Water immersion calorimetry

It is with this type of equation that, for instance, Micale el al. (1976) was able to check the consistency of the isosteric approach (from gas adsorption isotherms) with immersion calorimetry, for the water-microciystalline Ni(OH)2 system. 

Lyklema (1995) pointed out that, in the absence of immersion calorimetry, the notion of surface hydrophilicity-hydrophobicity remains vague. Once the molar enthalpy of immersion in water is assessed it can readily be compared with the value 44 kJ molwhich corresponds to the enthalpy of condensation of water at room temperature. If it is higher, the surface is considered to be hydrophilic if lower, the surface is defined as hydrophobic. 

Figure 5.8 gives the main types of curve listed by Zettlemoyer and Narayan (1967) for this type of immersion calorimetry experiment with pre-coverage of the sample. Curve (a) is obtained with homogeneous surfaces with respect to the immersion liquid (e.g. chrysotile asbestos in water, Zettlemoyer et ai, 1953). Curve (b) is given by... 

This is an indirect way of assessing the energetics of gas adsorption in micropores. The pre-adsorbed vapour can be that of the immersion liquid or it can be another adsorptive for instance, to study the water filling mechanism in microporous carbons, Stoeckli and Huguenin (1992) devised an experiment with water pre-adsorption prior to immersion calorimetry (in water or in benzene). 

Water has been widely used as a probe molecule for the characterization of zeolites, especially of those with a high aluminium content [9]. Water adsorption on hydrophilic zeolites has been used to measure their pore volume, and it has been shown that the amount of water adsorbed is a linear function of the aluminium content [10]. Additionally, water adsorption is also highly sensitive to the nature, valence and accessibility of extra-framework cations [11]. Immersion calorimetry allows for the measurement of the degree of interaction between the zeolite and water, and this can be compared with the interaction between the zeolite and other molecules with different polarity. In this way, the polar character of the zeolite surface can be assessed. 

The porous structure of active carbons can be characterized by various techniques adsorption of gases (Ni, Ar, Kr, CO ) [5.39] or vapors (benzene, water) [5,39] by static (volumetric or gravimetric) or dynamic methods [39] adsorption from liquid solutions of solutes with a limited solubility and of solutes that are completely miscible with the solvent in all proportions [39] gas chromatography [40] immersion calorimetry [3,41J flow microcalorimetry [42] temperature-programmed desorption [43] mercury porosimetry [36,41] transmission electron microscopy (TEM) [44] and scanning electron microscopy (SEM) [44] small-angle x-ray scattering (SAXS) [44] x-ray diffraction (XRD) [44]. 

The chemical nature of a solid determines its adsorptive and wetting properties. Now, the energy of immersion mainly depends on the surface chemistry but also, to some extent, on the nature of the bulk solid. For example, the interaction between water and silica has contributions from the bulk Si02 together with contributions from the silanol groups of the interface. Polar molecules are very sensitive to the local surface chemistry, whereas nonpolar molecules are more sensitive to the bulk composition. Interactions between a bulk Hquid and a bulk solid through an interface are often described in terms of Hamaker constant [16]. Immersion calorimetry in apolar liquids was proposed to estimate the Hamaker constant [17]. The sensitivity of immersion calorimetry to the surface polarity has justified its use for characterising the surface sites. 

Numerous surface modifications were followed by immersion calorimetry. The energy of immersion and the kinetics of the process may help to distinguish between the removal ofphysisorbed water and the dehydroxylation as a function... 

Lopez-Ramon, M.V., Stoeckli, F., Moreno-Castilla, C., and Carrasco-Marin, F. (2000). Specific and non-specific interactions of water molecules with carbon surfaces from immersion calorimetry. Carbon, 38, 825—9. 

