Colloids and Surfaces B: Biointerfaces 165 (2018) 182–190 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces journal homepage: www.elsevier.com/locate/colsurfb Biopolymer assisted synthesis of silica-carbon composite by spray drying Debashish Sarkar a,∗ , Debasis Sen b , B.K. Nayak a , Pramod Bhatt b , M.N. Deo c , Bijaideep Dutta d a Physics Group, Bhabha Atomic Research Centre, Mumbai, 400085, India b Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085, India, India c High Pressure & Synchrotron Radiation Division, Bhabha Atomic Research Centre, Mumbai, 400085, India d Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India a r t i c l e i n f o Article history: Received 12 October 2017 Received in revised form 18 January 2018 Accepted 17 February 2018 Available online 19 February 2018 Keywords: Biopolymer Gum arabic Spray drying SAXS Solar absorber a b s t r a c t Spray drying had been used to synthesize silica-carbon black nanocomposite micrometric granules with a uniform distribution of the two components. This was achieved by hindering the preferential diffusion of hydrophobic carbon and hydrophilic silica particles in the water droplets during evaporative assembly by introducing gum arabic as a stabilizing agent and network former. Both positive and negatively charged silica nanoparticles were used to check the stability of the sol and its effect on the morphology of the spray dried granules. X-ray and neutron scattering, complemented with electron microscopy, were used to investigate the correlation and distribution of the nanoparticles within the granules. Porous silica granules, having surface area of 157 m 2 /g, were obtained after removal of carbon black by calcination. An environment-friendly solar absorbing coating had been prepared using as synthesized granules. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Composite nanomaterials have been employed in various appli- cations such as bio-imaging, drug-delivery, electrode for Li-ion batteries, microwave absorber, reinforcing filler material, solar absorber [1–8]. It would be advantageous to mass produce these composite nanomaterials using well established industrial man- ufacturing techniques. Spray drying, a well-established industrial technique, is widely used for mass production of powder gran- ules for food, pharmaceutical and chemical industries [9–11]. With recent advances in spray drying technology [12–15], there has been an ongoing effort to produce composite functional nanomaterials using this technique [5,16,17]. We have furthered this effort by pro- ducing composite carbon black-silica microgranules using spray drying. Among various composite materials, carbon-silica compos- ites stand out due to its numerous applications such as duel phase filler to enhance durability and mechanical performance of natu- ral rubber and SBR based tires [7,18], precursor for silicon carbide ceramic [19,20], solar absorber [21–23] and in radar technology as microwave absorbing material [6,24,25]. ∗ Corresponding author. E-mail address: debashish@barc.gov.in (D. Sarkar). Often two problems hinder the production of composite powder granules by spray drying: i) The stability of feed solution, containing two or more different suspensions having different physicochemi- cal properties. For example, an aqueous solution containing carbon black or graphene or CNTs would not be stable as these carbon types tend to form large agglomerates due to Van der Waals attrac- tion and precipitates [26,27] and therefore would not be suitable for spray drying. Thus, it remains a challenge to realize stable feed solution of mixed components with contrasting hydrophilic- ity/hydrophobicity for the spray drying. ii) Segregation of particles during spray drying due to different colloidal particle sizes and sur- face polarities [28,29]. According to Stokes-Einstein relation, the diffusion rate of a spherical particle in a liquid medium is given by D = k B T 6r where, D is the diffusion coefficient, r is the particle radius,  is the medium viscosity, k B and T are the Boltzmann constant and absolute temperature respectively. As diffusion coefficient is inversely proportional to the particle radius, smaller particles would have a higher rate of diffusion compared to larger parti- cles. As a result, segregation among particles of various sizes would occur. For example, spraying milk colloids causes bigger free fats to reside at the surface and smaller protein globules and lactose to reside at the core of the dried granule due to difference in diffusion rate[30]. To obtain homogeneous mixing of smaller nanoparticles and much larger as well as hydrophobic carbon aggregates in spray https://doi.org/10.1016/j.colsurfb.2018.02.040 0927-7765/© 2018 Elsevier B.V. All rights reserved.