Rod-like colloids

One model for rod-like colloids is tire tobacco mosaic vims (TM V), which consists of rods of diameter D about 18 nm and lengtli L of 300 nm [17,18]. These colloids have tire advantage of being quite monodisperse, but are hard to obtain in large amounts. The fd vims gives longer, semi-flexible rods (L = 880 nm, D = 9 nm) [18,19]. Inorganic boehmite rods have also been prepared successfully [20]. 

R. G. Winkler, K. Mussawisade, M. Ripoll, and G. Gompper, Rod-like colloids and polymers in shear flow a multi-particle-collision dynamics study, J. Phys. Condens. Matter 16, S3941 (2004). 

The added small colloids may be of a similar colloid shape (i.e., spheres) or a different shape such as rod-like colloids. In Sect. 2.4 we found that rod-Uke colloids give rise to a strong depletion interaction and in this chapter we will see that rod-Uke colloids influence the phase behaviour of a colloidal suspension significantly at very low concentrations. 

In the introduction of this chapter we mentioned that rod-like colloids influence the phase behaviour of suspensions of spherical colloids significantly at very low concentration. For a review see [32]. This is not surprising as rod-like colloids give rise to a strong depletion interaction at low concentration, see (2.107). Here we will see that FVT (correctly) captures the above mentioned pronounced depletion effect caused by rod-like particles. 

Phase Transitions in Suspensions of Rod-Like Colloids Plus Polymers... 

The experimental results refer to three types of rod-like colloidal particles which in suspension give rise to isotropic-nematic phase separation above a critical concentration ... 

Probably the best examples of rod-like colloidal particles are stiff vims particles such as the plant vims tobacco mosaic virus (TMV) and the bacteriophage feline distemper (fd). In Table 6.1 we summarize the characteristics of TMV and fd, including their linear charge densities at neutral pH. 

Here we outline how these more highly ordered phases can be accounted for in the phase diagram of mixtures of rod-like colloids and flexible polymers using FVT and follow the work of Bolhuis et al. [46]. The FVT requires the pressure, the chemical potential of the hard spherocylinder (HSC) reference system, and the free volume fraction (cf. (6.40) and (6.41)) as input. The computer simulations presented in [2, 4] contain the necessary information on the pressure and chemical potential of the HSC reference system and in [46] the free volume fraction was obtained using the Widom insertion method [47]. In this method one attempts to insert the polymers (represented by phs with diameter cr) at random positions in the simulation box. The fraction of insertions that does not result in an overlap corresponds to the free volume fraction. The free volume fraction measured in this way at different volume fractions of the HSC was fitted to a functional form similar to the SPT expression for the free volume fraction and used in (6.40) and (6.41). In Fig. 6.21 we present the simulation results for L/D = 5 and q= 1.0, q = 0.65 and = 0.15 obtained in [46] using the method outline above. In the upper graph of Fig. 6.21 q = 1) we compare the results for the Ii—12 transition... 

P. B. van Bruggen, F. M. van der Kooij, and H. N. W. Lekkerkerker, Liquid crystal phase transitions in dispersions of rod-like colloidal particles, J. Phys. Condens. Matter %, 9451-9456 (1996). 

Protein filaments. Here, we can use the example of the actin filaments and bundles to demonstrate the analysis of SAXS solution scattering. In Section 6.4.1, we introduced the filamentous protein F-actin and its self-assembly. The filaments will form networks or bundles of filaments under different solution conditions we can use fluorescence microscopy to observe these structures in the cell (Figure 6.18). F-actin is a negatively charged filament, and we can also think of it as a semiflexible, long, rod-like colloid when in solution. 

Winkler, R.G., Mussawisade, K., Ripoll, M., and Gompper, G. (2004) Rod-like colloids and polymers in shear flow ... 

IU.2. Liquid crystal phase transitions in dispersions of rod-like colloidal particles... 

This phase separation was subsequently observed in a variety of systems with the common feature that they contain rod-like colloidal particles dispersions of colloidal P-FeOOH52,53 and y-AlOOH particles, dispersions of tobacco mosaic virus >57 and the rod-like bacterial viruses fd and PfP9, solutions of deoxygenated sickle-cell haemoglobin O, dispersions of cellulose microcrystals and quite recently in dispersions of poly(tetrafluoroethylene) microcrystals. ... 

So far I have discussed the occurrence of nematic and smectic phases in dispersions of rod-like colloidal particles. Stroobants et dlM observed in their Monte Carlo simulations of systems of hard parallel spherocylinders for L/D > 3 a columnar phase intermediate between the smectic and crystalline phases. In their freeze-fracture electron microscopy study of dispersions of the rod like bacterial virus fd, Booy and Fowler may have observed the columnar phase. They report one texture (Figure 2b, in Ref. 69), where the nearly parallel fd particles are arranged randomly in the longitudinal direction but the lateral packing is regular. This is indeed characteristic of a columnar phase. 

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