We show that the class of combinatorial entropy models, such as the Guggenheim-Staverman model, in which the many conformations of a molecule are taken into account, does not fulfill the Gibbs probability normalization condition. The root cause for this deviation lies in the definition of the pure and mixture state. In the athermal limit, mandatory to define the combinatorial entropy, the number of molecules in a particular conformation does not change upon mixing. Therefore each set of molecules with a particular conformation in the pure state can be regarded as a distinguishable subclass of rigid molecules. When this subdivision is applied to the ‘shape’ models, they fulfill the Gibbs probability normalization condition. The resulting equations simplify to the Flory–Huggins entropy model. Implications of this finding to the existing activity coefficient models are discussed.

The development of simulation methods to study the structure and dynamics of a macroscopically sized piece of polymer material is important as such methods can elucidate structure-property relationships. Several methods have been reported to construct initial structures for homo- and co-polymers; however, most of them are only useful for short linear polymers since one needs to pack and equilibrate the far-from-equilibrium initial structures, which is a tedious task for long or hyperbranched polymers and unfeasible for polymer networks. In this method article, we present PolySMart, i.e., an open-source python package, which can effectively produce fully equilibrated homo- and hetero-polymer melts and solutions with no limitation on the polymer topology and size, at a coarse-grained resolution and through a bottom-up approach. This python package is also capable of exploring the polymerization kinetics through its reactive scheme in realistic conditions so that it can model the multiple co-occurring polymerization reactions (with different reaction rates) as well as consecutive polymerizations under stoichiometric and non-stoichiometric conditions. Thus, the equilibrated polymer models are generated through correct polymerization kinetics. A benchmark and verification of the performance of the program for several realistic cases, i.e., for homo-polymers, co-polymers, and crosslinked networks, is given. We further discuss the capability of the program to contribute to the discovery and design of new polymer materials.

Contrary to continuous phase transitions, where renormalization group theory provides a general framework, for discontinuous phase transitions such a framework seems to be absent. Although the thermodynamics of the latter type of transitions is well-known and requires input from two phases, for melting a variety of one-phase theories and models based on solids has been proposed, as a generally accepted theory for liquids is (yet) missing. Each theory or model deals with a specific mechanism using typically one of the various defects (vacancies, interstitials, dislocations, interstitialcies) present in solids. Furthermore, recognizing that surfaces are often present, one distinguishes between mechanical or bulk melting and thermodynamic or surface-mediated melting. After providing the necessary preliminaries, we discuss both types of melting in relation to the various defects. Thereafter we deal with the effect of pressure on the melting process, followed by a discussion along the line of type of materials. Subsequently, some other aspects and approaches are dealt with. An attempt to put melting in perspective concludes this review.

To assess the surface energy of solids, normally a set of probe liquids comprising polar and apolar compounds is used. Here we survey the surface tension of some frequently used probe liquids as given in the literature, for which a significant scatter appears to be present, and compare them with experimentally determined values. We discuss the influence of the liquid purity as well as the contact angle between the liquid and the Wilhelmy plate, which is commonly used for surface tension measurements. For hygroscopic polar probe liquids such as dimethyl sulfoxide, ethylene glycol, and formamide, water impurities appear to be of limited importance. Similarly, the amount of halogen impurities is of minor importance for diiodomethane and 1-bromonaphthalene, which decompose under the influence of light. Conversely, the influence of the contact angle for liquids that do not fully wet the plate, such as diiodomethane, is large in many cases, rendering a rather accurate determination of the contact angle necessary. Some discrepancies in the literature are indicated, and brief recommendations for future studies using such liquids are given.

Collagen mineralization is a biological process in many skeletal elements in the animal kingdom. Examples of these collagen-based skeletons are the siliceous spicules of glass sponges or the intrafibrillar hydroxyapatite platelets in vertebrates. The mineralization of collagen in vitro has gained interest for two reasons: understanding the processes behind bone formation and the synthesis of scaffolds for tissue engineering. In this paper, the efforts toward collagen mineralization in vitro are reviewed. First, general introduction toward collagen type I, the main component of the extracellular matrix in animals, is provided, followed by a brief overview of collagenous skeletons. Then, the in vitro mineralization of collagen is critically reviewed. Due to their biological abundance, hydroxyapatite and silica are the focus of this review. To a much lesser extent, also some efforts with other minerals are outlined. Combining all minerals and the suggested mechanisms for each mineral, a general mechanism for the intrafibrillar mineralization of collagen is proposed. This review concludes with an outlook for further improvement of collagen-based tissue engineering scaffolds.

