Manolis Doxastakis

The propagation of both catalyst diffusion and reaction fronts in a polymeric chemically amplified resist (CAR) is evaluated by time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling, and is compared with the propagation of catalyst diffusion fronts in inert resist analogues. We report that catalysts display accelerated and highly non-Fickian dynamics in the reactive CAR, even when located well behind the propagation front, while simple Fickian diffusion is observed for the same conditions in inert resist analogues. The complex catalyst dynamics of reactive systems is attributed to two key factors: (1) Transient free volume following deprotection events, which is a long-hypothesized acceleration mechanism acting on the diffusion front; and (2) a newly identified plasticization process induced by inert, nonvolatile byproducts of catalyst photoactivation. We propose a physics-informed model of enhanced catalyst diffusion due to the independent contributions of these two processes, and demonstrate that this model coupled to a first-order reaction provides a reasonable prediction of both the diffusion and reaction fronts. Our study presents a critical evaluation of mechanisms that control the spatial extent of reaction in CARs, and suggests that quantitative models of the patterning process should account for the impact of nonvolatile catalyst activation byproducts.

The behavior and properties of polymer–resin blends are critical for the design of advanced polymeric systems in a wide range of applications. In this work, we present an atomistic molecular dynamics study of the effects of hydrogenated dicyclopentadiene (H-DCPD) resin on the structural, dynamical, and viscoelastic properties of polymer matrices. Two different systems are examined: linear 1,4-cis polyisoprene (PI) and a four-component styrene–butadiene rubber (SBR) copolymer. The results reveal lower miscibility of H-DCPD resin in PI compared to that in SBR, as evidenced by the formation of resin-rich domains, revealed by the magnitude of local peaks in resin–resin radial distribution functions. Temperature-dependent analysis shows that structural and dynamical properties are most sensitive at ambient conditions (T = 300 K, P = 1 atm), with PI exhibiting significantly reduced molecular mobility due to its proximity to the glass transition temperature. This restricted dynamics directly influences the viscoelastic response, leading to increased structural rigidity upon resin addition. Furthermore, the effect of resin concentration is systematically assessed, demonstrating that, while 17 vol% resin has a negligible impact on both systems, increasing the concentration to 34 vol% in PI, results in pronounced changes in its structural and viscoelastic behaviors. Overall, this study highlights atomistic molecular dynamics simulations as powerful predictive tools for the rational design of resin–elastomer blends.

Chain relaxation in melts of moderately entangled macromolecules presents the first signs of topological constraints that are commonly manifested in the rheology of long commercial- grade polymers. In this study, we employ multiscale molecular dynamics simulations to examine the relaxation characteristics of model polyisoprene (PI) melts through the transition from the Rouse regime to entangled systems. We probed the impact of molecular weight and stereochemistry, and we evaluated the accuracy of theory in modeling the end-to-end relaxation. Our results support that trans-PI dynamics is distinct, with entanglements forming at a lower degree of polymerization than other compositions due to differences in the characteristic ratio and packing of this polymer. For all moderately entangled systems, modeling the end- to-end relaxation with the original Likhtman-McLeish theory with contour-length fluctuations presents deviations from recorded data both in the early-time and terminal regime. We propose numerical modifications that significantly improve the model for all systems studied without introducing additional parameters. Our approach allows accurate predictions for long macromolecules based on data from detailed simulations with moderately entangled polyisoprene systems.

In this research work, we provide a detailed investigation of the structural and viscoelastic properties of crosslinked styrene butadiene rubber (SBR) networks that are studied using atomistic molecular dynamics simulations.

Crosslinking macromolecules is an important process that aims to modulate mechanical properties of elastomers and meet desired specifications based on the application sought. The impact of crosslinking density on rubber moduli has been well established by theory, experiments and computational studies. However, several reports imply a role for the length of the sulfide bond and the attachment location. In this study, we construct all-atom models of polyisoprene (PI) networks using equilibrated precursor melts and sulfide crosslinks of a specific chemical architecture. We first examine network characteristics which follow expectations based on our random crosslinking approach. We report the presence of a substantial number of intramolecular connections formed. Thermodynamics and microscopic dynamics of the resulting networks are also probed. Comparing systems with the same number of crosslinks, we find that local mobility is most decelerated in the presence of long quaternary connections. To resolve any impact on mechanical properties we resorted to extensive characterization of moduli via equilibrium (stress-stress fluctuations) and non-equilibrium processes (constant-rate and oscillatory deformations). Both equilibrium and non-equilibrium simulations (at times/frequencies accessible to our all-atom models) confirm that quaternary linkages provide for the highest moduli with linker length holding a secondary role during moderate deformations.

The achievement of sufficient dispersion of vulcanization accelerators is critical to tailoring superior cross-linked elastomers. Modern recipes rely on multicomponent formulations with silica particles covered by coupling agents. We study the molecular properties of select accelerators in polyisoprene melts and their affinity for functionalized surfaces via extensive all-atom molecular dynamics simulations. We focus on the common (N-cyclohexyl)-2-benzothiazole sulfenamide (CBS), 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (DBTH), and diphenyl guanidine (DPG) molecules and their mixing characteristics at curing temperatures. Our results support a low self-association affinity for CBS and DBTH within polyisoprene, whereas DPG forms small hydrogen-bonded aggregates. Subsequently, we examine systems in contact with silica interfaces, bare or grafted with (3-mercaptopropyl)triethoxysilane (MPTES), (3-octanoylthio) 1-propyl-triethoxysilane (NXT), and bis[3-(triethoxysilyl)propyl]disulfide (TESPD). Accelerator-substrate affinity is first assessed at infinite dilution using free energy calculations and subsequently at finite concentrations. Accelerators exhibit high substrate affinity (DPG > CBS > DBTH) irrespective of functionalization. However, coupling agents are able to displace from the surface a significant amount that increases with the grafting density and the size of the coupling agent. Finally, we investigate the behavior of DPG in binary DPG-CBS formulations, where the former can act as a covering agent that solubilizes CBS into the bulk polymer.

The achievement of sufficient dispersion of vulcanization accelerators is critical to tailoring superior cross-linked elastomers. Modern recipes rely on multicomponent formulations with silica particles covered by coupling agents. We study the molecular properties of select accelerators in polyisoprene melts and their affinity for functionalized surfaces via extensive all-atom molecular dynamics simulations. We focus on the common (N-cyclohexyl)-2-benzothiazole sulfenamide (CBS), 1,6-Bis((dibenzylthiocarbamoyl)disulfanyl) hexane (DBTH) and diphenyl guanidine (DPG) molecules and their mixing characteristics at curing temperatures. Our results support a low association affinity for CBS and DBTH with polyisoprene, whereas DPG forms small hydrogen-bonded aggregates. Subsequently, we examine systems in contact with silica interfaces, bare or grafted with (3-Mercaptopropyl) triethoxysilane (MPTES), (3- Octanoylthio) 1-propyl-triethoxysilane (NXT), and bis (triethoxypropyl) disulfide (TESPD). Accelerator-substrate affinity is first assessed at infinite dilution using free energy calculations and subsequently at finite concentrations. Accelerators exhibit high substrate affinity (DPG >CBS >DBTH) irrespective of functionalization. However, coupling agents are able to displace from the surface a significant amount that increases with the grafting density and the size of the coupling agent. Finally, we investigate the behavior of DPG in binary DPG-CBS formulations, where the former can act as a covering agent that solubilizes CBS into the bulk polymer