• Vol 10, No 3 (2019)
  • Chemical Engineering

Volume Fraction Dependent Morphological Transition of Silica Particles Derived from Sodium Silicate

Lailatul Qomariyah, W. Widiyastuti, Sugeng Winardi, K. Kusdianto, Takashi Ogi

Corresponding email: swinardi@chem-eng.its.ac.id

Cite this article as:
Qomariyah, L., Widiyastuti, W., Winardi, S., Kusdianto, K., Ogi, T., 2019. Volume Fraction Dependent Morphological Transition of Silica Particles Derived from Sodium Silicate. International Journal of Technology. Volume 10(3), pp. 603-612
Lailatul Qomariyah Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia
W. Widiyastuti Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia
Sugeng Winardi Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia
K. Kusdianto Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia
Takashi Ogi Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan
Email to Corresponding Author


The volume fraction dependent morphological transition of droplets during the evaporation of colloidal silica solution was investigated using the spray-drying method. The colloidal solution was prepared from sodium silicate using the sol-gel method. Spray drying with a tubular reactor was used in the experiment, with the volume fraction of the colloidal silica varying from 15 to 2%. It was demonstrated that a morphological transition from a sphere shape to a donut-like shape takes place at a colloidal volume fraction of between 4% and 2%, even when the drying rate remains moderate and is not extremely fast. A spherical silica particle shape was found at a colloidal volume fraction of between 15% and 8%. The morphological transition depends strongly on the volume fraction of the colloids in the droplets. Further, the ?-potential of the particles in the droplet also affects the transition by applying an interparticle electrostatic force. The same high surface charge of sol silica provides a repulsive interaction between the sol particles inside the droplet. The transition is hindered when the colloid volume fraction is increased because of the inherent spatial constraint. The Fourier-transform infrared (FT-IR) spectra of both the spherical and donut-like particles confirm the chemical bonding of the powder silica product. Moreover, X-ray diffractometry (XRD) analysis revealed an amorphous phase of the silica particles produced from spray drying. These preliminary results open up a new path for controlling the formation of a wide variety of silica particles using the spray-drying method. In addition, the different silica particle morphologies enable a variety of particle applications.

Colloidal silica; Particle morphology; Sodium silicate; Spray drying; Volume fraction


The spray-drying method is an established technology for synthesizing a material with controllable morphology. The method enables continuous production of nanostructure powders with high surface area and high purity, and it can be scaled up to ton-order quantities (Xiong et al., 2017). In addition, the particles produced from this method are agglomeration-free and have a monodisperse size, which is highly useful for material processing (Nandiyanto & Okuyama, 2011). The industrial-scale spray-drying method has been long established because it is a simple, cost-effective system (Isobe et al., 2005).

The production of silica particles by spray drying has attracted much interest in recent decades because of the ability of the method to produce several kinds of particles with different morphologies (Tsapis et al., 2005; Vehring et al., 2007). The morphology of silica particles determines their practical applications (Qomariyah et al., 2018a). Spray drying of colloidal precursors containing silica particles has been reported by several researchers (Waldron et al., 2014; Dixit et al., 2016). The reported applications of silica particles from spray drying include their use as catalysts and absorbents, as well as in chromatography and drug delivery systems (Bahadur et al., 2011; Wang & Friess, 2017).

Iskandar et al. (2003) used an aerosol-assisted spray method to produce silica particles, using a commercial colloidal silica suspension as the precursor. However, application on a large scale has been limited because of the high cost of the silica source (Ui et al., 2009). This drawback is an interesting topic for further study of the production of silica particles with controllable morphology using the spray-drying method with a low-cost silica source. In general, silica particles are synthesized using tetraethyl orthosilicate (TEOS) (Cho et al, 2009; Wang et al., 2010) or trimethoxy vinyl silane (TMVS) as the silica source to obtain monodisperse and spherical-shaped particles (Zainal et al., 2013; Wilson & Mahmud, 2015). Particle size can be altered by adding higher concentrations of TEOS and TMOS. Unfortunately, reliable preparation of larger amounts of silica particles and effective control of the reaction mechanism is difficult because of the high cost and rapid hydrolysis and condensation reaction rate of this silica source. Industry would prefer to use an alternative low-cost source of silica such as sodium silicate, which is also known as water glass.

