Chapter 13
Dynamic Surface Tensions of Spray Tank Adjuvants New Concepts and Techniques in Surfactants 1
1
P. Berger, C. Hsu, A. Jimenez, D. Wasan , and S. Chung
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Witco Corporation, 3200 Brookfield Street, Houston, TX 77045
The Dynamic Surface Tensions of several spray tank ad juvants were measured using the maximum bubble pressure method (MBP). The e f f e c t of concentration and water hardness on the dynamic surface tension was studied. The correlation between dynamic surface tension and wetting and s o i l penetration was determined. A good correlation was found for both. No differences i n dynamic surface tension was found due to changes i n hardness although t h i s may be due to the nature of the surfactants selected which were designed to be insensi tive to changes i n water hardness. Using the MBP tech nique, the dynamic surface tension was found to be con centration dependent and increases i n the rate of sur face tension lowering were measured well above the CMC. Based on the experimental r e s u l t s , the MBP technique was judged to be a rapid, simple, sensitive, and accurate procedure for determining the dynamic surface tension of a g r i c u l t u r a l spray tank adjuvants. This study i s part of a series which involves the a p p l i c a t i o n of new or improved laboratory techniques to study the surface and i n t e r f a c i a l properties of surfactants employed i n the a g r i c u l t u r a l industry. In this p a r t i c u l a r exercise, the dynamic surface tensions of several spray tank adjuvants are determined by the maximum bubble pressure technique using laboratory equipment designed and b u i l t at the De partment of Chemical Engineering of I l l i n o i s Institute of Technology. Several d i f f e r e n t types of adjuvants have been studied as shown i n Table I. In this f i r s t study, no attempt was made to study v a r i a tions i n each p a r t i c u l a r adjuvant formulation, however, this i s the intent of future work. Kao (1) has determined the dynamic surface tensions for research and i n d u s t r i a l grade sodium dodecylsulfate and found considerable differences between the two. In this work, we Current address: IIT Center, Chicago, IL 60616 0097-6156/88/0371-0142$06.00A) ° 1988 American Chemical Society
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
13.
BERGERETAL.
Surface Tensions of Spray Tank Adjuvants
143
have worked with i n d u s t r i a l grade surfactants and have made no a t tempt to further purify them. The e f f e c t of selective absorption due to mixtures present i n i n d u s t r i a l grade surfactants has not been con sidered. I t i s hoped that this work w i l l help the formulator design the most e f f e c t i v e products f o r f i e l d application. We intend to dem onstrate that dynamic surface tensions can be obtained e a s i l y with the maximum bubble pressure technique and that the values obtained are s i g n i f i c a n t i n determining the speed and effectiveness of sur factant blends used as wetting agents.
Downloaded by CORNELL UNIV on October 11, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch013
Table I. Adjuvants Used i n Investigation
Product
Application
Active Ingredient
Adsee 775 Adsee 799 Adsee 801 Adsee AK31-64 Adsee AK31-69 Sponto 168D Emcol H-3AM
Sticker S o i l Cond Wetting Foaming Spray O i l Emul Compatibility Activator
Copolymer Fatty Acid Ester Alcohol Ether Sulfate/Sulfonate Nonionic Blend Phosphate Ester Sulfosuccinate
THEORY The technique of measurement of dynamic surface tension has recently been reviewed by Mysels (2) and has been used by various investiga tors i n the past (1,3,4,5). The maximum bubble pressure method de pends on the fact that i f a small bubble of a gas (e.g. a i r ) i s blown at the t i p of a c a p i l l a r y immersed i n a l i q u i d , the pressure i n the bubble increases i n i t i a l l y , while the bubble grows and i t s radius of curvature decreases. I f the bubble i s small enough to be considered as spherical, the maximum pressure occurs when i t becomes a hemisphere, and at t h i s point, the radius of curvature i s at i t s minimum value. Growth beyond t h i s point r e s u l t s i n a drop i n pres sure, l i q u i d rushes i n , and the bubble i s blown from the t i p of the c a p i l l a r y . A theoretical treatment and j u s t i f i c a t i o n of the techni que i s described by Joos and R i l l a e r t s (6). In practice, the pressure increases within the c a p i l l a r y at a constant gas flow rate u n t i l the bubble appears at the t i p of the c a p i l l a r y o r i f i c e . The o r i f i c e has been immersed i n the l i q u i d to a known depth (h). The pressure difference between the inside and the outside of the bubble i s related by the Laplace equation: p - p - = 2y/r + dgh where y i s the surface tension, d i s the density of the l i q u i d , p' i s the atmospheric pressure, p i s the pressure within the bubble, g i s the gravitational acceleration and r i s the radius of the c a p i l lary.