Raman investigation of uncoated and coated magnetic fluids

We report on room-temperature Raman spectra of OH stretching modes associated to the surface of uncoated, single-coated, and double-coated nanomagnetic particles in hydrocarbon and water-based magnetic fluids. The data are compared with liquid water and discussed in terms of the suppression of symmetric and asymmetric hydrogen bonded modes. The hydrogen bond strength associated to the hydroxyl-group in the uncoated nanomagnetic particle is enhanced by 14% with respect to liquid water. In contrast, in the double-coated nanomagnetic panicle the hydrogen bond strength is reduced by 13% with respect to liquid water. Within the sensitivity of our experimental setup, however. no indication of hydrogen bond was found in the case of the single-coated nanomagnetic particle. Finally, in the single-coated sample the hydroxyl grafting coefficient is reduced by a factor of 3.2 with respect to the double-coated sample.