In the drying process of the small droplets containing nanoparticles, evaporation drives the shrinkage of the droplets, and the constituent particles are assembled through particle interaction (Lyonnard et al., 2002). Furthermore, the oscillation of the droplet shape is a basic mechanism for the buckling process of the droplet. It has been observed that the drying process strongly affects the shrinkage of the droplet. When the rate of drying is slow enough, the droplet shrinks in an isotropic manner and the final particle shape remains spherical because of the high internal surface energy. However, if the rate of drying is sufficiently fast, droplet deformation occurs because of its instability. This leads to the formation of non-spherical shapes, such as donut-like particles. The formation of this kind of morphology can be affected by various factors, such as the volume fraction of the precursor. The parameter that determines the formation of particles inside the spray-drying reactor is called the Peclet number (Pe), which is defined as the ratio of the mixing time of the nanoparticles on the droplet to the droplet drying time. A Pe value much greater than 1 is regarded as a fast-drying process, which can produce hollow or donut-like morphologies. However, if Pe << 1, the drying process is slow enough for the particle to produce a spherical morphology because of isotropical shrinking of the droplet. Therefore, in addition to the volume fraction of the colloidal solution, the drying process plays a role in determining particle morphology.

In addition, the morphology of the synthesized particle through spray drying can be tuned by the physical properties of the drying medium. This tuning of the particle-particle interaction inside the droplets affects the final particle morphology (Qomariyah et al., 2018b). Other parameters, such as the particle concentration inside the initial droplet, droplet size, surface tension and hydrodynamic properties, can affect the sphericity of the final particle morphology (Iskandar et al., 2003; Widiyastuti et al., 2016). Several researchers (Iskandar et al., 2003; Pitchumani et al., 2009) have attempted to control the morphology of silica particles produced by the spray-drying method using sodium silicate solution as the silica source. However, to the best of the present authors’ knowledge, none of the studies has considered the morphology change based on the drying process (slow or fast) in the spray-drying reactor. The morphology of particles is an important issue in the application of silica particles. Hollow particles are preferred for inorganic catalyst, adsorption and gas separation applications. On the other hand, spherical and donut-like particles are desirable for pigments and as carrier particles in drug delivery.

This study was conducted to investigate the morphological transition of droplets consisting of sol silica particles with different volume fractions. It was observed that the morphology transition from spherical to donut-like shapes takes place solely by varying the volume fraction of sol silica particles in the initial droplet. Furthermore, the presence of particle interactions inside the droplets also strengthens the buckling process, even at a slow drying rate. A possible mechanism of the morphological transition is also discussed in this paper. An understanding of the morphological transition of silica particle formation will enable wider application of silica. The use of the spray-drying method is also feasible for large-scale production in industry.


The morphological transition of silica particles from spherical to donut-like particles was investigated regarding the dependence on volume fraction, which varied from 15% to 2%. Sodium silicate solution was used as the silica source. Even at a slow drying rate, the buckling process took place by hydrodynamic and particle-particle interactions, which eventually caused the morphological transition when the colloid volume fraction was small. The spherical particles formed at colloidal volume fractions of between 15% and 8%, whereas the donut-like particles formed at lower volume fractions (4% to 2%). However, the higher colloid volume fractions of between 8% and 15% are favorable for spherical-shaped particle formation, because of the inherent constraints on space availability; the morphological transition to the donut-like shape is hindered. Particle interaction in the droplets containing sol silica particles also plays an important role in the formation of donut-like morphology. FTIR analysis revealed that the silica particles were formed by the presence of siloxane bonding in all the samples. XRD analysis also proved the formation of silica particles with an amorphous phase. This preparation method offers an economical approach that exploits an abundant and cheap material, sodium silicate, and the well-understood spray-drying technique. Furthermore, the method is suitable for economical and large-scale production of silica powder.?


