Fabrication of polyelectrolyte multilayered nano-capsules using a continuous layer-by-layer approach Iuliia S. Elizarova ⇑ , Paul F. Luckham Department of Chemical Engineering and Chemical Technology, Imperial College London, Prince Consort Road, London SW7 2AZ, UK graphical abstract article info Article history: Received 17 December 2015 Revised 20 February 2016 Accepted 22 February 2016 Available online 23 February 2016 Keywords: Layer-by-later self-assembly Continuous Polydiallyldimethylammonium chloride PDADMAC Polystyrenesulfonate PSS Lambda carrageenan Poly-L-lysine Nano-capsules Calcium phosphate abstract The layer-by-layer approach is a highly versatile method for the fabrication of multilayered polymeric films and capsules. It has been widely investigated in research for various polyelectrolyte pairs and core template particles. However, the fabrication of nano-sized capsules at the larger scale is difficult and time consuming, due to the necessity of washing and centrifugation steps before the deposition of each poly- electrolyte layer. This results not only in a very long fabrication time, but also in the partial loss of par- ticles during those intermediate steps. In this study, we introduced a continuous approach for the fabrication of multilayer polyelectrolyte based nano-capsules using calcium phosphate core nanoparti- cles and a tubular flow type reactor with the potential for synthesizing tens of milligrams of capsules per hour. Adsorption of the polyelectrolyte layer occurred in the tubing where particles and polyelec- trolyte solution of choice were mixed, creating a layer of polyelectrolyte on the particles. After this, these newly surfaced-modified particles passed into the next segment of tubing, where they were mixed with a second polyelectrolyte of opposite charge. This process can be continuously repeated until the desired number of layers is achieved. One potential problem with this method concerned the presence of any excess polyelectrolyte in the tubing, so careful control of the amount of polymer added was crucial. It was found that slightly under dosing the amount of added polyelectrolyte ensured that negligible unad- sorbed polyelectrolyte remained in solution. The particles created at each deposition step were stable, as they all had a zeta potential of greater than ±25 mV. Furthermore the zeta potential measurements showed that charge reversal occurred at each stage. Having achieved the necessary number of polyelec- trolyte layers, the calcium phosphate cores were easily removed via dissolution in either hydrochloric or acetic acid. Ó 2016 Published by Elsevier Inc. 1. Introduction The deposition of materials of opposite charge sequentially onto surfaces or particles has become increasingly well studied in recent http://dx.doi.org/10.1016/j.jcis.2016.02.052 0021-9797/Ó 2016 Published by Elsevier Inc. ⇑ Corresponding author. E-mail addresses: i.elizarova14@imperial.ac.uk (I.S. Elizarova), p.luckha- m01@imperial.ac.uk (P.F. Luckham). Journal of Colloid and Interface Science 470 (2016) 92–99 Contents lists available at ScienceDirect Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis