More Like this

1. CONTROLLING ASSEMBLY OF POLYMER-GRAFTED NANOPARTICLES TO ENHANCE MECHANICAL PROPERTIES IN POLYMER NANOCOMPOSITE FILMS

   Zhang, Aria (May 2025, University of Pennsylvania)

   Polymer nanocomposite (PNC) films are of interest for many applications including electronics, energy storage, and advanced coatings. In phase-separating PNCs, the interplay between thermodynamic and kinetic factors governs the assembly of polymer-grafted nanoparticles (NPs), which directly influences material properties. Understanding how processing parameters affect the structure-property relationship of PNCs is important for designing advanced materials. This thesis provides insight by investigating a model PNC system of poly(methyl methacrylate)-grafted nanoparticles (PMMA-NPs) embedded in a poly(styrene-ran-acrylonitrile) (SAN) matrix. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was developed to quantify the distribution of NPs within PMMA-NP/SAN films, enabling precise 3D reconstruction of PNC structures. Experimental parameters such as primary ion beam angle and charge compensation were optimized to enhance secondary ion signals and depth resolution. Upon annealing in the twophase region, PMMA-NP/SAN films exhibited phase separation and surface segregation, leading to morphological evolutions characterized by atomic force microscopy (AFM), ToF-SIMS, water contact angle measurements, and transmission electron microscopy. By systematically exploring the effects of film thickness on PNC structures, we found that film thickness-induced confinement reduces lateral phase separation and enhances NP dispersion at the surface. A dimensional crossover from three to two dimensions was observed around 240 nm, below which surface-directed spinodal decomposition is suppressed. As a result of phase separation and surface segregation, six distinct bulk morphologies were identified, allowing for the construction of a morphology map correlating film thickness and annealing time. Among these morphologies, percolated structures were found to improve mechanical properties such as hardness and reduced modulus, as measured using AFM nanoindentation. Notably, interconnected networks show the highest hardness and modulus at both low and high force loadings. Additionally, Marangoni-induced hexagonal honeycomb patterns were observed in spin-coated as-cast PMMA-NP/SAN films. By changing to a less volatile solvent, these defects were eliminated, demonstrating the importance of solvent selection in achieving uniform and high-quality thin films. These findings demonstrate the potential for precise control of surface-enriched and phase-separated microstructures in PNC films through tailoring processing conditions. This thesis advances the understanding of processing-structure-property relationships in PNCs, providing a foundation for designing highly functional materials with broad industrial applications. 

   more » « less
2. Hierarchical Dynamics in Polymer Nanocomposites─Insights from Neutron and X-ray Scattering

   https://doi.org/10.1021/acs.macromol.6c00919  

   Koga, Tadanori; Nagao, Michihiro; Wiegart, Lutz; Carrillo, Jan-Michael Y; Endoh, Maya (July 2026, Macromolecules)

   The incorporation of nanoparticles (NPs) into polymers is one of the most effective strategies for reinforcing polymeric materials. The impact of NP reinforcement is exemplified by automobile tires, where it enhances a broad range of performance metrics, including fracture toughness, wear resistance, wet traction, rolling resistance, and fatigue durability. Reinforcement arises from the coupled evolution of hierarchical structures and hierarchical dynamics of polymers and NPs across multiple length and time scales. A comprehensive understanding of reinforcement mechanisms remains elusive. The advancement of PNCs depends on fundamental research investigating the hierarchical structures and dynamics of polymers and NPs by employing integrated measurements, analysis, and predictions. In this Perspective, the emphasis is placed on elucidating the hierarchical dynamics of PNCs at the nano-to-mesoscale through the integration of neutron spin echo (NSE) and X-ray photon correlation spectroscopy (XPCS). We highlight recent advances in understanding the hierarchical dynamics of bound polymer, nanoparticle networks, and cross-linked polymer networks. NSE combined with isotope labeling provides unique access to the segmental and chain dynamics─including entanglement dynamics─of labeled polymer chains across length scales from subnanometers to tens of nanometers and time scales from picoseconds to several hundred nanoseconds. In contrast, XPCS provides unique access to the collective dynamics of hierarchical structures of NPs in a polymer matrix over relevant time scales (submilliseconds to 1000s of seconds) and length scales (nanometers to hundreds of nanometers). Furthermore, recent advancements in in operando XPCS have enabled the investigation of the nonequilibrium evolution of structures and dynamics in PNCs under industrially relevant processing conditions. Together with complementary computational and experimental approaches, these advanced neutron and X-ray scattering techniques establish quantitative hierarchical structure–dynamics–property relationships that provide a molecular foundation for the rational design of next-generation PNCs. 

