Study of fabrication of PMMA microspheres for applications in large scale manufacturing

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY HOANG MINH KIEN STUDY OF FABRICATION OF PMMA MICROSPHERES FOR APPLICATIONS IN LARGE SCALE MANUFACTURING MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY HOANG MINH KIEN STUDY OF FABRICATION OF PMMA MICROSPHERES FOR APPLICATIONS IN LARGE SCALE MANUFACTURING MAJOR: NANOTECHNOLOGY CODE: 8440140.11QTD RESEARCH SUPERVISOR: Dr NGUYEN TRAN THUAT Dr PHAM TIEN THANH Hanoi, 2020 ACKNOWLEDGEMENTS I would like to express my gratefulness to my first supervisor Dr Nguyen Tran Thuat, Nano and Energy Center, Hanoi University of Science, Vietnam National University, for giving me guidance and help me finalize the thesis During the research, I have learned from him the way of processing results after each experiment and important skills when working in scientific field I would like express my gratitude to my second supervisor Dr Pham Tien Thanh, Vietnam Japan University, for giving me support and encouragement His ideas and suggestions were useful for not only my current but also future work I also would like to show my appreciation to MK Group for the fund of the project for most of the chemicals and equipment I would like to sincerely thank Nano and Energy Center for providing me the working space and allow me to use their equipment for my research I would like to thank my project group members Nguyen Ngoc Anh, Bui Thi Nga and Chu Hong Hanh for all the assistance and help me accomplish these results I learned a lot from working with them, especially how to work in a team and discuss with others to advance the work Finally, I am deeply grateful for the knowledge, the encouragement and support from lecturers and my friends from Vietnam Japan University It has been two meaningful years of studying, training myself and working in this Master program I will bring all these experiences with me and utilize them for my career in the future TABLE OF CONTENTS Page INTRODUCTION 1.1 Poly(methyl methacrylate) microspheres and anisotropic conductive films 1.2 Aim of work 1.2.1 Particles quality requirement 1.2.2 Large scale manufacturing 1.3 Poly(methyl methacrylate) fabrication 1.3.1 Polymerization 1.3.2 Dispersion polymerization 1.3.3 Suspension polymerization 1.3.4 Microwave-assisted polymerization 10 1.3.5 Seeded polymerization 10 1.3.6 Polymerization using microfluidic system 11 EXPERIMENTS .15 2.1 Dispersion polymerization 15 2.2 Suspension polymerization 16 2.2.1 Conventional heating polymerization 16 2.2.2 Microwave-assisted polymerization 16 2.3 Seeded polymerization 17 RESULTS AND DISCUSSION .18 3.1 Dispersion polymerization 18 3.1.1 250-ml reaction container 18 3.1.2 500-ml reaction container 21 3.1.3 2000-ml reaction container 24 3.2 Suspension polymerization 29 3.2.1 Conventional heating polymerization 29 3.2.2 Microwave-assisted polymerization 30 3.3 Seeded polymerization 32 3.4 ACF demonstration 34 3.4.1 Silver-plating of PMMA 34 3.4.2 ACF Fabrication 36 CONCLUSION 39 REFERENCES .40 LIST OF ABBREVIATIONS ACF Anisotropic Conductive Film BPO Benzoyl peroxide DI Deionized ICC Integrated Circuit Card MeOH Methanol MMA Methyl methacrylate PCB Printed Circuit Board PMMA Poly (methyl methacrylate) PVA Polyvinyl alcohol PVP Polyvinylpyrollidone RPM Round per Minute RT Room Temperature SEM Scanning Electron Microscope LIST OF TABLES Page Table 3.1 Reaction conditions for studying effect of MMA on PMMA products using 250-ml reaction container 18 Table 3.2 Reaction conditions for studying effect of BPO on PMMA products using 250-ml reaction container 20 Table 3.3 Reaction conditions for studying effect of BPO on PMMA products using 500-ml reaction container 21 Table 3.4 Reaction conditions for studying effect of MMA on PMMA products using 500-ml reaction container 21 Table 3.5 Reaction conditions for studying effect of MMA on PMMA products using 2000-ml reaction container 24 Table 3.6 Polymerization efficiency when varying the monomer amount 25 Table 3.7 Reaction conditions for studying effect of BPO on PMMA products using 2000-ml reaction container 27 Table 3.8 Reaction conditions for suspension polymerization .29 Table 3.9 Reaction condition for microwave-assisted suspension polymerization 30 Table 3.10 Reaction condition for seeded polymerization 32 Table 3.11 Electrical resistance results of conductive sample 36 Table 3.12 Electrical resistance result of the fabricated ACF 38 LIST OF FIGURES Page Figure 1.1 Particles comparison of a) PMMA; b) PS products sharing the same polymerization process (solvent, initiator and surfactant) Figure 1.2 Bonding mechanism of a conventional ACF Figure 1.3 a) Model for bonding a flip chip and a substrate in a smart card; b) Schematic for connection