A phase study was completed on aqueous sodium dodecylbenzenesulfonate (SDBS) and tetra-n-butylammonium bromide (Bu 4 NBr) systems, and consolute boundaries were drawn through cloud points. Samples were selected from both miscibility regions [under the lower consolute boundary (LCB) and above the upper consolute boundary (UCB)] for small-angle neutron scattering (SANS) studies. In the first set of experiments, the effect of varying Bu 4 NBr concentration on micellar parameters of 100 mM SDBS was studied at 30°C. The pure SDBS micelle has an aggregation number (n s ) of 51, and the effective charge on the monomer (α) is 0.17. With the addition of Bu 4 NBr, the n s of SDBS micelles increases while α decreases. The system with [Bu 4 NBr] = 39.5 mM (an above-UCB sample) showed clouding near room temperature (≈29°C) and had a high n s value (300) and a low α (= 0.09). The data indicated that the micelles lose ionic character in the presence of Bu 4 NBr. The temperature effect on this sample shows that α remains almost constant, while n s decreases on heating. A similar effect was observed with samples of lower Bu 4 NBr concentration (32 or 25 mM) in the presence of 100 mM SDBS. The same type of temperature effect was seen on a sample of under-LCB region (50 mM SDBS + 32 mM Bu 4 NBr); the n s values increased significantly as the LCB was approached. The overall SANS observations suggest that the micelles have low ionic character together with high n s values (a case of micellar growth) near LCB/UCB. Paper no. S1505 in JSD 9, 77-82 (Qtr. 1, 2006). KEY WORDS:Cloud point, consolute boundaries, smallangle neutron scattering, sodium dodecylbenzenesulfonate, tetra-n-butylammonium bromide.The observation of partial miscibility in binary surfactant/water micellar solutions is commonplace (1-5). Reports of both lower and upper consolute curves for nonionic and zwitterionic surfactants are frequent (1,2). There even exist a few reports of lower consolute curves for ionic surfactants in water (3,6-8).The phase boundary curve of the miscibility gap is commonly known as the "cloud" or "consolute" curve (9) in view of the pronounced turbidity of the solutions close to the phase separation. Initially this clouding was ascribed to an increase in size and aggregation number, n s (10), of the micelles and to the formation of giant micelles, which were believed eventually to become insoluble in water (11). Later, it was realized that the clouding results from the clustering of micelles as a result of attractive intermicellar interactions, and the term "coacervate curve" was coined for concentrated micellar solutions with a conjectured liquid-like packing of the micelles (12,13). In the last two decades considerable attention has been paid to scattering behavior (14-17) close to the critical point of these solutions. Hayter et al. (15) concluded from small-angle neutron scattering (SANS) experiments that the observed increase in the forward scattering is due to the formation of larger particles consisting of spherical micelles of fixed siz...

Newtonian flow conditions were adopted to take viscosity measurements at 30°C of solutions of cationic surfactants (cetyltrimethylammonium bromide, C 16 TAB, and tetradecyltrimethylammonium bromide, C 14 TAB) with the addition of n-heptylamine (C 7 NH 2 ) and quaternary salts (tetra-npropylammonium bromide, Pr 4 NBr; tetra-n-butylammonium bromide, Bu 4 NBr; tetraamylammonium bromide, Am 4 NBr; tetra-n-octylammonium bromide, Oc 4 NBr; tetra-n-butylphosphonium bromide, Bu 4 PBr; tetraphenylphosphonium bromide, Φ 4 PBr; n-propyltriphenylphosphonium bromide, PrΦ 3 PBr) by having either a fixed C 7 NH 2 or salt concentration and varying the other. Systems containing a comparatively higher Bu 4 NBr content showed a dramatic decrease in viscosity at higher C 7 NH 2 concentration. Further, the viscosity-salt concentration profiles of 0.1 M C 16 TAB solutions containing fixed C 7 NH 2 concentrations showed a peaked behavior. The peak positions and salt contents at the peaks were dependent on the length of the alkyl part of the particular salt and the connecting atom (N or P) but independent of the nature of the surfactant and C 7 NH 2 concentration. The behavior is discussed in the light of a change in the solubilization site of C 7 NH 2 caused by the presence of quaternary salts. Cavities in the quaternary salts present in the bulk solvent are proposed to be the new sites of solubilization.

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The photodegradation of high density polyethylene (HDPE) using CaO nanoparticles as a catalyst was carried out using 500 W lamp. After exposure, morphology as well as thermal properties of the HDPE was investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). SEM results showed that the HDPE is more prone to crack into small fragments, which indicated a rise in crystallinity with different amounts of catalyst i.e. CaO nanoparticles. The DSC results confirmed the remarkable influence of photodegradation on degree of crystallinity (XC%), fusion enthalpy (ΔH J g-1) and melting temperature (Tm) of HDPE. Infrared spectrometry (FTIR) demonstrated all functional groups of HDPE, present before and after photodegradation. Overall results showed that HDPE was photodegraded into small fragments successfully by using CaO nanopartilces, where different functional groups such as carbonyl, esters and vinyl were obtained during chain scission.