Bottlebrush polymers are complex macromolecules with tunable physical properties dependent on the chemistry and architecture of both the side chains and the backbone. Prior work has demonstrated that bottlebrush polymer additives can be used to control the interfacial properties of blends with linear polymers but has not specifically addressed the effects of bottlebrush side chain microstructures. Here, using a combination of experiments and self-consistent field theory (SCFT) simulations, we investigated the effects of side chain microstructures by comparing the segregation of bottlebrush additives having random copolymer side chains with bottlebrush additives having a mixture of two different homopolymer side chain chemistries. Specifically, we synthesized bottlebrush polymers with either poly(styrene- ran -methyl methacrylate) side chains or with a mixture of polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains. The bottlebrush additives were matched in terms of PS and PMMA compositions, and they were blended with linear PS or PMMA chains that ranged in length from shorter to longer than the bottlebrush side chains. Experiments revealed similar behaviors of the two types of bottlebrushes, with a slight preference for mixed side-chain bottlebrushes at the film surface. SCFT simulations were qualitatively consistent with experimental observations, predicting only slight differences in the segregation of bottlebrush additives driven by side chain microstructures. Specifically, these slight differences were driven by the chemistries of the bottlebrush polymer joints and side chain end-groups, which were entropically repelled and attracted to interfaces, respectively. Using SCFT, we also demonstrated that the interfacial behaviors were dominated by entropic effects with high molecular weight linear polymers, leading to enrichment of bottlebrush near interfaces. Surprisingly, the SCFT simulations showed that the chemistry of the joints connecting the bottlebrush backbones and side chains played a more significant role compared with the side chain end groups in affecting differences in surface excess of bottlebrushes with random and mixed side chains. This work provides new insights into the effects of side chain microstructure on segregation of bottlebrush polymer additives.
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Coarse-grained molecular dynamics integrated with convolutional neural network for comparing shapes of temperature sensitive bottlebrushes
Quantification of shape changes in nature-inspired soft material architectures of stimuli-sensitive polymers is critical for controlling their properties but is challenging due to their softness and flexibility. Here, we have computationally designed uniquely shaped bottlebrushes of a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), by controlling the length of side chains along the backbone. Coarse-grained molecular dynamics simulations of solvated bottlebrushes were performed below and above the lower critical solution temperature of PNIPAM. Conventional analyses (free volume, asphericity, etc.) show that lengths of side chains and their immediate environments dictate the compactness and bending in these architectures. We further developed 100 unique convolutional neural network models that captured molecular-level features and generated a statistically significant quantification of the similarity between different shapes. Thus, our study provides insights into the shapes of complex architectures as well as a general method to analyze them. The shapes presented here may inspire the synthesis of new bottlebrushes.
more » « less- Award ID(s):
- 1933525
- NSF-PAR ID:
- 10364050
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- npj Computational Materials
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2057-3960
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)This article reports on the conformational behavior of binary heterografted three-arm star molecular bottlebrushes composed of poly(ethylene oxide) (PEO) and either poly(2-( N , N -dimethylamino)ethyl methacrylate) (PDMAEMA, the brushes denoted as SMB-1) or poly(2-( N , N -diethylamino)ethyl methacrylate) (PDEAEMA, the brushes denoted as SMB-2) side chains in aqueous solutions in response to pH changes and addition of salts containing chaotropic anions (CAs). PEO was introduced into the brushes as a stabilizer when the tertiary amine-containing side chains collapsed. While a small size decrease of SMB-1 was observed with increasing pH from acidic to basic, SMB-2 exhibited a large and abrupt size transition caused by the pH-induced solubility change of PDEAEMA. Atomic force microscopy imaging revealed a star-to-globule shape transition of SMB-2 upon increasing pH across the p K a ; in contrast, SMB-1 stayed in the starlike state at both low and high pH values. Intriguingly, both SMB-1 and -2 displayed star-to-globule shape transitions in acidic solutions upon addition of salts containing sufficiently strong CAs such as ClO 4 − , with SMB-2 showing a greater sensitivity to moderate CAs than SMB-1. Moreover, superchaotropic anions ( e.g. , Fe(CN) 6 3− and S 2 O 8 2− ) were significantly more efficient in inducing shape changing than common CAs. The CA-induced shape transitions resulted from the ion pairing of CAs and protonated tertiary amine groups and the high propensity of CAs to associate with hydrophobic moieties in the brushes, which decreased the solubility of the tertiary amine-containing side chains and caused the brushes to collapse. The findings reported here may enable potential applications of molecular bottlebrushes in, e.g. , encapsulation and release of ionic substances.more » « less
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Bottlebrush polymers are a class of macromolecules that have recently found use in a wide variety of materials, ranging from lubricating brushes and nanostructured coatings to elastomeric gels that exhibit structural colors. These polymers are characterized by dense branches extending from a central backbone and thus have properties distinct from linear polymers. It remains a challenge to specifically understand conformational properties of these molecules, due to the wide range of architectural parameters that can be present in a system, and thus there is a need to accurately characterize and model these molecules. In this paper, we use a combination of viscometry, light scattering, and computer simulations to gain insight into the conformational properties of dilute solution bottlebrush polymers. We focus on a series of model bottlebrushes consisting of a poly(norbornene) (PNB) backbone with poly(lactic acid) (PLA) side chains. We demonstrate that intrinsic viscosity and hydrodynamic radius are experimental observations sensitive to molecular architecture, exhibiting distinct differences with different choices of branches and backbone lengths. Informed by the atomistic structure of this PNB–PLA system, we rationalize a coarse-grained simulation model that we evaluate using a combination of Brownian dynamics and Monte Carlo simulations. We show that this exhibits quantitative matching to experimental results, enabling us to characterize the overall shape of the bottlebrush via a number of metrics that can be extended to more general bottlebrush architectures.more » « less
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Abstract By combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli‐responsive polymers, we show that MBBs with randomly grafted poly(
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