Robertson, Megan L.Conrad, Jacinta C.2022-06-18August 2022021-08August 202Portions of this document appear in: Li, T.-H.; Yadav, V.; Conrad, J. C.; Robertson, M. L., Effect of Dispersity on the Conformation of Spherical Polymer Brushes. ACS Macro Lett. 2021, 10 (5), 518-524.https://hdl.handle.net/10657/9369Polymer-grafted nanoparticles (PGNPs) exhibit prominent performance in applications, such as tough thin films,1-3 optics and electrics,4-7 ultrafiltration membranes,8 biomolecular and drug delivery vehicles,9-12 colorimetric sensors,13-15 and lubrication,16-18 partly due to uniform dispersion and/or morphology of polymer brushes with varying chain conformation. Polymer brush properties, such as grafting density \sigma and degree of polymerization N, can drastically affect conformation of neutral and pH-responsive PGNPs and further influence their efficacy in applications. Surprisingly, how dispersity Đ (related to the breadth of the polymer molecular weight distribution) affects the brush conformation is still underexplored. First, we examined the brush length l_b of neutral poly(tert-butyl acrylate) (PtBA) brushes in dilute solutions. l_b bifurcated as a function of weight-average degree of polymerization N_w: l_b increased with Đ at low N_w in the concentrated polymer brush (CPB) regime but was less dependent on Đ at high N_w in the semidilute polymer brush (SDPB) regime. We proposed that the variation of l_b with Đ in the CPB regime was due to the presence of a stretched conformation of the stem near the particle surface in high-Đ brushes. SANS data obtained from low- and high-Đ PtBA brushes in the CPB and SDPB regimes were analyzed using a core-chain model and demonstrated the differences in l_b obtained from SANS and DLS increased with Đ in the SDPB regime due to the long chain effect. The monomer density \rho profiles at the periphery decayed in a linear and power-law for brushes in the CPB at low and high Đ, respectively. In the SDPB regime, \rho decayed in a power-law at the periphery regardless of Đ. Next, we explored the conformation of pH-responsive poly(acrylic acid) (PAA) brushes, in which the extent of pH-response of l_b was enhanced with increased N_w or Đ (when N_w is low). We hypothesized the low-N_w and low-Đ brush adopted a highly extended conformation at all pH values, whereas the other brushes with higher N_w and/or Đ transitioned from a collapsed to extended conformations with increasing pH. Together, these results suggest Đ is a tunable parameter to control chain conformation of PGNPs depending on brush molecular weight.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Polymer brush, conformation2022-06-18Thesisborn digital