The Interaction of Sodium Dodecylsulfate with (Hydroxypropyl)Cellulose

Abstract

ABSTRACT:(Hydroxypropyl)cellulose (HPC) in aqueous solution interacts with sodium dodecylsulfate (SDS) to give micelle-like SDS clusters bound to the polymer at concentrations well below the critical micelle concentration of SDS itself. We have used the steady-state fluorescence quenching method (fluorophore: pyrene, quencher: benzophenone) to determine mean aggregation numbers (N, molecules of SDS per cluster) for the system. these N values vary with both surfactant and HPC concentrations. The data are consistent with a constant number of cluster binding sites per polymer. These clusters increase in size as the ratio of SDS to HPC is increased. This behavior is very different from that described for the interaction of SDS with poly(ethylene oxide).KEY WORDS Fluorescence Quenching / Neutral Water-Soluble Polymer / Polymer-Surfactant Interaction / Micelle / Mean Aggregation Number / Pyrene, Benzophenone / Critical Micelle Concentration / Several years ago we reported that the interaction of surfactants with (hydroxypropyl)cellulose (HPC), a hydrophobic watersoluble polymer, was different from their interaction with hydrophilic water-soluble polymers, such as poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP).l We used a fluorescent probe technique as well as fluorescence labeling experiments to show that sodium dodecylsulfate (SDS) forms mixed aggregates with HPC at lower concentration than with PEO or PVP. In addition we showed that cationic surfactants, such as cetyltrimethylammonium chloride, which do not interact with PEO or PVP, 2 also form mixed aggregates with HPC. More recently, Lindman and coworkers used pulsed gradient NMR measurements to establish that another hydrophobically modified cellulosic polymer, ethylt To whom correspondence should be addressed. 482(hydroxyethyl)cellulose, also interacts with a cationic detergent, dodecyltrimethylammoniurn bromide. 3 One of the most fascinating discoveries about the interaction of PEO with SDS is the type of aggregation which occurs, and how the aggregate structures vary as the surfactant-topolymer ratio is changed. Elucidated largely by Cabane et al. 4 using NMR and neutron scattering techniques, the picture which emerges is one in which the surfactant forms stoichiometric complexes in the form of small spheres, 20 A in radius, adsorbed onto the PEO strands. The polymer becomes incorporated into the head group region of the SDS clusters. While these clusters are similar in size to pure SDS micelles, they have a lower critical aggregation concentration (cae), and a mean aggregation number (N = 38 ± 30%) signifiPolym.

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“…Similarly, SDS adsorption onto the drug nanoparticles increased with increasing SDS concentration in the nanosuspensions [ 83 ]. When HPC and SDS are used in combination, they interact, forming aggregates or micelle-like SDS clusters bound to HPC [ 111 ]. These clusters can co-adsorb on drug surfaces [ 109 , 110 ], facilitating adsorption of HPC on drug particles [ 57 ], and enabling electrosteric stabilization [ 112 ].…”

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“…A manifestation of HPC-SDS interactions above the CMC of SDS is illustrated in Figure 5. The HPC-SDS solution had a much higher viscosity than the HPC solution, which can be attributed to the formation of HPC-SDS aggregates or micelle-like SDS clusters bound to the polymer [47][48][49] . It is expected that such interactions could lead to enhanced electrosteric stabilization (Figure 1c), i.e.…”