Spin-on zeolite films deposited from Silicalite-1 nanocrystal suspensions prepared by hydrothermal treatment of clear solutions have the required properties for insulating media in microelectronics. However, on the scale of the feature sizes in on-chip interconnects of a few tens of nanometers, their homogeneity is still insufficient. We discovered a way to overcome this problem by combining the advantages of the clear solution approach of Silicalite-1 synthesis with a sol-gel approach. A combination of tetraethyl orthosilicate and methyltrimethoxysilane silica sources was hydrolyzed and cocondensed in the presence of an aqueous tetraalkylammonium hydroxide template. The resulting suspension of nanoparticles of a few nanometers in size together with residual oligomeric silica species were spun onto support. The final zeolite-inspired low-k films (ZLK) with respect to pore size and homogeneity satisfied all requirements and presented excellent hydrophobicity, stiffness, and dielectric constant. The size and content of initially formed nanoparticles and the spatial hindrance promoted by occluded tetraalkylammonium molecules were found to be crucial elements in the definition of the final pore network.
Reactor fouling caused by preformed latexes is investigated using 50 wt% solids content latexes of different colloidal stability. In the absence of agitation, a rapid adsorption equilibrium is achieved for pH below the isoelectric point of the stainless steel (pH = 4.3). The equilibrium fouling decreases as solids content decreases and by increasing the pH above the isoelectric point of the stainless steel. The stability of the latex is a major factor determining fouling, which strongly decreases as latex stability increases. Under agitation, fouling increases with time, solids content, and temperature, and it decreases as the colloidal stability of the latex increases. The flow patterns in the reactor determine the distribution of fouling in the baffles. A mechanism for fouling formation is proposed by combining computational fluid dynamics and experimental results.
Surfactants are vital components of almost all heterogeneous polymerizations for maintaining colloidal stability, but they also play an important role in the kinetics and mechanism of particle nucleation. Despite many decades of research, the knowledge of adsorption-desorption surfactant kinetics and their application in (mini)emulsion polymerization is largely based on qualitative arguments. In this paper we show that the use of a quartz crystal microbalance with dissipation monitoring can provide quantitative information on both the adsorption equilibrium of ionic and nonionic surfactants, and also the kinetics of adsorption/desorption, that can be applied to the understanding of nucleation processes in (mini)emulsion polymerization. We show that surfactant dynamics and nucleation phenomena in (mini)emulsion polymerization are not dominated by diffusion phenomena linked to molecular size of surfactant as previously thought but rather are driven by the large differences in the rate of surfactant adsorption and desorption at the polymer-water interface. Finally, we show the application of this knowledge to explain the differences between nucleation processes for ionic and nonionic surfactants in emulsion polymerization.
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