between bumps of integrated circuit chip and terminals of a glass substrate formed by an ACF .4 Figure 1.4 Three main steps in polymerization A: Initiation, B: Propagation, C: Termination Figure 1.5 Particle size ranges of different polymerization methods .7 Figure 1.6 Schematic for dispersion polymer mechanism .8 Figure 1.7 Schematic for suspension polymer mechanism Figure 1.8 Schematic for seeded polymerization process 11 Figure 1.9 Schematic of the channel layouts 12 Figure 1.10 Patterns of droplet formation observed in the T-junction/pocket 13 Figure 1.11 Microwave heating and conventional heating integrated microfluidic systems 13 Figure 2.1 Apparatus for 250-ml and 500-ml Reaction Containers a) Schematic; b) Real system for 500-ml Reaction Container 15 Figure 2.2 Apparatus for 2000-ml Reaction a) Schematic; b) Real system 15 Figure 2.3 Apparatus for microwave-assisted polymerization a) Schematic; b) Real system 17 Figure 2.4 Schematic of apparatus for seeded polymerization 17 Figure 3.1 Microscopic images of samples a) A% MMA; b) 1.3A% MMA and c) 1.5A% MMA 19 Figure 3.2 Microscopic images of damples a) B% BPO; b) 1.3B% BPO 20 Figure 3.3 Microscopic images of samples a) 1.3B% BPO; b) 2B% BPO and 3B% BPO 22 Figure 3.4 Microscopic images of samples a) 0.5A% MMA; b) 0.8A% MMA and c) A% MMA 23 Figure 3.5 Microscopic image of the sample A% MMA and 2B% BPO .25 Figure 3.6 Microscopic images of samples a) 1.1A% MMA; b) 1.3A% MMA and c) 1.5A% MMA 26 Figure 3.7 Microscopic images of samples a) 2B% BPO; b) 1.7B% BPO; c) 2.3B% BPO and d) 2.7B% BPO 28 Figure 3.8 Microscopic images of samples a) A% MMA; b) 0.3A% MMA 30 Figure 3.9 Microscopic images of microwave-assisted polymerization samples after a) h of reaction; b) h of reaction 31 Figure 3.10 Microscopic images of conventional heating polymerization samples after a) h of reaction; b) h of reaction 32 Figure 3.11 a) Microscopic image of PMMA seeding particles; b) Microscopic image of products after 60 min; c) Microscopic image of products after 100 33 Figure 3.12 Sample fabricated using 2000-ml reaction container, with MMA% = 1.1A% and BPO = 2B % a) optical microscopic image and b) SEM image 34 Figure 3.13 Silver-plated PMMA particles a) optical microscopic image; b) SEM image 35 Figure 3.14 Schematic for electrical resistance measurement system 36 Figure 3.15 Optical microscope of anisotropic conductive films after fabrication using conductive silver-plated PMMA microspherical particles 37 Figure 3.16 Schematic for measuring anisotropic conductivity of fabricated ACFs 38 ABSTRACT Monodispersed poly(methyl methacrylate) microspheres with the size from µm to 13 µm were prepared by using a dispersion polymerization method Three reaction containers with volume of 250 ml; 500 ml and 2000 ml were used to study the scalability of the fabrication process In the case of 2000-ml reaction container, more than 80 g of microspheres were synthesized with high efficiency, which could be utilized for the fabrication of more than 100 m of anisotropic conductive film The products were proved to have a good quality and to be ready for carrying forward to the silver-plating process and the fabrication of anisotropic conductive films Other two methods including microwave-assisted polymerization and seeded polymerization were also performed to decrease the reaction time and to increase particles size However, the two methods still need more optimization to yield better quality of products and efficiency of process INTRODUCTION 1.1 Poly(methyl methacrylate) microspheres and anisotropic conductive films Polymers extracted from nature in the early days were already utilized in the production of clothing, buildings and daily equipment However, only since the th revolution of synthetic polymers in the first half of 20 century - the period which can be known as the age of polymers, this material had attracted great deal of attention and had been developed rapidly due to their surprisingly low density, high tensile strength and good flexibility During this time, especially from 1930 to 1960, almost all the polymers we commonly use today had been discovered, for example, Polyethylene terephthalate (PET) for plastic bottles; Polyvinylchloride (PVC) for pipes or waterproof clothing; and Poly(methyl methacrylate) (PMMA) used for transparent container such as acrylic glass for aquarium Initially, polymers were developed for the use of macroscale manufacturing such as clothing, transportation or food preservation With the growth of microtechnology, polymer microparticles have attracted huge attention due to their flexibility, spherical shape and low-cost production Among the types of polymer particles, PMMA and Polystyrene (PS) microspheres are the most popular The chemicals used for the production of