scholarly journals Odd-Even Effect in the Elastic Modulii of α,ω-Alkanedicarboxylic Acids

2014 ◽  
Vol 70 (a1) ◽  
pp. C551-C551
Author(s):  
Manish Mishra ◽  
Sunil Varughese ◽  
Upadrasta Ramamurty ◽  
Gautam Desiraju
Keyword(s):  
Elastic Modulus ◽  
Melting Point ◽  
Crystal Engineering ◽  
Weak Interactions ◽  
Molecular Crystals ◽  
Relative Strength ◽  
Molecular Solids ◽  
Structure Property ◽  
Depth Of Penetration ◽  
Molecular Conformations

Nanoindentation is a probe used to quantitatively assess mechanical behavior of small volume materials. In this technique, load applied vs. the depth of penetration of the indenter into the specimen are measured simultaneously and with high precision and resolution. By analyzing the data, one can obtain the elastic modulus and hardness of crystals. Though this technique has been extensively used to characterize inorganic and engineering materials, we have recently extended its utility to study weak interactions and to establish structure-property relationships in molecular crystals. Being able to assess the relative strength of weak interactions such a technique has become relevant to the subject of crystal engineering which is concerned with the design of molecular solids with desired properties and functions. In our recent studies through nanoindentation on the alkanedicarboxylic acids reveals that the elastic modulus shows similar alternation property as the melting point alternation. Our results are endorsing the strained molecular conformations hypothesis for the melting point alternation of diacids, proposed by Thalladi et al. These results support the development of crystal engineering because nanoindentation may be used as a direct measure of molecular and crystal energies of molecular crystals.

scholarly journals Plasticity in zwitterionic drugs: the bending properties of Pregabalin and Gabapentin and their hydrates

IUCrJ ◽  
2019 ◽  
Vol 6 (4) ◽  
pp. 630-634 ◽  
Author(s):  
U. B. Rao Khandavilli ◽  
Matteo Lusi ◽  
Patrick J. Frawley
Keyword(s):  
Mechanical Properties ◽  
Crystal Engineering ◽  
Weak Interactions ◽  
Molecular Crystals ◽  
Structural Features ◽  
Microscopic Structure ◽  
Bending Properties ◽  
Crystalline Materials ◽  
Area Of Interest ◽  
Macroscopic Plasticity

The investigation of mechanical properties in molecular crystals is emerging as a novel area of interest in crystal engineering. Indeed, good mechanical properties are required to manufacture pharmaceutical and technologically relevant substances into usable products. In such endeavour, bendable single crystals help to correlate microscopic structure to macroscopic properties for potential design. The hydrate forms of two anticonvulsant zwitterionic drugs, Pregabalin and Gabapentin, are two examples of crystalline materials that show macroscopic plasticity. The direct comparison of these structures with those of their anhydrous counterparts, which are brittle, suggests that the presence of water is critical for plasticity. In contrast, structural features such as molecular packing and anisotropic distribution of strong and weak interactions seem less important.

scholarly journals Four- and five-component molecular solids: crystal engineering strategies based on structural inequivalence

IUCrJ ◽  
2016 ◽  
Vol 3 (2) ◽  
pp. 96-101 ◽  
Author(s):  
Niyaz A. Mir ◽  
Ritesh Dubey ◽  
Gautam R. Desiraju
Keyword(s):  
Solid Solution ◽  
Crystal Engineering ◽  
Molecular Crystals ◽  
Chemical Constituent ◽  
Molecular Solids ◽  
Number Of Components ◽  
Synthetic Strategy

A synthetic strategy is described for the co-crystallization of four- and five-component molecular crystals, based on the fact that if any particular chemical constituent of a lower cocrystal is found in two different structural environments, these differences may be exploited to increase the number of components in the solid. 2-Methylresorcinol and tetramethylpyrazine are basic template molecules that allow for further supramolecular homologation. Ten stoichiometric quaternary cocrystals and one quintinary cocrystal with some solid solution character are reported. Cocrystals that do not lend themselves to such homologation are termed synthetic dead ends.

The localization of injected charges in polymers and molecular solids

1985 ◽  
Vol 63 (1) ◽  
pp. 236-242 ◽  
Author(s):  
Charles B. Duke
Keyword(s):  
Weak Interactions ◽  
Molecular Crystals ◽  
Localized States ◽  
Molecular Solids ◽  
Molecular Glasses ◽  
Thermally Induced ◽  
Molecular Identity ◽  
Localized State ◽  
The Individual ◽  
High Degree

Polymers and molecular solids are characterized by two fundamental features: the retention of molecular identity in the solid state and the occurrence of relatively weak interactions between the individual molecular entities. The weak interactions lead to a high degree of disorder caused both by defects and by thermally induced motions of the molecules. A model of charges injected into polymers and molecular solids is developed. Photoemission and transport measurements are utilized to evaluate the parameters in this model. Results for metal free phthalocyanine are presented as an illustrative example. For molecular glasses and aromatic pendant-group polymers this analysis predicts that disorder causes injected charges to form a Fermi glass of self-trapped polarons, i.e., they occupy localized states characterized by a high degree of local atomic and electronic polarization. Successful interpretations of photoemission spectra, contact charge exchange, and injected carrier drift mobilities verify this prediction. The boundary of the Fermi-glass region of localized-state molecular-ion behavior is identified by consideration of molecular crystals in which injected charges may occupy extended energy-band states at low temperatures.

scholarly journals Intermolecular interactions in molecular crystals: what’s in a name?

