The purpose of this study was to investigate the interaction between a nonionic polymer, (hydroxypropyl)methyl cellulose (HPMC), and cationic gemini surfactants, bis(hexadecyldimethylammonium)hexane dibromide (16-6-16), bis(hexadecyldimethylammonium)pentane dibromide (16-5-16), and their corresponding monomeric counterpart cetyltrimethylammonium bromide (CTAB), by using electrical conductometry, fluorescence, and viscometry methods. It was found that the gemini surfactants interact strongly with HPMC as compared to conventional surfactant CTAB. The free energies of aggregation, ΔG agg, micellization, ΔG mic, and transfer, ΔG t, associated with the binding interaction between surfactant and polymer, have also been evaluated. The negative values of ΔG t confirm the feasibility of interaction between the surfactant and polymer. The aggregation number (N agg) obtained from steady state fluorescence measurement with CTAB was found to be more than with the geminis. A significant viscosity increment was observed in the case of gemini surfactants as compared to CTAB. The rapid increase of the viscosity with surfactant concentration was, therefore, attributed to the considerable cross-links among micelles and polymers (transient network).

Nonionic cellulose ether−water systems have a characteristic feature of phase separation at certain temperatures, also termed the cloud point. The effect of various surfactants as additives on the phase behavior of nonionic cellulose ether, hydroxypropylmethyl cellulose (HPMC), has been studied. It was found that in the presence of ionic surfactants the cloud point (T CP) of HPMC decreased when small amounts of surfactant were added, and at higher concentration it increased. In the case of alkyltrimethylammonium bromides, surfactants with a longer alkyl chain (cetyltrimethylammonium bromide, CTAB, and tetradecyltrimethylammonium bromide, TTAB) influenced the T CP much more than that with a shorter alkyl chain (dodecyltrimethylammonium bromide, DTAB). Cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) were utilized to see the counterion effect on the T CP of polymer. Anionic surfactant sodium dodecyl sulfate (SDS) was found to be more effective as compared to its cationic counterpart with the same alkyl chain (DTAB), whereas nonionic surfactants showed no influence. From these observations it was concluded that the driving force was the interaction between the charged head groups of the surfactants and polar sites present in the nonionic HPMC. Gemini surfactants (α,ω-bis(hexa/tetradecyldimethylammonium)alkane dibromides) showed more influence on the T CP as compared to their conventional counterparts. The energetic parameters of clouding in HPMC in the presence of all surfactants used in the study were also calculated. Conventional surfactants had shown the contrast behavior of enthalpy and entropy changes at lower and higher concentration regions; i.e., ΔH c 0 and TΔS c 0 were positive at low concentration of surfactants but negative at higher surfactant concentrations. In the presence of gemini surfactants, both the enthalpy and entropy changes were always negative.

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The aim of the present work is to investigate the effect of various salts such as NaCl, KCl, NaBr, KBr, NaNO3, Na2SO4, and Na3PO4 as additives on the phase behavior of nonionic polymer hydroxypropylmethyl cellulose, HPMC. The cloud point of HPMC has been found to be induced by the addition of above salts. On the basis of cloud point values obtained at different [HPMC], the energetics of the clouding process have been calculated. It was found that in the presence of salts the cloud point (T CP) of HPMC decreased almost linearly with the salt concentration dependent on the type of salt used. Further, it was observed that the T CP decreases on increasing HPMC concentration at a fixed salt concentration, followed by minima except for NaCl and Na3PO4 for which T CP increases slightly after achieving a minimum value. Also, the free energy of clouding (ΔG c) becomes less negative indicating that the process is becoming energetically less favorable on increasing the polymer concentration.

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The interactions of two gemini surfactants (16s-16, s = 5, 6) and their conventional counterpart cetyltrimethylammonium bromide (CTAB) with polyethylene glycols (PEG 3000 and PEG 35000) have been investigated using conductivity, steady state fluorescence, viscosity and TEM techniques. The results indicate that there is no interaction between the PEG 3000/CTAB complex at lower polymer concentrations. However, a very weak interaction is observed at higher concentrations (0.5 and 1.0 wt% PEG 3000), while PEG 3000 and PEG 35000 interact with the gemini surfactants. Both critical aggregation concentration (CAC) and critical micelle concentration (CMC) increases with polymer concentration but are independent of the polymer molecular weight. From steady state fluorescence it is found that the addition of PEG results in no drastic decrease in the aggregation number (N) for all surfactants. This suggests that the atmosphere surrounding the polyion-bound micelles, with respect to the influence on the forces acting at the micelle surface, is equivalent to the counterion/water atmosphere surrounding free micelles. The relative viscosity (g r ) results show an enhancement in g r for all the surfactants. The increase in g r is quite significant with gemini surfactants. Polymer-surfactant interaction also depends on the polymer molecular weight. Also, the interaction seems to affect both inter polymer-polymer association as well as chain expansion. Additionally the surfactant induced changes in the polymer conformation depicted by TEM study at the micro structural level confirmed previously observed interactions determined by different analytical techniques.