these two polymers are cheap and commercially available as well as the polymerization yields high efficiency Comparing PMMA with PS, the particles size overall for PS is smaller, mostly smaller than µm, while size of PMMA can vary from submicron size to hundreds of micro in diameter Figure 1.1 compares the particles fabricated by polymerization of PMMA and PS using the same reaction condition, size of PMMA microspheres is significantly larger than size of PS microspheres PMMA can yields larger particles size of µm, and even larger than 10 µm with some modification In contrary, for PS polymerization, large particles of or µm can be hardly obtained, even with modified conditions to increase the particles radius PMMA can be observed to be more flexible in terms of creating polymer particles having micro size, indeed, PMMA particles can as large as 100 µm Table 3.7 Reaction conditions for studying effect of BPO on PMMA products using 2000-ml reaction container Sample name 13 14 15 16 In the study of initiator effect, we use the high amount of MMA at 1.5A% instead of A% to see if we can maximize the use of chemicals for our process However, although the result follows the trend, the monodispersity was not achieved as expectation When increasing the amount of initiator to 2.3B% and 2.7B%, the particles become smaller in major but size distribution is not narrower At 2.3B% BPO in MMA, size varies from to 22 µm with majority of to µm particles (Figure 3.7c); and at 2.7B%, size range is from to 10 µm (Figure 3.7d) When decreasing BPO to 1.7B%, larger particles is formed but the size distribution is somehow narrower where the size varies from to 14 µm (Figure 3.7b) This phenomenon can be explained with the nucleation rate of the dispersion polymerization Increasing the amount of MMA leads to a more amount of oligomer particles, the faster nucleation rate, and hence less thermal stability When decreasing the amount of initiator, the nucleation rate reduces making nucleation step more thermally stable which ensures the same nucleation of macroradicals In can be seen that, the thermal stability of nucleation step is important in determine the size distribution of products from dispersion polymerization 27 Figure 3.7 Microscopic images of samples a) 2B% BPO; b) 1.7B% BPO; c) 2.3B % BPO and d) 2.7B% BPO 28 3.2 Suspension polymerization 3.2.1 Conventional heating polymerization In suspension polymerization, both monomer and initiator is insoluble in the medium In our experiment, DI water is used as solvent as it cannot dissolve MMA and BPO Polyvinyl alcohol (PVA) surfactant was used instead of PVP because PVP tended to give bigger particles with size from 100 µm to mm in our optimization experiment Table 3.8 Reaction conditions for suspension polymerization Sample name 17 18 Two concentration of MMA in water is studied, A% and 0.3A% From Figure 3.8, it can be seen that when using high concentration of monomer, the particles seems to be agglomerated due to high number of droplets during agitation This result in a way agree with the equation for the average size of polymer product (Equation 1) The high concentration of monomer leads to a high volume ratio of monomer to liquid medium, hence, the size distribution becomes wider with increasing average size or in our case, higher probability of agglomeration When decrease the monomer usage to 0.3A%, no agglomeration is observed However, the size distribution is wide with value ranging from to 80 µm, with big particles majority The obtained product does not satisfy the requirement for the particles used for ACF; however, the condition can still be carried for the investigation of microwave effect on the polymerization 29 Figure 3.8 Microscopic images of samples a) A% MMA; b) 0.3A% MMA 3.2.2 Microwave-assisted polymerization For the microwave, same condition as using conventional heat was used in order to compare the reaction rate of the two heating strategies Microwave with power 600 W was used, which means the heating to polymerization point is very fast using microwave Table 3.9 Reaction condition for microwave-assisted suspension polymerization Sample name 19 From Figure 3.9 and Figure 3.10, it can be seen that the reaction rate of using microwave heating for polymerization is much faster than using the normal convention heating method After h and h of polymerization using conventional 30 heating, the number of big particles is small, while the small particles are majority Meanwhile by using microwave heating, after h, a large number of particles are formed and after h, the reaction finished and the conversion of particles is high at around 82% Comparing to the normal method taking 24 h for the reaction to finish, using microwave increase the reaction rate drastically However, with