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Assessing and predicting granular‐materials hydrophobicity by parametrizing a general equation of state §
Author(s) -
RamírezFlores Juan Carlos,
Bachmann Jörg
Publication year - 2012
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/jpln.201000417
Subject(s) - wetting , surface tension , wilhelmy plate , contact angle , chemistry , context (archaeology) , equation of state , capillary action , thermodynamics , physics , paleontology , biology
Wettability is related to forces or surface tensions (σ) acting at the solid–liquid–vapor interface. Given that surface tensions are difficult to assess directly, contact angles (CA) are used as indicators of the balance of forces acting in the system. In this context, the ES theory was developed as an alternative to assess the σ parameters of the Young's equation. This research evaluates the applicability of a proposed equation of state (ES), which is in theory also able to predict the CA of a sample when two σ parameters of the Young's equation and two fitting parameters (β and α) of the function Φ = (σ SL ) are known (Φ: molecular interaction parameter, σ SL : solid–liquid surface tension). These parameters were determined by different experimental methods assessing the CA, in order to determine which method is more suitable to validate the ES theory: Capillary Rise Method (CRM) and Wilhelmy Plate Method (WPM). For WPM, two modes (advancing and equilibrium CA) were applied. Finally, results of CA between the experimental measurements obtained by WPM and those predicted by the ES were compared. Samples of coarse silt, fine sand, and nonporous glass beads with different levels of water repellency were used as test materials. In line with previous research, all methods showed lower values of σ for samples with increasing hydrophobicity. At the same time, Φ reduces consistently with higher hydrophobicity, up to ≈ 0.5–0.6 based on CRM and WPM‐ECA data, and even lower (≈ 0.1–0.2) in WPM‐ACA. α increased with higher hydrophobicity, having relatively stable values in samples having σ SV > 40 mN m –1 . β showed stable values for samples having σ SV > 35–40 mN m –1 . In hydrophobic samples (σ SV < 35 mN m –1 ), β decreased in calculations based on WPM‐ACA data, and to a minor degree in WPM‐ECA. The agreement between the CA directly measured (WPM) and those predicted by the ES was low, although better for the WPM‐ECA, suggesting that this last approach can be considered more suitable to evaluate the ES theory.