Some Properties of Solutions of Long-chain Compounds.

Huggins, Maurice L.

doi:10.1021/j150415a018

Cited by 1,295 publications

(707 citation statements)

References 2 publications

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“…The chain length dependence of the critical properties of the n-alkanes is, with this assumption, identical to the dependence of a polymer solution. Interestingly, the Flory-Huggins theory [69][70][71][72] for polymer solutions also predicts that the critical density decreases with chain length, i.e., c ϰn Ϫ1/2 .…”

Section: Critical Properties Of the Alkanesmentioning

confidence: 99%

Computer simulations of vapor–liquid phase equilibria of n-alkanes

Smit

Karaborni

Siepmann

1995

The Journal of Chemical Physics

483

188

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For petrochemical applications knowledge of the critical properties of the n-alkanes is of interest even at temperatures where these molecules are thermally unstable. Computer simulations can determine the vapor-liquid coexistence curve of a large number of n-alkanes ranging from pentane ͑C 5 ͒ through octatetracontane ͑C 48 ͒. We have compared the predicted phase diagrams of various models with experimental data. Models which give nearly identical properties of liquid alkanes at standard conditions may have critical temperatures that differ by more than 100 K. A new n-alkane model has been developed by us that gives a good description of the phase behavior over a large temperature range. For modeling vapor-liquid coexistence a relatively simple united atom model was sufficient to obtain a very good agreement with experimental data; thus it appears not necessary to take the hydrogen atoms explicitly into account. The model developed in this work has been used to determine the critical properties of the long-chain alkanes for which experiments turned out to be difficult and contradictory. We found that for the long-chain alkanes ͑C 8 -C 48 ͒ the critical density decreases as a function of the carbon number. These simulations were made possible by the use of a recently developed simulation technique, which is a combination of the Gibbs-ensemble technique and the configurational-bias Monte Carlo method. Compared with the conventional Gibbs-ensemble technique, this method is several orders of magnitude more efficient for pentane and up to a hundred orders of magnitude for octatetracontane. This recent development makes it possible to perform routinely phase equilibrium calculations of complex molecules.

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Section: Critical Properties Of the Alkanesmentioning

confidence: 99%

Computer simulations of vapor–liquid phase equilibria of n-alkanes

Smit

Karaborni

Siepmann

1995

The Journal of Chemical Physics

483

188

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“…The intrinsic viscosity [η] of grewia solutions was determined at 20 °C with an Ubbelohde capillary viscometer and calculations were made according to the Huggins equation (Huggins, 1942):…”

Section: Intrinsic Viscositymentioning

confidence: 99%

Evaluation of some important physicochemical properties of starch free grewia gum

et al. 2016

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Highlights: High glucose content of grewia gum is the result of high starch content. Grewia gum contains highly acetylated uronic acids. Removal of starch has an impact on the physicochemical properties of the extracts. Rheological behaviour of grewia gum is influenced by changes in pH. 3 AbstractGums obtained by extraction from the inner bark of stems can be found in association with starch, which must be digested in order to obtain a refined polysaccharide isolate. In the present study, grewia gum obtained from the inner bark of the stems of Grewia mollis was shown to co-exist with starch and the effect of starch digestion on the physicochemical properties of the resultant polysaccharide was evaluated.The gum was extracted by maceration of the inner bark in deionized water and isolated by a combination of filtration, centrifugation and finally precipitation with absolute ethanol to produce the crude grewia gum extract (GG). The presence and content of starch in the gum sample was determined followed by enzymatic digestion of the starch using α-amylase (Termamyl 120L) to give a starch-free extract (GGDS). Physicochemical properties of the extracts such as total carbohydrates, total protein, differential sugar composition, NMR, intrinsic viscosity and rheological behaviour of the samples were evaluated.The GG extract had total carbohydrate content of ~ 60 % out of which 11.8 % was starch, and a protein content of 2.3 %. Samples also contained galacturonic and glucuronic acid which were highly acetylated. Both samples had a higher proportion of galacturonic acid than glucuronic acid and contained rhamnose, arabinose, galactose, glucose and xylose as neutral sugars in varying proportions. Rheological measurements on 2 %w/w dispersions of the extracts show minor differences between both the original extract and the de-starched material but were influenced by changes in pH. Keywords:Grewia mollis; polysaccharides; uronic acids; neutral sugars, starch 4 IntroductionGrewia mollis is a shrub native to sub-Saharan Africa belonging to the Malvaceae family. It is cultivated in the middle belt region of Nigeria where the inner bark from the stems of the shrub is pulverised and often used as a thickener in various food formulations.This crude extract has previously been identified to contain polysaccharides (Okafor, Furthermore, the high glucose content of the gum coupled with the fact that the gum is obtained by extraction from the inner bark of the plant Grewia mollis, creates the likelihood of starch being present with the gum. In the present study, the starch content of grewia gum (GG) was evaluated and was subsequently enzymatically digested to give a starch-free extract (GGDS). The physicochemical properties of the two extracts were evaluated, which included a comprehensive evaluation of the uronic and neutral sugar composition, and rheological properties. and 60% were prepared by mixing appropriate amounts of two of the procured commercial standards. Termamyl 120L (heat-stable alpha-amylase) was a kind donation f...

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“…gives the free energy of mixing as For a simple mixture of homopolymers, Flory-Huggins theory (4,16) where n A and n B are the numbers of A and B molecules, respectively. Since we wish to compare phase separation under conditions which are similar to those that occur in domain formation (equal numbers of A and B molecules) we take n A = n B and find that AG, = 0 when If we now divide eq.…”

Section: Predicted Radii Of Polystyrene Domainsmentioning

confidence: 99%

Theory of block copolymers. I. Domain formation in A-B block copolymers

Meier

1996

J. Polym. Sci. B Polym. Phys.

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SynopsisMicrophase separation occurs in many block copolymers to give domain structures. In this first paper in a series dealing with domain formation and the consequences thereof, a theory is presented for the formation of spherical domains in A-B block copolymers. The theory establishes criteria for the formation of domains and their size in terms of molecular and thermodynamic variables. It is shown that the considerable loss in configurational entropy due to the constraints on the spacial placement of chains in a domain structure requires that the critical block molecular weights required for domain formation are many-fold greater than required for phase separation of a simple mixture of the component blocks. The relation between domain radius R and molecular dimensions is obtained from the requirement that space in the domain must be filled with a constant density of segments. Segment densities are evaluated from solutions of the diffusion equation, treating the constraints on chain placement as boundary value problems. This gives the relationship R = 413 >"', where "2 is the root-mean-square end-to-end chain length. Because of chain perturbations in a domain system, < L 2 >' / 2 is larger than the unperturbed value < L2 >A" normally expected for bulk polymers. A means to evaluate the perturbations is shown. The agreement between the predictions of the present theory and the limited published experimental information appears quite satisfactory.

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Some Properties of Solutions of Long-chain Compounds.

Cited by 1,295 publications

References 2 publications

Computer simulations of vapor–liquid phase equilibria of n-alkanes

Computer simulations of vapor–liquid phase equilibria of n-alkanes

Evaluation of some important physicochemical properties of starch free grewia gum

Theory of block copolymers. I. Domain formation in A-B block copolymers

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