the use of suspension polymerization, the obtained particles have a wide size distribution, and most of particles are larger than the required size from to 30 µm In further research, by changing the power of microwave to lower amount (100 W; 200 W or 300 W), we can apply this heating strategy for methanol as using lower power microwave, boiling point of methanol is not exceeded significantly lead to unstable reaction Figure 3.9 Microscopic images of microwave-assisted polymerization samples after a) h of reaction; b) h of reaction 31 Figure 3.10 Microscopic images of conventional heating polymerization samples after a) h of reaction; b) h of reaction 3.3 Seeded polymerization The seed particles were prepared by dispersion polymerization using 500-ml reaction containers, and the average size of microspheres is 7.5 µm For the reaction condition, monomer is drop wisely rather than all at once in order to prevent the deform effect of monomer to the polymer particles Moreover, after finishing adding, the mixture was kept stirring for 30 for the seed particles become swollen by monomer, which is an essential point of this method Table 3.10 Reaction condition for seeded polymerization Sample name 20 From Figure 3.11b, it can be seen that after 60 min, larger particles with size from 25 to 35 µm were fabricated However, the number of particles having small size are formed by the polymerization of monomer not surrounding the polymer These small particles is the main reason after 100 of seeding, the particles become very large with wide size distribution (Figure 3.11c) Furthermore, at this period, the particles become non-spherical due to the uncontrolled amount of macroradicals newly formed The reaction needs to be optimized with the chosen monomer amount as well as initiator amount to prevent this new polymer from forming while the seeding process is prioritized Figure 3.11 a) Microscopic image of PMMA seeding particles; b) Microscopic image of products after 60 min; c) Microscopic image of products after 100 33 3.4 ACF demonstration 3.4.1 Silver-plating of PMMA For the next step of the project, a silver-plating process, particles which were prepared from the 2000-ml reaction container experiment using 1.1A% MMA in methanol and 2B% BPO in MMA was used The process contains three main steps: pre-treatment with stannous chloride, silver “seeding” and electroless plating The products obtained from this step are the conductive silver-PMMA shell-core particles Figure 3.12 shows the microscopic and SEM images of initial particles having smooth surface After plating, Silver layer surrounding polymer particle can be observed using SEM and light reflection can be observed using the optical microscope (Figure 3.13) Figure 3.12 Sample fabricated using 2000-ml reaction container, with MMA% = 1.1A% and BPO = 2B % a) optical microscopic image and b) SEM image 34 Figure 3.13 Silver-plated PMMA particles a) optical microscopic image; b) SEM image Besides SEM observation, another method to investigate the quality of silver on PMMA particles is to measure electrical conductivity 0.2 g of silver-plated particles was added to the measurement system illustrated in Figure 3.14 and the electrical resistance of sample is measured Table 3.11 shows the results of this measurement Before compression, the electrical resistivity is 32 Ω Upon compression, the conductive particles in the sample holder stack close together, hence, the resistance reduces For our sample, when using compression pressure around 600 bar, the particles are well stacked and the measured electrical resistance is below Ω, which means the plated particles have a good electrical conductivity 35 The silver-plated PMMA microspherical particles satisfy the conductive particles quality used for ACF fabrication, hence the sample was carried to the next process Figure 3.14 Schematic for electrical resistance measurement system Table 3.11 Electrical resistance results of conductive sample Compression Pressure (bar) 3.4.2 ACF Fabrication The conductive particles were brought to the final step of making anisotropic conductive films In this process, conductive particles were mixed thoroughly in a polymer matrix The mixture was casted on a piece of decal and a doctor blade is used to control the thickness and smoothness of the films The sample was let dried in air ambient for and a sample was taken for measurement Figure 3.15 shows the microscopic image of our ACF products The particles inside the film maintain their shape and distributes nicely as no significant agglomeration is observed throughout the film 36 Figure 3.15 Optical microscope of anisotropic conductive films after fabrication using conductive silver-plated PMMA microspherical particles Figure 3.16 illustrates the schematic