Clay particles in suspension and at interfaces

High aspect ratio colloidal particles (either rod-like or plate-like) may form either liquid crystal or gel structures at low concentration. They serve as viscosity modifiers in formulations and as fillers in polymer nanocomposites. We focus on natural clay particles, and use (polymer) surfactants to control particle interactions in either oil or water.

Montmorillonite clay can be delaminated into individual 1 nm thick platelets with very high aspect ratio (1:400) [1]. Adsorbing amine-based surfactants in water results in a shift of the sol / gel transition to a much higher clay concentration, compared to suspensions of bare clay particles. A nematic phase remains elusive however [2]. Modified clays also allow preparing oil-in-water Pickering emulsions [3]. When adsorbing polyethylenimine to the particles, such droplets could be cross-linked into microcapsules [4].

Sepiolite consists of rod-like particles. Surface modification results in suspensions which form a nematic phase in line with predictions for hard rods - however with the coexistence region broadened due to polydispersity [5]. Porous channels in the particles allow preparing dyed (dichroic) or fluorescent rods [6,7].

[1] E.S.H. Leach, A. Hopkinson, K. Franklin and J.S. van Duijneveldt, Langmuir, 21: 3821-3830, 2005. [2] Y. Cui, C.L. Pizzey and J.S. van Duijneveldt, Phil. Trans. R. Soc. A 371: 20120262, 2013. [3] Y. Cui, M. Threlfall, and J.S. van Duijneveldt, J. Colloid Interface Sci. 356: 665-671, 2011. [4] Y. Cui and J.S. van Duijneveldt, Langmuir 28, 1753-1757, 2012. [5] Z. X. Zhang and J.S. van Duijneveldt, Langmuir , 22: 63-66, 2006. [6] N. Yasarawan and J.S. van Duijneveldt, Langmuir, 24: 7184 - 7192, 2008. [7] N. Yasarawan and J.S. van Duijneveldt, Soft Matter, 6: 353-362, 2010.}, time={2:00pm