Study of Relationship between Morphology and Mechanical Properties of SiO 2 -Polyacrylate Hybrid Nanocomposite
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Study of Relationship between Morphology and Mechanical Properties of SiO2-Polyacrylate Hybrid Nanocomposite Yi-Hsiao Kao1, Wei-Fang Su1,2, K. C. Lin3 1 Institute of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 2 Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 3 Department of Physics, FuJen Catholic University, Taipei, Taiwan ABSTRACT The atomic force microscopic technique is utilized to study the spatial distribution of silica nanoparticles embedded in poly(tetraethylene glycol diacrylate) matrix. The cast samples of these hybrid materials show distinct mechanical property change as the weight ratio (SiO2/polyacrylate) reaches 40%. The morphological observation from spin-coated films on silicon substrates shows pronounced nanoparticle network formation correlated to the elasticity transition. The percolating particles reduce the local strain field, i.e. inhibit the deformation of the stratum, and cause the dramatic increase in the Young’s modulus. Our experimental result is consistent with recent theoretical prediction [1]. INTRODUCTION Polymer blends and composites have improved the mechanical properties of some otherwise fragile matters. To design materials in a more controlled fashion, the linkage between macroscopic elasticity and micro-morphology needs to be fully understood [2, 3]. Recent interests of blending nanoparticles and copolymers to create materials for applications such as optical-electronic components justify the attempt further [4-7]. Whether the encapsulating nanoparticles form a percolated network within the composites and how the interaction between individual constituents (particles and polymer matrix) is under investigation [8]. We have chosen our composites as a model system to build the correlation between the reinforcing microstructure and the measured elasticity parameters. EXPERIMENTAL Material preparation Chemicals used for our composites and their compositions are listed in Table 1. The inorganic filler is commercial colloid silica in methanol (40 wt % silica) from Nissan Chemical Company with 20-25 nm of particle sizes. The organic matrix is polyacrylate made from monomers TEGDA (Tetraethylene glycol diacrylate). The coupling agent is organo-silanes,
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abbreviated as MPS for (3-(trimethoxysilyl)propyl methacrylate). The silica particles are first added with MPS for hydrolysis and condensation processes, i.e. the sol-gel method, to obtain acrylate-modified SiO2 nanoparticles. The acrylate monomers and photoinitiators ( Irgacure 651 from Ciba-Geigy Chemical Company) are then added. Either the mixture is cast in molds or spin-coated on the silicon substrates, then it is placed in a vacuum to remove the solvent and exposed to UV for curing. Table 1 Compositions of SiO2-polyacrylate hybrid nanocomposites Samples
SiO2 (wt %)
MPS (wt %)
TEGDA(wt %)
TEGDA
0
0
100
NS11-10
9.05
4.52
86.43
NS11-20
18.10
9.05
72.85
NS11-30
27.13
13.57
59.28
NS11-40
36.20
18.10
45.70
NS11-50
45.25
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