Control over the assembly and morphology of nanoscale functional building blocks is of great importance to hybrid and porous nanomaterials. In this paper, by combining different types of spherical nanoparticles with different size ratios in a hierarchical assembly process which allows us to control the final structure of multi-component assemblies, we discuss self-assembly of an extensive range of supraparticles, labelled as AB particles, and an extension to novel ternary particles, labelled as ABC particles. For supraparticles, the organization of small nanoparticles is known to be inherently related to the size ratio of building blocks. Therefore, we studied the formation of supraparticles prepared by colloidal self-assembly using small silica nanoparticles (SiO2 NPs) attached on the surface of large polystyrene latex nanoparticles (PSL NPs) with a wide size ratio range for complete and partial coverage, by controlling the electrostatic interactions between the organic and inorganic nanoparticles and their concentrations. In this way hierarchically ordered, stable supraparticles, either fully covered or partially covered, were realized. The partially covered, stable AB supraparticles offer the option to create ABC supraparticles of which the fully covered shell contains two different types of nanoparticles. This has been experimentally confirmed using iron oxide (Fe3O4) nanoparticles together with silica nanoparticles as shell particles on polystyrene core particles. Cryo-electron tomography was used to visualize the AB binary and ABC ternary supraparticles and to determine the three-dimensional structural characteristics of supraparticles formed under different conditions.

Simulating structural and thermodynamical properties of liquids has always been a challenge. Typical examples of liquids that demonstrate particular structure and properties are water and the low molecular weight alcohols, for which hydrogen bond interactions lead to their distinctive properties, such as cage -like structures and temperature-dependent properties. Modeling these materials at the coarse-grained level is even a bigger challenge due to the loss of atomistic-level interactions. Nevertheless, one is inter-ested in mimicking these typical properties at the coarse-grained level due to the relevance of these sys-tems in complex environments, for which fully atomistic simulations still remain a challenge. In this paper, we introduce a mesoscopic level parameterization of DPD interactions to study the particular structural and thermodynamic properties of liquid water, methanol, ethanol and 1-propanol. The conser-vative repulsive DPD interactions are explicitly computed by a bottom-up parameterization, in which experimental thermodynamics data are used. A previously developed statistical mechanics approach is used to compute the hydrogen bond strength. The transport properties, such as viscosity, and thermody-namical properties, such as isothermal compressibility, are found to agree reasonably well with experi-mental data. Moreover, the structure as characterized by the radial distribution function and angular distributions of three neighboring molecules are in line with the atomistic simulations performed in this work. Furthermore, the temperature-dependency of the repulsive DPD interactions is modeled by incor-porating the experimental isothermal compressibilities at different temperatures. The effect of the tem-perature on the hydrogen bond strengths is considered as well and the structural properties are predicted via the DPD simulations. In general, our work can be viewed as an attempt to model systems by the DPD simulations, where hydrogen bonds play a crucial role. The computed parameterization of DPD interac-tions is believed to pave the way towards extending the current applicability of DPD method to more complex systems. (c) 2022 Elsevier B.V. All rights reserved.

Bone is a complex natural material with a complex hierarchical multiscale organization, crucial to perform its functions. Ultrastructural analysis of bone is crucial for our understanding of cell to cell communication, the healthy or pathological composition of bone tissue, and its three-dimensional (3D) organization. A variety of techniques has been used to analyze bone tissue. This article describes a combined approach of optical, scanning electron, and transmission electron microscopy for the ultrastructural analysis of bone from the nanoscale to the macroscale, as illustrated by two pathological bone tissues. By following a top-down approach to investigate the multiscale organization of pathological bones, quantitative estimates were made in terms of calcium content, nearest neighbor distances of osteocytes, canaliculi diameter, ordering, and D-spacing of the collagen fibrils, and the orientation of intrafibrillar minerals which enable us to observe the fine structural details. We identify and discuss a series of two-dimensional (2D) and 3D imaging techniques that can be used to characterize bone tissue. By doing so we demonstrate that, while 2D imaging techniques provide comparable information from pathological bone tissues, significantly different structural details are observed upon analyzing the pathological bone tissues in 3D. Finally, particular attention is paid to sample preparation for and quantitative processing of data from electron microscopic analysis.

