Phase Behavior of Aqueous Dispersions of Colloidal Boehmite Rods

Abstract

We report the phase behavior of aqueous dispersions containing rodlike boehmite particles with two different average lengths, 130 and 280 nm, with length-to-width ratios of approximately 8 and 20, over a range of ionic strengths. At low salt concentrations, where the particle interaction is predominantly repulsive, a separation into an isotropic upper phase and a birefringent lower phase occurs in the system containing the high-aspect-ratio particles. This phase separation was not observed in the case of dispersions containing the shorter particles. This seems to indicate that the phase separation is driven by the excluded volume effect. Above a critical (low) particle concentration, the repulsive 280 nm longrods form a monophasic birefringent glassy phase. This concentration is much lower than that at the isotropic-nematic transition as predicted from Onsager's theory for charged rods. Above a critical ionic strength a regime is entered where the phase behavior is largely governed by the attractive interaction. Then for both aspect ratios a space-filling amorphous gel is formed.

Critical behavior in the presence of an order-parameter pinning field

“…Thus, the present setup of a pinning-field line can be experimentally realized by considering an elongated cylindrical colloid immersed in a critical binary mixture, in the limit of small radius and large length of the colloid. A variety of rodlike particles are experimentally available, such as Boehmite rods [77,78], gold nanorods [79], carbon nanotubes [80], microtubules [81], lipid tubules [82], the mosaic tobacco virus [83], and cylindrical micelles [84].…”

Phase separation in mixtures of a rodlike colloid and two or more rodlike polymers

“…4,17,22 The strong dependence of the phase behavior on the size of the polymer has been stressed; 1,19,[21][22][23] below a certain minimum polymer size there is no demixing in the fluid phase. Varying the size of the polymer allows the effective colloid-colloid interaction to be varied in a way which is impossible for simple substances such as argon.…”

“…[1][2][3] Earlier work by one of us and Jackson 1 has shown that a mixture of rods of finite diameter with rods of zero diameter shows extensive immiscibility in the isotropic fluid phase. The mixture is an idealized model of a mixture of synthetic colloidal rods 4 and a rigid rodlike polymer. 5 Here we generalize the theory of Ref.…”

Preparation and properties of polyamide-6-boehmite nanocomposites

“…Their aqueous dispersions exhibit flow birefringence, thixotropy and elasticity [5]. Like many of the colloidal rod-like systems, they are capable of forming a nematic phase above a certain particle concentration.…”

“…In addition to boehmite, well-known inorganic examples that form a nematic phase are imogolite, V 2 O 5 and b-FeOOH [6]; whereas cellulose microcrystals, poly(tetrafluoroethylene) whiskers and tobacco mosaic virus are some other examples of organic systems. [5] In aqueous boehmite dispersions, the particles are stabilized by electrical double-layer repulsion [7]. Addition of an organic solvent destroys the repulsive interaction and results in flocculation of the particles.…”