Molecular Level Properties

Plant fibers are composed of three main components  

Cellulose is insoluble in water under normal conditions but it can be dissolved in near-supercritical water [11] and several other solvents e.g., Na0H/H20, NaOH/PEG/H20, dimethyl acetamide/ lithium chloride, aqueous N-methylmorpholine-N-oxide, CdO/ ethylene-diamine and in many ionic liquids [53]. The density of cellulose varies from 1.27 to 1.60 g/cm . The heat capacity depends 

Cellulose presented in plant fibers can be categorized as follows  

Lignins are the group of complex compounds (mainly aromatic pol5miers] which cement plant cells together. From papermaking 

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A gas condenses to a liquid if it is cooled sufficiently. Condensation occurs when the average kinetic energy of motion of molecules falls below the value needed for the molecules to move about independently. Thus, the molecules in a liquid are confined to a specific volume by intermolecular forces of attraction. Although they cannot readily escape, liquid molecules remain free to move about within the liquid phase, hi this behavior, liquid molecules behave like the molecules of a gas. The large-scale consequences of the molecular-level properties are apparent. Like gases, liquids are fluid, so they flow easily from place to place. Unlike gases, however, liquids are compact, so they cannot expand or contract significantly. 

In the present work, such a systematic approach to the physical characterization of pharmaceutical solids is outlined. Techniques available for the study of physical properties are classified as being associated with the molecular level (properties associated with individual molecules), the particulate level (properties pertaining to individual solid particles), and the bulk level (properties associated with an ensemble of particulates). Acquisition of this range of physical information yields a total profile of the pharmaceutical solid in question, whether it is an active drug, an excipient, or a blend of these. The development of a total profile is a requirement for successful manufacture of any solid dosage form. 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

Problem 12.17. Methane, octane, and polyethylene are members of the alkane family. Combustion of methane (gas heating) and octane (liquid-burning engines) are used as sources of energy. In eontrast polyethylene is used for producing objects such as milk, food, and detergent bottles. What macroscopic property is responsible for this difference What molecular-level property determines this difference ... 

Guggenheim EA (1945) The principle of corresponding states. J Chem Phys 13 253-265 Hantal G, Darvas M, Partay LB, Horvai G, Jedlovszky P (2010) Molecular level properties of the free water surface and different organic Uquid/water interfaces, as seen from ITIM analysis of computer simulation results. J Phys Condens Matter 22(28) 284112-1/14 Henderson MA (2002) The interaction of water with solid surfaces fundamental aspects revisited. Surf Sci Rep 46 1-308... 

We understand the molecular level properties of gases (either pure or mixed) at low pressures sufficiently well enough to make confident predictions of bulk properties. The relative simplicity of gases is due to the low cohesive energies between the molecules and between the molecules and container walls. In contrast, relating bulk properties to molecular properties in condensed phases (liquids and solids) becomes more complex, because of the greatly increased cohesive energies between the molecules. Nonetheless, the macroscopic properties of eondensed matter in the form of pure phases are now well understood from first principles. 

What molecular-level properties of a liquid are most important in determining (a) its ability to flow (b) its tendency to bead up on a surface for which it has no appre-... 

G. Hantal, P. Terleczky, G. Horvai, L. Nyulaszi, and P. Jedlovszky,/. Phys. Chem. C, 113,19263 (2009). Molecular Level Properties of the Water-DichloromethaneLiquid/Liquid Interface, as Seen from Molecular Dynamics Simulation and Identification of Truly Interfacial Molecules Analysis. 

G. Hantal, M. Darvas, L. B. Partay, G. Horvai, and P. ]edlovs7ky, J. Phys.-Condensed Matter, 22, 284112 (2010). Molecular Level Properties of the Free Water Surface and Different Organic Liquid/Water Interfaces, as Seen from ITIM Analysis of Computer Simulation Results. 

Studies of surfaces and surface properties can be traced to the early 1800s [1]. Processes that involved surfaces and surface chemistry, such as heterogeneous catalysis and Daguerre photography, were first discovered at that time. Since then, there has been a continual interest in catalysis, corrosion and other chemical reactions that involve surfaces. The modem era of surface science began in the late 1950s, when instmmentation that could be used to investigate surface processes on the molecular level started to become available. 

The representation of molecular surfaces, including the display of molecular surface properties, can be regarded as the next level of this hierarchy, but will be addressed in Sections 2,10 and 2,11 in this volume. 

Most hydrocarbon resins are composed of a mixture of monomers and are rather difficult to hiUy characterize on a molecular level. The characteristics of resins are typically defined by physical properties such as softening point, color, molecular weight, melt viscosity, and solubiHty parameter. These properties predict performance characteristics and are essential in designing resins for specific appHcations. Actual characterization techniques used to define the broad molecular properties of hydrocarbon resins are Fourier transform infrared spectroscopy (ftir), nuclear magnetic resonance spectroscopy (nmr), and differential scanning calorimetry (dsc). 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The solvophobic model of Hquid-phase nonideaHty takes into account solute—solvent interactions on the molecular level. In this view, all dissolved molecules expose microsurface area to the surrounding solvent and are acted on by the so-called solvophobic forces (41). These forces, which involve both enthalpy and entropy effects, are described generally by a branch of solution thermodynamics known as solvophobic theory. This general solution interaction approach takes into account the effect of the solvent on partitioning by considering two hypothetical steps. Eirst, cavities in the solvent must be created to contain the partitioned species. Second, the partitioned species is placed in the cavities, where interactions can occur with the surrounding solvent. The idea of solvophobic forces has been used to estimate such diverse physical properties as absorbabiHty, Henry s constant, and aqueous solubiHty (41—44). A principal drawback is calculational complexity and difficulty of finding values for the model input parameters. 

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