The newly developed forced Rayleigh light scattering (FRS) method has been applied to the measurement of anisotropicmass diffusion in well‐aligned nematic samples of  p‐azoxy anisol (PAA) and  p‐methoxy benzilidene‐p‐n‐butyl aniline (MBBA). Since both materials are photochromic and can thus be photochemically labeled, self‐diffusion can be studied as well as impurity diffusion. In the latter case, the diffusing species was chosen to be methyl red (MR), which is photochromic but had also been used as a regular dye in optical tracer diffusion experiments. The FRS data for self‐diffusion are shown to agree well with this earlier determination; a satisfactory result if one considers that MR and both PAA and MBBA have very similar molecular structures. They also agree to within 10% with the Franklin theory of self‐diffusion in liquid crystals. On the other hand, the FRS measurements of impurity diffusion with photochemically labeled MR give diffusion coefficients that are considerably smaller. This discrepancy can, in principle, be explained through nonequilibrium thermodynamic considerations which show that the diffusion coefficient actually measured by FRS is different in the two cases of self‐ and impurity diffusion. However, the observed variation seems anomalously large. We tentatively suggest that photoactivated MR molecules tend to form aggregates, a problem apparently not encountered with photoexcited MBBA or PAA molecules. This demonstrates that, although FRS is undoubtedly a powerful technique to measuremass transport, the possibility of photoinduced spurious intermolecular interactions between the diffusing species must always be considered with care.

The forces between two cylindrically curved mica surfaces have been measured in aqueous dextran solution in the presence of NaCl. At various NaCl concentrations (10-4, 10-3, 10-2 M) we observe an additional attractive contribution to DLVO forces when dextran is added to the aqueous solution. The most striking consequence of this effect is that the jumps into primary minimum contact occur at larger distances and at weaker forces than with pure electrolyte solution; moreover in some cases where hydration forces prevent the jump in primary minimum contact (NaCl 10-2 M), the addition of dextran produces this jump. In all cases the primary minimum contact takes place at zero distance which proves that no adsorbed dextran is trapped between the two mica surfaces. These experimental results are analysed and compared with the recent theories of polymer depletion effect on colloid stability.

An in situ adsorption measurement method at the mica/protein solution interface is described.

An apparatus especially constructed for this purpose permits direct and continuous measurement of total adsorption (reversible and Irreversible) of ¹⁴ C-labelled proteins.

Bovine submaxillary mucin (BSM), extracted from salivary glands, was acetylated with (CH₃, ¹⁴CO)₂ O. The results show the increase of BSM adsorbed on mica surfaces with its concentration in solution and adsorption time. Pseudo plateaux are obtained for all concentrations studied, Indicating the formation of thick layers. The loosely bound fraction of adsorbed mucin is proportional to the bulk concentration in solution. The amount of BSM adsorbed increases in the neighbourhood of the isoelectric point of BSM (pH 3).

The behaviour of three egg-lecithin (EL)—water (W) mixtures, 60% (w/w):I, 50% (w/w):II and 30% (w/w):III, squeezed out or sucked in between two mica surfaces was investigated using an apparatus designed by J.N. Israelachvili. Mixture I is a lyotropic-smectic liquid crystal (LSLC), in contrast to II and III in which the LSLC is in equilibrium with a separated phase of excess water. The force F applied to the micasheet holders, the “separation” D between the mica surfaces and the average refractive index were measured for 1 < D < 200 nm.

A stepwise-thinning process was mainly observed on compressing mixtures I and II from separation 30 < D < 60 nm down to the minimum reproducible separation D_min, 9.0 ± 0.7 nm, which corresponded to the flattening of the mica surfaces. The steps ΔD were equal to multiples of λ = 5.5 ± 0.4 nm for sample I and of λ = 5.3 ± 0.3 nm for sample II.

The contact area of the flattened-mica sheets increased with the force F at separation D_min. Assuming that an effective elastic parameter can be defined for our composite system (mica sheet + glue), we interpret the F—contact-area dependence using the theory of Johnson et al. and deduce values of average normal pressures or stresses of the order of 10 mN m⁻² on the flat mica—mica contact. At such pressures the values of λ and the repeat distance of the LSLC formed by EL + W and measured by X-ray diffraction are similar.

The refractive index n of I is independent of separation for D_min < D < 50 nm but its value increases when D decreases for II and III. It appears that excess water is selectively extruded when F increases and D decreases. We suggest that, at maximum stress and D_min = 9 nm, the two mica surfaces are separated by two poorly hydrated EL bi-layers, while the EL polar groups in contact with the mica surface are almost completely dehydrated.

Bovine submaxillary mucin (BSM) was obtained from salivary glands through successive precipitations and dissolutions. It was labelled by acetylation with [1 -¹⁴C] acetic anhydride. Direct and continuous measurement of the total (reversible and irreversible) adsorption has been taken on muscovite mica, polyethylene, oxidized polyethylene, silicone and poly-(vinyl pyrrolidone) grafted silicone films. Force measurements between mucin layers adsorbed on two mica surfaces have been made in the distance range 0–600 nm. Adsorption/ desorption and force distance measurements allow us to distinguish between reversibly and irreversibly adsorbed protein molecules. The results also show that chemical modification of polymer surfaces enhances mucin adsorption.