Fabrication of coreshell structures of modified poly(divinylbenzene)gold and of carboxylic functional polystyrenegold

Master Thesis Fabrication of Core/shell Structures of Modified Poly(divinylbenzene)/Gold and of Carboxylic Functional Polystyrene/Gold By KIM XUYEN PHAN Advisor: Professor YOUNGKWAN LEE The Graduate School of Sungkyunkwan University Department of Chemical Engineering June 2006, Suwon, Korea CHAPTER INTRODUCTION Electronic package technology has many applications in the electronics industry, and is particularly useful in the computer, information technology, mobile communications, and high technology electronic appliance industries [1-3] In particular, flip chip technology has numerous applications in the smart cards, liquid crystal displays, and communication system industries [4-5] Flip chip technology was developed based on anisotropic conductive connection processes using solder as the conducting particles Commercially conducting particles are composed normally composed of materials such as Ni, Au/polymer, Ag, and insulating resins [6-7] In this context, conducting polymers which have greater reliability lower resistance and higher adhesives strength, guarantee a better flip interconnection on an organic substrate For this purpose, several routes for the fabrication of gold shells on polystyrene (PS) cores have been investigated [8-9] Khan et al [10] examined the morphology of metallic gold overlayers deposited onto conducting polymer-coated PS using an electroless deposition method Their results showed that the gold nanoparticles were randomly dispersed over the surfaces of the PS particles It is believed that these gold-coated, conducting polymer-coated PS particles might be useful as a novel supportive catalyst Davidov et al [1] combined self-assembly and surface seeding methods using polyelectrolytes as adhesive glue between the PS core and gold nanoparticles They produced clusters of Au nanoparticles on a PS surface instead of a continuous gold shell Gao et al [11] and Ming et al [12] groups previously developed continuous metallic nanoshells on PS particles using a layer-by-layer deposition -1- technique with 4-aminothiophenol as the binder, and a solvent-assisted route, respectively However, very rough gold shells were obtained in both cases In most cases, it is very difficult to tune the thickness and surface roughness of the metallic shells, and only rough gold shells are obtained In an attempt to overcome this drawback, we investigated two novel methods to fabricate core-shell structures of both modified-polydivinylbenzene/gold (modified-PDVB/Au) and carboxylic functional polystyrene/gold (PS-COOH/Au) Part A: A novel (modified-PDVB)/Au core-shell structure was investigated by reducing a gold-phenanthroline complex to produce Au nanoparticles followed by gentle growth of gold layer using the HAuCl4/NH2OH system The PDVB cores (2-4 ) were synthesized by precipitation polymerization to yield a fully crosslinked structure [13-20] The surface of the cores was then modified by introducing thiol and sulfonic acid groups The presence of -SO3H and –SH groups on the surface of the PDVB cores facilitated the deposition of gold nanoparticles by imparting hydrophilicity to hydrophobic cores and anchoring the gold nanoparticles The resulting gold nanoparticles served as gold seeds for shell growth which was obtained using a mixed solution of HAuCl4 and NH2OH to obtain completely uniform gold shells The three advantages of this deposition method are as follows: 1) (-SO3H and –SH)modified PDVB cores are more effective in depositing gold than the polyelectrolyteemployed PS cores In particular, PDVB-SO3H cores were successfully produced with high –SO3H concentration but a perfect core-shape was still maintained This overcomes -2- the morphological deformation problems associated with linear or partly crosslinking the PS cores during the sulfonation reaction [22] 2) The PDVB core is a fully crosslinked polymer with good physical and chemical properties, as well as high thermal resistance They can withstand pressure and heat, which makes these particles suitable for creating the necessary electrical contact This electrical contact needs to be between the two bond pads of the chip and the substrate in the anisotropic conductive adhesive [21] 3) The method is facile, versatile, and suitable for the coating other metals whose complex or cations can be reduced in solution Part B: We investigated a novel (PS-COOH)/Au core-shell structure prepared by impregnating an aqueous gold nanoparticle solution into the PS-COOH cores The presence of polar carboxylic groups on the surface of PS core facilitated the deposition of the gold nanoparticles The resulting gold nanoparticles served as gold seeds for the gentle shell growth which was obtained by employing a mixed solution of Au(OH)3 and NH2OH to obtain completely uniform -3- and smooth gold shells CHAPTER THEORETICAL BACKGROUND 2-1 Core-shell structure To make gold nanoshells, manufactured gold nanoparticles are attached to the functionalized surface of a somewhat larger sphere of a core such as SiO2 or polystyrene, and then grown by further reduction or by layer-by-layer attachment of metallic particles (fig 2.1) Functionalizing on the core surface is performed with something like an ωterminated trialkoxyorganosilane [22-23] in the case of SiO2 or 2-aminoethanethiol hydrochloride in the case of polystyrene spheres [24] Figure 2.1 Randomly generated gold-on-core with monodisperse gold particles, shown from left to right growth of gold nanoshell by further reduction -4- 2-2 Application of conductive core-shell particles The research relates to a method of preparing the anisotropic conductive film (ACF) for interconnection of flip chips onto plastic substrates [21] Anisotropic conductive adhesive excels from isotropic conductive sticking and soldering in that it is only conductive in the Z-axis (vertical direction), whereas the aforementioned procedures conduct electrical current in all directions [25-26] Thus, anisotropic conductive adhesive can be applied over the whole chip surface, improving manipulation and enabling further miniaturization (Fig 2.2) The anisotropic conductive adhesive is filled with conductive particles having the same dimensions, and with a content that is so selected that the particles are not coming in contact with each other or only insignificantly With adequate pressure the particles create electrical contact between the bondpad of the chip and the bondpad of the the subtrate Through the input of heat the adhesive becomes hard, which leads to an intact mechanical and electrical connection [27-28] -5- Figure 2.2 Operating principle of anisotropic adhesive -6- 2-3 Preparation of polydivinylbenzene by the precipitation polymerization A variety of polymer dispersions, consisting of suspending medium and polymer particles, are an important class of polymeric materials Because the properties of polymer dispersions are dominated by the base polymer, such materials have been utilized in a wide range of traditional applications, including coatings, adhesives, inks, leather finishing, and construction [29] Furthermore, polymer dispersions in a suspension state or polymer particles in a dried state are now being used in more sophisticated areas by precise controlling the chemical or physical characteristics of the base polymer, where special attention is paid to characteristics include size, uniformity of the size, functionality of the base polymer, morphology of the polymer particles, and degree of crosslinking Polymer particles with optimized characteristics also can be candidate materials for use in information technology, electric and electronic applications, and biotechnology [30-32] Unfortunately, to date, no versatile method has been developed that can produce polymer spheres with the desired size and uniformity by a single-step process Therefore, different methods or sometimes one method that combines several processes should be carefully chosen to prepare target polymers with desirable spherical particles For example, submicron-sized monodisperse polymer spheres up to are prepared by conventional (macro), mini-, or microemulsion polymerization techniques using water as the reaction medium Dispersion polymerization simply provides supermicrometer-sized monodisperse polymer spheres in the range of 1–15 in organic media Suspension polymerization is also used to prepare supermicrometer-sized polymer beads in the broad -7- range of 20–2000 nm in aqueous media, especially when size uniformity is not a concern Based on those conventional polymerization methods, several variations have been developed, including Shirasu porous glass (SPG) membrane emulsification technique [33-34] electrostatic coagulation method [35-36] and seeded polymerization [37-40] In these processes, having a long and meticulous procedure or needing additional instruments are substantial disadvantages Monodisperse micron-sized polymer spheres that have a highly crosslinked structure cannot be easily obtained by any of the