The mineralization of collagen in vitro has been extensively investigated for hydroxyapatite, silica, calcium carbonate and lepidocrocite (γ-FeOOH). Henceforth, it is interesting to investigate whether collagen also could serve as a generic mineralization template for other minerals, like magnetite. To this end, and inspired by the partial oxidation approach, first a ferrous hydroxide (Fe(OH)2) intermediate is synthesized via the titration of base to a solution of Fe2+. Subsequently, the Fe(OH)2 is mixed with collagen fibrils and poly(aspartic acid) is added to promote the formation of intrafibrillar crystals. Platelet-shaped lepidocrocite crystals being present throughout the entire thickness of the collagen fibrils can be realized, as was confirmed with electron tomography. The formation of lepidocrocite, which is an Fe3+ compound, is hypothesized to be induced via oxidation of the Fe2+ species and, therefore, the oxygen concentration during titration, TEM sample preparation and drying of TEM samples are investigated. Although the reaction is sensitive to small changes in experimental conditions, highly mineralized collagen fibers can be realized.

ADVERTISEMENT RETURN TO ISSUEViewpointNEXTHow Reliable Are Surface Tension Data?Bernette M. Oosterlaken*Bernette M. OosterlakenLaboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands*Email: [email protected]More by Bernette M. OosterlakenView Biographyhttps://orcid.org/0000-0002-8083-2581 and Gijsbertus de With*Gijsbertus de WithLaboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands*Email: [email protected]More by Gijsbertus de WithView Biographyhttps://orcid.org/0000-0002-7163-8429Cite this: Acc. Mater. Res. 2022, 3, 9, 894–899Publication Date (Web):August 11, 2022Publication History Received30 June 2022Published online11 August 2022Published inissue 23 September 2022https://pubs.acs.org/doi/10.1021/accountsmr.2c00129https://doi.org/10.1021/accountsmr.2c00129article-commentaryACS PublicationsCopyright © 2022 The Authors. Co-published by ShanghaiTech University and American Chemical Society. This publication is licensed under CC-BY 4.0. License Summary*You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:Creative Commons (CC): This is a Creative Commons license.Attribution (BY): Credit must be given to the creator.View full license*DisclaimerThis summary highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. Carefully review the actual license before using these materials. This publication is Open Access under the license indicated. Learn MoreArticle Views2780Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (3 MB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Contact angle,Liquids,Surface energy,Surface tension,Transition metals Get e-Alerts

Hypothesis: Block copolymers (BCP) consisting of a polar block and a surface active apolar block are widely used for surface functionalization of polymer films. The characteristics of the copolymer blocks determine whether surface segregation and/or phase separation occurs, for a given bulk mixture. This data can be used to find the optimal BCP composition where high surface enrichment is obtained without accumulation of phase separated BCP in the bulk. Methods: The distribution of poly(ethylene oxide)-polydimethylsiloxane (PEO-PDMS) BCP in a polymer formulation relevant for coating applications is systematically investigated. The surface segregation is studied in liquid formulations with surface tension measurements and dried films with X-ray photoelectron spectroscopy (XPS), whereas phase separation is quantified using turbidity measurements. The results are compared with Scheutjens-Fleer self-consistent field (SF-SCF) computations, which are also applied to determine the effect of film drying on BCP phase stability and surface segregation. Findings: Longer PDMS blocks result in lower interfacial tension of the liquid polymer mixture, whereas for the cured films, the largest PDMS concentration at the interface was obtained for intermediate PDMS block lengths. This is explained by the observation that phase separation already occurs at very low BCP concentrations for long PDMS blocks. The SCF predictions qualitatively agree with the experimental results and reveal that the BCP distribution changes significantly during film drying. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Formation of superstructures from colloidal dispersion involves a continuous increase in particle concentration, resulting in increasingly more complicated interparticle interaction. At high particle concentration, the presence of the super-crowding effect, strong non-ideality in addition to significant light absorption and scattering makes particle analysis very difficult. Here we report quantitative molecular, microscopic and macroscopic experimental results on like-charged colloids with concentration up to 60 vol%, close to the densest possible packing of spheres. It is achieved by conducting sedimentation-diffusion-equilibrium analytical ultracentrifugation (SE-AUC) on a concentrated dispersion of colloidal silica nanoparticles in a refractive-index-matching solvent. Surprisingly, we observed the self-association and even colloidal gel formation of like-charged colloids at very high concentration. Further experiments indicate that the attraction force may be counter-ion mediated. These results represent an important step forward in understanding complicated interparticle interaction in extremely high concentration, which is vital for the controlled fabrication of colloidal superstructures.

