Fig. 3: Cluster formation in suspensions of positively charged particles in primary alcohols.
From: Chemical control of colloidal self-assembly driven by the electrosolvation force
a Representative image of positively charged aminated silica NH2-SiO2 particles (pink) and negatively charged SiO2 particles (blue) in primary alcohols of increasing chain length from methanol (\(n=1\), left) to 1-octanol (\(n=8\), right) (see Supplementary Table 4 for experimental conditions). All amine particle experiments contained \({10}^{-5}\) M HCl. Measured zeta potentials (\(\zeta\)) are noted. b Radial probability density distributions as a function of alcohol chain length for the experiments shown in (a). c Inferred pair-interaction potentials, \(U(x)\), from BD simulations that best reproduce the experimental \(g(r) {{\rm{s}}}\) for select cases (see Supplementary Table 26 for parameters). Well depths \({|w|} \approx 1 \, {{{{\rm{k}}}}}_{{{{\rm{B}}}}}T\) and \(\approx 3 \, {{{{\rm{k}}}}}_{{{{\rm{B}}}}}T\) were sufficient to capture the \(g(r)\) profile of NH2 particles in methanol and 1-propanol, respectively. Larger values |\({w|}\approx 7 \, {{{{\rm{k}}}}}_{{{{\rm{B}}}}}T\) were required to capture the strong cluster formation observed in the higher chain alcohols 1-pentanol and 1-heptanol. Purely repulsive pair potentials described interactions of negatively charged SiO2 particles in alcohols (Supplementary Table 26). Error bars denote estimated uncertainties of ± 100 nm on particle diameter and ± 1.5 \({{{{\rm{k}}}}}_{{{{\rm{B}}}}}T\) in \(w\). d Effect of pH on cluster formation, shown for NH2 particles in 2-propanol (IPA). Negatively charged SiO2 and COOH particles in IPA display no evidence of interparticle attraction as a function of pH (Supplementary Fig. 5). Scale bars \(20\) μm.
