Session K52: Polymer Nanocomposites II: Block Copolymers and More

Quantum Metamaterials from Block Copolymer Nanocomposites: Synthetic Pathways to Mesostructured Carbonitride Superconductors

In recent decades, block copolymer (BCP)-inorganic nanocomposite co-assembly has emerged as a highly tunable route to the synthesis of crystallographically ordered, mesoporous inorganic materials. These materials have found numerous applications in catalysis, energy conversion and storage, and other areas. One notable area in which BCP-directed assembly has made few inroads, however, is the production of electronic-grade materials suitable for studies of emergent phenomena, i.e. quantum metamaterials. For example, superconductors with mesoscale ordering are expected to have properties different from their bulk counterparts. The exploration of these properties has been limited by the lack of tunable, robust synthesis methodologies. We have developed a route to gyroidal NbN superconductors from poly(isoprene-b-styrene-b-ethylene oxide)-Nb₂O₅ nanocompositesusing high-temperature annealing in ammonia gas. In recent work, we have developed synthesis routes using methane gas that enable the synthesis of carbonitrides with superconductor quality comparable to bulk samples and tunable morphology across the BCP phase diagram. These morphologies exhibit differences in the transition onset and magnetization behavior, potentially the first hallmarks of quantum metamaterial behavior.   

In Situ Grazing Transmission Small Angle X-Ray Scattering Study of Supramolecular Nanocomposites

Thin film assembly of nanoparticles in block copolymer-based supramolecules provide a versatile platform to generate hierarchically structured materials with varying compositions, structures and properties. In order to select and tune these films, the pathway of assembly must be understood. Using in situ X-ray scattering studies, the formation of structure can be monitored. Here, in situ grazing transmission small angle X-ray scattering (GTSAXS) was used to investigate the drying process of supramolecular nanocomposites. Data collected via GTSAXS does not contain complex correlations nor is it distorted by refraction and reflection the way grazing incident small angle X-ray scattering (GISAXS) is. It also gives information for small and negative q_z values, making it idea for use in in situ studies where changes in structure may be subtle. It was observed that highly ordered structures form quickly after casting. As the drying process continues, the order degrades somewhat and the structure becomes anisotropic. These in situ studies provide insight into how order is formed in supramolecular nanocomposites.
  

Nanoparticle Templating via Block Copolymer Self-Assembly

Many applications of polymer nanocomposites require an ordered configuration. To address this challenge, our group is studying the templating of nanoparticles by block copolymers within a thermoset resin. However, much remains to be understood about the fundamental phase behavior of block copolymers when blended with a thermoset. In this presentation, we will discuss our recent work characterizing the self-assembly behavior of an asymmetric block copolymer blended in an epoxy resin. The nanostructures formed as a function of block copolymer weight fraction within the thermoset resin are characterized by SAXS and TEM, and the evolution of these structures during epoxy curing is evaluated. The effect of increasing weight fraction of block polymer on the thermal characteristics of the cured network are probed using DSC. In addition, we present preliminary work on the abilities of these nanostructures to template gold nanoparticles. The suitability of these materials for high performance applications is also discussed.   

Entropy-driven assembly in multicomponent nanocomposite

Hierarchically structured nanocomposites show unique collective properties from nanoparticle (NP) assemblies. Successfully structure control in nanocomposite remains as bottleneck to advance the field. Block copolymer (BCP) and supramolecular systems have been effective in achieving nanoscopic dispersion of fillers. However, NPs with size larger than 30% of the BCP specific domain size tend to aggregation due to the large conformational entropy penalty. This limitation in the particle size restricts the NP incorporation for targeted functionality. Here, we will discuss a new approach to modulate thermodynamic contribution from various components with a special focus of maximizing translational entropy. The present studies suggested that manipulating entropic contribution in multiple components system will lead to new path and opportunity toward structure control and access functionality.   

Electrically Conductive Block Copolymer Nanocomposites for Large-Scale Coating Applications

Electrically conductive coatings have been widely applied to convert insulators to electronics for sensing, energy harvesting, or actuator applications. However, commercially available conductive paints have issues regarding low mechanical properties and fatigue resistance. Furthermore, mass production is limited due to the extremely high price of conductive fillers and complicated manufacturing processes. Here, we introduce a low price block copolymer and carbon black nanocomposite possessing superb mechanical flexibility and electrical conductivity. Attractively, its mechanical and electrical properties can be recovered with a thermal annealing process after applying cyclic loadings with high frequencies. The nanocomposite can be coated on a variety of substrates, such as fabric, wood, glass, and plastic. This self-healing composite could be used to design wearable electronics, soft robotics, and strain sensors, which require high flexibility.   