2017 ◽  
Vol 203 ◽  
pp. 93-112 ◽  
Author(s):  
Alison J. Edwards ◽  
Campbell F. Mackenzie ◽  
Peter R. Spackman ◽  
Dylan Jayatilaka ◽  
Mark A. Spackman
Keyword(s):  
Hydrogen Bonds ◽  
Intermolecular Interactions ◽  
Crystal Engineering ◽  
Molecular Electrostatic Potential ◽  
Molecular Crystals ◽  
Interaction Energies ◽  
Structure Property ◽  
Structure Property Relationships ◽  
Crystal Properties ◽  
Tetrel Bonds

Structure–property relationships are the key to modern crystal engineering, and for molecular crystals this requires both a thorough understanding of intermolecular interactions, and the subsequent use of this to create solids with desired properties. There has been a rapid increase in publications aimed at furthering this understanding, especially the importance of non-canonical interactions such as halogen, chalcogen, pnicogen, and tetrel bonds. Here we show how all of these interactions – and hydrogen bonds – can be readily understood through their common origin in the redistribution of electron density that results from chemical bonding. This redistribution is directly linked to the molecular electrostatic potential, to qualitative concepts such as electrostatic complementarity, and to the calculation of quantitative intermolecular interaction energies. Visualization of these energies, along with their electrostatic and dispersion components, sheds light on the architecture of molecular crystals, in turn providing a link to actual crystal properties.

Molekulare Schwingungsexzitonen in Fliissigkeiten

1973 ◽  
Vol 28 (6) ◽  
pp. 919-932 ◽  
Author(s):  
G. Döge
Keyword(s):  
Melting Point ◽  
Collective Excitation ◽  
Molecular Crystals ◽  
Dipole Interaction ◽  
Pair Interaction ◽  
Band Shape ◽  
Vibrational Bands ◽  
Motional Narrowing ◽  
Vibration Coupling ◽  
Interaction Approximation

The intermolecular coupling of molecular vibrations in molecular crystals is usually treated by the exciton concept. This is identical with the assumption that a potential, which describes the interaction of a vibrating molecule with its neighbours, perturbs the isolated molecule energies and thereby couples the motions of molecules. In most cases this potential will be the transition-dipoletransition- dipole interaction. If one assumes validity of the pair interaction approximation this concept should be able to describe the effects in the liquid state, too. The aim of these considerations is to show, how collective excitation can influence the shape of vibrational bands. Because dipoledipole interaction is strongly orientation dependent, molecular reorientations perturb the coupling of the vibrations and cause motional narrowing. The behaviour of the shapes of the vibration bands of CH3J is discussed on the basis of these considerations. One finds that the band shape of ν2 is mainly broadened by vibration coupling. As expected a distinct motional narrowing is observed, if one increases the temperature from the melting point to the boiling point.

Macroscopic and Microscopic Properties of High Performance Concrete with Partial Replacement of Cement by Fly Ash

2019 ◽  
Vol 292 ◽  
pp. 108-113 ◽  
Author(s):  
Josef Fládr ◽  
Petr Bílý ◽  
Roman Chylík ◽  
Zdeněk Prošek
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Fly Ash ◽  
High Performance ◽  
High Performance Concrete ◽  
Partial Replacement ◽  
Experimental Program ◽  
Second Phase ◽  
Depth Of Penetration ◽  
Cement Replacement

The paper describes an experimental program focused on the research of high performance concrete with partial replacement of cement by fly ash. Four mixtures were investigated: reference mixture and mixtures with 10 %, 20 % and 30 % cement weight replaced by fly ash. In the first stage, the effect of cement replacement was observed. The second phase aimed at the influence of homogenization process for the selected 30% replacement on concrete properties. The analysis of macroscopic properties followed compressive strength, elastic modulus and depth of penetration of water under pressure. Microscopic analysis concentrated on the study of elastic modulus, porosity and mineralogical composition of cement matrix using scanning electron microscopy, spectral analysis and nanoindentation. The macroscopic results showed that the replacement of cement by fly ash notably improved compressive strength of concrete and significantly decreased the depth of penetration of water under pressure, while the improvement rate increased with increasing cement replacement (strength improved by 18 %, depth of penetration by 95 % at 30% replacement). Static elastic modulus was practically unaffected. Microscopic investigation showed impact of fly ash on both structure and phase mechanical performance of the material.

