Physisorption of SDS in a Hydrocarbon Nanoporous Polymer

Abstract

Surface modification of nanoporous 1,2-polybutadiene of pore diameter approximately 15 nm was accomplished by physisorption of sodium dodecyl sulfate (SDS) in water. Loading of the aqueous solution and the accompanying physisorption of SDS into the hydrophobic nanoporous films were investigated in a wide range of concentrations. The loading showed varying dependence on the SDS concentration. No loading was observed for SDS concentrations below 4.0 mM. At concentrations above 5.0 mM, the initial part of loading showed a linear dependence on the square root of time, which can be interpreted as diffusion-controlled dynamics. Both the specific equilibrium loading and the final SDS adsorption reached plateau values at concentrations above 6.8 mM. The infiltration of SDS into the nanoporous film was mainly followed by gravimetry and for a few samples confirmed by X-ray photoelectron spectroscopy (XPS). The SDS adsorption isotherm can be well described by the Langmuir model, consistent with a monolayer adsorption onto the pore walls. The surface modified by the surfactant clearly showed water wettability, in contrast to the original hydrophobic nanoporous 1,2-PB. We also looked at the release process of SDS out of the nanopores in the presence of excess of water or methanol. A discussion of the very different time scales of release in the two media is presented at the end of the paper.

Sodium Dodecyl Sulfate (SDS)-Loaded Nanoporous Polymer as Anti-Biofilm Surface Coating Material

“…This can be ascribed to low release rate of SDS after 72 h, as already reported in [21]. However, increasing the film thickness or slowing down the release rate by exposing the skin layer side to the solution did reduce long-term biofilm formation (74% reduction for T 2 , 92% reduction for T 3 and S skin , Figure 6).…”

“…For this reason SDS loading was realized by first conditioning the nanoporous 1,2-PB film in methanol before dipping it into SDS aqueous solution (Figure 1c). We have recently reported a detailed study on the load-release of SDS into-from nanoporous cross-linked 1,2-PB [21]. At the loading conditions applied in the present study SDS is adsorbed onto the hydrophobic pore walls creating a dense monolayer as depicted in the inset of Figure 1c.…”

“…At the loading conditions applied in the present study SDS is adsorbed onto the hydrophobic pore walls creating a dense monolayer as depicted in the inset of Figure 1c. At equilibrium more than 99% of the SDS inside the pores is in the adsorbed state, the rest being either free molecules or organized in micelles [21]. After SDS loading the nanoporous film (Figure 1d) was then challenged in the culture medium with the biofilm model organism E. coli to evaluate its efficiency on preventing bacterial attachment and biofilm formation.…”

“…After SDS loading the nanoporous film (Figure 1d) was then challenged in the culture medium with the biofilm model organism E. coli to evaluate its efficiency on preventing bacterial attachment and biofilm formation. As already mentioned virtually all SDS inside the nanopores is adsorbed on the pore walls; its release in the presence of water is slow and happens by multiple release-adsorption steps [21]. More information on the SDS release kinetics will be given in the Experimental Section.…”

“…A systematic study of SDS infiltration from aqueous solutions with SDS concentration between 0.5 and 50 mM into the nanoporous 1,2-PB matrix has been recently reported [21]. It has been shown that the SDS adsorption onto the inner surface of nanoporous 1,2-PB film saturates at concentrations above 6.8 mM.…”