Polymethylmethacrylate adsorption

The way in which these factors operate to produce Type III isotherms is best appreciated by reference to actual examples. Perhaps the most straightforward case is given by organic high polymers (e.g. polytetra-fluoroethylene, polyethylene, polymethylmethacrylate or polyacrylonitrile) which give rise to well defined Type III isotherms with water or with alkanes, in consequence of the weak dispersion interactions (Fig. S.2). In some cases the isotherms have been measured at several temperatures so that (f could be calculated in Fig. 5.2(c) the value is initially somewhat below the molar enthalpy of condensation and rises to qi as adsorption proceeds. In Fig. 5.2(d) the higher initial values of q" are ascribed to surface heterogeneity. 

Fig. 5.2 Type III isotherms, (a) n-hexane on PTFE at 25°C (b) n-octane on PTFE at 20 C (c) water on polymethylmethacrylate at 20°C (d) water on bis(A-polycarbonate) (Lexan) at 20°C. The insets in (c) and (d) give the curves of heat of adsorption against fractional coverage the horizontal line marks the molar heat of liquefaction. (Redrawn from diagrams in the original papers, with omission of experimental points.)...

Let us consider the separation of polymethylmethacrylate (PMMA) on a nonmodified silica column as an example. In THE (medium polar eluent) the PMMA eludes in size exclusion mode because the dipoles of the methylmethacrylate (MMA) are masked by the dipoles of the THE. Using the nonpolar toluene as the eluent on the same column, the separation is governed by adsorption because the dipoles of the carbonyl group in the PMMA will interact with the dipoles on the surface of the stationary phase. The separation of PMMA in the critical mode of adsorption can be achieved by selecting an appropriate THF/toluene mixture as the eluent. In this case all PMMA samples... 

The following plain example might demonstrate the usefulness of the e° data. In benzene (e° = 0.32) polystyrene samples are eluted from a silica column, whereas polymethylmethacrylates and its copolymers are not. In THF (0.57) even PMMA homopolymers leave the column. Hence, THF is strong enough to prevent PMMA from adsorption. In chloroform (0.40) random copolymers with no more than 50%... 

Previous attempts to estimate Drago parameters for solid surfaces met with limited success. Fowkes and co-workers (198-201) calculated Q and Ex values for SiOj, TiOj, and Fe Oj using a combination of UV and IR spectroscopies and a flow calorimeter. They determined heats of adsorption of pyridine, triethylamine, ethyl acetate, acetone, and polymethylmethacrylate (PMMA) in neutral hydrocarbon solutions. However, their results did not provide consistent Q/Ea parameters for the surface acid sites. It should be noted that the heats determined were for high surface coverages, and these values provide a lower bound for the actual acid strength distribution. 

As expected, a significant increase of Q with augmenting amounts of Si02 impurities is observed. This has consequences on the polymer adsorption capacity (polymethylmethacrylate) as shown elsewhere [13]. 

While surfactant adsorption on weakly polar surfaces such as polyesters and polymethylmethacrylate is often sufficiently nonspecific to allow the use of models based on nonpolar sohds, interactions with more polar ionic surfaces tend to be more complicated. Even those cases, however, can be successively analyzed in terms of the concepts described above, so that the modification of wetting characteristics by surfactant adsorption can be predicted with reasonable confidence, possibly saving a great deal of time (= money) in various processes. 

Experimental results for polymethylmethacrylates in 1,4-dioxane/methanol have been reported, which indicate that the size of the substituent in the polymer ester group exerts an influence on the specific interaction between the methanol molecule and the carbonyl of the ester. In fact, the preferential adsorption of methanol is completely hindered when the lateral group is bulky enough. Similar results have been reported for substituted poly(phenyl methacrylate)s in the mixture tetrahydrofuran/water. 

An alternative (and perhaps more efficient) polymeric surfactant is the amphipathic graft copolymer consisting of a polymeric backbone B (polystyrene or polymethylmethacrylate) and several A chains ( teeth ) such as polyethylene oxide. The graft copolymer is referred to as a comb stabilizer—the polymer forms a brush at the solid/liquid interface. The copolymer is usually prepared by grafting a macromonomer such as me-thoxy polyethylene oxide methacrylate with polymethyl methacrylate. In most cases, some polymethacrylic acid is incorporated with the polymethylmethacrylate backbone this leads to reduction of the glass transition of the backbone, which makes the chain more flexible for adsorption at the S/L interface. Typical commercially available graft copolymers are Atlox 4913 and Hypermer CG-6 (ICI). 

Vaudaux P, Suzuki R, Waldvogel FA, et al. Foreign body infection role of fibronectin as a ligand for the adherence of Staphylococcus aureus. J Infect Dis October 1984 150(4) 546-53. Vaudaux PE, Waldvogel FA, Morgenthaler JJ, et al. Adsorption of fibronectin onto polymethylmethacrylate and promotion of Staphylococcus aureus adherence. Infect Immun September 1984 45(3) 768-74. 

The adsorption of HMI on solid particles was investigated [11] using two different latex dispersions, namely polystyrene (PS) and polymethylmethacrylate (PMMA). Both lattices have a narrow particle size distribution with PS having a diameter of 321 nm and polydispersity index of 0.03 and PMMA having a diameter of 273 nm and polydisper-sity index of 0.05. The results are shown in Figure 15.5, which shows the amount of adsorption F in pmol/m versus HMI concentration (pmol/dm ). 

---