Surface properties of silica nanoparticles modified with polymers for polymer nanocomposite applications

doi:10.1016/j.jiec.2008.02.002

Journal of Industrial and Engineering Chemistry

Volume 14, Issue 4, July 2008, Pages 515-519

https://doi.org/10.1016/j.jiec.2008.02.002 Get rights and content

Abstract

The surface of silica nanoparticles was modified with poly(ethylene glycol) methacrylate (PEGMA) or poly(propylene glycol) methacrylate (PPGMA) in order to improve the dispersion of nanoparticles in a polymer matrix. Nanosized silica particles were synthesized by the Stöber method with tetraethyl orthosilicate (TEOS). Silica nanoparticles were treated with triethoxyvinylsilane (VTES) as a coupling agent to introduce reactive groups and the PEG or PPG were then grafted onto the particle surface via UV-photopolymerization. Various analytical methods, i.e., scanning electron microscopy (SEM), thermogravimetry (TG), zeta potential measurement, and water vapor adsorption measurement were used to comprehensively characterize the unmodified(pure) and modified silica particles. The SEM images of the pure and modified particles demonstrated that both particles have a spherical shape and a uniform size without agglomeration. The silica particles modified with polymers showed higher weight loss than unmodified silica particles because of the decomposition of the organic polymers grafted onto the particles. The surface modification of silica particles with polymers decreased the zeta potential values of the silica surface. Modified silica particles had lower water vapor adsorption due to the hydrophobic surface property resulting from the polymers grafted onto the silica surface. In addition, we have developed an electrical conductivity measurement as a novel method to analyze the surface properties of silica nanoparticles. The modified silica particles had lower electrical conductivity than that of unmodified silica particles.

Introduction

The functionalization of particle surfaces is one method for tuning the overall properties of particles to fit targeted applications. In recent years, there has been an increased interest in the surface modification of inorganic nanoparticles with organic materials in numerous areas including photocatalysts, sensors, pharmaceuticals, and electronic devices [1], [2], [3], [4], [5], [6], [7], [8]. In the fabrication of polymer nanocomposites, the incorporation of silica nanoparticles with an extremely large surface area into polymers improves the polymer mechanical performance significantly [9], [10], [11]. However, the dispersion of nanoparticles in the polymer matrix is rather poor due to their incompatibility with the polymers and their large surface-to-volume ratio. For instance, physical blending of hydrophobic polymers (e.g., polystyrene or polypropylene) with hydrophilic inorganic particles (e.g., silica particles) may lead to phase separation or agglomeration of particles, resulting in poor mechanical, optical, and electrical properties [12]. Furthermore, particles with high surface energy are easily able to agglomerate as the size of the particles decreases [13], [14]. To solve these problems and to achieve a uniform dispersion of particles in the polymer matrix, we propose in this study the surface modification of silica nanoparticles with polymers. Although the effect of functional groups on the surface properties of the particles is not yet clearly understood, it is expected that the introduction of polymers on the silica surface will increase the surface hydrophobicity, leading to better dispersion of particles in the polymer matrix.

In this study, the surface modification of silica particles was carried out by a hybrid method using organosilane coupling agents [15], [16], [17], [18], [19], [20]. Nanosized silica particles were synthesized by the Stöber method and silica particles were then treated with triethoxyvinylsilane (VTES) as a coupling agent to introduce vinyl groups [21], [22]. Finally, the surface that was treated with VTES was grafted with poly(ethylene glycol) (PEG) or poly(propylene glycol) (PPG) via UV-photopolymerization. To investigate the surface properties of unmodified and modified silica particles, scanning electron microscopy (SEM), thermogravimetry (TG), and water vapor adsorption measurement were used. In addition, we developed an electrical conductivity measurement as a novel method to analyze the surface properties of silica nanoparticles.

Section snippets

Materials

Tetraethyl orthosilicate (TEOS), VTES, poly(ethylene glycol) methacrylate (PEGMA MW 360 and MW 526) and poly(propylene glycol) methacrylate (PPGMA MW 375) were obtained from Aldrich (USA). 1-Hydroxycyclohexyl phenyl ketone (otherwise known as Igacure^®184) was obtained from Ciba Specialty Chemicals (USA). Absolute ethanol and ammonia solution (28 wt.% ammonia) were obtained from Duksan (Korea). All chemicals were used as received without further purification.

Preparation of the pure silica particles

The spherical silica particles were

Size and shape

SEM images of the pure and modified silica particles are shown in Fig. 2. These images demonstrate that both pure and modified particles have a uniform size and spherical shape. It was also observed that there was no agglomeration of particles after surface modification. The sizes of pure particles and particles modified with PEGMA526 were 150.7 nm and 174.7 nm, respectively. The average sizes of each particle sample are shown in Table 1. The size of silica particles modified with polymers is

Conclusions

Nanosized silica particles were modified with PEG or PPG through UV-photopolymerization. Various analytical methods were used to comprehensively characterize the unmodified and modified silica particles. The surface modification of silica particles changed some properties on the surface, i.e., electric charge and hydrophilic nature. Modified silica particles showed a larger weight loss at 500 °C in TG analysis and a lower zeta potential value than that of unmodified silica particles. The silica

Acknowledgments

B.K. is grateful for the financial support by 2006 Hongik University Research Fund. K.L. acknowledges the financial support by the Korea Energy Management Corporation (KEMC) and the Ministry of Commerce, Industry, and Energy (MOCIE) (No. 2006-E-ID-11-P-19-0-000-2007).

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Surface properties of silica nanoparticles modified with polymers for polymer nanocomposite applications

Abstract

Introduction

Section snippets

Materials

Preparation of the pure silica particles

Size and shape

Conclusions

Acknowledgments

Mat. Sci. Eng. R

Adv. Colloid Interf. Sci.

J. Non-Cryst. Solids

Appl. Surf. Sci.

Prog. Polym. Sci.

J. Colloid Interf. Sci.

J. Chromatogr. A

Appl. Surf. Sci.

J. Colloid Interf. Sci.

Powder Technol.

J. Colloid Interf. Sci.

Environ. Sci. Technol.

Biomed. Mater. Res.