Search NASA⌕ Search

SEARCH · Search NASA

Results for “Rigidity function”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Low–Cost Bio-Based Carbon Fiber for High-Temperature Processing

GrafTech International Holdings Inc. (GTI), worked with Oak Ridge National Laboratory (ORNL) under CRADA No. NFE-15-05807 to develop lignin-based carbon fiber (LBCF) technology and to demonstrate LBCF performance in high-temperature products and applications. This work was unique and different from other reported LBCF work in that this study was application-focused and scalability-focused. Accordingly, the executed work was based on meeting criteria based on technology development, cost, and application suitability. The focus of this work was to demonstrate lab-scale LBCF from at least 4 different precursor feedstock sources that could meet the estimated production cost of $5.00/pound and have ash level of less than 500 ppm in the carbonized insulation-grade fiber. Accordingly, a preliminary cost model was developed based on publicly available information. The team demonstrated that 4 lignin samples met the cost criteria, as highlighted in Table 1. In addition, the ash level for the 4 carbonized lignin samples were below 500 ppm. Processing asreceived lignin to produce a high purity lignin fiber was a significant accomplishment in that most industrial lignin, prior to purification, had greater than 4X the ash level needed for this project, and prior to this work there was not a clear path of how to achieve the purity target. The lab scale development of LBCF was performed with a specific functional application in mind, specifically for high temperature rigid insulation. GTI is currently a consumer of foreignsourced pitch and rayon based carbon fibers for use in its high temperature insulation products, and the motivation was that LBCF had potential to decrease costs and increase product competitiveness in the marketplace through lowered raw material costs, lowered energy costs, and decreased environmental footprint. At the end of this project, the Technology Readiness Level (TRL) remained at 5 for LBCF in high temperature insulation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Low-Cost Bio-Based Carbon Fibers for High Temperature Processing

GrafTech International Holdings Inc. (GTI), under Award No. DE-EE0005779, worked with Oak Ridge National Laboratory (ORNL) under CRADA No. NFE-15-05807 to develop lignin-based carbon fiber (LBCF) technology and to demonstrate LBCF performance in high-temperature products and applications. This work was unique and different from other reported LBCF work in that this study was application-focused and scalability-focused. Accordingly, the executed work was based on meeting criteria based on technology development, cost, and application suitability. High-temperature carbon fiber based insulation is used in energy intensive industries, such as metal heat treating and ceramic and semiconductor material production. Insulation plays a critical role in achieving high thermal and process efficiency, which is directly related to energy usage, cost, and product competitiveness. Current high temperature insulation is made with petroleum based carbon fibers, and one goal of this protect was to develop and demonstrate an alternative lignin (biomass) based carbon fiber that would achieve lower cost, CO2 emissions, and energy consumption and result in insulation that met or exceeded the thermal efficiency of current commercial insulation. In addition, other products were targeted to be evaluated with LBCF. As the project was designed to proceed in stages, the initial focus of this work was to demonstrate lab-scale LBCF from at least 4 different lignin precursor feedstock sources that could meet the estimated production cost of $5.00/pound and have ash level of less than 500 ppm in the carbonized insulation-grade fiber. Accordingly, a preliminary cost model was developed based on publicly available information. The team demonstrated that 4 lignin samples met the cost criteria. In addition, the ash level for the 4 carbonized lignin samples was below 500 ppm. Processing as-received lignin to produce a high purity lignin fiber was a significant accomplishment in that most industrial lignin, prior to purification, had greater than 4X the ash level needed for this project, and prior to this work there was not a clear path of how to achieve the purity target. The lab scale development of LBCF was performed with a specific functional application in mind, specifically for high temperature rigid insulation. GTI is a consumer of foreign-sourced pitch and rayon based carbon fibers for use in its high temperature insulation products, and the motivation was that LBCF had potential to decrease costs and increase product competitiveness in the marketplace through lowered raw material costs, lowered energy costs, and decreased environmental footprint. At the end of this project, the Technology Readiness Level (TRL) remained at 5 for LBCF in high temperature insulation.

