The rôle of surface tension and contact angle in the performance of spray liquids

Ebeling, Walter

doi:10.3733/hilg.v12n11p665

Cited by 36 publications

(18 citation statements)

References 13 publications

(10 reference statements)

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“…All the drops were placed within 2 cm of the midpoint of the leaf. Following the methods of O' Kane,Westgate&GIover (1932), Ebeling (1939) and Fogg (1947) the dimensions of the images of the droplets were measured and their contact angles determined. From the contact angle and the volume of each droplet it was possible to calculate the area of contact between the droplet and the leaf surface (O'Kane, Westgate, Glover & Lowry, 1931).…”

Section: Retentionsupporting

confidence: 89%

The influence of the nitrogen status of oat plants (Avena sativa L.) on the interception and retention of foliar sprays

Lutman

Sagar

1975

Weed Research

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Resum6: ZusammenfassungYoung oat plants grown at a high soil nitrogen level retained more spray tban plants grown at a lower nitrogen level. The greater retention by tbe bigb nitrogen plants appeared to be due both to tbeir greater leaf area and to tbe less vertical angle of tbe leaves.The angles of contact of water droplets on the leaf surfaees were lower for high nitrogen plants. Therefore water droplets hitting tbe surface of the leaves of these plants would be less likely to be reflected and would spread over the leaf surface more readily tban droplets hitting tbe leaves of low nitrogen plants.These results are discussed in relation to earlier work wbich sbowed that high nitrogen plants were more susceptible than those grown at a low nitrogen level to the foliar-applied herbieide, paraquat. * Present address: Weed Research Organization, llcgbroke Hill Varnlon. Oxford. Der Einfluss der Stk!

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Section: Retentionsupporting

confidence: 89%

The influence of the nitrogen status of oat plants (Avena sativa L.) on the interception and retention of foliar sprays

Lutman

Sagar

1975

Weed Research

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“…The low free energy surface of the cuticle resulting in large contact angles contributes to this effect. It must be stressed, however, that the large contact angle alone would not prevent infiltration of the intercellular space if stomatal apertures were cylindrical, for the contact angle of water on most leaf surfaces is smaller than 900 (5,8,9,15). With stomata, the effects of small wall angles and a low energy surface combine to present a formidable barrier to penetration of liquids with high surface tension such as water or aqueous solutions.…”

Section: Resultsmentioning

confidence: 99%

Penetration of Stomata by Liquids

1972

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Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Bruckn. was estimated to be 25 to 30 dyne cm-'. Liquids having a surface tension less than 30 dyne cm'i gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm-' did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 /m) was of little importance.Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.tionship between any of these parameters and penetration has been generally poor. In this paper we present a systematic assessment of stomatal penetration by liquids based on the theory of capillary rise. THEORY When a liquid enters a capillary of circular cross-section the pressure difference (P) across the liquid meniscus is represented by equation 1,where '/L represents the surface tension of the liquid and R, and RI the principal radii of curvature of the liquid meniscus (1). In a narrow cylindrical capillary the meniscus is a segment of a sphere; R, and R, are equal and can be expressed in terms of the advancing contact angle (09) (4,22,27) unless external pressure is applied (6, 7). Some organic liquids, however, are known to penetrate readily, which led to attempts to estimate the degree of stomatal opening from substomatal penetration of certain organic liquids (18,22,25). Reports concerned with the effect of surfactants on promoting penetration into stomata and the substomatal space by aqueous solutions are contradictory (3, 4. 11, 14). Surface tension, viscosity, contact angle, diameter of the stomatal aperture, final height and initial velocity of capillary rise have been implicated in controlling penetration of liquids into the stomatal pore and substomatal chamber (4,6,7,18,26,27) A liquid will rise in the capillary spontaneously only if P is positive. The sign of P is determined by the term cos O.,; P being positive when OA < 90', zero when 9A = 900 and negative when O., > 900. The magnitude of P increases as r decreases.For a conical capillary (Fig. 1)

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“…The wetting properties of coastal leaves was thought to affect the rate of entrance of chlorides regardless of whether they entered the leaves through traumata or by other means. Martin (1938) and Ebeling (1939) studied the wetting and spreading of spray liquids on leaves. Wetting properties were defined as the ability of the liquid to form a persistent liquidsolid surface when the excess liquid is drained from the surface and were assessed by the value of the receding contact angle e. Perfect wetting results when this angle is equal to zero.…”

Section: Wetting Of Leavesmentioning

confidence: 99%

“…Outlines of the hemi&pheres on the leaf surfaces were drawn on white paper and the contact angles were measured with a protractor. This method is possibly not so accurate as the micro-projection method of Ebeling (1939); however, it is sufficiently accurate to measure the variation between species.…”

Section: Wetting Of Leavesmentioning

confidence: 99%