Short term kinetics of polymer adsorption on glass substrate

Colloids and Surfaces, 30 (1988) 401-403 Elsevier Science Publishers B .V., Amsterdam - Printed in The Netherlands

401

Brief Note

Short Term Kinetics of Polymer Adsorption on Glass Substrate P . SOMASUNDARAN and A . SIVAKUMAR School of Engineering and Applied Science, Columbia University, New York, NY 10027

(U.S .A .) (Received 27 October 1987 ; accepted 28 October 1987)

ABSTRACT Short term kinetics (1 to 60 s) of polymer adsorption on glass and the variation of the adsorption density along the surface have been studied using a new technique . This method also gives information on how the polymer is distributed spatially along the interface . The effect of polymer concentration and chemical pretreatment of the substrate with an inorganic on polymer adsorption is discussed . It appears that polymer adsorption does not take place uniformly and linearly with time. Initiation of polymer adsorption by some surface controlled factors appears to be necessary before it is followed by a rapid polymer uptake .

Polymer adsorption on solids often takes place extremely rapidly so that the kinetics involved could not be studied using conventional depletion techniques . Depletion can be determined only after the removal of the solids from the suspension and this requires at least a few minutes during which time adsorption is often complete . A new method that permits determination of adsorption kinetics down to a second and even less is reported here . Adsorption of a cationic polymer on a glass slide is determined to be complete in less than 10 to 60 s depending on the polymer and inhibitor levels. Most interestingly, the polymer adsorption under most conditions is found to be an abrupt rather than a progressive phenomenon (with no adsorption in the beginning and then a sudden burst of adsorption) . This "nucleation and precipitation" type of adsorption not observed before could not be detected using the traditional techniques . The oriented adsorption obtained under sparse adsorption conditions also suggests the adsorption process to be a "wait and go" type phenomenon . The method used is a modification of a new thin film coating technique [ 1 ] and involves dipping the substrate, a microscope glass slide, in the solution of a cationic polymer (preceded by treatment with inhibitors if any) for the desired time interval and rinsing the polymer-coated slide in a stream of water to remove the excess polymer and then depositing silica spheres on the slide followed by further rinsing to remove the unattached spheres . Figure 1 shows 0166-6622/88/$03 .50

© 1988 Elsevier Science Publishers B .V.



40 2

Fig. 1 . Diagram illustrating short term adsorption kinetics of polyacrylamide (PAM) . Concentration 600 ppm, pH 5 .7 . 100

80 A w 60

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T = 25°C pH 5 .6-5 .8 CONCENTRATION OF PAM • 30O PPM • 600 ppm • 1000 ppm

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a 0 N

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7 5 10 POLYMER CONTACT TIME, sec

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Fig. 2 . Adsorption of PAM as a function of time for different PAM concentrations .



4 03 100

a

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w UU

T=25°C pH OF PAM = 5 .6 - 5 .8 pH OF Ca(N0 3 ) 2 O NO Cc(N0312 o 0 .1M Ca(NO3)2 • IM Ca(N0312

40 U

N 20

CONCENTRATION OF PAM= 600ppm I 0 1

5 7 10 POLYMER CONTACT TIME, sec

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I 70

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Fig . 3 . Effect of calcium nitrate concentration on adsorption of PAM .

photomicrographs of coating obtained with contact of the polymer for various time intervals and Fig . 2 shows coverage obtained as a function of time of contact of the polymer for different polymer concentrations . It can be seen that adsorption is complete in 20 s at the 600 ppm polymer level . At a higher polymer level (1000 ppm), the adsorption is complete in 5 s . Exposure of the slide to the calcium inhibitor shows the adsorption such that the "wait and go" phenomenon can now be observed clearly even at this level . In this case, as seen from Fig . 3, the adsorption is inhibited at short times but is the same as in the absence of the inhibitor at longer times . The type of coating obtained under sparse adsorption conditions again suggests the polymer adsorption to be a nucleation type phenomenon . Once the polymer begins to adsorb at a site, it appears to deposit along or around such a site . This type of adsorption might explain catastrophic biological reactions involving macromolecules leading to deposition, clotting and cell nucleations .

REFERENCES 1 G. Onoda and P . Somasundaran, Two and One Dimensional Flocculation of Silica Spheres on Substrate, J . Colloid Interface Sci ., in press.