09 BIOMASS FUELS↗
DOE OSTI2017

Towing Tank and Flume Testing of Passively Adaptive Composite Tidal Turbine Blades: Preprint

Composite tidal turbine blades with bend-twist (BT) coupled layups allow the blade to self-adapt to local site conditions by passively twisting. Passive feathering has the potential to increase annual energy production and shed thrust loads and power under extreme tidal flows. Decreased hydrodynamic thrust and power during extreme conditions meann that the turbine support structure, generator, and other components can be sized more appropriately, resulting in a higher utilization factor and increased cost effectiveness. This paper presents new experimental data for a small-scale turbine with BT composite blades. The research team tested the turbine in the Kelvin Hydrodynamics Laboratory towing tank at the University of Strathclyde in Glasgow, United Kingdom, and in the recirculating current flume at the l Institut Francais de Recherche pour l Exploitation de la Mer Centre in Boulogne-sur-Mer, France. Tests were also performed on rigid aluminum blades with identical geometry, which yielded baseline test sets for comparison. The results from both facilities agreed closely, supporting the hypothesis that increased blade flexibility can induce load reductions. Under the most extreme conditions tested the turbine with BT blades had up to 11 percent lower peak thrust loads and a 15 percent reduction in peak power compared to the turbine with rigid blades. The load reductions varied as a function of turbine rotational velocity and ambient flow velocity.

17 WIND ENERGY↗
DOE OSTI2018

Rigidity of the Laughlin Liquid

We consider general N-particle wave functions that have the form of a product of the Laughlin state with filling factor 1/ℓ and an analytic function of the N variables. This is the most general form of a wave function that can arise through a perturbation of the Laughlin state by external potentials or impurities, while staying in the lowest Landau level and maintaining the strong correlations of the original state. We show that the perturbation can only shift or lower the 1-particle density but nowhere increase it above a maximum value. Consequences of this bound for the response of the Laughlin state to external fields are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Structure/property relationships in copolymers comprising renewable isosorbide, glucarodilactone, and 2,5-bis(hydroxymethyl)furan subunits

Carbohydrates and their derivatives have great potential as building blocks for the development of renewable materials that are cost and performance competitive with conventional petroleum-based materials. To this end, the rigid carbohydrate-derived diols, glucarodilactone and isosorbide were functionalized with a castor oil derivative, 10-undecenoic acid, forming α,ω-dienes suitable for acyclic diene metathesis (ADMET) polymerization. Equimolar copolymerizations of these two monomers, glucarodilactone undecenoate (GDLU) and isosorbide undecenoate (GDLU), transform brittle homopolymers into elastic materials with shape memory capabilities. To understand the source of these properties, a series of copolymers consisting of a range of GDLU and IU compositions (100:0, 77:23, 76:24, 52:48, 48:52, 18:82, 0:100 mol percent GDLU to IU) was synthesized. The material and chemical properties were characterized by uniaxial tensile testing, small-amplitude oscillatory shear rheology, X-ray scattering and hydrolytic degradation testing. Small compositional changes in this family were shown to have a drastic impact on the observed mechanical performance and degradability of these materials. Rheological measurements of GDLU-containing copolymers found evidence for the presence of transient networking within these materials. We posit that the transient network within this material is responsible for the elasticity and shape memory abilities of the GDL-containing materials. In confirmation of these properties, a novel α,ω-diene 2,5-bis(hydroxymethylfuran) undecenoate (BHMFU) was developed and served as a direct replacement for either GDLU or IU in copolymerizations. The replacement of GDLU resulted in a total loss of the elasticity and shape memory of the copolymers, supporting the role of GDLU in the mechanical performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Unusual magnetotransport in twisted bilayer graphene from strain-induced open Fermi surfaces

