Speckle-visibility spectroscopy of depolarized dynamic light scattering

We show that the statistical analysis of photon counts in depolarized dynamic light scattering experiments allows for the accurate characterization of the rotational Brownian dynamics of particles. Unlike photon correlation spectroscopy, the technique is accurate even at low temporal resolution and enables discontinuous data acquisition, which offers several advantages. To demonstrate the usefulness of the method, we present a case study in which we analyze aqueous suspensions of tunicate cellulose nanocrystals and silica particles, and discuss aspects that are specific to particle sizing

Taylor Dispersion of Polydisperse Nanoclusters and Nanoparticles: Modeling, Simulation, and Analysis

The dimensions of ultrasmall inorganic nanoparticles (US-NPs) is in the heart of the design of diagnostic and therapeutic efficacy; yet its accurate measurement is challenging for most experimental techniques. We show here how to design and analyze Taylor dispersion experiments to characterize the two most sought-after parameters describing size distributions: the number-averaged mean size and polydispersity index. To demonstrate the power of the method, we simulated and analyzed taylograms corresponding to gold US-NPs distributed normally. By using simulation and including experimental noise, we had the advantage that the true values describing size distribution were known exactly, and thus, we were able test the absolute accuracy of our analysis and its robustness against noise. Theory and computational experiments were found in very good agreement, providing a significant step in the analysis of ultrasmall inorganic nanoparticles and Taylor dispersion experiments

Isophthalic Acid–Pyridine H‑Bonding: Simplicity in the Design of Mechanically Robust Phase-Segregated Supramolecular Polymers

We report a new series of supramolecular polymeric networks based on the isophthalic acid–pyridine (IPA–Py) H-bonding motif. The IPA units were attached as end-groups to telechelic poly­(ethylene-<i>co</i>-butylene) to create a tetrafunctional macromonomer, which was cross-linked by the addition of various bispyridines. Some of the supramolecular polymer networks thus made display surprisingly good mechanical characteristics. We show that their structure and properties are strongly influenced by the nature of the bispyridine motif and by the fact that some of the IPA–Py motifs aggregate into particularly well-defined hard phases

Multistimuli, Multiresponsive Fully Supramolecular Orthogonally Bound Polymer Networks

Their dynamic and stimuli-responsive nature makes supramolecular bonds useful for the design of functional polymers with adaptable properties. The combination of multiple types of supramolecular interactions in one material permits, in principle, access to multistimuli, multiresponsive polymers, but examples of solid materials in which different supramolecular interactions have led to useful orthogonal responses toward different stimuli are rare. Here we report a new materials platform that involves two orthogonally bound supramolecular networks. The network components are based on a trifunctional poly­(propylene oxide) that was terminated with either 2,6-bis­(1′-methyl­benzimidazolyl)­pyridine (Mebip) ligands or 2-ureido-4­[1<i>H</i>]­pyrimidinone (UPy) groups. Supramolecular cross-linking was achieved by complexing the Mebip motifs to Zn²⁺ ions and UPy dimerization via hydrogen bonding, respectively. Orthogonal binding of the metal–ligand complex and the hydrogen-bonding motifs was confirmed via spectroscopically monitored titrations. Dynamic mechanical analyses and small-angle X-ray scattering data reveal that the properties of the supramolecular networks are governed by the microphase segregation of the binding motifs into two well-defined hard phases. The ability to independently disassemble the metal–ligand complexes and UPy dimers by chemical and thermal stimuli was exploited to access double and triple shape-memory and selective healing behaviors

Multistimuli, Multiresponsive Fully Supramolecular Orthogonally Bound Polymer Networks

Their dynamic and stimuli-responsive nature makes supramolecular bonds useful for the design of functional polymers with adaptable properties. The combination of multiple types of supramolecular interactions in one material permits, in principle, access to multistimuli, multiresponsive polymers, but examples of solid materials in which different supramolecular interactions have led to useful orthogonal responses toward different stimuli are rare. Here we report a new materials platform that involves two orthogonally bound supramolecular networks. The network components are based on a trifunctional poly­(propylene oxide) that was terminated with either 2,6-bis­(1′-methyl­benzimidazolyl)­pyridine (Mebip) ligands or 2-ureido-4­[1<i>H</i>]­pyrimidinone (UPy) groups. Supramolecular cross-linking was achieved by complexing the Mebip motifs to Zn²⁺ ions and UPy dimerization via hydrogen bonding, respectively. Orthogonal binding of the metal–ligand complex and the hydrogen-bonding motifs was confirmed via spectroscopically monitored titrations. Dynamic mechanical analyses and small-angle X-ray scattering data reveal that the properties of the supramolecular networks are governed by the microphase segregation of the binding motifs into two well-defined hard phases. The ability to independently disassemble the metal–ligand complexes and UPy dimers by chemical and thermal stimuli was exploited to access double and triple shape-memory and selective healing behaviors

Luminescent Nanoparticles with Lanthanide-Containing Poly(ethylene glycol)–Poly(ε-caprolactone) Block Copolymers

