Clean all the glass instruments and tidy the des

16、k.ReportDescribe the goal, introduction, materials, apparatus, and experimental in your own words.Answer the following questions:What are the characteristics of solvent polymerization, suspension polymerization, emulsion polymerization and dispersion polymerization? How to control the surface proper

17、ties and sizes of the particles? How to functionalize further of these particles and apply these microspheres?Reference:Anthony J. P., Wayne L. and James M. Dispersion Polymerization of Styrene in Polar Solvents. 6. Influence of Reaction Parameters on Particle Size and Molecular Weight in Poly(N-vin

18、ylpyrro1idone)-Stabilized Reactions, Macromolecules, 1990, 23: 3104-3109. HYPERLINK /science/article/pii/S0021979706000075 Jeongwoo L., HYPERLINK /science/article/pii/S0021979706000075 Jin U. H., HYPERLINK /science/article/pii/S0021979706000075 Soonja C., HYPERLINK /science/article/pii/S0021979706000075 Chang-Soo L., and HYPE