Anisotropic hopping in a toy Hofstadter model was recently invoked to explain a rich and surprising Landau spectrum measured in twisted bilayer graphene away from the magic angle. Suspecting that such anisotropy could arise from unintended uniaxial strain, we extend the Bistritzer–MacDonald model to include uniaxial heterostrain and present a detailed analysis of its impact on band structure and magnetotransport. We find that such strain strongly influences band structure, shifting the three otherwise-degenerate van Hove points to different energies. Coupled to a Boltzmann magnetotransport calculation, this reproduces previously unexplained nonsaturating B 2 magnetoresistance over broad ranges of density near filling ν = ± 2 and predicts subtler features that had not been noticed in the experimental data. In contrast to these distinctive signatures in longitudinal resistivity, the Hall coefficient is barely influenced by strain, to the extent that it still shows a single sign change on each side of the charge neutrality point—surprisingly, this sign change no longer occurs at a van Hove point. The theory also predicts a marked rotation of the electrical transport principal axes as a function of filling even for fixed strain and for rigid bands. More careful examination of interaction-induced nematic order versus strain effects in twisted bilayer graphene could thus be in order.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Galactic Bar Resonances with Diffusion: An Analytic Model with Implications for Bar–Dark Matter Halo Dynamical Friction

Abstract The secular evolution of disk galaxies is largely driven by resonances between the orbits of “particles” (stars or dark matter) and the rotation of non-axisymmetric features (spiral arms or a bar). Such resonances may also explain kinematic and photometric features observed in the Milky Way and external galaxies. In simplified cases, these resonant interactions are well understood: for instance, the dynamics of a test particle trapped near a resonance of a steadily rotating bar is easily analyzed using the angle-action tools pioneered by Binney, Monari, and others. However, such treatments do not address the stochasticity and messiness inherent to real galaxies—effects that have, with few exceptions, been previously explored only with complex N -body simulations. In this paper, we propose a simple kinetic equation describing the distribution function of particles near an orbital resonance with a rigidly rotating bar, allowing for diffusion of the particles’ slow actions. We solve this equation for various values of the dimensionless diffusion strength Δ, and then apply our theory to the calculation of bar–halo dynamical friction. For Δ = 0, we recover the classic result of Tremaine and Weinberg that friction ultimately vanishes, owing to the phase mixing of resonant orbits. However, for Δ > 0, we find that diffusion suppresses phase mixing, leading to a finite torque. Our results suggest that stochasticity—be it physical or numerical—tends to increase bar–halo friction, and that bars in cosmological simulations might experience significant artificial slowdown, even if the numerical two-body relaxation time is much longer than a Hubble time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Kinematic Flexibility Analysis: Hydrogen Bonding Patterns Impart a Spatial Hierarchy of Protein Motion

Elastic network models (ENMs) and constraint-based, topological rigidity analysis are two distinct, coarse-grained approaches to study conformational flexibility of macromolecules. In the two decades since their introduction, both have contributed significantly to insights into protein molecular mechanisms and function. However, despite a shared purpose of these approaches, the topological nature of rigidity analysis, and thereby the absence of motion modes, has impeded a direct comparison. We present an alternative, kinematic approach to rigidity analysis, which circumvents these drawbacks. We introduce a novel protein hydrogen bond network spectral decomposition, which provides an orthonormal basis for collective motions modulated by noncovalent interactions, analogous to the eigenspectrum of normal modes. The zero modes decompose proteins into rigid clusters identical to those from topological rigidity, while nonzero modes rank protein motions by their hydrogen bond collective energy penalty. Our kinematic flexibility analysis bridges topological rigidity theory and ENM, enabling a detailed analysis of motion modes obtained from both approaches. Analysis of a large, structurally diverse data set revealed that collectivity of protein motions, reported by the Shannon entropy, is significantly reduced for rigidity theory compared to normal mode approaches. Strikingly, kinematic flexibility analysis suggests that the hydrogen bonding network encodes a protein-fold specific, spatial hierarchy of motions, which goes nearly undetected in ENM. This hierarchy reveals distinct motion regimes that rationalize experimental and simulated protein stiffness variations. Kinematic motion modes highly correlate with reported crystallographic B factors and molecular dynamics simulations of adenylate kinase. A formal expression for changes in free energy derived from the spectral decomposition indicates that motions across nearly 40% of modes obey enthalpy–entropy compensation. Taken together, our results suggest that hydrogen bond networks have evolved to modulate protein structure and dynamics, which can be efficiently probed by kinematic flexibility analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Understanding the Structure and Dynamics of Conjugated Polymers by Advancing Deuteration Chemistry and Neutron Scattering (Final Report)

