Translocation Behaviors of Synthetic Polyelectrolytes through Alpha-Hemolysin (α-HL) and Mycobacterium smegmatis Porin A (MspA) Nanopores.

DNAs have been used as probes for nanopore sensing of noncharged biomacromolecules due to its negative phosphate backbone. Inspired by this, we explored the potential of diblock synthetic polyelectrolytes as more flexible and inexpensive nanopore sensing probes by investigating translocation behaviors of PEO-b-PSS and PEO-b-PVBTMA through commonly used alpha-hemolysin (α-HL) and Mycobacterium smegmatis porin A (MspA) nanopores. Translocation recordings in different configurations of pore orientation and testing voltage indicated efficient PEO-b-PSS translocations through α-HL and PEO-b-PVBTMA translocations through MspA. This work provides insight into synthetic polyelectrolyte-based probes to expand probe selection and flexibility for nanopore sensing.

Impact of a Lightly Branched Star Polyelectrolyte Architecture on Polyelectrolyte Complexes.

The effect of charge density in blocky and statistical linear polyelectrolytes on polyelectrolyte complex (PEC) properties has been studied with the finding that increased charge density in a polyelectrolyte tends to increase the salt resistance and modulus of a PEC across various polyelectrolyte pairs. Here, we demonstrate the ability to orthogonally alter PEC salt resistance while maintaining rheological properties and internal structure by going from linear to lightly branched architectures with similar total degrees of polymerization. Using a model system built around glycidyl methacrylate (GMA) and thiol-epoxy "click" functionalization, we create a library of homologous linear, 4-armed, 6-armed, and 8-armed star polyelectrolytes. The PECs formed from these model polyelectrolyte pairs are then characterized via optical microscopy, rheology, and small-angle X-ray scattering to evaluate their salt resistance, mechanical properties, and internal structure. We argue that our results are due to the difference between linear charge density or charge per unit length along backbone segments for each polyelectrolyte and spatial charge density, the number of charges per unit volume of the polyelectrolyte prior to complexation. Our findings suggest that linear charge density is the dominant factor in determining intermolecular interactions of the complex, leading to identical rheological and structural behavior, whereas the spatial charge density primarily influences the stability of the complexes. These distinct mechanisms for altering various sought-after PEC properties offer greater potential applications in precision design of polyelectrolyte complex materials.

Intrinsically thermally conductive polymers.

Here, we describe the design features that lead to intrinsically thermally conductive polymers. Though polymers are conventionally assumed to be thermal insulators (<0.3 W m-1 K-1), significant efforts by the thermal transport community have shown that polymers can be intrinsically thermally conductive (>1.0 W m-1 K-1). However, these findings have not yet driven comprehensive synthetic efforts to expose how different macromolecular features impact thermal conductivity. Preliminary theoretical and experimental investigations have revealed that high k polymers can be realized by enhancing the alignment, crystallinity, and intermolecular interactions. While a holistic mechanistic framework does not yet exist for thermal transport in polymeric materials, contemporary literature suggests that phonon-like heat carriers may be operative in macromolecules that meet the abovementioned criteria. In this review, we offer a perspective on how high thermal conductivity polymers can be systematically engineered from this understanding. Reports for several classes of macromolecules, including linear polymers, network polymers, liquid-crystalline polymers, and two-dimensional polymers substantiate the design principles we propose. Throughout this work, we offer opportunities for continued fundamental and technological development of polymers with high thermal conductivity.

Effect of Charged Block Length Mismatch on Double Diblock Polyelectrolyte Complex Micelle Cores.

Polyelectrolyte complex micelles are hydrophilic nanoparticles that self-assemble in aqueous environments due to associative microphase separation between oppositely charged blocky polyelectrolytes. In this work, we employ a suite of physical characterization tools to examine the effect of charged block length mismatch on the equilibrium structure of double diblock polyelectrolyte complex micelles (D-PCMs) by mixing a diverse library of peptide and synthetic charged-neutral block polyelectrolytes with a wide range of charged block lengths (25-200 units) and chemistries. Early work on D-PCMs suggested that this class of micelles can only be formed from blocky polyelectrolytes with identical charged block lengths, a phenomenon referred to as chain length recognition. Here, we use salt annealing to create PCMs at equilibrium, which shows that chain length recognition, a longstanding hurdle to repeatable self-assembly from mismatched polyelectrolytes, can be overcome. Interestingly, D-PCM structure-property relationships display a range of values that vary systematically with the charged block lengths and chemical identity of constituent polyelectrolyte pairings and cannot be described by generalizable scaling laws. We discuss the interdependent growth behavior of the radius, ionic pair aggregation number, and density in the micelle core for three chemically distinct diblock pairings and suggest a potential physical mechanism that leads to this unique behavior. By comparing the results of these D-PCMs to the scaling laws recently developed for single diblock polyelectrolyte complex micelles (S-PCMs: diblock + homopolymer), we observe that D-PCM design schemes reduce the size and aggregation number and restrict their growth to a function of charged block length relative to S-PCMs. Understanding these favorable attributes enables more predictive use of a wider array of charged molecular building blocks to anticipate and control macroscopic properties of micelles spanning countless storage and delivery applications.

Advances in the Structural Design of Polyelectrolyte Complex Micelles.

Polyelectrolyte complex micelles (PCMs) are a unique class of self-assembled nanoparticles that form with a core of associated polycations and polyanions, microphase-separated from neutral, hydrophilic coronas in aqueous solution. The hydrated nature and structural and chemical versatility make PCMs an attractive system for delivery and for fundamental polymer physics research. By leveraging block copolymer design with controlled self-assembly, fundamental structure-property relationships can be established to tune the size, morphology, and stability of PCMs precisely in pursuit of tailored nanocarriers, ultimately offering storage, protection, transport, and delivery of active ingredients. This perspective highlights recent advances in predictive PCM design, focusing on (i) structure-property relationships to target specific nanoscale dimensions and shapes and (ii) characterization of PCM dynamics primarily using time-resolved scattering techniques. We present several vignettes from these two emerging areas of PCM research and discuss key opportunities for PCM design to advance precision medicine.