From a Landau theory the static scattering intensity distribution I(q) of microemulsions is obtained. As essential ingredient we have included a negative gradient term in the free energy expression. The form of I(q)∼(a2+c1q2+c2q4)−1 yields for a2>0, c1 0 a single broad scattering peak and a q−4 decay at large q, both properties experimentally observed for a variety of microemulsions containing comparable amounts of water and oil. The peak originates from the modulation in the corresponding space correlation function given by γ(r)=(d/2πr)⋅e−r/ξ⋅sin(2πr/d). It is shown that the scattering intensity relation describes experimental literature data remarkably well, using only three fit parameters.

Origin of the scattering peak in microemulsions

The ANNNI model — Theoretical analysis and experimental application

Experimental studies of structurally incommensurate crystal phases

The general, axial next-nearest neighbour Ising (or ANNI) model in d dimensions consists of ( d — 1)-dimensional layers of spins, s i = + 1, with nearest-neighbour ferromagnetic coupling, J 0 > 0, within layers but competing ferromagnetic, and antiferromagnetic, J 2 -2J o / k B T , extended to all orders where necessary, it is shown for d > 2 that in the vicinity of a multiphase point at T = 0 and k = —J 2 /J 1 = 1/2 there occurs an infinite sequence of distinct, commensurate modulated phases characterized by wavevectors + l) j (T), and corresponding free energies and interfacial tensions are derived explicitly for low temperatures.

Low Temperature Analysis of the Axial Next-Nearest Neighbour Ising Model near its Multiphase Point

The Lifshitz point: Phase diagrams and critical behavior

A paramagnetic (I)-ferromagnetic (II)-sinusoidal (III) phase diagram near a Lifshitz point is studied for the case of uniaxial magnetization. The shape of the phase diagram in the vicinity of this point is determined. It is found that the II \ensuremath{\rightleftarrows} III phase transition line is tangent to the order-disorder (I \ensuremath{\rightleftarrows} II and I \ensuremath{\rightleftarrows} III) transition line at the Lifshitz point. The II \ensuremath{\rightleftarrows} III phase transition is shown to be first order, with latent heat and metastability regions. The behavior of magnetic susceptibility is determined. Binary alloy systems are suggested in which the considered type of phase diagram may be expected.

Phase diagrams near the Lifshitz point. I. Uniaxial magnetization

Phase diagrams near the Lifshiftz point. II. Systems with cylindrical, hexagonal, and rhombohedral symmetry having an easy plane of magnetization

"Selection rule" for irreducible representations inducing second-order phase transitions in magnetic structures

We predict that anomalous absorption of transverse ultrasonic waves ${\ensuremath{\sigma}}_{\mathrm{yz}}\ensuremath{\propto}{e}^{i(kz\ensuremath{-}\ensuremath{\omega}t)}$, ${\ensuremath{\sigma}}_{\mathrm{xy}}\ensuremath{\propto}{e}^{i(kx\ensuremath{-}\ensuremath{\omega}t)}$ is possible near ${T}_{c}$ in triglycine-sulfate-type ferroelectrics in spite of the fact that there is no piezoelectric or electrostrictive coupling between ${\ensuremath{\sigma}}_{\mathrm{yz}}$ (or ${\ensuremath{\sigma}}_{\mathrm{xy}}$) and ${P}_{y}$. A new coupling term $\ensuremath{\nu}{\ensuremath{\sigma}}_{\mathrm{yz}}\frac{\ensuremath{\partial}{P}_{y}}{\ensuremath{\partial}z}$ allowed by symmetry is introduced to account for this absorption. The Landau-Khalatnikov theory is applied to obtain in both phases $\ensuremath{\kappa}\ensuremath{\propto}\frac{{\ensuremath{\omega}}^{4}{\ensuremath{\tau}}^{2}}{(1+{\ensuremath{\omega}}^{2}{\ensuremath{\tau}}^{2})}$, where $\ensuremath{\tau}\ensuremath{\propto}{|T\ensuremath{-}{T}_{c}|}^{\ensuremath{-}1}$.

A. Michelson

Papers

Phase diagrams near the Lifshitz point. I. Uniaxial magnetization

Phase diagrams near the Lifshiftz point. II. Systems with cylindrical, hexagonal, and rhombohedral symmetry having an easy plane of magnetization

"Selection rule" for irreducible representations inducing second-order phase transitions in magnetic structures

Possibility of anomalous absorption of transverse ultrasonic waves near the Curie points of triglycine-sulfate-type ferroelectrics