The overarching goal of the proposed work was to set up a partnership between the University of Southern Mississippi (USM) and Oak Ridge National Laboratory (ORNL) to develop novel approaches to measure the backbone rigidity of conjugated polymers (CPs) and understand the critical role of sidechains on the backbone conformation and the materials macroscopic property. The backbone rigidity greatly influences the electronic properties of CPs, which ultimately determines the functionality and performance of these materials. Improvements in the electronic properties of CPs would allow for enhanced charge transport in semiconductor devices, improved photovoltaic performance, recycling of waste heat in thermoelectrics, and discovery of new phenomena that will enable the next generation of energy technologies. Although significant progress has been made to optimize the optical and electronic properties of CPs, largely through Edisonian methodologies, it remains a challenge to experimentally characterize conjugated backbone conformation (chain rigidity, torsion, planarity, and short-range order) and relate these to the fundamental optical and electronic properties (electronic coupling, charge transport, etc.). This has left fundamental gaps in our knowledge of the most basic structure/property relationships within these systems, precluded the study of fundamental physical phenomena, and constrained the design and realization of new electronic and device functionalities. Thus, the major goal of this work is to use novel deuteration methodologies via systematic synthetic approaches, and neutron scattering techniques to comprehensively characterize the structural and dynamic properties of CPs in contrast-matching solvents. Our work would, for the first time, elucidate the relationship between backbone rigidity and macroscopic properties. They will also allow a rational formulation of design principles for next-generation CPs that are resilient to disorder through precise control of the delocalized electrons along the polymer backbone. Overall, this project will advance our understanding of the structure, dynamics, and fundamental physics of these materials, which is crucial for enabling the prediction, design, control, and manipulation of current and emerging material electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Integrated System of Thermal/Dimensional Analysis for Quality Control of Metallic Melt and Ductile Iron Casting Solidification

The main objective of the present work is to introduce a specific experimental instrument and technique for simultaneously evaluating cooling curves and expansion or contraction of cast metals during solidification. Contraction/expansion analysis illustrates the solidification parameters progression, according to the molten cast iron characteristics, which are dependent on the melting procedure and applied metallurgical treatments, mold media rigidity and thermal behavior [heat transfer parameters]. The first part of the paper summarizes the performance of this two-mold device. Its function is illustrated by representative shrinkage tendency results in ductile cast iron as affected by mold rigidity (green sand and furan resin sand molds) and inoculant type (FeSi-based alloys), published in part previously. The second part of the paper illustrates an application of this equipment adapted for commercial foundry use. It conducts thermal analysis and volume change measurements in a single ceramic cup so that mold media as well as solidification conditions are constants, with cast iron quality as the variable. Experiments compared gray and ductile cast iron solidification patterns. Gray iron castings are characterized by higher undercooling at the beginning and at the end of solidification and lower graphitic expansion. Typically, ductile cast iron exhibits higher graphitic, initial expansion, conducive for shrinkage formation in soft molds.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Strain dependent electronic and optical responses of penta-BCN monolayer

We report here, structural, dynamic, and mechanical stability in pentagonal boron carbon nitride (p-BCN) monolayer, a new member of direct bandgap two-dimensional (2D) semiconductor. The identified visible range bandgap with excellent mechanical strength allows it to be a promising candidate material in optoelectronics, nanomechanics, and optomechanical sensors. By employing density functional theory (DFT), we reveal a unique geometrical reconstruction with rigidity in B–N and C–N bond lengths with applied strain. These quasi-sp 3 hybridized short and strong covalent bonding and unique geometry support the monolayer to possess extraordinary mechanical response. The desired bandgap is manipulated by loading the biaxial strain. Most importantly, our predictions on p-BCN show excellent optical response such as good static dielectric constant and refractive index, strong optical absorption (up to 1.08 x 10 5 cm -1 in VR and 7.01 x 10 cm -1 in UV) with small energy loss and reflectance both appearing in visible and ultraviolet regions (UV). The desired optical response along with the blue and red shift is demonstrated by tailoring with tensile and compressive strain. The predicted strong optical anisotropy provides it’s application in polarized photodetection.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Integrable Variable Dissipation Systems on the Tangent Bundle of a Multi-Dimensional Sphere and Some Applications