Denoyel et al. [45] derived the pore size distributions of two sets of activated carbons (one activated in water vapor and the other activated with phosphoric acid) using immersion calorimetric data. They concluded that immersion calorimetry is a convenient technique to assess the total surface area available for a given molecule and the micropore size distribution. More recently, Villar-Rodil et al. [46] have followed this approach to characterize the porous texture of a series of NomexO-derived carbon fibers activated to various bum-offs using liquids with different molecular dimensions as well as N2 and CO2 adsorption Isotherms. Table 3 includes the immersion enthalpies and corresponding surface areas. Relative changes in surface area accessible to the different adsorbates were ascribed to... 

Enrichment in S/L interfaces is of great importance in numerous industrial purification processes (solvent purification, separation, water treatment, decoloriza-tion, flotation, oil recovery, detergency, and so on). The surface area of industrial adsorbents is also often derived from S/L adsorption isotherms. Adsorption at S/L interfaces can be divided into two types, namely adsorption from pure liquids and adsorption firom solutions. Interaction with pure liquids is often characterized by immersion calorimetry. 

Friedrich, M., et al Adsorption of water on activated carbon A thermodynamic study by immersion calorimetry. Adsorpt. Sci. Technol., 7(3), 133-139 (1991). 

Immersion calorimetry using polar liquids gives another insight to the characterization of the solid surfaces. Here, specific interactions between the liquid molecules and active centers at the solid surface play a major role. The comparison between enthalpies of immersion of liquids with different polarity provides a refined picture of the surface properties of the solid. This point can be illustrated by the following example. Stoeckli et al. (1983, 1998) measured the enthalpies of immersion of two non-porous illites, with different BET surface areas (N2 77 K) into benzene and water. Whereas the area enthalpy of immersion into benzene was similar for both samples, about 73mJm , the area enthalpies of immersion into water were quite different, 371 and 782 mJ m respectively, Stoeckli et al. (1998). Clearly, the compositions of these illite surfaces differ. 

A common variety of constant-volume calorimetry is bomb calorimetry, a technique in which a reaction (often, a combustion reaction) is triggered within a sealed vessel called a bomb. The vessel is immersed in a water bath of known volume. The temperature of the water is measured before and after the reaction. Because the heat capacity of the water and the calorimeter are known, you can calculate heat flow from the change in temperature. 

Most carbon blacks have a low affinity for water, i.e. they are hydrophobic. However, the level of hydrophobicity is reduced by the presence of chemisorbed oxygen and certain functional groups (Walker and Janov) 1968 Bradley et al., 1995). The relative extents of the polar and hydrophobic areas of carton blacks have been studied by various methods (Boehm, 1994), including energy of immersion measurements (Barton and Harrison, 1975) and by liquid flow calorimetry (Groszek,... 

Water absorption of the resultant cured materials was measured after immersion for 24 hrs at room temperature and reported as % weight gain. The modulus was measured according to ASTM D 2240, and the dielectric constant and dissipation factor were measured using a method similar to ASTM D 150. Glass and melting transitions were measured by differential scanning calorimetry (DSC). The thermal stability was determined in a forced air oven... 

The interesting property of the MPC copolymer is its affinity for phospholipids (5,72-74). The amount of a phospholipid, dipalmitoylphosphatidylcholine (DPPC), adsorbed on MPC copolymers was larger than that on polystyrene, poly(BMA) and poly(HEMA) and increased with increasing MPC moiety when the MPC copolymers were contacted with a liposomal solution of DPPC (5). This tendency was the same as that of the adsorption of phospholipid from human plasma which is indicated in Fig. 3. Thus, the affinity of poly(MPC-co-BMA) for the phospholipids could be observed even in the plasma. The DPPC molecules adsorbed on the poly(MPC-co-BMA) surface assumed an organized structure like that for a bilayer membrane, which was confirmed by differential scanning calorimetry(DSC) and X-ray photoelectron spectroscopy(XPS) when the poly(MPC-c -BMA) membrane was immersed in the solution containing DPPC (72,74) It is therefore concluded that the MPC copolymers stabilized the adsorption layer of phospholipids on the surface. Stabilization of the liposomal structure in water by a water-soluble MPC copolymer was also found (75). 

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