The authors are grateful for the financial support provided by the PMDSU research grant 2018 from the Directorate of Research and Public Service, Directorate General of Research Strengthening and Development, Ministry of Research, Technology and Higher Education of the Republic of Indonesia, with contract No. 819/PKS/ITS/2018. We also extend our gratitude to Mr. Fahad Nizar Sasmita and Mr. Hafidz Rifki Novaldi for their assistance with the experiment.  


Bahadur, N.M., Furusawa, T., Sato, M., Kurayama, F., Siddiquey, I..A., Suzuki, N., 2011. Fast and Facile Synthesis of Silica Coated Silver Nanoparticles by Microwave Irradiation. Journal of Colloid and Interface Science, Volume 355(2), pp. 312–320

Chang, H., Park, J., Dong, H., 2008. Flame Synthesis of Silica Nanoparticles by Adopting Two Fluid Nozzle Spray. Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 313-314, pp. 140–144

Cho, K., Chang, H., Kil, D.S., Park, J., Jang, H.D., Sohn, H.Y., 2009. Mechanism of the Formation of Silica Particles from Precursors with Different Volatilities by Flame Spray Pyrolysis. Aerosol Science and Technology, Volume 43(9), pp 911–920

Dixit, C.K., Bhakta, S., Kumar, A., Suib, S.L., Rusling, J.F., 2016. Fast Nucleation for Silica Nanoparticle Synthesis using a Sol–gel Method. Nanoscale, Volume 8(47), pp. 19662–19667

Eslamian, M., Ashgriz, N., 2006. Effect of Precursor, Ambient Pressure, and Temperature on the Morphology, Crystallinity, and Decomposition of Powders Prepared by Spray Pyrolysis and Drying. Powder Technology, Volume 167(3), pp. 149–159

Iskandar, F., Gradon, L., Okuyama, K., 2003. Control of the Morphology of Nanostructured Particles Prepared by the Spray Drying of a Nanoparticle Sol. Journal of Colloid and Interface Science, Volume 265(2), pp. 296–303

Isobe, H., Utsumi, S., Yamamoto, K., Kanoh, H., Kaneko, K., 2005. Micropore to Macropore Structure-designed Silicas with Regulated Condensation of Silicic Acid Nanoparticles. Langmuir, Volume 21(17), pp. 8042–8047

Lyonnard, S., Barlett, J.R., Sizgek, E., Finnie, K.S., Zemb, T., Woolfrey, J.L., 2002. Role of Interparticle Potential in Controlling the Morphology of Spray-dried Powders from Aqueous Nanoparticle Sols. Langmuir, Volume 18(26), pp. 10386–10397

Nandiyanto, A.B.D., Okuyama, K., 2011. Progress in Developing Spray-drying Methods for the Production of Controlled Morphology Particles: From the Nanometer to Submicrometer Size Ranges. Advanced Powder Technology, Volume 22(1), pp. 1–19

Pitchumani, R., Heiszwolf, J.J., Schmidt-ott, A., Coppens, M.-O., 2009. Continuous Synthesis by Spray Drying of Highly Stable Mesoporous Silica and Silica-alumina Catalysts using Industrial Raw Materials. Microporous and Mesoporous Materials, Volume 120, pp. 39–46

Qomariyah, L., Arif, AF., Widiyastuti, W., Winardi, S., Taniguchi, S., Ogi, T., 2018a. Hexagonal Hollow Silica Plate Particles with High Transmittance under Ultraviolet-visible Light. RSC Advances, Volume 8(46), pp. 26277–26282