abovementioned methods By conventional methods, (1) micronsized polymer particles are not produced in emulsion polymerization, (2) highly crosslinked spherical polymer particles are not obtained in dispersion polymerization, and (3) monodispersity of particles is not achieved in suspension polymerization To prepare such polymer particles Stoever’s group [41] relatively recently introduced precipitation polymerization which the stabilization mechanism is quite different from that in emulsion, dispersion or suspension polymerization Surprisingly, no chemical agent is involved in the stabilization mechanism for the formation of spherical particles from crosslinkable monomers such as divinylbenzene or diethyl glycol dimethacrylate The stabilization of the particles originates from the resistance against the interfusion of particles caused by a high degree of crosslinking [42] Therefore, using crosslinkable monomers is essential to form spherical particles in precipitation polymerization.In the precipitation polymerization of vinyl monomer, it has been thought that discrete (i.e., uncoagulated) spherical particles are not synthesized because no stabilizing agent is involved in the course of the polymerization Therefore, the formation of agglomerated final particles is evident even under a mild agitation [42] -8- Mechanism of the precipitation polymerization method: Because pores were not detected on the surface of the particles collected, not only in the course of polymerization, but also when changing the concentration of the polymerization ingredients, a new mechanism for the formation of the microspheres in the precipitation polymerization is proposed based on the morphology of the particles and the specific surface area values, as illustrated in figure 2.3 At the initial stage of precipitation polymerization, the mechanism is identical to that proposed by Stoăver [43], of which primary stable microspheres are 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of thiol and sulfonic acid groups The degree of sulfonation was measured according to its ion exchange capacity (IEC, 5.72 meq/g), and the surface concentration of thiol group was examined by FT-IR and XPS The modified PDVB cores were immersed in a solution of a gold-phenanthroline complex and subsequently reduced to form gold-seeds These were grown in a solution of HAuCl4 and NH2OH to - 70 - form gold nanoshells The effects of the functional groups on the PDVB cores on fabrication of the core-shell structure were examined SEM and XPS were used to characterize the gold nanoshells The presence of the functional groups could be of great assistance for the gold shell formation Keywords: polydivinylbenzene, modification, core-shell, gold-phenanthroline complex - 71 - Preparation of a novel carboxylic functional polystyrene/gold core-shell structure by the impregnation of gold nanoparticles Kim Xuyen Phan, Misuk Cho†, Jae-Do Nam‡ and Youngkwan Lee* Dept of Chemical Engineering and †Polymer Technology Institute ‡ Department of Polymer Science & Engineering Sungkyunkwan University, Suwon, Korea 440-746 Tel.:+82-31-290-7248 Fax.:+82-31-290-7272 *Correspondance:yklee@skku.edu Abstract A novel PS/Au core-shell structure was prepared by the electroless deposition of gold onto carboxylic acid functional PS cores (PS-COOH) The PS-COOH cores with a diameter of µm were synthesized by the copolymerization of methacrylic acid and divinyl benzene on the surface of polystyrene seed particles having a diameter of 1.3 µm The presence of the carboxylic acid moieties was confirmed by FT-IR Gold nanoparticles were initially impregnated into the PS-COOH cores and the uniform and smooth gold shells were grown gently on the PS-COOH cores by employing a mixed aqueous solution of Au(OH)3 and NH2OH The characteristics of the PS-COOH/Au core-shells were investigated by SEM, EDS and XPS - 72 - Key words: gold nanoparticles, gold nanoshells, core-shell, carboxylic functional polystyrene, micro-particles - 73 - CONTENTS Figure Captions iv CHAPTER INTRODUCTION .1 CHAPTER THEORETICAL BACKGROUND .5 2-1 Core-shell structure 2-2 Application of conductive core-shell particles 2-3 Preparation of polydivinylbenzene by the precipitation polymerization 2.4 Dispersion polymerization .12 CHAPTER EXPERIMENTAL SECTION 16 -i- Part A: Fabrication of modified-poly(divinybenzene)/Au core-shell structure 17 Abstract .17 A.1 EXPERIMENTAL SECTION 17 A.1.1 Materials .18 A.1.2 Synthesis 18 (a) Preparation of PDVB cores by Rotation-Precipitation Polymerization (b) Chloromethylation of