Surface area affects hydration

Hydrate induction times from water are approximately proportional to the displacement from equilibrium conditions (e.g., subcooling). Other variables, which affect nudeation include guest size and composition, geometry, surface area, water contaminants and history, the degree of agitation or turbulence. 

Occlusion of the skin, seen with application of water-impermeable drug vehicles or patches, alters the rate and extent of toxicant absorption. As the skin hydrates, a threshold is reached where transdermal flux dramatically increases (approximately 80% relative humidity). When the skin becomes fully hydrated under occlusive conditions, flux can be dramatically increased. This occlusive effect must be accounted for when extrapolating toxicology studies conducted under occlusive conditions to field scenarios where the ambient environmental conditions are present. Hydration may also markedly affect the pH of the skin, which varies between 4.2 and 7.3. Therefore, dose alone is often not a sufficient metric to describe topical doses when the method of application and surface area become controlling factors. Dose must be expressed as mg/cm2 of exposed skin. 

Particle Size of Raw Materials in Solution Particle size is affected by the breaking process of the particle, crystal form, and/or salt form of the drug. The particle size can affect the rate of dissolution of raw materials in the manufacturing process. Raw materials of a finer particle size may dissolve faster because they have a larger surface area in contact with the solvent than those of a larger particle size when the product is compounded [6], Mixing faster causes the particle to break down and dissolve more quickly. In addition, hydrated particles are less soluble than their anhydrous partners [37],... 

Purity of phospholipid is essential to develope stable liposomes. Moreover, nature of the dry lipids, its surface area, its porosity, and hydration of dry lipid film (temperature, pH and ionic strength of hydration medium) affect the lamelarity and morphology of formulated liposomes. 

The effect of water will be described more thoroughly in a future paper [8], As shown by Table 1 data, water affects the activity of manganese dioxides. It also dramatically reduces the time needed to obtain a stable conversion. The two effects can be explained by a hydration of the oxide surface. As far as the specific activity of the different catalysts is concerned, the order of catalyst activity is not modified, but Ae differences are very much attenuated. Figure 2 presents the activity of the different Mn02 samples in the presence of water vapor corrected for the variation in surface area. The order of activity is different from... 

The sodium and silica content of the aluminas, originally present in small quantities in the hydrates or added in processing, can be important for certain catalyst applications. Besides affecting the catalytic properties, they can influence thermal stability greatly. One procedure for imparting thermal stability to support materials is by doping. Thus, alumina can be stabilized to prevent conversion to the low area a form (when area is reduced from about 250 to 1 m /g). If alumina is doped with small amunts of oxides from group IIA such as CaO and subsequently calcined at 1200°C for 2 hs, a stable surface area of 20-100 m /g is obtained for use as a thermally stabilized support. Such materials have found applications iln automobile exhaust catalysts and other combustion catalysts. 

Several substance properties can affect dissolution and/or solubility, such as purity particle size and distribution surface area and the presence of polymorphs, hydrates or other solvates or amorphous forms. To avoid misleading or inconclusive results in extensive solubility or dissolution studies, it is important to characterise the drug substance form with respect to such properties, especially in the later biopharmaceutical preformulation phase. Methods for such characterisation are described in more detail in Chapters 3 and 7. 

With the change in surface area and porosity, acid activation invariably affects acidity of the catalysts. Acidity as measured by STPD of ammonia is given in fig.2. Initially, an increase in the total acidity is observed with the increase in activation time however there is not much change observed after 2h activation. It is well known that the hydrated leached... 

The results for the adsorption of crude oil on columns, and the BET surface area for the studied samples are summarized in Table 8.1. The adsorption factor (AF) is defined here as (oil mass)/(vermiculite mass). For both, expanded and FIV samples, the adsorption studies were performed at two different mass values 2.0 and 4.0 g. However, it was found that the AF values were not affected by the used vermicuHte mass. Adsorption experiments were also performed for hydrated (not expanded) vermiculite samples, and it was observed that the AF for these sample is very low (0.3). All adsorption experiments were performed in triplicate, and it was verified that the results are reproducible. 

Water can fill 70%-90% (dependent on filling conditions) of the total pore volume of LiChrolut EN adsorbent possessing nanopores and narrow mesopores of hydrophobic and partially hydrophilic characters. Adsorbed water is characterized by high associativity. It does not contact to the total surface area of the adsorbent. It is weakly affected by co-adsorbed polar DMSO. Weakly polar chloroform can displace a portion of adsorbed water from narrow pores into larger one or onto the outer surface of polymer particles. Methane can form the hydrate system with water adsorbed in narrow pores of LiChrolut EN adsorbent at low pressures. 

The effects of the aqueous suspension of fumed silica A-300 onto water bound in bone tissue of the M37 sample are close to that of pure aqueous medium (Table 7.14). Silica surface is strongly hydrated (Strange et al. 2003, Gun ko et al. 2005d) however, the total amount of water bound to this surface is smaller than that bound in bone tissue. Perhaps, penetration of silica nanoparticles into narrow pores of the studied spongy component of bone tissue (where major amounts of structured water locate) does not occur therefore, silica particles being out (or in macropores) of bone tissue are not capable to affect water locating in bone tissue. An increase in the S value by 21% with the presence of silica is due to its high specific surface area. 

Poly(vinyl alcohol) has also been shown to provide mechanically adaptive properties to composite films comprised of a PVOH electrospun mat and a PVAc or EO-EPI matrix. Films made from such composites exhibited controlled response to hydration that resulted in a two fold decrease of the storage modulus which, in the case of the PVAc composite, was fully reversible. Expanding on this concept and in a similar motif to the aforementioned CNC composites, Korley and coworkers have recently showcased the potential use of montmorillonite in mechanically adaptive composite materials. Montmorillonite is a layered silicate with high aspect ratio and surface area and is often used in polymer composites to mechanically reinforce the resulting material, while its dispersibility and tunable surface chemistiy make its use particularly attractive. In this case, the incorporation of montmorillonite in the PVOH fibrous filler resulted in enhanced moduli when the polymer matrix consisted of EO-EPI, as opposed to the limited enhancement observed in the case of a PVAc matrix. Nonetheless, both composites showed mechanically switching properties upon hydration, with the weight fraction of montmorillonite affecting the mechanical contrast as well as the response time. ... 

The characteristies of cement pastes or concrete from the initial slump to strength and durability are directly or indirectly related to the type, the rate formation, and the amount of the hydration products. Several faetors have to be taken into consideration in the elucidation of the role of superplasticizers on the hydration of cement. Some ofthe factors that affect the rate of hydration include the type of cement, the characteristics of the ions in the solution (sulfate, OH, and alkalis), the particle size/surface area of cement, the relative amoimts of the individual phases of cement, the dosage ofthe superplasticizer, the cation associated with the superplasticizer, the type of superplasticizer, its molecular weight, the dosage, the temperature of hydration, and the water cement ratio. 

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