Polystyrene-<i>block</i>-poly(ethylene oxide) Bottlebrush Block Copolymer Morphology Transitions: Influence of Side Chain Length and Volume Fraction

A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-<i>block</i>-poly­(ethylene oxide) (PS-<i>b</i>-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction (<i>f</i>_PEO) from 22% to 81%. A series of PS-<i>b</i>-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO–norbornene (PEO-NB) (<i>M</i>_n ∼ 0.75, 2.0, or 5.0 kg/mol) and PS–norbornene (PS-NB) (<i>M</i>_n ∼ 3.5 kg/mol) macromonomers (MM). A map of <i>f</i>_PEO versus side chain asymmetry (<i>M</i>_n(PEO-NB)/<i>M</i>_n(PS-NB)) was constructed to describe the BBCP phase behavior. Symmetric and asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of <i>f</i>_PEO from 28% to 72%. At high <i>f</i>_PEO, crystallization of PEO was evident. Temperature-controlled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature <i>T</i>_MST was observed over a temperature range of 150–180 °C. This temperature was relatively insensitive to both side chain length and volume fraction variations. The findings in this study provide insight into the rich phase behavior of this relatively new class of macromolecules and may lay the groundwork for their use as templates directing the fabrication of functional materials

Fast Production of High-Quality Graphene via Sequential Liquid Exfoliation

A novel and practical approach of exfoliating graphite into graphene uses a sequence of flow and sonication on graphite suspensions. Graphite sediment after intense mixing is found to be altered, graphite having curled-up edges, which increases its sensitivity to ultrasound. Quadrupled graphene yield is achieved through introducing flow pretreatment

Structural Diversity and Phase Behavior of Brush Block Copolymer Nanocomposites

Brush block copolymers (BBCPs) exhibit attractive features for use as templates for functional hybrid nanomaterials including rapid ordering dynamics and access to broad ranges of domain sizes; however, there are relatively few studies of the morphology of the BBCPs as a function of their structural variables and fewer still studies of BBCP composite systems. Here we report the structural diversity and phase behavior of one class of BBCP nanocomposites as a function of the volume fractions of their components and the side chain symmetry of the BBCPs. We conducted a systematic investigation of gold nanoparticle (NP) (∼2 nm) assembly in a series of poly­(<i>tert</i>-butyl acrylate)-<i>block</i>-poly­(ethylene oxide) (P<i>t</i>BA-<i>b</i>-PEO) BBCPs with a fixed side chain length of P<i>t</i>BA (<i>M</i>_n = 8.2 kg/mol) but with different PEO brush lengths (<i>M</i>_n = 5.0, 2.0, or 0.75 kg/mol) as well as volume fractions (<i>f</i>_PEO = 0.200–0.484). The gold NPs are selectively incorporated within the PEO domain via hydrogen bond interactions between the 4-mercaptophenol ligands of the gold NPs and the PEO side chains. A number of morphological transitions were observed and were dependent on the total volume fraction (<i>f</i>_NP/PEO) of NPs and PEO domain. Symmetric or asymmetric lamellar morphologies of NP arrays were readily created through simple variation of <i>f</i>_NP/PEO. Interestingly, a lamellar structure was obtained at a small <i>f</i>_NP/PEO of only 0.248 for nanocomposites based on BBCPs with comparable side chain lengths (MW_PEO/MW_PtBA = 0.63). In contrast, NP morphological transitions from wormlike through cylindrical to lamellar structures were observed with the increase of <i>f</i>_NP/PEO for nanocomposites based on BBCPs with a large difference in side chain length (MW_PEO/MW_PtBA = 0.09). Highly deformed cylinders were observed in the cylindrical morphology as clearly identified by high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) tomography. This work represents a starting point for understanding BBCP composite phase behavior, and it provides new insight toward strategies for control over the microstructure of NP arrays assembled in BBCP templates, which is essential for functional materials design