Influence of polydispersity on the phase behavior of colloidal goethite

Abstract

The effect of fractionation on the phase behavior of colloidal goethite dispersions with different polydispersities ͑17%, 35%, and 55% in length͒ has been studied by small angle x-ray scattering and transmission electron microscopy. All systems show at least nematic and smectic phases. The occurrence of the latter phase at such a high polydispersity is remarkable. It is shown that in the highly polydisperse systems strong fractionation occurs, which is able to reduce the local length polydispersity up to a factor of 2. A columnar phase was only found in the 35% and 55% polydisperse systems. It seems that the columnar phase accommodates the particles that do not fit into the smectic layers and, thus, reduces the length polydispersity within the smectic phase even further. The fact that a columnar phase was not found in the system of lowest polydispersity indicates that the smectic phase is the most stable phase at higher concentrations.

Biaxial nematic phases in fluids of hard board-like particles

“…However, from the computational point of view, this task is exceedingly difficult, since there exist three, in principle not completely independent, polydispersity parameters [37]. Efforts in this direction are now being undertaken in our group.…”

Liquid crystal phase transitions in suspensions of mineral colloids: new life from old roots

“…Depending on the details of the reaction and the subsequent centrifugation procedure, different (relative) sizes and polydispersities can be obtained. Samples of different volume fractions quickly performed an I-N phase separation, which through sedimentation and fractionation (continuing over months to years) formed clear isotropic, nematic [79] and smectic [80] phases (at polydispersities above 20% in combination with columnar phases [81]; figure 6). …”

Interplay between columnar and smectic stability in suspensions of polydisperse colloidal platelets

“…Black points correspond to polydispersities of the parent distribution for suspensions of goethite nanorods [27,30], which phase separate into C and S phases. Finally, blue circles with δ h = 0 represent values for which stable S [27] or smectic B [31] phases were found in suspensions of goethite nanorods [27] or of charged colloidal gibbsite platelets [31]. The blue circle with δ h = 0 is a result from recent experiments on Zirconium-Phosphate mineral platelet suspensions of constant thickness but polydisperse in diameter [18].…”

“…A possible explanation for this lies in the microfractionation mechanism: for large polydispersities larger particles tend to occupy the sites of the periodic lattice (whether one dimensional in the case of the S phase or two-dimensional for the C phase) and small particles tend to occupy the lattice interstitials; this mechanism may be more effective in the S phase than in the C phase. In fact, experiments show [1] that the C phase accepts a polydispersity of at least δ l = 0.25, but recent studies on length-polydisperse rods of goethite [27] indicate that the S phase is stable for polydispersities as large as δ h = 0.55 (with due allowance for macrofractionation mechanisms which reduce the polydispersity of the parent sample).…”