Rationally designed anionic diblock copolymer worm gels are useful model systems for calcite occlusion studies

Binary mixtures of anionic and non-ionic macromolecular chain transfer agents (macro-CTAs) are utilized in order to rationally design diblock copolymer nanoparticles with tunable morphologies and anionic character via pseudo-living radical polymerization. More specifically, poly(methacrylic acid) (PMAA) and poly(glycerol monomethacrylate) (PGMA) macro-CTAs are pre-mixed prior to reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). This strategy facilitates the formation of PHPMA-based diblock copolymer spheres, worm-like micelles and vesicles via polymerization-induced self-assembly (PISA). The presence of the anionic PMAA stabilizer block has a dramatic impact on the resulting copolymer morphology, particularly if the degree of polymerization (DP) of the PMAA stabilizer chains is longer than that of the PGMA. Two phase diagrams have been constructed to investigate the effect of the relative proportion and molar mass of the two macro-CTAs. Such a systematic approach is essential for the reproducible synthesis of pure worm-like micelles, which occupy relatively narrow phase space. The rheological behavior of a series of soft, free-standing worm gels is investigated. Finally, such gels are examined as model matrices for the growth of biomimetic calcite crystals and the role of the anionic PMAA stabilizer chains in directing crystal growth is evaluated

Physical Confinement Promoting Formation of Cu2O−Au Heterostructures with Au Nanoparticles Entrapped within Crystalline Cu2O Nanorods

Building on the application of cuprite (Cu2O) in solar energy technologies and reports of increased optical absorption caused by metal-to-semiconductor energy transfer, a confinement-based strategy was developed to fabricate high aspect ratio, crystalline Cu2O nanorods containing entrapped gold nanoparticles (Au nps). Cu2O was crystallized within the confines of track-etch membrane pores, where this physical, assembly based method eliminates the necessity of specific chemical interactions to achieve a well-defined metal−semiconductor interface. With high-resolution scanning/transmission electron microscopy (S/TEM) and tomography, we demonstrate the encasement of the majority of Au nps by crystalline Cu2O and show crystalline Cu2O−Au interfaces that are free of extended amorphous regions. Such nanocrystal heterostructures are good candidates for studying the transport physics of metal/semiconductor hybrids for optoelectronic applications

Round-robin study for ice adhesion tests

Ice adhesion tests are widely used to assess the performance of potential icephobic surfaces and coatings. A great variety of test designs have been developed and used over the past decades due to the lack of formal standards for these types of tests. In many cases, the aim of the research was not only to determine ice adhesion values, but also to understand the key surface properties correlated to low ice adhesion surfaces. Data from different measurement techniques had low correspondence between the results: Values varied by orders of magnitude and showed different relative relationships to one another. This study sought to provide a broad comparison of ice adhesion testing approaches by conducting different ice adhesion tests with identical test surfaces. A total of 15 test facilities participated in this round-robin study, and the results of 13 partners are summarized in this paper. For the test series, ice types (impact and static) as well as test parameters were harmonized to minimize the deviations between the test setups. Our findings are presented in this paper, and the ice- and test-specific results are discussed. This study can improve our understanding of test results and support the standardization process for ice adhesion strength measurements

Anionic block copolymer vesicles act as Trojan horses to enable efficient occlusion of guest species into host calcite crystals

We report a versatile ‘Trojan Horse’ strategy using highly anionic poly(methacrylic acid)–poly(benzyl methacrylate) vesicles to incorporate two types of model payloads, i.e. either silica nanoparticles or an organic dye (fluorescein), within CaCO3 (calcite). Uniform occlusion of silica-loaded vesicles was confirmed by scanning electron microscopy, while thermogravimetry studies indicated extents of vesicle occlusion of up to 9.4% by mass (∼33% by volume). Efficient dye-loaded vesicle occlusion produces highly fluorescent calcite crystals as judged by fluorescence microscopy. In control experiments, silica nanoparticles alone are barely occluded, while only very weakly fluorescent calcite crystals are obtained when using just the fluorescein dye. This new ‘Trojan Horse’ strategy opens up a generic route for the efficient occlusion of various nanoparticles and organic molecules within inorganic host crystals

Bio-Inspired Crystallization Of Oxides In Inorganic Matrices

The energy crisis facing our planet requires solutions that take an interdisciplinary approach to the improvement of existing energy systems as well as the development of new energy sources. Moreover, the composition of the materials is important: thermally- and chemically-stable materials based on abundant, non-toxic elements are needed to support the sustainability of both the technology and our environment. Biological organisms present multiple examples of hierarchical structures that are optimized for a given function. In particular, biomineralized materials: (i) display crystallographic control across length scales; (ii) are often organic-inorganic composites due to the occlusion of components from the associated organic growth matrix; (iii) and exhibit tailored mechanical properties that are unique to their function. Of great importance to the development of advanced energy materials is the observation that biomineral architectures are built from crystallographically-defined structural elements with interfaces that span multiple length scales. Synthetically, the translation of biological mineralization strategies to oxide compounds is hindered by the low melting temperatures of biopolymer hydrogels that compose extracellular matrices. In order to successfully crystallize oxide compounds using a (bio-inspired) matrix-mediated approach, I had to identify and develop a hydrogel system with thermal stability and chemical compatibility to the growth conditions needed for the oxide. By moving to inorganic networks based on silica, I achieved a thermally-stable growth matrix. By forming these networks at low pH, I obtained a growth environment that was compatible with the crystallization of hematite. With these two features, hematite was crystallized under diffusion-limited conditions, which provided a means to to manipulate its structure and assembly from the atomic- to the microscale. By combining inductively coupled plasma atomic emission spectroscopy with Rietveld refinements to x-ray diffraction data, expansion of the hematite lattice along the c-axis was found to be correlated to increasing silicon in the crystals and the preferential growth of the coherent domains along [110] (perpendicular to the strained c-axis). Using single particle manipulation in a focused ion beam system, electron-transparent thin sections were prepared from precisely-defined geometric locations within the hematite crystals for analysis by transmission electron microscopy. Quantitative analysis on selected area electron diffraction patterns was used to unravel the net orientation of the hematite lattice with respect to the quasi-spherical form and to calculate the misorientation (mosaicity) between the coherent domains. The combined results of these analyses showed that silicon from the growth environment had consistently modified the architecture of hematite, from the atomic to the microscale, leading to microscale structures with surfaces composed of nanoscale, high catalytic activity {110} facets. With hydrogel growth as a demonstrated route to tune the hierarchical structure of a transition metal oxide to preferentially express desired planes, the bandgap and photocatalytic activity of the samples was studied, to reveal that these micro-scale hierarchical architectures outperform their nano-sized counterparts, presenting a new approach to the design of materials for advanced energy applications

Mosaic anisotropy model for magnetic interactions in mesostructured crystals

We propose a new model for interpreting the magnetic interactions in crystals with mosaic texture called the mosaic anisotropy (MA) model. We test the MA model using hematite as a model system, comparing mosaic crystals to polycrystals, single crystal nanoparticles, and bulk single crystals. Vibrating sample magnetometry confirms the hypothesis of the MA model that mosaic crystals have larger remanence (Mr/Ms) and coercivity (Hc) compared to polycrystalline or bulk single crystals. By exploring the magnetic properties of mesostructured crystalline materials, we may be able to develop new routes to engineering harder magnets