THE ROLE OF TRITON X-100 AS AN ADSORBATE AND A MOLECULAR SPACER ON THE SURFACE OF SILVER COLLOID - A SURFACE-ENHANCED RAMAN-SCATTERING STUDY

The ability of the nonionic surfactant Triton X-100 [p-(1,1,3,3-tetramethylbutyl)phenylpoly(oxyethylene)] to act as a molecular spacer between the surface of Ag colloid and an adsorbate [free base 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin = TPPC4] is investigated by surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of Triton X-100 and of poly(ethylene glycol) (PEG) 400 (poly(oxyethylene)) adsorbed on Ag colloid are reported. The identity of both spectra indicates that Triton X-100 is adsorbed on the surface via its hydrophilic (poly(oxyethylene)) part. SERS spectra of Ag colloid/Triton X-100/TPPC4 and of Ag colloid/PEG 400/TPPC4 systems are also reported. A good-quality SERS spectrum of free base TPPC4 was obtained for the former system, in contrast to the latter one. The role of the hydrophobic part of the Triton X-100 molecule in prevention of the porphyrin metalation as well as in its attraction to the vicinity of the surface is thus demonstrated.