(560hy) Contact Angle Measurements of Binary Mixtures for Determination of Surface Free Energy | AIChE

(560hy) Contact Angle Measurements of Binary Mixtures for Determination of Surface Free Energy


Zhang, Z. - Presenter, Worcester Polytechnic Institute
He, P., Lamar University
Timko, M. T., Worcester Polytechnic Institute
Lambert, C., Worcester Polytechnic Institute

Surface energy is a fundamental material property that quantifies intermolecular interactions between solid and liquid. Typically, surface energy is determined by making contact angle measurements of multiple pure solvents followed by estimation using theoretical models such as the Owens-Wendt, Zisman, or Neumann methods. However, multiple pure solvents approach suffers from problems such as solvent toxicity, volatility, swelling or chemical competitivity and limited liquid surface tension parameter. These limitations contribute to the uncertainty of the surface energy determination, making it as great as 50% in some cases. Uncertainty of 50% is not sufficient for most applications, meaning that the need exists for superior, yet convenient surface energy estimation methods.

Here, we present a simple and precise technique that uses static contact angle data obtained for binary liquid mixtures to determine surface energy using the Owens-Wendt model. Unlike the multiple liquid approach, the mixture approach can be used to determine an arbitrary number of independent measurements, since each mixture composition can be adjusted systematically across the entire range that includes both pure solvents as end points. A new equation was developed to separate liquid mixture surface tension into its polar and dispersive components suitable for use in a modified version of the Owen-Wendt model. To test the method, contact angle data were obtained on two model surfaces, PDMS and silane-derivatized glass. Water was used in all mixtures, and the other liquids were glycerol, ethylene glycol, formamide, and DMSO. Subsequent analysis indicates that the multiple liquid approach yields estimates of surface energy parameters (dispersive and polar) that agreed with values obtained using multiple liquids and with literature values (where available), but with uncertainty less than 10%. Uncertainty decreased with the square root of the number of independent data points, indicative of random error being the main source of uncertainty and suggesting that uncertainty can be reduced further by increasing the number of data points in the analysis. Likewise, tests with silane-derivatized glass indicated that the method could be used to differentiate surface energy of engineered surfaces. This work provides a simple, convenient method for estimating contact angle with greater precision than any comparable method. We are in the process of extending the binary mixture approach to study surface wetting of hydrophilic surfaces and rough surface (patterned surfaces) to demonstrates its precision compared with other approaches.


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