The effect of chemical structure on the morphology, ion transport, and modulus of hybrid inorganic-organic diblock copolymer electrolytes

Poly(ethylene oxide)-b-polyhedral oligomeric silsequioxane (PEO-POSS) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is a nanostructured hybrid organic-inorganic diblock copolymer electrolyte that may enable lithium metal batteries. The organic poly(ethylene oxide) block solvates lithium ions and facilitates ion transport while the inorganic polyhedral oligomeric silsequioxane (POSS) block provides mechanical rigidity, decoupling typically antagonistic mechanical and ion conducting properties. PEO-POSS with different alkyl chain substituents on the POSS monomer’s silica cage were synthesized to study the effect of chemical structure on morphology, ion transport, and modulus. Ionic conductivity, salt diffusion coefficient, and steady-state cation transference number were measured for a range of salt concentrations. In general, increasing the alkyl chain length was found to promote ordering and increase mechanical stiffness, while decreasing ionic conductivity.   

Ionomer Nanocomposites: The Interplay Between Structural Dynamics and Water Transport

Ionomer nanocomposites are gaining popularity as proton exchange membranes (PEMs) in vanadium redox flow batteries due to reduced vanadium ion crossover as compared to traditional PEMs. Understanding the impact of silica nanoparticles (SiNPs) on the structural dynamics and transport kinetics of these nanocomposites can provide vital insights into the mechanism of crossover reduction. Presently, segmental and swelling dynamics of a series of ionomer nanocomposite membranes were characterized using neutron spin echo and time-resolved Fourier transform infrared attenuated total reflectance (tFTIR-ATR) spectroscopy. We found that both viscoelastic relaxations and segmental dynamics in the ionomer network were impeded by the presence of SiNPs. Further, the dynamics of the membranes were highly dependent on the surface chemistry of the SiNPs, for both cationically or anionically charged surfaces. In addition to swelling dynamics, tFTIR-ATR was used to evaluate water sorption kinetics, which were found to be strongly coupled with the viscoelastic relaxation in these hybrid membranes. Anomalous, multi-stage water sorption kinetics were observed and attributed to different stages of structural rearrangement in the ionomer network during membrane hydration.

  

Metal Organic Framework assisted ionic conductivity in solid polymer electrolyte for application in lithium-ion battery

Solid polymer electrolytes are safer alternatives to the current flammable liquid electrolytes used in lithium-ion batteries. We are using crystalline PEO₆/LiX (X= anion) as the potential polymer electrolyte. In this structure, pairs of PEO chains wrap around each other to form cylindrical tunnels. Inside the tunnel each Li+ coordinates with six ether oxygens. The anions are located outside the tunnel. Low molecular weight PEO₆ has been found to be more conductive than its amorphous counterpart. However, it is not useful for practical applications as at room temperature this structure is like viscous liquid. Although increasing molecular weight improves the structural stability of PEO₆, it doesn’t improve conductivity. High molecular weight PEO₆ chains fold into lamellae, preventing direct pathway for lithium ion conduction. We propose that incorporating high aspect ratio nanofillers, containing lewis acidic surface sites, with PEO₆ can resolve the issue. Using metal organic framework as the nanofiller, we have obtained conductivity greater than 10^-5 S/cm at 30°C.

Reference:
Gadjourova, Z., Andreev, Y. G., Tunstall, D. P., & Bruce, P. G. (2001). Ionic conductivity in crystalline polymer electrolytes. Nature, 412(6846), 520.   

EFFECT OF FILLER CONTENT ON ENHANCEMENT OF THERMAL CONDUCTIVITY OF ALIGNED POLYMER GRAPHENE NANOCOMPOSITES

In this work a systematic study of the effect of increment of filler content on enhancement of thermal conductivity(k) of aligned polymer-graphene nanocomposites has been conducted. Using Angstrom Method, it is found that aligned graphene nanoplatelets (GnPs) significantly increase the heat-conducting properties of pure polyethylene (PE) compared to randomly oriented nanoplatelets. The increment in amount of GnPs from 9 weight% to 13 weight% is studied. A combination of melt extrusion processing and compression molding is used to obtain an even dispersion of the filler in the polymer matrix. Alignment of PE and GnPs is observed through confocal laser scanning microscopy. Comparison with effective medium theory reveals the measured thermal conductivity enhancement to be larger than theoretical predictions. Cause of this discrepancy between measurement and theory will be discussed.   

Molecular Simulations of the Motion of Polymer-Tethered Nanoparticles in Unentangled Polymer Melts

Polymer-tethered nanoparticles are commonly added to a polymer matrix to yield superior material properties. Critical to the fabrication and processing of such a composite is the mobility of polymer-tethered nanoparticles. We study the motion of polymer-tethered nanoparticles in unentangled polymer melts using molecular simulations, which offer a precise control of the grafted chain (tail) length N_tail and the number Z of tails per particle. For loosely-grafted particles with small Z, the diffusion coefficient decreases with increasing N_tail, exhibiting a crossover from particle-dominated to tail-dominated diffusion. If the diffusion is tail-dominated, there are two sub-diffusive regimes in the mean squared displacement 〈△r²(t)〉of particles before diffusion. The sub-diffusion at small t arises from the dynamical coupling of the particle and the melt chains, while the one at large t results from the participation of the particle in the dynamics of the tails. For densely-grafted particles with large Z, 〈△r²(t)〉can be approximated as that of a larger particle. The friction coefficient of the tails is smaller than the prediction based on Rouse dynamics of tails. These results suggest that the particle and tails move as one object with the tails hydrodynamically coupled to each other.   

