Transient instability upon temperature quench in weakly ordered block copolymers

Abstract

We report a novel transient instability upon temperature quench in weakly ordered block copolymer microphases possessing a soft direction or directions, such as the lamellar and hexagonal cylinder ͑HEX͒ phases. We show that reequilibration of the order parameter is accompanied by transient long wavelength undulation of the layers or cylinders-with an initial wavelength that depends on the depth of the temperature quench-that eventually disappears as the structure reaches its equilibrium at the new temperature. Such undulation leads to a transient transverse broadening of the scattering peaks near the Bragg positions. We argue that this instability might be responsible for the experimentally observed unusual ordering dynamics of the HEX phase of a diblock copolymer after quenching from the disordered state.

Kinetics of microphase segregation in one-dimensional symmetric diblock copolymer systems

“…Although the results [14] are qualitatively similar to what we predict for the 2nd stage, there are several important distinctions between the two theories: 1) They analyze transverse modes with q = q 0 + ∆q, where ∆q is perpendicular to the basic wave vector q 0 defining the lamellar structure. On the other hand, we considered longitudinal modes with ∆q parallel to q 0 (transverse modes are impossible for a 1-dimensional model).…”

“…The first stage is characterized by a nearly exponential increase of the amplitude of the composition order parameter. The dynamics of the structure formation during this stage is described by equations (14) and (26). The duration of the first stage is inversely proportional to the relative distance ε 2 to the critical temperature for the onset of the microphase segregation (we assume weak segregation, i.e.…”

“…After this paper was submitted we became aware of a recently published theory [14], where dynamics of transient structures (non-equilibrium structure factor) in lamellar block copolymers in 3 dimensions are considered. Although the results [14] are qualitatively similar to what we predict for the 2nd stage, there are several important distinctions between the two theories: 1) They analyze transverse modes with q = q 0 + ∆q, where ∆q is perpendicular to the basic wave vector q 0 defining the lamellar structure.…”

“…2) It is the transient dynamics after a temperature quench from an ordered (lamellar) state to a similar state that was considered in paper [14]. Accordingly the structure factor is considered [14] as a sum of the main δ-functional peaks and minor contribution due to thermal fluctuations.…”

“…Accordingly the structure factor is considered [14] as a sum of the main δ-functional peaks and minor contribution due to thermal fluctuations.…”