Latex particles diffusion experiments

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

Hull and Kitchener (2) measured the rate of deposition of 0.3- an-diameter polystyrene latex particles onto a rotating disk coated with a film of polyvinyl formaldehyde. In electrolytes of high ionic strength (where the double-layer repulsion is negligible), they found close agreement between experiments and the prediction of Levich s boundary-layer analysis (Eq. 3]), indicating that a diffusion boundary layer exists and that its thickness is large compared to the domain of van der Waais and hydrodynamic interactions. These are neces-... 

Figure 3.13 CompEirison of experiment and theory for the deposition of monodisperse latex particles on a free-slanding wafer 4 in. in diameter. The air mainstream velocity normal to the wafer was 30 cm/sec, typical of microelectronics clean room operations. The diffu-sion equation wa.s solved numerically using calculated velocity and temperature distributions. The curves show that a small increase in surface temperature eHeelivcly suppresses deposition over a wide intermediate particle size range. Larger particles deposit by sedimentation smaller ones break through the thermal barrier by Brownian diffusion. (After Ye et aL, 1991.)...

In solution the latex spheres will experience van der Waals forces of attraction, which at a separation r will be proportional to r. For coagulation to not occur, these forces must be balanced by the repulsive electrostatic force arising from either the ionic functional groups on the latex, or adsorbed ionic surfactant. Hence, a latex particle in an electrol3Ae will support a tightly bound layer of one ion balanced by a diffuse layer of an oppositely charged ion. This diffuse layer is equivalent to the diffuse layer at an electrode-solution interface and so can be described by Gouy-Chapman theory [46]. Therefore, the width of the diffuse layer will be equal to the Debye... 

Adsorption dynamics. IH NMR was employed beyond spectral studies by performing diffusion measurements Applying IH PFG-NMR diffusion experiments to surfactants adsorbed to latex particles in dilute dispersions, a method was developed for the investigation of surfactant adsorption dynamics [23, 26]. Since surfactant molecules were occurring in two sites, i.e. in solution and as adsorbed surfactant, each site exhibited a different diffusion coefficient and was distinguished in a PFG experiment. This offered a convenient way to vary the relevant experimental time scale, which is determined by the spacing of the gradient pulses A... 

In the reported particle collision experiments with negatively charged latex, polystyrene, and silica spheres, most of the step features in the recorded chronoamperograms showed a cmrent decrease due to the blocking of redox mediator diffusion by adsorbed particles. However, a small number of steps showed a current increase, suggesting removal of a particle from the surface. However, in... 

Here we report experimental results in which both types of phenomena are observed. These experiments involve poly(/i-butyl methacrylate) [PBMA] latex films prepared from core-shell latex particles in which PBMA is the core polymer. One set of particles has a shell containing methacrylic acid [MAA] as a comonomer [P(BMA-ct -MAA)]. Films prepared from the ion-exchanged latex have a carboxylic-acid-group-rich phase as an interparticle membrane, whereas films prepared from the same particles at high pH form an ionomer phase in the membrane. These structures retard but do not prevent interparticle polymer diffusion. A second type of PBMA, prepared from a... 

There seem to be two factors at play. First, many of the experiments on latex films involve samples with a broad molar mass distribution. The distribution of diffusion coefficients broadens the concentration profile at the interface so that the measurements become insensitive to the difference between the two diffusion mechanisms. Second, in the experiments employing emulsified particles comprising essentially monodisperse PS, where reptation effects should be most pronounced, the SANS technique is less sensitive to early-time diffusion than DET. In the SANS experiment, one monitors the consequences of the increase in radius of gyration of the labelled particles. Reptation effects should be most prominent when changes in the radius are small. In contrast, DET experiments are sensitive to volume of mixing. Small increases in the radius of a donor-labelled particle correspond to large changes in or No DET experiments have been reported for polymer particles of narrow molar mass distribution, and so the prediction that DEX experiments should be more sensitive than SANS experiments to reptation effects remains untested. 

Sheetz [10c] developed a model which tried to rationalize the observation that most latex dispersions diy from the peripheiy inward. He construded experiments using dispersion-saturated blotting paper whidi avoided die problem. In this system, he noted that latex dispersions containing vinylidene chloride as a comonomer dried more slowly, at later stages, than poly[(ethyl aciylate)-co-(methyl methacrlyate) (P(EA-co-MMA)) latex dispersions, and noted that the latter formed films more permeable to water vapour. He therefore proposed that protrusion of the meniscus below the tops of the latex at close packing was accompanied by skin formation that closed the pores to further evaporation of water. Water vapour then had to diffuse through the continuous polymer film, and the resulting (osmotic) pressure led to particle deformation and film densification. 

The most interesting from the practical viewpoint was to determine the significance of the diffusion and interception effects as a function of particle size. The results of such measmements obtained by using the impinging-jet cell and monodisperse polystyrene latex suspensions [173] are plotted in Fig, 46, The ionic strength in these experiments was kept relatively high (10 M)... 

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