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1. A Two‐Step Intermolecular Interaction Of Molecular Macroions With Multivalent Counterions

   https://doi.org/10.1002/chem.202402359  

   Xiao, Kexing; Zhou, Yifan; Xu, Xiaohan; Szymanowski, Jennifer_E S; Yang, Yuqing; Afsari, Bahareh; Burns, Peter C; Liu, Tianbo (October 2024, Chemistry – A European Journal)

   Macroion‐counterion interaction is essential for regulating the solution behaviors of hydrophilic macroions, as simple models for polyelectrolytes. Here, we explore the interaction between uranyl peroxide molecular cluster Li68K12(OH)20[UO2(O2)OH]60 (U60) and multivalent counterions. Different from interaction with monovalent counterions that shows a simple one‐step process, isothermal titration calorimetry, combined with light/X‐ray scattering measurements and electron microscopy, confirm a two‐step process for their interaction with multivalent counterions: an ion‐pairing betweenU₆₀and the counterion with partial breakage of hydration shells followed by strong U60‐U60 attraction, leading to the formation of large nanosheets with severe breakage and reconstruction of hydration shells. The detailed studies on macroion‐counterion interaction can be nicely correlated to the microscopic (self‐assembly) and macroscopic (gelation or phase separation) phase transitions in the dilute U60 aqueous solutions induced by multivalent counterions. 

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2. Structural correlations in highly asymmetric binary charged colloidal mixtures

   https://doi.org/10.1039/d2cp01343f  

   Allahyarov, Elshad; Löwen, Hartmut; Denton, Alan R. (June 2022, Physical Chemistry Chemical Physics)

   We explore structural correlations of strongly asymmetric mixtures of binary charged colloids within the primitive model of electrolytes considering large charge and size ratios of 10 and higher. Using computer simulations with explicit microions, we obtain the partial pair correlation functions between the like-charged colloidal macroions. Interestingly the big–small correlation peak amplitude is smaller than that of the big–big and small–small macroion correlation peaks, which is unfamiliar for additive repulsive interactions. Extracting optimal effective microion-averaged pair interactions between the macroions, we find that on top of non-additive Yukawa-like repulsions an additional shifted Gaussian attractive potential between the small macroions is needed to accurately reproduce their correct pair correlations. For small Coulomb couplings, the behavior is reproduced in a coarse-grained theory with microion-averaged effective interactions between the macroions. However, the accuracy of the theory deteriorates with increasing Coulomb coupling. We emphasize the relevance of entropic interactions exerted by the microions on the macroions. Our results are experimentally verifiable in binary mixtures of micron-sized colloids and like-charge nanoparticles. 

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3. Mapping the phase behavior of coacervate-driven self-assembly in diblock copolyelectrolytes

   https://doi.org/10.1039/c9sm00741e  

   Ong, Gary M.; Sing, Charles E. (June 2019, Soft Matter)

   Oppositely-charged polymers can undergo an associative phase separation process known as complex coacervation, which is driven by the electrostatic attraction between the two polymer species. This driving force for phase separation can be harnessed to drive self-assembly, via pairs of block copolyelectrolytes with opposite charge and thus favorable coulombic interactions. There are few predictions of coacervate self-assembly phase behavior due to the wide variety of molecular and environmental parameters, along with fundamental theoretical challenges. In this paper, we use recent advances in coacervate theory to predict the solution-phase assembly of diblock polyelectrolyte pairs for a number of molecular design parameters (charged block fraction, polymer length). Phase diagrams show that self-assembly occurs at high polymer, low salt concentrations for a range of charge block fractions. We show that we qualitatively obtain limiting results seen in the experimental literature, including the emergence of a high polymer-fraction reentrant transition that gives rise to a self-compatibilized homopolymer coacervate behavior at the limit of high charge block fraction. In intermediate charge block fractions, we draw an analogy between the role of salt concentration in coacervation-driven assembly and the role of temperature in χ -driven assembly. We also explore salt partitioning between microphase separated domains in block copolyelectrolytes, with parallels to homopolyelectrolyte coacervation. 

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4. Solution Self-Assembly of Coil-Crystalline Diblock Copolypeptoids Bearing Alkyl Side Chains

   https://doi.org/https://doi.org/10.3390/polym13183131  

   Naisheng Jiang; * Donghui Zhang* (September 2021, Polymers)

   Polypeptoids, a class of synthetic peptidomimetic polymers, have attracted increasing attention due to their potential for biotechnological applications, such as drug/gene delivery, sensing and molecular recognition. Recent investigations on the solution self-assembly of amphiphilic block copolypeptoids highlighted their capability to form a variety of nanostructures with tailorable morphologies and functionalities. Here, we review our recent findings on the solutions self-assembly of coil-crystalline diblock copolypeptoids bearing alkyl side chains. We highlight the solution self-assembly pathways of these polypeptoid block copolymers and show how molecular packing and crystallization of these building blocks affect the self-assembly behavior, resulting in one-dimensional (1D), two-dimensional (2D) and multidimensional hierarchical polymeric nanostructures in solution. 

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5. Building blocks of non-Euclidean ribbons: size-controlled self-assembly via discrete frustrated particles

   https://doi.org/10.1039/D2SM01371A  

   Hall, Douglas M.; Stevens, Mark J.; Grason, Gregory M. (February 2023, Soft Matter)

   Geometric frustration offers a pathway to soft matter self-assembly with controllable finite sizes. While the understanding of frustration in soft matter assembly derives almost exclusively from continuum elastic descriptions, a current challenge is to understand the connection between microscopic physical properties of misfitting “building blocks” and emergent assembly behavior at the mesoscale. We present and analyze a particle-based description of what is arguably the best studied example for frustrated soft matter assembly, negative-curvature ribbon assembly, observed in both assemblies of chiral surfactants and shape-frustrated nanoparticles. Based on our particle model, known as saddle wedge monomers, we numerically test the connection between microscopic shape and interactions of the misfitting subunits and the emergent behavior at the supra-particle scale, specifically focussing on the propagation and relaxation of inter-particle strains, the emergent role of extrinsic shape on frustrated ribbons and the equilibrium regime of finite width selection. Beyond the intuitive role of shape misfit, we show that self-limitation is critically dependent on the finite range of cohesive interactions, with larger size finite assemblies requiring increasing short-range interparticle forces. Additionally, we demonstrate that non-linearities arising from discrete particle interactions alter self-limiting behavior due to both strain-softening in shape-flattened assembly and partial yielding of highly strained bonds, which in turn may give rise to states of hierarchical, multidomain assembly. Tracing the regimes of frustration-limited assembly to the specific microscopic features of misfitting particle shapes and interactions provides necessary guidance for translating the theory of size-programmable assembly into design of intentionally-frustrated colloidal particles. 

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