+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Measurement of density distributions for colloidal beta-FeOOH rods in suspensions exhibiting phase separation: the role of long-range forces in smectic ordering



Measurement of density distributions for colloidal beta-FeOOH rods in suspensions exhibiting phase separation: the role of long-range forces in smectic ordering



Journal of Chemical Physics 121(24): 12655-12665



We prepared monodisperse colloidal beta-FeOOH rods with length-to-width ratios L/W of 3.6-7.0 (L=210-330 nm and W=40-58 nm). Density gradients of the rods occurred in the suspensions by gravity, inducing a phase separation. The denser phase showed smectic (Sm) liquid crystalline structures exhibiting iridescent colors in a wide range of pH from 1.2 (at which the rods interact attractively) to 4.7 (repulsively). The lower density phase was disordered, but frequently emitted diffuse colors locally (at pH>2.6), implying the occurrence of short-range order. The nematic phase was not observed in the beta-FeOOH systems, being consistent with theoretical predictions. The particle density distributions were measured over the whole region of the suspensions (separated into two phases) at various pH values using a rapid freezing method. A phase diagram was determined thereby, where the critical (minimal) packing fraction of the particles for the Sm phase showed a nonlinear decrease from 0.43 to 0.12 with increasing pH. Rod-rod spacings in the Sm phase estimated experimentally at various pH were well explained using Derjaguin-Landau-Verwey-Overbeek (DLVO) type pair potentials. It is suggested that Sm ordering can be induced by attractive minima at pH<2.2, while driven by soft repulsions at pH>2.6. The former Sm ordering is expected to be the condensation-type phase transition and the latter the disorder-order transition.

Please choose payment method:






(PDF emailed within 0-6 h: $19.90)

Accession: 049541573

Download citation: RISBibTeXText

PMID: 15606291

DOI: 10.1063/1.1807820


Related references

Smectic filaments in colloidal suspensions of rods. Physical Review. E Statistical Nonlinear and Soft Matter Physics 66(4 Pt 1): 041606, 2002

Gelation and phase coexistence in colloidal suspensions with short-range forces: generic behavior versus specificity. Physical Review. E Statistical Nonlinear and Soft Matter Physics 81(1 Pt 1): 011407, 2010

Volume-term theories of phase separation in colloidal systems and long-range attractive tail in the pair potential between colloidal particles. Physical Review. E Statistical Nonlinear and Soft Matter Physics 63(1 Pt 1): 011503, 2001

Surface freezing and a two-step pathway of the isotropic-smectic phase transition in colloidal rods. Physical Review Letters 91(16): 165701, 2003

Lyotropic smectic B phase formed in suspensions of charged colloidal platelets. Journal of the American Chemical Society 134(13): 5985-5990, 2012

Electro-optic and dielectric study of the de Vries-type smectic-A* phase exhibiting transitions to smectic-C*A and smectic-C* phases. Physical Review. E Statistical Nonlinear and Soft Matter Physics 77(4 Pt 1): 041707, 2008

Stable smectic phase in suspensions of polydisperse colloidal platelets with identical thickness. Physical Review. E Statistical Nonlinear and Soft Matter Physics 80(4 Pt 1): 041704, 2009

Elementary Edge and Screw Dislocations Visualized at the Lattice Periodicity Level in the Smectic Phase of Colloidal Rods. Physical Review Letters 121(9): 097801, 2018

Oxidation of HSO3- in aqueous suspensions of alpha-Fe2O3, alpha-FeOOh, beta-FeOOH and gamma-FeOOH in the dark and under illumination. Environmental Pollution 95(3): 283-288, 1997

Phase diagram exhibiting a smectic-A-smectic-C-smectic-F meeting point. Physical Review. A Atomic Molecular and Optical Physics 46(2): R726-R728, 1992

Dynamics of simultaneous ordering and phase separation and effect of long-range Coulomb interactions. Physical Review Letters 70(10): 1477-1480, 1993

Density-functional approach to phase transitions of submonolayer films. I. The role of the intrinsic and extrinsic ordering forces. Physical Review. B Condensed Matter 35(7): 3376-3383, 1987

Phase transitions, aggregation and crystallization in mixed suspensions of colloidal spheres and rods. Faraday Discussions 112: 173-181, 1999

Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study. Journal of Chemical Physics 139(14): 144901, 2013

Colloidal ordering from phase separation in a liquid-crystalline continuous phase. Nature 407(6804): 611-613, 2000