This paper is a survey of integrable cases in dynamics of a multi-dimensional rigid body under the action of a nonconservative force field. We review both new results and results obtained earlier. Problems examined are described by dynamical systems with so-called variable dissipation with zero mean. The problem of the search for complete sets of transcendental first integrals of systems with dissipation is quite topical; a large number of works are devoted to it. We introduce a new class of dynamical systems that have a periodic coordinate. Due to the existence of nontrivial symmetry groups of such systems, we can prove that these systems possess variable dissipation with zero mean, which means that on the average for a period with respect to the periodic coordinate, the dissipation in the system is equal to zero, although in various domains of the phase space, either energy pumping or dissipation can occur. Based on the facts obtained, we analyze dynamical systems that appear in the dynamics of a multi-dimensional rigid body and obtain a series of new cases of complete integrability of the equations of motion in transcendental functions, which can be expressed through a finite combination of elementary functions. As applications, we study dynamical equations of motion arising in the study of the plane and spatial dynamics of a rigid body interacting with a medium and also a possible generalization of the obtained methods to the study of general systems arising in the qualitative theory of ordinary differential equations, in the theory of dynamical systems, and also in oscillation theory.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Catalytic Porphyrin Framework Compounds

Porphyrins are frequently observed in nature and play a vital role in many biological functions, including light-harvesting, oxygen transport, and catalytic transformations. The rigid, robust, and multifunctional features of porphyrins enable the construction of framework compounds such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) for use in several important applications. This short review here summarizes the types of porphyrin building blocks with varying connectivity, their assembly into framework compounds, and key structural factors governing porphyrin ligand design. Furthermore, we highlight emerging catalytic applications of these porphyrin framework compounds as Lewis acid catalysts, oxidation catalysts, photocatalysts, and electrocatalysts. Together, this review supplies a timely update on porphyrin ligand design and framework compound synthesis and guides the future development of porphyrin framework compounds with diverse functionalities for efficient catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Topology and ground state control in open-shell donor-acceptor conjugated polymers

Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character represent an emerging class of materials whose rich behavior emanates from their collective electronic properties and diminished electron pairing. However, the structural and electronic heterogeneities that define these materials complicate bandgap control at low energies and connections linking topology, exchange interactions, and (opto)electronic functionality remain nascent. To address these challenges, we demonstrate structurally rigid and strongly π-conjugated copolymers comprised of a solubilizing thiadiazoloquinoxaline acceptor and cyclopenta[2,1-b:3,4-b']dithiophene or dithieno[3,2-b:2',3'-d]thiophene donors. Atom-specific substitution modulates local aromatic character within the donor resulting in dramatic differences in structural, physicochemical, electronic, and magnetic properties of the polymers. These long-range π-mediated interactions facilitate control between low-spin aromatic and high-spin quinoidal forms. This work provides a strategy to understand the evolution of the electronic structure within DA CPs, control the ground state spin multiplicity, tune spin-spin interactions, and articulate the emergence of their novel properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Manipulation of intramolecular hydrogen bonds in conjugated pseudoladder polymer for semiconductivity and solution-processability

The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. The conformational coplanarity and local rigidity of π-conjugated backbones are critical for the semiconducting performance of organic electronic materials. While fusing the aromatic system into a ladder-type structure effectively enhances these properties, it also often results in poor solution processability and hence limits their transition to device application. To address this challenge, an intramolecularly hydrogen-bonded pseudoladder polymer (HPLP) system based on alternating hydrogen bond donating benzobisimidazole (BBI) and hydrogen bond accepting benzodifuran (BDF) units, is designed and synthesized. A Boc-protected precursor of HPLP allows for feasible solution processing of the polymer into thin films. Subsequently, in situ thermal Boc-deprotection generates the HPLP polymer, in which intramolecular hydrogen bonds form between each pair of neighboring repeating units, inducing coplanarity and rigidity throughout the entire backbone. This process is accompanied by a significant red-shift of the absorption spectrum, reduced bandgap, and enhanced rigidity, as confirmed by NMR, UV-Vis, and density functional theory analyses. HPLP films exhibit a three-order-of-magnitude enhancement in charge carrier mobility compared to the Boc-protected precursor and demonstrate excellent solvent resistance in organic thin-film transistors.

