Reversibility of polyester adsorption on glass

Abstract

The adsorption of poly(ethylene a-phthalate) from chloroform solution on glass powdcr and aluminum oxide was studied . The adsorption of a number of fraction s vary in{T in number ave. rag~ mol ecular weight from 97 0 to 6250 showed a decrease in the mol~s of poly~ner a d sorbed with mcrease m mol ec ular weight. The results are interpreted to indicate that this polymer molecule lies in a relatively flattened conformation on the gla ss s urface. More polymer was a dsorbed on glass powder at 50°C than [l,t 0 °C. Adsorption on glass powder that had been ou tgassed to remove adsorbed water was less than on untreated glass. Initia l adsorptIOn at one temperature followed b y exposure at t he other temperature r esulted in complete reversibility of sorption on the untreated glass. DecreaSing th e temperat ure from 50 to 0 °C resulted in desorption from t he outgassed glass, but increasing t h e temperature did not res ult in addi tional adsorption. These dir· rcrences are ascribed in part t o adsorption across an a dsorbed water layer on t he untreated glass. An explanat ion fo r t hc "one-direction reversibili ty" observed for t h e outgassed glass is presented. I . IntroductionMost studies of polymer adsorption h ave been concerned with r elatively high molecular weight materials. Their b ehavior is, of course, very different from that of small molecules. Molecules of intermediate molecular weight are also of interest, but have not b een extensively investigated. In previous work in thi.s area, the adsorption of a series of r elatively low molecular weight poly (ethylene glycols) on a porous carbon [1] 3 and of several polyesters with molecular weights of the order of 4000 on glass, silica, and alumi.na [2] has been studied. The adsorption isotherms for the polyesters were not n early as steep at low conccntrations as were those for higher JJ?-olecular weight polymers; a plateau was not attallled until relatively high solution concentrations were reached.The adsorption-desorption behavior of polymer molecules has been of interest, in part, b ecause of the information implied regarding the conformation of the polymer molecule and interactions 'with the surface. Polymer molecules have been reported to adsorb relatively rapidly [2, 3, 4, 5] on nonporous surfaces, although some r ecent measurements indicate that this is not necessarily so under all conditions [4,6]. A recent theoretical treatment [7,8] has con~luded that times to equilibrium are long, caused m part by r earrangements of the molecule at . the surface. The times required for desorption, usmg the ame solvent, can be of a different order of magnitude from those required for adsorption. For some systems no desorption occurs within practical units of time (see, e.g., ref.[2]) , while for others some desorption does occur [3,5,6]. In one study, 601S?xhl ct extraction removed only negligible amoun Ls of polystyrene that lutd been adsorbed on c<LI'bon black [9]. In systems in which no deso rp tion ocCUlTed wiLh the same solvent used for adsorption, it h as bee...

Rates of adsorption and desorption of polystyrene on chrome surface

“…To achieve sensitivity in such measurements, the change in solution concentration must be relatively large, and the adsorption would therefore occur over a considerable solution concentration range. It has been well established that the rate of desorption of polymers can in some cases proceed so slowly that the appearance of an irreversible process is created [e.g., 1, 2, 3]. 1 The results of adsorption experiments that begin at a high concentration and end at a lower concentration may not represent equilibrium values.…”