A series of cubic network phases was obtained from the self-assembly of a single-composition lamellae (L)-forming block copolymer (BCP) polystyrene-block-polydimethylsiloxane (PS-b-PDMS) through solution casting using a PS-selective solvent. An unusual network phase in diblock copolymers, double-primitive phase (DP) with space group of Im3¯m, can be observed. With the reduction of solvent evaporation rate for solution casting, a double-diamond phase (DD) with space group of Pn3¯m can be formed. By taking advantage of thermal annealing, order–order transitions from the DP and DD phases to a double-gyroid phase (DG) with space group of Ia3¯d can be identified. The order–order transitions from DP (hexapod network) to DD (tetrapod network), and finally to DG (trigonal planar network) are attributed to the reduction of the degree of packing frustration within the junction (node), different from the predicted Bonnet transformation from DD to DG, and finally to DP based on enthalpic consideration only. This discovery suggests a new methodology to acquire various network phases from a simple diblock system by kinetically controlling self-assembling process.
Nanonetwork-structured materials can be found in nature and synthetic materials. A double gyroid (DG) with a pair of chiral networks but opposite chirality can be formed from the self-assembly of diblock copolymers. For triblock terpolymers, an alternating gyroid (GA) with two chiral networks from distinct end blocks can be formed; however, the network chirality could be positive or negative arbitrarily, giving an achiral phase. Here, by taking advantage of chirality transfer at different length scales, GA with controlled chirality can be achieved through the self-assembly of a chiral triblock terpolymer. With the homochiral evolution from monomer to multichain domain morphology through self-assembly, the triblock terpolymer composed of a chiral end block with a single-handed helical polymer chain gives the chiral network from the chiral end block having a particular handed network. Our real-space analyses reveal the preferred chiral sense of the network in the GA, leading to a chiral phase.
Chiral plasmonic films with gold nanohelices in polymer matrix are fabricated by templated electroless plating using self‐assembled enantiomeric polylactide‐based block copolymers (BCPs) as templates. By taking advantage of the helicity control of forming helical phase from the self‐assembly of chiral BCPs, mirror‐image signals from Cotton effect in electronic circular dichroism spectra can be clearly identified. The polymeric films with gold nanohelices show chiral plasmonic properties, as further evidenced by simulation from finite‐difference time‐domain method. This study may shed the light on fabrication of chiral plasmonic materials with adaptability in the applications for optical devices.
This work aims to suggest a represented block copolymer (BCP) system, polystyrene-b-poly(L-lactide) (PS-PLLA), for examination of the phase behaviors of semiflexiblecoil BCPs under different segregation strengths. Owing to the chiral polylactide with intrinsic chirality and semiflexible behavior, PS-PLLA can be referred to as a semiflexible-coil chiral block copolymer (BCP*), giving rise to a variety of self-assembled phases due to multiple effects of conformational asymmetry and rod−rod interaction as well as chirality on BCP self-assembly. With increasing segregation strength, conformational asymmetry and chirality effect lead to the formation and the enlarged forming window of the helical phase as PS being the major component. As PLLA becomes the major component, only the lamellar phase can be formed due to the rod−rod interaction. Interestingly, in the strong segregation region, the lamellar phase with out-of-phase undulation due to conformational asymmetry and in-phase undulation due to chirality effect (referred to as undulated lamellar phase) can be found.
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