Periodic nano- or microscale structures are used to control light, energy and mass transportation. Colloidal organization is the most versatile method used to control nano- and microscale order, and employs either the enthalpy-driven self-assembly of particles at a low concentration or the entropy-driven packing of particles at a high concentration. Nonetheless, it cannot yet provide the spontaneous three-dimensional organization of multicomponent particles at a high concentration. Here we combined these two concepts into a single strategy to achieve hierarchical multicomponent materials. We tuned the electrostatic attraction between polymer and silica nanoparticles to create dynamic supracolloids whose components, on drying, reorganize by entropy into three-dimensional structured materials. Cryogenic electron tomography reveals the kinetic pathways, whereas Monte Carlo simulations combined with a kinetic model provide design rules to form the supracolloids and control the kinetic pathways. This approach may be useful to fabricate hierarchical hybrid materials for distinct technological applications.

Liquid-Phase (Scanning) Transmission Electron Microscopy (LP-(S)TEM) has become an essential technique to monitor nanoscale materials processes in liquids in real-time. Due to the pressure difference between the liquid and the microscope vacuum, bending of the silicon nitride (SiNx ) membrane windows generally occurs. This causes a spatially varying liquid layer thickness that makes interpretation of LP-(S)TEM results difficult due to a locally varying achievable resolution and diffusion limitations. To mediate these difficulties, it is shown: 1) how to quantitatively map liquid layer thickness for any liquid at less than 0.01 e- Å-2 total dose; 2) how to dynamically modulate the liquid thickness by tuning the internal pressure in the liquid cell, co-determined by the Laplace pressure and the external pressure. It is demonstrated that reproducible inward bulging of the window membranes can be realized, leading to an ultra-thin liquid layer in the central window area for high-resolution imaging. Furthermore, it is shown that the liquid thickness can be dynamically altered in a programmed way, thereby potentially overcoming the diffusion limitations towards achieving bulk solution conditions. The presented approaches provide essential ways to measure and dynamically adjust liquid thickness in LP-(S)TEM experiments, enabling new experiment designs and better control of solution chemistry.

The adsorption mechanism of small positively charged silica nanoparticles (SiO2 NPs) onto larger polystyrene latex nanoparticles (PSL NPs) forming hybrid particles was studied. CryoTEM showed the morphology of these supraparticles to be raspberry-like. After surface modification of the SiO2 NPs, the optimum pH regime to initiate the formation of nanoraspberries was determined. Thereafter, their size evolution was evaluated by dynamic light scattering for different surface charge densities. Reversibility of nanoraspberry formation was shown by cycling the pH of the mixture to make interparticle forces either attractive or repulsive, while their stability was confirmed experimentally. The number of SiO2 NPs on the PSL NPs as determined with cryoTEM matched the theoretically expected maximum number. Understanding and controlling the relevant parameters, such as size and charge of the individual particles and the Debye length, will pave the way to better control of the formation of nanoraspberries and higher-order assemblies thereof.

