Phase diagram of a solution undergoing inverse melting

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Phase diagram of a solution undergoing inverse melting

R. Angelini, G. Ruocco, and S. De Panfilis

Phys. Rev. E 78, 020502(R) – Published 8 August 2008

Abstract

The phase diagram of $α$ -cyclodextrin/water/4-methylpyridine solutions, a system undergoing inverse melting, has been studied by differential scanning calorimetry, rheological methods, and x-ray diffraction. Two different fluid phases separated by a solid region have been observed in the high $α$ -cyclodextrin concentration range $(c ⩾ 150 mg ∕ ml)$ . Decreasing $c$ , the temperature interval where the solid phase exists decreases and eventually disappears, and a first-order phase transition is observed between the two different fluid phases.

Received 26 June 2007

DOI:https://doi.org/10.1103/PhysRevE.78.020502

Authors & Affiliations

R. Angelini¹, G. Ruocco^1,2, and S. De Panfilis¹

¹Research Center SOFT INFM-CNR, Università di Roma “La Sapienza” I-00185, Roma, Italy
²Dipartimento di Fisica, Università di Roma “La Sapienza” I-00185, Roma, Italy

Comments & Replies

Reply to “Comment on ‘Phase diagram of a solution undergoing inverse melting’ ”

R. Angelini, G. Ruocco, and S. De Panfilis

Phys. Rev. E 79, 053502 (2009)

Comment on “Phase diagram of a solution undergoing inverse melting”

M. Plazanet, M. R. Johnson, and H. P. Trommsdorff

Phys. Rev. E 79, 053501 (2009)

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Issue

Vol. 78, Iss. 2 — August 2008

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Images

Figure 1
DSC thermograms of solutions of $α CD$ -water-4MP at the indicated concentrations of $α CD$ in 4MP and at a heating rate $r = 10 K ∕ \min$ . The transition peaks are indicated by the arrows.Reuse & Permissions
Figure 2
Phase diagram of $α CD$ -water-4MP solutions. The transition temperatures obtained with DSC measurements at a heating rate $r = 10 K ∕ \min$ are plotted as a function of the concentration of $α CD$ in 4MP. The full squares and the full circles represent the onset and the peak transition temperatures, respectively. The error bars are calculated through the standard deviation on five measurements at the same concentration. The transition temperatures as obtained by x-ray-diffraction measurements are also shown: the full triangles and the empty stars represent, respectively, the temperatures of the jump in the $Q$ position of the first maximum and first minimum of the scattered intensity shown in Fig. 4. Our DSC and x-ray data are also compared with previous neutron scattering measurements on similar samples [11] (open circles), performed at a heating rate $r = 6 K ∕ h$ .Reuse & Permissions
Figure 3
Normalized DSC thermograms of $α CD$ -water-4MP solutions. The measurements have been performed at the indicated concentrations of $α CD$ in 4MP and at a heating rate $r = 10 K ∕ \min$ . A peak of endothermic nature is observed, and is associated to a phase transition between the LTL and HTF disordered fluid phases. In the inset, the normalized area of the peaks is shown as a function of concentration together with a guideline to the eyes. The error bars represent the standard deviation on five measurements performed at the same concentration.Reuse & Permissions
Figure 4
(Color online) Viscosity as a function of the shear rate at the two indicated concentrations. The samples at $c = 50 mg ∕ ml$ ( $T = 293 K$ , $T = 373 K$ ) and $c = 125 mg ∕ ml$ $(T = 293 K)$ in the LTL phase show shear thickening, while the sample $c = 125 mg ∕ ml$ $T = 371 K$ in the HTF phase shows shear thinning. As shown in panel (A) the viscosity profile is perfectly reversible and it can be obtained by increasing (full symbols) or by decreasing (open symbols) the applied shear rate.Reuse & Permissions
Figure 5
(Color online) Scattered intensity from a solution of $α CD$ , water, and 4MP. The measurement has been done at the concentration $108 mg ∕ ml$ of $α CD$ in 4MP as a function of temperature in the range $295 - 413 K$ . In the inset the $Q$ position of the maxima $Q_{A}$ (left panels) and the minima $Q_{B}$ (right panels) of the scattered intensity are plotted as a function of temperature for the three indicated concentrations of $α CD$ in 4MP. The arrows indicate the LTL-HTF transition temperature as derived by DSC.Reuse & Permissions

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