Entropy-induced smectic phases in rod coil copolymers

Abstract

We present a self-consistent field theory (SCFT) of semiflexible (wormlike) diblock copolymers, each consisting of a rigid and a flexible part. The segments of the polymers are otherwise identical, in particular with regard to their interactions, which are taken to be of an Onsager excludedvolume type. The theory is developed in a general three-dimensional form, as well as in a simpler one-dimensional version. Using the latter, we demonstrate that the theory predicts the formation of a partial-bilayer smectic-A phase in this system, as shown by profiles of the local density and orientational distribution functions. The phase diagram of the system, which includes the isotropic and nematic phases, is obtained in terms of the mean density and rigid-rod fraction of each molecule. The nematic-smectic transition is found to be second order. Since the smectic phase is induced solely by the difference in the rigidities, the onset of smectic ordering is shown to be an entropic effect and therefore does not have to rely on additional Flory-Huggins-type repulsive interactions between unlike chain segments. These findings are compared with other recent SCFT studies of similar copolymer models and with computer simulations of several molecular models.

Molecular theory of liquid-crystal ordering in rod-coil diblock copolymers

“…Another version of the SCF theory, in which the evaluation of the path integral along the chain is replaced by solving the Edwards equations [29][30][31], appears to be more suitable for the qualitative description of rod-coil block copolymers because it has been possible to describe the variety of different phases and the orientational ordering of rigid chains. In this approach, however, both the flexible chain and the rigid rod are modeled using the same formalism of ideal Gaussian chains where the rod like chain is characterized by a larger persistence length.…”

“…In the alternative approach, a fluid of rod-coil diblock copolymers is modeled by worm-like chains using the selfconsistent field theory and simulations [29][30][31]. In this theory, both coil and rod blocks are described within the same formalism, but the rod block is characterized by a larger persistence length.…”

Smectic phase in suspensions of gapped DNA duplexes

“…It is also worth mentioning, that existing theoretical and simulations studies of self-assembly in purely steric model systems4950515253, each consisting of stiff and flexible blocks, predict that the introduction of flexibility could possibly stabilize the smectic-A phase at the expense of nematic. However, in the systems considered, the flexible block is a terminal tail attached to a stiff rod, whereas in our gapped DNA system, flexibility is introduced locally within the DNA rod.…”

Development of a Novel Low Temperature Co-Fired Ceramics System Composed of Two Different Co-Firable Low Temperature Co-Fired Ceramics Materials

“…Experimental work that has been focused in this direction is limited due to the time scales (nanoseconds) and length scales (nanometres) involved. These limitations provide a relevant application for modelling and simulation approaches, which have been demonstrated as powerful tools for the prediction of phase ordering behaviour in similar systems [8]. Applications of these films to enhance current photolithographic techniques in the semiconductor industry are key to advancement in this field [9].…”