Breakdown of fractal dimension invariance in high monomer-volume-fraction aerosol gels

Aerosol gels are volume-spanning, semi-rigid networks of solid nanoparticles possessing ultralow density and high surface area (Dhaubhadel et al. 2007; Chakrabarty et al. 2014). The current consensus is that aerosol gels have a hybrid morphology with equal mass (Dm) and surface (Ds) fractal dimensions 2.5 at super-micron length scale and 1.8 at submicron length scale, respectively (Sorensen et al. 2003; Dhaubhadel et al. 2006; Kim et al. 2006; Chakrabarty et al. 2014; Liu et al. 2015). In this study, we show that this consensus is partially complete and not universal. Gels, when formed under high monomer-volume-fraction (fv) conditions, have a Ds 2 implying solid-like surfaces while retaining their Dm 2.5. In other words, the conventional assumption of dimensional invariance (Dm1⁄4Ds) breaks down for monomer-dense gels. Using our static light scattering (SLS) apparatus, which is similar to Wang et al. (2015), we studied the structure factor S(q) in the angular range 1 –168 of carbon aerosol gels produced from a buoyancy-opposed flame (BoF) aerosol reactor (Chakrabarty et al. 2014). The details of the experimental setup are available in the accompanying online supplementary information (SI). The hybrid fractal morphology of the gel particles was probed by plotting the scattered intensity as a function of the magnitude of scattering wave vector q, where q 1⁄4

[1]  Dan Fry,et al.  Observation of Soot Superaggregates with a Fractal Dimension of 2.6 in Laminar Acetylene/Air Diffusion Flames , 2003 .

[2]  C. Sorensen,et al.  A three parameter description of the structure of diffusion limited cluster fractal aggregates. , 2012, Journal of colloid and interface science.

[3]  C. Sorensen,et al.  Structural crossover in dense irreversibly aggregating particulate systems. , 2004, Physical review. E, Statistical, nonlinear, and soft matter physics.

[4]  C. Sorensen,et al.  Hybrid superaggregate morphology as a result of aggregation in a cluster-dense aerosol. , 2006, Physical review. E, Statistical, nonlinear, and soft matter physics.

[5]  R. Botet,et al.  Aggregation and Fractal Aggregates , 1987 .

[6]  C. Sorensen.  Light Scattering by Fractal Aggregates: A Review , 2001 .

[7]  C. Sorensen,et al.  Aerosol Gelation: Synthesis of a Novel, Lightweight, High Specific Surface Area Material , 2007 .

[8]  Rajan K. Chakrabarty,et al.  Fractal scaling of soot packing density across five size decades , 2017 .

[9]  Christopher M. Sorensen,et al.  The Morphology of Macroscopic Soot , 1996 .

[10]  Yang Wang,et al.  Synthesis of Titanium Dioxide Aerosol Gels in a Buoyancy-Opposed Flame Reactor , 2015 .

[11]  P. Meakin.  Off lattice simulations of cluster-cluster aggregation in dimensions 2–6 , 1985 .

[12]  C. Sorensen,et al.  Comparison of size and morphology of soot aggregates as determined by light scattering and electron microscope analysis , 1993 .

[13]  C. Sorensen,et al.  Test of static structure factors for describing light scattering from fractal soot aggregates , 1992 .

[14]  Rajan K. Chakrabarty,et al.  Trapping and aerogelation of nanoparticles in negative gravity hydrocarbon flames , 2014 .

[15]  C. Sorensen,et al.  Soot aggregates, superaggregates and gel-like networks in laminar diffusion flames , 2006 .

[16]  Christopher M. Sorensen,et al.  A light-scattering study of the scattering matrix elements of Arizona Road Dust , 2015 .