Determination of the Surface Energy Distributions of Different Processed Lactose
ABSTRACT Particulate interactions between drug and lactose carrier in dry powder inhaler formulations are affected by the heterogenous energy distribution on the surface of the individual compounds. A new method based on Inverse Gas Chromatography at finite concentration is applied to study the energy heterogeneity of untreated, milled, and recrystallized lactose of similar particle size distribution. Energy distributions for the dispersive surface energy and the specific free energy of ethanol are obtained. Milling causes an increase in surface energy due to formation of amorphous regions. Untreated and recrystallized materials have similar surface energies at low surface coverages but show clear differences in energy distribution.
- SourceAvailable from: Mohammad Amin Mohammad
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- "The reason for this discrepancy is that IGC is usually used at infinite dilution conditions at which n-alkanes preferentially probe the higher energy sites on the solid surface  . To probe the whole surface, Thielmann et al. developed the method of IGC at finite concentration conditions . Then, Ho et al. compared the values of d s measured by IGC at finite concentration conditions with those measured by the contact angle method, and they found that IGC also generated higher values in the case of heterogeneous solid surfaces compared to the contact angle method, but similar values in the case of homogenous solid surfaces . "
ABSTRACT: Methylene middle parameter [Formula: see text] , the product of the methylene group's cross-sectional area ( [Formula: see text] ) and the root square of its dispersive free energy ( [Formula: see text] ), is the key parameter to calculate the dispersive surface components of solids (γs(d)) using inverse gas chromatography (IGC) at different temperatures. The only method reported to calculate [Formula: see text] as a function of temperature is the Dorris-Gray method. However, the conventional values of [Formula: see text] calculated by the Dorris-Gray method depend heavily on theoretical aspects. This paper establishes a novel equation calculating the actual [Formula: see text] as a function of temperature using the latest and most accurate surface parameters of seven successive n-alkanes. The obtained actual [Formula: see text] values are slightly higher those of the conventional [Formula: see text] . At 20°C, the actual [Formula: see text] generates γs(d) values less than those generated using the conventional [Formula: see text] by ∼3%, and this reduction in calculated γs(d) values increases linearly to become ∼5% at 100°C. Therefore, using the new actual [Formula: see text] seems to mitigate the discrepancy between the γs(d) values measured by IGC and those measured by the contact angle method. Copyright © 2015 Elsevier B.V. All rights reserved.Journal of Chromatography A 07/2015; 1408. DOI:10.1016/j.chroma.2015.07.003 · 4.26 Impact Factor
- "This however results in the probe molecules preferentially interacting with the higher energy sites on the material surface, and interaction with lower energy sites is limited, if not excluded   . More advanced methodologies have been developed in the last decade, that allow the characterisation of the surface energy heterogeneity by using IGC under finite concentration conditions   . "
Article: Heterogeneity of carbon fibre[Show abstract] [Hide abstract]
ABSTRACT: A range of polyacrylonitrile (PAN) and pitch based carbon fibre types (high, standard and intermediate modulus fibres) have been characterised using both physical and chemical techniques, the results highlighting the heterogeneity of the fibre. Nano-indentation showed variation in stiffness between different fibres of the same type as well as variation along a 20 μm length of a single fibre. Tensile tests showed variance of approximately 25% in tenacity for three different carbon fibre types but less variability in modulus with values from 8% to 19%. Raman spectroscopy showed variation in the graphitic content both between fibres of different origin as well as variation, with 0.5 μm spatial resolution, along the length of a single fibre. Inverse gas chromatography surface energy measurements of larger samples of fibres were carried out using the novel approach of incremental surface coverage by varying the probe molecule concentration and revealed different levels of energetic heterogeneity for PAN based fibres collected at different stages of carbon fibre production. The heterogeneity of the unoxidised fibres (collected after carbonisation) was restricted to about 15% of the fibre surface whereas the surface oxidised fibre sample (collected after the electrolytic oxidation bath) was heterogeneous over more than 30% and the sized fibres were shown to be quite homogeneous.Carbon 03/2014; 68:240–249. DOI:10.1016/j.carbon.2013.10.084 · 6.16 Impact Factor
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- "Applications of inverse gas chromatography (IGC) are wide ranging and include the monitoring of batch-to-batch variation (Gamble et al., 2010; Ticehurst et al., 1996), the impact of different processing routes (Thielmann et al., 2007), the detection of low levels of process induced disorder (Feeley et al., 1998), interactions of excipients and drug substances (Tay et al., 2010; Traini et al., 2008) and the impact of milling processes on the surface properties of materials (Balard et al., 2008; Chamarthy and Pinal, 2008; Gamble et al., 2012; Heng et al., 2006; York et al., 1998). However, applications of the approach to binary systems are almost as common and previously reported work has encompassed applications to investigate lubricated pharmaceutical systems (Swaminathan et al., 2006; Tay et al., 2010; Das and Stewart, 2012), surfactant systems (Bardavid et al., 2007), and dry coating or mechanofusion based coating of powders (Rousset et al., 2002; Kumon et al., 2006; Das et al., 2011). "
ABSTRACT: The aim of this study was to investigate the applicability of surface energy characterization tools such as inverse gas chromatography for the analysis of binary systems. Drug substance was coated with two grades of silicon dioxide and the surface energy characteristics determined using a Surface Energy Analyser. The results demonstrated that the measured dispersive surface energy of such intermediate samples were as a consequence of probe interactions with both constituent components, however, the degree and order of interaction with each species was related to surface energy heterogeneity and surface availability. A method to predict the degree of probe-surface preferentiality within the intermediate samples was applied to the data, demonstrating to closely match the measured data whilst suggesting notable differences in probe-surface preferentiality. Specific probe interactions were also assessed and the results suggested that probe surface preferentiality was not equivalent to that of the dispersive probes, possibly due to differences in ranges of the dispersive/specific forces. An equivalent physically mixed sample was analysed and the results demonstrated that the measured heterogeneity curve mirrored that of the pure drug substance suggesting that the driver for probe interaction is different for the physically mixed and the coated intermediate samples.International Journal of Pharmaceutics 02/2013; 445(1-2). DOI:10.1016/j.ijpharm.2013.01.061 · 3.65 Impact Factor