Impact of hydrogen bonding interactions on graft-matrix wetting and structure in polymer nanocomposites

Properties of polymer nanocomposites (PNCs) are linked to their morphology which is dictated by the dispersion/aggregated state of nanoparticles in a polymer matrix. Grafting polymeric ligands onto the nanoparticle surface offers a greater control over morphology by allowing for tuning of effective interactions between graft and matrix polymers. One way to tailor interactions between graft and matrix chemistries is by the introduction of inter-molecular hydrogen bonds between graft and matrix polymers. In this talk, we present our work on the development of a coarse-grained (CG) model that allows us to capture hydrogen bonding type directional and specific interactions between graft and matrix polymers. Using this CG model, we run molecular dynamics (MD) simulations to elucidate the effect of these directional and specific interactions on the PNC morphology by comparing grafted layer wetting, graft and matrix chain conformations and free volume for each graft monomer between PNCs with isotropic graft-matrix interaction and PNCs with hydrogen bonding type graft-matrix interaction. We explore effects over a large design space comprising of grafting density, polymer flexibility, and strengths of isotropic graft-matrix attraction and hydrogen bonding interaction.   

Influence of Nanoparticle Surface Chemistry on Properties of Iron Oxide–Poly(ethylene oxide) Nanocomposites

Heating using magnetically susceptible nanoparticles has shown promise in biomedical applications in areas such as tissue engineering and drug delivery. In the current work, the effect of surface coating on iron oxide nanoparticles heated via an alternating magnetic field (AMF) was explored. Two coatings were investigated in addition to bare nanoparticles: poly(ethylene glycol), PEG, coated and amine coated 50–nm–diameter iron oxide nanoparticles. These nanoparticles were dispersed in concentrations varying from 0.010–0.750% by weight in poly (ethylene oxide), PEO. PEO was chosen due to its known biocompatibility and use in the healthcare industry. A significant increase in temperature was observed considering the low loading of particles in all samples. Analysis of heating curves revealed an unusual result. The amine coated particles had a much more significant and rapid response than either the uncoated or PEG coated nanoparticles. Healing properties of samples were also investigated as a function of AMF parameters and iron oxide surface chemistry.   

Functional polymer nanocomposites : structural issues in relation to the piezoelectric response

Poly(Vinylidene Fluoride) (PVDF) is a semi-crystalline polymer with complex polymorphism that has attracted considerable interest, owing to the electroactive properties displayed by its polar β and γ phases. Regarding PVDF-based nanocomposites, two strategies are considered in the following :
- The first one deals with the incorporation of piezoelectric inorganic nanofillers (BaTiO3), with primary issues related to nanoparticle dispersion and monitoring of interfacial cohesion, together with promoting the development of the highly polar β phase in the PVDF matrix. It is shown that the piezoelectric response may be modulated as a function of filler content, going through a zero value at some critical filler fraction.
- Alternatively, the introduction of carbon nanotubes in the PVDF matrix is achieved, with the result that the nanotubes induce the formation of the γ polar phase in their vicinity. The local structural organization of the α and γ phases in the PVDF nanocomposite is probed by atomic force microscopy and specific attention is paid to the local electroactive properties through the use of piezoelectric force microscopy (PFM).   

Optical Properties of Plasmonic Nanoparticles Polymer Nanocomposites

Plasmonic nanoparticles–polymer nanocomposites are used in functional optical materials and devices where light management is essential. However to modulate the optical properties of these nanocomposites, control over the orientation and spatial distribution of the nanoparticles within polymer matrix is very critical. Here we synthesized two-dimensional (2D) Ag nanoplates (AgNPs) with plasmon resonance across the visible and near infrared (NIR) light range via a multi-step approach. Layer-by-layer (LbL) assembly was utilized to control the orientation and density of the AgNPs in the nanocomposite films. The composite thin-films effectively controlled the light transmittance and reflectance across the visible and NIR range. In contrast to the conventional polymer nanocomposites in which the polymer grafted nanoparticles were randomly mixed within the matrix, the thin-film polymer nanocomposites comprise a single layer (~10 nm), or any desired multiple layers, of planarly oriented plasmonic AgNPs separated by a polymer with tunable interlayer thickness. The plasmonic composites filter light selectively and will have enormous effect on energy-efficient tinted glass.