In the search for the formation of Frank–Kasper phases from diblock copolymer self‐assembly, a series of compositionally asymmetric poly(dimethylsiloxane)‐b‐poly(2,2,2‐triflouroethyl acrylate)s (PDMS‐b‐PTFEAs) are synthesized to produce PDMS‐rich phases with PDMS volume fractions (fPDMS) ranging from 0.746 to 0.869. As determined by small‐angle X‐ray scattering analysis, the Frank–Kasper σ and C14 phases are identified at fPDMS = 0.796 and 0.851, respectively, plausibly due to high conformational asymmetry (ε ≈ 2.20) between the two blocks. Intriguingly, the σ phase develops during heating from a short‐range liquid‐like packing (LLP) state, whereas the C14 phase is achieved at room temperature, which are both followed by a disordering at higher temperatures. Based on thermal experiments from a super cooled disordered state, the findings further provide compelling evidence of an LLP‐hexagonally packed cylinder‐σ transition and a direct pathway to the C14 phase during heating from an LLP state.
We propose a new
approach to fluorine-containing, high-χ
styrenic block copolymers (BCPs) via side-chain modification in one
block. Polystyrene-b-poly(2,2,2-trifluoroethyl acrylate)s
(PS-b-PTFEAs) were synthesized by high-conversion
transesterification in acrylate units of polystyrene-b-poly(tert-butyl acrylate)s (PS-b-PtBAs) with the narrow dispersity being unchanged.
A simple modification from PtBA into PTFEA block
effectuates a remarkable increase in Flory–Huggins interaction
parameter (χ) between the two blocks, which measures χ
= 30.86/T + 0.160, where T (K) is
absolute temperature. The smallest half-pitch feature size of lamellae
was evaluated to be 5 nm in 6.3 kg/mol PS-b-PTFEA.
For versatility in thin film application, our results also offer a
rapid perpendicular orientation of lamellar microdomains in PS-b-PTFEA films supported on a neutral homopolymer mat (cross-linked
poly(4-trifluoromethylstyrene)), in which the lamellar spacing
(L
0) between the as-spun film and equilibrium
bulk gets closer as the molecular weight of BCPs increases.
We demonstrate a novel approach for fabricating vertically orientated, sub-10 nm, block copolymer (BCP) nanodomains on a substrate via molecular tailoring of poly(styrene-bmethyl methacrylate) (PS-b-PMMA) BCP, one of the most widely used BCPs for nanopatterning. The idea is to incorporate a short middle block of self-attracting poly(methacrylic acid) (PMAA) between the PS and PMMA blocks, where the PMAA middle block promotes phase separation between PS and PMMA, while maintaining the domain orientation perpendicular to the substrate. The designed PS-b-PMAA-b-PMMA triblock copolymers, which were synthesized via well-controlled anionic polymerization, exhibited order−disorder transition temperatures higher than that of pristine PS-b-PMMA BCPs, indicating the promotion of phase separation by the middle PMAA block. For PS-b-PMAA-b-PMMA BCPs with total molecular weights of 21 and 18 kg/mol, the domain spacing corresponds to 19.3 and 16.7 nm, respectively, allowing us to fabricate sub-10 nm nanodomain structures. More importantly, it was demonstrated that the PMAA middle block, which has a higher surface energy than PS and PMMA, does not significantly alter lateral concentration fluctuations, which are responsible for phase-separation in the lateral direction. This enabled the vertical orientation of microdomains with sub-10 nm feature size on a PS-r-PMMA neutral surface without an additional neutral top layer. We anticipate that this approach provides an important platform for next-generation lithography and nanopatterning applications that require sub-10 nm features over large areas with simple process and reduced cost.
We present a compelling evidence
for thickness dependence on the
order-to-disorder transition (ODT) behavior in cylinder- and lamella-forming
polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films. Such an asymmetric wetting condition that confines
the films with selective interactions of the PS/air and P2VP/substrate
interfaces generates a parallel orientation of cylindrical and lamellar
microdomains. We evaluated thickness-dependent phase transition as
a function of interlattice distance (L
0) using ex situ grazing incidence small-angle X-ray
scattering (GISAXS) and transmission electron microscopy (TEM). Below
an onset thickness (t
0) above which the
ODT temperatures (T
ODTs) of the films
are independent of film thickness, the T
ODTs of cylinder- and lamella-forming PS-b-P2VP films
remarkably increase as the film thickness decreases. Our results confirmed
that preferential wetting at the PS/air and P2VP/substrate interfaces
in very thin films substantially leads to an ordered state over accessible
temperature range up to ∼260 °C. More interestingly, the t
0 of lamellar morphology (∼22L
0) is thicker than that of cylindrical morphology
(∼10L
0), indicating that the interfacial
interactions are more influential to a 1D multilayer structure of
lamellar microdomains than a 2D hexagonally packed order of parallel
cylinders. Our theoretical calculation utilizing the self-consistent
field theory (SCFT) of a discrete bead–spring model with finite-range
interactions exhibited the similar thickness dependence of ODTs for
cylinder- and lamella-forming PS-b-P2VP films confined
in such an asymmetric wetting condition.
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