Surface tension and contact angle of herbicide solutions affected by surfactants

Abstract Contact angle and surface tension were measured for distilled and hard water solutions of adjuvants, Ortho X‐77, Span‐20, Sterox‐NJ. Surfactant‐WK, Triton B‐1956, Triton X‐114, Tween‐20, and Sun Oil 11E. The same parameters were measured for suspensions of atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] and ametryne [2‐(ethylamino)‐4‐(isopropylamino)‐6‐(methylthio)‐s‐triazine] with and without each adjuvant. All adjuvants reduced surface tension and contact angle of distilled water; Surfactant‐WK was most effective and Tween‐20 was least effective. Increasing concentration of surfactants from 0 to 0.1% (v/v) gave progressive reduction in surface tension and contact angle while higher concentrations, 0.1 to 2.0% (v/v), had no further effect. Surfactant‐WK at 0.1% (v/v) in distilled water reduced the surfact tension from 72.8 dynes/cm to 27 dynes/cm and contact angle from 110° to 41°. An additional increase in Surfactant‐WK concentration from 0.1% (v/v) to 2% (v/v) did not further reduce surface tension and contact angle. Sun Oil 11E was identical in behavior except that it was less effective than the surfactants. Water hardness up to 1,000 ppm as Ca ions did not affect surface tension and contact angle in surfactant solutions. An aqueous solution of atrazine had a higher surface tension and contact angle than ametryne in the absence of surfactants. However, these differences were not observed when surfactants were added to either herbicide.