Enhanced density fluctuations in fluid systems with competing interactions

Model colloidal fluid with competing interactions: Bulk and interfacial properties

“…5. For a temperature-independent two-Yukawa potential with the same inverse-range parameters Z 1 = 1 and Z 2 = 0.5 as those considered here, 19 the liquidgas transition is found to disappear when the relative amplitude of the repulsion A / ⑀ is larger than 0.097. For A = 0.082 this requires ⑀ −1 Ͼ 1.18.…”

“…1 of Ref. 19 shows that T th * Ӎ 1.7⑀ which, for ⑀ −1 Ӎ 1.18, is indeed above unity. Therefore, the SCOZA solution disappears as soon as ⑀ −1 Ͼ 1.18.…”

“…For the case where A =0 ͑not displayed͒, the present theory yields a critical density within 5% of the value obtained from the more accurate SCOZA. 19 However, as A is increased the discrepancy increases. The general trend that the value of ⑀ −1 at the critical point is decreased as A is increased is found in both theories.…”

“…Rather, K is regarded as an unknown state-dependent quantity, to be determined in such a way that consistency between the compressibility and the energy route to thermodynamics is enforced. The previous applications of SCOZA, including the study of fluids with competing interactions, 19,20 were aimed at thermal systems with a temperature-independent potential, such that the phase diagram can be plotted as a function of density and temperature. For thermal fluids, the consistency condition amounts to requiring that the reduced compressibility red and the excess internal energy per unit volume u satisfy the condition…”

“…On the basis of the discussion at the end of Sec. IV, the value of A above which SCOZA fails to converge is determined by requiring that the threshold value of the relative amplitude 19 A / ⑀ = 0.097 is reached when the corresponding threshold temperature T th * Ӎ 1.7⑀ is equal to unity. This gives A տ 0.057.…”