Phase Transitions in Nanoconfined Binary Mixtures of Highly Oriented Colloidal Rods Articles uri icon

publication date

  • May 2010

start page

  • 10831

end page

  • 10841

issue

  • 36

volume

  • 12

international standard serial number (ISSN)

  • 1463-9076

electronic international standard serial number (EISSN)

  • 1463-9084

abstract

  • We analyse a binary mixture of colloidal parallel hard cylindrical particles with identical diameters but dissimilar lengths L1 and L2, with s = L2/L1 = 3, confined by two parallel hard walls in a planar slit-pore geometry, using a fundamental-measure density functional theory. This model presents nematic (N) and two types of smectic (S) phases, with first- and second-order N-S bulk transitions and S-S demixing, and surface behaviour at a single hard wall which includes complete wetting by the S phase mediated (or not) by an infinite number of surface-induced layering (SIL) transitions. In the present paper the effects of confinement on this model colloidal fluid mixture are studied. Confinement brings about profound changes in the phase diagram, resulting from competition between the three relevant length scales: pore width h, smectic period d and length ratio s. Four main effects are identified: (i) second-order bulk N-S transitions are suppressed; (ii) demixing transitions are weakly affected, with small shifts in the mu1 − mu2 (chemical potentials) plane; (iii) confinement-induced layering (CIL) transitions occurring in the two confined one-component fluids in some cases merge with the demixing transition; (iv) surface-induced layering (SIL) transitions occurring at a single surface as coexistence conditions are approached are also shifted in the confined fluid. The trends with pore size are analysed by means of complete mu1 − mu2 and p − (pressure-mean pore composition) phase diagrams for particular values of pore size. This work, which is the first one to address the behaviour of liquid-crystalline mixtures under confinement, could be relevant as a first step to understand the self-assembling properties of mixtures of metallic nanoparticles under external fields in restricted geometry.