Qomariyah, L., Sasmita, F.N., Novaldi, HR., Widiyastuti, W., Winardi, S., 2018b. Preparation of Stable Colloidal Silica with Controlled Size Nano Spheres from Sodium Silicate Solution. In: IOP Conference Series: Materials Science and Engineering, Volume 395(1)

Sen, D., Spalla, O., Belloni, L., Charpentier, T., Thill, A., 2007. Slow Drying of a Spray Nanoparticles Dispersion. In Situ SAXS Investigation. Langmuir, Volume 23(8), pp. 4296–4302

Sen, D., Mazumder, S., Melo, J.S., Khan, A., Bhattyacharya, S., D’Souza, S.F., 2009. Evaporation Driven Assembly of a Colloidal Dispersion during Spray Drying: Volume Fraction Dependent Morphological Transition. Langmuir, Volume 25(12), pp. 6690–6695

Tsapis, N., Dufresne, E.R., Sinha, S.S., Riera, C.S., Hutchinson, J.W., Mahdevan, L., Weitzs, D.A., 2005. Onset of Buckling in Drying Droplets of Colloidal Suspensions. Physical Review Letters, Volume 94(1), pp. 018302-1– 018302-4

Ui, S., Lim, S., Lee, S.H., Choi, S.C., 2009. Control of the Size and Morphology of Nano-size Silica Particles using a Sodium Silicate Solution. Journal Cermic Process Research., Volume 10(4), pp. 4–9

Vehring, R., Foss, W.R., Lechuga-Ballesteros, D., 2007. Particle Formation in Spray Drying, Journal of Aerosol Science, Volume 38(7), pp. 728–746

Waldron, K., Wu, W.D., Wu, Z., Liu, W., Selomulya, C., Zhao, D., Chen, X.D., 2014. Formation of Monodisperse Mesoporous Silica Microparticles via Spray Drying. Journal of Colloid and Interface Science, Volume 418, pp. 225–233

Wang, B., Friess, W., 2017. Spray Drying of Silica Microparticles for Sustained Release Application with a New Sol-gel Precursor. International Journal of Pharmaceutics, Volume 532(1), pp. 281–288

Wang, X.D., Shen, Z.X., Sang, T., Cheng, X.B., Li, M.F., Chen, L.Y., Wang, Z.S., 2010. Preparation of Spherical Silica Particles by Stöber Process with High Concentration of Tetra-ethyl-orthosilicate. Journal of Colloid and Interface Science, Volume 341(1), pp. 23–29

Widiyastuti, W., Maula, I., Nurtono, T., Taufany, F., Machmudah, S., Winardi, S., Panatarani, C., 2014. Preparation of Zinc Oxide/Silica Nanocomposite Particles via Consecutive Sol-gel and Flame-assisted Spray Drying Methods. Chemical Engineering Journal, Volume 254, pp. 252–268

Widiyastuti, W., Machmudah, S., Nurtono, T., Winardi, S., 2016. Effect of the Duration of Ultrasonic Irradiation and the Atmospheric Environment on the Characteristic of ZnO Nanostructures via a Sonochemical Method. International Journal of Technology, Volume 7(6), pp. 981–988

Wilson, L.D., Mahmud, S.T., 2015. The Adsorption Properties of Surface-modified Mesoporous Silica Materials with ?-Cyclodextrin. International Journal of Technology. Volume 6(4), pp. 533–545

Xiong, Z., Lei, Z., Chen, X., Gong, B., Zhao, Y., Zhao, H., Zhang, J., Zheng, C., 2017. Flame Spray Pyrolysis Synthesized ZnO/CeO2 Nanocomposites for Enhanced CO2 Photocatalytic Reduction under UV-Vis Light Irradiation. Journal CO2 Utilization, Volume 18, pp. 53–61

Zainal, N.A., Shukor, S.R.A., Wab, H.A.A., Razak, K.A., 2013. Study on the Effect of Synthesis Parameters of Silica Nanoparticles Entrapped with Rifampicin. Chemical Engineering Transactions, Volume 32, pp. 2245–2250