The estimated self-diffusion coefficients of the aliphatic ester promoters with methanol present are depicted in fig. . These data show trends identical to those discussed above, in that longer chain lengths result in decreased self-diffusion coefficients. When the promoter is of comparable size to methanol, such as methyl formate, competitive diffusion reduces the total diffusion of both species. Where promoter and methanol differ substantially in size (e.g., methyl n-hexanoate), there is an increase in the preference for diffusion of the promoter in the straight pores (b direction). Methanol thus influences the diffusion pathways of the large aliphatic promoters, mitigating the effects of the bottleneck observed in the straight pore.