Shear Thinning from Bond Orientation in Model Unentangled Bottlebrush Polymer Melts

Abstract

The rheology of molecular brushes remains challenging to control due to the multiple length scales and relaxation processes involved and the lack of direct observation of molecular conformation during flow. We use molecular dynamics simulations to determine the shear thinning of unentangled bottlebrush polymers with varying architecture, from linear chains to combs, to densely grafted bottlebrushes, to star-like and star polymers. We find shear thinning exponents in line with theoretical and experimental results and characterize the shape and orientation of bottlebrushes in steady-state flow. Many shape parameters derived from the gyration tensor show molecular alignment with the flow for all systems. Yet, the orientation of individual bonds is what most strongly correlates with the architecture-dependent shear-thinning exponents. In densely grafted bottlebrushes, the packing of side chains prevents alignment with the flow, causing a reduction in shear thinning. The molecular insight from our simulations is useful to tune the architecture of bottlebrushes to control their rheology.

Synergistic Drug‐Loaded Shear‐Thinning Star Polymer Hydrogel Facilitates Gastrointestinal Lesion Resection and Promotes Wound Healing

“…In the case of entangled βCP brushes, the initial reduction in viscosity during the onset of shearing can be attributed to the unwinding of polymer side‐chains between star polymers. [ 18 ] In addition, βCP hydrogel also exhibits a remarkable self‐healing property. The strain amplitude scanning at a fixed frequency of 0.1 Hz at 25 °C reveals that the G' curve intersects the G'' curve when the shear strain reaches 464.8% (Figure 2e).…”

Comparison of Cyclic and Linear PEG Conjugates

“…Despite these successful examples, the conjugation of PEG to proteins has led to deleterious effects, such as contributing to vacuolization in vivo and inducing immunogenic responses as a result of the formation of anti-PEG antibodies. , Although there has been extensive research using linear polymers other than PEG to conjugate to biologics, the effects of more complex polymer architectures on protein–polymer conjugate properties is largely limited to branched and brush polymers . Namely, branched and brush polymers are known to possess longer circulation times and high stability to proteolysis compared to their linear counterparts. , Brush polymers also possess lower solution viscosity compared to linear analogues due to their elongated “rod-like” structures that align with solution flow direction. , Low viscosity biologic formulations are likely to increase patient compliance as thinner needles can be used for injection. To date, linear and singly branched PEG polymers are the only polymer architectures available on the protein–polymer therapeutic market …”

“… 13 , 14 Brush polymers also possess lower solution viscosity compared to linear analogues due to their elongated “rod-like” structures that align with solution flow direction. 15 , 16 Low viscosity biologic formulations are likely to increase patient compliance as thinner needles can be used for injection. To date, linear and singly branched PEG polymers are the only polymer architectures available on the protein–polymer therapeutic market.…”

Molecular Dynamics Simulations and Mechanistic Insights into Wrinkle Formation in TPU under Supercritical CO2 Flow Field

“…The process employing the scCO 2 flow field is capable of producing dense wrinkles with a highly controllable wavelength in the range of 0.5–3 μm, which is highly favorable for various functional applications such as energy absorption, anticounterfeiting, self-cleaning, and catalysis. ,,− This study performs an in-depth molecular dynamic research on the motion behavior of TPU molecular chains in the scCO 2 flow field, aiming to reveal the underlying wrinkle formation mechanism. Previous studies employing fluorescence labeling techniques were limited to dilute − or semidilute systems. − Molecular dynamics (MD) simulations and nonequilibrium molecular dynamics (NEMD) simulations play a crucial role in macromolecular physics, enabling researchers to observe and analyze the behavior and interactions of polymer chains such as stretching, orientation, and twisting under shear flow at the atomic level with precision. − …”