Miranda, Octavio↗
DOE OSTI2020

Modular repeat protein sculpting using rigid helical junctions

The ability to precisely design large proteins with diverse shapes would enable applications ranging from the design of protein binders that wrap around their target to the positioning of multiple functional sites in specified orientations. We describe a protein backbone design method for generating a wide range of rigid fusions between helix-containing proteins and use it to design 75,000 structurally unique junctions between monomeric and homo-oligomeric de novo designed and ankyrin repeat proteins (RPs). Of the junction designs that were experimentally characterized, 82% have circular dichroism and solution small-angle X-ray scattering profiles consistent with the design models and are stable at 95 °C. Crystal structures of four designed junctions were in close agreement with the design models with rmsds ranging from 0.9 to 1.6 Å. Electron microscopic images of extended tetrameric structures and ~10-nm-diameter “L” and “V” shapes generated using the junctions are close to the design models, demonstrating the control the rigid junctions provide for protein shape sculpting over multiple nanometer length scales.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Helical side chain chemistry of a peptoid‐based SP‐C analogue: Balancing structural rigidity and biomimicry

Abstract Surfactant protein C (SP‐C) is an important constituent of lung surfactant (LS) and, along with SP‐B, is included in exogenous surfactant replacement therapies for treating respiratory distress syndrome (RDS). SP‐C's biophysical activity depends upon the presence of a rigid C‐terminal helix, of which the secondary structure is more crucial to functionality than precise side‐chain chemistry. SP‐C is highly sequence‐conserved, suggesting that the β‐branched, aliphatic side chains of the helix are also important. Nonnatural mimics of SP‐C were created using a poly‐ N ‐substituted glycine, or “peptoid,” backbone. The mimics included varying amounts of α‐chiral, aliphatic side chains and α‐chiral, aromatic side chains in the helical region, imparting either biomimicry or structural rigidity. Biophysical studies confirmed that the peptoids mimicked SP‐C's secondary structure and replicated many of its surface‐active characteristics. Surface activity was optimized by incorporating both structurally rigid and biomimetic side chain chemistries in the helical region indicating that both characteristics are important for activity. By balancing these features in one mimic, a novel analogue was created that emulates SP‐C's in vitro surface activity while overcoming many of the challenges related to natural SP‐C. Peptoid‐based analogues hold great potential for use in a synthetic, biomimetic LS formulation for treating RDS.

Brown, Nathan J.↗
DOE OSTI2019

Impact of Rigidity on Molecular Self-Assembly

Rigid, cage-like molecules, like diamondoids, show unique self-assembly behavior, such as templating 1-D nanomaterial assembly via pathways that are typically blocked for such bulky substituents. We investigate molecular forces between diamondoids to explore why molecules with high structural rigidity exhibit these novel assembly pathways. The rigid nature of diamondoids significantly lowers configurational entropy, and we hypothesize that this influences molecular interaction forces. To test this concept, we calculated the distance-dependent impact of entropy on assembly using molecular dynamics simulations. To isolate pairwise entropic and enthalpic contributions to assembly, we considered pairs of molecules in a thermal bath, fixed at set intermolecular separations but otherwise allowed to freely move. By comparing diamondoids to linear alkanes, we draw out the impact of rigidity on the entropy and enthalpy of pairwise interactions. We find that linear alkanes actually exhibit stronger van der Waals interactions than diamondoids at contact, because the bulky structure of diamondoids induces larger net atomic separations. Yet, we also find that diamondoids pay lower entropic penalties when assembling into contact pairs. Thus, the cage-like shape of diamondoids introduces an enthalpic penalty at contact, but the penalty is counterbalanced by entropic effects. Investigating the distance dependence of entropic forces provides a mechanism to explore how rigidity influences molecular assembly. Our results show that low entropic penalties paid by diamondoids can explain the effectiveness of diamondoids in templating nanomaterial assembly. Hence, tuning molecular rigidity can be an effective strategy for controlling the assembly of functional materials, such as biomimetic surfaces and nanoscale materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