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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PESTICIDE FORMULATIONS: INNOVATIONS AND DEVELOPMENTS
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APPARATUS The maximum bubble pressure apparatus used for measuring the dynamic surface tension i s i l l u s t r a t e d i n Figure 1. The T shaped c a p i l l a r y tube (A) with a radius of 67 microns, was fused into the tensiometer container (TC) b u i l t by Reliance Glass Works, Bensenville, IL. I n i t i a l l y , a i r i s blown into the tensiometer container to keep the t i p of the c a p i l l a r y dry. The sample solution i s then introduced into the tensiometer container to a predetermined depth. The a i r flow rate i s adjusted with a Cole Parmer Masterflex speed c o n t r o l l e r (PC) and any irregular bubbling at the t i p of the c a p i l l a r y i s eliminated using a Swagelock fine metering valve (MV). The time e f f e c t on the surface tension of a freshly formed bub ble i s studied by generating bubbles from the t i p of the c a p i l l a r y tube. The frequency of bubble formation i s measured using an o p t i c a l technique. A pair of co-linear glass rods direct a l i g h t beam across the c a p i l l a r y t i p . A l i g h t diode (L) i s attached to one of the glass rods for transmitting l i g h t and a photodiode detector (PD) located on the other glass rod i s attached to a frequency counter (FC) available from J . Flude Mfg., Model 1953A, to monitor the bubble generating frequency within the accuracy of + 0.005 Hz. The pressure within the bubble i s measured with a d i g i t a l manometer (M) available from Meriam Instruments, Model LP-200I, and i s monitored with an o s c i l l o scope (OS) from Leader Instruments, Model LBO-5825. The accuracy of the maximum bubble pressure method was checked by determining the surface tension between deionized water and a i r , known i n the l i t e r a t u r e to be 72.3 dyne/cm at 25°C. Separately, the c a p i l l a r y was calibrated by measuring the o r i f i c e using a d i f f e r e n t i a l interference microscope. Comparison of both measurements gave a 0.6 micron difference which corresponds to a 0.1 dyne/cm e r r o r . The s e n s i t i v i t y of the method was found to be + 0.02 dyne/cm with a t o t a l uncertainty of + 0.30 dyne/cm. DISCUSSION The r e s u l t s of measuring dynamic surface tensions at various bubble generating rates for the various adjuvant solutions at 0.1% weight percent i n 342 ppm water i s shown i n Figure 2. These r e s u l t s show that several of the samples show s i g n i f i c a n t surface tension reduc tion even a f t e r 40 milliseconds while others show hardly any change over the entire time frame. Of those that show s i g n i f i c a n t rapid surface tension reduction, ADSEE 801, i s the most pronounced, f o l lowed by SPONTO 168D and ADSEE AK31-64. Table I I shows the d i f f e r ences i n surface tensions a f t e r 30 and 180 milliseconds as well as the s t a t i c surface tensions obtained with a Du Nouy r i n g (7) at 25°C. Although the s t a t i c surface tensions of a l l the spray tank adjuvants are similar at 0.1%, their surface tensions after small time i n c r e ments d i f f e r considerably from each other. Because of the pronounced e f f e c t with ADSEE 801, i t was chosen f o r further study to determine the e f f e c t on dynamic surface tension of changes i n concentration and water hardness.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
Surface Tensions of Spray Tank Adjuvants
BERGER ET AL.
Downloaded by CORNELL UNIV on October 11, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch013
oscilloscope
aJ-D f
frequency counter
photo detector iflow pump
manometer
»t*rlna DURID metering pump valve controller
^
Figure 1. Schematic Diagram o f the maximum bubble pressure apparatus.
SURFACE TENSION dyne/cm 70
'II
60
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