Nanoscale chemical analysis of functional polymer systems by electron microscopy, to gain access into degradation processes during the materials life cycle, is still a formidable challenge due to their beam sensitivity. Here a systematic study on the different stages of degradation in a P3HT-PCBM organic photo-voltaic (OPV) model system is presented. To this end pristine samples, samples with (reversibly) physisorbed oxygen and water and samples with (irreversibly) chemisorbed oxygen and water are imaged utilizing the full capabilities of cryogenic STEM-EELS. It is found that oxygen and water are largely physisorbed in this system leading to significant effects on the band structure, especially for PCBM. Quantification proves that degradation concomitantly decreases the amount of C C bonds and increases the amount of C O C bonds in the sample. Finally, it is shown that with a pulsed electron beam utilizing a microwave cavity, beam damage can be significantly reduced which likely extends the possibilities for such studies in future.

The exchange of Ca2+ ions in hydroxyapatite (HAp) with Zn2+ ions into Zn-HAp is of interest for applications ranging from bone tissue engineering to the use as a precursor in subsequent ion-exchange reactions. Previous studies, using direct synthesis, showed that ~ 20 mol% Zn2+ ions can be incorporated into HAp, before byproducts are observed. However, this is realized at the cost of a loss in crystallinity and control over crystal size and shape with increasing amounts of Zn2+ ion incorporation. In this work a simple post-synthetic ion-exchange strategy for the formation of Zn-HAp has been investigated. By merely exposing HAp to high concentrations of zinc nitrate in water, up to 22 mol% of the Ca2+ ions can displaced by Zn2+ ions without any measured loss in crystallinity and preservation of crystallite size and shape. It was found that the incorporation of Zn2+ ions destabilizes the HAp crystals resulting in their gradual dissolution and reprecipitation. Consequently, promoting the exchange of Ca2+ with Zn2+ions using increased reaction times, sonication and increased temperature results in an increased dissolution of HAp and precipitation of hopeite crystals, thereby preventing the formation of more zinc rich Zn-HAp.

The mineralization of collagen via synthetic procedures has been extensively investigated for hydroxyapatite as well as for silica and calcium carbonate. From a fundamental point of view, it is interesting to investigate whether collagen could serve as a generic mineralization template for other minerals, like iron oxides. Here, bio-inspired coprecipitation reaction, generally leading to the formation of magnetite, is used to mineralize collagen with iron hydroxides. Platelet-shaped green rust crystals form outside the collagen matrix, while inside the collagen, nanoparticles with a size of 2.6 nm are formed, which are hypothesized to be iron (III) hydroxide. Mineralization with nanoparticles inside the collagen solely occurs in the presence of poly(aspartic acid) (pAsp). In the absence of pAsp, magnetite particles are formed around the collagen. Time-resolved cryo-TEM shows that during the coprecipitation reaction, initially a beam-sensitive phase is formed, possibly an Fe3+–pAsp complex. This beam-sensitive phase transforms into nanoparticles. In a later stage, sheet-like crystals are also found. After 48 h of mineralization, ordering of the nanoparticles around one of the collagen sub-bands (the a-band) is observed. This is very similar to the collagen–hydroxyapatite system, indicating that mineralization with iron hydroxides inside collagen is possible and proceeds via a similar mechanism as hydroxyapatite mineralization.

The intrinsic high diffusion rate of colloids at low Péclet number results in an extremely fast crystallization process and instant formation of colloidal crystals, even at an ultracentrifugal field of extremely high intensity. By introducing a small number of clusters in sedimention, it should be possible to slow down the crystallization process, thus making the assembly order tunable in preparative ultracentrifugation experiments. Here, we used sodium dodecyl sulfate-stabilized polystyrene nanoparticles (with a size dispersity of 1.07) dispersed in a solution of high ionic strength. Sedimentation and assembly of these nanoparticles were done using preparative ultracentrifugation at various angular velocities. The sedimentation process was also analyzed in situ by analytical ultracentrifugation in real time. By creating as low as 3% of clusters into these nearly uniformly sized polystyrene nanoparticle dispersions during the sedimentation process, the superstructure order becomes easily tunable between glassy and crystalline. Theoretical calculations complemented the experiments to explain the mechanism of cluster formation in sedimentation. This work provides a novel methodology to produce superstructures with a tunable packing order for colloids at low Péclet number.