A. Gul, M. Muzzammil Mohammad, M. Bockstaller, K. Matyjaszewski, A. Karim
University of Houston,
United States
Keywords: hyperuniformity, entropic phase separatin, PGNPs
Summary:
Polymer-grafted nanoparticles (PGNPs) have attracted widespread attention for their ability to combine nanoscale precision with tunable properties, making them ideal candidates for advanced technological applications. This study investigates two critical aspects of PGNP systems: the formation of hyperuniform structures and the entropic phase separation in binary blends. Both phenomena arise from the complex interplay of entropic and enthalpic interactions, positioning PGNPs as a versatile platform for fundamental research and application-driven material design. Hyperuniform structures, defined by suppressed density fluctuations across long length scales, are highly desirable for applications in photonics, energy storage, and mechanical reinforcement. In this work, hyperuniform assemblies are demonstrated in PMMA-g-SiO2 thin films, achieved using sequential solvent vapor annealing (SVA) followed by thermal annealing (TA). These processing techniques enable precise control over structural ordering, promoting hyperuniformity. The degree of hyperuniformity is evaluated using the structural factor S(q)/S(0), derived from two-dimensional fast Fourier transforms (2D FFT) of atomic force microscopy (AFM) and transmission electron microscopy (TEM) images. To provide a more comprehensive and accurate understanding of structural factors, grazing-incidence small-angle X-ray scattering (GISAXS) and neutron scattering are also employed. These complementary methods confirm the enhanced hyperuniformity achieved through optimized annealing conditions. The findings highlight the potential of PGNPs for creating materials with exceptional uniformity and tunable nanoscale properties. Simultaneously, this study examines the entropic phase separation in binary blends of PMMA/PSAN homopolymers and PMMA-g-SiO2/PSAN-g-SiO2 PGNPs. Homopolymer blends exhibit complete miscibility across all compositions and temperatures, driven by dominant entropic contributions. However, in PGNP blends, phase separation is observed near a 50/50 composition. This phase behavior is attributed to the reduced configurational entropy of grafted polymer chains, which restrict their degrees of freedom and enhance phase separation. The semi-dilute polymer brush (SDPB) regime plays a significant role in this behavior, as it limits chain interdigitation, weakening enthalpic interactions and narrowing the miscibility window. The interplay between entropy and enthalpy in these systems sheds light on the unique phase behavior of grafted polymer blends compared to their homopolymer counterparts. This research provides a comprehensive understanding of the dual capabilities of PGNP systems: forming hyperuniform structures through controlled processing and exhibiting unique entropic phase separation behavior. The ability to manipulate hyperuniformity through SVA and TA offers opportunities to develop systems with highly tailored optical, mechanical, and functional properties. At the same time, the insights into phase separation enhance the understanding of PGNP blends, enabling the design of materials with specialized structural characteristics. In conclusion, this work advances the fundamental knowledge of PGNP systems while offering practical guidelines for their application in emerging technologies. By combining hyperuniformity and phase separation insights, PGNPs represent a versatile and robust platform for designing innovative materials. These findings pave the way for breakthroughs in photonics, energy storage, and smart technologies, highlighting PGNPs as a cornerstone for future material science advancements.