Inter-domain Spacing Control via an Interdigitating Structure to Bilayers in Lamellae-Forming Star-Block Copolymers

Abstract

Herein, we aim to examine the topological effects of block copolymer (BCP) architecture on the self-assembly of lamellae-forming star-BCPs composed of polystyrene (PS) and poly(dimethylsiloxane) (PDMS) blocks with equivalent arm length and therefore almost identical volume fraction. An interesting wet-brush-like lamellar phase with an interdigitating structure for chain packing was found in the solution-cast (PS-b-PDMS) n (n = 1, 3, or 4) samples regardless of the value of n which corresponds to the number of PS-b-PDMS arms attached. While the temperature is gradually increasing, an order−order transition from the interdigitating structure to bilayers in the self-assembled lamellar phase can be observed in the bulk state, exhibiting approximately 50% increase on d-spacing. These results implicitly indicate that it is possible to acquire the smaller spacing of microphase-separated lamellae from casting. Also, as examined by in situ temperature-resolved small-angle X-ray scattering, transformation occurs once the temperature is over the glass transition of PS and the formation of stable lamellae with bilayers is able to be expedited by increasing the arm number because of the low degree of formation of wet brushes benefited by the topological effects. Moreover, an interesting transition was found in which the forming interdigitating chain packing can be restructured after cooling down from the stable lamellae, while the thermal treatment is not able to completely disentangle the polymer chains. Such an observation is an additional evidence for the suggested mechanism and corresponding kinetics for the formation of lamellar phases with such a large variation on d-spacing. This discovery provides an insight for the transformation mechanisms of the self-assembly of BCPs; it indicates the strong dependence of the self-assembling process on the topological effects from star-block architecture, making these materials valuable for the engineering of nanostructured BCPs with temperatureresponsive d-spacing variation.

Superlattice Structure from Self-Assembly of High-χ Block Copolymers via Chain Interdigitation

“…Apart from that after the temperature rises over the T g of PS, the splitting reflections of the first-order peak ( q *) experience significant variation on their scattering intensities at which the remaining reflection with low intensity (blue line) gradually decay and ultimately vanishes near 140 °C while the appearing reflection with larger d -spacing becomes dominate. According to our previous study, the splitting of the first-order reflection ( q *) is attributed to the order–order transition between the self-assembled lamellae with chain interdigitation and bilayers texture; that can be further evidenced by the peak intensity variations at which the bilayer one appears and becomes the major one as compared to the interdigitating one (Figure B). Indeed, there are small traces of the lamellar structure with chain interdigitation above 140 °C since the continuous transformation from typical lamellar morphology with chain interdigitation to the typical lamellar morphology with bilayer texture is a kinetic process during the heating for in situ SAXS experiments.…”

“…The thermodynamics based on the self-consistent field theory of the self-assembled BCPs and its topological effects have been well established and were used mainly to investigate on the phase behaviors from microphase separation. − However, it is discovered that order–order transitions could be occurred in mesoscale, showing interesting morphology during the transition. The order–order transitions among the lamellae-to-lamellae transition of the two morphology-adjacent phases have been reported in several systems during thermal annealing, showing chain interdigitation and bilayer texture, resulting in a significant increase in the d -spacing of lamellar morphologies. − The discovered transitions in mesoscale offer new insights into the fundamental mechanisms in soft matters where BCPs could behave like titanic-sized atoms that governs epitaxial symmetry analogous to a classical example of the graphite–diamond transition in hard matters . Furthermore, the order–order transitions in mesoscale brings out an intriguing researching area: can we find the routes to acquire superlattice structure in self-assembled BCPs?…”

Hydrolysis-Induced Self-Assembly of High-χ–Low-N Bottlebrush Copolymers

“…As a result, the slope of the linear relationship between L 0 and N bb /pitch increases after hydrolysis. In general, the lamellar microdomains of BCPs consist of bilayers, although by modification of the chain architecture to a star-type architecture, interdigitating structures have been observed . For bottlebrush copolymers, the side chains are densely packed over the length of the backbone, while at the ends of the backbone, the side chains are less densely packed .…”

“…In general, the lamellar microdomains of BCPs consist of bilayers, although by modification of the chain architecture to a star-type architecture, interdigitating structures have been observed. 71 For bottlebrush copolymers, the side chains are densely packed over the length of the backbone, while at the ends of the backbone, the side chains are less densely packed. 72 Both before and after hydrolysis, the linear relationship between L 0 and N bb /pitch gives positive intercepts when N bb is extrapolated to zero.…”

Ultrafast Self-Assembly of Bottlebrush Statistical Copolymers: Well-Ordered Nanostructures from One-Pot Polymerizations

“…Over the past several decades, block copolymers have garnered significant interest in academia and industry due to their ability to microphase separate into well-defined nanoscale structures. − Directed self-assembly, in particular, has been widely explored as an alternative patterning approach for electronic devices and data storage. − However, the self-assembly of linear block copolymers (LBCP) is rather constrained when forming well-ordered, defect-free structures, particularly with large lattice spacings, due to the kinetic frustrations in entangled systems of high-molecular-weight polymers. − In the pursuit of alleviating the constraints in LBCPs and expanding upon the achievable range of nanostructures, recent studies have explored the self-assembly of alternate architectures of copolymers, such as multiblock, mitko star, − comb block copolymers, and bottlebrush block copolymers (BBCP). − BBCPs are densely grafted macromolecules with polymeric side chains tethered to a linear backbone in separate block segments . Combining short side chains with high grafting density leads to a reduction in the overall chain entanglements in the system, increasing molecular mobility and overcoming many barriers of assembly present in entangled LBCPs .…”