A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction ( f PEO ) from 22% to 81%. A series of PS-b-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO−norbornene (PEO-NB) (M n ∼ 0.75, 2.0, or 5.0 kg/mol) and PS−norbornene (PS-NB) (M n ∼ 3.5 kg/mol) macromonomers (MM). A map of f PEO versus side chain asymmetry (M n (PEO-NB)/ M 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 f PEO from 28% to 72%. At high f PEO , crystallization of PEO was evident. Temperaturecontrolled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature T 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.

We report the microphase-separated morphologies of model bottlebrush block copolymers (BBCPs) over a wide range of architectural design parameters. Densely grafted polystyrene-block-poly­(dimethylsiloxane) (PS-b-PDMS) BBCPs rapidly self-assemble into ordered lamellar, cylindrical, and deformed spherical morphologies depending on the volume fraction (f), side chain length (N sc), and overall backbone length (N bb). The microstructure was characterized by using electron microscopy and X-ray scattering. An experimental phase map is constructed, describing the dependence of morphologies and order–order transitions with respect to the design parameters. A lamellar morphology is primarily observed at symmetric f, while ordered cylindrical and deformed spherical morphologies appear at asymmetric f. The relative flexibility of the PS-b-PDMS backbone facilitates the accessibility of morphologies with curved interfaces and exceptionally large domain spacing. We also find that the breadth of the lamellar window decreases with increasing backbone length and side-chain asymmetry. These findings provide a comprehensive experimental description of the PS-b-PDMS BBCPs and provide insight into the rich phase behavior of this class of macromolecules.

We have performed small-angle X-ray scattering (SAXS) measurements to study the evolution of length-scale-dependent nanoparticle (NP) correlations over a wide range of loadings in miscible silica–poly­(2-vinylpyridine) polymer nanocomposites (PNC) characterized by strong interfacial attraction. The local cage and intermediate-scale correlations evolve in a commonly observed manner with increasing silica concentration, while long-wavelength concentration fluctuations exhibit a complex behavior. Higher-loading PNCs show a nonmonotonic change in the structure factor amplitude with wavevector because of an upturn on the longest length scales, which is the most intense for the highest NP concentration sample. These observations suggest that the PNC is approaching a spinodal demixing transition of an unusual polymer bridging-induced network type. PRISM integral equation theory is quantitatively applied, captures the key features of the SAXS data, and provides a theoretical basis for a network-like phase separation analogous to polyelectrolyte coacervation. The theory with validated parameters is then used to make predictions of real-space pair correlation functions between all species, the small- and large-wavevector collective polymer structure factor, spatially resolved NP coordination numbers, the interfacial cohesive energy density, and a measure of an enlarged effective NP radius because of polymer adsorption. With increasing NP loading, intensification of tight secondary bridged NP configurations, but weakening of interpolymer and polymer–NP correlations due to packing frustration, is predicted. This local reorganization of the polymer structure coexists with macro- and microphase separation such as features at low wavevectors which vary distinctively with NP loading. The predictions for the collective polymer structure are potentially testable using scattering experiments. Our results provide an important starting point for building an understanding of collective NP dynamics.

We investigate the linear viscoelastic behavior of poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) AB diblock brush copolymer materials over a range of volume fractions and with side-chain lengths below entanglement molecular weight (PS M n ∼ 3.5 kg/mol and PEO M n ∼ 5 kg/ mol). The high chain mobility of the brush architecture results in rapid microphase segregation of the brush copolymer segments, which occurred after mild thermal annealing. Master curves of the dynamic moduli were obtained by time− temperature superposition (tTS). The reduced degree of chain entanglements leads to a unique liquid-like rheology similar to that of bottlebrush (BB) homopolymers, even in the microphasesegregated state. The microphase-segregated domains were found to align at exceptionally low strain amplitudes (γ = 0.01) and mild processing temperatures as confirmed by small-angle X-ray scattering (SAXS). Domain/grain orientation occurred readily at strains within the linear viscoelastic regime (LVR) without noticeable effect on the dynamic moduli. This interplay of high molecular mobility and rapid phase segregation contrasts the viscoelasticity of brush block copolymers (BBCP) compared to conventional linear block copolymer (LBCP) analogues and opens up new processing possibilities of BBCP materials for a wide range of nanotechnology applications.

Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here,...

The addition of nanoparticles (NPs) to polymers is a powerful method to improve the mechanical and other properties of macromolecular materials. Such hybrid polymer–particle systems are also rich in fundamental soft matter physics. Among several factors contributing to mechanical reinforcement, a polymer-mediated NP network is considered to be the most important in polymer nanocomposites (PNCs). Here, we present an integrated experimental–theoretical study of the collective NP dynamics in model PNCs using X-ray photon correlation spectroscopy and microscopic statistical mechanics theory. Silica NPs dispersed in unentangled or entangled poly­(2-vinylpyridine) matrices over a range of NP loadings are used. Static collective structure factors of the NP subsystems at temperatures above the bulk glass transition temperature reveal the formation of a network-like microstructure via polymer-mediated bridges at high NP loadings above the percolation threshold. The NP collective relaxation times are up to 3 orders of magnitude longer than the self-diffusion limit of isolated NPs and display a rich dependence with observation wavevector and NP loading. A mode-coupling theory dynamical analysis that incorporates the static polymer-mediated bridging structure and collective motions of NPs is performed. It captures well both the observed scattering wavevector and NP loading dependences of the collective NP dynamics in the unentangled polymer matrix, with modest quantitative deviations emerging for the entangled PNC samples. Additionally, we identify an unusual and weak temperature dependence of collective NP dynamics, in qualitative contrast with the mechanical response. Hence, the present study has revealed key aspects of the collective motions of NPs connected by polymer bridges in contact with a viscous adsorbing polymer medium and identifies some outstanding remaining challenges for the theoretical understanding of these complex soft materials.

The evolution of nanoscale properties is measured during the thermally triggered curing of an industrial epoxy adhesive. We use x-ray photon correlation spectroscopy (XPCS) to track the progression of the curing reaction through the local dynamics of filler particles that reflect the formation of a thermoset network. Out-of-equilibrium dynamics are resolved through identification and analysis of the intensity–intensity autocorrelation functions obtained from XPCS. The characteristic time scale and local velocity of the filler is calculated as functions of time and temperature. We find that the dynamics speed up when approaching the curing temperature (Tcure), and decay rapidly once Tcure is reached. We compare the results from XPCS to conventional macroscale characterization by differential scanning calorimetry (DSC). The demonstration and implementation of nanoscale characterization of curing reactions by XPCS proves useful for future development and optimization of epoxy thermoset materials and other industrial adhesive systems.

Additive manufacturing (AM) is a promising technique to rapidly produce polymeric materials into complex 3-dimensional (3D) geometries. While AM is widespread and relevant for a range of applications, implementation in industry has outpaced our fundamental understanding of polymer dynamics and structure development during the printing process. Characterization and quantification of such dynamics is necessary to optimize final material properties and design future materials and processes for 3D printing. Here, we utilize X-ray photon correlation spectroscopy (XPCS) to measure spatial and time-resolved, out-of-equilibrium dynamics during direct ink write (DIW) 3D printing. Specifically, we investigate the progression of structural dynamics in a dual cure (UV/thermal) nanocomposite during and directly after printing. As the filament is printed and cured in situ, the relaxation processes of the cross-linking network are measured through the dynamics of inorganic filler particles. The characteristic relaxation time of the dynamics is calculated through the intensity–intensity autocorrelation function g 2 and directly correlated to the printing process parameters, such as printhead velocity and UV light intensity. The time-resolved evolution of nanoscale dynamics follows a power-law dependence as the filament is cured. Bulk rheological characterizations reveal the macroscopic solidification of the resin, providing correlation of material properties across a wide range of length and time scales. The measurement of multiscale, out-of-equilibrium dynamics provides insight into the development of structure in polymer nanocomposite filaments during 3D printing and is used to further understand the influence of such parameters on the AM process.