D. Frenkel, H.N.W. Lekkerkerker and A. Stroobants, Thermodynamic stability of a smectic phase in a system of hard rods. Nature 332 (1988) 822
G.J. Vroege and H.N.W. Lekkerkerker, Phase transitions in lyotropic colloidal and polymer liquid crystals. Rep. Prog. Phys. 55 (1992) 1241
H.N.W. Lekkerkerker, W.C.K. Poon, P.N. Pusey, A. Stroobants and P.B. Warren, Phase behaviour of colloid + polymer mixtures. Europhys. Lett. 20 (1992) 559
M.H.J. Hagen, E.J. Meijer, G.C.A.M. Mooij, D. Frenkel H.N.W. Lekkerkerker, Does C60 have a liquid phase? Nature 365 (1993) 425
H.N.W. Lekkerkerker and A. Stroobants, Ordering entropy, News and views, Nature 393 (1998) 305
M.P.B. van Bruggen, J.K.G. Dhont and H.N.W. Lekkerkerker, Morphology and kinetics of the isotropic-nematic phase transition in dispersions of hard rods. Macromolecules 32 (1999) 2256
F.M. van der Kooij, K. Kassapidou and H.N.W. Lekkerkerker, Liquid crystal phase transitions in suspensions of polydisperse plate-like particles, Nature, 406 (2000), 868-871
H.N.W. Lekkerkerker and B. Widom, An exactly solvable model for depletion phenomena, Physica A, 285 (2000) 483-492
E.H.A. de Hoog, W.K. Kegel, A. van Blaaderen and H.N.W. Lekkerkerker, Direct observation of crystallization and aggregation in a phase-separating colloid-polymer suspension Phys. Rev. E, 64 (2001) 021407-1
V.J. Anderson and H.N.W. Lekkerkerker, Insights into phase transition kinetics from colloid science Nature, 416, (2002) 811-815
D.G.A.L. Aarts, M. Schmidt and H.N.W. Lekkerkerker, Direct visual observation of thermal capillary waves Science (2004) 304 847-850
We have developed new model systems for hard colloidal rods and colloidal plates. The hard colloidal rods consist of a Boehmite (AlOOH) core and a steric stabilization layer of polyisobutylene. Dispersions of these particles show an isotropic-nematic phase separation. Using polarization microscopy and small angle light scattering we observed that depending on the concentration the pathway of phase separation is either nucleation and growth or spinodal decomposition . The effect of attractive interactions on the phase behavior of colloidal rods has been studied by the addition of non-adsorbing polymer. Now four pathways of phase separation can be distinguished; nucleation and growth, spinodal decomposition aggregation and gelation . The hard colloidal plates we developed consist of a Gibbsite (Al(OH)3) core and again a steric stabilization layer of polyisobutylene. In dispersions of these particles we discovered an Isotropic -Nematic  and Nematic-Columnar  phase transition. Especially the latter transition is fascinating and unexpected as it persists for a polydispersity up to 25%. Our results imply that liquid crystalline order in synthetic mesoscopic materials may be easier to achieve than previously thought. We also investigated the phase behavior of mixed dispersions of hard colloidal rods and colloidal platelets. Here we were able to show experimentally that phase separation in two coexisting uniaxial nematic phases occurs and not a single biaxial nematic . This issue has been the subject of considerable theoretical debate.
We developed a theory of the phase behavior of colloidal rod-sphere mixtures . From this theory it follows that in such systems a colloidal fluid colloidal crystal phase transition can occur at very low concentrations of added colloidal rods. In subsequent experimental work  we showed this indeed to be the case. At the same time we were able to follow the morphology of the aggregation process that eventually leads to crystallization .
Using the spinning drop method we were the first to determine the ultra low interfacial tensions of the interface in a demixed colloidal polymer system . As predicted by simple scaling relations these interfacial tensions are indeed as low as a few µN/m. We were able to confirm this result by analyzing the rate of break up of long filamentous droplets. Using ellipsometry we studied for the first time the interfacial profile . The thickness of the interfacial profile is of the order of the diameter of the colloidal particles.
1. M.P.B. van Bruggen, J.K.G. Dhont and H.N.W. Lekkerkerker, Morphology and kinetics of the isotropic-nematic phase transition in dispersions of hard rods, Macromolecules 32, 2256 (1999)
2. M.P.B. van Bruggen and H.N.W. Lekkerkerker, Tunable attractions directing nonequilibrium states in dispersions of hard rods, Macromolecules, 33, 5532 (2000)
3. F.M. van der Kooij and H.N.W. Lekkerkerker, Formation of nematic liquid crystals in suspensions of hard colloidal platelets, The Journal of Physical Chemistry B 102, 7829 (1998)
4. F.M. van der Kooij, K. Kassapidou and H.N.W. Lekkerkerker,Liquid crystal phase transitions in suspensions of polydisperse plate-like particles, Nature, 406, 868 (2000)
5. F.M. van der Kooij and H.N.W. Lekkerkerker, Liquid-crystalline phase behavior of a colloidal rod-plate mixture, Phys. Rev. Lett. 84, 781 (2000)
6. G.A. Vliegenthart and H.N.W. Lekkerkerker, Phase behavior of colloidal rod-sphere mixtures, J. of Chem. Phys. 111, 4153 (1999)
7. G.H. Koenderink, G.A. Vliegenthart, S.G.J.M. Kluijtmans, A. van Blaaderen, A.P. Philipse and H.N.W. Lekkerkerker, Depletion-induced crystallization in colloidal rod-sphere mixtures, Langmuir 15, 4693 (1999)
8. G.A. Vliegenthart, A. van Blaaderen and H.N.W. Lekkerkerker, Phase transitions, aggregation and crystallization in mixed suspensions of colloidal spheres and rods, Faraday Disc. 112, 173 (1999)
9. E.H.A. de Hoog and Henk N.W. Lekkerkerker, Measurement of the interfacial tension of a phase-separated colloid-polymer suspension, Journal of Physical Chemistry B 103, 5274 (1999)
10. E.H.A. de Hoog, H.N.W. Lekkerkerker, J. Schulz and G.H. Findenegg, Ellipsometric study of the liquid/liquid interface in a phase-separated colloid-polymer suspension, The Journal of Phys. Chem. B. 103, 10657 (1999)