Poly surface pressure dependence

Figure 5 Surface pressure(mN/m) dependence on time(hrs.), of aqueous poly(oxyethylene) copolymers M = 103 with propylene oxide (POEOP-7.7 mole %) 0 5ppm ...

The properties of poly(D, L-lactic acid) monolayers spread at the air - water interface were also shown to be strongly dependent of the nature of the spreading solvent. In this case, the monolayers spread from acetone and tetrahydrofuran exhibited typical reversible collapse behavior in the compression - expansion cycle with a quasi - plateau at large areas followed by a steep rise in the surface pressure at small areas. Conversely, the monolayers spread from chloroform, dichloromethane,... 

As our first case study, dealing with pol)miers, we consider Langmuir mono-layers of poly(methacrylic ester), PMA, at the water-air interface. Data for these layers can be used to illustrate some trends and principles, laid down in sec. 3.41. In that section we discussed how the surface pressure of physisorbed polymers depends on surface concentration. In a dilute monolayer of pancakes, the surface pressure was found to be given by the ideal term plus an excluded-area contribution. We rewrite [3.4.56] in terms of the adsorbed amount r = n°/A = N°/ N A) in moles of chains per unit area... 

Fig. 13.3. The distance dependence of the surface pressure of a monolayer of latex particles sterically stabilized by poly(vinyl pyrrolidone) of molecular weight 40000 in 2 M NaCl (after Garvey et al., 1979).

Two-dimensional surface micelles were formed of poly(slyrene)-it/ocA -poly(N-alkyl-4-vinylpyridinum iodide) by spreading a solution in a slightly selective solvent mixture onto the water/air interface by means of LB techniques. The resulting patterns showed a transition from a starfish conformation at low compression to a jellyfish conformation at high surface pressure. This transition does not depend on the degree of polymerization of the PVP chains but only on the length of the aUcyl chain used for quaternization. These patterns could be transferred to sohd substrates without structural changes. 

The PEO-lipid (12,13) represents another type of amphiphiles. Spread molecules of PEO-lipid (12,13) form stable monolayers with hydrophobic C12 chains protruding into the air phase and the hydrophilic poly(ethylene oxide) chain immersed in the aqueous subphase. The com-pressional behavior of such a molecule strongly depends upon the hydrophilic chain length [10]. While an amphiphile with a short PEO chain (5 ethylene oxide monomers) was shown to form condensed-type monolayers characteristically displaying a steep increase in surface pressure, a moderate slope, characteristic of an expanded film behavior was observed for longer PEO chain Hpid... 

FIG. 48 Dependence between surface pressure and the distance between polystyrene particles covered by hydrolyzed poly(acrylamide) for first (1, 3), second (2, 5), and third (4, 6) cycle of compression-decompression. (From Ref. 91.)... 

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