Elastomeric Polyether-Ester Block Copolymers. I. Structure-Property Relationships of Tetramethylene Terephthalate/Polyether Terephthalate Copolymers

1977 ◽  
Vol 50 (4) ◽  
pp. 688-703 ◽  
Author(s):  
J. R. Wolfe
Keyword(s):  
Phase Separation ◽  
Melting Point ◽  
Block Copolymers ◽  
Low Temperature ◽  
Chain Length ◽  
Chemical Structure ◽  
High Water ◽  
Structure Property ◽  
Tear Strength ◽  
Structure Property Relationships

Abstract The properties of elastomeric tetramethylene terephthalate/polyether terephthalate copolymers have been related to the chemical structure, chain length, and concentration in the copolymers of the PTMEG-, PEG-, and PPG-derived polyether units. Low-temperature properties and tear strength are dependent on all three polyether-related variables. Melting point, hardness, and stress at 100% elongation appear to be independent of polyether structure. Polyether glycols of low MW volatilize during copolymer preparation. High-MW polyethers tend to crystallize when present in the copolymers. Polyether glycols of intermediate MW (∼ 1000) yield copolymers with the best resistance to low-temperature stiffening. Copolymer synthesis is most difficult with PPG as the polyether glycol. Inherent viscosities are low, and phase separation occurs at lower polyether MW than with PTMEG or PEG. The PEG-based copolymers exhibit high water swell, particularly at intermediate and high PEG MW. The PTMEG-based copolymers are easiest to synthesize and exhibit the best overall combination of properties.

scholarly journals Direct evidence for 2-fold to 3-fold change of interpenetration in a MOF

2014 ◽  
Vol 70 (a1) ◽  
pp. C636-C636
Author(s):  
Himanshu Aggarwal ◽  
Prashant Bhatt ◽  
Charl Benzuidenhout ◽  
Leonard Barbour
Keyword(s):  
Single Crystal ◽  
Crystal Engineering ◽  
Molecular Level ◽  
Metal Organic Framework ◽  
Structural Rearrangement ◽  
Structure Property ◽  
Ambient Conditions ◽  
Physical Conditions ◽  
Structure Property Relationships ◽  
Metal Organic

Single-crystal to single-crystal transformations has recently received much attention in the field of crystal engineering. Such transformations not only provide insight into the changes taking place within the crystal at the molecular level, but they also aid our understanding of the structure-property relationships. Discrete crystals have been shown to tolerate considerable dynamic behavior at the molecular level while maintaining their single-crystal character. Examples that are common in the literature include bond formation/cleavage,[1] guest uptake,[2] release or exchange as well as polymorphic phase transformations. However, there are rare examples of the structural transformations on the host framework initiated by removal of guest or change in physical conditions such as temperature or pressure. We have investigated a known doubly-interpenetrated metal organic framework with the formula [Zn2(ndc)2(bpy)] which possesses minimal porosity when activated. We have shown not only that the material converts to its triply-interpenetrated analogue upon desolvation, but that the transformation occurs in a single-crystal to single-crystal manner under ambient conditions.[3] This contribution probes the limits to which a single-crystal material can undergo structural rearrangement while still maintaining the macroscopic integrity of the crystal as a discrete entity.

Mechanical Properties of the Human Elbow Bones Measured by Nanoindentation and Microindentation

2018 ◽  
Author(s):  
Dilpreet Singh ◽  
Pulak Mohan Pandey ◽  
Dinesh Kalyanasundaram
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Hierarchical Structure ◽  
Longitudinal Direction ◽  
Measurement Scales ◽  
Depth Of Penetration ◽  
Mechanical Environment ◽  
Physiological Loading ◽  
Bone Properties ◽  
Osteonal Bone

In this article, the nano and microhardness and the elastic modulus of the human elbow bones (humerus, ulna and radius) were studied. The nano properties were studied using load controlled technique with a load of 20 mN, while the micro properties were studied under 1 N load. A total of nine bone samples from three cadavers of ages between 45 and 55 years were tested. The measurements were carried out on both osteonal and interstitial bone in the longitudinal direction. The nanoindentation results indicated higher values for interstitial bone (hardness: 0.74 ± 0.09 GPa, elastic modulus: 19.05 ± 1.92 GPa) than for osteonal bone (hardness: 0.53 ± 0.05 GPa, elastic modulus: 16.66 ± 1.55 GPa). Consistent results were obtained at a depth of penetration between 1.1 μm to 1.5 μm in nanoindentation. In the case of microindentation, the microhardness and elastic modulus of interstitial bone was found to be 0.65 ± 0.07 GPa and 20.60 ± 2.27 GPa. Whereas for osteonal bone it was observed to be 0.60 ± 0.08 GPa and 14.56 ± 1.42 GPa respectively. The depth of penetration varies between the 8 μm to 11 μm for microindentation studies. In both measurement scales, a noticeable difference was observed between the osteonal and interstitial bone properties. As bone is a hierarchical structure, identifying the mechanical properties at the lamellar level helps in understanding the local mechanical environment of basic elements of the bones and predicting the behavior of the bone due to physiological loading.

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