Effect of Alcohol Chain Length on Formation of Cetyltrimethylammonium Bromide‐templated Mesoporous Silica Layer on Gold Nanorods

Abstract

This is the first study that elucidates the effect of alcohol alkyl chain length on the formation of mesoporous silica (mSiO2) layers on cetyltrimethylammonium bromide (CTAB)‐stabilized gold nanorods (CGNRs). The growth tendencies of the mSiO2 layers on the CGNRs (CGNR@mSiO2) in various alcohol solvents differed quite substantially from those observed for previously reported spherical silica particles. The formation of the mSiO2 layer was closely related to the interaction between the CTAB bilayer and alcohol.

Mesoporous Silica-Layered Gold Nanorod Core@Silver Shell Nanostructures for Intracellular SERS Imaging and Phototherapy

“…As shown in Figure 1 c, a 4.5 nm thick Ag layer was homogeneously coated onto the GNRs. However, the mSiO 2 layer did not uniformly coat the GNR@Ag surface and seemed to be preferentially coated on one side, as indicated by the arrows in Figure 1 d. In our previous study, we successfully created a uniform mSiO 2 layer on GNRs by adjusting the ratio of EtOH to H 2 O within the range of 0.25 to 0.5 [ 39 ]. At this optimized ratio of EtOH to H 2 O, an EtOH-rich phase developed in the hydrophobic tail region of the CTAB bilayer attached to the GNR surface because of the variance in the dielectric constants of EtOH ( ε = 25.3) and H 2 O ( ε = 80.1), whereas a water-rich phase was generated in the hydrophilic head group.…”

“…At this optimized ratio of EtOH to H 2 O, an EtOH-rich phase developed in the hydrophobic tail region of the CTAB bilayer attached to the GNR surface because of the variance in the dielectric constants of EtOH ( ε = 25.3) and H 2 O ( ε = 80.1), whereas a water-rich phase was generated in the hydrophilic head group. Therefore, hydrophobic TEOS, as a silica precursor, tends to diffuse preferentially into the lipophilic hydrocarbon chain region with the EtOH-rich phase of the CTAB bilayer [ 39 , 40 ]. In other words, the presence of a homogeneous surfactant bilayer on the GNR surface is crucial for the formation of a uniform mSiO 2 layer [ 41 ].…”