   more » « less
3. Ligand‐Mediated Interaction of Nanoparticles with Lipid Membranes

   https://doi.org/10.1002/mats.202300058  

   Mathew, Sandeep; Laradji, Mohamed; Kumar, P.B. Sunil (December 2023, Macromolecular Theory and Simulations)

   Abstract While many studies are performed on the effect of ligands on the adhesion and endocytosis of NPs, the effects of ligand length and surface density on the NPs' interaction with lipid membranes are poorly investigated. Here, a computational investigation is presented, based on molecular dynamics of a coarse‐grained implicit‐solvent model, of the interaction between ligand‐decorated spherical NPs and lipid membranes. Specifically,the case is considered where the ligands interact attractively with lipid membranes only through their ends. In particular, the effects of ligand grafting density, ligand length, and strength of ligand‐lipid interaction is investigated on the degree of wrapping of the NP by the membrane and on the morphology of the membrane close to the NP. Whereas the degree of wrapping is found to increase with increasing the grafting density for a given interaction strength and ligand length, it decreases with ligand length for a given grafting density and interaction strength. For moderate values of the adhesion strength and long ligands, it is found that the end ligands form long linear clusters, which lead to an anisotropic conformation of the membrane around the NP. For short ligands, the wrapping of the membrane around the NP is almost complete, with the wrapped NP showing a regular faceted structure for high adhesion strength. 

   more » « less
4. Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions

   https://doi.org/10.1039/C8SM01834K  

   Chen, Renjie; Poling-Skutvik, Ryan; Howard, Michael P.; Nikoubashman, Arash; Egorov, Sergei A.; Conrad, Jacinta C.; Palmer, Jeremy C. (February 2019, Soft Matter)

   The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length l p to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes – subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes–Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid ( i.e. as l p increases) indicate that the NP motions become decoupled from the bulk viscosity of the polymer solution. Likewise, polymer stiffness leads to deviations from PCT, which was developed for fully flexible chains. Independent of l p , however, the long-time diffusion behavior is well-described by MCT, particularly at high polymer concentration. We also observed that the short-time subdiffusive dynamics are strongly dependent on polymer flexibility. As l p is increased, the NP dynamics become more subdiffusive and decouple from the dynamics of the polymer chain center-of-mass. We posit that these effects are due to differences in the segmental mobility of the semiflexible chains. 

   more » « less
5. The Effect of Nanoparticle Shape, Orientation, and Heterogeneity on the Optical Birefringence of Polymer Nanocomposites

   https://doi.org/10.1021/acs.jpcc.5c07736  

   Li, Chen; Edamadaka, Sathya; Glor, Ethan; Vettelson, Melissa J; S_Watkins, Nathaniel; Faber-Rico, Jacob; Composto, Russell J; Ferrier, Robert C; Fakhraai, Zahra (February 2026, The Journal of Physical Chemistry C)

   Embedding plasmonic nanoparticles (NPs) into polymer nanocomposites (PNCs) is a facile method for integrating them into functional devices, whose properties are tunable through varying NP size, shape, and loading. Using anisotropic NPs adds an additional degree of tunability to their orientation order in the PNC, as properties such as conductivity and charge transport can be enhanced in specific directions. In thin films, the film thickness and block copolymer self-assembly can affect the degree of NP orientation, which can be used as a method of control over these properties. However, large-scale control of orientation order in randomly distributed NPs, with both anisotropic NP shapes and heterogeneous shape distributions, remains a chal-lenge. This is partly due to the lack of cost-effective, ensemble-level characterization methods that can independently determine the orientation order and degree of aggre-gation of anisotropic NPs. Here, we model the complex index of refraction of PNCs with plasmonic NP inclusions in the optical frequency domain by using an effective medium approximation. We quantitatively relate the simulated optical birefringence of the medium to the orientation order parameter of plasmonic nanorods and nanodisks in a robust manner insensitive to heterogeneity in simulated NP size and shape. Exper-imentally, we measure this orientation order parameter through the birefringent index of refraction using variable-angle spectroscopic ellipsometry (VASE). We demonstrate that we can independently determine the orientation order and degree of aggregation for various PNCs with gold nanorods and nanosphere inclusions. This facile tech-nique provides a powerful method to broadly measure the average orientation order of anisotropic particles in PNCs, which can be correlated to their functional properties. 

   more » « less