the PDVB cores (PDVB-Cl) 20 (c) Conversion of the chloro group into the thiol group (PDVB-SH) .21 (d) Sulfonation of the PDVB cores 22 (e) Preparation of modified PDVB/Au core-shells 22 A.1.3 Characterization 24 A.2 RESULTS AND DISCUSSION 25 A.2.1 Preparation of PDVB cores 25 A.2.2 Preparation of modified-PDVB cores .28 A.2.3 Preparation of modified PDVB/Au core-shells33 A.3 CONCLUSION FOR PART A 38 PART B: Preparation of a novel carboxylic functional polystyrene/gold core-shell structure by the impregnation of gold nanoparticles 39 Abstract .39 B.1 EXPERIMENTAL 40 - ii - 18 B.1.1 Materials .40 B.1.2 Synthesis .40 (a) Preparation of the uniform PS-COOH cores 42 (b) Preparation of aqueous gold nanoparticle solution43 (c) Impregnation of gold nanoparticles into the PS-COOH cores 45 (d) Gold shell growth .45 B.1.3 Characterization 46 B.2 RESULTS AND DISCUSSION 47 B CONCLUSION FOR PART B 63 CHAPTER 4: CONCLUSION 64 Acknowledgements 65 References .66 - iii - Figure Captions Chapter 2: Figure 2.1 Randomly generated gold-on-core with monodisperse gold particles, shown from left to right growth of gold nanoshell by further reduction Figure 2.2 Operating principle of anisotropic adhesive Figure 2.3 Proposed mechanism for the formation of stable nonporous spherical particles in precipitation polymerization 11 Figure 2.4 Three models for the formation of particles nuclei 15 Chapter 3: Part A: Figure 3A.1 Photo of rotation evaporator for DVB precipitation polymerization Figure 3A.2 Chloromethylation of the PDVB cores20 Figure 3A.3 Conversion of the chloro group into the thiol group 21 Figure 3A.4 Structure of [AuCl2( phen)]Cl .22 - iv - 19 Figure 3A.5 Overall scheme for the preparation of (a) sPDVB/Au core-shells, (b) PDVB-SH/Au core-shells and (c) sPDVB-SH core-shells 23 Figure 3A.6 SEM images of the PDVB cores prepared in neat acetonitrile with DVB volume concentration of (a) %, (b) %, (c) % and in a toluene/acetonitrile solvent mixture (3 vol % DVB) with a toluene fraction of (d) 5%, (e) 10 % 27 Figure 3A.7 FTIR spectra of (1) PDVB, (2) PDVB-Cl and (3) sPDVB-SH 29 Figure 3A.8: XPS spectra: (a) survey and (b) S2p XPS core-line spectrum of the PDVB-SH 30 Figure 3A.9: EDS analysis of (a) PDVB-Cl, (b) PDVB-SH, (c) sPDVB-SH 31 Figure 3A.10 SEM image of the sPDVB-SH cores at different bar-scale 32 Figure 3A.11 SEM images of (a) sPDVB/Au core-shells, (b) PDVB-SH/Au coreshells and (c) sPDVB-SH core-shells34 Figure 3A.12 EDS analysis of the sPDVB-SH/Au core-shells 36 Figure 3A.13 XPS spectra: (a) survey and (b) Au4f XPS core-line spectrum of the sPDVB-SH/Au core-shells 37 Part B: Figure 3B.1 Overall scheme for the preparation of the (PS-COOH)/Au core-shell structure 41 Figure 3B.2 Procedure of preparing aqueous gold nanoparticle solution Figure 3B.3 SEM images of PS-seeds with (a) 1% and (b) 2% AIBN, at constant of co-solvent ratio (ethanol : methoxy ethanol: water = 0.55: 0.4: 0.05 -v- 44 w/w) 48 Figure 3B.4 SEM images of PS-seeds with the volume ratio of ethanol/methoxy ethanol of (a) 6/4, (b) 5/5 and (c) 4/6, at constant of 2% AIBN 49 Figure 3.B.5 SEM images PS-COOH cores with the volume ratio of MAA/SM/DVB of (a) 4/4/0.5, (b) 4/4/1, (c) 4/4/2 and (d) 4/4/4 51 Figure 3B.6 FT-IR spectra of (1) PS seed particles and (2) PS-COOH cores 52 Figure 3B.7 SEM image of PS-COOH cores after being impregnated gold nanoparticles 54 Figure 3B.8 UV/Vis spectrum of gold nanoparticles in water 55 Figure 3B.9 AFM topography of a PS-COOH core after impregnating 6nm-Au naoparticles: (a) 2D image, (b) 3D image and (c) height profile analysis 56 Figure 3B.10 AFM topography of a PS-COOH core: (a) 2D image, (b) 3D image and (c) height profile analysis 57 Figure 3B.11 SEM images of (PS-COOH)/Au core-shells after electroless depositon at different bar-scales58 Figure 3B.12 EDS analysis of (PS-COOH)/Au core-shells 61 Figure 3B.13 XPS spectra: (a) survey and (b) Au 4f XPS core-line spectrum of the (PS-COOH)/Au core-shells 62 - vi - ... of HAuCl4 and NH2OH SEM was used to examine the morphology of the PDVB cores and gold shells, and the formation of metallic gold was confirmed by both EDS and XPS - 37 - Part B: Preparation of. .. structure & Part B: Preparation of a novel carboxylic functional polystyrene/gold core-shell structure by the impregnation of gold nanoparticles - 15 - Part A: Fabrication of modified- poly(divinybenzene)/Au... effects of the functional groups on the PDVB cores on fabrication of the core-shell structure were examined SEM and XPS were used to characterize the gold nanoshells The presence of the functional