Lanthanide-containing nanoparticles have attracted much attention due to their unique optical properties and potential in nanotechnological applications. An amphiphilic block copolymer of poly­(ethylene glycol)-<i>b</i>-poly­(ε-caprolactone) methyl ether (mPEG-PCL) was functionalized with a dipicolinic acid (dpa) moiety and coordinated to lanthanide ions to afford [Ln­(dpa-PCL-PEG-OCH₃)₃]­(HNEt₃)₃ (Ln = Eu³⁺, Tb³⁺). Micelle-like nanoparticles of dpa-PCL-PEG-OCH₃ macroligand and metal-centered polymers were prepared by solvent displacement methods. Dynamic light scattering analysis (DLS) and cryogenic transmission electron microscopy images confirmed the presence of solid sphere (<47 nm in diameter) and vesicle (>47 nm in diameter) morphologies. The viability and stability of the lanthanide complexes in micelle-like nanoparticles was explored by DLS and luminescence spectroscopy, and found to be stable for several weeks

Supramolecular Polymers with Orthogonal Functionality

Supramolecular polymers with orthogonal interactions are of broad interest, and reports on such materials with multifunctional stimuli-responsive behavior are rare. Polymer blends based on a poly­(ethylene-<i>co</i>-butylene) core (PEB) terminated with either 2-ureido-4­[1<i>H</i>]-pyrimidinone (UPy) hydrogen-bonding motifs (UPy-PEB-UPy) or 2,6-bis­(1′-methylbenzimidazolyl)­pyridine (Mebip) ligands coordinated to metal ions ([M­(Mebip-PEB-Mebip)]²⁺ (M = Zn, Fe)) were prepared. The degree of orthogonality of the supramolecular polymer blends was explored by UV–vis spectroscopy, small-angle X-ray scattering, and dynamic mechanical thermal analysis (DMTA). Polymer blends of [Zn­(Mebip-PEB-Mebip)]­(NTf₂)₂ and UPy-PEB-UPy resulted in a statistical mixture of noncovalent interactions, whereas blends with [Fe­(Mebip-PEB-Mebip)]­(ClO₄)₂ and UPy-PEB-UPy assembled in an orthogonal fashion. Additionally, the DMTA showed two transitions for the disassembly of UPy (ca. 60 °C) and Fe²⁺-Mebip (ca. 180 °C) phases. The Fe²⁺-Mebip interactions were selectively disrupted by the addition of a competitive ligand, demonstrating that each supramolecular motif can be targeted with either a thermal or chemical stimulus

Epoxy Resin-Inspired Reconfigurable Supramolecular Networks

With the goal to push the mechanical properties of reconfigurable supramolecular polymers toward those of thermoset resins, we prepared and investigated a new family of hydrogen-bonded polymer networks that are assembled from isophthalic acid-terminated oligo­(bisphenol A-<i>co</i>-epichlorohydrin) and different bipyridines. These materials display high storage moduli of up to 3.9 GPa, can be disassembled upon heating to form melts with a viscosity of as low as 2.1 Pa·s, and fully reassemble upon cooling. We show that the new polymers can readily be reconfigured, reprocessed, or recycled and that the reversible (dis)­assembly makes them useful as hot-melt adhesives that permit debonding on demand

Synthesis and Biophysical Characterization of an Odd-Numbered 1,3-Diamidophospholipid

Nanomedicine suffers from low drug delivery efficiencies. Mechanoresponsive vesicles could provide an alternative way to release active compounds triggered by the basic physics of the human body. 1,3-Diamidophospholipids with C16 tails proved to be an effective building block for mechanoresponsive vesicles, but their low main phase transition temperature prevents an effective application in humans. As the main phase transition temperature of a membrane depends on the fatty acyl chain length, we synthesized a C17 homologue of a 1,3-diamidophospholipid: Rad-PC-Rad. The elevated main phase transition temperature of Rad-PC-Rad allows mechanoresponsive drug delivery at body temperature. Herein, we report the biophysical properties of Rad-PC-Rad monolayer and bilayer membranes. Rad-PC-Rad is an ideal candidate for advancing the concept of physically triggered drug release

Radiation Grafted Ion-Conducting Membranes: The Influence of Variations in Base Film Nanostructure

The proton exchange membrane (PEM) is a key element of a polymer electrolyte fuel cell, and radiation-grafting is an attractive option for the synthesis of PEMs. Via a systematic investigation of a well-defined model material, sulfonated polystyrene grafted poly­(ethylene-<i>alt</i>-tetrafluoroethylene), ETFE-<i>g</i>-PS­(SA), we show that the performance and stability of radiation-grafted PEMs in fuel cells strongly depends on the microstructure of the underlying base polymer. The nanoscale structure of the base polymers, grafted films, and membranes is probed by small-angle scattering, and the nanoscale proton dynamics is probed by quasi-elastic neutron scattering. The results of these techniques correlated with fuel cell relevant propertiesincluding proton conductivity and water uptakeand fuel cell performance clearly indicate that differences in the arrangement of the crystalline phase in the otherwise chemically identical semicrystalline base films can have considerable impact, representing an essential aspect to consider in the development of proton exchange membranes prepared via preirradiation grafting