for the anisotropic conductivity measurement of our fabricated ACFs In order to investigate the anisotropic conductivity of the ACF, a printed circuit board (PCB) was designed with 10 separated conductive sections made from copper Then the ACF was sandwiched between two aligned PCBs The PCBs should be aligned properly to ensure the electrical conductivity between respective sections For example, section should have electrical conductivity with section of other PCB when checking electrical resistance, but have no conductivity with section or of the same board After an ACF being put into the system and PCBs alignment, a measurement was made at rest point to ensure there is no electrical contact between the two boards Then the PCBs were o heated to 200 C for 10 min, a pressure was applied for compression and electrical measurement was taken Finally, heating and compressing were stopped and electrical resistance of PCBs was taken at resting point A good ACF should show a 37 low electrical resistance or good conductivity between respective PCB sections, but no electrical conductivity with others According to Table 3.12, for our ACF sample, even though most parts show good conductivity with low resistance, there are still some connection without conductivity Still, no conductivity with different section numbers is observed, which shows the anisotropic properties of the ACF In conclusion, the fabrication of all processes needs to be optimized in further research to obtain high quality ACFs Figure 3.16 Schematic for measuring anisotropic conductivity of fabricated ACFs Table 3.12 Electrical resistance result of the fabricated ACF Compression pressure (bar) (before) 300 600 (after) O.L : over loaded 38 CONCLUSION With the use of dispersion and suspension polymerization method, PMMA microspheres can be synthesized Regarding dispersion polymerization, scalability and large scale manufacturing is proven to be achievable By increasing the reaction containers volume and optimizing the reaction conditions for each 250-ml; 500-ml and 2000-ml containers, monodispersed particles having size smaller than 13 µm were produced Moreover, the reaction has a high efficiency more than 75% and more than 80 g of particles can be produced in 24 h using the 2000-ml containers reaction condition This amount of particles theoretically can be used for the fabrication of more than 100 tapes of ACF which used for the connection of millions of ICC The synthesized PMMA microspherical particles were carried to the next process of Silver-plating and ACF fabrication process and good results are obtained in terms of electrical conductivity For the next step of the project, bigger container volume such as 10 l or 20 l will be employed for the industrial scale manufacturing Also, microwave-assisted polymerization and seeded polymerization will be further investigated and optimized for the reduction in reaction time as well as monodispersed particles size increase 39 REFERENCES Michael F.Ashby (2009), Nanomaterials, Nanotechnologies and Design, 1820 Songjun Li (2004), Biosystem, 77(1-3), 25-32 Eunhee Kim (2012), Material Chemistry and Physics, 134, 814-820 Young-Sung Eom (2008), Microelectronic Engineering, 85, 327-331 Smith (2008), William F ,Hashemi, Javad, Foundations of Materials Science and Engineering (4th ed.), 509 Chris Corum (2005, May 24), A primer on „flip chip‟ manufacturing techniques for smart card ICs, retrieved from https://www.secureidnews.com/ Dexerials Corporation (2014, October 29), Development of a ParticleArrayed Anisotropic Conductive Film (ACF) for Chip on Glass (COG) connection with Minimum Bump space of 10 µm, retrieved from https://www.dexerials.jp/ R.Ashady (1992), Colloid Polym Sci, 270, 717-732 S.Shen (1993), Journal of Polymer Science Part A: Polymer Chemistry, 31(6), 1393-1402 10 J.Jacob (1997), Journal of Applied Polymer Science, 63(6), 787-797 11 Liu Z (2013), Journal of Applied Polymer Science, 127, 628 12 Richard Hooganboom (2016), Microwave-assisted Polymer Synthesis, 8-9 13 Mingliang Ma (2012), Soft Engineering and Knowledge Engineering: Theory and Practice, 853-861 14 Takashi Nishisako (2004), Chemical Engineering Journal, 101, 23-29 40 ... scale manufacturing In terms of the PMMA microspheres fabrication using for large scale manufacturing, another main factor studied in the research is the scalability For example, in order to produce... for studying effect of BPO on PMMA products using 250-ml reaction container 20 Table 3.3 Reaction conditions for studying effect of BPO on PMMA products using 500-ml reaction container... terms of creating polymer particles having micro size, indeed, PMMA particles can as large as 100 µm Therefore, for the purpose of providing the polymer microspheres for the use of most of current