Effects on Barrier Properties

The permeability of small penetrant molecules through an organic matrix is determined by the solubility and diffusivity of the small molecule in the matrix as well as by the mean-square displacement (total path length traveled) divided by the sample thickness. In principle, the addition of a filler in the polymer matrix is expected to affect the solubility and diffusivity of a penetrant molecule, especially in the vicinity of the filler (i.e in the filler-polymer interfacial region and at least one polymer Rg away from the filler surface). Also, it is expected that fillers will affect the path tortuosity (mean-square displacement of penetrant versus film thickness) directly, when penetrants are forced to travel around impermeable fillers, and indirectly, when fillers induce polymer chain aUgnment or alignment and modification of polymer crystallites.  

Theoretical approaches on the barrier properties of nanocomposites beat fillers as impermeable nonoverlapping particles and assume no permeability changes in the polymer matrix. Effectively, this means that the permeability of the composite will be smaller than the permeability of the matrix (unfilled polymer) by a factor equal to path tortuosity in the composite (simply assuming that the penetrant path cannot cross any filler particles). This path tortuosity was calculated by Nielsen for completely aligned filler particles (aU fillers have then-larger surface parallel to the film surfaces, but there is no order in the filler center of mass), and its contribution to the composite permeability was derived to be 

FIGURE 2.9 Comparison of theoretical models quantifying the effect of path tortuosity on the permeability of a composite Nielsen model [eq. (2.8)], Friedrickson-Bicraano [eq. (2.10)], modified Nielsen [eq. (2.9)], and Cussla--Aris [eq. (2.11)]. 

FIGURE 2.10 Theoretical predictions based on path tortuosity [eq. (2.9)], as a function of (a) filler aspect ratio a = 1 to 1000 (b) filler aspect ratio and alignment (5 = 1 perfect smectic alignment—dashed lines S = 0 random orientation —solid lines) (c) filler aspect ratio for a constant volume fraction (pv = 5%. (d) Comparison of the same theoretical predictions (parameters as indicated) with experimental values for water vapor permeabilities in various polymer-montmorillonite nanocomposites. (From Refs. 39-41.) 

Other important parameters (such as permeant solubiUty changes and polymer crystallinity effects) when it comes to predicting permeability changes upon nanocomposite formation. 

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Thus, a systematic evaluation of excipients focusing on the concentration dependence of effect on barrier properties, biochemical integrity, and cell viability is still needed. 

Humidity - [SIMULTANEOUS HEAT AND MASS TRANSFER] (Vol 22) -ceramic sensors for [CERAMICS - ELECTRONIC PROPERTIES AND MATERIAL STRUCTURE] (Vol 5) -effect on barrier properties [BARRIER POLYMERS] (Vol 3) -sensors for [SENSORS] (Vol 21)... 

The ratio of i-enantiomers to n-enantiomers (l/d ratio or l d) is known to affect the properties of PLA, such as melting temperature, degree of crystallinity, and barrier properties. Control of the l d monomer content is an important molecular feature of PLAs that has a large effect on barrier properties. Generally, higher L-lactide content should result in higher barrier properties of the polymer because of greater stereochemical purity [12]. 

The nitrocellulose coated films were the only type available until the early 1950 s, when vinylidene chloride copolymer coatings were introduced. The method of coating is essentially the same as that used for the nitrocellulose type. This later type of coating has the advantage that subsequent conversion, eg printing and bag making, does not have as marked an effect on barrier properties as on the nitrocellulose coatings where the water vapour permeability can be increased quite appreciably. 

Debeaufort, F., and Voilley, A. (1995). Effect of surfactants and drying rate on barrier properties of emulsified edible films. Int. J. Food Sci. Technol. 30(2), 183-190. 

Electrochemical impedance spectroscopy (EIS) is a valuable method with which to study the barrier property and corrosion protection performance of polymer-coated metals it has been widely used in this field in recent years [11-15]. Many examples can be found in the literature, which illustrate the performance deterioration of different coatings on metals as well as pretreatment effects on the properties of... 

Changez M., Varshney, M., Chander, J. and Dinda, A.K. (2006) Effect of the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions on barrier properties of mice skin for transdermal permeation oftetracaine hydrochloride In vitro. Colloid Surf. B, 50,18-25. 

WEINKAUF PAUL Effects of Structural Order on Barrier Properties... 

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