Wetting enthalpy

Figure 5. The molar immersional wetting enthalpy on illite organocomplexes with different hydrophobicity (O) in methanol, and ( ) in benzene.

Figure 8. The molar immersional wetting enthalpy on organo-montmorillonite with different hydrophobicity in methanol (----nonswelling illite,--swelling montmorillonite).

Next we shall examine how an increase in the hydrophobicity of the surface affects immersion wetting enthalpy in polar solvents such as methanol. It has been pointed out already in the discussion of hydrophobic illites that molar immersion wetting enthalpy decreases exponentially with an increasing extent of hydrophobization. The same holds for swelling hydrophobic montmorillonites as well. The difference between swelling hydrophobic montmorillonite and non- swelling illite of identical hydrophobicity yields the value of swelling enthalpy, AHs, which is endothermal and increases with the extent of hydrophobicity. 

Immersional wetting enthalpy on Na-Y and dealuminated Y zeolites (after heating at 623 K) in different organic liquid... 

For both, hydrated and dehydrated vermiculite samples, the wetting enthalpy values are the same AH, vett = 5.30 0.20Jg. This shows that at least for the considered reaction time (5.0 min), the dehydrated vermuclite does not behave as a hydrophilic matrix. This hypothesis is reinforced by the X-ray powder dif action patterns for contact times (between dehydrated vermiculite and water) of 24, 48, and 72 h, as shown in Fig. 8.5. 

Although cellulose is a hydrophilic material, sorption of saturated water vapor for CNP is relatively low due to increased crystallinity degree (Table 9.7). The highly crystalline CNP have also low wetting enthalpy in comparison with the starting cellulose material. 

Table 9.7 Water Vapor Sorption (A) and Wetting Enthalpy (AW ) for CNP from Various Sources...

Due to the amorphous structure, ANP acquires such specific features as increased content of functional groups, high accessibility, and sorption ability (loelovich, 2013a, 2014a). Freeze-dried amorphous nanocellulose has an enhanced wetting enthalpy (—125 to — 130J/g), absorbs up to 35—40% water vapor, and completely decomposes under action of cellulolytic enzymes. Moreover, the chemical modification of ANP is carried out faster and deeper than other kinds of nanocellulose. 

Due to the amorphous structure, ANP acquires an enhanced water sorption and wetting enthalpy, as well as complete decomposition under action of cellulolytic enzymes. Increased content of negative-charged sulfonic groups imparts a stable phase state of dilute aqueous dispersions of ANP. Study of rheological... 

FIG. 11 Classification of immersional wetting enthalpy isotherms (a) U-shaped excess isotherm, with corresponding enthalpy of irmnersion isotherm, (b) S-shaped excess isotherm, with corresponding enthalpy of immersion isotherm. 

FIG. 15 Immersional wetting enthalpy isotherms on Na-illite and on HDP-illite derivatives in methanol (l)-benzene (2) mixtures. Na sodium illite 1,2,3, hexadecylpyridinium illites. 

The specific immersion wetting enthalpies of kaolinite, illite, and their organo-philic derivatives were investigated in methanol and benzene in our earlier publications [35,37,38]. These data reveal that the heat of immersion in methanol is the highest in the case of the dialyzed hydrophilic mineral, and with increasing surface modification its value decreases. The comparison of immersion wetting enthalpies relative to unit mass of the adsorbent is justified only when the specific surface area of the adsorbent is constant. It is also known, on the other hand, that the value of liquid sorption capacity, is a function of surface modification 02 = where 2flm,2 is the hydrophobic surface area and a is the total... 

FIG. 17 Immersional wetting enthalpies as a function of alkylammonium chain lengths in (O) methanol and ( ) toluene. 

FIG. 18 Immersional wetting enthalpies on hydrophobized montmoriUonite in toluene as function of surface coverage (82) with hexadecylpyridinium cation. 

FIG. 18 Immersional wetting enthalpies as function of aUcylammonium chain length in methanol (O) and toluene ( ). 

Measurements of the enthalpy changes accompanying the immersion and wetting phenomena may be performed with a Tian-Calvet type differential calorimeter [49, 54]. The experimental procedure includes several intermediate stages which may take much time, especially when the wetting enthalpy is measured as a function of the surface coverage by the vapour of the immersional liquid. 

Study of the heat effects of interaction between cellulose samples and water showed that wetting enthalpy is exothermic. Moreover, the heat effect is higher for the samples having the lower crystallinity. As a result of the investigations of interaction cellulose with water, the significant rules were discovered ... 

Wetting enthalpy does not depend on DP-values and type of crystalline pol5miorph of cellulose. 

Figure 7.38 Dependence of wetting enthalpy on amorphicity degree [V] of cellulose samples.

Based on Eq. (7.42), the reverse task can be solved, and namely to calculate the amorphicity (F) and crystallinity degrees of the cellulose sample from results of the wetting enthalpy ... 

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