Face-to-face and edge-to-edge free energy interactions of Wyoming Na-montmorillonite platelets were studied by calculating potential of mean force along their center to center reaction coordinate using explicit solvent (i.e., water) molecular dynamics and free energy perturbation methods. Using a series of configurations, the Gay-Berne potential was parametrized and used to examine the meso-scale aggregation and properties of platelets that are initially random oriented under isothermal-isobaric condition.Aggregates of clay was defined by geometrical analysis of face-to-face proximity of platelets with size distribution described by a log-normal function. The isotropy of the microstructure was assessed by computing a scalar order parameter. The number of platelets per aggregate and anisotropy of the microstructure both increases with platelet plan area. System becomes more ordered and aggregate size increases with increasing pressure until maximum ordered state. Further increase of pressure slides platelets relative to each other leading to smaller aggregate size. The geometrical arrangement of aggregates affects mechanical properties of the system. The elastic properties of the meso-scale aggregate assembly are reported. It is found that the elastic properties at this scale are close to the cubic systems. The elastic stiffness and 1 anisotropy of the assembly increases with the size of the platelets and the level of external pressure.

Smectites are an important group of clay minerals that experience swelling upon water adsorption. This paper uses molecular dynamics with the CLAYFF force field to simulate isothermal isobaric water adsorption of interlayer Wyoming Na-montmorillonite, a member of the smectite group. Nanoscale elastic properties of the clay-interlayer water system are calculated from the potential energy of the model system. The transverse isotropic symmetry of the elastic constant matrix was assessed by calculating Euclidean and Riemannian distance metrics. Simulated elastic constants of the clay mineral are compared with available results from acoustic and nanoindentation measurements.

This article reviews fundamental and applied aspects of silk–one of Nature’s most intriguing materials in terms of its strength, toughness, and biological role–in its various forms, from protein molecules to webs and cocoons, in the context of mechanical and biological properties. A central question that will be explored is how the bridging of scales and the emergence of hierarchical structures are critical elements in achieving novel material properties, and how this knowledge can be explored in the design of synthetic materials. We review how the function of a material system at the macroscale can be derived from the interplay of fundamental molecular building blocks. Moreover, guidelines and approaches to current experimental and computational designs in the field of synthetic silklike materials are provided to assist the materials science community in engineering customized finetuned biomaterials for biomedical applications.

The elastic and failure properties of a typical clay, illite, are investigated by means of molecular simulation. 2 We employ a reactive (ReaxFF) as well as a non-reactive (ClayFF) force field to assess the elastic properties 3 of the clay. As far as the failure properties are concerned, ReaxFF was used throughout the study, however 4 some calculations were also performed with ClayFF. A crack parallel to the clay layers is found to have low 5 fracture resistance (equivalent fracture toughness K Ic = 0.09 MPa.m 1/2) when submitted to a tensile loading 6 perpendicular to the crack (mode I). The nanoscale mechanism of both yield and fracture failures is 7 decohesion in the interlayer space, and the critical energy release rate characterizes both failures. In contrast, 8 under shear loading (mode II), the nanoscale failure mechanism is a stick-slip between clay layers. No fracture 9 propagation is observed as the clay layers slide on top of each other. The low fracture resistance in mode I and 10 the stick-slip failure in mode II are both the consequence of the lack of chemical bonds between clay layers 11 where the cohesion is provided by electrostatic interactions only. We also consider the mode I loading of a 12 crack perpendicular to the clay layers and find that, in this case, the material exhibit strain softening as the 13 result of the clay layers breaking one after the other. In this orientation illite displays a much higher fracture 14 resistance (0.61 MPa.m 1/2) due to the breaking of chemical bonds involved when fracturing in this direction. 15 This work, which provides a description of the failure properties of clays at the microscopic scale, is a first 16 step needed to describe the failure of clays at a larger scale where the polycrystalline distribution of clay 17 grains is a key parameter that must be taken into account.

Tailored biomaterials with tunable functional properties are crucial for a variety of task-specific applications ranging from healthcare to sustainable, novel bio-nanodevices. To generate polymeric materials with predictive functional outcomes, exploiting designs from nature while morphing them toward non-natural systems offers an important strategy. Silks are Nature's building blocks and are produced by arthropods for a variety of uses that are essential for their survival. Due to the genetic control of encoded protein sequence, mechanical properties, biocompatibility, and biodegradability, silk proteins have been selected as prototype models to emulate for the tunable designs of biomaterial systems. The bottom up strategy of material design opens important opportunities to create predictive functional outcomes, following the exquisite polymeric templates inspired by silks. Recombinant DNA technology provides a systematic approach to recapitulate, vary, and evaluate the core structure peptide motifs in silks and then biosynthesize silk-based polymers by design. Post-biosynthesis processing allows for another dimension of material design by controlled or assisted assembly. Multiscale modeling, from the theoretical prospective, provides strategies to explore interactions at different length scales, leading to selective material properties. Synergy among experimental and modeling approaches can provide new and more rapid insights into the most appropriate structure-function relationships to pursue while also furthering our understanding in terms of the range of silk-based systems that can be generated. This approach utilizes nature as a blueprint for initial polymer designs with useful functions (e.g., silk fibers) but also employs modeling-guided experiments to expand the initial polymer designs into new domains of functional materials that do not exist in nature. The overall path to these new functional outcomes is greatly accelerated via the integration of modeling with experiment. In this Account, we summarize recent advances in understanding and functionalization of silk-based protein systems, with a focus on the integration of simulation and experiment for biopolymer design. Spider silk was selected as an exemplary protein to address the fundamental challenges in polymer designs, including specific insights into the role of molecular weight, hydrophobic/hydrophilic partitioning, and shear stress for silk fiber formation. To expand current silk designs toward biointerfaces and stimuli responsive materials, peptide modules from other natural proteins were added to silk designs to introduce new functions, exploiting the modular nature of silk proteins and fibrous proteins in general. The integrated approaches explored suggest that protein folding, silk volume fraction, and protein amino acid sequence changes (e.g., mutations) are critical factors for functional biomaterial designs. In summary, the integrated modeling-experimental approach described in this Account suggests a more rationally directed and more rap...