Contact angles interactions measurements

In order to calculate polymer/filler interaction, or more exactly the reversible work of adhesion characterizing it, the surface tension of the polymer must also be known. This quantity is usually determined by contact angle measurements or occasionally the pendant drop method is used. The former method is based on the Young, Dupre and Eowkes equations (Eqs. 21,8, and 10), but the result is influenced by the surface quality of the substrate. Moreover, the surface (structure, orientation, density) of polymers usually differs from the bulk, which might bias the results. Accuracy of the technique maybe increased by using two or more liquids for the measurements. The use of the pendant drop method is limited due to technical problems (long time to reach equilibrium, stability of the polymer, evaluation problems etc.). Occasionally IGC is also used for the characterization of polymers [30]. 

Counterion Interactions with Water and Poly cations. The wide range of contact angles measured for the different counterions is no doubt related to the extent of their interaction with water relative to that with the polycations. 

An empirical method to estimate the surface tension of a solid is Zisman s plot (cos 9 as a function of yl), which obtains the critical surface tension of wetting. In the absence of specific interaction between the surface and the liquids used for the measurement of contact angles, the critical contact angle of wetting can be accurately estimated and its value used as the surface tension of the surface. However, if a surface interacts with liquids used as the sessile droplet for the contact angle measurement, to the extent that the surface tension is altered, Zisman s plots deviate from the ideal linear relationship. In a strict sense, the plot is applicable only to imperturbable surfaces with which liquid contact does not alter surface configuration, i.e., no surface dynamics applies. 

Spin-coated PS/PMMA films were used as samples to study silica-polymer interactions. For this purpose, solutions of 10 mg polymer in 1 mL toluene were prepared flom each polymer. The PMMA and PS solutions were mixed in a ratio of 2 1. When the mixed solution was spin-coated on a fleshly cleaned silicon surface a phase-separated film of 100 nm thickness was obtained. Cantilevers were modified either by deposition in the saturated atmosphere of hexamethyldisilizane or immersion in a 2% solution of dimethyldichlorosilane in toluene. Typically, measuring the contact angle of the sample after modification gives proof of hydrophobization. However, because of the small size of the tips the contact angle cannot be estimated. Thus, at the same time as the cantilever modification, small pieces of silicon wafers were modified to enable contact angle measurements to be made. 

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